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BMR shenanigans
Due to a PE sale plus quantity discount I got a few pairs of TEBM35C10-4 2" BMRs for cheap to play around with. I also have some 1/8" kydex that I hadn't gotten around to using yet. It is 60deg out today and only a few hours until rain rolls in. Time to bust out the router for some quick prototyping!
The TEBM35C10-4 seems difficult to physically adapt into a speaker design due to the very small flange. The idea is to make them into a self contained unit like dome tweeters/mids. The kydex becoming the faceplate and 3" pvc "socket cap" as a back cup.
(cup not attached, just showing the idea)
The surround on the BMR is very shallow, probably less than 1/16" tall. So I knocked the inner edge down with a small ogee bit.
Planning to just permanently glue everything in place. Being a thermoform plastic I would have guessed Kydex was ABS, but apparently it is a varient of PVC. So it should work with PVC cements. I bet the frame of the BMR is ABS though so I got an all purpose PVC/ABS compatible cement to try. Failing that, CA/superglue along with silicone to seal it as a last resort.
Comments
The 3" PVC socket cap calculated out to ~.35 liter. Giving up a bit of volume for the driver I get Qtc 1.01 with a 1.25db hump peaking ~250hz. But that is without stuffing too. Probably add some felt and polyfill.
At the rated 10watts RMS it only gets up to ~89db at 1meter. So definately limited. At that power level it is estimated to breach xmax by 210hz in .33liter sealed. So should allow a reasonable range to cross a woofer. I imagine it would be fine for normal listening in a small room like my living room where listening distance is around 8ft. Would probably struggle at the DIY gatherings.
Nifty!
I think you should be ok. I have used PVC glue with ABS successfully. The glue is MEK solvent based which softens both types of plastic.
I didn't realy get any action shots of the guts but not missing much. Glued the BMR in and soldered on leads. Drilled lead holes in the cups and found some leftover ultratouch to put in. Then glued the cups on. I decided to drill a second hole to periodically blow in so I could slowly evacuate the fumes from all the glue that made it inside. Hopefully that will prevent softening the glue holding the driver together. I'll probably wait a few days before sealing up the holes.
Out of curiosity I am taking impedance sweeps as I go. Before (bare driver) and after enclosed. With the holes in the cup I'm not sure how useful the measurement is.
picked up little pair of those bugars as was getting some inductors and rubber feet, struggling to get to the 100 dollar mark for free shipping and the ny2025 discount.... much smaller than expected compared to the 3.5
Thanks to a Christmas list snafu, I ended up with 24 of them. But due to poor packing, 6 of them were rattling around loose in the box.
Ouch!
1st Q: From PE? I'm sure they would make it right.
2nd Q: 24!?!? Whacha got cookin?
Yes - from PE.
I only wanted 8 of them. I had planned to build an WMMTMM at some point. I put these on my Christmas list and our daughter bought them for me. Apparently my wife didn't check with the group. She thought she ordered 8 but it somehow ended up being 8x2.
Same issue - I got a dozen, 4 or 5 got loose inside the PE box. They are in a very flimsy little clamshell that apparently just pops open almost spontaneously. I did not see any real damage to the drivers however.
Wait, 8x2 is 24? Huh, no wonder I'm no good at math😛
Id be curious if Kydex wouldnt make for a decent wave guide for a tweeter. Heat and press a couple layers together , seems to hold its shape well once cooled. Maybe some type of insulation material between the layers?
No - just my bad explanation. Our daughter gave me 8, wife gave me 16 by mistake. She meant to order 8, but must have added 8 to the cart twice. I know the PE site was really sketchy before Christmas, so maybe she thought the first click didn't put them in the cart.
Ugh yeah I did something like that yesterday, I guess.... but for a $1200 item
Reealy hoping they respond to email.
yup https://diy.midwestaudio.club/discussion/2501/kydex-diy-waveguides
That was the original idea behind picking up the kydex. I just hadn't quite convinced myself how I'd go about making a mold/die for it. That, and I was planning on trying smaller waveguides ~4" for 3/4" tweeters and it seems there probably isnt much interest in that. Much larger and I'd have to do something more than just a toenail router bit to make the profile... More like something off @ugly_woofer 's waveguide cutter (wink wink, nudge nudge).
As I side note.. I've always wanted a pcc. Keltec is my wavelength. I've shot the sub2k, but instantly hated it once I got the skin of my hand badly pinched on the stupid charging knob. That and I'm not a fan of peephole sights. I realy wish someone would do a locked breach pcc that doesn't cost an arm and a leg... and not make it look horrible. Straight blow back is such a kludge with all that mass swinging around. Just seems unnecessary for the technology we have now.
Spitballing what to pair these with. Figured I'd treat them like a widebander and just pair with a woofer.
Initially I was eyeballing the LW150 6" flat/low-pro woofer pretty hard since IMO it would be funny (insert joke about speaker "flatness")... and would do OK in a pretty small enclosure. But a little pricy for what I imagine is an average performer at best. Yeah I know they are 20% off right now. But I'm trying to not purchase more drivers.
I've got some of the buyout 8" dvc woofers that would do alright in ~.75cf sealed. But a bit mismatched in output capability. Which renders the extra cabinet size a bit unnecessary (gentle giants?)
I've got a bunch of Peerless 830855 4"ers that I have yet to completely nail down projects for. One per channel would work in smallish bookshelf enclosure. And it's sensitivity and output capabilities seem to match up better to the BMR. Sofar this is the top idea running around my head.
Drew, are you thinking one of each Peerless & bmr per side? Will you be factoring in much BSC or are these for a desktop near the wall where you might not need it?
About 5 years ago I made a CBT24 array with the little 2 inch BMRs. Still in storage now. Never did get the EQ dialed in satisfactorily. Another project on the back burner.
A couple feet from walls in my smallish living room (<8ft listening distance). 1ea was the initial thought since the TEBM35C10-4 is ~79-80db 2.83V/1m. They max out at 10watts so never going to get very loud for a larger room. The 830855 is around 4-5db higher sensitivity. Though I don't realy have experience yet with tiny woofers and their low end dropoff. 2 per ch advisable?
Could do a 2.5way and yield more boost lower in the bass to make the 4" load the room more. However, a single should be all that you need for balance. 3.5ltrs PR loaded is all you really need for a single.
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I think it'll be a nice combo. I wish those Peerless were still available. I recall someone saying they can take a good bit of abuse with little complaint. I can't help but think about a WWWWMMTMM using those drivers.
Those SDS 830855 4" were billed as a 3.5" subwoofer to be paired with 2x of the 3.5" 830878 PRs. That particular woofer thinks it's much larger than it is, kind of a terrier breed of small scrappy woofer. I've heard it play bass extension that would make a decent low-priced 8" woofer green with envy.
Peerless was always known for great bass response, and over the years I've heard many Peerless I felt that way about. The Exclusive 8", 830855, XLS10, XLS12, 831709, 830881, etc...
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They do stack nicely..
I've got 16x currently. I was going to try an MTM to start then invest that experience into a WWWWMTM. But if I'm going to use some for other projects that throws a wrench in. I still want to try an MTM with em. I might just save 8x for woofer section in a tower and use PC105 or PC83 for mid/s along with some SB21RDCs I scored on sale a while ago. That is.. whenever I get over my loathing of 3-way projects. I hadn't fabricated anything (non woodworking) for a while. So right now I've got a hankering for somewhat weird projects that let me flex that muscle again.