barrage of DIY questions about my polk audio subwoofer? [Archive] - Audio & Video Forums


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10-04-2005, 04:23 PM

Well it's given me musical pleasure (and annoyed my neighbors) for 7 years now, but recently the cone of my 8" subwoofer started breaking up. I'm not sure why, maybe it's just old, or the protection cct isnt doing it's job but I was looking for a little advice about fixing it.
Here are some of the specs, and some questions to boot...

Is there any way to determine if it's the driver or the cone that's blown?

since none of the user manuals (from my receiver or speakers) clearly specify the important numbers, I would like someone to confirm or tell me how to determine these numbers.
First (maybe I should cross post this question) I have a Sony STR-DE915 receiver. I just dived into the back of the wire rats nest to determine the impedence of the connection for the subwoofer (on the receiver). It doesnt say! I expected this info to appear in the users manual, but it only gives the following cryptic info:
Outputs: Woofer: Voltage: 2V ; Impedence 1KiloOhm. I'm not sure if this is under 5.1 or stereo output. Does it matter?
Can anyone interpret this for me?

I assumed that the receiver, being rated for an output of 100W per channel (5.1) means 100W RMS and that the sub is included in this rating, would this be a fair assumption?

I opened up the subwoofer box, pulled the speaker cone and measured the impedence over the terminals of the speaker cone and found 4ohms. First question, is this the right place to measure the impedence? This contradicts the impedence at the back of the receiver (1kOhm).

Another technical point, is there any way of finding out the peak wattage that the receiver pumps out? This is a powered subwoofer, so I looked at the back of the sub and where the mains 110v input is going, it says 120Watts max. Does this mean that the rating of the subwoofer speaker is 120W peak? or is there a big capacitor inside thats charged to pound a big punch when it's needed?

So I believe I need the following specs to purchase an appropriate cone:
size: I managed to figure this out all by myself - 8"
impedence: is it the 1kOhm or 4Ohms or something else (could you please explain the difference)
Wattage RMS
Wattage Peak

I was attracted to this car speaker...

It's rated at 900W peak and 220W RMS, is this totally overkill?

Would a car speaker be ok hooked up to my powered sub / HT? I imagine that so long as impedence, size and power ratings were the same it would be fine?????

Furthermore, given these specs, can someone out there recommend a brand, price range , bang for buck in mind, supplier websites and any other advice would be much appreciated.

Thanks in advance, cant wait to get my LF back!!!!


N. Abstentia
10-04-2005, 07:44 PM
First of all, a car subwoofer will not work good in the house...unless your room is the same shape and dimensions as a car. I assume your room is larger than that so the car sub is out.

Secondly, you are seeing two different impedance measurements because the port on the back of the receiver is just simply line level output. It's not amplified until after it gets to your sub then goes through the amp, then finally to the speaker which is where your 4 ohms is important.

So, what you need is a replacement sub designed for home use that's also designed to work in the exact size and tuning of your existing enclosure. So why not contact Polk to buy a replacement driver?

That's assuming the speaker is the problem. Could very well be the amp. Only way to find out is replace the speaker and see if that was the problem. Is the dealer where you bought it still around? If so take it to them and they will find out for sure.

10-05-2005, 09:40 AM
Maybe somebody out there has a record of the T/S params for this driver, I know speakers are infinitely varied, so it comes back to your other question about OEM products, yes, I called Polk, they have a repalcement driver for $100. Maybe it is tuned to the encolsure, but if it's 160W peak and they dont disclose the SPL (maybe they're ashamed of it) I was wondering if I can do better - at least pick a good quality driver with an SPL of around 90 that's recommended for that price range. Would you say that response with respect to the inclosure would outweigh any benefits I gain from a better driver spec?
Oh and thanks for the response.