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... how important is Damping factor in determining what amp to buy

Hi there...

Just how important is damping factor in determining what amp to buy?

In literature and specs - I find this is an often left-out bit of info...


justvintagestuff
atmasphere's avatar
atmasphere
11,793 posts
 
@mapman, if I recall, your speakers are 4 ohms. Damping factor as a spec is usually stated with respect to 8 ohms. So in reality your speakers seem to need an amp with a damping factor of about 25, once you correct for the impedance. As I stated elsewhere, no speaker needs a damping factor of more than about 20:1 or so; your speakers seem to be within that ballpark.

kijanki's avatar
kijanki
4,428 posts
 
Vibration of the speaker membrane, without signal, causes back EMF producing current that flows in opposite direction working against membrane motion, hence damping vibration. This current (damping effect) depends on the total resistance in the circuit including amp’s output, wires resistance, woofer’s choke resistance and speaker’s impedance (source impedance) itself, that is mostly resistive. All this will limit maximum possible "DF" to about 1. As long a amplifier doesn’t add to this limitation, there should be no difference in sound. AMP with DF =10 will affect overall damping only by 10%. Very high DF (my amp has 4000), come either from the output configuration or negative feedback used to reduce distortions, widen the bandwidth etc. Even shallow 20dB negative feedback will reduce output impedance ten times.

Damping Factor plays one very important role - it can be used to impress customers.

As for NGF - it is a wonderful tool when it is used wisely. It improves pretty much everything (bandwidth, distortions, output impedance etc). It might produce TIM distortions (higher odd harmonics, overshoot in time domain) for faster changing signals, because of increased amps gain caused by late summing of delayed output signal (phase shift). Reducing bandwidth at the input, perhaps to one that amp had without feedback, should prevent TIM. That would require designing a stable wide bandwidth amp with low distortions to start with. The main problem is that designers use cheap parts and poor circuits trying to fix it with deep feedback. For instance, very popular output transitors 2N3055 have very nonlinear h21e (Beta) - a current gain vs current. There are much better choices but they cost more money (2N3055 cost less than $1). NGF is pretty much free.
mapman's avatar
mapman
22,189 posts
 

Atmasphere OHM generally indicates 6 OHM nominal impedance for their Walsh line speakers.

I have seen measurements and impedance curves on some models that show fairly high impedance >8 ohms over extended ranges with the greatest dip down to almost 4 ohm in the bass region possibly associated with the port.

Users over the years have indicated best results with higher damping amp ratings and I would agree. How high is needed is debatable but I always find the higher the better even if Justas an insurance policy and nothing concrete theoretically to support the need.

If I had to rate them based on what I know and what others report I would say they are moderately tube amp friendly, probably more so than many speakers in their class.


The Dynaudios most likely have lower impedances and are also generally known to not be very tube amp friendly and I would agree. In fact even with SS amps I find results can vary widely with Dynaudios whereas its very hard to find any good quality amp that sounds bad with the OHMs.

Remember also that the OHMs operate totally different than most dynamic speakers ie based on Lincoln Walsh’s transmission line principles. I suspect this may make them very unique in regards to impedance considerations but do not know enough about it technically to say for sure.


I have two OHM models, larger ones with 12" main drivers and smaller with 8".    The higher damping in the amps seem to make more difference with the larger models to me than the smaller although I'd say there are audible differences in general with both..

almarg's avatar
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almarg
9,670 posts
 
Hi Kijanki,

I pretty much agree with your post, as far as it goes. But your comments about damping factor just address ... damping. Keep in mind, as has been said, that damping factor is inversely proportional to output impedance, and once output impedance gets above negligible levels (as it will in the case of most tube amps, and at least a few solid state amps), it can certainly matter, as a result of impedance interactions between the amp and the speaker.

Best regards,
-- Al
justvintagestuff OP
104 posts
 
OH MAN AGAIN...

Interesting to hear you Gurus going back and forth...

Need to reread this several times , list those for and against an effect, throw out the high and the low - and then consult the Russian Judge!

And in a some-what related question: I am presently using a Phillips High Fidelity Labratories Pre-Amplifier(1980?) - would the damping factor be affected if I switched to a Line-Level triode preamp (like the Wolze I have)? Does/can the preamp affect the damping factor of a amplifier?
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