[Jose R.]

Hi

I am designing a new baffle for my open baffle line arrays - currently I am have 8 Raal ribbons and 8 Scan Illuminators (6.5") on an MDF baffle.  Sound very good but I have bought some B&G Neo 10 drivers to cover about 500Hz to 3000Hz.
I am having an aluminium baffle made, 12mm thich with the option to box the woofers. 

I was thinking of mounting the drivers on the rear of the baffle with rounded cutouts for the B&G's and ribbons.  Mainly for aesthetic reasons but am interested in the possible acoustic impact.

Essentially this could be seen as a shallow horn or a step in the baffle and I would appreciate any advice on whether this would be good or bad. 

Have any of you played around with rear mounting mids or tweeters?  All opinions would be welcome

Regards

Jose

[JohnR]

 

Can you make some test baffles and measure them?

[Jose R.]

Hi John

unfortunately I would not be able to make a test baffle due to the multiple cutouts required and then I would have to use 12mm MDF which would be unsuitable.
This is why I am trying to get opinions from others who may have tried and measured these options before I go ahead with the final design.

Jose

[D OB G]

johnk... on DiyAudio, with his new speakers, the Notes, mounts his Neo tweeters in from the surface, but there is a curved "waveguide" shape instead of an edge, like you describe.  John is an authority!
This would go to aligning the acoustic centres and controlling the dispersion in one go.
I don't know how this would effect the lower freqs., but aliminium is expensive so, as JohnR says, it would be good to play with shapes in mdf, or something, and take polar measurements, before settling on a final shape.
(BTW Briggs in the 50s said it was definitely a compromise  )

David

[Jose R.]

Thanks David

Still doing some research and waiting for some replies.  Sould be an interesting project if things turn out as I hope.

Regards

Jose

[versus rider]

I have mounted my woofers and full range driver behind the baflle that is 54mm thick without any issues. I have just a champher on the baffle edge.

[Jose R.]

Hi

I tried to simulate a shallow wave guide on my existing ribbon array (current arrays shown in the picture) by placing two strips of 50mm wide 12mm thick MDF with the inner edges bevelled at 45 degrees.  I then measured the frequency response at the listening positiom and compared the curves with the "wave guides" on and off.  The curve with the tweeter array flush mounted was smoother.  With the "wave guide" on, there was a dip of about 2dB at 3000Hz and the curve was less smooth.
While this experiment may not quite simulate a shallow wave guide in an otherwise flat baffle, it suggests to me me that I should perhaps go with the more usual practice of mounting the drivers flush on the front of the baffle.

Regards

Jose

[Jose R.]

Hi

I got a reply from Aleksandar at Raal Ribbons regarding the ribbon array mounting and thought it may be of interest.
 
I’m against any beveling. That’s why I did the zig-zag edge at the thinnest face plate possible, to spread the first diffraction in time domain, as the edge has no specific distance from the ribbon.
I could have done a regular, 8mm Aluminum beveled face plate, but it doesn’t work well, as it severely contaminates the impulse response.
 
I tried everything, shallow waveguides included, but it happens to be even worse to move the edge further away from the ribbon opening. Granted, it will decrease the problem in it’s intensity, but it will push the anomaly further down the frequency range, to important regions of the spectrum.
 
My warm recommendation is to flush-mount the ribbon from the front and keep everything as smooth and step-less as possible.

I think I will go for the simple solution and flush mount from the front....

Regards

Jose

[THWO]

Hi Jose

could a sandwich construction be an option for you? I.e. by mounting the drivers onto a MDF-board which itself would be mounted behind the aluminium front?

If you consider making cutouts into the alu-front in a size that the screw holes of the drivers would be covered, it may be a good idea to flush-mount them into the MDF-board.

However, it is my own (not necessarily generally correct) impression / experience that such drivers - except subwoofers - don´t like anything coming into their way when radiating their signals, they may tend to take revenge by coloring the music.

If that should be the case here, too, it might be a good idea to either get the drivers flush mount with the alu-frame itself or to "engrave" (please excuse my poor English) sufficient space into the rear side of the alu-panels so that the remaining thickness covering the drivers will be just some few millimeters.

Focussing on the MDF-board again which sits behind the alu-frame, the drivers may be then mounted either on top of the Panel (flush mounting no longer necessary due to the "engraving" of the alu-frame) or even mounted on an additional distance ring (i.e. MDF 3-6 mm) to bring the drivers as close to the thin alu-frame as possible.

As the drivers, in this imagination, would be mounted on the front side of the MDF-boards, the alu-frame and the MDF-board should be able to be separated again in case of need any repair etc.The most simple way would be to joint both boards by using double-coated sturdy scotch tape (both sides adhesive function) - do you know what I mean? I don´t know the English word for it. Such tapes are used i.e. for fixing carpets on the floor and they are sticky like hell.

Other idea to hold drivers in place ma be to use clamps made of alu or MDF or wood which are fixed to the back side of the alufront a bit firther outside than the diamter of the drivers itself.

Hope I am not writing too complicated...

Best regards from Frankfurt / Germany

Till

[Jose R.]

Hi Till

Thanks for the interesting ideas.
I have decided to go for front mounted flush fit of the various drivers as this will be a conventional solution, supported by the Raal designer who has experimented with different mounting schemes.  I will probably also have a thin (2-3mm) baffle made with cut outs for all the active parts of the drives which I can then fit to the front of the baffle with bolts quite easily.  I will then be able to do measurements of the naked baffle and with the extra front plate to see what effects this has.  removal of the front plate would be easy and will not involve removing drivers etc.  I can then have a fairly simple arrangement allowing me to have a standard look and an aesthetic look 
It will certainly be interesting to listen to and measure the different arrangements.  I will provide some follow-up once I have the baffles done.

Regards

Jose

[THWO]

.
Best success!
It would be great if we could see photos and/or measurements and are hungry for your personal impression...

Reagards
Till