A Audio and hi-fi forum. AudioBanter

Go Back   Home » AudioBanter forum » rec.audio » Tech
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Damping Factor in drivers



 
 
Thread Tools Display Modes
  #1  
Old July 2nd 18, 09:19 AM posted to rec.audio.tech
gregz
external usenet poster
 
Posts: 127
Default Damping Factor in drivers

I understand effects of electrical damping of woofers. I'm wondering how It
may affect midranges and tweeters. Is it the same, or does it dimish at
higher frequencies. Remove any crossover components for direct feed to amp.
Tone bursts should Show any difference in DF. Without testing, I'm
guessing.

Greg
Ads
  #2  
Old July 3rd 18, 03:27 PM posted to rec.audio.tech
[email protected]
external usenet poster
 
Posts: 307
Default Damping Factor in drivers

On Monday, July 2, 2018 at 1:41:13 PM UTC-4, G wrote:
> I understand effects of electrical damping of woofers. I'm wondering how It
> may affect midranges and tweeters. Is it the same, or does it dimish at
> higher frequencies. Remove any crossover components for direct feed to amp.
> Tone bursts should Show any difference in DF. Without testing, I'm
> guessing.


To cut to the chase: forget about "damping factor." It's essentially
a made-up "spec" that indicates very little about the performance of
loudspeaker drivers. Really. The important number, if you're worried about
how well a driver is controlled at its resonance, is it's total Q
factor: in the case of the driver itself, it's the Qts of the driver.

The Q of any resonant system is a measure, essentially, of the
ratio of the amount of energy stored in the resonance to the amount
of energy dissipated. In the case of a driver, you have essentially
three ways by which that energy is dissipated, or lost or, if you prefer,
how it is removed from the system. These a

1. Electrical losses, which, for most drivers, is the largest
loss mechanism (and is usually specific Qes),

2. Mechanical losses, which, for most drivers, is secondary
to the electrical losses (designated as Qms),

3. Acoustical losses, i.e., the sound that is actually radiated
into the room which, for almost all drivers, is an insignificant
loss mechanism (this is why speakers are so inefficient).

Now, #1 might seem contradictory to me declaration that damping
factor is essentially useless, since we are (I assume) talking
about electrical damping, but it becomes clearer once you realize
the fact that it's the total resistance in the circuit that's
responsible for the electrical Q. That not only includes the output
resistance of the amplifier (which is where the "damping factor"
spec comes from), it not only includes the electrical resistance
in the crossover (not impedance, not inductance, but resistance),
it also includes the DC resistance of the voice coil.

The problem is, far and away, the single largest resistance in that
collection is the DC resistance of the voice coil. That resistance
dominates all others, and attempting to reduce the other resistances
(crossover, speaker wire, amplifier) won't make a hill of beans
difference in the damping of the system.

Le's take a typical 8-ohm woofer, with an equally typical DC
resistance of about 6.5 ohms. Let's assume the mechanical Q
of the driver is 4, the electrical Q is 0.85, and the resulting
total Qts is about 0.701 (Qts = Qes*Qms/(Qes+Qts). How is this
going to perform with an amplifier whose damping fact is, say,
1000 vs one whose damping factor is 50. One might be inclined
to say that there will be a factor of 20 difference in the
damping of in each case (1000/50=20), but it turns out not to
be so.

Whatever with a damping factor of 1000, our "highly-damped"
amplifier has an output resistance of 0.008 ohms, while our
"not-so-well-damped" amplifier has an output resistance of `0.16
ohms.

The amplifier output resistance will increase the electrical
Qes: in the case of the first amplifier, it will increase it from
0.85 to 0.851 (Qes' = Qes * (Re+Rg)/Re. In the second case, it
will increase it from 0.85 to 0.87. NOt much.

But it's the TOTAL Qts that we're interested in. In the first case,
it will change from 0.701 to 0.702. In the second case, it will change
from 0.701 to 0.714. In both cases, the actual damping of the system
changes by less than 2%. This is less than the typical variation in
these kinds of parameters one finds from one sample of a driver
to another.

The situation with midranges and, especially, tweeters is even
more the case where these external resistances have little
effect, because in these cases, the total Qts is more heavily
dominated by the mechanical losses, and thus changes in the
electrical Q have even less of an effect. Further, in many systems,
the principle resonance is designed outside of the operating
bandwidth of the driver by the crossover, so it has even LESS
of an effect.

> Tone bursts should Show any difference in DF.


Tone bursts are very likely to tell you nothing useful at all.
They're not a terribly useful test in and off themselves and,
given the very small changes you're likely to encounter in
the changes you're proposing, a tone burst is not going to
reveal anything. Further, tone bursts are very hard to measure.
Bump your microphone a little bit, change its position, and
you'll measure a different tone burst


  #3  
Old July 5th 18, 07:41 AM posted to rec.audio.tech
gregz
external usenet poster
 
Posts: 127
Default Damping Factor in drivers

> wrote:
> On Monday, July 2, 2018 at 1:41:13 PM UTC-4, G wrote:
>> I understand effects of electrical damping of woofers. I'm wondering how It
>> may affect midranges and tweeters. Is it the same, or does it dimish at
>> higher frequencies. Remove any crossover components for direct feed to amp.
>> Tone bursts should Show any difference in DF. Without testing, I'm
>> guessing.

