ISOBARIC 16 ohms load powered by 8 ohms Amp - Page 2 - diyAudio
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Old 11th October 2006, 03:50 AM   #11
dangus is offline dangus  Canada
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Isobaric also requires a big tunnel to join the two drivers, unless you're going clamshell style, which means the volume saving is never as good as 50%, and even halving the volume of a box doesn't really make it look 1/2 the size.
I just don't see the point of isobarics. If you have two drivers, build two boxes and and you'll have higher efficiency and higher max SPL from the same amp power, and probably lower distortion at a given SPL compared to the isobaric box (since the two drivers won't be working as hard). If reducing box volume is so important, use a more appropriate driver, or mass-load the one you have.
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Old 11th October 2006, 07:12 AM   #12
eddi0 is offline eddi0  United States
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I see your point. Here are the spec of the sub woofers and the box size:

Please let me know if these would work or you recommendation is helpful, b/c I have not bought the speakers yet.

Box:

31.5" x 23.5" x 23.5"

8.4 cubic air space (4.2 per side)

Dual 2" x 22" x 6" slot vents (.15 cubic feet per vent)

7 ply 3/4" Birch construction




Speakers (18" Madison Executioners):

RMS Power Handling: 500 watts

TS Parameters
FS 40 hz
VAS 7.56
SD 213.82
Qts 0.927
Qes 0.969
Qms 21.45
BL 16.91
Re 5.5
Nominal Ohms 8
Le (mH) 1.117
Mms 201.39
X max (inches) 0.375
X mech (inches) 0.75
Peak Power Handling: 1000 watts
Ohms: 8
Frequency Response: 38 to 3100hz
Sensitivity: 100 dB
Magnet: 100 oz.
Basket: Cast Aluminum
Voice Coil: 4" Copper Clad Aluminum
Cone: Treated Paper
Surround: Accordion
Binding Posts: Clip Type
Pole Piece: .
Overall Diameter: 18 13/16"
Overall Depth: 7 5/8"
Mounting Diameter: 16 13/16"
Mounting Depth: 7 1/16"

Thanks, Edward
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Old 11th October 2006, 07:34 AM   #13
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I don't believe those are subwoofers, man. Are they made for PA loudspeakers or something?
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Old 11th October 2006, 09:25 PM   #14
Svante is offline Svante  Sweden
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This may happen if the Mms-to-box-mass ratio is too high. The box wanders across the floor...
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Old 11th October 2006, 09:48 PM   #15
dangus is offline dangus  Canada
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100 dB sensitivity and "accordian surround" sound like PA speakers to me. That 38 Hz cutoff is probably 10 dB down, which is not much of a subwoofer by diyaudio standards.

For audio and home theater subs you should be looking at drivers with lower efficiency and more Xmax (12 mm and up). If you really want PA subs, check out other threads on horn-loaded subs.
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Old 12th October 2006, 07:42 AM   #16
eddi0 is offline eddi0  United States
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thanks....That helps to understand the concept of subs. Any other advice is welcome.
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Old 12th October 2006, 07:58 AM   #17
eddi0 is offline eddi0  United States
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Svante,

Thanks for that little video......i see now.

Edward



Hey Guyz,

What 18in subs do you recommend for this Isobaric Box????


Edward
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Old 12th October 2006, 08:12 AM   #18
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Is there any reason you want an isobaric box so bad?
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Old 12th October 2006, 09:15 AM   #19
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Quote:
Originally posted by dangus
I just don't see the point of isobarics. If you have two drivers, build two boxes and and you'll have higher efficiency and higher max SPL from the same amp power, and probably lower distortion at a given SPL compared to the isobaric box (since the two drivers won't be working as hard). If reducing box volume is so important, use a more appropriate driver, or mass-load the one you have.
For the same power input, 2 drivers in Isobaric gives 3dB down on a similar single driver in a box with internal volume twice the size, and is 6dB down on a 2 driver box (or 2 single driver boxes) with 4 times the internal volume. Distortion is improved slightly, depending on the enclosed internal volume between the 2 drivers.

If you have the room, and no spouse to complain about it, the the 2 box solution is the most efficient. For myself, a single 200l box (including drivers) is about all I am allowed in the house. 2x335l boxes was just not going to cut it - and the extra expense of another amplifer sealed the bargain.

In a world without compromise, I know what I would have done...
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Old 12th October 2006, 03:15 PM   #20
eddi0 is offline eddi0  United States
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I had two bandpass 18s. Did not like them. Had LAP 15, love them but too big. All of these subs were big and bulkie. I am trying to cut my size down and get better response.

So I'm thinking of using Peavey Black Widow 18s...any advice on these?

Thanks,
ed
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