I’ve had a few folks ask me about testing subwoofers. I had been avoiding subwoofer tests for one main: measurement of Frequency Response, Harmonic Distortion, and Intermodulated Distortion. I can provide LSI data and I think it’s necessary, however I think it’s good to see FR and HD at a minimum as well.
The reason for this is simple: to measure at the output levels to make testing subwoofers/drivers worthwhile, I need to have a mic that can withstand those SPL levels. My current mic is great for my current set of testing because it doesn’t necessarily require the SPL levels a subwoofer would be pushed to. The contributing factor here is that subwoofer testing needs to be done in the nearfield so the room’s influence is negated. Essentially, to raise the signal to noise ratio. Otherwise the room should be taken out of the measurement by measuring outside far away from any reflective surface. Audioholics’ site has a great writeup about this here. I’d like to test a subwoofer in the farfield but I can’t easily do that due to weather and the room I test in.
Therefore, in order to obtain reliable and repeatable subwoofer data at a level that is worth performing the test, I need to do so in the nearfield. In the nearfield, the SPL level increases by approximately 18dB from 1 meter to ~5 inches (where every doubling of distance is 6dB in output).
Consider that most subwoofer tests are performed in the farfield of at a level of 120dB or more then add 18dB on this for nearfield SPL. This is why a microphone with high SPL capability is needed and therefore why those who test subwoofers do so in the farfield. There really is no explicit right or wrong method of testing a subwoofer in this regard. However, I believe nearfield testing is paramount to accurate testing within my own criteria and a high SPL capable microphone provides me the opportunity to do this.
Great.. why do you care? Well, the truth is I am looking for contributions to do this. I need about $350 to purchase the LinearX M51 Measurement Microphone. So, that’s my target. The sooner I am able to obtain the new mic, the sooner I can get started providing even more data.
If you want to help out the site and ultimately the audio community by pitching in a few bucks via the Contribute button at the bottom of the page, it would be greatly appreciated.