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Multi-Way Conventional loudspeakers with crossovers

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Old 11th July 2010, 02:07 AM   #6671
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To simplify, there are 3 things that can potentially be issues with cabinets. Physical panel resonances, standing waves, and the direct reflection off the back of the cabinet back through the driver cone. The first thing is to properly brace the cabinet putting any physical resonance well above the intended range the cabinet will be used over. The closer the braces, the higher you push this resonance point in frequency. Secondly you want nonparallel surfaces and unequal distances to help avoid standing waves from developing. This can be as crazy as fully irregular walls to as simple as a brace at an angle behind the driver. The more irregular the better, however absorption inside the cabinet also helps to eliminate these issues. Finally you will want to redirect and or absorb any sound that may be coming from the back wave of the driver. Heavily packed insulation can do ok, but a soft polyurethane foam often works best for this.

John
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Old 11th July 2010, 05:45 AM   #6672
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I would like to know how the particular drivers were chosen.
Were they auditioned first or were the chosen based on TS parameters?
What about the Radian 745PB? Why not 850PB?

I am not criticising here, just want to know how you chose the drivers/horns.
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Old 11th July 2010, 06:09 AM   #6673
ScottG is offline ScottG  United States
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Originally Posted by thanh1973 View Post
I would like to know how the particular drivers were chosen.
Were they auditioned first or were the chosen based on TS parameters?
What about the Radian 745PB? Why not 850PB?

I am not criticising here, just want to know how you chose the drivers/horns.

Have you read through this thread?

I can tell you that the 745 vs. the 850 is down to horn size vs. low freq. extension. The larger the diameter of the compression driver, the larger the horn for the same low freq. extension. Simply put, the 745 enables the use of a smaller horn. The 745's exit diameter was also similar to another driver Lynn was interested in trying from Great Plains Audio. It's also similar to 18Sound's aluminum diaphragm driver. (..though the exit angle for each is different.)
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Old 11th July 2010, 06:13 AM   #6674
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The notches in the MDF corners are 3/4" deep. A front panel of 12 mm Baltic birch is set into these notches, leaving about 1/4" of remaining depth. The grill frames will be made from 1/4" fiberboard. When these are in place, their front surface will be flush with both the driver and the MDF corners. Neat, huh?
Gary Dahl
Huh! This is surprising! I was doing exactly this back in 1974 - for mid range drivers and tweeters, too - and I have been surprised that I have seen no manufacturer do the same.
This is the first reference I have seen to this little nicety in all these years.

Last edited by Russell Dawkins; 11th July 2010 at 06:16 AM.
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Old 11th July 2010, 06:18 AM   #6675
ScottG is offline ScottG  United States
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Originally Posted by John_E_Janowitz View Post
To simplify, there are 3 things that can potentially be issues with cabinets.
Actually I have a thread on this..

The "Voodoo" of Vibration in Loudspeakers

I'd also note that standing waves (or modes) in a cabinet requires that both the cabinet volume is relatively large AND that the driver is being used higher in freq. (..midrange). Though of course the 12M is being used in precisely this manner.
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Old 11th July 2010, 06:50 AM   #6676
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Have you read through this thread?

I can tell you that the 745 vs. the 850 is down to horn size vs. low freq. extension. The larger the diameter of the compression driver, the larger the horn for the same low freq. extension. Simply put, the 745 enables the use of a smaller horn. The 745's exit diameter was also similar to another driver Lynn was interested in trying from Great Plains Audio. It's also similar to 18Sound's aluminum diaphragm driver. (..though the exit angle for each is different.)
I have read about 100 pages so far, only another 560 to go.

Ok I have now discovered this has turned into a 3 way system.
What about 2 way or 2.5 way? Is this possible with the RAAL ribbons and the pro drivers mentioned so far?
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Old 11th July 2010, 12:13 PM   #6677
soongsc is offline soongsc  Taiwan
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Originally Posted by John_E_Janowitz View Post
To simplify, there are 3 things that can potentially be issues with cabinets. Physical panel resonances, standing waves, and the direct reflection off the back of the cabinet back through the driver cone. The first thing is to properly brace the cabinet putting any physical resonance well above the intended range the cabinet will be used over. The closer the braces, the higher you push this resonance point in frequency. Secondly you want nonparallel surfaces and unequal distances to help avoid standing waves from developing. This can be as crazy as fully irregular walls to as simple as a brace at an angle behind the driver. The more irregular the better, however absorption inside the cabinet also helps to eliminate these issues. Finally you will want to redirect and or absorb any sound that may be coming from the back wave of the driver. Heavily packed insulation can do ok, but a soft polyurethane foam often works best for this.

John
Stuffing density distribution also makes a significant impact.
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Old 11th July 2010, 04:54 PM   #6678
g3dahl is offline g3dahl  United States
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Stuffing density distribution also makes a significant impact.
I agree. I will be using Bonded Logic UltraTouch R-13. Some experimentation will most definitely be in order.

Gary Dahl
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Old 11th July 2010, 05:39 PM   #6679
badman is offline badman  United States
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Originally Posted by g3dahl View Post
I agree. I will be using Bonded Logic UltraTouch R-13. Some experimentation will most definitely be in order.

Gary Dahl
One of the challenges is how far you can go with the top/bottom mode, which is the toughest to deal with in most constructions. With vented constructions the difficulty increases more because you can't overdamp the box volume and still have usable vent output (though I'd say that damped box tuning is an underused technique). I'm using a half-cylendar with those same "L" edge rounds (4" dia), and will have a stuffing chamber- about 4" of Ultratouch at the bottom, constrained between two shelf braces (with windows, roundovers on all exposed edges. I also used some layered materials to break up the surface of the top panel (as well as stiffen it) so I'm hopeful that I can leave the rest of the cab fairly minimally damped and keep that one significant mode suppressed. The rest of the cab is a 3/4" shell, with ribs of 3/4 stock, which are coupled to the shelf braces.

I'll try to get some pics up.
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Old 11th July 2010, 09:40 PM   #6680
SunRa is offline SunRa  Romania
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Thank you for the answer, Mr. Dahl, it makes more sense to me now!
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