John Curl's Blowtorch preamplifier part II - Page 2413

gpapag · 28th June 2012, 10:35 AM

Quote:

Originally Posted by Tom Danley

…if you place the drivers less than a quarter wavelength apart where they interact they add coherently and do that within a large horn, you get a much more even /constant spectrum vs position and radiate a lot less energy to the sides, rear and up and down than the arrays do (good for inteligibility in a room).

If one does this properly, one has the radiation of a single wide band driver on a large horn, some can even reproduce a square wave over a broad band. Very much unlike the “arrays” which radiate an interference pattern, when the wind also has very little effect on a real point source and they sound the same nearly everywhere in the pattern.

Best,
Tom Danley

Well, as very few professional implementations escape the diy torture path, I would like to ask Mr. Danley:
Is there a minimum distance/space required for your designs to work as intended?
Our stadium is a living room (for most people here)

George

simon7000 · 28th June 2012, 02:03 PM

Quote:

Originally Posted by gpapag

Well, as very few professional implementations escape the diy torture path, I would like to ask Mr. Danley:
Is there a minimum distance/space required for your designs to work as intended?
Our stadium is a living room (for most people here)

George

George,

The idea is that there is a point of radiation from any driver that folks want to treat as an acoustic center. The idea is that this is the origin of the wavefront and by proper alignment the energy from multiple source will combine coherently.

Now for a piston such as a normal paper cone loudspeaker many folks consider the voice coil to the acoustic center. It of course is not! As the motion propagates out through the cone the speed of propagation is faster through the cone than it is through the air. So the air from the dust cap starts moving forward and by the time that motion reaches the rim it is already behind the air moved by the edge of the cone. So for practical purposes the acoustic point of origin is the Centroid of the cone/dust cap combination.

Now as there still is a spread in the arrival time from all surfaces of the piston (cone) to any given angle there will be areas of partial phase reinforcement and cancellation. The simple test for finding an acoustic center is to take two drivers and place them side by side. When the path length difference to a measuring position is 1/2 wavelength there will be a null in the level. the null will not go to zero as mentioned because the piston is not a point source. Of course the wavelength will vary with frequency. What is interesting is that the acoustic center also moves with frequency!

But with a modern measurement setup it is possible to map the acoustic center.

Now in a horn loudspeaker the center is not at the voice coil or diaphragm. It is at a point on the horn walls.

Now there are some neat tricks to getting drivers to align. There are two great methods I know of. One is patented, the other a trade secret. Now you would think once the trade secret version is sold others would figure it out. I did see a copy of it from a major pro manufacturer, but they got it all wrong! They thought they understood what the pieces did, but I am not going to tell them what they missed.

The other method is to design higher powered drivers. There is one manufacturer who is best at this. They also understand a bit more about horn behavior than most.

ES

john curl · 28th June 2012, 10:09 PM

I would like to talk about audio education, research, and development, especially as it involves the AES (today) compared to the AES of 25-60 years ago.
First, the AES. When the AES was started, it would have seemed to be a 'redundant' organization for engineers, because the IRE (later IEEE) had an Audio and Electroacoustics' section, and there was also 'The Acoustical Society of America', to present papers at. Why then did some founders of the audio industry, actually mainly designers, and NOT promoters, start a new society for Audio Engineers?
It is my personal opinion that they needed a place to show their continuing research in audio, and they were probably squeezed out by refereed journals of the other organizations, so much that they were frustrated. Usually there was a sort of difference in intent that existed between the existing journals, (usually scholarly papers) and the AES, as to what an actual design engineer was allowed to present, (normally just about anything at a conference), with selected papers chosen for the journal. This gave a chance for NEW IDEAS, even half-baked or impractical ones, to be seen by other audio engineers and we could learn from each other. That is NOT the situation today. (more later)

gpapag · 28th June 2012, 10:34 PM

Quote:

Originally Posted by simon7000

George,

The idea is that there is a point of radiation from any driver that folks want to treat as an acoustic center. The idea is that this is the origin of the wavefront and by proper alignment the energy from multiple source will combine coherently.

Now for a piston such as a normal paper cone loudspeaker many folks consider the voice coil to the acoustic center. It of course is not! …….
ES

Thank you Mr. Simon for sharing.
That the acoustic center is a moving goal post is something that always gave me worries. But this is a trouble affecting all –save for a single-speaker system designs, not only horns. Or no?

Quote:

Originally Posted by simon7000

The other method is to design higher powered drivers
ES

This, I don’t get it.

Quote:

Originally Posted by gpapag

Well, as very few professional implementations escape the diy torture path, I would like to ask Mr. Danley: ....

