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-   -   Unusual design for desktops - The Wedge (http://www.diyaudio.com/forums/full-range/165604-unusual-design-desktops-wedge.html)

Dr_EM 22nd April 2010 09:26 PM

Unusual design for desktops - The Wedge
 
Here's a design I'm considering for use in a Uni bedroom. The concept is a Monacor SPH-30X in a ~2L ported enclosure. This doesn't give massive bass extension, but I have heard this confguration and it gives a suprisingly good rendering of most bass lines.

http://img685.imageshack.us/img685/8...osureports.png

As these speakers will be on a desktop, it's nearly unavoidable they will be near a wall (in my case they will have to be right next to it) Hence, the enclosure is made very flat so as to gain baffle reflections from the whole wall, a bit like if the speaker were mounted in-wall (in theory). It should not require baffle step correction. The ports are mounted on the thin edges at the bottom, placing them very near to the wall, with the intention of gaining boundary reinforcement from the wall as well as the desk.

http://img203.imageshack.us/img203/3...edgebaffle.png

(image shows effect of baffle if compensated electrically. the driver is located to reduce frequency anomalies and make them complimentary to the driver's natural response where possible.)

The Monacor driver is very shallow as it uses a small neodynium motor. It is rather efficient and works in a small box volume, essential for such a flat design. It has a nasty looking peak at 10KHz, but this generally sounds ok slightly off axis. I'd probably build the front, back, top and bottom from 9mm plywood, but heavily braced. The edges would likely be made from timber planks, 12-18mm thick. The sloped enclosure both angles the driver toward the listener and reduces parallel internal walls.

http://img227.imageshack.us/img227/1...ewedgetest.png
http://img406.imageshack.us/img406/9...ewedgecrop.png

I'd probably apply a roundover along the left and right edges, but it's hard to show on Sketchup.


I have concerns with this design (aside from the, imo, unappealing aesthetic!). The driver rear side is placed very near the back wall, how concerned should one be about reflections back through the light cone? What are good measures to avoid smearing the sound; acoustic foam behind the driver? The Edge gives a 'F2' frequency at 441Hz, is the enclosure thin enough to take advantage of the wall reinforcement with this in mind? I would assume so myself, the wavelength at this frequency is 780mm and the enclosure thickness is just 74mm at most, but this isn't something I'm experienced with. Would there be more leakage into a room behind these due to thier close proximity to the wall, or does it make no difference? They don't exactly pound out bass so I'm guessing not.

Any input appreciated!

preiter 22nd April 2010 09:41 PM

It there going to be a computer on the desk? If so, are you worried about the monitor being in front of the speaker or is it a very wide desk?

Dr_EM 23rd April 2010 12:12 PM

A good point! I only have a photo of the desk to work from, but there are some CDs on it, which will be 120cm. I'd say there's enough room for the pair and my 17" non-widescreen monitor. For a lot of people that could be an issue, but in this case I have a rather broad desk and narrow monitor. At worst, the bass-port end would sit just slightly behind the monitor, which shouldn't be an issue.


Any other input on this design? I actually have one 4ohm SPH-30X driver, so could try it out if it is likely to be successful?

GM 23rd April 2010 04:54 PM

FWIW, making the baffle proper just big enough to mount the driver and feathering (slanting) the top and sides of the baffle is both aesthetically and acoustically superior if you have the room and IME using slit vent terminations on one or both of the sides is superior overall to 1 pi loading unless the response is rolled off down low.

I've yet to try it on desktop speakers, but the MLTLs I've done for tiny room/whatever apps have all been crowd pleasers.

GM

Dr_EM 23rd April 2010 06:01 PM

1 Attachment(s)
Thanks for your input! I think I know what you mean and I can certainly see how that would be better. I doubt I have the building skills to do it in practise though, annoyingly. I've been mulling over how to even do the single slope on the front with my tools!

