I tend to make the midrange chamber rear wall never parallel to the baffle to negate any reflection. I also tend to make it deeper and less wide. If possible, multiple sealed chambers with an aperiodic orifice between them really helps in the midrange.
Some thoughts on structural damping.
When I built my textreme (TXT) system, the mid/tweeter box was well braced, with ¾ inch plywood walls, and a double layer baffle. As an afterthought, I added two layers of 80 mil Noico butyl rubber damping material to all interior walls. I did not think it would do much good, but I had it on hand, so I used it. The result was a very low signature cabinet, both from a measurement standpoint and subjectively.
Later, I followed @augerpro and his cabinet resonance research and thread. I began to consider if that butyl rubber material might be doing more than I thought.
My latest high-end project (Purifi midrange + Satori waveguide tweeter) used a dedicated enclosure for the midrange. All 6 walls are double thick, a layer of ¾ inch plywood and a layer of 0.8 inch cherry.
My expectation was that the cabinet signature would be lower than the TXT system, due to the very thick cabinet walls. It was not. I would say they are equal in performance.
My method to evaluate the cabinet signature is to use a mechanic’s stethoscope to probe the cabinet while playing pink noise, and listen for distinct tones. If it sounds like pink noise, that spot has no resonance. It is pretty easy to detect an emphasis at some frequency. Then I measure a FR sweep of that spot with a nearfield mic, and compare that to the nearfield driver response at the same voltage level. This gives a conservative estimate of the audibility of the cabinet signature.
Butyl rubber damping compound has a positive effect, given how I design and build cabinets. At one time I was concerned about blending a high stiffness cabinet strategy with added structural damping, but now I believe the two methods can be used together. Although I do not have definitive proof of this, I also believe that a double layer (160 mil total) is an improvement over a single layer, for the way I design and build cabinets.
j.
When I built my textreme (TXT) system, the mid/tweeter box was well braced, with ¾ inch plywood walls, and a double layer baffle. As an afterthought, I added two layers of 80 mil Noico butyl rubber damping material to all interior walls. I did not think it would do much good, but I had it on hand, so I used it. The result was a very low signature cabinet, both from a measurement standpoint and subjectively.
Later, I followed @augerpro and his cabinet resonance research and thread. I began to consider if that butyl rubber material might be doing more than I thought.
My latest high-end project (Purifi midrange + Satori waveguide tweeter) used a dedicated enclosure for the midrange. All 6 walls are double thick, a layer of ¾ inch plywood and a layer of 0.8 inch cherry.
My expectation was that the cabinet signature would be lower than the TXT system, due to the very thick cabinet walls. It was not. I would say they are equal in performance.
My method to evaluate the cabinet signature is to use a mechanic’s stethoscope to probe the cabinet while playing pink noise, and listen for distinct tones. If it sounds like pink noise, that spot has no resonance. It is pretty easy to detect an emphasis at some frequency. Then I measure a FR sweep of that spot with a nearfield mic, and compare that to the nearfield driver response at the same voltage level. This gives a conservative estimate of the audibility of the cabinet signature.
Butyl rubber damping compound has a positive effect, given how I design and build cabinets. At one time I was concerned about blending a high stiffness cabinet strategy with added structural damping, but now I believe the two methods can be used together. Although I do not have definitive proof of this, I also believe that a double layer (160 mil total) is an improvement over a single layer, for the way I design and build cabinets.
j.
My input is based on discussing dampening of the midrange and replying to @fluid , regardless of box LF design. I'm also volunteering my input to the OP, not to you. Comment if you like, but I'm not here for your need to nit pick everything I say or to answer to you policing my responses.
Easiest way I've found to avoid resonances is just don't excite them.
Steep high and low pass filters can dramatically help keeping energy out of resonance frequencies.
Only price is the need for the steep filters to be complementary linear phase, but that's not really a price...as it ends up being much more of a blessing.
CSD's get cleaner, and bracing needs diminish greatly.
Since the incoming angle is the same as the outgoing angle, the waves basically always reflect back into its enclore
Especially for a midrange, in my experience this is rarely an issue, since you can stuff the entire volume with damping material.
Depending on the distance of the walls, you can push this first reflection pretty high up, since f=344/(2*L).
