Damping factor - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th May 2004, 11:12 AM   #11
moamps is offline moamps  Croatia
diyAudio Member
 
Join Date: Oct 2002
Location: Croatia
Quote:
Originally posted by Joe Rasmussen
.... damping factor really is a myth. It's an arbitrary mathematical curiosity that has no real world import........ Low Z is important to keep bass alignments on track....
Hi,
if DF=K/Z, and DF is a myth, what is Z? (k/myth)?

Regards
  Reply With Quote
Old 4th May 2004, 11:18 AM   #12
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Send a message via MSN to Joe Rasmussen
Quote:
Originally posted by roddyama

Just for the record, Small actually makes the assumption that the output Z of the amp is small compared to the Z of the speaker. His analysis does not extend to the case where the amp has a large output Z and the DF is "small".
... the DF is "small".

Is that an unintentional pun?

Joe R.
__________________
The "Elsinore Project" DIY Speaker System
Custom Analogue Audio - we also support and promote non-profit DIY
  Reply With Quote
Old 4th May 2004, 11:23 AM   #13
diyAudio Moderator Emeritus
 
roddyama's Avatar
 
Join Date: Jan 2002
Location: Michigan
Quote:
Originally posted by Joe Rasmussen


... the DF is "small".

Is that an unintentional pun?

Joe R.
Eh... Sorry Joe, all.
__________________
Rodd Yamashita
  Reply With Quote
Old 4th May 2004, 01:00 PM   #14
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Send a message via MSN to Joe Rasmussen
Quote:
Originally posted by roddyama

Eh... Sorry Joe, all.
Speaking of Small. I remember many years ago having a conversation with him, I think he was at Sydney University in those days. I was disagreeing with him re his idea of of adding a series resistor to modify Qe (and hence Qts) and tuning its value to vary Qts as well as increasing Vb of a sealed box.

I was of the opinion that this would ruin the damping factor. Now I have a different opnion altogether.

But it does show that Small realised that adding resistance does no more than varying the Re of the driver and by using a larger Vb, one could get a targeted Qc and lower Fc at the same time. So the use of a larger box, corrected Qc (higher due to resistor), lower Fc, you could get much more extended bass. The sacrifice is lower sensitivity/efficiency. But this is then an alternative to mass loading of the cone, as used by manufacturers like Dunleavy.

But again, this example shows that DF is a myth and Small had already discarded it in those days.

Joe R.
__________________
The "Elsinore Project" DIY Speaker System
Custom Analogue Audio - we also support and promote non-profit DIY
  Reply With Quote
Old 4th May 2004, 01:11 PM   #15
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
DF is not a myth, it is simply one way to express an amp's output resistance. Nothing more, nothing less.
The expression is somewhat misleading and furthermore the value shown is just valid under specific conditions (e.g. a static signal into a real load).

Regards

Charles
  Reply With Quote
Old 4th May 2004, 01:31 PM   #16
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Send a message via MSN to Joe Rasmussen
Quote:
Originally posted by phase_accurate
DF is not a myth, it is simply one way to express an amp's output resistance. Nothing more, nothing less.
The expression is somewhat misleading and furthermore the value shown is just valid under specific conditions (e.g. a static signal into a real load).

Charles
I would say that the amp's output Z is not a myth, it's real alright. And it is irrespective of the load, whereas 'damping factor' is the load divided by the output Z. Why should that supposedly be of any importance?

And what significance is it when the output Z and the Re of the driver becomes one and the same thing? The fact is the Re is many times that of output Z, so Z is not to be seen in isolation. Add to that the cable's resistance, the choke (as used in passive LPF), all are in series, all are really added to Re.

So damping factor is a myth.

Just to prove it, try this example:

We have an 8 Ohm bass driver. Let's assume it has Re = 6 Ohm. We now short the terminals together, to simulate an amp having zero output Z. Do we now have infinite damping factor? No we don't. Here is why:

If we were to push the cone in and out, we would generate current into a dead short. Here we are simulating back EMF which should be shortened out by the zero output Z, hence creating damping. But this doesn't actually happen, since the current has to travel through 6 Ohm of resistance.

