How bad is it to have a high qtc for a 12" woofer?

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Hi,

With a Qts of 0.69 a box sim will suggest silly sized boxes for Qbox = 0.71.

You have to accept a higher Q alignment, and the driver is intended to
be used in boxes with a Qbox >1. Qbox =1 is 5.5cuft which is similar
to Vas and going bigger won't help that much, you need 10 cuft to
get to Q=0.9, and 20cuft to get to Q=0.8.

You should accept that the driver works best an 3 to 4 cuft box with a
box Q of 1.1 to 1.2, probablty intended to be about 2cuft. If you think
Q=1.4 is bad, try some of the other cheap PE 12" in a 2 cuft box ......
One comes out with a Qbox near 3 ....

The Dayton Audio DC300-8 12" works well in a 2 to 3 cuft
sealed box, and well in 3 to 4 cuft boxes tuned low at 25Hz.

rgds, sreten.
 
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Perhaps the designer had the Linkwitz Transform in mind.

I would not be afraid of Q slightly over 1. Room modes will probably do a lot more harm.


For many years I have listened with pleasure to AR16's , they worked very well in our family room 8x4x2.7 meter.
Bass was quite qood...

AR16 Qtc=1,15 @55Hz according to AR specification.
 
TOO LOUD MUSIC

0.85 Qtc calculates a ~0.43 dB peaking around 70 Hz in well stuffed ~115.44 L, so plenty good enough.

GM
IF I WANT TO TEST A HI FIDELITY SET I TURN THE VOLUME DOWN SO THAT I CAN HEAR THAT HORRIBLE DRY SOUND AND THEN SEND THEM TO THE TRASH CROSS-OVER DISTORTION IS BAD AND INAUDIBLE WHEN MY EARS RING FROM LOUD NOISE.......I MEAN "MUSIC" GUYS HONESTLY MY WORKMATES GOT DEAF AND IF YOU GOT TO WORK IN DISCO'S WEAR SAFETY EAR BUDS IT IS HORRIBLE TO HEAR THE SWISHING SOUND OF AN OLD F.M. RADIO THAT IS NOT TUNED TO A STATIONALL THE TIME THAT YOU ARE AWAKE
Krokkenoster
 
Or no box at all?
Maybe this driver is intended for infinite baffle, i.e. a hole in the
wall between two rooms that are isolated from each other.

Hi,

No. Most drivers of this type are intended for boxes with higher Q
than 1.0. They also generally don't have any BSC so it sounds far
less worse than you might think, used in many commercial speakers.

rgds, sreten.
 
Using various speaker box designers, I'm coming up with very large Vb when using a qtc of 0.707. How bad would it be to have a higher qtc (0.8 or 0.85) for this woofer:

12" Square Frame Paper Cone Woofer White 290-914

How much will sound quality suffer?
Coming from a guy with considerably less experience than some of the other gentlemen in your thread I'll stop short of saying box size isn't all that important ... it is ... but, you'd be hard pressed to actually tell the difference in driver response from Q =0.7 up to Q =1.0 I'd bet. Even Q =1.2 isn't like "holy crap, that's waaayyy too much bass for me" territory ... unless you can sense another 1db of gain down there :p

As somebody has pointed out, your room would have a bigger influence on the bass response than the 0.707 to 0.8/8.5 Q would. I wouldn't even sweat this.
 
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Greets!

The formulas were for a HP computer program in a JAES paper done by Gary Margolis [JBL] and Richard Small sometime around 1980, but my copy is long gone, so best I can do ATM. I do remember it either not elaborating on the various values or me not understanding the math, so asked my contact at Altec about how to interpret it and according to him it basically boiled down to 1"^3 of acoustic fiberglass insulation = 1.5"^3 of air.

From experience I know that in doing ~aperiodic alignments that it equates to a Ql = ~1 in BoxPlot 3.07, if that helps.

Bottom line, we're talking about this type/amount of stuffing where a net is put over the driver, etc. to protect it and would have posted this if the OP wanted to go with this alignment. IIRC bjorno has posted some math about how this much stuffing alters the driver's T/S specs.

GM
 

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that is equivalent to saying the speaker hehaves as if the box had 50% more volume.

I have seen figures quoted around +20% for sealed boxes. I wonder if that applies to an open box?

The '50s, '60s era DIY books I have lists 1.4x using fiberglas or Cellu-down insulation due to a pressure-temperature change from adiabatic to isothermal for a 'heavily constructed, well braced and sealed cab' with a picture of a small sealed cab, so was rather surprised when I was told an even higher percentage, but when I initially posted this on the old bass-list, several folks said that the 1.4x was only in theory and not to expect nearly as much, around 20%.

Having no documentation from Altec or any of my builds to prove otherwise, I let it go. Then someone posted Tom Nousaine's tests that showed some interesting results that somewhat proved my claim, but more importantly for me it used pillow stuffing, which others confirmed had superceded the traditional insulation material I did/still do use and in a few experiments proved to my satisfaction that it isn't nearly as efficient for heavy damping, though I still haven't seen any rigorous test results for fiberglass: http://www.nousaine.com/pdfs/Box Stuffing.pdf

GM
 
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