Using a 4 channel Amp to power a Polk Audio db1040 DVC sub

TJeep_1999

I have (3) 4 channel amps that have been sitting in the garage for awhile and I've decide that rather than buying yet another new amp I will use one of these to power a sub. When bridged it is rated at 150 x 2 at 4 ohms. If I use Y splitters on the singnal so both sets of bridged inputs and outputs use the same signal is there any reason I should be concerned running a Polk Audio db1040 DVC with one coil using channels 1&2 bridged and the other coil using channels 3&4 bridged? Will this set up void my warrenty?

MacLeod

Yeah I wouldn't want to do that. The output stages will be a little different and if you've got one voice coil getting say 200 watts and the other getting 225 it could be an issue. Plus you don't really want to use Y splitters cause they add noise and just aren't good. Plus, it wouldn't be a mono signal which could also screw things up. So no, I wouldn't do it. I would rather you buy a $150 Sony sub amp from Walmart than try to run a single sub off a 4 channel amp like that. Not only will it not sound it's best but it could potentially damage the sub.

TJeep_1999

We'll cover the second point first b/c I can speak to it and eliminate it as a point of concern. You don't need a mono amp to run a sub. I may be dating myself here, but class A/B amps have pushed subs for years long before mono amps were even invented. As long as the amp is Class A/B and it has a LPF (which it does) you'll be fine.

Just thinking this thru on the first point (the Y split concern asside) how would one coil getting 200W and the other getting 225W hurt the speaker? Why is it an issue? What does it actually do to the speaker that will hurt it? How is this any different then a single cone speaker playing low, mid, and high range different strength signals? The coils just push in one dirrection (up) so they would not be working against each other. Can you please explain why this is an issue?

MacLeod

TJeep_1999 wrote: »

We'll cover the second point first b/c I can speak to it and eliminate it as a point of concern. You don't need a mono amp to run a sub. I may be dating myself here, but class A/B amps have pushed subs for years long before mono amps were even invented. As long as the amp is Class A/B and it has a LPF (which it does) you'll be fine.

Back in the day they didn't have dual voice cool subs either. If you can find a 2 channel amp thst is stable at 2 ohms or 1 ohm bridged mono then you'd be perfectly fine using it. However it's gonna be a whole lot easier and cheaper to find a mono amp stable at that load.

Just thinking this thru on the first point (the Y split concern asside) how would one coil getting 200W and the other getting 225W hurt the speaker? Why is it an issue? What does it actually do to the speaker that will hurt it? How is this any different then a single cone speaker playing low, mid, and high range different strength signals? The coils just push in one dirrection (up) so they would not be working against each other. Can you please explain why this is an issue?

They're pushing in the same direction but they're pushing the same suspension so I'd want them both to be in sync as much as possible. Don't get me wrong, I'm not saying your sub will catch fire just thst I don't think it's ideal and could wear out the sub faster.

TJeep_1999

MacLeod wrote: »

Back in the day they didn't have dual voice cool subs either.

To clarify I don't have the DVC sub yet so if it really is an issue I'll go with the single voice coil (4 ohm load) and just bridge one one set of channels. In this 2nd scenario I think we both agree the A/B class amp and LPF would be fine. I just don't want to get hung up on switching the amp. It's going into a 17 year old Jeep wrangler and I literally have at least (3) higher end 4 channel amps sitting in the garage that haven't been used in 4+ years. I just can't justify buying a 4th amp for this application...

I could see how the sound quality could be impacted if they were not in sync, but in theory I can adj the gain levels enough for that to be a non issue at least to the naked ear. I'm still not seeing how it could "hurt" the speaker tho... one coil would just keep pushing up when the other stopped. Not sure why it would matter... what am I missing??

Looks like you are the only one engaging in the dialogue... appreciate your input in trying to sort this out.

MacLeod

Give it a try. Like I said, it's not going to blow up or anything and while I think it could add the wear and tear if you're not hammering on it then it might not matter that much.

