tomtt, can you give a link ?
I'd be interested in running the google translator to see what they say about it.
Norman
I'd be interested in running the google translator to see what they say about it.
Norman
http://www.iar.co.jp/kikan/kikan0604.htm
http://www.iar.co.jp/
iar.co.jp - Google Search
these people can get these magazines -
Kinokuniya Book Store Home Page
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撮影:前村 学･西山元和氏 Photographer: Mr. Maemura Satoru sum・Nishiyamamoto
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Murphy Corner-Line-Array question about ceilings
The Murphy Corner-Line-Array project is interesting, but the project paper states: "There is one basic requirement for the room. The room must have about an 8 foot ceiling which is parallel to the floor with two corners available for placement of the line arrays." What might one expect with this line array if you have a vaulted ceiling that slopes up and away from the corners? Would this type of ceiling be an absolute disaster with this project?
George
The Murphy Corner-Line-Array project is interesting, but the project paper states: "There is one basic requirement for the room. The room must have about an 8 foot ceiling which is parallel to the floor with two corners available for placement of the line arrays." What might one expect with this line array if you have a vaulted ceiling that slopes up and away from the corners? Would this type of ceiling be an absolute disaster with this project?
George
The vaulted ceiling would cause the ceiling acoustic reflections to be angled just as a mirror would show. You woulod still have a first floor reflection in line with the source array and the corner reflections would be correct in all cases. It would probably give very good results but the required EQ correction is likely to be a little different from the EQ settings I give. I don't thik it would be a disaster at all.
There is more discussion of the Murphy Corner Line Array here:
Murphy Corner Line Array (MCLA) - Techtalk at Parts-Express.com
Cheers!
John
I always felt that the suggestion to offset the drivers in the vertical column was the easiest design idea to help keep the combing to a minimum.
I wish I had known that when I build my arrays several years ago.
I am completely satisfied with the two arrays in my work area. There are 20 3or 4 inch, can not remember, aluminum/magnesium full range drivers from Tang Band in each column.
They do not like mixed up hard rock, but most easy listening jazz with piano and vocal is astonding. Placing them in the corner has it's affects but it is not a major difference than even spacing on a long wall.
The one big thing is to run them open baffle. Any attempt, to me, to close the backs or add damping material destroys all of the detail and clarity.
I made an exact copy of Roger Russells layout figuring after 40 years he should know a thing or two.
Tad
I wish I had known that when I build my arrays several years ago.
I am completely satisfied with the two arrays in my work area. There are 20 3or 4 inch, can not remember, aluminum/magnesium full range drivers from Tang Band in each column.
They do not like mixed up hard rock, but most easy listening jazz with piano and vocal is astonding. Placing them in the corner has it's affects but it is not a major difference than even spacing on a long wall.
The one big thing is to run them open baffle. Any attempt, to me, to close the backs or add damping material destroys all of the detail and clarity.
I made an exact copy of Roger Russells layout figuring after 40 years he should know a thing or two.
Tad
Seems it is gone.
I can link to my thread, most pics are gone, but a few of mine are still there.
Mr. Bates, your focused arrays...
I can link to my thread, most pics are gone, but a few of mine are still there.
Mr. Bates, your focused arrays...
In my opinion the best curved array configuration would be one derived from Don Keele's CBT (constant beamwidth transducer) work. Concave (or focused) configurations have limitations.
I agree, cbt much better option for mostly everybody.
But for those wanting more output and no crossover, it is an option.
One of the best projects i've ever done, very high waf also.
But, rolls at 150hz, needs baffle step, make sure internal boxes arn't 6" cube or you peak past 1khz, and quite pricy tricky build.
Lol, have i discouraged you from it ?
I hope so because it is for the very very few........
But for those wanting more output and no crossover, it is an option.
One of the best projects i've ever done, very high waf also.
But, rolls at 150hz, needs baffle step, make sure internal boxes arn't 6" cube or you peak past 1khz, and quite pricy tricky build.