One of the reasons why we see these closed off midrange units.
For a mid-woofer doing low-end as well as midrange, this can be a lot trickier.
Avoid parallel wall prismatic boxes. Unfortunately, those are the easiest to build.
If you must make prismatic boxes, line the inside immediately adjacent (line of sight with the rear membrane) to the drivers with dampening felt, melamine foam, or eggcrate foam. The melamine works really well.
One way is to make an odd sided tall pyramid. This was the reasoning behind the “Dagger” rear chamber. Very close to this is simply using a sports pylon as a rear chamber. Stuff with fiberglass or polyfill. Line wall of first 3in with melamine foam.
Here is a 3 sided Dagger:
Here is sports cone:
The above was used with a Visaton B80 in a first order XO at 1kHz. The distortion is very low:
I have found the spiral wall a la Nautilus, works really well. Almost like it wasn’t there and openess of an open baffle.
https://www.diyaudio.com/community/threads/the-nautaloss-ref-monitor.247598/
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Non-parallel walls do not remove resonant energy. Modal presence is comparable for each type, it is merely redistributed..
Regarding the interior shape of the midrange enclosure, I am guided by the discussion on this thread
https://www.diyaudio.com/community/threads/midrange-enclosure-internal-shape.369316/post-6572084
Particularly post #6.
There is (or seems to be) a collective subjective preference for odd-shaped midrange enclosures, whether odd-polygons, or cone shaped, or labyrinth, or tapered transmission lines. But this thread revealed no measurable advantage to these odd-shapes. Whatever advantage they might have, it is not revealed in near field FR measurements, CSD plots, impedance plots, or impulse responses. Certainly I have never discovered a measurable impedance blip, FR aberration, or resonance/stored energy coming from a conventional rectangular box enclosure which was well stuffed with high quality fill.
So I have chosen to assume that whatever advantages come from these odd shaped enclosures, it is a small secondary or even third level type of advantage.
j.
https://www.diyaudio.com/community/threads/midrange-enclosure-internal-shape.369316/post-6572084
Particularly post #6.
There is (or seems to be) a collective subjective preference for odd-shaped midrange enclosures, whether odd-polygons, or cone shaped, or labyrinth, or tapered transmission lines. But this thread revealed no measurable advantage to these odd-shapes. Whatever advantage they might have, it is not revealed in near field FR measurements, CSD plots, impedance plots, or impulse responses. Certainly I have never discovered a measurable impedance blip, FR aberration, or resonance/stored energy coming from a conventional rectangular box enclosure which was well stuffed with high quality fill.
So I have chosen to assume that whatever advantages come from these odd shaped enclosures, it is a small secondary or even third level type of advantage.
j.
More construction photos. The side walls are attached.
The outer baffle has been cut and routed, and I glued up the first cabinet last night. I will do the second one today. I don't have enough clamps to do two at the same time.
In other news, I have been experimenting with the MiniDSP 2x4HD. The software has a very different look and feel compared to Hypex HFD (which is my only frame of reference). But it seems to work well and I got it up and running, updated with its latest firmware.
j.
The outer baffle has been cut and routed, and I glued up the first cabinet last night. I will do the second one today. I don't have enough clamps to do two at the same time.
In other news, I have been experimenting with the MiniDSP 2x4HD. The software has a very different look and feel compared to Hypex HFD (which is my only frame of reference). But it seems to work well and I got it up and running, updated with its latest firmware.
j.
As was once said, "You can't be too rich or too thin". I would add "or have too many clamps!"
Looking great!
Looking great!
When I first start gluing up the panels, I use titebond wood glue for the first couple of joints. For these first few joints, there is no tolerance buildup, so no gap-filling is needed, and PVA wood glue is the easiest to work with. I use right-angle cabinet clamps to get the first few joints completely square and aligned.
Once the I have several pieces coming together, I switch to construction adhesive to fill any gaps. With PVA wood glue, a gap of 0.02 inch or 0.5 mm significantly degrades the strength of a wood glue joint. So it is important that the joint fits together tightly. With construction adhesive, gaps as large as 1/8 inch or 3mm can easily be accommodated.
