Polk mm840 possibly overpowered?

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Banks1329
Banks1329 Posts: 2
edited May 2014 in Car Audio & Electronics
Hi there, I own two Polk MM840 4ohm svc subwoofers - Rms: 250 / Peak: 500.

I am in the process of putting together a fairly high end Polk sound system in my car however I am stuck with a predicament...

I have a found a fairly high end 5 channel amplifier that I really like and I think it will work perfectly for my system expect for the sub channel.

The amplifier is a Phoenix Gold Ti2 1600w 5 Channel amp. The amp puts out 125 x 4 @ 4ohm and 800 x 1 @ 2ohm.

I will be wiring my 2 svc 4ohm subs in parallel series down to 2 ohm and therefore they will be receiving 800 watts (400 each) from my amp. I am a little worried that I may be powering my subs too close to their peak wattage? I know that you should try and match your amp rms to sub rms but there are very few amps that produce the 4 channel output that I need, with a powerful enough sub channel to sufficiently power two subs.

Basically my question is, will my polk mm840s be able to perform properly and maintain their sound quality over a long period of time if they receive 400 rms each?

Regard
Josh

Just out of interest, why does the bottom of my Polk mm840 say "Rms: 300" but the box and other websites say that the Rms is 250?
Post edited by Banks1329 on

Comments

  • Jstas
    Jstas Posts: 14,754
    edited May 2014
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    If your RMS rating is only 250 watts (or 300, either way, doesn't matter) on the subs then pushing 400 watts through them is not advisable. That's 100-150 watts too many. I can see squeaking by with 20 watts more. Maybe even as high as 50 watts more on the RMS rating. But 100-150 you are going to shorten the life of your subs significantly.

    As far as the conflicting ratings, your best bet is to call Polk Audio Customer Service 1-800-377-POLK (7655)
    Expert Moron Extraordinaire

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  • Banks1329
    Banks1329 Posts: 2
    edited May 2014
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    Cool, thank you.

    Yes that's what I've been worrying about and on top of that the Phoenix Gold Ti2 1600.5 amplifier is also not CEA complicate and some people have been able to get readings as much as 940 Rms out of the sub channel at 2 ohms... That makes things even worse. I might however try to swap my 4 ohm SVC's for 4 ohm DVC and then I will have a few more wiring options to play around with and that should be able to balance out the rms from the amp.

    Thank you for the reply.
    I am still open to any other opinions or experiences, i'm trying to gather as much knowledge as possible.
  • Jstas
    Jstas Posts: 14,754
    edited May 2014
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    Well, if you still want to go with the 8 inch subs, you can run the DVC version with 4 ohm coils, wire them in series to present an 8 ohm load between the two voice coils. Then you can wire the two subs now presenting 8 ohm loads to the amp in parallel to present a 4 ohm load.

    With 250 watts RMS per voice coil as your limit, the amp is only going to push about 200 watts per coil at the 800Wx1 @ 4 ohms rating. Even if it's unregulated power supply will still push 940 watts, you're still going to be under the 250 watt max RMS by about 20 watts or more. So that would be a better option for you.

    Or just find another amp.



    Some references:

    Parallel and Series wiring calculators: http://www.the12volt.com/caraudio/boxcalcs.asp

    Wiring Wizard to show you how to wire the subs: http://www.the12volt.com/caraudio/woofer_configurations.asp

    This should be you wiring diagram for your options on how to wire two subs with dual 4 ohm voicecoils:

    http://www.the12volt.com/caraudio/woofer_configurations.asp?Q=2&I=42#results

    This is the wiring diagram you would want to use to do what I wrote about above:

    2_4ohm_dvc_4ohm.gif


    And you can ask for other opinions all you want. I doubt anyone else is going to come up with anything other than what I wrote above. If they do, I wouldn't listen to them if I were you. They likely don't know what they are talking about. This stuff is governed by the laws of physics. Like Scotty says..."Ya cannah change tha laws of Physics, Jim!"

    They aren't open for interpretation.
    Expert Moron Extraordinaire

    You're just jealous 'cause the voices don't talk to you!