Troels' PMS (multilayer assembly) build thread

Hi all,

I am new to the DIYaudio-forum and would like to introduce myself with this thread.

After having built my first DIY-Loudspeakers with multiple layers of MDF (see thread on homecinema-fr.com in FRENCH ) I rapidly wanted to validate the assembly method with threaded rods on a bigger loudspeaker.

At this moment the loudspeakers are built up, run in (around 250 hours I guess) and waiting for their paint-job before getting a new home in my parents living-room.

They were actually a present for my father's birthday on September 8.

I decided on going with a pair of 3-way loudspeakers "inspirated" by the PMS-project from Troels Gravesen using SEAS Prestige speakers.

Have a look at his PMS-project here.

I want to thank Mr. Gravesen for putting his excellent work online, making it available to all of us.

I started designing the cabinets on my return from holidays on August 2 and it took me about 15 hours to complete (i.e. 3 "night shifts" beside my everyday daylight job), machining has been done on August 6 & 7.

The loudspeakers were put in service one month later, the day before his birthday, having taken care to start running in all the speakers on the first completed cabinet. Mono sound in the workshop...

As for the first set of speakers (see link above) the cabinets are designed of multiple layers of MDF (exclusively CNC-machined) and assembled with the help of threaded rods.

When realizing the SA2K-Clone I had noticed several points that could be optimized referring to both machining and assembly.

Modifications for the PMS concerned milling cutter types, assembly tolerances on the front-plates, anticipation of dilatation and some more.

The speakers used are CA22RNX, MCA15RLY and the well-known T27TFFC, the cross-over will be as per Mr. Gravesen's layout.

All cross-over parts have been chosen with a fair quality in order to keep costs in the budget... audyn cap KP-QS 630V, IT air core 14/10 and 10/10. Only RC and RLC are fitted with bi-polars and "cheap" stuff.

Enough talking, here are the first pics:

View on the working CNC-machine
[IMGDEAD]http://img109.imageshack.us/img109/2164/12082009428.jpg[/IMGDEAD]

Giving you an idea of the layout plan
[IMGDEAD]http://img405.imageshack.us/img405/8450/12082009430.jpg[/IMGDEAD]

The scrapings after machining one board (3 bins of 70 liters in total)
[IMGDEAD]http://img341.imageshack.us/img341/5512/12082009431.jpg[/IMGDEAD]

MDF-Fishbones
[IMGDEAD]http://img101.imageshack.us/img101/87/12082009434.jpg[/IMGDEAD]

Who said "sexy" ?
[IMGDEAD]http://img340.imageshack.us/img340/656/16082009482.jpg[/IMGDEAD]

First box full of puzzle-pieces
[IMGDEAD]http://img209.imageshack.us/img209/6645/12082009432.jpg[/IMGDEAD]

Another view
[IMGDEAD]http://img209.imageshack.us/img209/5813/12082009429.jpg[/IMGDEAD]

All of them... which will have to get brushed to get all the dust out
[IMGDEAD]http://img405.imageshack.us/img405/3893/13082009435.jpg[/IMGDEAD]

Although the pic is dark you can see that the central slot is totally clogged
[IMGDEAD]http://img341.imageshack.us/img341/9374/13082009438.jpg[/IMGDEAD]
 
Some more pics

Bits 'n pieces...every piece gets some brushing and a quick grind with abrasive paper..getting tanned at the same time
[IMGDEAD]http://img209.imageshack.us/img209/2299/14082009440.jpg[/IMGDEAD]

[IMGDEAD]http://img340.imageshack.us/img340/8200/14082009441.jpg[/IMGDEAD]

[IMGDEAD]http://img522.imageshack.us/img522/8200/14082009441.jpg[/IMGDEAD]

What it looks like once cleaned up
[IMGDEAD]http://img209.imageshack.us/img209/2767/13082009439.jpg[/IMGDEAD]
 
Here we go, having a closer look at the different parts.

First the floor-stand assembly.

