Subwoofery - by Jim Smith
Part 1 –Full-range speakers need subs too…
…But not necessarily to achieve someone’s notion of “better bass”.
No matter how deep or authoritative the bass from a “full-range”speaker may be,no matter if it costs hundreds of thousands of dollars,it’s probably not going to let you have your (audio)cake and (hear)eat it too.
For exameple,here are just a few of the many large and/or expensive speakers that have benefited from subs: Wilson,YGA,Magico,Vandersteen,Raidho,Tannoy,etc.
Are they somehow deficient in the bass? Absolutely not. It’s about having the smoothest and deepest bass speaker location coincide exactly with the other requirements for great sound. Coincide is a good word,because it would be a huge coincidence if it ever happens!
It’s really simple. When you place your speakers for the absolute best overall presentation,with maximum intimacy,presence,tone,etc.,as well as a convincing spatial reproduction,there is almost no chance that the same place will be the best position for the best bass. In fact,I’ve never seen it happen. Sometimes it can be close,but I’ve never heard a system that didn’t perform at a higher level with properly matched and integrated subs. Of course, properly matched and integrated is the key…
That does not mean that you have to go out and buy a pair of subwoofers. Perhaps your budget or room couldn’t easily accommodate them.
It does mean that you do have to make YOUR best choice for the most acceptable compromise. For me,I’ll take the smoothest bass I can get and opt for the best dynamics,presence,tone,etc.,instead of getting deeper bass. We will discuss how to do that in a future article.
Getting back to the topic at hand… for example,my Tannoy Canterburys with outboard Duelund crossovers are relatively flat in my room to a bit below 30 Hz.
I have a pair of REL subs that are placed for their highest performance. They are rolled off at about 28 Hz. They are never audible as a source of sound. But there is no disputing the system’s reproduction of the sense of the venue and the presence of seemingly live persons & instruments in the room.
In my case,I did it for a more compellingly musical sound,not for “better bass”. Maybe on 1-2% of the recordings that I play,I might notice the bass being a bit deeper or more authoritative,but the rest of the time,I’m never aware of the subs. Well,except for the fact that the listening experience is so much more musically involving.
Subs – again,properly implemented – will alwaysenhance the sense of space and especially the sense of presence of vocalists and instruments,whether recorded up close or well back on a stage. The result? A more engaging musical experience.
But it’s not just the sense of space or hearing low bass instruments the few times when they are actually present. For example,I can play a recording of a guitar solo,and when the subs are on,it’s as if you could walk over and pluck the guitar strings! Yet,you are not aware of the subs in any way as far as making a sound. They increase the sense of tangibility of instruments and voices.
My experience (something like 800 systems voiced)has shown that even the most expensive/exotic speakers – often which claim subterranean bass – still benefit from properly implemented subs. In fact,I have never known this outcome to be untrue,no matter what is claimed or what the loudspeaker costs.
It’s important to recount that when I have heard reports of how a pair of subs didn’t blend properly with a pair of full-range loudspeakers,when I heard that system,the reports were nearly always correct! Sometimes I could fix the problem in a few minutes,sometimes a few hours. But it was always solved and more musical engagement was the outcome.
Part 2– Fast bass? Really???
Part 3– Finding the anchor for the best Dynamics,Presence & Tone
Part 4– Why a RTA is useful,even if you are not technical – and how to get a good one nearly free
Part 5– Sub set-up info you probably haven’t seen (but you should)
Part 6– X-over freq. vs. level;location,location,location
Part 7– The role of EQ and room correction when working with subs
Part 8– A true story with a good outcome and lots of documentation
Comments
Part 2 – “Fast”bass? Really??? …
… Just when I think some errant audiophile terminology is finally extinct,it rears its ugly head again. I am still amazed when audio reviewers describe subwoofer bass as fast or slow.
First,let me get the most insulting statement out of the way: If a subwoofer could be described as very fast,it would be a tweeter!
When a subwoofer is described as slow,it’s nearly always poor integration with the main speaker. Poor integration can range from wrong location (this is much more than simply finding where to put it)to wrong crossover implementation to wrong levels and more. These factors can be just a bit off and still affect the sound – and they are inter-related.
If a sub can be described as fast,that’s also a problem. You shouldn’t be aware of it – in much the same way that you never think about how fast or slow it is when listening to live music.
A relatively straightforward goal can be best described as never feeling the need to readjust the sub with different recordings or types of music. When you get that aspect working you are done,or at least well on the way.
We will explore these topics and techniques later in this series.
However,there are some other pesky performance issues with some subs that can also contribute to the illusion of fast or slow bass:
(1) The main issue about speed that I encounter isn’t how fast the woofer starts – but how quickly does it stop? This issue can definitely contribute to the slow bass illusion. It’s one reason why speaker manufacturers are continually looking for more rigid,but lower mass drivers. Not for speed,but for control.
