Damping Factor in bass heads?

[DJJazzV]

Why is it that the Damping Factor is never listed for bass heads? Why is it only for poweramps? Shouldn't that be important? It certainly is for poweramps.
I had an A/B experience a while back that really opened my ears. I had an Ampeg SVT-8 Pro head, and A/B'd that with the exact preamp (SVP-CL) + a Crest CA9 poweramp with a damping factor of >700. The Pre/Power combo was slightly faster and more defined then the all-in-one SVT-8 head. I could be wrong, but I would attribute that to the damping factor of the poweramp. (I was told that in general, the damping factor is the ability to pull the speaker back, ready for the next note. That could be way off, but it makes sense.)
Both amps sounded great, but there was a noticeable difference that made me sell the SVT-8. A few months later, I couldn't remember why I sold the SVT-8, so I bought another, then did the same A/B again, and had the same conclusion. (I do go nuts with gear every once in a while. N. V. T. S., nuts!)
I am looking forward ot hearing some opinions and facts on this. Yes, I already know I shouldn't have sold/traded the SVT-8's as well.
I would consider buying bass heads partially based on the Damping Factor, if the information was available. Higher the better. Wouldn't that make sense for a purchase?

[jelwood]

Perhaps the manufacturers are assuming that if you're buying a power amp separately then you know a little more about equipment and specs? Anyone can buy an all in one head but only people who have put forth a little time to learn somewhat know that there exists a pre/power setup as a whole different option.

P.S. if you want an amp that has superb ability to maintain control of cones, get a GK. They don't use current limiters

[seamonkey]

What you heard likely had nothing to do with damping factor.
It was probably all preamp - gain, eq settings.

[DJJazzV]

Originally Posted by seamonkey

What you heard likely had nothing to do with damping factor.
It was probably all preamp - gain, eq settings.

Everything was matched perfectly between the 2, multiple times.

I should have also included my other tests of quite a few different preamps, and playing them with the Crest CA9. I then put those preamps into the Effects Return only of a few different bass heads (so it isolated the power section of the head - bypassed it's preamp) and compared the tone. The pre/poweramp was always slightly better. That's been done with many different preamps and amp heads. Using any preamp with the power section only of any bass head has never sounded better then using the preamp with a separate (solid state) poweramp (CA9 in my tests).
I won't get into the tube poweramps. That's a different story altogether.

[Rick Auricchio]

It isn't the damping factor; all modern amps have very high damping factors.

What you (may) be hearing is differences in the amplifier design.

[billfitzmaurice]

Originally Posted by DJJazzV

Shouldn't that be important? It certainly is for poweramps.

No, it isn't. Power amps list damping factor because they list everything. You can find damping factors in the high hundreds on a $139 SS power amp and less than 100 on a $25k tube power amp. If damping factor was really significant it would be the other way around.

[Jim C]

Isn't the CA-9 (depending on mono vs. stereo) a much more powerful amplifier?
Don't know about damping factor but do think high powered amps generally sound better & more robust (within reason) from mid volume on up, especially when driving ineffecient speakers
(based on my experience with the SVP-CL pre I bought from you!).

[A440Hz]

If the damping factor is low enough, the impedance curve of the speaker starts to affect the frequency response.

Damping factor is the inverse of the output impedance of the amp; tube amps have output transformers and have somewhat high output impedances --> low damping factors (the output tranny is there to lower the output impedance, but they're not perfect). SS amps have emitter follower (or some such) outputs, which can have insanely low impedances --> high damping factor.

So damping factor has to do with the ability of the amp to drive signal voltages (or currents) independently of the impedance of the speaker. The speaker impedance is a function of frequency.

Incidentally, since the peak impedance of many speaker drivers is in the bass to low-mid range, you will often get a bass bump with lower damping factors. This is part of what you're hearing in a classic SVT/810 setup.

[wynsmth]

Here's what I found on Wikipedia which coincides with my understanding of dampening factor & the ability to control undesireable speaker movements following a note. To me, a higher dampening factor means less ghosting of notes & a cleaner, more precise sound.

