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How does amplifier power relate to a sub capabilities?

Discussion in 'Archived Threads 2001-2004' started by Keir H, Jul 27, 2001.

  1. Keir H

    Keir H Second Unit

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    I've noticed power sub having many variations of amp power and wanted to know if there are things to look for when choosing a sub. Does it matter as far as driver size? Does more power = more [email protected](x)hz? I've seen sub's with 1000 watt amps and some with 15" drivers with only 100 watts. Why is this. ALso, for SVS unpowered or nay other unpowered sub, many say "any" amp would do, if so then why buy the optional amps many companies offer that are more expensive and more power if you don't "need" it? EX: old Sony receiver driving a SVS 25-31 or Marantz MA 700...would there be a difference in sound quality? Hope this makes sense..thanks guys.
     
  2. John M Miller

    John M Miller Stunt Coordinator

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    along the same lines, i've thought about buying a paradigm sb-100 passive sub. is it just as good as a powered sub if i get an amp to hook them up? thanks in advance.
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  3. Keir H

    Keir H Second Unit

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    anyone??? I guess there's many of us which are stumped on this question...
     
  4. Tom Vodhanel

    Tom Vodhanel Cinematographer

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    >>>I've noticed power sub having many variations of amp power and wanted to know if there are things to look for when choosing a sub.> ALso, for SVS unpowered or nay other unpowered sub, many say "any" amp would do, if so then why buy the optional amps many companies offer that are more expensive and more power if you don't "need" it? EX: old Sony receiver driving a SVS 25-31 or Marantz MA 700...would there be a difference in sound quality? Hope this makes sense..thanks guys.
     
  5. Mark Nelson

    Mark Nelson Agent

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    Keir
    The first thing to understand about subwoofer amps is that they are not rated like a receiver. There are no government regulations on how they must be rated. A receiver power rating is specifically regulated as to how it can be advertised. Even so, receiver "spec-manship" is an art in itself.
    Since a sub amp that is sold as part of a "powered sub" is directly connected to the driver(or drivers) inside the box, it only has to be rated for that driver's impedance load, efficiency rating, and operating frequency and most of the time we don't know this information about the internal driver. So the power ratings can sound really wild (WOW..a 1000 watt amp with a 15" woofer for $299.00). Remember wattage is a measure of volume capacity under specific loading criteria and is NOT a measure of quality.
    If these same amps were rated according to regulated ratings like receivers their power rating would have to be based on much stricter criteria (most commonly with all channels driven at full volume into an 8 ohm load over the frequency range of 20 hz to 20,000 hz). Who knows how these sub amps would spec out when tested that way?
    This is why buying a powered sub can be so difficult. Like most things audio, listening is your final defense.
    People say that it is OK to use any good amp into a passive sub and get good results. This is usually true, but not always. Most passive subs are not difficult loads to drive so they can be powered by any decent amp. But there some loopholes in this. If the passive driver is an unusual load for any reason (2-4 ohm driver, very low efficiency, etc.) a regular amp will stumble trying to play it. So you have to know a bit about the driver to be really sure that hooking up any old amp will work.
    Also subwoofer drivers almost all demand a large current dumping capacity from the amp in order to reproduce large bass dynamics cleanly. It's also true that subs (especially large diameter subs) generally sound better when powered by an amp with a high "damping" factor. Loosely defined this means the amps ability to control the driver motion. This spec is not usually given for amps, but happily it is usually a direct by-product of higher wattage.
    OK, so most subs will sound their best when driven by an amp that can deliver a high current reserve very fast, has high wattage at the driver's impedance/efficiency/frequency rating , and can provide enough wattage to drive the sub to the desired volume with high control (damping factor). Because of this it's easy to see that some amps are going to make a good passive sub sound better than others. An old receiver that you may have available will "probably" be OK but not great.
    The easiest way for most people to find a good sub is to buy one with a good reputation from a good company that is a "powered sub". That way you don't have to know all the dynamics of WHY it works. These powered subs also have the crossover, phase, volume, Hi-pass filters and sometimes rolloff adjustments that can really help in integrating a sub into your system. A regular power amp running a passive sub rarely gives you these adjustments.
    This forum is infected with HT hobbyists like me who are always interested in the WHY so we can get a better result for less. THAT's the Holy Grail of the hobbyist. Getting to the WHY is part of the fun, but it's very difficult sometimes to follow a direct route to it, so we learn to love trial and error.
    If you would like to try the "hobbyist" approach on a subwoofer, be as sure as possible that you learn from all our mistakes. Get a good driver. A 12" driver is usually more than enough for most rooms and is easier to make go really low than most larger drivers(3db down @ 25-28 hz is a worthy goal, and there are many excellent 12" choices to buy).
    Then build an enclosure that closely meets the design criteria of that driver and your own needs. Then design the crossover as carefully as possible using the best components you can get(or just use the surround processor to set the crossover point and forget building one).Then power it with the biggest beefiest amp with lots power and current reserve.
    The guys on the HTF always have no hesitation in pointing out the bad results they've had along with the good, so you can really get ahead by listening to them. Best of Luck!
    MTN
    [Edited last by Mark Nelson on July 30, 2001 at 02:01 AM]
     
  6. Chip E

    Chip E Screenwriter

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    "Still, look for the subwoofer performance as a whole first.(just like looking at a car's performance number's instead of listening to a guy bench race all night about how fast his car is SUPPOSED to be...because he has a pocket slide rule HP/weight convertor that says he's going to run 11s."
    Ah...yea... that's just what my 20-39PC reminds me of.. my first car.. 69' chevelle SS 396. But my rat motor had a street/strip job. Ran low 12's.. Boy, those were the days.. Still have all my time cards from Atco dragway too, lol. (except for when we dragged on Friday nights on Front street & Delaware ave. in South Philly)
    - Chip
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