(2) Cabinet resonances can also contribute to the slow illusion. Although the sub may only be working up to 35 Hz,if its enclosure has a sympathetic (…what a weird adjective!…)resonance at 140 Hz,it can often be described by some as being slow.
(3) An out-of-band subwoofer anomaly (fortunately this is rare)can also add to the illusion. If it is flat to your 40 Hz crossover point,but it has a peak at 80,then here comes the illusion again (though it depends somewhat on the slope of the crossover).
To close out this section,let’s agree that we want the sub to disappear as an obvious source of the sound. If you are aware of it,especially as to its speed,you probably have some work to do. It’s not rocket science (sorry,couldn’t think of a better descriptor),and the rewards for your effort will pay musical dividends for years to come.
Part 3 – Finding the anchor point for the best Dynamics,Presence & Tone
This has to be my pet peeve when evaluating audio installations. It is so very important – but rarely mentioned – and sadly,it is done even less.
First,a description of the issue:
Dynamics are essential in order to have the music “pluck your heartstrings”. That’s why the current overuse of compression (of dynamics)in recordings is so damaging – but hey,that’s another topic…
Here,we are discussing the effects of bass peaks and dips in your playback system. The peaks destroy dynamic range as they were never intended to be there. They mask musical dynamic subtleties in the recording that are meant by the musician to be heard,but you can’t fully experience them,as they are overshadowed by the excess bass sounds.
The same lack of dynamics is true (but for a different reason)whenever there are dips in the bass frequency response. These dips detract from the music’s intended impact and definitely diminish its intended dynamics,and sadly,sometimes in a major fashion.
I have heard too many systems that – depending on the frequency – were almost missing some bass notes,while other notes were booming away. Both bass anomalies detract from the music’s dynamic contrasts,with a potentially far greater effect than those that may occur elsewhere in the midrange and treble.
Please understand that we are not considering uneven speaker response. We are concentrating on the room resonances that all rooms have,based on the room’s dimensions. Peaks in bass frequency response are additive resonances and dips are subtractive. Even though we are talking about subwoofers,we are still intensely concerned with all bass anomalies,in the boundary dependent region from 25-250 Hz.
Since all rooms suffer from these issues,how can we overcome them? While some may wish to immediately employ electronic EQ and Room Correction (another upcoming topic in this series),I have found that it’s always best to first smooth out the bass response in an organic fashion (meaning working with the room rather than against it),rather than immediately resorting to using electronic EQ and/or Room Correction.
And since I’m up against my word limit,we’ll explore how to successfully accomplish our goal in the next issue. Hint – it’s probably not what you’ve heard.
We interrupt our regularly scheduled Subwoofery series for a Special Announcement!
In the past couple of weeks,as I voiced several systems around the country and conducted set-up classes at my RoomPlay Reference listening room here in the Atlanta area,I realized that I knew something vital to this series – in fact,I have always used it and taught it – but I had not communicated it in Copper! Sheesh!!! Brain fade? Anyway,we need to correct the omission before going further with our Subwoofery series.
First,a few excerpts from the previous issue in order to illustrate the point I am about to make related to the need for seamless blending of subs with full-range speakers (which always results in a far more musically engaging experience).
From Copper – Issue 14 –
“Subs – again,properly implemented – will always enhance the sense of space and especially the sense of presence of vocalists and instruments,whether recorded up close or well back on a stage. The result? A more engaging musical experience.
But it’s not just the sense of space or hearing low bass instruments the few times when they are actually present. For example,I can play a recording of a guitar solo,and when the subs are on,it’s as if you could walk over and pluck the guitar strings! Yet,you are not aware of the subs in any way as far as making a sound. They increase the sense of tangibility of instruments and voices.
My experience (something like 800 systems successfully voiced)has shown that even the most expensive/exotic speakers – often which claim subterranean bass – still benefit from properly implemented subs. In fact,I have never known this outcome to be untrue,no matter what is claimed or what the main loudspeaker costs.
It’s important to recount that when I have heard reports of how a pair of subs didn’t blend properly with a pair of full-range loudspeakers,when I heard that system,the reports were nearly always correct! Sometimes I could fix the problem in a few minutes,sometimes a few hours. But it was always solved and more musical engagement was the outcome.”
There are several reasons that very smart audiophiles often miss the benefits of this topic:
Reason #1 –
This first point isn’t actually the one I wanted to make with this injection into our series,but it is vitally important. It’s really more of a rant. (insert angry emoji here).
Without exception,I have found that audiophiles rarely experience the full capabilities of their systems because they don’t really have a reference. So,even when their systems are sounding good to them,how do they know if there is more to be had from their investment? Do they know what to consider,and how to go about it? Are they really getting the full return for which they paid?
Show sound – and dealer sound (with a few exceptions)– can almost always be significantly bettered by most serious home audio systems. Therefore,if your sound approaches (but doesn’t exceed)that of the best you have heard at a show or at a dealer,it probably means that you have more work to do (the bad news)and more musical involvement to enjoy for years to come (the great news).
