Subwoofer?

puukkoman

puukkoman

Joined
Sep 30, 2004
Messages
6,997
Hey all you audio geeks, I have a question.
I just got a powered sub-woofer whose guts are toasted, and I'd like to still use the speaker and box. It appears to be a 2-ohm speaker (tested it it with my multi-meter), and I'm wondering if there's a way I can hook it up to my stereo.

My receiver is an old Panasonic (80s, I think), and each speaker output connection is labeled 8-ohm only. I imagine I'll simply blow the speaker if I wire it up directly, maybe even damaging the receiver.

Now, my receiver also has an output jack (RCA plugs) that I'm not currently using. Can I, say, solder connectors onto the ends of my speaker wire and use it that way?

Do I have any options here, as far as you guys can tell? Wire another resistor in line with the speaker? Another speaker perhaps?

Thanks!
Alex
 
You probably burn the amplifyer running it into a 2 ohm speaker.

Also you should have a crossover so the speaker only sees low frequecies.
 
Resistance and impedance are not the same thing. Your ohm meter measured resistance. The total impedance is normally higher than the measured resistance.

you should be able to tap into the wiring and drive the woofer with an amp, but as you noted there are risks if the amp and woofer impedance don't match.

You have some other issues to deal with too.

Crossover. The amp may have electronically filtered out the higher notes to save power and distortion. Or it may do so passively or by box design (6th order boxes and so on). For best results, you need to filter the signal to your subwoofer.

The built in amp was probably mono bridged to sum both left and right channel signals. This is more complex than simply hooking up the left and right channel wires to the speaker. (which doesn't work)

OR, the woofer may be a dual voice coil model and have the L and R channels wired to separate voice coils.

Lastly, the built-in amplifier may have been designed to amplify unevenly to offset of enhance aspects of the sub-woofer design, or to balance the output to a particular set of speakers. You normal amp won't have that sort of response and it won't sound right.

If you have an amp stable into low impedance loads and with good self protection circuitry, it's fine to experiment with the sub and see how it responds. But my guess is you won't be that happy.
 
phatch said:
Resistance and impedance are not the same thing. Your ohm meter measured resistance. The total impedance is normally higher than the measured resistance.

you should be able to tap into the wiring and drive the woofer with an amp, but as you noted there are risks if the amp and woofer impedance don't match.

You have some other issues to deal with too.

Crossover. The amp may have electronically filtered out the higher notes to save power and distortion. Or it may do so passively or by box design (6th order boxes and so on). For best results, you need to filter the signal to your subwoofer.

The built in amp was probably mono bridged to sum both left and right channel signals. This is more complex than simply hooking up the left and right channel wires to the speaker. (which doesn't work)

OR, the woofer may be a dual voice coil model and have the L and R channels wired to separate voice coils.

Lastly, the built-in amplifier may have been designed to amplify unevenly to offset of enhance aspects of the sub-woofer design, or to balance the output to a particular set of speakers. You normal amp won't have that sort of response and it won't sound right.

If you have an amp stable into low impedance loads and with good self protection circuitry, it's fine to experiment with the sub and see how it responds. But my guess is you won't be that happy.
Click to expand...

if you arent a super big audiophile, you will be able to find a decent and cheaper replacement plate amplifier on http://www.partsexpress.com. that would be your best bet.
 
phatch said:
Resistance and impedance are not the same thing. Your ohm meter measured resistance. The total impedance is normally higher than the measured resistance.
Click to expand...

In a speaker, impedance is always higher than DC resistance.
 
To add to the above, and give you a general baseline (no pun intended), most car drivers are 4 ohms, and most home ones 8 ohms. I don't know how stuff quite as well as car stuff, but if it's just your run of the mill powered sub in a box that cost a couple hundred bucks new, and not something weird (random sub from a set of computer speakers) or higher end, you can bet on it being a regular old 8 ohm sub, not voice coil or anything else.

Still wouldn't run it off of a random amp, unless you're acknowledging it's a thrown together setup which might work ok for a long time or might crap out randomly. You could try taking it to an electronics shop (privately owned, won't be worthwhile at a big place) to see if they'll fix it, but chances are even that won't be worth it.

Don't rig up anything to the RCA outs on your amp...those are almost certainly pre-amp outputs for you to pass an un-amplified signal to another amp. Also, don't throw a resistor in line with the speaker...you work so hard to get a clean, semi-ear-quality signal to your speaker and adding a resistor would just trash it.

There's no real reason not to try hooking the sub up directly to your receiver output, if it puts out some kind of power and has a crossover. By "try" I mean start it out at very low volume, don't crank it above say 20-25% and see if the sound output is decent. If you have next to no sound coming out, your sub could be much higher impedance. If it's a lower resistance, you're not going to blow your receiver unless you're cranking it.

Remember, you approximately double your power for every 6 dB gain in volume. That means if your setup is too quiet it takes a lot to make it louder, but from the other end it means that every step down in volume from max is significantly cutting the power. So, if your sub is lower impedance but is loud enough at your 20 or 25% volume setting, and it sounds good enough for you, you'll be running your amp slightly hotter at the same volume than if you had the proper impedance, but you shouldn't blow it since you're nowhere near pushing it.
 
bobby.t said:
To add to the above, and give you a general baseline (no pun intended), most car drivers are 4 ohms, and most home ones 8 ohms. I don't know how stuff quite as well as car stuff, but if it's just your run of the mill powered sub in a box that cost a couple hundred bucks new, and not something weird (random sub from a set of computer speakers) or higher end, you can bet on it being a regular old 8 ohm sub, not voice coil or anything else..
Click to expand...

when it comes to woofers in a car you commonly see dual and quad coils ranging from 1-4 ohms each. most SVC's are 4 or 2 ohm.

most mids, tweets, and coaxials are 4 ohms though.

in home, i see lots of 4 ohm bass setups. and i see lots of 4/8 ohm drivers.
 
Partsexpress.com is a fun site. I've used them in the past too. I have one of their between-the-joist subwoofers. Great way to hide the sub.

www.madisound.com is a good source of raw speakers and passive crossover components as well as some worthwhile kit speakers and car audio.

Phil
 
You must log in or register to reply here.
Back
Top