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Damping/dampening factor and low-end response

Discussion in 'Amps and Cabs [BG]' started by j-raj, Mar 28, 2005.


  1. j-raj

    j-raj Bassist: Educator/Soloist/Performer Staff Member Supporting Member

    Jan 14, 2003
    Atlanta, GA!
    I was in the studio last night/this morning and one of the cat's that is doing some of the gopher duties (getting our crack, brown m&m's and bitches), is a power amp guru. He mentioned to me that when ever you are picking a power amp, make sure to look for Damping/dampening factor .

    The higher the number the better your low end response will be.

    Is this true? What is the Damping/dampening factor?
     
  2. Well, not better low end response, just tighter low end response. Damping factor is a gauge by which to measure an amp's ability to control the movement of the speaker cones. A cone going in one direction wants to keep going in that direction even after the signal has stopped.
     
  3. j-raj

    j-raj Bassist: Educator/Soloist/Performer Staff Member Supporting Member

    Jan 14, 2003
    Atlanta, GA!

    ahh, I see.

    What are other indicators that relate to bass performance?
     
  4. There are a lot of other performance specs that go with power amps, but as far as I know frequency response and damping factor are the big two where bass is concerned. Any of the big names in power amps will give you all the performance you may need in building a bass rig. If you're doing pro sound like your amp guru buddy, your demands might be a great deal higher and certain amps would be unacceptable for certain applications. But by and large for the rigs we bassists build, just about anything from Crest, Crown, QSC, Yorkville...etc has the specs to meet our needs just fine as long as the amp you select has enough power for your needs.
     
  5. j-raj

    j-raj Bassist: Educator/Soloist/Performer Staff Member Supporting Member

    Jan 14, 2003
    Atlanta, GA!

    Thanks man, this is what I have right now (granted it is a tad bit heavy and I would like to go to a 4-space rack):

    [​IMG]

    I currently picked up a Crown XLS402, which I thought would be a lighter option with a better bass friendly response... So I think that I'm going to eBay both and save up for a QSC PLX... sounds like the best for bass for my $, right?
     
  6. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Sort-of..... If its bad enough, the damping factor can lead to a "loose and tubby" sounding low end.

    But, pretty much any power amp has good enough damping factor to be OK. Like at or above maybe 100.

    A very over-rated spec.....

    It is the ratio of the speaker nominal impedance to the amplifier "output resistance" (usually is a relatively pure resistance). This amplifier output resistance is NOT the same as a load impedance rating, it is a property of the amplifier, and is normally is a very small fraction of an ohm.

    The majority of the speaker impedance is resistance. A 4 ohm speaker has maybe 2.5 to 3 ohms resistance, for instance. An 8 ohms speaker may have 6 ohms resistance.

    All the resistance in the circuit, speaker resistance, wire resistance, and amplifier output resistance, adds up to some number. That TOTAL is the limiting factor to controlling the speaker movement.

    So, there is a certain amount of futility in concerning oneself about a small fraction of an ohm in the amplifier, while the speaker has several ohms resistance.......

    An amplifier with a DF of 100 at 8 ohms has an output resistance of about 0.08 ohms. That is 8 percent of one ohm.

    So, if the speaker has 5 ohms resistance, an amplifier with a DF of 100 adds 0.08 ohm, and the total is 5.08 ohms. That's if the speaker wire and connectors have zero resistance.

    A "really good" amplifier with a damping factor of 1000, would improve that total to 5.008 ohms. about a 1.6% change. Big deal.

    Now, a "really bad" damping factor of 10 would make a difference. Then the total would be about 5.8 ohm, or a change of about 16%. THAT you could credibly notice.
     
  7. The PLX is a great choice. I prefer my CA9, but the CA9 weighs as much as a fully growed Missouri mule so it's definitely not for people looking to cut back on the poundage. :cool:
     
  8. That's right about where your average tube amp lies, isn't it?
     
  9. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    I think a bit better than that, depending. Could be that low.

    And, we all know about "warm" sounding tube amps..........

    It's a good point, and shows that even relatively low DF can exist and the amp isn't horrible for everything. But you could tell the difference between 10 and 200 with relatively little trouble.

    Now, an SS amp with a "real" DF of 10 is likely to have some other problems as well. In SS amps, the damping factor tends to tell a story about the amount of feedback in the amp, etc, etc.

    A guitar amp is different than bass or PA amps. Most decent sounding SS guitar amps have the DF artificially made higher by tricky circuits...some may have a DF of 0.5.....yes, one-half. That wouldn't be too good for PA, but suits guitar fine.
     
