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Old 4th December 2008, 11:33 AM   #21
electroaudio is offline electroaudio  Sweden
diyAudio Member
Join Date: Mar 2004
Location: stockholm
Originally posted by andrew_87
i have calculated a theorical spl at 1 meter in a 0.5phi emission...
so real 115-120dB are enoght!

i would create this system for a carnival wagon...

You should calculate the horn for 2pi instead of 0.5pi ,since that is a lot closer to the reality on the wagon.

Click the image to open in full size.
0.5pi is a concrete corner. And there are no corners on a wagon, just a lot of free air.
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Old 4th December 2008, 12:14 PM   #22
andrew_87 is offline andrew_87  Italy
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Join Date: Nov 2008
@ electroaudio:

yes, but i will put 4 scoop in a stack...
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Old 4th December 2008, 12:31 PM   #23
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
using that pic just posted as an example.

They look like Labhorns.
If we assume they perform similar, then in a corner, 0.5Pi, you need 1.5 cabinets.

If you lay them on the floor up against a wall, Pi, you need 3 cabinets.

If you lay them on the floor without close wall support, 2Pi, you need 6 cabinets.

If you fly them, 4Pi, you need 12 cabinets.

This stacking adjusts the mouth area to suit the loading.
Any bass horn with a similar mouth area and similar frequency response will require a similar number of cabinets.

That truck is getting close to flying. I guess it should have 8 to 12 cabinets to work properly down to the Labhorn's 27Hz lower limit.
By using only 4 cabinets the lower end of the frequency response becomes very ragged.
But worse, because he used too few cabinets, the drivers are not properly loaded at the low frequency end and will as a result use more Xmax. This potential problem can only be solved by changing the steep cut high pass filter to a higher frequency to prevent damage to the drivers.
regards Andrew T.
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Old 4th December 2008, 12:48 PM   #24
andrew_87 is offline andrew_87  Italy
diyAudio Member
Join Date: Nov 2008
i will put the stack near the floor (circa 30cm fo distance), so:

1 scoop is design for 0.5phi

i can use 2 scoop in 1phi
4 scoop in 2phi (my case)
8 scoop in 4phi...

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Old 4th December 2008, 04:33 PM   #25
HK26147 is offline HK26147  United States
diyAudio Member
Join Date: Jan 2008
* It is not my intent to dissuade you into using piezos, rather to benefit from what others have found:

Arguable there are no bigger fans of piezos and their implementations then the members of the Fitzmaurice forum, so from there you can get some ideas of what can be done with piezos.
I ( and others ) experimented with arrays of piezos when they first came to market. The limitations they had then, still exist today.

This is a recent finding about piezos from an individual ( on the BF forum ) who has to provide high SPL for concerts:

1) Lack of overall output, leading to minor distortion when pushed hard.
2) Poorer performance in transient response (ie distortion) due to limited peak handling (not easily observed in DJ/music playback scenarios)
3) High crossover point considering the boxes are 2 way designs. Pattern control will suffer as a result below the crossover point, particularly from about 1-3K in some of the designs.
4) Jagged frequency response before processing
5) Not very even phase response, hard to correct.

30cm ( 11.8" ) distance to ground is fairly close...
In a 'blind" test I dropped the bass cabs from a distance of 28" ( 71.12 cm ) above the ground to resting on the ground and the difference was significant enough to spontaneous prompt the unaware to ask if the bass had been turned up.
Good luck!
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Old 9th December 2008, 09:00 AM   #26
andrew_87 is offline andrew_87  Italy
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Join Date: Nov 2008
thanks to all for all!!!

i will give you more info!
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