[qscott]

Hello All,

I'm currently looking at buying a new 4BSST2 and just noticed that the Tech sheet on Bryston website for the old 4BSST (one I currently own) is rated at over 500 at 20 Hz, ref. 8 ohms and the new Sq version is rated at over 300 at 20 Hz, ref. 8 Ohms.

Am I missing something or has the new model dropped some control over the speakers to gain something else?

Cheers,
Q

[James Tanner]

Hi Q.

DAMPING FACTOR: is a measure of the amplifier's ability to control the woofer, and is measured by dividing the speaker impedance, (normally 8 ohms), into the amplifier's output impedance, (usually in the range of 0.02 ohms). The lower the amplifier's output impedance, the less the amplifier's output level is affected by variations in the speaker impedance. Also, since the woofer's voice-coil can act as a generator, within its magnet structure, the amplifier needs a low output impedance to act as a method of damping the woofer's tendency to keep moving after the signal has stopped. In the example above, the damping factor would be 8/.02 = 400.

Bryston amplifiers have output impedance slightly below 0.01 ohms, and therefore have a calculated damping factor of over 800, (though we conservatively rate them between 300 and 500). This parameter is affected by the speaker cable resistance. Even heavy 12- gauge wire has a resistance of about 0.0016 ohms per foot. (Remember we need to double that for twin-lead speaker cable). Thus, it would require only 6.25 feet of 12 gauge per speaker to have a total resistance of 0.02 ohms, (.0016 X 2 X 6.25 = 0.02), cutting a damping factor of 400 in half, to 200. Bryston recommends keeping speaker lead length to a minimum for this reason.

Keep in mind that damping factor is also affected by other real-world impedances, including the speaker-cable resistance, and the varying resistance of the speaker's own voice-coil. The voice-coil of a typical 8-ohm loudspeaker has a DC resistance of between 4 and 6 ohms. This resistance increases with temperature by 0.4%/Deg. C. It would thus require only a 25-degree rise in voice-coil temperature to increase its impedance by 10%. If it started with a DC resistance of 4 ohms, the extra 10%, (0.4 ohms), would reduce the actual damping factor to twenty, (8/0.4=20)!

It is worth noting that it would probably take only about 5-10 Watts to raise the voice-coil temperature by that amount. Add in the likely speaker-cable resistance of about 0.1 ohms, (10 feet of 16 gauge. cable), and it is obvious that the amplifier's contribution to the overall, real-world damping factor of the system is close to nil.

Whether the amp measures 300 or 3,000,000 under ideal conditions, the actual damping factor of the system will almost never exceed 100 anyway.

james

[avahifi]

I always thought that damping factor meant how much beer you could spill into the amplifer and still have it work.   

Regards,

Frank Van Alstine

[James Tanner]

I always thought that damping factor meant how much beer you could spill into the amplifer and still have it work.   

Regards,

Frank Van Alstine

Good one!

[95Dyna]

I always thought that damping factor meant how much beer you could spill into the amplifer and still have it work.   

Regards,

Frank Van Alstine

Yes, that was my impression as well.  Since I'm older now and am much more likely to have a glass of Merlot with my Beethoven quartet I paid no attention to the damping factor spec.  Now thanks to James' comprehensive scientific explanation I feel much better about my decision.

[b5pt9]

Great explanation on damping factor, thanks!  Still wonder why the SST2 is rated lower than the SST though?

Can someone describe the sonic impact as damping factor is reduced?  Less bass overall, muddy sounding base, etc?  What do you tend to hear in the extreme caes?

[Levi]

That is a good question that I am interested to know as well.  I tried 12ft speaker vs 3ft speaker cables (same kind) with my 7B/PMC and did not hear a difference.  Hmmm...

[95Dyna]

That is a good question that I am interested to know as well.  I tried 12ft speaker vs 3ft speaker cables (same kind) with my 7B/PMC and did not hear a difference.  Hmmm...

I recently replaced a pair of 20 year old Adcom GFA 555's with a pair of 7B SST2's without changing anything else and immediately noticed that the bass was cleaner, tighter and more precise.  I think the term muddy as opposed to more or less is more applicable with a reduction in damping factor.  The main cause would be the woofer having to handle a new low frequency signal while still recovering or vibrating from the previous signal.  I agree with James that this is a very elusive amplifier spec that is affected by outside variables.  If you look at the McIntosh 402 or 501's they publish damping factor specs at 100 and these are great amps by anybody's measure.  An amp can't be considered great without tight control over the woofers.

