He also asked to me to position the mic at the precise spot of my ears. No kidding!!yup, no kidding! this is where you found the drivers to integrate best & the DEQXpert leveraged off that info to make the measurements. Any closer & you would have had the similar timing errors that Almarg wrote about. Makes sense....
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Thanks everyone for the good responses. I guess part of the answer to the issue I described, about the possibility of correcting a non-problem in the case of large speakers that can't be measured from an optimal distance due to reflection constraints, is that under such conditions speaker corrections would (or at least should, per Nyal's (AcousticFrontier's) recommendations) be performed only at frequencies above the point where the woofer(s) are likely to be significantly rolled off. For example, the crossover point of the woofers in Bruce's (Bifwynne's) speakers are indicated as being at 230 Hz, with a 12 db/octave rolloff above that point. (I don't know what the corresponding figures are for my speakers, as they aren't published and haven't been measured as far as I am aware). Bombaywalla, thanks for your inputs as well. As you aptly stated, there are always tradeoffs. Re your last post, though, undoubtedly the measurement they had Bruce perform at the listening position was for room correction, not speaker correction, room correction generally being done with DEQX only at frequencies below around 200 Hz or so, where room effects predominate. Speaker correction, including time alignment, would have been performed at the 36 inch distance he mentioned, and only at higher frequencies as I indicated. On another note, would anyone have any comments on the possibility of surrounding the measurement microphone during the close-up speaker measurements with two of these (four panels total, surrounding the mic on three sides). Acoustic specs are here, and look impressive. Or, alternatively, a mic baffle such as this one, which is apparently made of the same material as the large panels. Best regards, -- Al |
Bruce previously sent me his files and Larry windowed at 24ms and 98% smoothing. My own outdoor measurements are windowed at 26ms & 0% smoothing because measuring 'anechoically', the plots are clear and have almost no reflections or impulses other than the speaker itself - it's an almost flat line until a clear and tiny reflection at 26.2ms which repeats every 3ms until fading away at 36ms However the windowing I quote is based on reflections made by Bruces' setup and will be different for yours. To be safe, I would suggest you try to look for a clear smoothish area after the main impulse and before the first obvious reflection. However, that may be difficult with a somewhat confused indoor measurement |
@Al ... just an fyi. Maybe Drewan can weigh in a little, but my general recollection is that my room wreaked havoc up to 500 Hz. Plus, my speakers weren't all that flat north of 500 Hz. Another point. Larry basically cut the S8's woofers out of the picture. He used my subwoofer to do the heavy lifting below 120 Hz. Part of the problem related to the room for sure. But also, the mid and tweeter drivers are wired in reverse polarity as compared to the woofers. So he reversed the overall polarity of the signal and matched the time alignment of the mid and tweeter drivers with the subwoofer. The S8's woofers are only working from 120 Hz to about 230 Hz. The sub is picking up the load from 13 Hz to 120 Hz. That's why I described the DEQX as turning my signal into a pretzel in order to tame my system. Drewan, if you have my e mail address, send me a PM and I will send you the latest files which reflect Larry's most recent "fine tuning" adjustments that he did on December 4, 2014. Same offer to you Al. Bruce |
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