# Retune confusion....



## Vader (Jul 8, 2006)

Hi all,

I just re-tuned my dual 20-39 PC+ cylinders down to 16Hz, and was somewhat confused with the resulting FR. Based on the FR postings at SVS and other reviews, I expected to lose 3-4 dB in the 28-32Hz band as a trade-off, but I thought the rest of the range (above 32Hz) would be comperable. As it turns out, I lost 3-4dB across the entire range (if I am reading the FR right), all in exchange for about 4Hz deeper extension. I checked several titles (WotW, The Incredibles, Episode I, etc), and I did indeed lose a great deal of "punch". Do the below FRs look right? Could this be indicitive of a damaged woofer? Thanks!









Green trace = 20Hz; Purple trance = 16Hz

I am thinking that, since the 20Hz tune yields about 17Hz in-room response, is the 13 Hz in-room really worth losing the "punch-in-the-gut" midrange?

P.S. I just ordered my BFD from the shack store! Ruler-flat response, here I come!


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## Ed Mullen (Jul 28, 2006)

Hi Derek:

The subwoofers lose sensitivity when a port is plugged and must be recalibrated. Bump the subwoofer channel level about 3-4 dB to account for the loss in sensitivity and you'll restore the same overall level as the 20 Hz tune.

Lost sensitivity is not the same as a reduction in headroom/output. There is indeed also a reduction in headroom in the 22-30 Hz region when a port is plugged because maximum woofer excursion will now occur in this bandwidth (as opposed to being previously damped by the ports in the 20 Hz tune), and this will indeed result in some loss of slam/impact. 

Whether or not this loss of headroom is a problem in your case really depends on your preferred playback level. If you don't listen at lease-breaking levels, you can take advantage of the extra extension the 16 Hz tune offers. Otherwise use the 20 Hz tune for max output.


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## Vader (Jul 8, 2006)

Ed,

Thanks for your explanation, it explains why the overall shape of the response is nearly identical, just lower (presumably from more-or-less uniform loss of sensitivity). As for my preferred listening levels, they are generally 10-15dB lower than reference. For grins, the other day I measured the max SPL I was getting in my 3200 ft^3 HT during the "tripod emergence" scene in WotW while in 20Hz tune (MV -15dB). It maxed out at 108dB (at a little over 3m). From other postings under comperable conditions, my understanding is that I should be able to pull about 114dB from the 20Hz tune, and assuming that I lose about 4dB headroom by tuning it down to 16Hz I would be just knocking at the door of bottoming them. Maybe I should quit while I am ahead......

As for the recalibration, I set the input levels in REW to a speaker calibration level of 80Hz for both the 20Hz and 16Hz readings (the AVR MV was tweaked upwards about 4dB to do this). And I re-calibrated the sub pink noise level settings using DVE (currently 75dB for all channels, LFE calibrated to 85dB). Me thinks I am playing with fire....


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