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Old 16th November 2008, 04:37 PM   #1
BWRX is offline BWRX  United States
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Default enclosure suggestions for peerless driver

I would like to use some 8" Peerless drivers as subwoofers for music/tv/home theater duty in an 18 ft by 12 ft by 8 ft room. I've got 4 of these drivers so there are a number of ways they could be configured. One driver as a sub for each front L/R channel was the initial idea.

Specs for the drivers:

Re 5.35
Fs 31.9
Qms 2.041
Qes 0.311
Qts 0.270
Vas 74.58L
Cms 0.000918
Mms 27.1g
Diameter 175mm
BL 9.66
SPL 90.75dB 2.83V
Sd 0.02405sq.m
Xmax 6.0mm

It is recommended that these drivers be used in vented enclosures. Anyone have any suggestions as to what enclosure volume and port size would be good for my application?
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Old 16th November 2008, 07:55 PM   #2
Mikey p is offline Mikey p  Canada
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For for music/tv yes, but skip the HT duty with these. 1.5 cu.ft tuned to 33hz with a 3 inch diameter port 9.5 inches long. It will handle 50 watts input power with a subsonic filter at 26hz. SPL would be around 104db at 40 hz, dropping to 98 db at 30hz, and falls off the face of the earth after that. A high Fs, 6mm xmax, and small Sd does not make for a lot of low end output.
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Old 16th November 2008, 10:15 PM   #3
BWRX is offline BWRX  United States
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Since the room is more or less rectangular do you think using a vented enclosure per channel and placing the boxes in the corners of the room would raise the low frequency gain enough for home theater use? If not, how about using the extra 2 woofers together in a separate enclosure just for HT use?
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Old 17th November 2008, 12:25 AM   #4
Mikey p is offline Mikey p  Canada
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Separate boxes in each corner would help get the most out of them although there won't be much below 25 hz where alot of the HT experience is. You will need a subsonic filter at 26hz, without it these subs will bottom out hard.
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Old 17th November 2008, 12:33 AM   #5
BWRX is offline BWRX  United States
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Good point about the LFE being beyond the capability of these drivers in ported enclosures. Looks like I'll need something else as a sub for home theater duty. Thanks for the advice about the enclosure/vent size.
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Old 17th November 2008, 01:51 AM   #6
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Well, four of these won't belt out DD/DTS/THX reference LFE down real low, but assuming the room is enclosed, then the room's first axial mode should be around 31 Hz, so all things considered, the drivers can be tuned to ~22 Hz in an EBS alignment where Vb = Vas, which in theory will couple well enough in the four corners to keep them from bottoming out at the limited power required to stay linear in the octave above Fb. Still, according to HR sims they should hit reference down to 20 Hz with only 20 W each, so if any hi-pass is required it should be minimal and below 20 Hz.

Like other Peerless sub drivers, this one requires a large/long vent, though a MLTL will shorten it a bit, but I recommend a TQWT for such alignments which tend to have the same or slightly less net Vb and better damping, but are long, so typically require some folding. This one only needs to be ~80.4" i.d. long though, so standing it up in the corner with the driver at the floor and vent up near the ceiling should make for a nice room filling bass with minimal room intrusion. Never tried putting a sub driver this high up, but flopping one or more to put the driver up high might help a bit with floor/ceiling modes as it does at ~2/3 room height.

FYI, the LFE is mono below 120 Hz and typically below 150 Hz for music if they still haven't adopted the DD/DTS/THX reference, so all can be driven off a common amp. White paper on multiple sub layout: http://www.harman.com/wp/pdf/multsubs.pdf

Anyway, let me know if either of these is what you want to build.

BTW, for my records, which model driver is this?

GM
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Old 17th November 2008, 03:48 AM   #7
BWRX is offline BWRX  United States
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Hi GM.

The room is an 18'x12' living room with a 10'x11' dining area adjacent to it (think of an L shape), so it is not an enclosed room. There is also a small closet on the wall adjacent to where the tv and front speakers would go that could potentially house a subwoofer. Who needs closet space anyway

The 8" Peerless driver is model NPT-11-047-1. It was the subwoofer driver in the NHT M2.5i speakers. I picked them up cheap earlier this year from the NHT surplus sale (and there are still drivers available I believe): http://home.comcast.net/~jhidley/index.html

So the EBS alignment would be a ~75L box tuned to 22Hz (the spreadsheet from diysubwoofers.org calculates that a 3" diameter vent should be about 16.5" long) and you think 4 of those in the corners of the room should get down to 20Hz at reasonable levels with around 20W each? That sounds very doable!

It's probably worth mentioning that this will be in an apartment, so I can't really listen to music or watch tv/movies at insanely loud levels anyway... I have an inkling that 2 of these boxes in the corners of the room behind the front L/R speakers will be enough, but the TQWT standing up in the corner of the room sounds really interesting. Do you think the drivers would work better in a TQWT?
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Old 17th November 2008, 03:25 PM   #8
GM is offline GM  United States
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Greets!

OK, the room modes are more complex and the room gain curve will shift to a lower frequency that may allow the drivers to unload below tuning and short of making them tapped horns they can't be reliably tuned below ~0.707*Fs. Also, you only have three potentially high gain corners, further reducing summed output down low, ergo probably still fine above tuning for most music, movies, but some pipe organ symphonies and action movies (particularly animated ones) will probably require some form of sharp cut below tuning if played at reference for those times when the neighbors are either away or enjoying it with you.

Power requirements go up too, theoretically pushing the drivers beyond Xmax, but considering Peerless driver's typically high Xmech, doubling power to 40 W/driver.

My experience with apt. living is that normally a small single sealed sub or mains that are tonally balanced down to even ~40 Hz is too much, but multiple subs to average out room modes is still worth the cost/effort IMO even if all they do is idle along as it will make the mains sound more 'full'/tonally balanced.

Yes, it's been my experience that anytime the driver's specs dictates a large/long vent for a given alignment it will perform better overall in a TQWT.

GM
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Old 17th November 2008, 06:43 PM   #9
Mikey p is offline Mikey p  Canada
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According to GM's recommendation, 4 of these subs in 75 liter cabinets tuned to 22 hz will produce 104 db at 20hz with a SSF applied at 19hz. Plus the effects of room gain. Live and learn.
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Old 17th November 2008, 07:49 PM   #10
BWRX is offline BWRX  United States
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Quote:
Originally posted by GM
Yes, it's been my experience that anytime the driver's specs dictates a large/long vent for a given alignment it will perform better overall in a TQWT.
GM, is there any chance you would have some free time to come up with a TQWT alignment for these drivers? I'd probably build 2 enclsodures and experiment with placement like is recommended in the harman multiple sub white paper you linked to.
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