Car Stereos: Amplifiers, dual voice coil, ohm load

Question
QUESTION: I'm looking into getting two subs and an amplifier. The place where i am going to be getting my subs and amp from, the multi-channels are cheaper than the two-channel amps. I have heard from people that i shouldnt run two subs off a multi-channel amp, and instead get a mono or two channel. Does it really make a difference?

ANSWER: Hi,

The answer to your question really depends on the subwoofers you choose.

In most cases, I recommend a mono amplifier for use with subwoofer systems.  They offer the most flexibility for matching the amp with the subs.  A typical mono amp can work effectively with a 4-ohm or a 2-ohm load; some can even handle 1-ohm loads.  Also, if you're using a ported box system, it's a good idea to use an amplifier with a subsonic filter.  This is a feature that's common on mono amps, but much rarer on 2-channel or multi-channel amps.

When you're using a 2-channel or 4-channel amp for subwoofers, you'll usually need to bridge the amp.  This limits your sub options, because a typical bridged amp can't support a load lower than 4 ohms (though there are a few exceptions).

If you're using typical 4-ohm, single voice coil subs, then a 2-channel amp might NOT be a good choice, because you can't combine the subs into a 4-ohm load.  You'd end up with a 2-ohm load, which a bridged amp can't support.  On the other hand, a 4-channel amp would work out, because you could bridge it down to two channels, then use one 4-ohm sub on each channel.

If you're using a pair of 4-ohm, dual voice coil subs, that changes things again.  A pair of these subs could be combined for a 4-ohm load.  In that case, a 2-channel amp might work well in bridged mode; while a 4-channel amp wouldn't work out, because each individual sub  would be a 2-ohm load.

There are quite a few other subwoofer and amplifier configurations available, which might or might not work well together.

To sum up, I don't have any particular problem with using multi-channel amplifiers for subs, as long as you've taken care to calculate the final impedance and match the amp and the subs correctly.  If that's done right, then the combination will work fine.  However, I think a mono amplifier might make things simpler for you, and give you more options if you decide to switch to a different subwoofer system later on.

If you'd like to follow up with the brand and models of the amp and subs you're considering, I can tell you whether I think they'd be a good match.

Hope this helps!

Brian

---------- FOLLOW-UP ----------

QUESTION: Thanks brian, here is the amp http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=19343

and here is the sub http://www.onlinecarstereo.com/CarAudio/ProductDetail.aspx?ProductID=19180

Thanks for your time.

ANSWER: Hi Matt,

Unfortunately, I can't seem to get your links to work (the site appears to be down).  If you can just tell me the brands and model numbers, I can look up the specs for myself.

Thanks

Brian

---------- FOLLOW-UP ----------

QUESTION: SoundStorm STS10D 10" 1000W Dual 4-Ohm Subwoofer
Crunch P1400.4 1400W 4-Channel Powerzone Series Car Amplifier
Thanks.


Answer
Matt,

Sorry about the delay in responding this time.

It's difficult to tell just how well the power output from the amp matches the power capacity of the subwoofers, because neither manufacturer will provide a genuine RMS power rating.  There's no particular standard for the "max" or "dynamic" ratings which are all the manufacturers will supply, so they're really useless as a basis for comparison.

Leaving aside the power consideration, though, a 4-ohm dual voice coil sub isn't really a good match for a 4-channel amp.  To use that amp for two subs, you'll need to bridge it down to 2 channels.  The ideal ohm load for each channel is 4 ohms.  If you go lower than 4 ohms, you'll overheat the amp and possibly damage it; if you use a higher impedance, the amplifier won't produce its maximum power.

With a 4-ohm DVC sub like yours, you have two wiring options: each sub can be wired as a 2-ohm load, or an 8-ohm load.  So you can see that the impedance of the subs won't be a good match for the amplifier.

You'd be better off with a 2-channel amp in this case.  If you want to stay with the same brand, the P1400.2 appears to have a similar power rating.  You can bridge a 2-channel amp down to one channel, and you can combine the two 4-ohm DVC subs in a way that will result in a 4-ohm load for a single channel amplifier.  The wiring diagram would look like this:  

http://mobile.jlaudio.com/graphics/Support/Tutorials/wiring_images/DVC_Series_2.

Hope this helps!

Brian