Tame the Effects of Your Room with EQ & Measurements

Whether you live in a McMansion, a hovel, or something in between, the most influential component in your audio or home theater system is the room. Given at least a basic level of quality in your components, it isn’t even close.

We do acclimate fairly easily to our own listening space, which allows one to overlook response deviations that would make you abandon audio for fly fishing were you to see them on a graph. I’ve had many different rooms over the years, and until I acquired some basic measurement equipment was often quite happy with them once I’d settled in.

A book can be written about how the room affects the listening results, and many have. Probably the best is Dr. Floyd Toole’s Sound Reproduction: Loudspeakers and Rooms. If you have a lazy couple of weeks, its 500+ pages are must-reading. But I’ll attempt a summary here, combined with some of my own thoughts and results.

1. Even the most carefully positioned stereo pair of full range loudspeakers, without a subwoofer, will almost never provide both the best bass and best imaging theoretically possible from those speakers under (generally unrealizable) optimum conditions. In a typical home environment (short of all glass walls and a tile floor!), the most significant impact from the room is in the bottom end below 300-400 Hz (some experts argue that it’s only below 125Hz—I’ve found dealing with the broader range more useful).

2. No. 1 is also true of a multichannel system without subwoofers.

3. Repositioning the speakers and/or the listener in the same room can improve the results at the primary listening seat but isn’t a total cure. Moreover the result is rarely as good in any other seat.

4. Using room EQ can help, sometimes at more than one seat, but without subwoofer(s) will still be less than ideal. And if not done carefully, EQ may tax those full range speakers in the deep bass, particularly on action-heavy film soundtracks.

5. A single subwoofer plus room EQ can help significantly at the primary listening seat, though only rarely at other seats. For this to work as it should, you must roll off the bass response in the full range speakers with your AVR’s high-pass filter and not let them play bass along with (and fighting) the subwoofer.

6. Using multiple subwoofers, optimally positioned, plus room EQ offers the optimum solution if you want the best possible bass performance in all seats, combined with the best performance from your main speakers in other respects. If you want the speakers to sound like they did when you first heard them (which we hope is why you bought them!) you might want to limit any EQ adjustments to around 400 Hz if your available EQ allows for this.

Even step 6 will not provide a technically perfect result. There is no such thing as a perfectly correctable room. But implementing it should greatly improve the sound.

Many two-channel audiophiles will have none of this, considering both equalization and subwoofers to be spawns of the devil. Fortunately, the more enlightened among them realize that there’s more to getting the best sound in their room than upgrading the amplifier, sources, and cables, or adding tweaks and accessories, from power conditioners to magic dots. These can all be useful (well, maybe not the dots), but for other reasons. They can’t improve what the room is doing to the sound.

But two-channel fans often have one advantage not possible in many multichannel setups: more flexibility in the loudspeaker and/or listener locations. For home theater, the setup is more complex so the setup options are more limited. But a pair of good, properly set up subwoofers is a start. Proper subwoofer setup is a story for another (very long) day, but there are already volumes available about this from on-line sites, including here. But good room EQ can be the icing on the cake. Many AV receivers offer some forms of it. The best known are Audyssey, Dirac Live, and ARC. The first two, especially Audyssey, are widely available on different brands of AVRs and pre-pros. ARC, or Anthem Room Correction, is exclusive to Anthem (and Martin Logan) products.

While many subwoofers now offer their own, effective on-board equalization, this will only help below the selected subwoofer crossover frequency, typically 80 Hz. This only covers part of the range that can cause problems. In some rooms this may be enough, in others it likely won’t.

But even without using dedicated room EQ I’ve also managed to get audibly impressive results by a simple combination of the eight-step graphic equalizer, treble and tone controls, and channel level controls on my Marantz AV8805 preamp-processor. While this is a high-end unit, many more affordable AV receivers offer similar adjustments. But going this manual route by ear is a blind alley; you’ll need a way to measure the results as you tweak all of the manual controls. I use the OmniMic system from Parts Express. While at $300 it isn’t cheap, it’s far more so than some options and accurate enough to provide reassurance that you’ve done the job properly. It’s also a good thing to have available as a separate check (a second “opinion”) even if you use an automated room EQ feature such as Audyssey.

Above (and below) are the left-channel, in-room measurements of speakers I’ve reviewed recently, all of them three-way towers. All of the results shown here were for the left channel, taken at the main listening seat with no averaging, and smoothed to 1/6th octave. All three speakers were located at least 3.5 feet from any side or rear walls. While placement so far from the walls limits the bass boost closer placement can offer, near-wall placement will often result in poorer imaging. Fig.1 (at the top of this blog) is of a full-range, relatively large, floor-standing tower speaker without a subwoofer. The equalized response is in blue. Only the three bottommost of the Marantz’ EQ controls (63 Hz, 125 Hz, and 250 Hz) were used, together with tweaking the bass control; note that none of the EQ adjustments have any effect above 400 Hz, but the deep bass is in better balance with the upper bass and is more powerful than without EQ.

Fig. 2, (below), is of a different tower speaker, crossed over to a small subwoofer at 100 Hz. The equalized response here is in red (sorry for the switch!). No EQ controls above 25 0Hz were used here either, but the bass control was also lowered to achieve this result. This produced a modest decrease in the response not only where it improves the result between 125 and 400 Hz, but to a lesser (and likely audibly innocuous extent) between 400 Hz and 1 kHz as well.


Fig. 2

Fig. 3

Fig.3 is yet another tower speaker crossed over to a different, larger subwoofer, but this time with no EQ used on the main channels. But the subwoofer itself features its own automatic EQ, which was used.

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