The cheapest PA system

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A

andrew_87

Member
Joined 2008
Hi guys! :)
i'm here to show you my new project: a PA system with a super performance/cost quotient.

target:
- f. response: 45hz(f3) - 16000hz circa
- hi max spl (near 140dB)
- stack use (0.5phi)
- low cost


after some ideas i have realised that to contain cost i have to create a 2way system:

- low frequency: 45hz to 500hz (if it is possible highest, like 800hz but i will test it)
- hi frequency: 500hz (800hz)to the highest possible frequency
- eventually piezo tweeters

to have a very high SPL i decide to use horns: frontloaded horn is probably impossible (due to freq. range), so i will project a rearloaded horn, i don't really like rearhorns but in this case i will use! :)

the driver that, in my opinion, has the best performance/cost quotient is the Skytronic 902.442:

http://export.skytronic.com/product/product.php?s=902.442

a cheap 12" whit big voice coil (100mm) and good t&s for a horn.


Here is the project using HornResp:

An externally hosted image should be here but it was not working when we last tested it.



and here is the project using AJhorn:

An externally hosted image should be here but it was not working when we last tested it.



GOOD! (in my opinion) :D


i would create 4 scoopbin, so i can create a stack and work in 0.5phi... probably i can get 140dB whit only 1.2KW from this bass system... :bigeyes:



for the high frequency i probably use this compression driver (but i don't know if they can go to 500hz):

http://www.usblaster.com/Products/DJ ⁄ Pro Audio/Speakers PA/Compression Horn Drivers//USB 387

or this:

http://www.usblaster.com/Products/DJ ⁄ Pro Audio/Speakers PA/Compression Horn Drivers/USB 384

(probably the first)

in my opinion i need 4 compression driver with few watts: so i can improve the durability of the system.


what do you think about this crazy project?
:D :D :D :D
 
H

HK26147

Member
Joined 2008
My opinion - though you may not not want to hear it is:
A 2 way PA with a clean output of 140db is a lofty goal. I won't say it's impossible, but you want it cheap as well?
I am unfamiliar with those drivers you mentioned, nor have I seen any feedback on them... Based upon the pdf specs:
The 12" driver has only a 4mm excursion - Excursion limited and Insufficient to generate that sort of SPL before mecahnical damage or thermal failure, I'm guessing.
It's been my experience that a PA made from cheapest parts can not be made to sound good, and will not be very durable and robust.
There is a huge sonic difference in a PA made with cheap parts and one made with name brand drivers.
You pay a lot of money for a driver like a 2206 or a 2226, but after over 8 years and thousands of watts they still sound better than new OEM drivers.
I repair drivers and so I would rather repair a used/damaged ( cone tear etc ) JBL then buy a new OEM despite price.
 
H

HK26147

Member
Joined 2008
Forum member Davygrvy built 6 horns each with an Eminence HL10 ( Total Driver cost $780 ). These horns formed a fairly small stack.
And when given enough power produced painful SPL.
I used to set up a parade float sound system myself, and I'm guessing his stack would fit your carnival wagon system.
But not as a 2 way.
 
A

andrew_87

Member
Joined 2008
HK26147 said:
My opinion - though you may not not want to hear it is:
A 2 way PA with a clean output of 140db is a lofty goal. I won't say it's impossible, but you want it cheap as well?
I am unfamiliar with those drivers you mentioned, nor have I seen any feedback on them... Based upon the pdf specs:
The 12" driver has only a 4mm excursion - Excursion limited and Insufficient to generate that sort of SPL before mecahnical damage or thermal failure, I'm guessing.
It's been my experience that a PA made from cheapest parts can not be made to sound good, and will not be very durable and robust.
There is a huge sonic difference in a PA made with cheap parts and one made with name brand drivers.
You pay a lot of money for a driver like a 2206 or a 2226, but after over 8 years and thousands of watts they still sound better than new OEM drivers.
I repair drivers and so I would rather repair a used/damaged ( cone tear etc ) JBL then buy a new OEM despite price.
Click to expand...

my metod to have an approx of the max thoerical output,

An externally hosted image should be here but it was not working when we last tested it.



i use it to note the difference between different thorical project...
isn't correct but for approx the difference between project is good...

:)
 
H

HK26147

Member
Joined 2008
Does that 1st simulation graph you just posted assume a no Xmax limit of 99mm?
The prediction of the 2nd graph does not seem reasonable to me with a 4mm Xmax driver that will probably start to experience thermal compression @ 1/10 power and will have 2.5db loss @ 1/2 power, as typical for a pro driver
 
A

andrew_87

Member
Joined 2008
HK26147 said:
Forum member Davygrvy built 6 horns each with an Eminence HL10 ( Total Driver cost $780 ). These horns formed a fairly small stack.
And when given enough power produced painful SPL.
I used to set up a parade float sound system myself, and I'm guessing his stack would fit your carnival wagon system.
But not as a 2 way.
Click to expand...


thanks!
:)

do you have a photo?? :)

the 2way system is a too bad idea?
:(
 
A

andrew_87

Member
Joined 2008
HK26147 said:
Does that simulation graph you just posted assume a no Xmax limit of 99mm?
Click to expand...



andrew_87 said:


my metod to have an approx of the max thoerical output,

An externally hosted image should be here but it was not working when we last tested it.



i use it to note the difference between different thorical project...
isn't correct but for approx the difference between project is good...

