Shoestring budget Subwoofer - will this work?

Alexrose1uk

Alexrose1uk

Alexrose1uk

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Ok, ok, shoestring budget might not cover everything as simply as it could, but to try and keep this as simple as possible:
I have some nice floorstander front speakers in my AV setup, unfortunately I had to sell my prized subwoofer when I moved house and got married to free up collateral (:().

A while back, I was given (yes given) a Pioneer SSLW500 PASSIVE subwoofer (rated up to 100w, not sure on sensitivity unfortunately), my amp is good, but it does not have active output as far as I am aware. In the future, I would like to get another decent active subwoofer, but for now, I am trying to make do, and would like to get a little bit more bass/bass depth into my setup.

I have an old Ariston stereo amp sitting at my parents which I believe is 30w per channel 8ohm, I'm going to guess the sub is 4ohm, and generally given I have seen 40wpc 6ohm for the Ariston, I'd take a wild guess it'd translate to about 50wpc 4ohm, so 2x 50w =100w, perfect(?). If I was to split the mono subwoofer output from my amp's subwoofer pre-out, and feed it into both Aux channels on the Ariston, could I use this as a makeshift subwoofer amp?
My subwoofer will deal with the filtering/frequency cutoff before passing to the pre-out, so essentially all my amp will be doing is amping the low frequency level my amp passes.

My mind is telling me there is no logical reason this shouldn't work, but I don't fancy spending money on the cables/splitters etc and waste my time messing around with it if A) It won't work B) It won't make any real improvement C) It'll just kill the amp.

What are your thoughts?
 
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SSLW500 specs:

driver....................16cm paper cone
impedance...........................4 Ohm
sensitivity..............................78dB
frequency range...........35Hz-2000Hz


Your idea about driving the sub from the Ariston is okay but there's a couple of things you'll need to be aware of...

You can't add the two speaker outputs from the amp together to drive a mono speaker. Part of the power from each channel will go up the other amp channel. That's not good. You need some way to isolate the amp channels from each other so that the power is directed at the speaker. Unsurprisingly that's called a Speaker Isolation Transformer. So far so good, except you're on a shoestring budget and the last one of these I saw was a KEF CITR-SM fetching the thick end of £50.

If you plan to use the Ariston then stick to one channel only.

Running a single channel means less power. The idea that power increases as resistance drops is correct. However, it overlooks the price paid. There's no free lunches in physics. The speaker is going to be drawing a lot more current from the amp.

Speakers don't have a fixed impedance. It varies with frequency. So a 4 Ohm speaker could have an impedance swing from 12+ Ohms down to 2 Ohms or even lower! That's going to be a real problem for an amp that's rated for a 6~8 Ohm load.

Since an amp is a voltage gain device, not unreasonable to expect an amp to output 20-25 Volts. So, 20V in to 6 Ohms gives 66W @ 3.3 Amps. Drop the impedance to 4 Ohms and the amp is being asked to produce 100W and deliver over 5 amps of current. At 2 Ohms it will be 200W and 10 Amps! If the amp is rated to deal with a 6 Ohm nominal impedance then it will be able to cope with the occasional excursion in to lower impedances, but asking it to deal with a 4 Ohm load that could drop to 1 or 2 Ohms would be too much. The output transistors will overheat and blow.

So, the only way to stop the amp killing itself is to limit the volume and hence limit the voltage. The question then is will there be enough power from the amp to make the sub audible?
 
Thanks for your in depth response. I will have to think further on this. The other obvious option would be trying to attach the sub to my av amp via speaker terminals but similar issues apply I would think.

Can you think of any cost effective ways to get this passive box working or is it essentially not worth it?
 
The other question is will a cheap passive sub really add anything that your floorstanders can't already do better? With a 6" driver I can't imagine it'll reach much lower than your existing speakers.
 
Alexrose1uk said:
Thanks for your in depth response. I will have to think further on this. The other obvious option would be trying to attach the sub to my av amp via speaker terminals but similar issues apply I would think.

Can you think of any cost effective ways to get this passive box working or is it essentially not worth it?
Click to expand...

BIB really. Sorry, but if the sub was worth anything in terms of performance then Richers wouldn't be selling them for £20 down from £60. I just wanted to let you down gently. :)
 
Don't worry about my feelings, I got the unit for free :)
Just figured it must have some use as I have NO sub at the moment and I can't see an AIO being that high powered. I have to wonder if they pass much more power than my Ariston to the amp!

My amp is a Yamaha RX-V1800 if that gives you any further ideas as to ways this could be utilised at minimal cost/if there is anything worth looking for on eBay. Unfortunately I have little soldering/electrical experience.

If not no worries :)
Just trying to make use of what I have lol
 
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Is this the isolation transformer I'd need to be able to allow me to use both channels from my audio amp?
http://www.ebay.co.uk/itm/121492264182?ssPageName=STRK:MEBIDX:IT&fromMakeTrack=true#ht_529wt_1399
If the channels can share the wattage current, that MIGHT be possible to drive the sub driver to be something useful?

If still no, completely understand, as I say above it was a freebie and just trying to think of ways to use it! :)
I think I've just got that obsession of trying to use something!
 
The transformer you found is for line level signals i.e. not 'high level' speaker wire connections. It's for isolating the earths between bits of gear that are picking up groundloop hum. It's not designed for making a stereo speaker signal in to mono. Don't waste your money.

If you really must use the sub then buy a PA/DJ amp that's designed to handle a 4 Ohm load. Get one cheap that's got a channel fault on one channel because all you need is one working channel. Don't be tempted to buy something that's got Bridged Mode, because in that mode the amp will want to see an 8 Ohm load.

When all is said and done the little Pioneer sub is more of a supplement for small satellite speaker rather than something to add extra kick to full range floor-standers. Yes, it will make a noise, but compared to the quantity and quality of bass from half decent Hi-Fi speakers then the Pioneer will bang and crash about untunefully like a truculent teenager. It won't be pleasant company. If you do manage to drive it with the Ariston then watch the thing like a hawk, because as soon as you turn your back it will stab a screwdriver in the tyres and light a rag in the petrol cap then dance around the burning wreck of your Ariston like an ASBO-weilding yob.

Please, for the love of God and all things holy......... put the Pioneer out where it belongs; on Ebay, Gumtree or just the tip. Wave goodbye to a truck load of problems and costs and endless soul destroying black-hearted gut-wrenching misery.
 
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Hahaha loving the honesty, thanks for your feedback :)
To be honest I'd already been thinking that based on the previous feedback, but I'm sure you know what it's like when you have something sitting there and there's a part of you that gets OCD on doing something with it :D

I think part of me is just sad I had to sell my lovely Quad L-ite sub which was a true beast! :(
 
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just go audio affair site. £40 a month for an £800 SVS ported box like I did. no one misses £40 a month. I don't even notice I'm paying it. It's the size of a washing machine but still makes even bigger subs seem rubbish.
 
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