In loudspeaker systems, the value of the damping factor between a particular loudspeaker and a particular amplifier describes the ability of the amplifier to control undesirable movement of the speaker cone near the resonant frequency of the speaker system. It is usually used in the context of low-frequency driver behavior, and especially so in the case of electrodynamic drivers, which use a magnetic motor to generate the forces which move the diaphragm.

Speaker diaphragms have mass, and their surrounds have stiffness. Together, these form a resonant system, and the mechanical cone resonance may be excited by electrical signals (e.g., pulses) at audio frequencies. But a driver with a voice coil is also a current generator, since it has a coil attached to the cone and suspension, and that coil is immersed in a magnetic field. For every motion the coil makes, it will generate a current that will be seen by any electrically attached equipment, such as an amplifier. In fact, the amp's output circuitry will be the main electrical load on the "voice coil current generator". If that load has low resistance, the current will be larger and the voice coil will be more strongly forced to decelerate. A high damping factor (which requires low output impedance at the amplifier output) very rapidly damps unwanted cone movements induced by the mechanical resonance of the speaker, acting as the equivalent of a "brake" on the voice coil motion (just as a short circuit across the terminals of a rotary electrical generator will make it very hard to turn). It is generally (though not universally) thought that tighter control of voice coil motion is desirable, as it is believed to contribute to better-quality sound.

A high damping factor indicates that an amplifier will have greater control over the movement of the speaker cone, particularly in the bass region near the resonant frequency of the driver's mechanical resonance. However, the damping factor at any particular frequency will vary, since driver voice coils are complex impedances whose values vary with frequency. In addition, the electrical characteristics of every voice coil will change with temperature; high power levels will increase coil temperature, and thus resistance. And finally, passive crossovers (made of relatively large inductors, capacitors, and resistors) are between the amplifier and speaker drivers and also affect the damping factor, again in a way that varies with frequency.

[Jerrold Tiers]

A damping factor is important up to about a factor of 20 or 30. Above that it declines in importance.

For an open-back guitar amp, or even many guitar heads, a desirable damping factor is around 0.3 . it would probably pay to be higher for most other applications....... including bass, but I would definitely NOT pay much attention to it.

Virtually any design with any pretensions to being a power amplifier will have enough D.F. to be fine.....

Remember....... a 4 ohm speaker has an inherent resistance of around 3 ohms....... I defy the most anal-retentive tech-head to come up with a reasonable explanation of how 0.04 ohms in one part of a series circuit makes a difference when there is 3 ohms resistance in another part......

"Control" of the speaker can only come from varying the current in the circuit, which provides force on the voice coil, and 0.04 ohms out of 3 ohms is not going to provide much variation of current even if totally removed, let alone reduced slightly or increased slightly.

[Bob Lee (QSC)]

Damping factor is not that important for power amps either, except to the marketing department.

[DJJazzV]

Thank you all for the detailed replies. Learn something new every day. Perhaps I should take 2 weeks off from buying and selling bass heads when I change my mind, then give it up altogether. Just kidding! I go nuts with gear, and there was some solid information in this thread. Thank you again.

[craig.p]

May I add a little context to this discussion? For this purpose, I won't call it "damping factor" but rather "amp tightness."

Some people don't want tightness. It would wreck their sound and the sound of the band. So, tightness isn't always benign.

A sloppy player can make a tight amp sound ten times looser than its damping factor would suggest. A tight, precise player can make a loose amp sound ten times tighter than its damping factor would suggest.

In a live setting, you lose much of an amp's characteristic tightness. It can be partially remedied, but never fully. Also in a live setting, with mains support, the tightest amp in the world can sound flabby as hell through the mains -- for various reasons.

The instrument itself can contribute to tightness. Compare, for example, a Precision, with a Jazz using only its bridge pickup and punched way up in the bass.

The speaker system (drivers and cab) can have a big effect. We all know how tight/defined some cabs sound, and how loose/flabby others sound.

WHERE the player is playing on the bass can contribute to tightness. In my experience, a much tighter sound can be had by playing softly near the bridge saddles (with the bass and volume boosted to compensate); a rounder, flabbier sound can be had by playing more energetically closer to the neck.