  10. Jerrold brings up a good point. All the pro sound guys I know, and they're a hell of a lot smarter about this stuff than me by the way, tell me that you reach a point of diminishing returns with damping factor. You get to a point where having more just doesn't make any difference. Crown disagrees with this incidently. Their K series amps have a damping factor of 3000. They're pretty damned proud of that and they'll tell you at great length why more is always better. But take it with a grain of salt and remember that they are after all trying to get you to buy their amps.
     
  11. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    North central Ohio
    Editor-in-Chief, Bass Gear Magazine
    Give Jim Bergantino a call. He'll talk your ear off on this topic! :p
     
  12. I always suspected, and I may be wrong, that the inherently low damping factor of tube amps is what inspired Ampeg to design the cab for the SVT the way they did. Ten inch speakers in a sealed enclosure. Such an arrangement would provide mechanical damping to compensate for the damping factor the tube head lacked. I know I've used 15 inch speakers in ported cabs with tube heads and sure wasn't satisfied with the results. The cones tended to flop all over the place.
     
  13. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    I don't know the real "back story" on that.

    I suspect part of it is "pre-mixing" the sound into a slot above the kick drum. The 60 and above range projects better and doesn't get lost as easily, especially with "only" 300 W. Plenty of threads covering that here.

    Yes, a sealed cabinet will control cone motion reasonably well. Not that it "damps" cone motion, it may resonate and produce an acoustic peak, with large cone motion.

    However, below system resonance, the cone motion is controlled by the stiffness of the air "spring" as the cone compresses the air in the cabinet. That reduces uncontrolled motion, over-excursion, etc, that might be described as "flap".

    A tuned cabinet has a big hole in it, and below system resonance it simply allows the cone or cones to pump air in and out of the port. There is no restriction on movement other than the cone suspension and whatever friction may exist. It is relatively easy for the cone to move too far and be damaged (typically cone folds and is creased).

    Damage in the sealed cabinet is harder to cause. It can be a split cone, or the voice coil loosened or torn off the cone. But probably you would just cook the voice coil first.
     
  14. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    One thing I know is that if you take a 1000W power amp with a damping factor of a bazillion, and connect it to speakers with a nice, long run of 18Ga speaker cable - sadly, a very common practice - then your damping factor is automatically SHOT! You can easily get it below ten like this.

    Use the biggest, hugest, shortest cable that you possibly dare, if D.F. means anything to you!

    Joe
     
  15. For bassists this generally isn't much of an issue because our speaker runs are so short. But yeah, for sound guys it's a very large issue.
     
  16. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    In tube amps, doesn't the output transformer actually MATCH the output tubes' plate impedance with the load impedance? That would be a D.F of ONE, right?

    ..Or do they always design-in global feedback to 'artificially' increase the factor? I've heard of audiophile valve amps that feature zero-feedback - how does that control speaker movement for the MOST discerning 'golden ears'?

    Joe
     
  17. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    For those of you are playing around with the WinISD program, as I am, you can add 0.08 ohms to the series resistance of the driver and see what happens. The answer is: Not much.
     
  18. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Typical tube bass amps incorporate feedback. This includes the legendary SVT.

    A lot of audiophile stuff is a pure crock. The discerning golden ears are easily fooled by expectation bias, just like the rest of us.
     
  19. jerry

    jerry Doesn't know BDO Gold Supporting Member

    Dec 13, 1999
    Hawaii
    If you want to see a amp in action with a low damping factor, check out how much a SWRSM400 will make your speakers dance :eyebrow:
     
  20. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    Wahhhhtt?? I gathered from what I read here that SWR amps exhibited a tight, controlled, un-colored 'hi-fi' sound??!

    What'da!..

    Man.. I think this ex-soundman (but forever a technician) is starting to zero-in on what he's going to do for his his long-desired Rig Of Doom (I don't remember who refered to their rig like that, but ever since I read it, I said "Yeah - that's what I'll have someday! A Rig Of Doooooom."). It's going to involve a nice, seperate, dedicated PA power amp!

    Yeah... If only the SVTClassic sound will do - why I'll just pump one of those puppies into a dummy-impedance, put a Jensen transformer across it, and feed that nice, balanced line signal to a nice, seperate, dedicated PA power amp. Yeah. Yeahh! That's what I'll do.

    Well - even if not, I think I'll connect a nice Crest or heavy-Crown or something into the ol' speaker terminals of doom.

    Joe
    (edit) WITH WELDING CABLE!!