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jbell's set of four tapped horns
jbell's set of four tapped horns
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Old 13th July 2010, 02:46 PM   #391
jbell is offline jbell  United States
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shawn:

scott says there is a dj around florida running around with 8 of the big cabinet -- so I guess you are in good company... And wheels are a necessity for that one.

Mike:
I attached a pic of the 2 places I'd put it. Neither place should affect the sound. The good part about the center option, is if you have to notch panel 'j' a little, that's ok, it doesn't create a 'leak' if you do. It should also get at least 3 screws into panels 'h' and 'i' with the slight possibility of getting the 4th into panel 'j' It's close to center of gravity, but not quite. I'm big on handles having something more than 1/2" of wood to connect to. Use the 'mouth' option if you plan on putting stuff on top of the cubes when carting in/out. You have the flexibility there to put them center of gravity. I am going to have to try jacks in these handles, as I think it should provide a nice 'protected' place for them.
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Old 16th July 2010, 11:50 PM   #392
shawnondrums is offline shawnondrums  United States
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Blue casters cheap. 3" Swivel Caster with Lock
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Old 20th July 2010, 03:16 AM   #393
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by jbell View Post
Here's a set of eight 24" cubes at 63v each in 2pi that is safe xmax wise to 35hz, that I'm starting a run of. Each cube can be made from a single 42lb sheet of 1/2" ply. (quite the contrast to 2 sheets of 72lb ply each.) Yea it takes more power/drivers to get there, but my back will like me better the next day.
Just a quick one - what's the measured Fc of your new TH?
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Old 20th July 2010, 01:29 PM   #394
jbell is offline jbell  United States
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Originally Posted by Brian Steele View Post
Just a quick one - what's the measured Fc of your new TH?
Funny you ask, and also funny that I'm not sure exactly how to answer...
There are lies, darn lies, and then there are specs....

Is measured Fc the point where efficiency starts to decline? or is it measured as lowest freq of a +-3db response ?

42hz is where the efficiency really starts to drop, but 40hz is still well within a +-3db of 100db overall efficiency. Hornresp says 40hz is the excursion null. I guess you could in theory use either number.


Here's what I posted earlier as the every 10hz responses...
30hz 87
40hz 98
50hz 100.5
60hz 100.5
70hz 99.5
80hz 98.5
90hz 99
100hz 100
110hz 102
120hz 103
130hz 102.5
140hz 101
150hz 98.5
160hz 93
170hz 83
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Old 20th July 2010, 02:02 PM   #395
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by jbell View Post
Funny you ask, and also funny that I'm not sure exactly how to answer...
There are lies, darn lies, and then there are specs....

Is measured Fc the point where efficiency starts to decline? or is it measured as lowest freq of a +-3db response ?

42hz is where the efficiency really starts to drop, but 40hz is still well within a +-3db of 100db overall efficiency. Hornresp says 40hz is the excursion null. I guess you could in theory use either number.
That would be the design Fc. The measured impedance response of the the TH is probably the best way to identify the actual Fc - it's at the first impedance mininum. A WT3 will measure the response in a few seconds. If you don't have access to a WT3, there are other ways to find this impedance minimum.
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Old 20th July 2010, 03:26 PM   #396
polviggen is offline polviggen  Belgium
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so it measures a bit better then hornresp predicts ?
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Old 20th July 2010, 03:43 PM   #397
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by polviggen View Post
so it measures a bit better then hornresp predicts ?
Looks so. I'll bet that mounting the driver backside out has resulted in the mouth being shaded a bit, which in turn perhaps has resulted in Fc being shifted downwards (similar to what happens if you partially block the port of a vented box). The smaller the mouth, or the larger the driver, the greater the effect. This is not necessarily a bad thing, and perhaps even preferable . It might be even possible to model the effect with Abakak, if you can correctly guesstimate the change in cross-section that's caused by the driver's magnet structure at that point in the TH.
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Old 20th July 2010, 04:50 PM   #398
jwmbro is offline jwmbro  United States
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Quote:
Originally Posted by salzburgsoundsystem View Post
Cubic inches:

4 Big uns:
4 x 36 x 46 x 24 = 158 976

8 Little uns:
8 x 24 x 24 x 24 = 110 592


Wood:

4 Big uns:
8 Sheets 0.75 inch plywood

8 Little uns:
8 sheets 0.50 inch plywood

Drivers:

4 Big uns:
4 Kappalite 3015lf

8 Little uns:
8 Kappalite 3015lf


What does it cost us? I'm guessing the US guys have cheaper plywood, so you are happy to build big high efficiency boxes.

In my case the wood makes costs almost as much as the driver on the big boxes.

Regards, Ben
Hi Ben. Have you shopped around thoroughly for MPX (plywood) prices? The price differences from store to store are very significant here in Munich. I recently bought 3/4 birch ply for 48€ per square meter, and then later found it in a different store for 28€ per square meter:

Click the image to open in full size.

At those prices, a pair of the little ones would cost 100€ in wood, and 330€ in drivers, so 430€ total per pair. An eightpack could be had for 1720€ then, which is not bad.

Anyways, jbell, these small cubes look quite good - I'd definitely build a pair if I had any use for them
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Old 20th July 2010, 07:29 PM   #399
jbell is offline jbell  United States
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Originally Posted by polviggen View Post
so it measures a bit better then hornresp predicts ?
I wouldn't say 'better' just different. When you fold a TH, the reflectors close to the driver play a big part in the response. I can sacrifice 40hz for more 80hz, and vice versa depending. I chose to use no reflectors and achieved more 40hz than hornresp predicted, at the expense of a larger dip in the 80hz range. If you go look at what screamersusa did on his, the 12degree reflectors and non parallel walls close to the driver show how he achieved a better 80hz-100hz range. A solid rear brace reduced his 40hz by a few db. Even my triangle braces reduced 40hz by a full db. So braces and reflectors play a big part in the overall response.

So, a TH is like a soup, yes hornresp gets you the main ingredients of a good TH, but then you have to season to taste.....
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Old 20th July 2010, 09:26 PM   #400
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by jbell View Post
I wouldn't say 'better' just different. When you fold a TH, the reflectors close to the driver play a big part in the response. I can sacrifice 40hz for more 80hz, and vice versa depending. I chose to use no reflectors and achieved more 40hz than hornresp predicted, at the expense of a larger dip in the 80hz range. If you go look at what screamersusa did on his, the 12degree reflectors and non parallel walls close to the driver show how he achieved a better 80hz-100hz range. A solid rear brace reduced his 40hz by a few db. Even my triangle braces reduced 40hz by a full db. So braces and reflectors play a big part in the overall response.

So, a TH is like a soup, yes hornresp gets you the main ingredients of a good TH, but then you have to season to taste.....

Did you try to account for the effect of those reflectors and braces in HornResp? They will all reduce Sd at points in the horn, which will in turn may affect the predictions if you try to account for them in the design.
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