There are many factors that figure into how tight an amp sounds. Damping factor is only one. I'm not saying it's unimportant, just that it's not the only contributor, and it's important not to yank it out of context and head straight down the garden path.

Having played through dozens of amps over three decades of playing bass, I'd have to say that it's the player himself who has the most influence over how tight an amp sounds.

[Bob Lee (QSC)]

Originally Posted by craig.p

May I add a little context to this discussion? For this purpose, I won't call it "damping factor" but rather "amp tightness."

Some people don't want tightness. It would wreck their sound and the sound of the band. So, tightness isn't always benign.

A sloppy player can make a tight amp sound ten times looser than its damping factor would suggest. A tight, precise player can make a loose amp sound ten times tighter than its damping factor would suggest.

In a live setting, you lose much of an amp's characteristic tightness. It can be partially remedied, but never fully. Also in a live setting, with mains support, the tightest amp in the world can sound flabby as hell through the mains -- for various reasons.

The instrument itself can contribute to tightness. Compare, for example, a Precision, with a Jazz using only its bridge pickup and punched way up in the bass.

The speaker system (drivers and cab) can have a big effect. We all know how tight/defined some cabs sound, and how loose/flabby others sound.

WHERE the player is playing on the bass can contribute to tightness. In my experience, a much tighter sound can be had by playing softly near the bridge saddles (with the bass and volume boosted to compensate); a rounder, flabbier sound can be had by playing more energetically closer to the neck.

There are many factors that figure into how tight an amp sounds. Damping factor is only one. I'm not saying it's unimportant, just that it's not the only contributor, and it's important not to yank it out of context and head straight down the garden path.

Having played through dozens of amps over three decades of playing bass, I'd have to say that it's the player himself who has the most influence over how tight an amp sounds.

How would you define or characterize "amp tightness"?

I agree that playing technique is the biggest contributor to one's sound. You might directly call that "player tightness," as opposed to "amp tightness," "wood tightness," "speaker tightness," "stage tightness," "rack tightness," etc.

[Rick Auricchio]

Craig, in an indoor setting the room acoustics play a huge part in perceived sound and "tightness," far more than the amplifier.

[craig.p]

+1 to that, Rick. My sound has often been "massacred by the room." I'm getting to the point now where I can see a room for the first time and either wipe my brow with relief, or mutter, "Uh-oh..."

Bob from QSC, I understand your question, but the problem I'm having is how to phrase the answer. I'll try anyway. It has to do with dynamic range but there's also a "quickness factor" to it. An amp's ability to respond instantly and accurately to huge input-signal level changes -- decreases as well as increases. But the kicker is: into real-world speaker loads. Would you agree or would you state it differently?

[Bob Lee (QSC)]

An amp that doesn't have that ability is broken.

[Bassflute]

Originally Posted by billfitzmaurice

No, it isn't. Power amps list damping factor because they list everything. You can find damping factors in the high hundreds on a $139 SS power amp and less than 100 on a $25k tube power amp. If damping factor was really significant it would be the other way around.

Originally Posted by Bob Lee (QSC)

Damping factor is not that important for power amps either, except to the marketing department.

that Peavey is marketing two 'adjustable' damping factors on their new tube heads...

http://www.peavey.com/products/proseries/index.cfm

Always wanted to hear two identical amps with hugely disparate damping factors so I could 'hear' what they actually do.

That and the slew rate...like to actually 'hear' what that's all about, if possible.

Cheers,
Cameron

[craig.p]

Hey Bob... I've heard lots of great-sounding tube audiophile power amps (room heater-class) that are seriously broken, then!

I mean LOTS of overhang down in the bass region.

I personally prefer tight for playing bass guitar. The tighter the better. On that point, I fondly recall my old Sunn Coliseum.

[Bob Lee (QSC)]

A lot of those are pretty fragile, but "overhang" is probably more of a loudspeaker or room acoustics issue. If the amp has an extremely high output impedance (perhaps it bould be an intentional quirk of an "audiophile" amp) it won't damp the loudspeaker's autonomous motions.