George

I read the US 6,411,718 B1 patent and I understand more things now.
Regardless if I will try to build a speaker in line with it, I have to say that from what I’ve read, I built a great respect for the inventor.
He went (text columns 5 to 8) into describing the crucial constructional details – placement of speakers along the horn, surface area of the opening for each speaker unit, x/over details for timing- and the reasoning behind, to an extent greater than that was required to support the patent claims, a proof of a honest technical minded person.
You have my humble complements Mr. Danley.

George

Tom Danley · 29th June 2012, 12:49 AM

Hi George, Simon

I guess there would be several layers of answer.
If you take two subwoofers and place them close together, they couple into one new source which has twice the efficiency of one because the size of the radiator is twice as large. This holds true until the sources are far enough or the wavelength short enough that the sources extend past a quarter wavelength apart. At larger spacing’s, say a half wavelength as Simon mentions or larger spacing, then what you get is a spatial interference pattern in which the level is related to the vector addition of the two sources. In between those two extremes one has an in between result again by Vector addition of the two.

The bottom line is that if you want two drivers to add coherently into one mutually coupled source, they can’t be farther than about a quarter wavelength apart.

Horn loading, the ”transformer” effect (shudder to use that term) in a horn which provides the increase in efficiency one usually desires, one finds there is a “high pass” function to it based on the rate the area expands. . For example a 60Hz flare would double it’s area about every foot of length while a 30hz horn is twice that length.

Also, one quickly finds the formula or discussion of how large the idea mouth has to be for a given low frequency cut off. In fact, when one considers where the knee in the radiation resistance curve is for a horn, one finds that once the horn is “large enough” making the horn larger does not increase radiation resistance but does confine the radiation pattern.
This is why exponential and most curved wall horns exhibit a narrowing radiation pattern with increasing frequency. It is also why the radiator size also governs how high it can feel the horns radiation resistance.

These things effect the dimensions where one can combine multiple drivers onto one horn passageway and not produce other than the needed axial mode. In the case of the horns I use for Synergy horns, they are straight conical horns because they produce a near constant radiation angle above the Keele thumb rule.
When you examine the expansion rate, it is clear that at the apex, the expansion rate is very fast making it a high frequency rate while a bit further down the rate has slowed to that of mid range. Further down the expansion rate is slower yet. Once one has an hf, mid and low range tied into the expansion where the high pass and coherent addition are possible and driven appropriately, then one has what by measurement of radiation appears to be one single broad band source.

One can resolve this passively with normal crossovers (Butterworth, L&R etc) which have the normal “all pass” summed phase behavior , or one can use the physical offset present and use a non-traditional crossover, one adapted to the measured mag and phase of the upper and lower ranges and seeking a summation with no phase shift and that allows one to reproduce the input waveshape like a square wave or musical waveshape over a broad band. This extra step then resolves the sources into a single source in time as well as space with a passive crossover if desired.

In that condition, one is adding the ranges so that they mutually feel the horn and are acoustically coupled at crossover (the latter you also can’t avoid with the drivers that close together in a horn). One can also use an acoustic low pass filter (the holes and trapped volume where the sound enters the horn) to reduce the harmonic distortion all drivers produce.
This is normally above the low pass crossover frequency.
The result of following these rules is that one can walk up to it and even place your head into the horn mouth with no clue at all there is more than a single driver.

The difficulty has been getting more power than one hf driver will permit, even with a very high degree of directivity (large difference between the energy in the pattern and everywhere outside it), there is a limit to the output.
About three years ago, I found a way to add high frequency drivers coherently. These are the speakers usually used in the stadium jobs we have been supplying.
Sadly, I have not been able to get much interest at the company for home hifi, although they work well for that if you don’t mind big ugly black boxes.

Here are a couple videos of one of the larger of these if you have headphones on your computer. Here is a video from December of a J-3 speaker at 1500 feet. This was from a demo where a bunch of the people hopped into cars to listen far away.

Jericho Horn J3 Debut - YouTube

Here is what it sounded like close up. Set the volume to scale the voice at 1:30. As this was for stadium sound and similar folks, they were about 150 yards out seen when he pans out at 2:15.
The guy filming also spent a lot of time with his microphones getting a work out next to the subwoofer.

