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It sounds like a massive undertaking. Better bring the gas grills and plenty of food for a big cook-out. :) Take plenty of pics - looking forward to seeing/reading everything. :emoji_thumbsup:

Wow - 10 dB is a big jump (a 300% increase in acoustic output). If the sub craps out between 10 dB intervals, maybe you could fall back on 5 dB intervals.

Looks like we lost some good posts during the HTF server/database problems - that's too bad. :frowning: Anyone willing to repost would be appreciated. Anyway......I ran some IMD tests over the long weekend on a review subwoofer. I did 30/53 and 30/72, both at 95 dB and 100 dB. This...

Yes, this is possible. SpectraPro has a multi-tone generator which can output up to 10 tones simultaneously, or you can pick/choose which ones. It would only take a few seconds to check all of them. However, which gives the higher %IMD and which gives what subjectively might be perceived as...

30/53 yields the following IM components: 83 23 7 76 113 136 166 46 189 143 129 37 16 99 196 219 67 182 173 242 249 69 272 226 152 14 295 203 And the following harmonics: 60106 90159 120212 150265 180318 210371 240424 270477 300530...

There are various permutations of the 0.618 "Golden Ratio" which Risch used for various SC/multitone experiments. Multipliers of 1.1618, 1.2618, 1.3618...etc. can be used, for example. Using 1.7618 yields 30/53 Hz and 2.1618 yields 30/65 Hz, for example. I don't have the IMD spreadsheet in...

My guess/vote for Subwoofer "C" is a Tumult-based DIY sub that Ilkka built. Failing that, my second vote defaults to the evergreen Bose Acoustimass module. ;)

Yes, you are correct, but in this case 30/70 are not harmonically related in the mathematical sense - i.e., multiples of 30 do not overlap 70 or multiples of 70. And the same applies to 30/78. What Roger was saying is - that for certain fundamental tones - some of the IM components end up...

He's only responding to comments from others that hiding the identity of the subwoofers (especially if they are competing internet brands) show impartiality and generates less hysteria and allows us to focus on the test results instead of the brands. While I can certainly appreciate that...

While the same can be said for IMD, a larger database needs to be built for SC before any interpretation of the test results can be performed. Once you defined the level of the noise floor (this is part subject to individual interpretation), the %SC is easy to calculate.

Yes, the mic, sound card, and software are all accurate to somewhat below 10 Hz, so 11.5 Hz shouldn't be a problem.

Indeed, a variation of the Fibonacci series listed in the Risch papers is what I used to generate the test frequencies for the spectral contamination test tones. 30 Hz and 78.5 Hz is easily doable and still satisfies the other previously listed criteria; thanks for the suggestion, Roger...

Hi Dave: You need to remember Ilkka's post represents preliminary research into this subject. The fact that he shared this research with everyone doesn't bother me in the least. With that said, it also shouldn't imply that this work is final. Peer review is an important part of research...

I’d just like to clarify the use of the term “Doppler Effect” or “Doppler distortion” as referred to in this context. It is not the same as intermodulation distortion, and the two should not be confused. Frequency modulation in a loudspeaker playing two tones simultaneously does exist. If...