The multiple vents idea is interesting. The intention of using many smaller vents distributed around the enclosure is to get more effective boundary reinforcement? I'm picturing vents a bit like those used in the Fonken designs on each side of the enclosure. I may be able to execute this if it is a worthwhile enhancement. The porting I had planned was going to be drilled into solid wood and act as corner bracing too (attached).

Any thoughts on the general consequences of such a flat design? It goes against my instincts to have a wall so near the rear of the driver but can it be done without audible problems? I guess many rear horn designs have walls close behind the driver.

Dr_EM 29th April 2010 07:18 PM

1 Attachment(s)
I had to re-think my port as it wouldn't physically fit on the side once the thickness of the front and back baffle were considered :o

I attach a model showing it with 3x13mm ports. I've moved them more towards the middle as I believe it's bad to have the internal port terminus too close to any internal surface, and in the original it'd be very near the bottom. As it is, they are still quite close to the rear panel, should I try to move them again? I could possibly drill them in at a slight angle to keep them away more.

I've tried to keep the bracing to the golden ratio, but only a few are in reality. Should it be sufficient? You're seeing 9mm plywood and 18mm solid timber in this model. With all the bracing, port and driver volumes taken away we arrive at about the 1.95L required volume. I'd plan to stuff along the bottom section, mabye the top too, and heavily at the port end of the enclosure (though not in front of the ports naturally!). I think I'll need heavy acoustic foam behind the driver and mabye on the rear side of the front baffle too. Thick felt may also be us some use, just to line things?

Overall, this will be difficult to build, due to the small sizes of many pieces and the sloping front. Any input appreciated! Perhaps it's a complete non-starter for reasons I may have overlooked? I don't know, it seems it should work technically, but it 'looks' wrong!

chrisb 29th April 2010 07:48 PM

Dr EM - if you reconfigured the ports as slot(s), they could probably constitute part of the bracing

speakrsrfun 29th April 2010 08:00 PM

I was just going to say the same thing Chris. Also with slot loading the ports you'd get far more rigid cabinet walls. I say slot load them to the thin side and near the bottom of the wedge. As Chris has already pointed out the slot could be incorporated into part of the bracing and will also provide much less port noise than 3 smaller diameter round ports....

Dr_EM 29th April 2010 09:16 PM

1 Attachment(s)
Hmm, I'm finding it hard to envisage exactly what you mean. I'm not sure how clear it is on my model but those 3 ports are drilled into a solid wooden block which will act as some degree of bracing. I couldn't reduce port noise without eating into more internal volume? I guess the slot is a little more volumetrically efficient though in an angular design.

I've drawn what I think you're suggesting, but am probably wrong! That is a larger port incidently, it was just clearer to show this way. I think this type of port would be quite difficult for me to build as it'd involve having a broad slanted profile bit of timber/board. I don't think it's exactly what you're suggesting though anyhow.

Thanks for your input!

chrisb 29th April 2010 09:56 PM

Quote:

Originally Posted by Dr.EM (http://www.diyaudio.com/forums/full-range/165604-unusual-design-desktops-wedge-post2170433.html#post2170433)
Hmm, I'm finding it hard to envisage exactly what you mean. I'm not sure how clear it is on my model but those 3 ports are drilled into a solid wooden block which will act as some degree of bracing. I couldn't reduce port noise without eating into more internal volume? I guess the slot is a little more volumetrically efficient though in an angular design.

I've drawn what I think you're suggesting, but am probably wrong! That is a larger port incidently, it was just clearer to show this way. I think this type of port would be quite difficult for me to build as it'd involve having a broad slanted profile bit of timber/board. I don't think it's exactly what you're suggesting though anyhow.

Thanks for your input!


For an idea as to how to incorporate slot port(s) into the cabinet bracing scheme , take a look at any of the Fonken-esque enclosure designs at

Meet the Fonkens


FWIW, I'd imagine that the narrow end of your contemplated wedge design is not where you'd need the most bracing, so the port(s) could be accomplished with simple small panel(s), and full width braces might be overkill.


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