What is the best sub set up cd.

[TooManyHobbies]

The Radio Shack SPL meter has two settings for filtering, "A" and "C" (often referred to as "weighting"). Some research defined "A" as being frequency compensated to hearing sensitivity (I assume Fletcher-Munson) and "C" as being flat frequency response. I could believe those add numbers using the SPL meter on "A", but I used "C" and would not expect this low frequency boost. If I adjusted my sub levels using the add numbers provided, I think that would result in setting the sub levels lower, although I have no idea what frequency the pre/pro test tone is. The sub level already seemed a little low on some recordings, not too high. Unfortunately, I'd need some adapter cables to hook my frequency generator up to the audio gear, but maybe I should try that sometime and see what the results look like with some known frequencies.

[RythmikAudio]

The Radio Shack SPL meter has two settings for filtering, "A" and "C" (often referred to as "weighting"). Some research defined "A" as being frequency compensated to hearing sensitivity (I assume Fletcher-Munson) and "C" as being flat frequency response. I could believe those add numbers using the SPL meter on "A", but I used "C" and would not expect this low frequency boost. If I adjusted my sub levels using the add numbers provided, I think that would result in setting the sub levels lower, although I have no idea what frequency the pre/pro test tone is. The sub level already seemed a little low on some recordings, not too high. Unfortunately, I'd need some adapter cables to hook my frequency generator up to the audio gear, but maybe I should try that sometime and see what the results look like with some known frequencies.

I have a full testing equipment to measure the frequency response of subs in room and in close-mic position. Even with that, I have found an SPL meter to be very valuable. I have compared the results of A-weighting with the results measured from lab grade microphone and they are reasonably close. Even though Radio shack analog SPL meter seems to be very popular, I do favor those made by Vellemen or other brands with digital readout and round windscreen sock (which helps prevent cone hitting mic during close-mic measurements). They can be found on Ebay and Amazon.

In addition to SPL meter, one also need a CD with various warbled tone frequencies. I have Stereophile test CD2. It starts with 1khz, and then jump to 200hz. A warble tone is a sine signal that warbles in frequency. By warbling the tone, we get an average over a finite bandwidth. If we use a single tone sine wave, the reading will be very unreliable as a slight hand movement can give you a different reading in a room. I use tripod too, out of convenience, not necessity.

Now the measurement method. There are basically two types of measurement methods, one is call near field (or close mic) and another is in-room. The in-room response will very much be affected by room modes below 200hz. Above 200hz, the reading from in-room response becomes very reliable as the frequencies of room modes are so dense between one and the next so that they certainly will fall into the bandwidth of a warbled tone and achieve the goal of returning an average value. On the other hand, the frequencies of room mode is farther away from one to another below 200hz, one can easily pick up all sorts of peaks and dips. In other words, the bandwidth of warbled tone cannot cover multiple room modes at the same time. To verify the "correctness" of subwoofer frequency response, I would recommend to do a close-mic first. For our subwoofers in particular, one should get flat frequency response with -3db at 14hz assuming the SPL meter is reasonably accurate. Then whatever the peaks and valleys one gets from the in-room measurement is due to phase alignment and room modes. These problems should be addressed differently.

The procedure of measurement is to start with a midrange reading as a reference. 1khz is a good one because our hearing is very sensitive to that frequency. Next I will jump to 200hz and go in smaller steps below that. BTW, prepare a spreadsheet and write down all readings and perform analysis later.

[TooManyHobbies]

Radio Shack also has a digital SPL meter for only a few dollars more than the analog model. I have had the digital model for at least 10 years. The Velleman digital meters have greater resolution, and I'm sure accuracy as well, but at least at the one source I looked at, they were more than three times the price. For my occasional use to set up the home theater, I've been happy with the Radio Shack meter, and for my non-professional use, I have a hard time justifying the extra cost. Doing the setup with a SPL meter has sure beat doing it without one.

I am in the middle of a system upgrade that is replacing large, floor-standing main speakers with a bookshelf and sub setup. Previously, a sub was only used for movies with the full-range main speakers used by themselves for music. It took me awhile to decide on subs for the new setup because of their use in reproducing music, and the final decision was dual F15's. My wife and I have been listening to this new setup for about a month, and we are very happy with my subwoofer selection. My wife's only regret is that the Rythmik subs are not available in wood veneer, but I'm sure that would be out of our budget.

Regards,
Bill