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I just finished building my sub and it sounds terrible - very boomy and I can't make out the tones, they all sound the same and very fluffy. It is a S=0.7 alignment and is designed with Fl=45, Fh=110, gain = 1.7, Qbp=0.79.
If it helps, the TS for the 12" driver are Fs=21, Qts=.23, Vas=400L, and I already know this is not a 'traditional' set of TS params for sealed/bandpass, but for the Fl,Fh and gain params that I required, this was the only driver that I could find that would fit the bill.The impedence turning points are measured as follows -
41.5 Hz - 30.1 ohm
63 Hz - 6.4 ohm
102 Hz - 33.4 ohmFrom what I have read, when the peaks have the same magnitude, then the box is tuned properly. Is 30.1 ohm near enough to 33.4 ohm to be considered the same?
According to the spreadsheet, the tuning frequency should be 73Hz.Follow the link to see the frequency response.
Please help!
Follow Ups:
Hmmm.. I might redesign for a sealed enclosure (highly acoustic suspension like with those TS params). Two of these drivers per enclosure should give me the gain that I need.
In my experience with bandpass enclosures, drivers with a Qts of between .35 and .45 seem to work best. I'm assuming yours is a 4th order bandpass. I did a quick run through with WinISD using your T/S parameters and came up with slightly different, although essentially the same figures as you did: fb=65Hz, -3dB (low):40 Hz, and on the high 106Hz. Vb(front):41.5 liters and the rear enclosure: 46.3 liters. Stuff the rear enclosure with about 1-1.5 lbs/cu ft with Acousta-stuff or fiber glass, and line the front chamber walls with 1" fiberglass. In the end, I abandoned the bandpass design for the same reasons you cite. They put out lots of one-note bass.
This might be a reeeaaaally dumb question, but I'm curious: how safe is it to use fiberglass in a ported speaker? Is there any risk of glass fibers being pumped out into the air? I've worked with fiberglass on surfboards and it's something you don't want to be breathing. Is fiberglass insulation different?
...cover the fiberglass with a thin sheet of dacron polyester padding.
that inhalation of fiber glass fibers is not a significant health risk unless you inhale large portions on a routine basis (ie you mfg the stuff or you are an insulation worker) OR you inhale quantities of very small respirable fibers. Fiber glass fibers (unlike some others) are shaped like a glass rod and break cleanly which reduces the damage when breathed into the lung. They are also more soluble in the lung that other mineral fibers.Best practice exposure guidelines allow 5 milligrams of inhalable fibers per cubic meter of air breathed on average over an 8 hour workday for a forty hour workweek over the course of a working lifetime. Thats quite a few fibers! I seriously doubt you would have any exposure concern from the relatively minor disturbance of air movement through a port. So the good news is that you should'nt have to don a respirator during those heavy bass passages!
Bet you never thought you see a toxicologist on the asylum! Happy building.
Regards,
Rich
P.S. These opinions are, of course, purely my own and in no way should be construed as a professional opinion..... (I do know there are some lawyers running around!)
"5 milligrams of inhalable fibers per cubic meter of air breathed on average over an 8 hour workday for a forty hour workweek over the course of a working lifetime"Holy cow, that's a lot. Just doing rough guestimates in my head, that works out to over a pound per year! So if I were to slowly inhale ALL of the insulation in my speakers over a year or two, I'd still be expected to show up for work. That's good to know.
Many thanks.
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