TJeep_1999

I was able to get some detailed information from another manufacturer:

"Essentially, if there is any difference between the signals driving each coil at any given point in time at a given frequency, the voice coils will either fight each other or help each other, depending on the phase relationship of the two signals at that frequency. This is not the same thing as bridging an amplifier and can create undesirable non-linearities and distortion because different input signals at each voice coil create shifts in the speaker's electrical parameters.

For this reason, it is advisable to mono-bridge the amplifier whenever possible and connect the voice coils of the dual voice coil speaker together in parallel or series. If a dual voice coil subwoofer must be wired to two independent channels, the inputs to both channels should ideally be the same (summed mono), and every effort should be made to match the gains of both channels as closely as possible."

So I guess it comes down to running SVC Sub off one channel close to max gain on the amp or a DVC with two channels which requires less gain. Both are technically achievable, but one set up will put more stress on the speaker and the other will put more stress on the amp. Since I can control the inputs into both channels on the amp and in theory be able to adjust gain levels I'm currently leaning twards the DVC option... thoughts?

MacLeod

Are you planning on using aftermarket front speakers? If so why not just buy a SVC sub and run it off the rear channels bridged mono and then the front channels can drive the front speakers. That would be a nice easy way to get things set up and I'm a big fan of running your entire system off a single amp.

Jstas

Aside from the issues Mac has stated about output on each bridged channel potentially being different, despite ratings, it is possible to do what you are asking.

IIRC, a DB1040 DVC is two 4 ohm voice coils.

If that is the case, the vast majority of car amplifiers handle 4 ohm impedance levels in discrete or bridged mode. So the simple answer is yes, you can do what you are asking.


But that's not the question that needs to be asked.

Should you do this? It's not advisable.

The reasons are simple. If you have unequal power levels going to each voice coil, the higher power level is going to want to move the voice coil it is attached to farther in the travel range.That's going to make that voice coil drag the entire motor structure with it, like it was intended to do. What happens then is that the second voice coil with less power is going to be pulled and pushed past it's maximum limit with it's own power level. This changes the impedance on that voice coil and can cause an over draw on the second set of bridged channels. That over drives the amp, or at least half the amp and creates heat problems in the motor assembly. It will end up blowing the amp, or half the amp or the sub, or half the sub or both.

The reason we use dual voice coils is not so we can power them with stereo amplifiers. Although, if you have a stereo amp that can push 150 watts per channel without being bridged then you will have an easier time running that because the channels are discrete, sometimes with their own power supplies for left and right channels. They are far more stable in discrete modes and will match from channel to channel better than if they were bridged. That's where stuff like "birth sheets" come in handy and the reason that people in the top echelons of competition are running stuff from companies like Zapco that costs a small fortune...or your first born or something.

Anyway, the reason we use DVC's is so that we can drop the impedance levels on an amp to get more power out of it's amplification circuits without having to add more speakers. Two 10" DVC subs are much more preferable to four 10" single voice coil subs when you're trying to stuff a competition level, slot-loaded sub box into, say, a Volkswagen Jetta trunk.

TJeep_1999

Jsta... that was exactly what I was looking for in the way of an explanation. I always feel better if I can explain the "why" behind it. Thank you!!

MacLeod... funny you would mention the single amp option as I already have a 4 channel amp in the Jeep (yes, yet another 4 channel amp) that is pushing component Polk's in the front dash and 6" JL's in the sound bar. I'm seriously debating dissconnecting either the front or rears from the amp and using those channels to power the sub. Space is very tight and this is by far the easiest installation option. The only down side is that both speakers require a bit of juice to run and I worry that pulling either of them off the amp and putting them onto the HU for power will cause a noticeable degradation of sound quality... then again cabin acoustics has never been the Wrangler's strong suit.

Either way it sounds like I'll be going the SVC route.

chanceyouwrng

So if the problem is having them run at mix signals why not match the 2 gains with a multimeter . Then bridge the 4 channels into one the run in series to the two coils . Everything then is happy happy happy . Problem solved enjoy you bass!!!

pitdogg2

Bet he got it figured out .....7 YEARS AGO!!

oldrocker

pitdogg2 wrote: »

Bet he got it figured out .....7 YEARS AGO!!