Subwoofers: Separating the Best From the Rest
I was testing some subwoofers the other day when something wonderful dawned on me. I realized that at long last, we have an easy way to separate the serious subwoofer manufacturers from the not-so-serious.
The tests I was doing involved CEA-2010 output measurements. CEA-2010 measures the maximum usable output of a subwoofer at six different bass frequencies. As I’ve written before, it’s by far the most useful test you can perform on a subwoofer.
Not only does CEA-2010 tell you the maximum output at those six different frequencies, it lets you see if a sub is tuned for, say, a relatively flat power output throughout the bass region, or maximum power at higher frequencies (50 or 63 Hz) but little or no output at 20 or 25 Hz.
CEA-2010 sets certain maximum thresholds for distortion harmonics. If you’re measuring the output at, say, 40 Hz, the 2nd harmonic at 80 Hz has to be at least -10 dB below the level of the 40 Hz fundamental tone. The 3rd harmonic has to be at least -15 dB below the fundamental, and so on. The higher the harmonic, the lower its acceptable maximum level, because higher harmonics are more readily audible.
My realization came when I was measuring a subwoofer that made some nasty buzzing noises. The noises, which were relatively high in frequency, caused the sub to exceed the maximum threshold CEA-2010 sets for upper distortion harmonics at a lower output level than if those noises weren’t there. But the noises weren’t the result of distortion. They were the result of either some mechanical noise inside the sub — i.e., something vibrating inside — or air turbulence around the port. “They definitely didn’t do CEA-2010 on this one,” I thought to myself.
If the manufacturer had done CEA-2010 measurements on that sub, they’d have found the problem and probably could have fixed it. It’s not like 2nd or 3rd harmonics, which are caused by the speaker or the amplifier exceeding its capabilities. To fix excess 2nd or 3rd harmonics in a subwoofer, the manufacturer may have to spend a lot more money on a better driver or a more powerful amp. But fixing problems at higher frequencies may require just a minor mechanical tweak that adds little to production cost.
Thus, if the manufacturer of your subwoofer publishes CEA-2010 results, you know the subwoofer has been fully tested and optimized for the maximum performance its driver and amp can deliver.
Performing CEA-2010 measurements isn’t particularly expensive; if a freelance reviewer like me can afford it, so can a manufacturer. Total cost of the gear and software I use is about $1,450 plus a PC to run the software on. (The website Audioholics uses a very similar rig, as do the manufacturers I’ve talked with.) A manufacturer can even do the test with nothing more than inexpensive spectrum analyzer software and a cheap measurement microphone; the results won’t be as consistent as using the CEA-2010 testing software, but they’ll be adequate. Even just running the CEA-2010 test tones (available on my website) through a subwoofer and cranking it up can reveal a sub’s flaws and limits in seconds.
However, it seems most manufacturers don’t perform CEA-2010 tests, and even fewer publish the results. In fact, I could find only one company that publishes CEA-2010 results on its website: Polk Audio. You rock, Polk.
I also know from speaking with the people at Hsu Research, SVSound, and Velodyne that those companies do CEA-2010 measurements. However, while these manufacturers sometimes share their CEA-2010 results on online forums, they don’t currently publish the results on their websites.
Instead of publishing CEA-2010 results, manufacturers typically cite a meaningless maximum output number. Let’s say a sub is rated at 115 dB max output. Well, at what frequency? At what level of distortion? At what distance?
It’s time for this to change. Despite my past complaints about CEA-2010’s repeatability, there’s no other test that so quickly and accurately gauges the quality of a subwoofer. Every manufacturer should be doing this test on all of its subwoofers — and publishing the results in the product specifications. If they do, you know they’re serious about their subwoofers. If they don’t. . .