Reason #2 –
If you are fortunate enough to have a custom designed room,and you have been told where the system should go,but the designer did not come to your place and evaluate/tweak the results,in my experience,it is definitely under-performing its true potential. And even if he/she did come,that is no certain assurance that you have the performance for which you have paid (more on that later in this series). Sadly,the performance shortfall is often dramatic.
Here are quotes from two recent RoomPlay clients who had relatively expensive rooms that were designed – but never checked after the system installation – by the designer:
• “Dammit! I have lived with about 20% of the sound I could’ve had.”
• “I cannot believe how much more alive my system sounds!”FWIW – his wife heartily agreed.
We will address the above listed issues – and more – in this series. By “address”,I mean that we will show you how to get there. Our goal is for you to reach that higher level of musical engagement.
Reason #3 –
When I have heard systems with subs that did not blend well with the main speakers,there have been a number of culprits. Sometimes it was the one we are about to address,but usually there were several.
For years I have been astonished at the lack of cohesiveness and musicality from mains/sub systems,and for a reason that seems so obvious (that I forgot to mention it).
No matter how excellent the subs,no matter how much effort went into their placement,the results will never be satisfying if the following process (which is has nothing to do with working with the subs)isn’t performed.
The main speakers need to be voiced for the smoothest bass possible! A great sub install will have little or no chance of blending with main speakers that have problems in the 25-250 Hz area. Please understand – I am NOT saying that the main speakers are problematic in the bass. Most likely they are performing well. It’s the room/listening position/speaker position that is the culprit. When attention to this vital detail has been properly applied (plus two more issues we will explore as well),only then can we begin think about working with the subs.
We’ll look at this issue in more depth in the next Copper…
Our last entry ended with this statement – “No matter how excellent the subs,no matter how much effort went into their placement,the results will never be satisfying if the following process (which has nothing to do with working with the subs)isn’t performed.
“The main speakers need to be voiced for the smoothest bass possible! Great subs will have little or no chance of blending with main speakers that have problems in the 25-250 Hz area. Please understand – I am NOT saying that the main speakers are problematic in the bass. Most likely they are performing well. It’s the room/listening position/speaker position that is the culprit. When attention to this vital detail has been properly applied (plus two more issues we will explore as well),only then can we begin to think about working with the subs.”
For our purposes in tuning our main speakers to our room,best bass is NOT the deepest,but the smoothest. We want to minimize peaks (which mask the true difference in recorded dynamics)and bass suck-outs (which minimize the true difference in recorded dynamics).
To achieve this foundational aspect of our music,we will be working with the room,rather than fighting it. Of course,various components have varying dynamic capabilities. But this is not about evaluating components – it’s about transforming the musical effects of the components that you have now.
Rather than employing electronic adjustment at this point in voicing the system to the room,I tend to think of the process as organic,not electronic. Therefore,we will not be introducing eq or speaker/room correction at this time. Our concept is simply to be working with the room/system as it is.
The steps we will take are interrelated. By far,the most foundational step is finding the best location for your listening seat in your room. This is the anchor point for everything that follows. Even if you cannot move your seat permanently due to decorative requirements,I’ve found that it’s nearly always possible to use a temporary location for tuning,and for listening those times when you really want to experience the full musical impact from what you purchased. Especially once you hear and feel the difference this tuning will make. I call it tuning,but it is really discovering how your speaker/room interface works and then working with it,rather than against it.
FWIW – I know that there are some so-called high-end audio rules – such as the “rule of thirds”. But in actual practice,I’ve rarely voiced a system that ended up following these precepts or other “rules”,because – once items are introduced into the room – the math changes (as does the room volume and even the dimensions).
Basically,we will locate the best seating location,establish a grid for our room,and then listen to the musical presentation. We will be making adjustments to speaker position,toe-in and separation,all the while using our grid to help us get back to and/or improve on our reference position musically.
More often than not,this process can be a bit lengthy. But not to worry – once it’s done,the music will pour from your system in a much more engaging manner. So the relatively small amount of time spent can pay dividends for many years of musically rewarding listening.
If you cannot change your seating position for tuning and serious listening,then you can skip ahead. While the overall results may not be as powerful,they should still be very worthwhile. However,you should at least read the following section on finding the “anchor”position in your room…
Part 1 – The anchor – establishing your listening position
The negative effects resulting from not addressing this critical issue simply cannot be overstated. Even so,I am constantly amazed at how many audiophiles,dealers,reviewers and manufacturers miss this fundamental aspect of music reproduction. When I see them worrying about speaker placement without having done the basic listening position evaluation first,I cringe. Certainly better speaker placement (including distance away from the listener and from walls;speaker separation;toe-in;etc.)can make a real improvement,but it will not have been as powerful as it could have been had those steps been built on the foundation of finding the best listening position.