Lol, have i discouraged you from it ?
I hope so because it is for the very very few........
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Combing is not present in ribbons(they beam in vertical dispersion. And if you cut the flanges on Dayton ND20FA's you can keep comb filter distortion from kicking in until about 15,500hz or above where its unlikely you will be able to distinguish it.
You will need to be careful where you cross the mid ranges. find the distance between the centers by dividing 1130 by the frequency that you want to cross and multiplying that answer by 12 to get the inches. Don't exceed that.
You will need to be careful where you cross the mid ranges. find the distance between the centers by dividing 1130 by the frequency that you want to cross and multiplying that answer by 12 to get the inches. Don't exceed that.
Has any research been done on how to implement this in multi way systems? The ones he built for parts express are narrow enough, but lets say you had a row of 10-12" woofers, would they need to be angled outwards to follow the curve of the sphere, or is it better for them to point in the same plane as the regular drivers (or in 3+ way systems, the tweeters)? Would it be better to have them on both sides or just one?
Most CBT examples in the Don Keele literature focuses on mid/high bands coverage with the curved/arc array. Keele usually adds stand alone subwoofer(s) along side the arrays and not part of the curved cabinet. Keele's constant beamwidth coverage seems to be limited to mid and high frequencies.
I suspect that subs and large woofers have near omni-directional coverage over their low frequency range so you would have difficulties extending constant beamwidth capability down low.
You might contact Don and ask him for advice. He is usually very approachable about technical matters.
I suspect that subs and large woofers have near omni-directional coverage over their low frequency range so you would have difficulties extending constant beamwidth capability down low.
You might contact Don and ask him for advice. He is usually very approachable about technical matters.
Its interesting that you should comment that closing the backs causes destruction of "all of the detail and clarity".
In my opinion this is because by closing the backs you are causing the backwave to return through the speaker material out of phase which will definitely muddy the waters.
I do something different and do in fact close the backs. But instead of using a shallow box, I use a long cylinder. I pack it with 4 lb/cu ft fiberglass insulation(in a .1 cu ft cylinder this means the fiberglass has to weight 6.4 oz---I have a scale), with wooden rods through it, as well as put a slanted back. This cuts off about 98% of the back wave from return through the front, and eliminates any standing waves. The fiberglass is way superior for converting the sound pressure into heat and absorbing it. If I push the line array speakers with this hard(which is difficult to do since there are 17 of them per channel), I can actually feel the PVC cylinder getting just a bit warmer.
The tube simply gets more rigid, the more volume of sound is put in it, reducing the resonance, but because its a cylinder not a box you can actually determine the exact resonance, and either accept it or address that frequency. Finally, the physics of sound in closed cylinders simply eliminates all even order mushy harmonics from the back wave, so the tiny little that makes it back to the front is only odd order harmonics, which (though out of phase), in small amounts actually increases clarity.
It does also increase the speed of sound in the tube very slightly, but I'm not sure what the result of that might be.
This is a lot of work...though.
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I use the tube length based on the WinISD's simulations of appropriate cu in in the enclosure. You can just as easily calculate the required dimensions in a cylinder as a box. The diameter of the tube has to, at a minimum, fit the speaker. For my first line array I used 4 inch tubes for 3.5 inch speakers. They were about 15 inches long. In the current line array the mids will be 2.5 and I will use 3 inch tubes, about 13 inches long based on the T/S parameters modeled in WinISD. I usually use sealed enclosures for speakers, since getting down into the deep bass is not required. Vance Dickerson in his books has quoted research using fiberglass as a stuffing that says the speaker will experience a stuffed fiberglass box as 20-30% bigger than it is. This only works for fiberglass(the wall insulation stuff that prickles). It will not work for fiberfill or acoutistuff or any of the other varieties. You can take that for real or not. In a sealed box its not that much different.
You also need to make sure that the tubes don't touch each other since you don't want them sharing their resonance.
