how to use stereo speakers with mono subwoofer

April 22, 2009 8:25 PM

i have some speakers: two small amplified stereo speakers and one mono amplified sub woofer. whats the best + simplest way to use these together?

Hello,

I have some stereo speakers:

apple pro speakers

which are plugged into an ifire

which makes them into a pair of amplified speakers with a headphone jack for input.


and I have an isub subwoofer which has been modified to take a headphone jack as input

i want to use these together.
I have read that when using a sub woofer its best to use a crossover filter so that bass frequencies go to the subwoofer and treble goes to the small speakers.

what are the simplest/best/cheapest ways to split the headphone jack output from my laptop into treble stereo and bass mono?

I'd be happy to solder up a simple circuit, I'd prefer not to spend a big chuck of money to buy a big piece of hardware like a mixing desk.

The speakers are all ready amplified so buying/making another amplifier seems like the wrong answer

thanks
mathew

posted by compound eye to Technology (7 answers total)

you can go a couple of ways.

1. Passive crossover. http://www.bcae1.com/passxovr.htm Usually these are used after the amp, but before the drivers. As I understand it though, the speakers themselves have built-in amplifiers. I don't know much about passive, low-power crossovers, and my google-fu is crippled at work.

2. Active crossovers. These are designed to go before your amp, and are usually much better at splitting the signal. As the name implies, they will need power (it's not much, run it off a wall-wart). You get into audiophile territory pretty quick, but once again hopefully somebody around here has a lead on a cheaper kit. A quick google turned up a kit for $75, seems a bit pricey for what you want.

Good luck.
posted by defcom1 at 10:23 PM on April 22, 2009

A passive crossover before the power amp is going to increase line noise significantly, because you are sending a lower signal to each powered speaker, thus more amplification needed on that end etc. The end result is much more hiss than an active crossover.
posted by idiopath at 11:10 PM on April 22, 2009

Most amplified subs will have inbuilt filters of some kind, and if these are properly designed they will roll off pretty much everything higher than the bass that will be missing from your satellites when those are fed from full-spectrum audio.

If you just feed your sub straight from a normal audio source, do you hear clear sound or just dull distant thudding? If it's the dull distant thudding, all you need to do is feed satellites and subs from the same source and you're done.
posted by flabdablet at 11:12 PM on April 22, 2009

Response by poster: These subs were designed to be plugged in via a special usb cable into an old apple computer.
When that happened the operating system did the frequency splitting, reducing the bass to the stereo speakers as well. But this sub has been modified to take a headphone jack, and current apples no longer support this anyway.

assuming that the sub speaker still contains some kind of frequency filter, what do i need to make a mono signal, not just picking one of the left or right channels?

cheers

mathew
posted by compound eye at 11:26 PM on April 22, 2009

Response by poster: oh forgot to say thank you for taking the time to help me

mat
posted by compound eye at 11:27 PM on April 22, 2009

I think you only need a stereo splitter jack,like you would use for two headphones, plugged into the ifire device, the amp in the sub will sum left and right into mono. the sub is advertised as stereo 20 watts.
posted by hortense at 11:38 PM on April 22, 2009

Response by poster: I should have said, this sub has been modified so it only has a single mono headphone jack coming out of it
posted by compound eye at 11:59 PM on April 22, 2009