Basically,we are concerned about the effects of room resonances in the bass (from 25-250 Hz). The resonances are related to the room dimensions,and to some extent,the shape of the room,the contents of the room,and even the entryways into the room. Sometimes referred to as the boundary dependent region (25-250 HZ),resonances in this region may appear as peaks in the response (phase reinforcement)or they may appear as dips (phase cancellation).
Essentially,these peaks & dips in the 25-250 Hz region are part of the sonic signature of the room. I have never encountered a room,no matter how much money was spent on designing and building it,that didn’t still have sonic irregularities in the boundary dependent region. It behooves the listener to locate a listening area where the room is most neutral in this region. The ultimate result of ignoring this aspect is reduced musical dynamics (and reduced musical engagement)as I mentioned earlier.
By most neutral listening area,I mean the area in the room where the bass is smoothest,not necessarily the deepest. In other words,resonant peaks are diminished and resonant suck-outs are less deep.
Can equalization help? Can room correction help? Maybe. Can bass traps help? Probably. But first,we will look at the organic process,one that you can do without spending money on additional items.
After we complete our examination of the best set-up for our main speakers,we’ll look at the issues that usually contribute to a less than satisfactory sub integration with “Full-range”speakers.
Teaser Hint – here are a few Subwoofery issues that we will cover in upcoming issues,which – IMO – are rarely addressed sufficiently or properly (if at all)by most audiophiles,many dealers,more than a few manufacturers,and all too often – a lot of reviewers:
1 & 2 – Subwoofer location and direction. Hey,isn’t bass omnidirectional? Why would location and direction matter?
3 – Subwoofer crossover frequency. Frequency & level adjustments can make or break seamless sub/main speaker integration. And it’s not what you think.
4 – Subwoofer level. Same as above.
5 – Subwoofer polarity. What is the effect of this adjustment? When do you make it? How do you recognize when it is right?
The above five issues (in bold type)will dramatically effect the performance of any sub-woofered system. That’s because they are completely interrelated. IMO,if only one of these is ignored or inadequately addressed,there is little chance that you will get optimum results. In fact,this is one of the areas where reports of “slow”woofers and/or “poor blending”occur,thereby assigning blame for the less-than-satisfying results on the innocent subwoofer…
Uh-oh,that reminds me that I should have introduced another topic earlier in this series.
For now,I’ll just mention it: I would far rather have no subwoofer than have to use one subwoofer. Or,to put another way,if you can’t have stereo subs,wait until you can. Don’t compromise your system with just one.
See you next time!
The Listening Position:
This series was implemented to assist music-loving audiophiles in gaining much more musical involvement with their systems that feature “full-range”loudspeakers. As such,it is not about adding subs to monitors to create a sub/sat system,although some of the upcoming info re sub positioning,levels,xover,& phase are applicable.
For this installment,we need to look at being sure that our main speakers are as smooth as possible through the boundary-dependent region (25-250 Hz). If not,we will never obtain the additional level of musical performance we could have enjoyed with subs – no matter how good they may be. That’s because the sub/main blend will never be as satisfactory as it could have been. Said another way,if you think you can simply add a couple of subs to your system as it is currently,and they will improve your system,I am afraid that I have bad news…
The Anchor – establishing your listening position first
Last issue,I said “the negative effects resulting from not addressing this critical issue simply cannot be overstated.” Basically,our mission is to find the best location/listening position for the smoothest bass in our acceptable listening area (‘acceptable’due to restraints in décor).
Of course,if you are fortunate enough to have a dedicated room,and thus you have even more placement (listening & system position)flexibility,it’s even better. Either way,we want to work with our room,not against it (you will hear this statement again & again as I believe that this is critical if we are to enjoy any significant success in getting our music systems to reach a higher,more musically involving level).
Two proven techniques to achieve the smoothest bass response from our main full-range speakers:
1- Play a recording that has bass notes that are rising or falling in frequency – or various bass notes in a complex tune – that have approximately the same volume. Last issue,Paul suggested music from Brian Bromberg’s Wood. That’s a good one – I also like his Wood II.
While the cut is playing,your mission is to listen through a chosen musical section,then move forward and backwards in the room – each time listening to the same selection of music – in what could be an acceptable listening area. Whenever possible,using a lightweight seat that you can easily move so that you can listen at a seated position – which will give a bit more accurate results. Walking around can work,but it won’t be as accurate due to vertical standing wave issues. I would suggest not moving more than a foot forwards or backwards before listening to the selection again. The bass will change in its character. You are listening for the smoothest rendition – no notes booming away or almost missing. This is NOT about the deepest bass. We want the main speakers to have no obvious peaks and/or dips in the 25-250 Hz region. When you locate the position that has the smoothest overall reproduction,that is the place where you will locate your seat for serious listening and definitely for your speaker/room tuning.
