Echo Chamber: Room Acoustics Part 1 Mar22


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Echo Chamber: Room Acoustics Part 1

At the very tail end of 2016, I decided it was time to leave my sleepy home in upstate NY and head west to Portland, OR. Rather than deal with shipping all of my audio gear out, I felt it was a better idea to use the opportunity to sell much of what I had and give my setup a major overhaul, and so I waved a fond farewell to my Naim Supernait, Lindemann DAC, and Silverline speakers. In their place are an Electrocompaniet AW-60FTT power amp and EC-4.7SE preamp, Simaudio Moon 380D DAC, and Audio Physic Virgo V speakers. All the new gear is great of course, but as soon as I first stepped foot in my Portland apartment, I knew that there would be a lot room treatment required before I could expect remotely good sound.

With headphones, the frequency response measurements and other test data that can be found on sites like Inner Fidelity can give you a pretty good idea of how any particular headphone will sound. These measurements are not the be-all, end-all of course – some headphones sound better than they measure and vice-versa. But at the very least, the frequency response that you see is what you can expect to get.

With speakers, things aren’t nearly so simple. Just about every company that makes speakers (other than Bose) will provide a list of specs including impedance, sensitivity measured in db/W/m, and frequency response. Companies with access to an anechoic chamber can use that to completely isolate the speaker and measure its pure frequency response with no outside interference. Lacking that, the use of ample amounts of absorption and close mic placement for measuring can provide at least an approximation of what anechoic measurements would look like.

Here’s the thing though, your room isn’t an anechoic chamber, nor would you want it to be. Even very quiet rooms will have a level of background noise that will measure at least in the mid 20dB range, and the typical room will be above 30dB. In contrast, the current world record holder for quietest space on earth is Microsoft’s anechoic chamber, which measures just over -20dB. Yes, negative 20dB. This is about as quiet as it’s literally possible to get – air molecules bouncing off of each other create a background noise of around -23dB. If you want less than that, you’ll need a ticket to space [One of these days Dave – POW! Straight to the moon! -Alex]. We humans simply aren’t accustomed to an environment where there is no sound. Stepping into an anechoic chamber is like entering an alien world, one where you can hear your heart beating, your blood pumping, and if you have even the tiniest bit of tinnitus, you’ll know about it.

In addition to having no background SPL, anechoic chambers also have no sonically reflective surfaces, which is another thing we aren’t used to. Live musicians playing in an anechoic chamber would sound awful. This is because it’s not just the direct sound from the instrument itself, but the combination of direct and reflected sound that makes music sound good. The reason Vienna’s Musikverein is world famous for its sound is due to the acoustic design of the hall.

So while a certain amount of reflection is required for good sound, room reflections can also turn those fancy new speakers with a rated response of 30Hz-20kHz +/- 3dB into 30Hz-20kHz +/- 20dB or more when actual room response is measured. In order to fix that, acoustic room treatments are required. EQ and DSP can also help to some degree, but they are more of a band-aid than a real solution, and there are certain room interactions that they simply can’t do anything about. Before you can get to treating the room however, you first need to figure out where your going to put your speakers, and yourself.

There are volumes of information out there on speaker positioning, so rather than delve really deeply into that here, I’ll simply invite you to seek out those sources if you’re interested in the topic, as the purpose of this series is much more about solving room issues with acoustic treatments than how and why you should place your speakers where. Instead, I’ll simply tell you what I did. My living room area is about 14.5’ wide x 10’ deep. Due to the layout of my apartment, placing the speakers on the short wall was not possible, they had to go on the long wall. I started off with the speakers in the generally recommended equilateral triangle arrangement, 7.5’ from the listening position, and 7.5’ from each other. After some experimentation, this is the arrangement that sounded best.

Next on the list was toe-in, or the angle that each speaker is turned inward toward the listener. There is no “correct” amount of toe-in. Some speakers are designed for none at all, and have an elevated on-axis treble response to compensate for the normal high frequency roll-off that occurs off-axis, and these speakers will sound much too bright if pointed right at you instead of straight into the room. In the case of my Virgos, Audio Physic recommends either a significant amount of toe-in so that imaginary straight lines drawn out from each tweeter will cross each other in front of the listening position, or a moderate amount so that these lines would cross behind the listening position. I’ve tried the former before and haven’t liked the results, and indeed that was the case with the Virgos as well. In the end I settled on about 1.75” of toe-in so that the tweeters crossed behind the listening position, which provided the best balance of soundstaging and imaging. With more toe-in, the soundstage width shrank unnecessarily, and with less, imaging lost coherence, and the sound seemed to separate into three distinct “left, center, and right” pieces instead of a whole. The bottom line here is that when you take home a new pair of speakers, you need to experiment for yourself of what toe-in makes sense for your room. Again, there is no “right” answer here. Just play with them until they sound right and you’re done.

With the speakers set, it was then time to start working on the room, which I will begin to cover next time in part 2.