Danley Sound Labs - YouTube

Not shown is when the unhappy "deputy Dan(s)" came to the demo.
Best,
Tom Danley

john curl · 29th June 2012, 01:09 AM

Back to the AES. 40 years ago, I gave a talk at an AES Convention. However, I did NOT write a pre-print for the presentation. I just brought slides and gave a talk. Today, I expect it would be virtually impossible to give such a presentation. Today, even WHAT you want to talk about, is checked and rechecked by AES 'authorities' before you can even PRESENT a paper at an AES convention. In other words, if 'they' don't like what you have to say, no matter what you measure, or mathematically generate, it will NOT be allowed to be presented at the AES. Well, what is left? Not audio engineering as I know it, that's for sure.
Now, what sort of things did I learn, because I attended an AES talk? And mostly only because I read an AES preprint such as Manger's paper on loudspeaker design at the London AES, back in 1975. His unique background gave me much more insight on the mathematics of loudspeaker, even though I had already worked on the GD 'Wall of Sound' in 1973, on horn loudspeaker design with John Meyer in 1974-1975, and a monitor loudspeaker for a Swiss company in 1975-1976.
At the same convention, I met and read the preprint of a designer of loudspeaker cabinets, AND their Q, or self resonance of the panels, AND how difficult it was to really tame these resonances. The cabinet designer said that he was VERY UNPOPULAR with many speaker manufacturers, because he showed where they had gone astray. At least he was ALLOWED to give his talk. This is why, today, I hold the Wilson WATT monitor speakers in such high regard. I know what is inside, and how difficult it was to make the speaker cabinet, and once used to listening through a well made speaker cabinet, I can't really be very happy with anything else.
This is just one example from a couple of papers given at one AES 37 years ago, that gave me real insight about what I was working around for years. (more later)

Tom Danley · 29th June 2012, 01:53 AM

Quote:

Originally Posted by john curl

I would like to talk about audio education, research, and development, especially as it involves the AES (today) compared to the AES of 25-60 years ago. (more later)

Please do continue.
I was a member and presented papers at both ASA and AES in the late 80’s and 90’s but gradually became turned off to the way things worked at AES. I was a bit angry that new transducer designs like the Servodrive subwoofer and eliminating power compression had so much interest “live” but so little interest for their publication. That appeared to be much more focused on academia and much less on invention and “new things”.
Best,
Tom Danley

john curl · 29th June 2012, 03:40 AM

I am glad to get 'collaboration' from someone here, regarding the present AES.

Wavebourn · 29th June 2012, 04:24 AM

Some people sometimes don't even need to step on something in order to know what it is.

My condolences.

Blues · 29th June 2012, 04:42 AM

Quote:

Originally Posted by john curl

I am glad to get 'collaboration' from someone here, regarding the present AES.

'Corroboration'?

29th June 2012, 12:49 AM	#24125
Tom Danley diyAudio Member Join Date: Apr 2005 Location: Sitting behind the 'puter screen, in Illinois, USA, planet earth	Hi George, Simon I guess there would be several layers of answer. If you take two subwoofers and place them close together, they couple into one new source which has twice the efficiency of one because the size of the radiator is twice as large. This holds true until the sources are far enough or the wavelength short enough that the sources extend past a quarter wavelength apart. At larger spacing’s, say a half wavelength as Simon mentions or larger spacing, then what you get is a spatial interference pattern in which the level is related to the vector addition of the two sources. In between those two extremes one has an in between result again by Vector addition of the two. The bottom line is that if you want two drivers to add coherently into one mutually coupled source, they can’t be farther than about a quarter wavelength apart. Horn loading, the ”transformer” effect (shudder to use that term) in a horn which provides the increase in efficiency one usually desires, one finds there is a “high pass” function to it based on the rate the area expands. . For example a 60Hz flare would double it’s area about every foot of length while a 30hz horn is twice that length. Also, one quickly finds the formula or discussion of how large the idea mouth has to be for a given low frequency cut off. In fact, when one considers where the knee in the radiation resistance curve is for a horn, one finds that once the horn is “large enough” making the horn larger does not increase radiation resistance but does confine the radiation pattern. This is why exponential and most curved wall horns exhibit a narrowing radiation pattern with increasing frequency. It is also why the radiator size also governs how high it can feel the horns radiation resistance. These things effect the dimensions where one can combine multiple drivers onto one horn passageway and not produce other than the needed axial mode. In the case of the horns I use for Synergy horns, they are straight conical horns because they produce a near constant radiation angle above the Keele thumb rule. When you examine the expansion rate, it is clear that at the apex, the expansion rate is very fast making it a high frequency rate while a bit further down the rate has slowed to that of mid range. Further down the expansion rate is slower yet. Once one has an hf, mid and low range tied into the expansion where the high pass and coherent addition are possible and driven appropriately, then one has what by measurement of radiation appears to be one single broad band source. One can resolve this passively with normal crossovers (Butterworth, L&R etc) which have the normal “all pass” summed phase behavior , or one can use the physical offset present and use a non-traditional crossover, one adapted to the measured mag and phase of the upper and lower ranges and seeking a summation with no phase shift and that allows one to reproduce the input waveshape like a square wave or musical waveshape over a broad band. This extra step then resolves the sources into a single source in time as well as space with a passive crossover if desired. In that condition, one is adding the ranges so that they mutually feel the horn and are acoustically coupled at crossover (the latter you also can’t avoid with the drivers that close together in a horn). One can also use an acoustic low pass filter (the holes and trapped volume where the sound enters the horn) to reduce the harmonic distortion all drivers produce. This is normally above the low pass crossover frequency. The result of following these rules is that one can walk up to it and even place your head into the horn mouth with no clue at all there is more than a single driver. The difficulty has been getting more power than one hf driver will permit, even with a very high degree of directivity (large difference between the energy in the pattern and everywhere outside it), there is a limit to the output. About three years ago, I found a way to add high frequency drivers coherently. These are the speakers usually used in the stadium jobs we have been supplying. Sadly, I have not been able to get much interest at the company for home hifi, although they work well for that if you don’t mind big ugly black boxes. Here are a couple videos of one of the larger of these if you have headphones on your computer. Here is a video from December of a J-3 speaker at 1500 feet. This was from a demo where a bunch of the people hopped into cars to listen far away. Jericho Horn J3 Debut - YouTube Here is what it sounded like close up. Set the volume to scale the voice at 1:30. As this was for stadium sound and similar folks, they were about 150 yards out seen when he pans out at 2:15. The guy filming also spent a lot of time with his microphones getting a work out next to the subwoofer. Danley Sound Labs - YouTube Not shown is when the unhappy "deputy Dan(s)" came to the demo. Best, Tom Danley __________________ Bring back mst3k and futurama

