PMA - 60; New arrayable double 12 and horn.

Chris Burns

Freshman
Nov 13, 2016
63
3
8
Connecticut
Finalizing the plans. Peter looking for a bit more volume, not critical but would be better with the Ciare. I know I can go taller if need be to get a bit more but can I go any wider on the front bafflewithout noticably screwing with the splay testing and comb filter testing you did? I’d really also like to get that horn centered. Not sure how critical you were on these tests so wanted to just ask the question.

Thanks much.


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Peter Morris

Senior
May 8, 2011
1,056
140
63
Australia
You can’t move the horn to the centre unless you make the box wider or reduce the wall angle.

I don’t know how much the array performance is comprised if you do that.

The simple rule for arraying is ¼ wavelength spacing of the drivers centre to centre.

When you look deeper at the problem, the cone does not just radiate from the centre, it radiates from the whole surface. If we had square cones operating as a piston and they were close together then they would couple up to a much high frequency. To get that to work with round cones is difficult because the gap between the drivers on average is too much.

In practice there aren’t too many problems until you go past ½ a wavelength. In this case ½ a wavelength is 486Hz … so we are pushing things – but it seems to work and sounds fine.

The idea behind this box was to build a nice small powerful general purpose 60 degree mid high speaker that could operate from 80Hz up, but design it in such a way that it could be arrayed as two or three boxes a side and have fewer problems than any other general purpose box on the market.

What I did was pushed every thing as close together as I could to minimize these problems. I was thinking of putting a phase plug Nexo style over the 12” drivers, but I don’t think I will gain that much … may be I will try it latter.

If you increase the box size you may need to retune the box to a lower frequency to get a smooth roll off. You don’t want a resonant bump around the port tuning frequency.
 

Chris Burns

Freshman
Nov 13, 2016
63
3
8
Connecticut
Peter, everything else being the same, would widening the front baffle width from your 360mm to 375mm (+7.5mm per side) have any significant detrimental effect on the 25deg/25deg splay cohesion? It’s a comprimise for other factors in my build version of this, however with both LF drivers and HF horn centered on that baffle, I would imagine the negative effects while there due to increased center to center distance, it will be very minor. Everything is a comprimise in this buisness.

Thanks


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Peter Morris

Senior
May 8, 2011
1,056
140
63
Australia
Peter, everything else being the same, would widening the front baffle width from your 360mm to 375mm (+7.5mm per side) have any significant detrimental effect on the 25deg/25deg splay cohesion? It’s a comprimise for other factors in my build version of this, however with both LF drivers and HF horn centered on that baffle, I would imagine the negative effects while there due to increased center to center distance, it will be very minor. Everything is a comprimise in this buisness.

Thanks


Sent from my iPhone
Can't imagine 7.5mm would make any noticeable difference Chris.
 

Chris Burns

Freshman
Nov 13, 2016
63
3
8
Connecticut
Thank You sir. Just wanted to confirm. My next post will be that of the build. Pretty excited to get this going. Spent most of today tweaking and optimizing (hence the mm micrometer question). Drivers and horns are in for two cabs, picking up the BB tomorrow. Once the first is done and tested, second third and fourth to go.

The other project I mentioned, is delayed until late Spring as I will be back out in the friendly skies again for a while.