Thiele-Small R_ms (mechanical losses) vs. "precise" sound?

capslock · 4th September 2002, 08:51 AM

Bernd Timmermanns (formerly editor of Klang und Ton, now of HobbyHifi), has maintained for years that there is a good correlation between the R_ms value in the T-S parameters and the sound of a driver. A woofer should have a low R_ms value to obtain a precise, clearly definded bass and a subjectively good reproduction of impulses. He stated explicitly that this is also true for all kinds of drivers, i.e. also mid range and tweeters. I have seen this statement mainly in connection with vented enclosures, but I believe it is supposed to be valid also for sealed and TML enclosures.

A driver has low R_ms if the voice coil carrier is non-conductive (i.e. Kapton rather than aluminum) and if the magnet has venting holes so the air can escape more easily (+ narrow cage ribs + low loss centering and sealing elements + ...).

Oh yes, and when comparing drivers, one should actually divide R_ms by the effective area of the cone.

Bernd Timmermanns has stood by his statement that a clear correlation is observable many times but he admits that there is no satisfactory theoretical explanation. He offered a tentative explanation that the air currents will have a strongly nonlinear dependence on the cone movement and exhibit hysteresis (i.e. an eddy will need a certain time to subside).

Has anybody made similar observations?

Is there any other explanation?

I think the nonlinear air current explanation could hold some truth.
However, if the voice coil carrier is conductive, eddy currents will have a large contribution to R_ms. On the other hand, eddy current losses will be a linear function of the speed of the voice coil except for very high movement amplitudes. So for this part of R_ms there is no nonlinear loss mechanism. And I can imagine that this highly linear damping might even be beneficial in some cases.

So one should try to separate R_ms_air=R_ms_nonlinear and R_ms_carrier=R_ms_linear and see if there is a general correlation between subjective impression and R_ms_total or rather R_ms_air.

The separation can be carried out be determining R_ms_total at two or more different drive amplitudes.

Eric

phase_accurate · 4th September 2002, 12:20 PM

Hi Eric

I have also read Mr. Timmermann's statement but I don't know any theory behind it either.

But the following statement is from Per Skaaning of Audio Technology Denmark, who also made some experiences in sonic differences between coil former materials (by "standard" he means aluminium hexacoil):

"We can deliver drivers with Kapton voice coil former. ........ If you choose Kapton for voice coil bobbin, you will not experience the "dynamic sound" but a more full bodied bass reproduction, even at the lowest levels."

But maybe this is due to the fact that it would otherwise be the SAME driver and the QTS of the aluminium voice-coil driver would be lower due to lower QMS.

Regards

Charles

capslock · 5th September 2002, 12:27 PM

If it were exactly the same driver except for the coil former, this is probably the way to conduct the experiment. One build two identical boxes, one with the aluminum and one with the Kapton former, and adjust the total Q electrically.

Problem: lots of work and money involved just to gain some knowledge. Would be interesting as a thesis for a BSEE degree though....

Eric

capslock · 16th September 2002, 02:21 AM

Quote:

Originally posted by phase_accurate
... sonic differences between coil former materials (by "standard" he means aluminium hexacoil):

Charles,

does hexacoil refer to the voice coil former/bobbin or to the cross-section of the wire?

Regards,

Eric

planet10 · 16th September 2002, 02:23 AM

Quote:

Originally posted by capslock
does hexacoil refer to the voice coil former/bobbin or to the cross-section of the wire?

the wire IB.

dave

capslock · 16th September 2002, 02:54 AM

What does IB stand for?

Eric

planet10 · 16th September 2002, 06:11 AM

IB = I believe

dave

phase_accurate · 16th September 2002, 09:32 AM

Hi Eric

About the standard voice-coil of Audiotechnology drivers:

It is consisting of an aluminium former with aluminium wire of hexagonal cross-section.

Non-standard (on request) would be a Kapton former with aluminium wire like above.

Sorry for being unclear.

Regards

Charles

4th September 2002, 08:51 AM	#1
capslock diyAudio Member Join Date: Feb 2002 Location: Germany	Thiele-Small R_ms (mechanical losses) vs. "precise" sound? Bernd Timmermanns (formerly editor of Klang und Ton, now of HobbyHifi), has maintained for years that there is a good correlation between the R_ms value in the T-S parameters and the sound of a driver. A woofer should have a low R_ms value to obtain a precise, clearly definded bass and a subjectively good reproduction of impulses. He stated explicitly that this is also true for all kinds of drivers, i.e. also mid range and tweeters. I have seen this statement mainly in connection with vented enclosures, but I believe it is supposed to be valid also for sealed and TML enclosures. A driver has low R_ms if the voice coil carrier is non-conductive (i.e. Kapton rather than aluminum) and if the magnet has venting holes so the air can escape more easily (+ narrow cage ribs + low loss centering and sealing elements + ...). Oh yes, and when comparing drivers, one should actually divide R_ms by the effective area of the cone. Bernd Timmermanns has stood by his statement that a clear correlation is observable many times but he admits that there is no satisfactory theoretical explanation. He offered a tentative explanation that the air currents will have a strongly nonlinear dependence on the cone movement and exhibit hysteresis (i.e. an eddy will need a certain time to subside). Has anybody made similar observations? Is there any other explanation? I think the nonlinear air current explanation could hold some truth. However, if the voice coil carrier is conductive, eddy currents will have a large contribution to R_ms. On the other hand, eddy current losses will be a linear function of the speed of the voice coil except for very high movement amplitudes. So for this part of R_ms there is no nonlinear loss mechanism. And I can imagine that this highly linear damping might even be beneficial in some cases. So one should try to separate R_ms_air=R_ms_nonlinear and R_ms_carrier=R_ms_linear and see if there is a general correlation between subjective impression and R_ms_total or rather R_ms_air. The separation can be carried out be determining R_ms_total at two or more different drive amplitudes. Eric

16th September 2002, 06:11 AM	#7
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 5	IB = I believe dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Need your opinion, how small gain can I use with LM3886 (how close to "flat amp")?	danielwritesbac	Chip Amps	20	30th November 2008 12:27 AM
looking for a small 2" or 3" driver with poor bass response	space-cake	Full Range	3	27th December 2007 01:16 AM
8" Subwoofer Enclosure Part 2 (with thiele-small now)	hernanstafe	Subwoofers	10	7th February 2007 02:45 AM
suspending a small tweeter in front of woofer for "coaxial" effect?	bikehorn	Multi-Way	3	2nd January 2006 02:04 PM
diy modification on drivers to lower mechanical losses	capslock	Multi-Way	28	16th October 2002 04:38 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

4th September 2002, 12:20 PM	#2
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	Hi Eric I have also read Mr. Timmermann's statement but I don't know any theory behind it either. But the following statement is from Per Skaaning of Audio Technology Denmark, who also made some experiences in sonic differences between coil former materials (by "standard" he means aluminium hexacoil): "We can deliver drivers with Kapton voice coil former. ........ If you choose Kapton for voice coil bobbin, you will not experience the "dynamic sound" but a more full bodied bass reproduction, even at the lowest levels." But maybe this is due to the fact that it would otherwise be the SAME driver and the QTS of the aluminium voice-coil driver would be lower due to lower QMS. Regards Charles

5th September 2002, 12:27 PM	#3
capslock diyAudio Member Join Date: Feb 2002 Location: Germany	If it were exactly the same driver except for the coil former, this is probably the way to conduct the experiment. One build two identical boxes, one with the aluminum and one with the Kapton former, and adjust the total Q electrically. Problem: lots of work and money involved just to gain some knowledge. Would be interesting as a thesis for a BSEE degree though.... Eric

16th September 2002, 02:54 AM	#6
capslock diyAudio Member Join Date: Feb 2002 Location: Germany	What does IB stand for? Eric

16th September 2002, 09:32 AM	#8
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	Hi Eric About the standard voice-coil of Audiotechnology drivers: It is consisting of an aluminium former with aluminium wire of hexagonal cross-section. Non-standard (on request) would be a Kapton former with aluminium wire like above. Sorry for being unclear. Regards Charles