As I said in Issue #17,moving your speakers about is important but it is of relatively small importance until you know where in the room you should listen because the bass is smoothest in that listening area. Then,once you have located that position,you can make other adjustments to speaker location without detrimental effects to the overall bass response smoothness… This is why I call the results of this step the Anchor Position. Once you have found it,then you can work on all else – presence,tone,etc…
2- These days,one can obtain a RTA (real time analyzer)or RTA app for very little expense and sometimes none at all. Why would you want to use one? Most certainly not for measuring your system’s overall response,and most certainly not for ultimate tuning of your system.
The RTA is great to have because it can save you a lot of time,compared to listening at a number of locations in the room. Although I have an expensive pro analyzer,the latest crop of apps (some free!)for phones and laptops make it easy to acquire and use one. You don’t need to have a technical background to use it at all.
The inexpensive-yet-more-than-accurate-enough app I use these days is AudioTools from Studio Six Digital. It is exclusively for iPhones & iPads. It cost me $19.95. All I ever use from this suite of tools is the RTA and the SPL (sound pressure level)loudness meter. Although it’s not necessary for our mission,you can purchase a calibrated microphone for your iPhone 5 or 6 or recent iPad from Studio Six/Audio Control for around $200. Their iTest mic has software that automatically calibrates that mic to the iOS device intended for it. I checked it against my much more expensive RTA rig,and it was almost exactly the same!
There are loads of RTA/SPL apps for operating systems other than Apple. Taking the time to find one on the Internet that you can use will be time well spent.
Note – at this point,it’s useful to determine what the ambient noise level is in your room. You can measure that with the SPL app. Set it on flat weighting if available. Measure from the existing listening position.
Once you determine how loud the room’s ambient noise level is,you want to be sure to run the pink nose about 20 dB over that level,so as to be certain that the measurements you will take will not be polluted by ambient room noise levels.
Now,what you’ll do is simply play pink noise (equal loudness per octave – same as music). There are numerous resources for obtaining pink noise. The Audio Tools app supposedly has a pink noise source,but I have never tried it.
We only want to look at third octaves in the 25-250 Hz band. They are 25,32,40,50,63,80,125,160,200,& 250 Hz. Be sure to maintain the mic height at or near seated ear height when measuring. If it is higher,then you may encounter other anomalies in the bass related to the vertical room dimension. Starting at the current listening seat position,slowly move the RTA forwards & backwards and you will see various third octave frequencies rise & fall. You are looking at the room’s effects on your system. Obviously,we want to work with the room,rather than against it.
Hint – systems in rooms – from 25-250 Hz – almost never look good. The fact is – all of the rooms of the size that we might use in our homes will have problems. We simply want to locate the area where the problems are less objectionable.
Regardless of which technique you employ,you will have located the spot in the room where you will listen. If you then have to move the speakers a fair amount due to the resulting listening position,the bass smoothness is not likely to change very much. That’s because of the room dimensions,which do not change. Congrats! You are working with,rather than against,the room! However,at this point it is worth a listen to music to see if you want to adjust the seat slightly – a few inches forward or backward – to make the bass even better.
Next issue,we will address subwoofer location (including the critical-but-often-overlooked sub firing angle)as well as making appropriate settings for the most coherent musical reproduction.
Afterwards (the following issue),we will look at the pros & cons of electronic eq & room correction,as well as a well-documented story about that topic.
See you then!
In Copper #18,we addressed the critical importance of getting the smoothest bass from our main (full-range speakers). This step is foundational for properly integrating our subs to the main speakers.
Before we get into our promised next section on installing/integrating our subs,we should briefly address two related issues…
1 – Power up,volume down– While you are getting your mains to have the smoothest bass,and when you are making final adjustments to them to achieve the best presence and tone they can provide,it’s important to have your subs powered up,but receiving no signal. Since you won’t be listening to them and they cannot make any sound if the input is turned down completely,the question is why even turn them on?
We don’t want the subs’bass driver(s)to be moving around in response to the sound emanating from the mains. I’ve heard this phenomenon referred to as sympathetic resonance. What a poor description! IMO,unsympathetic resonanceis more correct. Why allow the subs to interfere with our voicing of the mains by allowing them to play along with the mains,but probably out of tune and time?
While not perfect in its effect,powering up the subs more effectively locks the sub driver in the ‘zero’position. During this time I keep the subs nearby the mains – in an area where I am likely to locate them after our upcoming tests – maybe three feet or so away,perhaps beside them but more likely in an arc somewhere slightly or even directly behind them.
2 – Time Delay– Without going into the sometimes argued time delay issue,let me say that it doesn’t seem to be an issue when we are likely going to bring the subs in at about 30 Hz,give or take a few cycles. At these frequencies,with their very long wavelengths (say,32-40 feet long),this issue seems to be irrelevant (although 0-180 polarity of the subs is still important – which we will discuss).
