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Another Retro Monkey Coffin Build
I have always wanted to build a retro monkey coffin style speaker after owning a pair of 70's Sansuis as a kid. I wanted something
where the speaker had a retro flush mounted grill that could be listened to with the grill on. So in this build I have tried a few tricks to limit diffraction on a basically terible design. I used a waveguide on the tweeter, and also made the grill into somewhat of a waveguide itself. I used the XT25 beastmode tweeter and HiVi L6-4R which I had laying around. I wanted the dimensions to be about the same as the Sansui SP-2500 which was similar to what I had as a kid. That gave me about 1.7 cubic feet for the woofer. I chose the Dayton Audio RS270p-4A. It will do about 35hz in that box with a decent sensitivity. I picked a vintage grill cloth from Parts Express and have built one speaker far enough to get some measurements and cobble together a crossover.
Comments
Here are a few pics of where I am at so far.
This shows the grill shape. I am hoping it somewhat limits diffraction. We will see.
I lined the box with some foam I removed from a homemade absorption panel I was given. I also stuffed the midrange box.
Here is where I am now, and how I measured the speaker.
Here is the box simulation. Should be good to just under 35hz. It will play to 106.5db before baffle step at 85 watts. I used a 3" port, which is on the small side and will give an air speed of 24m/s at max volume. a 4" port would need to be too long.
Here is the crossover I am going to try. I ordered a couple of the inductors from Meniscus quick before they close. The rest I had on hand. I am a little concerned with the 2.5ohm impedance dip, but the amp I am using should be fine. This woofer was weird. It did not like much of an inductor on it. Anything larger, and it really tilted the low end response down. I needed to use a larger capacitance than usual, which is what gives the low resistance between 100 and 200hz. The mid and woofer did not want to play well together.
Fuckin right !!
I haven’t seen that grill technique since Weems - very appropriate ! You could additionally consider adding a thin felt strip along the beveled wood grill frame.
I LOVE it!
Very cool! I also have a set of those RS270P's allotted for a set of garage rocking monkey coffins. Totally digging the vibe🤘🏼
I made a little tweak to the crossover to try and get the impedance up a bit. I have a full 6db of baffle step still, but my phase is not tracking quite as well through the woofer/midrange. It is only off by about 10-15 degrees in the crossover region, so it should be ok still. It may be a good compromise for a little bit higher impedance.
I have a pair of enclosures (just under 1.5 cuft each) I built last year with the RS270P-4. Those were "going" to be my 2023 Indy theme build (2 ways). Anyway I ditched that build and then used them as bass bins for a 3 way project. The bass response and dynamics from those RS270P-4 are pretty amazing! I'm not a huge PE/Stahl/Dayton fan boy but those woofers are solid and a great value IMHO.
These are in a pretty ghetto state at the moment. I just started voicing these. Had to make a few resistor changes already, but overall pleased with them. Next will be stand building and veneering. I will be doing these in a cherry veneer and painting the front baffles black.
Here is the measured in room (red) vs. predicted (blue). I did not have any gating on in room just smoothing.
Looks a few dB too hot from 2 kHz up.
Funny you say that. I am working from home today and listening while I work. They are a bit hot and sibilant right now. Easy change to remove a little capacitance across the tweeter input resistor.
Yup, bring that down a bit. I'd also tune in some BBC dip, personal preference.
These look great! Love me some little coffins.
I tilted the upper end down a couple db. Was definitely needed. The 10" woofer in these really sound good. They are super punchy and impactful in the bass. They also get pretty loud. I think I am going to really like these. I will keep running them for a bit to make sure there aren't anymore crossover changes needed. Here is where I am now.
nice, and looks to also bring down the BBC target range as well (around 2 - 4g) for those so inclined...
That looks very nice.
Listen and voice. Pending some off axis anomaly or distortion this should sound great. You should be proud.
Let the veneering begin.
Diggin the NHRA banner hanging in the background!
I have the veneer on and applied the pre stain prep. Now to stain. This is where all my imperfections rear their ugly head.
Well, the staining went well. I got stands started also. Tgey are MDF with 2" wood dowels. The MDF will be painted black. Plan on applying clear tomorrow on the speakers, then will paint the front baffles black on Monday.
Awesome!
Paint and stain complete. I can put the drivers back in tomorrow.
Old time esthetics too!
I got the speakers complete this weekend, but the stands didn't go so well. Painting them outdoors in the heat left a rough finish. I will need to sand them and repaint later this week. These are beasts at 65lbs.
Those came out great! Rock🤘🏼
I got the stands done. Not super happy with them, but are better than drywall buckets for now. I will probably build something else this winter.
wont lie , looks sexy
Nice, and did you build the diffusers ?