Connecting plates from speaker bottom-plate to the floor plate , giving the PMS a 5° tilt backwards
[IMGDEAD]http://img301.imageshack.us/img301/2351/15082009466.jpg[/IMGDEAD]

Speakers bottom-plate with grooves for the connecting plates above and holes for the vents
[IMGDEAD]http://img4.imageshack.us/img4/2929/15082009468.jpg[/IMGDEAD]

Floor-plate with grooves for connecting plates
[IMGDEAD]http://img405.imageshack.us/img405/3711/15082009472.jpg[/IMGDEAD]

Dry assembled bottom-plate of the speaker
[IMGDEAD]http://img101.imageshack.us/img101/7132/15082009469.jpg[/IMGDEAD]

The whole floor-stand assembly
[IMGDEAD]http://img22.imageshack.us/img22/8972/14082009443.jpg[/IMGDEAD]

[IMGDEAD]http://img101.imageshack.us/img101/3925/14082009444.jpg[/IMGDEAD]

[IMGDEAD]http://img109.imageshack.us/img109/7233/14082009445.jpg[/IMGDEAD]

More to come...
 
Going on with the other parts.

The Front-plate which will receive the midrange-driver MCA15RLY and the tweeter T27TFFC. Design goals were flush-mounting both of the drivers and backside ventilation of the mid.

Front-side view
[IMGDEAD]http://img301.imageshack.us/img301/8481/15082009478.jpg[/IMGDEAD]

Back-side view
[IMGDEAD]http://img195.imageshack.us/img195/3973/15082009479.jpg[/IMGDEAD]

Same story for the woofer CA22RNX
[IMGDEAD]http://img267.imageshack.us/img267/8746/15082009476.jpg[/IMGDEAD]

and the back-side view
[IMGDEAD]http://img205.imageshack.us/img205/8746/15082009476.jpg[/IMGDEAD]
 
Construction layout of the speakers is, as mentioned in the header, piling up multiple layer of MDF, commonly called trans-lamination/stack-lamination as stated by Brett earlier in this thread.

In order to create the volume for the midrange and to strengthen the speaker construction certain parts are designed so that they cover the whole periphery of the speaker, actually like a (more or less) full slice.

Others parts, in order to optimize raw material consumption (see layout plan in the very first pictures of this thread) are designed as 1/2 or 1/4. The pics will show it better than words.

The top layer sealing the cabinet
[IMGDEAD]http://img101.imageshack.us/img101/9633/15082009474.jpg[/IMGDEAD]

The layer used to seal the volume for the mid, 2 per cabinet, i.e. upper and lower enclosure.
[IMGDEAD]http://img405.imageshack.us/img405/7055/15082009475.jpg[/IMGDEAD]

The layer used to create the volume for the mid. Design is "rounded" in order to minimize standing waves. Only the layers forming the upper and lower enclosure(see above) have parallel faces, making it 2 compared to 6 in a more classic square cabinet.On top of the picture you can clearly see the notch for the insertion of the front-plate.
[IMGDEAD]http://img341.imageshack.us/img341/6469/15082009467.jpg[/IMGDEAD]
There's a total of 10 of those layers per cabinet, 7 to form the enclosure for the mid, 2 behind the woofer and finally 1 in the upper part of the cabinet used for bracing.

The layer bracing the woofer on the upper and lower side. 2 used per cabinet, the LPF will be fixed to the lower one.
[IMGDEAD]http://img301.imageshack.us/img301/4962/15082009473.jpg[/IMGDEAD]

That's it for the peripheral parts.
 
Let's finish the floor-stand:

The bottom-plate with 2 alloy brackets that will help to securely fix the floor-plate assembly to it
[IMGDEAD]http://img341.imageshack.us/img341/656/16082009482.jpg[/IMGDEAD]

[IMGDEAD]http://img522.imageshack.us/img522/4590/16082009485.jpg[/IMGDEAD]

Connecting plates in the grooves of the bottom-plate, hold in place by 4 x 4mm screws
[IMGDEAD]http://img403.imageshack.us/img403/9475/16082009487.jpg[/IMGDEAD]

[IMGDEAD]http://img694.imageshack.us/img694/3864/16082009488.jpg[/IMGDEAD]

The finished assembly, grooves filled with a mixture of glue and woodsaw (had some left actually ;) ), alloy brackets in place
[IMGDEAD]http://img22.imageshack.us/img22/8271/20082009517.jpg[/IMGDEAD]

First binding post
[IMGDEAD]http://img522.imageshack.us/img522/9199/20082009518.jpg[/IMGDEAD]

And both of them
[IMGDEAD]http://img4.imageshack.us/img4/4996/20082009519.jpg[/IMGDEAD]
 
Wow, really amazing. A lot of planning!