So let’s get on with our sub installation/integration…
Aim to Please
No one seems to talk about this issue,nor have I ever seen it in practice,except on my voicing sessions,but – short of balance,crossover frequency selection,subwoofer volume,and polarity – (all of which we will discuss after this article),it is the vitally important next step to properly integrating your mains to your subs. And when done,the musical impact is substantial,as compared to before,with one possible exception to be mentioned later.
Everyone sits their subs down (hopefully in a good place),and points them essentially straight ahead. That means that,unless they get lucky,chances are that their subs could perform at a higher level,and they will never experience the potential improvement.
May I suggest a better placement method?
And it is not the oft-repeated “place the woofer at the seat and walk or crawl around the room near the main speakers to hear/discover the best place to put the subs”. We are gonna do something with a substantiallyhigher success ratio.
Before we go into the sub placement and direction technique,I want to make another suggestion that you obtain an RTA: a Real-Time Analyzer. (Hold on now – this is not about using it to measure the set-up – please hear me out.) As I mentioned earlier,they can be quite inexpensive,and sometimes almost free.
If you own just about any full-range speakers and a pair of subs,the expense of a RTA system is relatively insignificant. Operating it is simple – it doesn’t require an engineering degree for what we will be doing. For example,we will only care about the frequencies below 100-120 Hz.
If you choose a system that requires a mic,be sure to get one with an omni (pick-up pattern)capsule. They are several inexpensive mics out there from Behringer,Dayton,Audix,& others. A quick search on Amazon or elsewhere will turn up a decent selection. Also,be sure that whatever system you use to display the measurements has an adequate mic preamp. This is one reason I tend to like the Studio Six Digital AudioTools RTA. Its onboard calibrated mic is generally acceptable for our task. And fir even higher accuracy,it’s a snap to use their iTest mic with your iPhone or iPad. Just plug its mic cable connector in to the charger outlet,and not only does it work,it automatically calibrates the system to that mic!
The reason we want to use a RTA when possible is that it dramaticallysaves time and it eliminates the typical human error that is prevalent when trying to evaluate the sub placement by ear at low frequencies.
FWIW – I have been using a 1/3 octave RTA for this particular room/speaker voicing task since 1979. Although I have occasionally had to voice sub placement & angle by ear,I cannot imagine being captive to that technique,particularly in this app/centric age in which we live.
Why 1/3 octave,you ask? I’ve found that 1 octave is too general,not showing what is really happening. Sixth octave or higher measurements tend to confuse the casual user (and me). Maybe it is TMI – Too Much Information. It seems as if 1/3 octave is more similar to what we are likely to hear.
We want to use pink noise as our source and set the RTA on flat,unweighted (not A or C weighting). As mentioned before,run the pink noise at a level that is 20 dB above the (flat weighting)ambient room noise level.
Of course you could do this by ear if need be,but as I mentioned above,it is much more difficult and time consuming.
Ten step process
1 – We will place our mic or other measurement device at the by-now-optimum listening position,at ear height. By now optimum,because we found it inCopper #18.
2 – To begin,assume the sub is approximately three feet away from the mains. We will test our directionality at each location in a 3 feet-from-the-speaker arc and try several other locations to find the best one. You may not end up at 3 feet,but this gives us a starting point.
3 – We’ll do one sub at a time. Keep the other one powered up but turned down. Be sure to cut off the main speakers.
4 – Set the sub to crossover at a much-higher-than-expected setting – say 100-120 HZ. We do this so that we can see any resonances that will be present before we apply the crossover at a lower setting. Even though we will roll-off the sub at a lower frequency,we do not want to allow a big peak (room resonance)at say,50-60 Hz. If the peak is large enough,it will still contribute to a muddiness sometimes attributed to a “slow”sub.
5 – After we have noted the frequency response (peaks and dips)of the sub when pointed straight ahead,let’s rotate it 90 degreesto the side,generally pointed at the opposite channel’s speaker. Before this rotation,we want be sure that we have noted (it’s best to write it down)any obvious peaks & dips,their amplitude,and their frequencies.
6 – We will do the same measurements with the sub now generally aimed at the opposite speaker. You will notice some change in response. For now,just keep a record of it.
7 – Do the same with the sub pointed backwards. Yes I know that it looks weird. But if that is the best direction,you can find a way to obscure the back panel. I know,because my own pair face backwards. And visitors who come here for the RoomPlay Referencesessions consistently report that it was the most musically involving listening session they’ve had,short of live music.
Again,note the differences.
8 – Fire the sub towards the adjacent wall.Again note the differences.
Depending on your curiosity and patience,do the same process again at another location along the arc. I generally do it at three positions.
9 – When you find the best location & direction for your sub (smoothest bass),depending on your curiosity and patience,you may want to try a position that is between the two best – in other words at 45 degree angles. This usually pays off,if for no other reason than you have confidence that you have found the best location & firing direction for that sub. Later,if you wish,you can try other locations – say on a slightly larger or smaller arc. However,what you have found almost certainly eclipses what you could have gotten otherwise,so I usually leave it there and may come back at a later time if I have the time & patience.