:)
Click to expand...



no scientist thoery... only an idea...
:)
 
H

HK26147

Member
Joined 2008
the 2way system is a too bad idea?
Click to expand...

I have yet to hear a 2way PA that meets your goals, or an individual horn driver or horn/cab that would give a good response over 5 octaves for a high SPL PA.
Realistically I try to give each PA driver section a bandpass of approx 3 octaves, so each section can be optimized for it's bandpass, and any high frequency anomalies from each horn are filtered out electronically.

I don't have a pic of David's sub stack, but if you msg him, I'm sure he would sent you the couple I saw. I think his stack was up for sale.
 
davygrvy

davygrvy

Member
Joined 2007
Here are a couple pics of my BFM AutoTuba (16" wide) sixpack.

47b8d929b3127cce985496367d4200000016108AbtGzdozcNF


An externally hosted image should be here but it was not working when we last tested it.


and the response chart

They calculate to 134dB(SPL) @ 40Hz in half space at 300W input each. I chose to make six little horns to run as a group due to space restrictions. Six HL10C drivers in much bigger horns will of coarse be more efficient and deeper, but this was to solve a space problem and compromised on using more drivers, thus more power, to achieve the goal.

I don't think it is realistic to do a loud full-range system as a 2-way. Even 3-way takes compromises for beamy midbass drivers run too high.
 
A

andrew_87

Member
Joined 2008
@ davygrvy:

thank you for the info! :spin: :wiz:

good project the autotuba of BFM, is a phi/8 horn and in a stack can sound very smooth and goes low...

my initial project was developed to reduce costs:
- max 4 woofer--> 0.5phi design
- max 4driver (in particoular i find this driver with a low low cost! [circa 30€])
- eventually piezo...

to extend the frequency of the woofer, enought for use the driver, i choosed a rearloaded bass horn: 40hz * 2^4 = 640hz (4octaves)
mid horn: 325hz (circa) * 2^4 = 5600hz

so:

12": 40hz to 500hz circa
mid driver: 500hz to 5000hz circa
piezo: 5000hz to 20000hz

i have choose 4 octaves because i readed that use horns for 3 octaves over the fb of the horn is wonderful for HIFi, 4octaves is for a compromise and 5octaves is not good!

but i have to test the driver and the woofer...
if they are **** I can create a system like yourse...

:)
 
H

HK26147

Member
Joined 2008
12": 40hz to 500hz circa
mid driver: 500hz to 5000hz circa
piezo: 5000hz to 20000hz
Click to expand...

So it isn't really a 2 way...
IHMO: If you try to driver that compression driver hard it will blow quickly.
That compression driver strikes me as a cheap knockoff of similar screw-on drivers from Eminence etc.
It doesn't have a published Fs, nor a graph of frequency response to know how it performs near it's Fs.
And it's spelled KAPTON, not CAPTON ( that to me is a red flag when a manufacturer doesn't provide performance measurement and can't proofread it's copy )
Even with an active xover with an aggressive slope rate (48db) I would not attempt a 500hz xover and then drive it as hard as you intend.

As far as the use of piezo: The members of the BF forum ( David just mentioned ) use arrays of piezos. For the most part they find they work fine, with accepted limitations...
It takes a bunch of them ( dozens ). They need EQ. They should be limited to 27V max for protection. They need to be implemented with stability resistors to keep amps from oscillation. To also protect them and get the most SPL out of them, they need to have a xover ( regardless of sales hype ).
SEE DIYAUDIO wiki on this:
Those individuals who really require high SPL ( on the level you desire ) found piezos unacceptable and switched to compression drivers ( BMS drivers mostly ).
Things to consider...
Syd
 
A

andrew_87

Member
Joined 2008
HK26147 said:


So it isn't really a 2 way...
IHMO: If you try to driver that compression driver hard it will blow quickly.
That compression driver strikes me as a cheap knockoff of similar screw-on drivers from Eminence etc.
It doesn't have a published Fs, nor a graph of frequency response to know how it performs near it's Fs.
And it's spelled KAPTON, not CAPTON ( that to me is a red flag when a manufacturer doesn't provide performance measurement and can't proofread it's copy )
Even with an active xover with an aggressive slope rate (48db) I would not attempt a 500hz xover and then drive it as hard as you intend.

As far as the use of piezo: The members of the BF forum ( David just mentioned ) use arrays of piezos. For the most part they find they work fine, with accepted limitations...
It takes a bunch of them ( dozens ). They need EQ. They should be limited to 27V max for protection. They need to be implemented with stability resistors to keep amps from oscillation. To also protect them and get the most SPL out of them, they need to have a xover ( regardless of sales hype ).
SEE DIYAUDIO wiki on this:
Those individuals who really require high SPL ( on the level you desire ) found piezos unacceptable and switched to compression drivers ( BMS drivers mostly ).
Things to consider...
Syd
Click to expand...


yes, the driver is an unknown quantity... probably i will use some 6" or some 8" horn loaded for the mid...
but i will take one driver, i will analyze the impedence, i will crox to 500hz... sound... i will try if it broke down or not ;)
it's cheap, no problem... :)

yes piezos has limits but also advantage like, manly, no power loss... in particoular an array of piezos, lots of time, could help... i know that they need a good EQ and a specific filter but, fortunately, i haven't problems in it... :)
 
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