[James Tanner]

I checked with engineering and the 300 is wrong - a misprint on the lit - the 4B SST-2's are in fact still rated at 500 - not that it matters all that much.

james

[konut]

As a "specs" guy, I pay attention to damping factor. Anything over 100 is A OK! Diminishing returns and all that........

[werd]

here i go again

is this what you mean by damping or is it dampening  factor? 
http://www.youtube.com/watch?v=i5yJsX-jRaA

[rob80b]

here i go again

is this what you mean by damping or is it dampening  factor? 
http://www.youtube.com/watch?v=i5yJsX-jRaA

Exactly, if they had used Bryston the sound would have been much better.

[Levi]

Thanks for pointing out the difference between the Adcom and Bryston amp. I am sure you noticed more than increased bass resolution.

That is a good question that I am interested to know as well.  I tried 12ft speaker vs 3ft speaker cables (same kind) with my 7B/PMC and did not hear a difference.  Hmmm...

I recently replaced a pair of 20 year old Adcom GFA 555's with a pair of 7B SST2's without changing anything else and immediately noticed that the bass was cleaner, tighter and more precise.  I think the term muddy as opposed to more or less is more applicable with a reduction in damping factor.  The main cause would be the woofer having to handle a new low frequency signal while still recovering or vibrating from the previous signal.  I agree with James that this is a very elusive amplifier spec that is affected by outside variables.  If you look at the McIntosh 402 or 501's they publish damping factor specs at 100 and these are great amps by anybody's measure.  An amp can't be considered great without tight control over the woofers.

[95Dyna]

Thanks for pointing out the difference between the Adcom and Bryston amp. I am sure you noticed more than increased bass resolution.

That is a good question that I am interested to know as well.  I tried 12ft speaker vs 3ft speaker cables (same kind) with my 7B/PMC and did not hear a difference.  Hmmm...

I recently replaced a pair of 20 year old Adcom GFA 555's with a pair of 7B SST2's without changing anything else and immediately noticed that the bass was cleaner, tighter and more precise.  I think the term muddy as opposed to more or less is more applicable with a reduction in damping factor.  The main cause would be the woofer having to handle a new low frequency signal while still recovering or vibrating from the previous signal.  I agree with James that this is a very elusive amplifier spec that is affected by outside variables.  If you look at the McIntosh 402 or 501's they publish damping factor specs at 100 and these are great amps by anybody's measure.  An amp can't be considered great without tight control over the woofers.

Yes, the 7Bs are superior in just about every way although the Adcoms were a very respectible amp in their day for the price (designed by no less than Nelson Pass).  That's why I thought the comparrison would be helpful in answering b5pt9's question about how lower damping factor would manifest sonically.

[qscott]

Hi James,

Thank you for clearing that up and providing such an in-depth explanation of how and what the damping factor is all about, I thought it might have been a typo.

I've had the 4B SST for about a month now and the difference it's made to my PMC PB1i is nothing short of speaker/life changing. The amount of control and information I'm now hearing from the speakers is amazing. Before I had the 4B SST I was wondering if I need to move up to the IB2i to get the bass that I like but no need now. (well for the moment anyway.)

Best thing I've did was to add the Bryston to the system.

I'll be looking to add a BP26, BDA-1 to the mix and upgrading the amp to the 4B SST-2. I'm sure it will be another leap forward. Keep you posted.

All the best,
Q

[math-geek]

As a former Bryston owner and now a Krell owner I would like to chime in that, as James said, damping factor is but a very small factor in bass reproduction.  I am sure that many of you have read some of the various audio "rags".  Have you ever heard anyone say that Krell has "flabby" bass"?  You may actually read that some think that they are overdamped but take a little time to check out their damping factor specs. (it will surprise you).  After listening to many fine (and not so fine) amps I believe that damping factor is way overated as a specification.  I have owned some junk amps. with a high damping factor that had soft, muddy bass and some with a low damping factor that could shake the floor with no overhang or flab.  Ymmv.

BTW, I have another post asking opinions of Krell vs. Bryston so feel free to chime in!

Thanks for your time.

Earl

[bummrush]

 
although not a Bryston or Krell owner,but of a amp with low damping factor,75 i believe, i can attest to numbers just being more confusing then anything,my Counterpoint ,as compared to some dig. amps i had ,which everybody know have very high damping figure numbers,the Counterpoint if anything is much more detailed and i feel accurate as to presentation of sound,the dig amps just smacked you over the head with too much wham,at first its great but after listening it becomes unrealistic,what the Counterpoint does is play whats on the disc no more no less,so much of the music depends on the recording,not these goofy high numbers.