liasom said:
Hi Mike,
The lower (woofer) chamber is 33 litres. The upper is about 6 litres. Neither is very deep - about 3 inches behind the mid and 5 inches behind the woofer. The hole for the midrange is about 3.5 inches wide.
The crossover points will (eventually) be 310Hz and 3100Hz, a 24dB/octave active filter. My first listen was with a cobbled together series/parallel passive, so too much low mid might have been getting to the woofer.
What I hear...maybe hollow is not the right word. There is a peaked quality, where (I assume) certain frequencies are being reinforced by standing waves and re-emitted through the cone.
It's the way every empty box I've ever stuck the driver in prematurely sounds.
I'm sure that if I had bothered to run a sweep, I could have isolated the "resonance". Drivers have been removed to finish the paint job on the baffles. All of this said, things will be different with the active filter (once again I assume).
Traditionally I would first line the box with commercial rubber back carpet tiles (salvaged from a Toronto library). This would usually prove to be the cure, but if not I would add a small amount of polyfil stuffing - well away from the driver.
This may be of some value in determining the height & arrangement of wedges:
http://www.pmerecords.com/Diffusor.cfm
and another with some frequency ~ relationship:
http://www.mhsoft.nl/DiffusorCalculator.html
don't overlook the link to the BBC paper in the latter
http://www.pmerecords.com/Diffusor.cfm
and another with some frequency ~ relationship:
http://www.mhsoft.nl/DiffusorCalculator.html
don't overlook the link to the BBC paper in the latter
Thanks Ed for a great contribution. I saw the BBC paper or had seen the Schroeder design sometime in the past and I've used a room before in a studio with that type of diffuser. To my ear they seemed to work well. Someday I'm going to build a few panels for my house. That calculator you found is great!
Anyhow that idea of the square shapes is in the mix. If you think of anything else post it.
Another paper I've found is from RPG Diffusor Systems, Inc.
http://www.rpginc.com/news/library/tyndall_paper.pdf.
My brain is getting a workout!
Anyhow that idea of the square shapes is in the mix. If you think of anything else post it.
Another paper I've found is from RPG Diffusor Systems, Inc.
http://www.rpginc.com/news/library/tyndall_paper.pdf.
My brain is getting a workout!
I was thinking of its use inside the enclosure as well. My reason for asking was that cutting up hundreds of pieces of mdf would be tedious in the extreme and the benefits not worth the effort, perhaps. However...............flooring insulation comes in 50mm dense sheets. Model airplanes are made of it. Blue foam by Sheffield Insulation in the UK are the largest suppliers I believe and there will be an equivalent in your neck of the woods. This dense foam cuts with a hot wire very quickly and with a good surface. Admittedly it is not lossy, but it does have lots of very tiny "bubbles". It is light and will glue to itself or wood with regular PVA glue. It would be relatively easy and quick to make up some panels to insert inside the enclosure. Just a thought.
SteveT2 said:
Yes, Styrofoam. This is a definite possibility. Might work better than MDF, and certainly easier to cut (I'd still cut it on the table saw). One drawback is that it will add nothing to the overall rigidity of the panels, unlike a solid like MDF.
I used about $1000.00 worth of that stuff to insulate my basement walls. About $22 for a 2' x 8' sheet of 2" thick.
I can often find scraps of it kicking around at work that would be big enough to try out.
My plan is to dive in the first chance I get, with the reasoning that if it doesn't work, I can always either rip it out or add stuffing.
Need to do a few drawings and I'll post my ideas. Hope to get that done before the end of the day.
Short answer on the wedge shapes is that I think a fat cross section (like the B&W design) may be just as effective as the lean one (like the sample wedges John cut). They'd also be less tedious to manufacture and require less gluing.
Short answer on the wedge shapes is that I think a fat cross section (like the B&W design) may be just as effective as the lean one (like the sample wedges John cut). They'd also be less tedious to manufacture and require less gluing.
Since Monday afternoon...hot water heater problem at my home...done with that now.
My progress so far. Did a good deal of research on acoustic treatments like this (unfortunately almost all of it that is available to me is in the context of large acoustic spaces, but some of it is scaleable), created some basic assumptions, completed frequency and wavelength calculations for standing wave modes based on a "golden ratio" box. Good that I didn't get to post Monday because since then I've had a little more time to think. Now I have some remaining work to do on wedge size and shape to maximize acoustic damping using this method.
My progress so far. Did a good deal of research on acoustic treatments like this (unfortunately almost all of it that is available to me is in the context of large acoustic spaces, but some of it is scaleable), created some basic assumptions, completed frequency and wavelength calculations for standing wave modes based on a "golden ratio" box. Good that I didn't get to post Monday because since then I've had a little more time to think. Now I have some remaining work to do on wedge size and shape to maximize acoustic damping using this method.
How about "whispermat" as Zaph suggests:
http://www.zaphaudio.com/blog.html
scroll down to the May 27 entry: cnc...
http://www.zaphaudio.com/blog.html
scroll down to the May 27 entry: cnc...
I've come to this fascinating discussion late but it's made a good evening reading.
Kudos to John for testing the three types of boxes, something not many of us would have taken the time to do.
Returning to the original debate, as far as I can see no one has mentioned the BBC research paper by Dudley Harwood. He tested materials and also came out against solid wood. He put forward the benefits of constrained layer damping (this is the source of using bitumin pads).
The original paper is available as a download here.
Kudos to John for testing the three types of boxes, something not many of us would have taken the time to do.
Returning to the original debate, as far as I can see no one has mentioned the BBC research paper by Dudley Harwood. He tested materials and also came out against solid wood. He put forward the benefits of constrained layer damping (this is the source of using bitumin pads).
The original paper is available as a download here.
Colin said:
We had a practical shootout of sorts with a set of Rogers LS3/5As in house for a couple days... where the Fonkens pretty much disappeared this (particular) pair of LS3/5As was very boxy... that gave us a bit of a boot to get the mFonken out which is roughly the size of an LS3/5A
dave
planet10 said:
Got your plane tickets for the July 27 WE? i could arrange to have the LS3/5As back here
What's this July 27 WE? I'm far too busy with work over 4 to 5 months to take even a Sunday off, let alone go on a foray into the wilds of BC to hear 2 speakers (as attractive as that sounds right now).
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