OT: Audio Query - what do you drive a passive subwoofer with ?

[phigmov]

I know Amin has a specialty audio forum up and running now but I figured I'd ask over here before joining another forum...

So - the Topic Subject pretty much says it all...
I picked up a great deal on some refurbished Boston Acoustics THX speakers (555x + tweeters & passive subwoofer). It was actually a refreshing upgrade for my old Gale bookshelf speakers.

I have these L & R speakers + tweeters hooked up to a Cyrus 3 amp that is fed from my Mac Mini I use for music & video (movies & tv via SiliconDust tuner & Elgato EyeTV). Works great and sounds nice.

I have a spare-centre & sub gathering dust - it'd be nice to put the sub to use.

As my amp doesn't have a sub-output (neither does my old NAD I use in another room for my turn-table) I'm a little stuck. What do I need to drive a passive sub properly ?

Can I add a small power-amp specifically for the sub and feed it from the normal speaker outputs of the Cyrus or should I just bite the bullet and go looking for a proper home-theatre amp with surround sound capability and relegate the Cyrus to stereo duty ?

Will a passive sub even work with a standard HT sub-out ? Are most HT amps expecting a powered-sub ?

Thanks in advance

 

[MoonMind]

Does the sub have a through-put option? And you actually need a amp to drive the sub anyway - it won't work with a "sub-out" that's only a cinch (or something) connector.

M.

 

[PeeBee]

The 2 passive subs I've had utilise frequency cross-overs in the inputs. The speaker outputs from the amp wire directly into sub inputs, and then continue to the front speakers. From memory, an old Mission sub I used to have only had one set of left and right spring connectors, and the wires had to be doubled up. I replaced that with a Technics unit (its also quite old now) that has dedicated in and out connectors.

The active sub on my main hi-fi has the choice of a low level input (from a dedicated sub output from the amp) or speaker level inputs. I also drive that sub via speaker level inputs, as I find it provides the best performance.

 

[phigmov]

Thanks @MoonMind & @PeeBee
Looks like I just have standard red/black speaker connector posts on the back of the sub.
If I need an amp to power it -
* Can I take the speaker output from the Cyrus and feed it directly into one of the amp inputs or will that do nasty things to the amp or the signal?
* Can I get away with powering the sub with any old amp and just crank up the bass on it?

 

[PeeBee]

I wouldn't take a speaker output from one amp directly to the input of another amp. It may cause damage to either or both components.

Does the sub have stereo inputs, or is it just a single channel input? Posting a photo of the sub's connectors could help.

 

[oldracer]

It depends on what you want. If you want the kind of bass that the boom-box car owners use to damage their hearing you'll probably need some new equipment.

if you just want to fill in the bottom where a recording has bass and your other speakers aren't reproducing it, I'd start like this:

Buy a small single-channel amp. MCM Electronics (MCM Electronics: Home and Pro Audio/Video, Security and Test Equipment) has this kind of thing. CraigsList may be your friend here, too, with an inexpensive stereo receiver or amp.

Your amp probably has "monitor out" or "tape" outputs. Plug into either left or right to feed your amp. Bass is very nondirectional, so unless the mix in the recording is really goofy, the bass will probably be about the same from either side. Popular music is more likely to be goofy; classical less so.

Connect your subwoofer to the amp's output. In theory you should have a lowpass filter on the amp input, but a subwoofer is effectively a sort of mechanical lowpass filter on its own, so you will not get a lot of highs anyway. (Since your speakers came as a kit, there may be a crossover or a low-pass filter in there somewhere already.) Play some music you like and set the subwoofer volume to a level where the sound seems smooth and without too much bass emphasis.

Upgrades from there would be to combine the left and right signals before they get to the subwoofer amp, giving you both sides' bass. You may need to add a crossover or a low-pass filter if there is an objectionable frequency peak where both the subwoofer and your main speakers are reproducing that frequency. MCM can probably help with these two things too.

There are audio frequency sweep files available on the internet which have samples of various single-frequency tones. You can use one of these to get a better feeling of how your system reproduces audio in the low frequency regions.

 

[phigmov]

I wouldn't take a speaker output from one amp directly to the input of another amp. It may cause damage to either or both components.

Does the sub have stereo inputs, or is it just a single channel input? Posting a photo of the sub's connectors could help.

Looks like this round the back...

Subscribe to see EXIF info for this image (if available)

 

[phigmov]

Thanks @oldracer - that sounds like the way to go... pretty sure the Cyrus has a tape output I can utilise & I should be able to find a mono amp online.

Very useful responses guys - also very handy to know the sub-output is not typically meant to be the sole source of 'power' on an HT amp.

Worst case, I can use it as a very heavy coffee table!

 

[PeeBee]

Looks like this round the back...

View attachment 576541

The subs I've owned have all had stereo through-puts. I have 8 posts on mine. Your sub is designed to work on a amp with a dedicated speaker level, mono subwoofer output. Oldracer's suggestion to use the amp's tape loop is a good idea. You could also use a cheap 2 channel mixer to merge the left and right audio channels into single mono channel.

I have a headphone 'y' splitter connected to the audio out of my PC. One leg is feeding a set of amplified PC speakers, the other goes to my second hi-fi in our dinning room, running 2 amps from a single output.

 

[oldracer]

Thanks @oldracer - that sounds like the way to go...

Well, it's kind of Mickey Mouse, but it should get you started getting a few noises from the subwoofer anyway.

Out of curiosity I did look at MCM and found this: Lanzar 500W X 2Ch at 2ohm Autosound Mosfet Amplifier | VCT2110 | Lanzar & also here: Lanzar - VCT2110 - 1000 Watt 2 Channel High Power MOSFET Amplifier You'll need a 12 volt power supply and at the price point most of the specs are probably BS, but it claims to take two line-level inputs, provide an adjustable low-pass filter, and combine the inputs to drive a single speaker. Too good to be true price, though and the downloadable manual model numbers don't quite match the catalog model number. Maybe be worth rolling the dice?

 

[phigmov]

Thanks again @PeeBee & @oldracer - some more ideas for me to ponder.

Using a splitter on the source is a handy thought - not something I'd considered before.

I'm in NZ so I'll look locally for an amp, however I did do a similar search here on our eBay equivalent and it returned a bunch of similar car-audio mono-amps for driving subs. Good to know I'm on the right track.

I also wondered about the little tripath digital amps that are out there - would they have enough oomph to drive a sub ?
They seem geared-up more for head-phones but are nice and compact.