>
> To cut to the chase: forget about "damping factor." It's essentially
> a made-up "spec" that indicates very little about the performance of
> loudspeaker drivers. Really. The important number, if you're worried about
> how well a driver is controlled at its resonance, is it's total Q
> factor: in the case of the driver itself, it's the Qts of the driver.
>
> The Q of any resonant system is a measure, essentially, of the
> ratio of the amount of energy stored in the resonance to the amount
> of energy dissipated. In the case of a driver, you have essentially
> three ways by which that energy is dissipated, or lost or, if you prefer,
> how it is removed from the system. These a
>
> 1. Electrical losses, which, for most drivers, is the largest
> loss mechanism (and is usually specific Qes),
>
> 2. Mechanical losses, which, for most drivers, is secondary
> to the electrical losses (designated as Qms),
>
> 3. Acoustical losses, i.e., the sound that is actually radiated
> into the room which, for almost all drivers, is an insignificant
> loss mechanism (this is why speakers are so inefficient).
>
> Now, #1 might seem contradictory to me declaration that damping
> factor is essentially useless, since we are (I assume) talking
> about electrical damping, but it becomes clearer once you realize
> the fact that it's the total resistance in the circuit that's
> responsible for the electrical Q. That not only includes the output
> resistance of the amplifier (which is where the "damping factor"
> spec comes from), it not only includes the electrical resistance
> in the crossover (not impedance, not inductance, but resistance),
> it also includes the DC resistance of the voice coil.
>
> The problem is, far and away, the single largest resistance in that
> collection is the DC resistance of the voice coil. That resistance
> dominates all others, and attempting to reduce the other resistances
> (crossover, speaker wire, amplifier) won't make a hill of beans
> difference in the damping of the system.
>
> Le's take a typical 8-ohm woofer, with an equally typical DC
> resistance of about 6.5 ohms. Let's assume the mechanical Q
> of the driver is 4, the electrical Q is 0.85, and the resulting
> total Qts is about 0.701 (Qts = Qes*Qms/(Qes+Qts). How is this
> going to perform with an amplifier whose damping fact is, say,
> 1000 vs one whose damping factor is 50. One might be inclined
> to say that there will be a factor of 20 difference in the
> damping of in each case (1000/50=20), but it turns out not to
> be so.
>
> Whatever with a damping factor of 1000, our "highly-damped"
> amplifier has an output resistance of 0.008 ohms, while our
> "not-so-well-damped" amplifier has an output resistance of `0.16
> ohms.
>
> The amplifier output resistance will increase the electrical
> Qes: in the case of the first amplifier, it will increase it from
> 0.85 to 0.851 (Qes' = Qes * (Re+Rg)/Re. In the second case, it
> will increase it from 0.85 to 0.87. NOt much.
>
> But it's the TOTAL Qts that we're interested in. In the first case,
> it will change from 0.701 to 0.702. In the second case, it will change
> from 0.701 to 0.714. In both cases, the actual damping of the system
> changes by less than 2%. This is less than the typical variation in
> these kinds of parameters one finds from one sample of a driver
> to another.
>
> The situation with midranges and, especially, tweeters is even
> more the case where these external resistances have little
> effect, because in these cases, the total Qts is more heavily
> dominated by the mechanical losses, and thus changes in the
> electrical Q have even less of an effect. Further, in many systems,
> the principle resonance is designed outside of the operating
> bandwidth of the driver by the crossover, so it has even LESS
> of an effect.
>
>> Tone bursts should Show any difference in DF.

>
> Tone bursts are very likely to tell you nothing useful at all.
> They're not a terribly useful test in and off themselves and,
> given the very small changes you're likely to encounter in
> the changes you're proposing, a tone burst is not going to
> reveal anything. Further, tone bursts are very hard to measure.
> Bump your microphone a little bit, change its position, and
> you'll measure a different tone burst


That tells me a lot about what I asked. Thanks.

Greg
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
The damping factor and the sound of real music Andre Jute Vacuum Tubes 53 December 31st 07 04:38 PM
The damping factor and the sound of real music Andre Jute Pro Audio 8 December 31st 07 04:38 PM
The damping factor and the sound of real music Andre Jute Tech 7 December 31st 07 04:38 PM
What is Q-factor? Peter Car Audio 10 December 16th 03 06:53 AM
Damping factor - tubes versus solid state? Scott Gardner Vacuum Tubes 8 December 5th 03 03:25 PM


All times are GMT +1. The time now is 11:31 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2004-2018 AudioBanter.
The comments are property of their posters.