10 – Now we will do the other sub. Caution,DO NOT expect that it will end up in a similar location or direction. Rooms can be different,and unless yours is especially well balanced dimensionally,or you get lucky,it may be different. We only care about the result at this point – the smoothest bass.
Be sure to turn the first sub down or disconnect its input.
We will finish with the set-up techniques (sub balance,level,crossover point,polarity,etc.)next issue. As with this issue,in Copper #20there will be some things you can do (that I do not generally see or hear mentioned)that can make a realperformance difference. And except for relative balance,the rest of the way will be by ear,not by measurement.
Oh,the possible exception that I mentioned in the Aim to Pleasefirst paragraph? Maybeyou will get lucky and your subs will work well without much effort and with them facing directly ahead.
Good luck with your project! Done properly,it will pay musical dividends for years to come.
See you next time!
Electronic Adjustments
Ok,now that we’ve accomplished the bassic(pun intended,sorry!)steps,we are on the home stretch. These final steps require personal choice/taste as well as some technical adjustments.
In the following sequence,we’ll be looking at sub balance (tech),sub volume level (tech/taste),sub polarity (tech),& sub fine-tuning at the crossover point/level (tech/taste),& crossover techniques (tech/taste)
Now,turn offthe main loudspeakers.
Sub balance –
Now that the position/angle of the subs have been determined,we need to get them to operate withe same relative level in each channel. For each sub,choose a similar crossover point – a bit higher in frequency than you think you will be using. For example,if you expect to crossover at 35 Hz or so,choose 45 Hz for the initial balance. Set the sub level at about 1/3 of the total available volume. Check each sub’s output individually. This is best done with a SPL meter,but it can be done by ear. You want to get them as equal in output as possible. When you have their individual acoustic outputs equal/balanced,it’s best to mark or record the volume setting. You’ll be turning the pair up or down shortly,and you want to make equal adjustments if possible.
Initial sub volume level –
Using some music tracks,such as the Brian BrombergWoodor Wood IIrecordings (or others that have variable bass notes and that seem to be a well balanced bass recording),raise or lower the subs’volume equally until the bass response is fairly smooth,not obviously too much or too little bass. We will get to fine adjustments after a few more steps.
Now,turn onthe main loudspeakers.
Sub polarity –
This step can dramatically affect the results of the next steps,so it should be addressed at this point. I have found that it is unpredictable depending on many variables in the set-up. We only care about the outcome,not the reasons why.
We want the subs to work withthe mains rather than againstthem. Improper acoustic polarity is an example of the mains & subs fighting against each other. It will result in diminished bass at & near the crossover point.
This aspect should be measured or listened to at the listening seat,not between the subs or elsewhere.
Play some pink noise if you have it. Measure the output in SPL,or if you are using a RTA,look at the crossover point/bass region and note the shape of the response. Then reverse the polarity on both subs and run the test same test again. One or the other polarity will have noticeably less output in the crossover region. That is incorrect – the speakers are out of phase at the crossover point and thereby cancelling the natural acoustic frequency balance of the recording. Note: this test can be performed by ear but it is a bit trickier.
Finally,some subs have infinitely adjustable (variable)polarity. I would start at ‘0’or ‘180’. Then I might check the response at ‘45’,90’,& ‘135’. You are looking for the setting that increases the output at the crossover point. You may see a difference or you may not. As before,you are picking the overall best polarity.
The reason we set polarity now is that we could possibly make crossover/level adjustments in the next step that are incorrect,and this would affect the smoothness of the subs/mains integration.
Sub fine tuning – crossover point & volume level –
This step assumes that you are NOT using an electronic crossover. The mains are playing smoothly through their range.
The crossover point on the subs that we were using for the balance test needs to be brought down to a point at which we think we will need to bring in the subs. We will make this final adjustment be ear.
It is critical to note that as you increase the level,you MAY need to reduce the crossover point. Visualize the mains’response as a straight line. As you increase the bass subs’bass output,its roll-off will intersect with the mains’response line at a higher frequency. And vice-versa for the occasions when you turn down the subs’bass volume.
Sometimes,adjusting sub level slightly is all that is required,but not that often.
In general,do not simply adjust sub volume without remembering that you are also slightly affecting the crossover point. I have encountered numerous sub/main speaker installations that were said not to be integrated smoothly,and when I listened to them,I agreed. Many times,it was an incorrect interplay of the volume and crossover points.
This is a combination of tech info that can serve the music,but only when you – as the owner – exercise your right to have the final call (taste).
This final tweaking of sub level and crossover point may take a bit of time,as you should listen to a variety of your recordings. For example,you don’t want piano lower registers to sound thick. I would mostly address instruments that have contributions in this area.