In my current configuration, the length of the mid woof and sub woof tube is limited to 23 inches, so the size of the tube diameter will be larger to compensate. The 12 incher will be in a 23 x 18 inch tube, and the 8 incher in a 12 x 23 inch tube. My tweeters in the current configuration are ribbons and don't need an enclosure.
When using fiberglass, you need to enclose the fiberglass in stapled acoustical cloth to keep the fiberglass fibers out of the speaker coil. Its also worthwhile to drive 1/8 inch and larger wood rods or flat pieces of would to break the tube into four sections, to completely eliminate any possible standing waves. You can also use a circle section of much denser fiberglass like they use in ceiling tiles, or both. I usually use both.
Preparation of the enclosure in my experience is very important to clarity in the speaker. Its often completely ignored.
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Why not run an impedance test and see what you get? Compare it to the impedance of the same driver in free air.
Every wiggle that isn't in the free air curve is a possible box resonance.
Two materials I tested stood out to drop the resonance peak (acting as a size increase).
- one is the Fiberglass itchy wall insulation
- the other one is Twaron's Angel Hair
Though combinations with different materials worked even better to remove resonances, seen as little wiggles in the impedance curves.
I ended up using fiberglass insulation combined with with real wool felt as the best overall package as I needed to use the speaker driver in the bottom range. Angel hair needed less stuffing to perform similar to fiberglass insulation at mid frequencies.
Seeing what you get with impedance curves is quite easy. Removing all traces of resonances can be a lot of work though. I ran quite a number of tests with a test enclosure and also with my final enclosure. Every wiggle is a potential dip/peak in the resulting frequency response curve.
A sample of the first test I ran:
I ran many more tests after this one to get all wiggles out of the impedance curve.
Every wiggle that isn't in the free air curve is a possible box resonance.
Two materials I tested stood out to drop the resonance peak (acting as a size increase).
- one is the Fiberglass itchy wall insulation
- the other one is Twaron's Angel Hair
Though combinations with different materials worked even better to remove resonances, seen as little wiggles in the impedance curves.
I ended up using fiberglass insulation combined with with real wool felt as the best overall package as I needed to use the speaker driver in the bottom range. Angel hair needed less stuffing to perform similar to fiberglass insulation at mid frequencies.
Seeing what you get with impedance curves is quite easy. Removing all traces of resonances can be a lot of work though. I ran quite a number of tests with a test enclosure and also with my final enclosure. Every wiggle is a potential dip/peak in the resulting frequency response curve.
A sample of the first test I ran:
I ran many more tests after this one to get all wiggles out of the impedance curve.
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Why not just read the research in Vance Dickerson's book, first?
Besides that I don't use boxes for speakers any more, I use closed cylinders because I like the impact of sound in a closed cylinder. The resonance is calculable with an app. And I can control way more than in a box.
Besides.... I'm not an electrical or acoustical engineer. The learning curve for all that you mentioned would not be a fun run for me. The last time I took any math studies was 52 years ago in my Junior year in high school. I actually had to switch out of biology 49 years ago in college when I discovered that the math needed for the chem courses was getting away from me, and I didn't have enough time to catch up. I do have the ability to learn it; my son is a nuclear physicist, and he sure didn't get that stuff from his mother. It just would take too much time.
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I did not read his book, though did read up on a lot of other material.
I want to know what I get, so I look into it.
I don't want to assume I have no resonance, I want to know if I have any.
It's a lot easier to do than most would think. All it takes is some clever wiring, a known resistor and REW.
I am an engineer, not electrically or acoustically schooled though. Mechanical engineer actually, that turned towards ICT later in my career. I'm always curious, that's why I do what I do. I don't expect others to do the same.
I want to know what I get, so I look into it.
I don't want to assume I have no resonance, I want to know if I have any.
It's a lot easier to do than most would think. All it takes is some clever wiring, a known resistor and REW.
I am an engineer, not electrically or acoustically schooled though. Mechanical engineer actually, that turned towards ICT later in my career. I'm always curious, that's why I do what I do. I don't expect others to do the same.
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