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Advice on 2 amps running 1 Sub

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Advice on 2 amps running 1 Sub

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I am in the pocess of upgrading my system. I like the older school stuff so I am getting a Fosgate Power HX2 sub (dual 2 ohms coil) that takes 500 rms per coil. I already have 2 Fosgate 500bd mono amps which each of course does 500rms @ 2 ohms so thought this would be perfect match for the sub.

I would have to run one coil per  amp......are there any drawbacks in doing that and/or will this be straight forward or risky. These Power HX2 subs are very rare (at least here in the UK) so I want to be careful not to damage it.

Any help appreciated........thanksin advance.

 

Verified Answer
  • Using multiple amps to power separate voice coils of one driver is always discouraged. If the amps aren't set perfect you run a good risk of having the voice coils work against each other which in the end would mean there are now even less "very rare subs in the UK". I want to say you'd have to have the gains set with an Oscilloscope for it to work, but even then I'd try to avoid doing so.

    J Ro is pretty well educated on these matters and pretty good at explaining things, perhaps he'll read the thread and chime in on why you shouldn't do it.

     

  • This thread is about what can happen when using 2 amps (that aren't strapped) to power a DVC sub. Basically, the sub will run hotter than usual, and efficiency is reduced.  It can be done, and i respect your desire to use old school amps, but it's tricky to pull off even if you're quite familiar with amps and subs.

All Replies
  • Using multiple amps to power separate voice coils of one driver is always discouraged. If the amps aren't set perfect you run a good risk of having the voice coils work against each other which in the end would mean there are now even less "very rare subs in the UK". I want to say you'd have to have the gains set with an Oscilloscope for it to work, but even then I'd try to avoid doing so.

    J Ro is pretty well educated on these matters and pretty good at explaining things, perhaps he'll read the thread and chime in on why you shouldn't do it.

     

  • I'm not an expert on it, but I don't think it's a matter of setting the gains on an oscilloscope as much as making sure each voice coil sees the same signal at the same time.

    i.e. - you don't want to send the L channel mono signal to amp 1 and the R channel mono signal to amp 2.  If you split and combine the signal to both amps, it is more likely to work well.

    Now, sometimes with identical amps you can "strap" or "bootstrap" the amps to make one really large amp to power the subs and that works fine, but the amps need to be designed for it with a special connecting cables (lots of Kicker and some Power Acoustik and SoundStorm amps are), but I don't see that the 500bd's support that.

    Hope This Helps!!!

    Anyone else have suggestions?

    2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

  • This thread is about what can happen when using 2 amps (that aren't strapped) to power a DVC sub. Basically, the sub will run hotter than usual, and efficiency is reduced.  It can be done, and i respect your desire to use old school amps, but it's tricky to pull off even if you're quite familiar with amps and subs.

  • Thanks for your response and help on this . I definitely wont be using the two 500bd amps then.

    I however have another amp which I might have to use, it is a RF 801S. I know this will not give 1000rms but I think the 800rms should give me some good service for now, until I can change the amp. Also, I very often hear that those older RF amps are always under rated, so would you tend to agree that I might get closer to 900rms from this amp?

    Secondly, as the RF 801s is a 2 channel amp, and I now understand that its not wise to use seperate channel on different coils.......am I correct  in saying that the only way I should use this amp to push the POWER HX2 (DVC 2ohm coils) will be to wire the sub in parallel to read 4ohm then bridge the amp to 4ohm  so that both sub and amp match? I cant afford to fry this sub.

    I also gather from your thread that a mono amp will be the best choice for my DVC sub...and I obviously have 3 amps which are not ideal for this sub. I like this sub as its a rare treasure so I would rather change my amp than changing the sub. Now this sub on its own can only be wired to 4ohm or 1ohm. Can you suggest a mono RF amp that will match this sub for 1000rms.....older model prefarably?

    Thanks again in advance for your help.

    Howard

     

     

     

  • howy
    Thanks for your response and help on this

    No prob... so rare that i get a kudos so thank you!!!

    howy
    I however have another amp which I might have to use, it is a RF 801S.

    Use it!!! the difference between 800 and 1000 watts is negligible... not even a whole decibel.

    howy
    I very often hear that those older RF amps are always under rated

    Factual statement.

    howy
    ...I now understand that its not wise to use seperate channel on different coils.......am I correct...

    Yes.  it's a better match-up than you think.  the 801s is known to make nearly a 1000 watts anyway.

    howy
    I also gather from your thread that a mono amp will be the best choice for my DVC sub...

    I should have said 'single channel' instead of 'mono amp.'  a bridged 2 channel amp is basically a mono amp with double the impedance rating (same is true when you strap 2 amps... the lowest impedance they can handle is doubled).  sorry for the confusion, i simplified it but now i see you're a bit more educated than some of the forum's drop-ins. 

    howy
    ...I would rather change my amp than changing the sub.

    Hey, i dig that.  it's a great sub and there isn't much on the market today for under a grand that compares to it.  I think the 801s will do great, tho. 

    Editorial

    My only beef with RF's MEHSA amps is that you can fry an egg on them.  You really need to consider carefully the location where u mount one, bcuz they are nearly as efficient as amplifiers as they are as space heaters.  They get really, really hot.  Great build quality, good features, always make rated power or more, but they can melt carpet.

     

  • Fantastic !  I will stick with my 801s then.

    Many thanks for the help......invaluable information !!

  • howy

    Fantastic !  I will stick with my 801s then.

    Many thanks for the help......invaluable information !!

    I still don't know why i give this info out for free... except that i just love a thank you!  you're welcome Yes

  • howy
    am I correct  in saying that the only way I should use this amp to push the POWER HX2 (DVC 2ohm coils) will be to wire the sub in parallel to read 4ohm then bridge the amp to 4ohm  so that both sub and amp match? I cant afford to fry this sub.

    Pretty sure you meant 'series' not 'parallel', but just want to polish the thread.  Series wiring will double the impedance, and parallel wiring will halve it.  You want series wiring in this case.

  • J Ro
    a bridged 2 channel amp is basically a mono amp with double the impedance rating

    There are a few other differences, though:

    • The bridged amp is more likely Class AB, while a mono amp is most likely Class D - so the bridged amp will draw more current.
    • The bridged amp is highly unlikely to have a subsonic filter (needed for ported boxes) and might not even have a low-pass filter.

    Other than that, I agree, either one should work fine.

    Hope This Helps!!!

    Anyone else have suggestions?

    2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs