John Curl's Blowtorch preamplifier part II - Page 2894 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

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 5th November 2012, 11:22 PM   #28931
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Let me interject some experience here.
Horn throat distortion is REAL and measurable. It is ALSO predictable, and there are equations to predict it, (more or less).
When I first mentioned it, some time ago, I stated the 40 years ago, I measured a JBL horn driver with a 1'' throat, driven at 1KHz with 2W input, and I got 3% distortion. This was almost entirely, HORN THROAT DISTORTION!
Now how loud was that? REALLY LOUD! However, the horn was being driven from 1KHz and above with 2W-20W! So, 3% (second harmonic) distortion was rather high, but it got even worse. Now, if the GD had 50 of the horns in parallel and only put a 200W amp (total) on them, then it might have been OK, but the GD used only 4 identical horns, AND we could hear the problem.
Now, at home, there would be no problem. It is almost impossible to sit in front of a horn like this with even 2W input, without losing your hearing, ultimately. BUT with an auditorium with 500+ people, perhaps it is a bit too audible.
Esperado, mentioned working with 10KW and horns! What did he do to get it to sound OK? That was the original question.
OUR solution was to REPLACE the horns with a large bank of quality direct radiators, in the Wall of Sound. It worked.
  Reply With Quote
Old 5th November 2012, 11:25 PM   #28932
diyAudio Member
 
Join Date: Feb 2004
Location: Queensland Australia
Hi kgrlee, when you speak of "our papers" and extending Fryer's work (which I have some from HFNRR) are these publications in the public domain? If so where abouts pls?
Cheers, Jonathan (a bit further south)
__________________
"It was the Springtime of the year when aunt is calling to aunt like mastodons bellowing across primeval swamps." P.G. Wodehouse.
  Reply With Quote
Old 6th November 2012, 12:12 AM   #28933
fas42 is online now fas42  Australia
diyAudio Member
 
fas42's Avatar
 
Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 11
Of possible interest to some, after doing a quick search, is this: Red Shift: Doppler distortion in loudspeakers | Stereophile.com. It mentions some work done by Fryer ...

Frank
  Reply With Quote
Old 6th November 2012, 12:21 AM   #28934
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Doppler distortion was first described in detail by Klipsch in the JAES, back in the '60's or so. It is important, but not so important as to discount the direct radiator from contention as a first class speaker. [ Spoken by a former K-horn owner '-) ]
  Reply With Quote
Old 6th November 2012, 12:32 AM   #28935
diyAudio Member
 
Join Date: Apr 2005
Location: Sitting behind the 'puter screen, in Illinois, USA, planet earth
Hi

Fwiw, sound does not “heat” air with the exception of what ever energy is absorbed. At the same time, air behaves following gas law and so if you compress it momentarily, it’s pressure rises but so does it’s temperature as you have the same heat energy confined into a smaller space, an important detail.

So far as sound, as Dick Heyser said "it's what happens when you push on air", it is a modulation of pressure above and below ambient and so, for that brief instant a cluster of air molecules are in the pressure side of the sound wave, their temperature is slightly higher.
At the same time, when those molecules are in he rarefied side of the sound wave, they are cooler than ambient.

In the 80’s and 90’s I worked developing very high intensity acoustic transducers for acoustic levitation.
The idea then was for acoustically containing a sample within a high temperature furnace and then melting and solidifying materials at very high temperatures without a container or physical contact.
We flew several high temp container less processing experiments on STS-7, STS-51a and several sounding rocket flights.
Anyway, in the link, scroll down to the video.

Scientists levitate liquid in order to develop better pharmaceuticals

Acoustic levitation becomes possible when the intensity is about 150dB SPL for a Styrofoam ball and for a liquid like he is demonstrating, about 165dB SPL.
The transducers here (a type I developed / patented back then) produces a narrow beam of high intensity sound and here around 22KHz.

If you set one of those sources up horizontally and took a microphone happy at >165 dB, one sees the wave shape is a sine wave but as you move say 6 inches away it is changing, a foot away and it is a saw tooth shape, not a sine wave.
What is happening is the pressure side of the wave is traveling slightly faster than the rarified side and so is no longer 180 degrees away. The longer the distance it travels, the more it catches up to the negative wave front ahead of it For what we were doing back then, this was not a good thing because that wave shape with a sharp transition had much more hf energy and so one had acoustic pumping, a moving column of air moving away from the source (which could both cool and destabilize the sample).
For a high frequency compression driver, the internal sound pressure is high enough to reach this level of nonlinearity but……. The thumb rule throat distortion formulas are based on the how fast the horn is expanding and so the SPL falling (via the low frequency corner) compared to the high frequency corner (the shortest wavelength involved) and then the SPL (rate the wave front precession happens) it has to produce.
The assumption is that a horn with a lower frequency corner will have a slower rate of expansion and so the region where the pressure up high is more wavelengths long.

Funny thing too about those levitation sources, there is a larger configuration using 6 orthogonal sources that can produce about 175dB at the intersection. That IS enough intensity to light a cigarette with the acoustic friction of the air rushing back and forth through the tobacco at 22KHz.
What a cool / semi dangerous coffee table conversation starter, great for gift giving eh?
Best,
Tom Danley
__________________
Bring back mst3k and futurama
  Reply With Quote
Old 6th November 2012, 12:59 AM   #28936
diyAudio Member
 
Join Date: Nov 2011
Location: Cooktown, Oz
Quote:
Originally Posted by Jonathan Bright View Post
Hi kgrlee, when you speak of "our papers" and extending Fryer's work (which I have some from HFNRR) are these publications in the public domain? If so where abouts pls?
Peter's stuff is all in AES. AES E-Library If you have a clean copy of the HFN article, I'd appreciate a scan. There's more detail in internal Engineering Memos but I no longer have access to these and they may have gone to the great library in the sky.

I worked with him when he was at Rank HiFi (Wharfedale/LEAK).
  Reply With Quote
Old 6th November 2012, 01:22 AM   #28937
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Quote:
Originally Posted by Tom Danley View Post
Hi

Fwiw, sound does not “heat” air with the exception of what ever energy is absorbed. At the same time, air behaves following gas law and so if you compress it momentarily, it’s pressure rises but so does it’s temperature as you have the same heat energy confined into a smaller space, an important detail.

So far as sound, as Dick Heyser said "it's what happens when you push on air", it is a modulation of pressure above and below ambient and so, for that brief instant a cluster of air molecules are in the pressure side of the sound wave, their temperature is slightly higher.
At the same time, when those molecules are in he rarefied side of the sound wave, they are cooler than ambient.

In the 80’s and 90’s I worked developing very high intensity acoustic transducers for acoustic levitation.
The idea then was for acoustically containing a sample within a high temperature furnace and then melting and solidifying materials at very high temperatures without a container or physical contact.
We flew several high temp container less processing experiments on STS-7, STS-51a and several sounding rocket flights.
Anyway, in the link, scroll down to the video.

Scientists levitate liquid in order to develop better pharmaceuticals

Acoustic levitation becomes possible when the intensity is about 150dB SPL for a Styrofoam ball and for a liquid like he is demonstrating, about 165dB SPL.
The transducers here (a type I developed / patented back then) produces a narrow beam of high intensity sound and here around 22KHz.

If you set one of those sources up horizontally and took a microphone happy at >165 dB, one sees the wave shape is a sine wave but as you move say 6 inches away it is changing, a foot away and it is a saw tooth shape, not a sine wave.
What is happening is the pressure side of the wave is traveling slightly faster than the rarified side and so is no longer 180 degrees away. The longer the distance it travels, the more it catches up to the negative wave front ahead of it For what we were doing back then, this was not a good thing because that wave shape with a sharp transition had much more hf energy and so one had acoustic pumping, a moving column of air moving away from the source (which could both cool and destabilize the sample).
For a high frequency compression driver, the internal sound pressure is high enough to reach this level of nonlinearity but……. The thumb rule throat distortion formulas are based on the how fast the horn is expanding and so the SPL falling (via the low frequency corner) compared to the high frequency corner (the shortest wavelength involved) and then the SPL (rate the wave front precession happens) it has to produce.
The assumption is that a horn with a lower frequency corner will have a slower rate of expansion and so the region where the pressure up high is more wavelengths long.

Funny thing too about those levitation sources, there is a larger configuration using 6 orthogonal sources that can produce about 175dB at the intersection. That IS enough intensity to light a cigarette with the acoustic friction of the air rushing back and forth through the tobacco at 22KHz.
What a cool / semi dangerous coffee table conversation starter, great for gift giving eh?
Best,
Tom Danley
Thanks very much for that fascinating contribution Tom!

I wonder if there would be any benefit, in the levitation app, to predistortion of the electrical signal, to compensate at a specific distance and have, locally, more-sinusoidal pressures?
  Reply With Quote
Old 6th November 2012, 01:26 AM   #28938
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
It is almost impossible to 'pre-distort' properly. There was the same problem with pre-distorting analog tape recorders to remove 3'rd harmonic distortion.
  Reply With Quote
Old 6th November 2012, 01:35 AM   #28939
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Default Where's the Bass?

Quote:
Originally Posted by jneutron View Post
If I remember correctly, a 99 dB 1 watt 1 meter is about 5% efficient.

500 watts.

jn
That's why I have 4-15 high effec. bass drivers and adding 2-18" subs with high power amps on all 6. To attempt some reasonable simulance of realism... realism with low distortion and no compression on my end of things. Two-way with 6.5" "bass" driver?? I don't think so. Nice for background music. -RNM
  Reply With Quote
Old 6th November 2012, 01:39 AM   #28940
diyAudio Member
 
scott wurcer's Avatar
 
Join Date: Jan 2004
Location: cambridge ma
Quote:
Originally Posted by john curl View Post
Doppler distortion was first described in detail by Klipsch in the JAES, back in the '60's or so. It is important, but not so important as to discount the direct radiator from contention as a first class speaker. [ Spoken by a former K-horn owner '-) ]
I thought Christian Doppler described it in 1842.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
  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



New To Site? Need Help?

All times are GMT. The time now is 11:19 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