A not so DIY line array

P

Peter Morris

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May 8, 2011
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I have started work on a small but extremely high quality line-array. I got sick of manufacturers say no you can't use your Powersoft amplifiers and Lake processors, you have to use our special (re-badged and inflated priced) amplifiers. ... so I decided to build my own.

Its probably beyond what I would call a DIY project but I though some people may be interested.

Here is a picture of my rough experimental test box and the most stunning impulse responses I have ever seen. line array.jpg
 

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Peter van Gils said:
Beyma TPL, mmm. I like the sound of ribbon drivers (I own several Stage Accompany cabinets with the SA8535). Nice sound, not so loud.

Do you think the distance between the drivers can be short enough to prevent comb filtering?
Click to expand...

Yes its a TPL200H ... these are not ribbon drivers like the Stage Accompany, they are air motion transformers. The operating principle is different. The displacement of the ribbon is the greatest in the centre and fixed at the ends. The displacement of the AMT diaphragm is the same over its entire length making it even more suited to line array applications.

Yes I think the distance between the drivers will be fine especially given how the ATM works and the phase plug used on the 8".

Horizontally to minimize problems I'm using a high slope FIR crossover. Its a compromise between making the design symmetrical with narrowing MF directivity ... and ... a non-symmetrical design with almost perfect horizontal directivity - the FIR brick wall crossover trick seems to work - its measures and sounds excellent both on and off the horizontal axis. FWIW this is the approach Martin Audio have taken with the MLA.

The use of a high slope FIR also allows a low-ish crossover frequency between the HF and MF driver further minimising the distance issue you mentioned.
 
Helge Dr. Bentsen said:
I like the idea :)

Did you consider using a horn loaded LF like on the DIY60/90?


Sent from my iPhone
Click to expand...

Not really - my application is theatre so I wanted a small compact array with extreme sound quality. To get a horn to work at the low frequency it needs to be big.

If you put a horn exit (or a driver) either side of the HF driver such as the DIY 60/90 the horizontal pattern becomes too narrow in the mid frequencies.

If you do that then you have to have some of the mid frequencies entering through the HF horn mouth or make the HF horn quite narrow. Having the mid frequencies enter through the HF horn mouth is tricky ... and difficult to build, making the horn mouth narrow compromises its directivity.

Using a AMT HF driver should give me the acoustic performance I wanted and minimize the interactions between each of the array elements ... but they are not that loud - 104 dB/W/m 120 watts AES 240 programme.

http://www.beyma.com/uploads/descargas/1355215071.pdf
https://www.supersonic.se/dokument/tpl-150 BEYMA_esen.pdf
 
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Peter Morris said:
Yes its a TPL200H ... these are not ribbon drivers like the Stage Accompany, they are air motion transformers. The operating principle is different. The displacement of the ribbon is the greatest in the centre and fixed at the ends. The displacement of the AMT diaphragm is the same over its entire length making it even more suited to line array applications.
Click to expand...
Yes, the operating principle is different, though the advantages and disadvantages are similar: they (can) have good frequency response, low distortion and good impulse response. There is low sensitivity and low power handling for both on the downside.
My experience (in theatres by the way): 1 cabinet sounds stunning, multiple gives you lobing. I'm using conventional tops with the upper top stacked upside down on the bottom top to get the ribbon drivers as close to each other as possible. I still hear the lobing when walking up the tribune. I need multiple cabinets because 1 cabinet (12" front loaded) does not provide sufficient output.
Your line array top should be better at coupling of multiple cabinets: due to the AMT and the distance between the drivers.

Funny thing is: I'm currently building your DIY mid/high design with 90x50 horn because I like the concept of having a single point source. Let's see what this brings... ;-)
 
Finally – the Line Array project is almost finished, and the initial results are fantastic ... … the best sounding PA speaker I have ever heard :razz:
 

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Peter Morris said:
Finally – the Line Array project is almost finished, and the initial results are fantastic ... … the best sounding PA speaker I have ever heard :razz:
Click to expand...

I have to tip my hat to your design / fabrication skills. That must've been a TON of hours put into those.
 
Josh Ricci said:
I have to tip my hat to your design / fabrication skills. That must've been a TON of hours put into those.
Click to expand...

The first trick with this project was to source suitable fly-ware while getting all the components to physically and acoustically match.

As all the boxes have to accurately rig together the boxes were cut out on a CNC multi-head router and all the holes pre drilled … then they were more or less glued and folded up.

This make construction quite quick … but doing everything 16 times over and over gets a bit painful.

… the next part of the project is to build and test the bumper / rigging :-)
 
Peter Morris said:
The first trick with this project was to source suitable fly-ware while getting all the components to physically and acoustically match.

As all the boxes have to accurately rig together the boxes were cut out on a CNC multi-head router and all the holes pre drilled … then they were more or less glued and folded up.

This make construction quite quick … but doing everything 16 times over and over gets a bit painful.

… the next part of the project is to build and test the bumper / rigging :-)
Click to expand...

No doubt...1 or 2 boxes is fun. That wears off quickly by box #11.

I assume you use Inventor, Solidworks or similar to model and design the finished assembly prior to building?
 
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