29th June 2012, 04:24 AM	#24129
Wavebourn diyAudio Member Join Date: Sep 2006 Location: Pleasant Hill, CA	Some people sometimes don't even need to step on something in order to know what it is. My condolences. __________________ If I disappear suddenly, that means I finally created a time machine and pushed wrong button that brought me to Stalin's Russia. In any experiment any result is the result. Even if it is negative.

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

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

28th June 2012, 10:09 PM	#24123
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	I would like to talk about audio education, research, and development, especially as it involves the AES (today) compared to the AES of 25-60 years ago. First, the AES. When the AES was started, it would have seemed to be a 'redundant' organization for engineers, because the IRE (later IEEE) had an Audio and Electroacoustics' section, and there was also 'The Acoustical Society of America', to present papers at. Why then did some founders of the audio industry, actually mainly designers, and NOT promoters, start a new society for Audio Engineers? It is my personal opinion that they needed a place to show their continuing research in audio, and they were probably squeezed out by refereed journals of the other organizations, so much that they were frustrated. Usually there was a sort of difference in intent that existed between the existing journals, (usually scholarly papers) and the AES, as to what an actual design engineer was allowed to present, (normally just about anything at a conference), with selected papers chosen for the journal. This gave a chance for NEW IDEAS, even half-baked or impractical ones, to be seen by other audio engineers and we could learn from each other. That is NOT the situation today. (more later)

29th June 2012, 01:09 AM	#24126
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Back to the AES. 40 years ago, I gave a talk at an AES Convention. However, I did NOT write a pre-print for the presentation. I just brought slides and gave a talk. Today, I expect it would be virtually impossible to give such a presentation. Today, even WHAT you want to talk about, is checked and rechecked by AES 'authorities' before you can even PRESENT a paper at an AES convention. In other words, if 'they' don't like what you have to say, no matter what you measure, or mathematically generate, it will NOT be allowed to be presented at the AES. Well, what is left? Not audio engineering as I know it, that's for sure. Now, what sort of things did I learn, because I attended an AES talk? And mostly only because I read an AES preprint such as Manger's paper on loudspeaker design at the London AES, back in 1975. His unique background gave me much more insight on the mathematics of loudspeaker, even though I had already worked on the GD 'Wall of Sound' in 1973, on horn loudspeaker design with John Meyer in 1974-1975, and a monitor loudspeaker for a Swiss company in 1975-1976. At the same convention, I met and read the preprint of a designer of loudspeaker cabinets, AND their Q, or self resonance of the panels, AND how difficult it was to really tame these resonances. The cabinet designer said that he was VERY UNPOPULAR with many speaker manufacturers, because he showed where they had gone astray. At least he was ALLOWED to give his talk. This is why, today, I hold the Wilson WATT monitor speakers in such high regard. I know what is inside, and how difficult it was to make the speaker cabinet, and once used to listening through a well made speaker cabinet, I can't really be very happy with anything else. This is just one example from a couple of papers given at one AES 37 years ago, that gave me real insight about what I was working around for years. (more later)

29th June 2012, 03:40 AM	#24128
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	I am glad to get 'collaboration' from someone here, regarding the present AES.