Adding a subwoofer to a compact shelf system

 

Stephanie
I recently got myself a sharp sd-nx10 mini system. The system has a separate 1-bit amp unit and the sounds from the stock speakers are really clear but I find the bass a bit lacking and I was wondering if I could buy a dedicated subwoofer to boost up the bass. However, I realized that the system doesn't have a sub/out, so do I just make 4 speaker wire connections from the subwoofer to the L/R speaker outputs on the amp? Also since I already have a separate amp on the mini system, can I get a passive subwoofer or must I get an active one? Any good subs under $100 that would be sufficient for a mini sytem? I would really appreciate if someone can help me. Thanks!!
 

John A.
If you get a subwoofer it should definitely be ACTIVE i.e. powered. Also, one that connects to the unit from its Left and Right front speaker outputs, then connects to give an output to the Left and Right speakers.

As an alternative you could get a pair of full-range speakers. Small "music center" type systems can be massively improved with better speakers. 25 W per channel can still give good results with large speakers as long as they are fairly efficient. But a powered sub could well let the Sharp speakers sound much better - asking them to provide bass (which they can't) is taking the edge off their whole performance.
 

Stephanie
Thanks John! Yes I was actually thinking of getting a pair of Polk Rti speakers for the system, but then again it would seem such a waste to just dump the Sharp speakers in a corner. That's why I think I'll just rig on a dedicated subwoofer. So to confirm again, each of the black/red speaker outputs at the back of my unit should have 2 wires connected to it right? 1 to its speaker and 1 to the subwoofer? I'm new at this and I'm really scared that I'll fry the amp of something.
 

John A.
Stephanie,

From your description, I think you have got the wrong idea for connection. Don't do it like that!

On the back of any simple stereo receiver/amplifier there are usually four speaker connectors. One black (negative) and one red (positive) for the left speaker; then the same for the right speaker.

You will need a sub where you connect the cables you previously used for the speakers to four input terminals labelled "Amplifier" "Receiver" "Input" or something similar, a black (or "-") and a red (or "+") for each channel, L (left) and R (right).

Then your sub should also have four terminals, coloured or labelled similarly, but for "Speakers" or "Satellites". This is the output to the speakers. Just hook those to the sub as you did previously to the receiver.

It is important to get the + connected to the + and the - to the - at both stages (receiver to sub; sub to speakers) and not to mix up L and R.

If you accidentally connect a + or red to a - or black for EITHER L or R then no harm is done to the equipment, but you will lose a lot of bass because the main speakers will be out-of-phase, and the long sound waves will cancel each other out. If you connect + to - for BOTH L and R you get you bass back, because they are in-phase, again.

If you are dissatisfied with the bass from the system you have already, check first that you have got the phasing correct (+ to +; - to -). Audio speaker cables always come in odd pairs, usually the insulation of one strand has a line or mark, so you can easily know you have connected to the correct terminal at each end. It doesn't matter whether the marked strand connects + (or red) to + (or red), or - (or black) to - (or black), as long as both L and R channels wired up so the two terminals are connected to the correct two at the other end. Your user manual should explain all this.

Do NOT connect the sub and speakers as you describe. Put simply, you will be connecting the sub and each speaker in parallel, and they should be connected as I described, which is in series (amp to sub; then sub to speakers - for each channel, L and R). The connection you describe will give the amp a much lower resistance than it was designed for, that will draw more current, and, yes, it could just fry the amp, or at least blow an internal fuse. And it won't sound good.

Hope this helps!
 

John A.
Stephanie,

Hold on, I have read some more....

I was curious about the Polk sub and looked it up. It will be one of the PSW range:

http://www.polkaudio.com/home/products.php?category=7

They have a good reputation and are recommended on this forum. They are more than $100!

Sharp is not exactly up-front about the system

http://www.sharpusa.com/products/ModelDetailedSpecs/0,1161,661,00.html

I was looking for frequency response and it gives 20 Hz - 25 kHz. I see it already claims to have a powered sub-woofer. It does say, after "Subwoofer out", "50", which makes no sense since it is neither "Yes" nor "No" If there is a sub-out connection on the receiver then you may be able to use a separate, single cable, and all that, above, may not be necessary. However, it is still the best way to connect for stereo sound, and you have to get speakers in-phase whatever you do.

Maybe if your system already includes a powered subwoofer (where is it, in the amp? Why are they hiding its spec?) then your only problem was with the phasing. But adding a Polk sub would probably still cheer it up quite a bit.
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