How thick is the MDF sheet, 25mm? Do you worry about the dimensional stability of the MDF at all?

Yes, MDF is 25mm is this case but not restrictive at all, thicker plates can be used. Dimensional stability has been taken into account, as an example I might quote "front-plate adjustments" ...
 
Installation of the cross-over components on the perspex boards. Holes are drilled to hold the components in place with zip ties.

Placement and orientation of the coils are as per the observation of Troels on his website. Have a look here:Placement of coils in crossover networks:

Figure 6 applies for the central coil to the 2 outer ones and figure 1 for the outer ones to each other.
[IMGDEAD]http://img403.imageshack.us/img403/3104/22082009531.jpg[/IMGDEAD]

[IMGDEAD]http://img260.imageshack.us/img260/1751/22082009532.jpg[/IMGDEAD]

[IMGDEAD]http://img4.imageshack.us/img4/6581/22082009534.jpg[/IMGDEAD]

Cutting the perspex board and drilling the holes
[IMGDEAD]http://img694.imageshack.us/img694/7099/22082009535.jpg[/IMGDEAD]

Holes drilled
[IMGDEAD]http://img403.imageshack.us/img403/5086/22082009536.jpg[/IMGDEAD]

Some parts installed
[IMGDEAD]http://img205.imageshack.us/img205/1431/22082009537.jpg[/IMGDEAD]

All of them installed
[IMGDEAD]http://img4.imageshack.us/img4/6579/22082009538.jpg[/IMGDEAD]
 
Every cleaned up (more or less) for soldering the cross-overs
[IMGHTTPDEAD]http://img267.imageshack.us/img267/1338/22082009539.jpg[/IMGHTTPDEAD]

First one done
[IMGHTTPDEAD]http://img22.imageshack.us/img22/4566/22082009540.jpg[/IMGHTTPDEAD]

Some hot melt glue helps holding wires and parts in place
[IMGHTTPDEAD]http://img694.imageshack.us/img694/2171/22082009543.jpg[/IMGHTTPDEAD]

[IMGHTTPDEAD]http://img403.imageshack.us/img403/7096/22082009544.jpg[/IMGHTTPDEAD]

Finished cross-over
[IMGHTTPDEAD]http://img267.imageshack.us/img267/9598/22082009541.jpg[/IMGHTTPDEAD]

[IMGHTTPDEAD]http://img22.imageshack.us/img22/5362/22082009542.jpg[/IMGHTTPDEAD]

[IMGHTTPDEAD]http://img522.imageshack.us/img522/2091/22082009584.jpg[/IMGHTTPDEAD]

The other one. Looks just the same, besides the white colored tape (no particular reason, I only ran out of black one)

[IMGHTTPDEAD]http://img403.imageshack.us/img403/2305/22082009583.jpg[/IMGHTTPDEAD]
 
Waveflex, it looks like you're doing wonderful work. Seems like pre-stressed concrete in a way once you tighten down the threaded rod?

But it appears you have weakened the loudspeaker where it needed strength the most: at the baffle openings. Perhaps there is bracing to compensate? (I understand that you were trying to improve airflow.)
(The same might apply to removing material from the center of the angled legs?)
 
Waveflex, it looks like you're doing wonderful work. Seems like pre-stressed concrete in a way once you tighten down the threaded rod?

But it appears you have weakened the loudspeaker where it needed strength the most: at the baffle openings. Perhaps there is bracing to compensate? (I understand that you were trying to improve airflow.)
(The same might apply to removing material from the center of the angled legs?)

Thanks for your appreciation of the project Tosh.

I will post the assembly of the different parts shortly, as mentioned earlier in this post there's indeed some bracing. Honestly airflow was not really an issue as far as the legs are concerned...