Subwoofery: Location, Location, Location

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!

You can read Jim’s work at his website. www.getbettersound.com