|
|
"While EQ can be useful to help tame the one or two worst modal peaks at very low frequencies, it is no substitute for bass traps."
"Unfortunately, the popular audio press gushes uncritically over products like these, printing press releases as fact and never actually testing the validity of manufacturer claims." |
By
Ethan Winer Regular readers are aware of our article from October 2005 comparing the effectiveness of bass traps versus equalization (EQ) to tame room acoustics problems. While EQ can be useful to improve the one or two worst modal peaks at very low frequencies, in our opinion it is no substitute for bass traps and other acoustic treatment. Over the past few years a number of products have appeared claiming to provide room "correction" based on EQ. Some of these products even claim to replace the need for acoustic treatment entirely. For example, JBL has a new line of powered loudspeakers with built-in equalizers that claim to "analyze and correct the problems in any room." The limitations of room EQ are described in great detail in the article linked above, but the three main ones are:
Recently several products have appeared claiming to do even more than EQ by using sophisticated DSP (Digital Signal Processing). They claim not only to flatten the frequency response, but also to reduce modal ringing and early reflections, and to do so successfully over the full range of audio frequencies for multiple seats in a room. One such product is the Audyssey MultEQ system, which is the subject of this commentary. Unfortunately, the popular audio press gushes uncritically over products like these, printing press releases as fact and never actually testing the validity of manufacturer claims. The appeal of a small electronic device that claims to replace large and visually imposing acoustic panels is undeniable. But wishful thinking does not make it so! Even the vendors themselves offer no real proof that their products work as claimed. I emailed Audyssey on October 29, 2006, regarding the technical descriptions and graphs shown in a series of pages on their web site. I asked if they had any data to support their claims of reducing ringing, and I also asked for clarification about how the tests on their site had been performed. For example, how large the room is and how far the measuring microphone was from the walls. I have yet to receive a reply from Audyssey. |
Click any image below for a full-size version.
|
PUTTING AUDYSSEY MULTEQ TO THE TEST As it happens, Stereophile magazine columnist Kal Rubinson lives near me, and he had just received an Audyssey MultEQ system for review. I was thrilled when Kal invited me to help him test it, and a few days later I arrived at his home with my Dell laptop, ETF software, and DPA precision microphone. Kal's room is especially problematic, being nearly square at 15 by 16 feet and with an 8 foot ceiling. In addition to a few well-placed high frequency absorbers, Kal has two RealTraps Tri-Corner bass traps, plus a pair of DIY traps he built to look like a shelf along the bottom of his front wall. I wanted very much to measure the room without any bass traps, to see what the MultEQ could do all by itself. But it would have been too much effort to remove Kal's DIY traps, so we removed only the Tri-Corners. Had we been able to remove all of the traps, the "without" graphs at left would surely have been even worse. Audyssey claims to flatten the response and reduce ringing over an area large enough to encompass multiple seats, so I measured at three adjacent locations on Kal's couch. It turns out this was not necessary because the MultEQ was unable to reduce ringing even at the same place it was calibrated for. As you can see in Figure 1 at left, the main improvement is a 6 dB reduction of the lowest response peak around 35 Hz. The graphs in Figures 1 and 2 show not only the raw low frequency response, but also the individual decay times for each peak frequency. This type of graph is called a waterfall plot, and the "mountains" come forward over time to display the decay times at each frequency. You can read a more complete explanation of waterfall plots and the ETF software I used for these tests in our Using ETF article. CONCLUSION Listening to a variety of music there was no question that the sound was improved when the MultEQ was engaged. In a nearly square room like Kal's, reducing the large modal peak via EQ removed the boominess that was apparent in all of the music tracks we auditioned. Improving the bass also increased clarity in the low midrange by contrast, since the low mids were no longer masked by the excess bass. Likewise with JBL's room correcting loudspeakers mentioned earlier. I recently had the opportunity to audition a pair of these in a typical small untreated room. With the EQ engaged the one worst resonance in the room was improved subtly. (You may find it interesting that four other professional recording engineers in attendance thought the sound was made slightly worse with the JBL speaker's EQ engaged.) I didn't measure ringing with the JBL speaker, and JBL does not claim their EQ reduces ringing. But clearly the ringing was not improved by the Audyssey system - not even at the prime location for which it was calibrated. To be clear, I am not opposed to the use of EQ to reduce the one or two lowest modal peaks in a room. Conventional broadband bass traps are less effective once you get below about 50 or 60 Hz. So even if an equalizer or DSP device cannot reduce ringing, just lowering a peak's level and the amount of its ringing (if not reducing the decay time) improves the sound in a very real way. Indeed, I have 40 RealTraps in my own living room home theater, but I also use the one-band cut-only EQ built into my SVS PB12-Plus/2 subwoofer to tame the worst modal peak around 40 Hz by a few dB. The MultEQ is certainly effective as an equalizer, and since it adjusts itself automatically it has the potential to be easy to install and setup correctly. However, Audyssey does not sell this device to end users, but rather requires you to hire a professional installer. It is also very expensive for an equalizer. In contrast, for about $150 you can buy a Behringer parametric equalizer and use the freeware Room EQ Wizard software to automatically control the EQ from your own computer. Even if you buy a separate computer just for the EQ, the total cost is still lower and you "own" the hardware and can recalibrate your system whenever you want without paying a professional installer. The Room EQ Wizard also performs a very thorough room analysis, showing much more information than the software bundled with the Audyssey MultEQ. Finally, I'd like to reiterate a point I have made many times in my acoustics articles and web forum posts. The frequency response in domestic size rooms changes drastically over very small distances, even at low frequencies. Therefore, unlike bass traps that always improve all locations, any EQ that improves the response at one location is sure to make it worse elsewhere, even a few inches away. Figure 3 at left shows the bass response I measured on a second visit to Kal Rubinson's home. Since Kal had already tweaked the Audyssey, its microphone was no longer set up and I had to guess where to place my microphone. I placed it at ear height above the center of the couch, and Kal agreed it was "in the ball park." As you can see in Figure 3, some of the corrections applied by the MultEQ are inappropriate for this location. The peak at label A was reduced about 8 dB more than it should have been, and the 3 dB peak at B was boosted by 5 dB rather than reduced 3 dB. A few other frequencies in the section between 164 Hz and 200 Hz were also made somewhat worse when compared to the "without" graph. Therefore, when using EQ manually to reduce low frequency peaks, I suggest you split the difference and apply only half as much reduction as the measurements indicate is needed. |
|
Entire contents
of this site Copyright © 2004- by RealTraps, LLC. All rights reserved. |
)
)
)
)
)
