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Old 22nd May 2004, 07:34 AM   #1
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Default blown sub

My subwoofer has a fried voice coil, and I'm trying to figure out how to replace it. (I can't complain too much, the driver lasted over ten years.) Its a 3 cubic feet sealed enclosure, downfiring, with a 12 inch Pyle Driver. It's driven with a Hafler 220 SS amp, bridged, putting out about 350 watts, and is crossed over with an old (18 years?) jbl active crossover. My questions:

I don't know if the old driver is 8 ohms or 4 ohms; it doesn't say on the back. Is there a way to tell?

I'm not sure if I should replace it with a 4 ohm or 8 ohm driver. A guy at a speaker repair shop said that some amps, even when advertised as stable into 4 ohms, aren't necessarily stable when they are bridged (the bridging was done using a manufacturers kit.)

I'm thinking of an NHT 1259, or something comparable.

There was a hunk of fiberglass insulation sitting in the box. Would an increased mass of audio quality stuffing be useful?

Any advice would be greatly appreciated. I'm hoping to integrate this sub with my 3/4 completed shamrock MTMs, which I am enjoying building!

Larry M
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Old 22nd May 2004, 09:18 AM   #2
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that guy is probably right...becoz if your amp is bridged into a 4 ohm load...it will in theory see a 2 ohm load...so it might not like it...as for the impedence of the VC...I'm not too sure...perhaps you might like to see into a replacement woofer of the same size and close specs...
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Old 22nd May 2004, 11:01 AM   #3
sreten is online now sreten  United Kingdom
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The NHT is 4 ohms nominal and not a good choice for a bridged
mosfet amplifier trying to effectively drive a 2 ohm load.

Probably your best bet is to remove the bridging and
use a DVC driver, simply wire the two inputs in parallel.

http://adireaudio.com/diy_audio/drivers/adire/shiva.htm

or

http://www.partsexpress.com/pe/pshow...=295-185&DID=7

Parameters are remarkably similar, with a 3Cuft box you'll
get a low Q (~0.6) alignment, alternatively reflexing will
give more low bass and low bass SPL capability.

(A whopping 12dB extra SPL capability at 20Hz)

sreten.
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Old 22nd May 2004, 11:14 AM   #4
sreten is online now sreten  United Kingdom
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sreten.
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Old 22nd May 2004, 11:28 AM   #5
sreten is online now sreten  United Kingdom
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For $70 the Peerless 831857 is good value, and can be used
with the amplifier bridged, gives a sealed Q of ~ 0.8 in 3 cuft.

Xmax is lower and reflexing is not recommended.

sreten.
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Old 23rd May 2004, 01:55 AM   #6
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Thanks for the suggestions. I'm not sure I can use a dvc driver with the current crossover, since it sums the channels for the low pass section. If I unbridge the amp and use a dvc driver, is there a good (and reasonably economical) way to cross it over? The nice thing about the electronic crossover is adjustable gain and crossover point. Most electronic crossovers I've seen cost more than a good plate amp. I would think a seperate amp and crossover would outperform most plate amps, but I've never used a plate amp sub so I don't know.

Larry M
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Old 23rd May 2004, 03:30 AM   #7
Rimband is offline Rimband  United States
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Hi Larry, look on the frame, it should have the model number of the woofer printed on it, ie..W1240, SW829, etc. With the model number, you may be able to backtrack the origin of the woofer and find it's impedance. Hope this helps!



P/S

Larry wrote;

My subwoofer has a fried voice coil, and I'm trying to figure out how to replace it. (I can't complain too much, the driver lasted over ten years.) Its a 3 cubic feet sealed enclosure, downfiring, with a 12 inch Pyle Driver. It's driven with a Hafler 220 SS amp, bridged, putting out about 350 watts, and is crossed over with an old (18 years?) jbl active crossover. My questions:

I don't know if the old driver is 8 ohms or 4 ohms; it doesn't say on the back. Is there a way to tell?

I'm not sure if I should replace it with a 4 ohm or 8 ohm driver. A guy at a speaker repair shop said that some amps, even when advertised as stable into 4 ohms, aren't necessarily stable when they are bridged (the bridging was done using a manufacturers kit.)

I'm thinking of an NHT 1259, or something comparable.

There was a hunk of fiberglass insulation sitting in the box. Would an increased mass of audio quality stuffing be useful?

Any advice would be greatly appreciated. I'm hoping to integrate this sub with my 3/4 completed shamrock MTMs, which I am enjoying building!

Larry M
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Old 23rd May 2004, 12:23 PM   #8
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by wharfrat
Thanks for the suggestions. I'm not sure I can use a dvc driver with the current crossover, since it sums the channels for the low pass section. If I unbridge the amp and use a dvc driver, is there a good (and reasonably economical) way to cross it over?
Larry M
I don't see how the amplifiers bridging arrangements are
related to the crossover. There is no need for a stereo
signal to drive a DVC subwoofer, its simply a way of
using both channels of the Hafler, as I said you wire
the Hafler inputs in parallel.

sreten.
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Old 23rd May 2004, 05:53 PM   #9
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Sreten - Sorry if I'm a bit dense, but I'm not sure I get it, and I'm trying to make up for ignorance with persistence. There are two channels from the preamp into the crossover, which devides it into one summed low frequncy output that goes to the subwoofer amp, and two stereo outputs. When you say the hafler inputs should be wired in parallel, I presume that means simply splitting the single subwoofer output from the crossover into two and connecting it to both channels of the unbridged amp? (sounds too easy!)

Larry M
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Old 23rd May 2004, 06:06 PM   #10
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by wharfrat
When you say the hafler inputs should be wired in parallel, I presume that means simply splitting the single subwoofer output from the crossover into two and connecting it to both channels of the unbridged amp? (sounds too easy!)
Larry M
Indeed it is that simple, sreten.
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