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Ping tomservo regarding US patent US4845759A

45.233.64.5
Posted on January 10, 2023 at 09:32:58
Rafaro
Audiophile

Posts: 158
Joined: July 30, 2005
 Hello Tom:
Regarding your patent "Sound source having a plurarity of drivers operating from a virtual point". Can this be applied to horn line arrays? Lets say horn cabs 16 inch in height designed to produce highest wavelength of 2200Hz=6.16 inches sitting on top of each other. Although they are not within the same horn considering they are horns whose mouths a joined together can it be assumed they would act as a point source and that their output would be more than the sum of the individual single cabs used as per your patent?
Rafaro

 

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RE: Ping tomservo regarding US patent US4845759A, posted on January 11, 2023 at 16:35:36
tomservo
Manufacturer

Posts: 8183
Joined: July 4, 2002
 Hi
Well a source that radiates from a single point has a wavefront that is curved on a radius while a line source has no curvature (technically one could say that is what you have infinitely far away from the point source).

One can do what you ask, IF what one makes is an astigmatic point source, a point source that has two different focal lengths (just like with ones eyes they can have that issue as well), one in the horizontal and an other in the vertical.

With the wavelength at 20KHz being about 5/8 inch, there is no simple way to put sources that close together to form a single radiation (1/4 wl or less apart), at least i couldn't think of a way and i tried hard.

What i did figure out is that if one formed curved the curved wavefront of a single source like longer horn would have, that you could make that with segments IF they were close enough together edge to edge so that they did form one big wavefront (and so have the vertical directivity of a horn that tall with that horn wall angle).

To curve the wavefront i used an acoustic lens I called a Paraline, the job was to take the radiation from individual drivers and make segments with a new radius one could add right up edge to edge.
Fast forward through a bunch of dull R&D;

Doug Jones (the guy behind the LEDR hearing test recordings) made a video for us that shows the idea behind that lens.

https://www.youtube.com/watch?v=b8cX5Xs_vZg

This fellow from another forum came to shop to hear some other speakers and saw one of those standing there in the warehouse and asked to hear it. He was playing something on his phone showing there are no seams, it sounds like a single source.

https://www.youtube.com/watch?v=8HxWGzelwNE

So it is in one place in time, like a single driver

Keep in mind that one has 8 coax drivers in it and most of our stuff, nearly all is for large scale listening, hifi and DIY is my hobby and my goal sound wise for our big stuff...
Best
Tom Danley




 

Lou Reed at DANLEY, posted on March 22, 2023 at 11:50:39
rickmcinnis@dogwoodfabrics.com
Audiophile

Posts: 3040
Location: Atlanta
Joined: December 15, 2003
 That made my day along with seeing the great Mr. Danley posting again.

 

Thanks for sharing!!, posted on January 13, 2023 at 06:28:10
Scholl
Distributor or Rep

Posts: 1357
Joined: March 8, 2001
 What is the lowest useable frequency for this topology? Can you build a larger one to say 300hz then stack a smaller one on top for a two way?

What could the high frequency bandwidth be with inexpensive drivers?

Since you're using coax what shape do you use to attach the coax drive to the Paraline lense?

 

RE: Thanks for sharing!!, posted on January 13, 2023 at 09:49:12
tomservo
Manufacturer

Posts: 8183
Joined: July 4, 2002
 Hi
Well the speaker in the 2nd video is good to 80Hz all by itself using 8 coax drivers (cone and normal compression driver).

For a paraline, the main limit to HF is how large the passageway is where the sound changes direction.
Sound can act like a fluid, go around corners (like inside a compression driver at the dome) but it does this elegantly only when the dimensions are small compared to the wavelength.

It's not to hard to make a 1 way paraline work but the larger it is, like any two radiating systems, the harder it is to make a seamless crossover.

The same thing applies to the last question, in that speaker, the mid energy is added into the hf horn where the dimension is about 3 inches in diameter and so at crossover, they can combine (less than 1/4wl across) into one single radiation.

That (radiating as a single point in time and space) and horns has been the thing that makes our company go, in a live sound world in love with hanging speaker bananas.
If you were ever at "Rivers of light", all the audience speakers are those SBH10's, the far away speakers are some of our bigger stuff.
Tom

 

RE: Thanks for sharing!!, posted on January 13, 2023 at 17:43:36
claudej1@aol.com
Audiophile

Posts: 816
Location: Detroit
Joined: August 17, 2007
 "hanging speaker banana"

Great new terminology, Tom!!! I'm adding to my official Audio Vocabulary.

 

RE: Ping tomservo regarding US patent US4845759A, posted on January 10, 2023 at 11:11:59
Bill Fitzmaurice
Industry Professional

Posts: 5370
Location: New England
Joined: October 20, 2002
 I'm not speaking for Tom, but what you describe isn't a point source, it's a line source.

 

RE: Ping tomservo regarding US patent US4845759A, posted on January 10, 2023 at 20:04:18
Rafaro
Audiophile

Posts: 158
Joined: July 30, 2005
 Hello Bill you are right but refer to Tom's patent for clarification. When sound sources are within 3 wavelengths distance of their maximal frequency they act as a point source and may have more output than the sum of their individual outputs together. Tom measures everything! Just wondering if it would apply in this case.


Rafaro

 

RE: Ping tomservo regarding US patent US4845759A, posted on January 11, 2023 at 04:53:11
Bill Fitzmaurice
Industry Professional

Posts: 5370
Location: New England
Joined: October 20, 2002
 They don't have more output than the sum of their individual outputs. Where a source is more than three wavelengths in dimension it operates in the near field, so the SPL reduction with doubling of distance is 3dB, rather than 6dB, subject to the distance to the listener. That can appear as multiple combined sources having higher output than the sum of the individual outputs if you're not aware of the difference between near field and far field, which is explained in Jim Griffin's line array white paper.

 

RE: Ping tomservo regarding US patent US4845759A, posted on January 11, 2023 at 15:02:52
Rafaro
Audiophile

Posts: 158
Joined: July 30, 2005
 Yes Bill but the sources in this design are Within the three wavelength max freq and horns uniting as they do may fullfill the criteria of Tom's patent. Just curious as to his opinion on this. The augmentation of SPL in Tom's patent and nearfield only 3dB per distance loss seems related to constructive interference of a more planar wave exit pattern. As far as Griffin's paper line arrays for home use been there done that. It has limited usefulness mainly limiting ceiling floor reflections. That is good but side reflections are still a major problem requiring room acoustic treatment. Having done professional recording mixing and mastering showed me the importance of room acoustic treatment...well worth the money! For home use the nearfield only 3dB per distance loss is irrelevant as opposed to live sound where it is very useful. The different arrival times intrinsic to long column arrays (necessary for nearfield critical distance) blurs the mid high freq resolution. The solution is a limited number of highly efficient horn line array cabs avoiding the long lines of inefficient direct radiation cabs. I notice you have designed similar DIY versions yourself!
Rafaro

 

RE: Ping tomservo regarding US patent US4845759A, posted on January 15, 2023 at 10:56:23
tomservo
Manufacturer

Posts: 8183
Joined: July 4, 2002
 Hi
There is a way to make a horn that is very narrow in the vertical and wide in the horizontal as described above.
The way that is used is aimed over the front row, in fact if one chooses the right radiation angle down angle and height, one can make the spl near constant over a large area. The old thumb rule was "Aim at the back row", it's more scientific now but the same concept.

People talk about it have cylindrical radiation and so half the spl change vs distance compared to a point source.

So let's imagine a simple array of say 32 small sources. Each one has a frequency below which the baffle governs the radiation angle and up high, the radiation pattern will become narrow and complex as the radiator becomes "large" acoustically.
To be clear, for two sources to combine into a single new source. If you were to invert one of them, they largely cancel each other out), they have to be less than 1/4 wavelength apart for this coherent addition. There is a transition to two separate radiations by the time they are 1/2 wl apart (and radiate a figure 8 pattern, inverting one, changes the direction of the lobes)

Two equal but opposite sounds cancel each other but in phase, they add.
When your in front of the imaginary array what you get depends where you are, the vector sum of the sound from each of those sources and because they are all different distances, they don't "add" in the normal sense like close coupled subwoofers do they add and cancel depending on the frequency, angle and distances (a polar pattern of lobes and nulls, an interference pattern).


So lets say your far away from this source and it is X SPL, next to it is a point source producing the same SPL at X distance. As you walk closer, the point source increases in loudness following the inverse square law but as you get closer to the line, the more spread out in time a single sound event is and less addition of the sources there is. If you look at the envelope time curve, you can see that an impulsive event is stretched out according to the span off arrivals in time from the different sources.

In the critical listening sense, a true floor to ceiling line is impressive, the image is "a tall wall" So is the mono phantom like D Krall instead of standing in front of you.

If you remove the things the loudspeaker produces that give it an identify-able location in space with your eyes closed, it also will more disappear in the stereo image. That can produce a very powerful stereo image where your not aware of the loudspeakers if done at the right scale also for an audience.

So as the large line increases less rapidly as you get closer and closer to this requires a large sale of amplifiers and loudspeakers, the solution i came up with for work is a large full range constant directivity horn.

Skip all the self cancellation and time smear, use horn loading for efficiency and pattern control and often one box replaces a large array and sounds better.
The problems with large rooms is a greater challenge than the home or studio sized rooms and like large rooms, horizontal directivity is your friend keeping the direct sound where it belongs and lets you keep the speakers as wide apart as desired.
Tom

 

RE: Ping tomservo regarding US patent US4845759A, posted on January 29, 2023 at 12:50:37
Rafaro
Audiophile

Posts: 158
Joined: July 30, 2005
 Thanks Tom the 2-3 wavelength limit in your patent threw me off. My approach to large scale sound reproduction was to use very efficient exponential horns in a "line array". But because of the efficiency just needing a very limited number of cabs (4) to equal the output of a long line of direct radiator cabs. Thus avoiding many of the problems you mentioned. Critical was to maintain a limited vertical exit angle not only in the HF but also in the MR. The design idea was for one person to be able to carry and set up the sound system. The benefits of such a system are obvious limited amps personnel trucks etc. So although it is not the ideal point source its close and and offers a practical alternative. The necessity of the idea came from playing bass in a band and in addition was dumped the job of setting up the sound system. Either way it appears dinosaurs (horns) are making a come back Jaja.
Rafaro

 

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