I use Loctite PL3x and Loctite PLMax. I don't have a preference between the two, I consider them interchangeable. The PL3x is less viscous, it flows more smoothly, and it is tan colored. The PLMax is thicker, denser, and is grey colored. The PLMax is more expensive, stronger, and is labled as "100% solids", but I don't think that is much of an advantage for this application.
I have also used other brands of construction adhesive, and they are generally all very similar in performance. I avoid mixing them in the same joint, because the chemistry of each adhesive may be different, and they could interfere with each others cure cycle.
j.
Once the I have several pieces coming together, I switch to construction adhesive to fill any gaps. With PVA wood glue, a gap of 0.02 inch or 0.5 mm significantly degrades the strength of a wood glue joint. So it is important that the joint fits together tightly. With construction adhesive, gaps as large as 1/8 inch or 3mm can easily be accommodated.
I use Loctite PL3x and Loctite PLMax. I don't have a preference between the two, I consider them interchangeable. The PL3x is less viscous, it flows more smoothly, and it is tan colored. The PLMax is thicker, denser, and is grey colored. The PLMax is more expensive, stronger, and is labled as "100% solids", but I don't think that is much of an advantage for this application.
I have also used other brands of construction adhesive, and they are generally all very similar in performance. I avoid mixing them in the same joint, because the chemistry of each adhesive may be different, and they could interfere with each others cure cycle.
j.
I don't think I have ever built a pair of speakers where there was not some sort of screw-up that I had to correct. A furniture maker once told me the real mark of craftsmanship is not avoiding all mistakes, but making only small mistakes and being able to manage and correct them... I take comfort in that wisdom every time I f**k-up 🙂
Hopefully this is the only mistake in this project. I had cut all my recesses, and I was cutting the thru-cut for the tweeter. It was supposed to be 75 mm. I cut 75 mm on the front side to half depth. Then I flipped the panel over and somehow misadjusted the circle jig, and cut a new diameter to a half depth... I did not discover it until the cut was fully made, and the circular puck did not fall out. The mistake cut on the back side was at about 100 mm
So obviously this was a problem. If I completed the thru-cut, I would have a very flimsy and unstable backing to the tweeter. In fact the screws might not have enough material to bite into.
The solution was to fill the entire 1/2 depth cut with epoxy. I always have west systems epoxy on hand for my boat refurbishment projects, so I mixed up some epoxy, thickened with microfibers and colloidal silica, and filled the cut. So far it seems to have worked.
Hopefully this is the only mistake in this project. I had cut all my recesses, and I was cutting the thru-cut for the tweeter. It was supposed to be 75 mm. I cut 75 mm on the front side to half depth. Then I flipped the panel over and somehow misadjusted the circle jig, and cut a new diameter to a half depth... I did not discover it until the cut was fully made, and the circular puck did not fall out. The mistake cut on the back side was at about 100 mm
So obviously this was a problem. If I completed the thru-cut, I would have a very flimsy and unstable backing to the tweeter. In fact the screws might not have enough material to bite into.
The solution was to fill the entire 1/2 depth cut with epoxy. I always have west systems epoxy on hand for my boat refurbishment projects, so I mixed up some epoxy, thickened with microfibers and colloidal silica, and filled the cut. So far it seems to have worked.
Oops! You remember me of all my mistakes… but when I do baffles, I always drill through the reference hole for the jig.
Otherwise, thanks for your laborous work on these pages too! I’m not sure I could motivate myself to such, but it’s fun reading!
Otherwise, thanks for your laborous work on these pages too! I’m not sure I could motivate myself to such, but it’s fun reading!
Oh now I read you readjusted the jig…
I often push the router wholly through at some point, change to a copying bit and proceed from the back side. Thus you don’t end up circling with your router on a centre that at some point gets loose. On woofers I alternatively take a roundover bit or a ‘fasefrees’ (45 degrees copying bit), so the chamfering can be done in one round.
I often push the router wholly through at some point, change to a copying bit and proceed from the back side. Thus you don’t end up circling with your router on a centre that at some point gets loose. On woofers I alternatively take a roundover bit or a ‘fasefrees’ (45 degrees copying bit), so the chamfering can be done in one round.