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Murphy's Corner Line Array project

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ppataki

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Another update: the 'sandwich' panels are done!
As you can see in the below pictures, Green Glue has been applied between the panels (2x12mm birch plywood)
There are some panels missing, they will be done a bit later
The next phase will be to put together the back of the speaker, paint it (with this), damp it and mount it on the wall - stay tuned


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ppataki

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A small update after Christmas :)

All the sides are done now. The front panel is not yet glued together - that will be the next step along with the speaker cutout
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ppataki

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We have made some progress today; one of the cabinets now has the cutouts done!

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Next step will be to do the same with the other cabinet too and then some final adjustments after which they will be transported to my garage where the paint job will start

Some additional comments:
The cabinet actually consists of two parts: the back part (two panels + top & bottom) that will be mounted to the wall, and the front part (three panels; I call it the 'shield') that has the cutouts for the speakers.
Doing the painting, installing the drivers, doing the cabling, etc. will all be simpler like this and then finally they will be put together sort of on the wall/in the corner as the finishing touch
More to follow!
 

abdo123

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We have made some progress today; one of the cabinets now has the cutouts done!

View attachment 176291
View attachment 176292

Next step will be to do the same with the other cabinet too and then some final adjustments after which they will be transported to my garage where the paint job will start

Some additional comments:
The cabinet actually consists of two parts: the back part (two panels + top & bottom) that will be mounted to the wall, and the front part (three panels; I call it the 'shield') that has the cutouts for the speakers.
Doing the painting, installing the drivers, doing the cabling, etc. will all be simpler like this and then finally they will be put together sort of on the wall/in the corner as the finishing touch
More to follow!
Looking sweet! Super jealous right now!

You could even (if the technology allows in the future) assign a delay to each driver so you would get a constant beam transducer instead.

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DanielT

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Good work! Impressive. Looking forward to the continuation of your project. As usual, we Hifi nerds like pictures (I dare say, that generalization), so we appreciate that you post nice pictures (as you do).:)

An inspiring thread.

I did not really understand. You mentioned paintjob,but what color? Glossy, matte paint?....aha now I see your link.Cool.They seem to have the potential to become real racers.:)
If I understood right now, that it's the color you were going to have on the speakers, racing green? Maybe it's another project you're working on?

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ppataki

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Thank you @DanielT - I will keep on posting pictures and measurements as well - very very excited to actually hear them :)
The color will be white (with texture)
Something like these:
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ppataki

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Forgot to mention that the reason I chose Raptor coating is that it seems to be able to decrease resonant vibration
I was skeptical about it but then I came across a car like you can see in the above pictures and I knocked the hood....I could totally hear the difference, it was like day and night; the resonant frequency was clearly lower, it sounded like if the hood was damped from the inside with bitumen or equivalent - but it wasn't, it was just the painting that made the difference
So I shall see what it does with a loudspeaker....this is also part of the project :)
(similarly to Green Glue as a constraining layer for the cabinet which I believe was a great idea but again, let's see/hear once the speakers are fully assembled)
 

Wesayso

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You're well on your way of finnishing these! Good job, it looks solid. Hope my next remark isn't too late, it's well meant. ;) Just think of it as a friendly suggestion.
Did you by any chance chamfer those driver holes on the inside? Highly recommended to do so! Well, it is depending slightly on the thickness of that front baffle.
Troels dedicated a page to it for a reason: http://www.troelsgravesen.dk/chamfer.htm
The idea is that the driver needs to be able to vent on the back side. A restriction might cause a tunnel resonance that causes unnecessary wiggles in an impedance plot and potentially a dip/peak there in the frequency curve. It would be there like that for all drivers, making it a potentially strong effect, not easy to EQ out.
Make sure the basket openings on the back have plenty of room to breathe. Unrestricted airflow so to speak.
A 45 degree angle where those openings are can do wonders. A rough wood file can get you there, although a router bit had been easier.
Just chamfer the driver holes and leave the material there where the driver mount screws are.

Here's what I did with my aluminum baffle of just 10 mm thickness...
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ppataki

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Thank you @Wesayso for the tip - unfortunately it is now a bit late so I am afraid I will not be able to incorporate this into the design
Also in my case the distance between drivers is at best 15mm (see picture below) - if I chamfer the cutouts by 45 degrees I am afraid I would lose too much material and the front baffle would become even more fragile
But there are other projects I am doing and I will definitely consider this with those

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Wesayso

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No problem. You can always do the sides if you want to. Every little bit helps.
 
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ppataki

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Paint job done!

First I applied a layer of lacquer coat then a layer of Raptor Epoxy primer:

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Then applied Raptor coating in 2 layers using the roller that they provide:

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I painted both the inside and outside in order for the Raptor to have a better vibration damping effect.

I have made a knock-knock video too:

Now I need to wait 72 hours for the Raptor to fully cure and then the next step will be to prepare the rear part and fix it on the wall
I want to do that before spending time with the fronts since I want to be sure that it fits (if not, we can still do some adjustments before proceeding any further)

A remark about Raptor: it covers everything, literally! There were some imperfections on the surface but it covered all of them perfectly; I cannot find them anymore even if I take a really close look at it. If this project succeeds I am planning to replace my rear speakers with a (truncated or Bessel) line array too and there I will test Raptor without lacquer coating and without the primer. According to their website it can be applied on plywood directly.

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Next update hopefully in the second half of the week
 
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ppataki

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Some further progress has been made

Internal damping was finished (using 400gr/m2 polyester fibre, 2.5cm thick)

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All the drivers are now mounted:
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Cabling has started:
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I have run out of crimp terminals so I will need to wait for the next shipment to arrive
By the end of next week I hope I will be able to send the pictures with these beasts in their final place:)
 

DanielT

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Nice. :)

Curious, you may have mentioned it I do not remember, what did you choose for Ohm on the speakers? And why that choice?

Edit:
But wait now, I think I can see it with the connections. Let others guess, he he.:). ... or maybe hum, I can guess what you were going to do. Tell it instead.
 
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ppataki

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@DanielT
I have mentioned that in the very first post:)

I will use 24 pcs of Dayton Audio ND91-8 drivers in each cabinet. The cabinet will not reach the ceiling (260cm) but it will get close to it (approx. 220cm)
Drivers will be grouped like 6 x 4, meaning four drivers will be wired in series and the six groups will be wired in parallel resulting in an impedance of 5.3 ohm. (4 x 8 = 32 / 6 = 5.3)
 

bigjacko

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Thanks for sharing, looking good! Can I ask how do you connect your terminals to the drivers and how are you going to put the baffle onto the back?
 

audio2design

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if he crosses at 100Hz then this project is pointless because one of the main points of this sort of project is to eliminate the effect of ceiling/floor bounce at all frequencies.

Line arrays don't really work like that, even with ceiling bounce. You start losing the benefit of the line array well above 100Hz and with a sub-array whether you have 1/R or 1/R^2 really does not matter.
 

audio2design

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@ppataki ,

Don't wire them like this,

Drivers will be grouped like 6 x 4, meaning four drivers will be wired in series and the six groups will be wired in parallel resulting in an impedance of 5.3 ohm. (4 x 8 = 32 / 6 = 5.3)

Wire 6 in parallel, then stack the parallel arrangement 4 up. This arrangement is less sensitive to driver electrical parameter variance. You could consider measuring the 24 (or 48) and put them in groups of 6 with the most similar characteristic.
 
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