I definitely would check some recordings with deep bass,but I wouldn’t go for lots of deep bass and subsequently mess up the delicate balance for other instruments that are much more likely to appear in most recordings. This is definitely a matter of taste at this point.
One way to be sure that you have finally settled on the best setting is when you no longer feel the urge to get up and adjust the subs’level/crossover. If you have followed this info and previous Subwooferyarticles about subs,and addressed your set-up accordingly,it will happen! Sometimes it takes days to be sure that it is dialed in,but again,it will happen. And your music will speak to you in a more impactful manner than ever before.
Note– At this point,I often go back to see if the subs are still balanced in output after making the other adjustments. If they are no longer as balanced as they were,then you should rebalance them now,and then make whatever slight level/crossover adjustments as may be required. Also,I always record & mark the ‘final’;settings. That way,a bit later,when I have decided to try a slight adjustment,I have a known reference point. If I do make a slight change,I mark & record that setting as well.
Crossover techniques –
There are those that think that the mains should be crossed over to the subs as well,via an electronic crossover. From a theoretical/technical viewpoint,I agree. It’s just that,for me,I haven’t heardany subwoofer crossovers that are transparent enough in the mids & highs. That’s not to say that it cannot happen – it’s simply that I have never heard it.
And sometimes,for whatever reason,those set-ups seem to be the very ones where the subs/mains integration – and thus the musical engagement,is diminished.
If you have such a set-up and it is working for you in the musical involvement area,congrats! My guiding principle is to only recommend that which I have heard & liked. Doesn’t mean that your set-up is compromised at all – it’s just that I haven’t yet heard a similar one that worked.
Possible pitfalls of electronic eq and/or DSP – plus a true story
I have two main concerns with EQ and DSP;
1 – It’s not a panacea. Some people think that if they get the response relatively flat,or “fix”time arrival and such,that is all it takes. If you wish to use these programs (as I have),don’t even think about it until you have first done all of the basic set-up as I have mentioned. I have referred to this as the organicprocess rather than the electronic.
2 – Sadly,I’ve heard all too many systems that sounded technically correct,but were utterly boring musicallybecause the owner or system tuner felt that once the measurement goals were achieved,they were done. Not so!
So here’s a story that is related to the concept,at least in the area of execution. Some of you may remember the San Francisco StereophileHome Entertainment Show in 2003. If so,you may recall the extraordinary and never-again-equaled response that happened in our (Avantgarde-USA,BAT,Running Springs,etc.)demo room. Srajan Ebaen – 6moons.com– wrote about it,as well as Robert Harley in TAS,and others.
As always at the shows where we exhibited,I voiced that system. We had a couple of less-than-pleasant peaks in the boundary-dependent-region (below 300 Hz). Expecting some difficulties,I had brought my Rives PARC (Parametric Adaptive Room Compensation),which is designed to solely address that region.
When I mentioned to Richard Rives Bird that I was bringing it to the show,he offered to tweak it with his computer program. True to his word,when I let him know I wanted him to drop by,he was nice enough to come by and run the program.
Richard had a ton of work to do throughout the show. He didn’t cut short his time,but he based his adjustments on near-perfect measurements. Satisfied with the results,he went on to other projects waiting at the show.
There was no question that the response was very flat now. Technically,it was superb. However,after listening for a while after Richard left,I began to feel that the system was missing a bit of musical involvement. The emotional hook was not quite there.
So the result of the correction was flat response. Unfortunately,after I listened later,my response to the music was similar. Flat.
I should mention that we were only using the PARC in the line from the BAT preamp to the amps driving the BASSHORNS. The amps driving the TRIOS were direct from the preamp.
So I spent another couple of hours building on what Richard had done (LOL – Richard might have had a different description). I didn’t change the frequency of the three cuts he introduced,but did slightly adjust their “q”(width)and the level of their amplitude.
When I was satisfied,I was feeling good about the sound – the music was engaging at all levels and with all genres. I privately wondered if the subsequent measurements would have been as precise. My guess was — probably not.
Here’s the cool thing – We got standing applauseat the end of every demo for three days – an almost-unheard-of response to a show demo! IMO – listeners weren’t responding to the technical aspects of the sound,they were releasing emotions stimulated by the musical experience.
FWIW – I have never before (or since)seen such response from show attendees. It was unique in my long experience in the industry. In addition to the original mention,Robert Harley mentioned it in TASagain recently.
I think it might be too simple for an installer of digital room correction systems to rely on the measurements. And indeed there are systems that have remote tuning. Some even offer automated adjustments. But who determines how the system speaks to you,in your room?
A technician onsite MAY have the requisite blend of science and art skills to do it,but not if he thinks the measurementsare the cure. And even if he doesn’t,can he make the system come alive in a musically compelling manner?
So I have 3 primary caveats:
Umm,weren’t there supposed to be 8 articles in this series?
Hey,I managed to combine the info into seven! Anyway,I have in mind a somewhat-related topic…