Joe R.
__________________
The "Elsinore Project" DIY Speaker System
Custom Analogue Audio - we also support and promote non-profit DIY
  Reply With Quote
Old 4th May 2004, 01:40 PM   #17
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
Quote:
So damping factor is a myth.
No it isn't ! Only what some people (e.g. scanting salespeople) make out of it is a myth. It is a simple measurement value like THD, output power etc..... It is howerver questionable if it should be mentioned at all.

A DF value of 10,000 does for sure look much better on paper than one of 200 even though the increase in damping is marginal (less than 0.5 % for a given Re and Qtc !).

DF = Rload / Ri

Regards

Charles
  Reply With Quote
Old 4th May 2004, 01:43 PM   #18
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Send a message via MSN to Joe Rasmussen
Quote:
Originally posted by phase_accurate


No it isn't ! Only what some people (e.g. scanting salespeople) make out of it is a myth. It is a simple measurement value like THD, output power etc..... It is howerver questionable if it should be mentioned at all.

A DF value of 10,000 does for sure look much better on paper than one of 200 even though the increase in damping is marginal (less than 0.5 % for a given Re and Qtc !).

DF = Rload / Ri

Regards

Charles
Hi Charles

I think you might have missed my last edit. Can you explain it?

Joe R.
__________________
The "Elsinore Project" DIY Speaker System
Custom Analogue Audio - we also support and promote non-profit DIY
  Reply With Quote
Old 4th May 2004, 02:39 PM   #19
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
I haven't missed your statements. But you seem to have missed that my opinion regarding DAMPING is basically the same as yours.

Damping FACTOR isn't defined as damping of the driver, it is the value given by Rload/Ri of an amp (It is DEFINED like that, this has nothing to do with personal taste or opinion, it is just a definition).
So an amp representing zero Ri would in fact give an infinite DF. It doesn't mean in turn that the damping of the driver as such is infinite. It is mainly magazine writers and salespeople that claim things like that.

One could easily be misled by the fact that very often amps with high DF have indeed very good control in the LF range. Since a high DF is not that easily achievable, the better control might as well be caused by the generally higher effort put into design and construction of some of these amps. One parameter might be better ability to deliver large currents into rective loads or a more signal - independant behaviour of Ri (who said that it is the same for all load conditions ?).

Regards

Charles
  Reply With Quote
Old 5th May 2004, 08:04 AM   #20
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Send a message via MSN to Joe Rasmussen
Quote:
Originally posted by phase_accurate
I haven't missed your statements. But you seem to have missed that my opinion regarding DAMPING is basically the same as yours.

Hi Charles

OK then, if our opnions coincide, then if you don't agree that DP is a myth, then perhaps we can agree that any claimed benefits are at least overstated.

Would you also agree with Lynn Olson's 'hard amp' concept.

It goes like this:

The output impedance, instead of approaching zero, is intentionally set to the impedance of the driver, - a damping factor of one or unity coupling. This requires realigning the bass enclosure... The impedance seen by the speaker driver is constant and equivalent to a fixed resistor. This is the essence of the 'hard amp' concept: the amplifier mimics a passive component under all operating conditions... This is very different from conventional [high feedback] transistor or PP pentode amplifiers, which enter undefined regions when the amp clips and feedback loses its grip on the amplifier... a 'hard amp' avoids gain transitions and treats back-EMF like a fixed low value resistor.

The output Z does not need to be quite that of the speaker's, but a high one of 2-4 Ohm is not a huge problem. Incidentally, when designing vented boxes I aim for one with Bessel like characteristics, as they are much more immune to high source Z than, say, 4th order Butterworth. Also low Q Sealed box with Fb below 50Hz, likewise copes quite well.

May I also refer to the point Richard Small (of Thiele-Small fame) made to me, that adding series resistance might actually improve bass. Are we in agreement here?

Joe R.
__________________
The "Elsinore Project" DIY Speaker System
Custom Analogue Audio - we also support and promote non-profit DIY
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Damping factor in DIY amp jaya000 Solid State 25 25th September 2008 11:27 AM
What is SI T-Amp DF (damping factor)? skrstic Class D 1 23rd April 2008 09:49 PM
Aleph4 damping factor alanyeoh Pass Labs 1 17th August 2004 09:11 PM
Damping factor thylantyr Solid State 9 14th March 2003 06:37 AM
Damping factor..????? emarald Solid State 15 30th January 2003 02:41 PM


New To Site? Need Help?

All times are GMT. The time now is 11:46 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2