Could someone please help - Passive subwoofer question (1 Viewer)

[BernieBl]

I hope that someone can answer my question.
This is not meant to start a discussion on the quality of Bose, but since I got this unit for cheap I am looking for an inexpensive solution until I can spend more on a quality piece.
So here is the question: This Bose subwoofer has 4 inputs from the receiver, 2 reds and 2 blacks (it drives two speakers internally). A friend of mine has an amp that only has 2 outputs, this amp is very close to what you will see here, http://www.smarthome.com/8275.html
Can I use such an amp to power the unit? And what would that be? 4 ohms or 8 ohms? How do I wire from the amp to the suwoofer?
Thanks for you time,
Bernie

 

[Dave Milne]

Bernie,
Are you sure the Bose uses two drivers and not a dual-coil driver?

Anyway, you can simply parallel the inputs, i.e. connect the two reds on the Bose to the red on your amp and the two blacks on the Bose to the black on your amp.

As far as impedance, I have no idea. If you have the Bose model number, someone probably can look it up for you. My guess is that the Bose loads (each coil or driver) would be 4 ohms. That would make the parallel combination 2 ohms. Many amplifiers do not like this.

If you have access to an ohmmeter, you can check for yourself. Most 8 ohm drivers have a dc resistance of about 5-6 ohms. If each Bose input reads in the 3 ohm range, they're probably 4 ohm drivers (or coils).

 

[BernieBl]

Hi Dave,

Thank you very much for your reply, I really appreciate it.

The Bose subwoofer that I have is model number AM-500. I have opened it and it has two physical speakers (drivers) inside, connected to some sort of electronics board, I am assuming that this is what you are referencing as coil.

If I connect it as you mention, it reads 3 ohms, if I connect only one side I get 6 ohms. So I guess I can assume that this is what they would call a 4 ohms setup. In that case I could use this amplifier selecting the 4 ohm setting.

Now if I do this, and for some reason it would cause some damage, would the damage be done to the small amplifier and not my receiver? Am I right. I don't mind damaging the small amp but want to make sure I don't fry the receiver.

Thanks again for all your help,

Bernie

 

[Dave Milne]

Bernie,
You're in luck. The parallel combination of the two drivers appears to be 4 ohm nominal. The amplifier shouldn't have a problem with that... especially if it has a "4 ohm setting". And you're right, if something went wrong, you would only damage the amp, not the receiver.

However, I am a bit curious about what you're calling an "electronics board". The "coils" I was referring to are the voice coils in the drivers themselves. I don't why there would be an "electronics board" in there... a passive low-pass filter perhaps? Any Bose experts out there??

One more thought... since we're on the DIY forum I can't help this shameless plug:

Realize that with a $100 driver, some MDF, and possibly a port, you can build a sub that will stomp all over that Bose unit...

 

[BernieBl]

Dave,

Thanks again for your reply. I am happy that this setup will work for now. I realize that Bose might not be my answer for the long term but for now, it will do. The one thing that I have to say that I really like about this subwoofer is the narrow footprint, I can easily place it behind a recliner and it does not look like a coffee table.

I wish I could give you more details on what this electronics board is, as you can see I have a lot to learn when it comes to Home Theater. But the board is where the leads from the speaker connects. The other prominent components ( 4 of them) are glass, transparent, looks like a resistor but are quite a bit bigger, maybe the size of a pen and about 1 - 1/2 inch long.

This will hopefully get me going for now, I hope I am not too disapointed in the result. It will give me some time to look around the DIY area to build a better unit. Any good links to recommend for starters?

Again, thanks for all your help so far.

Bernie