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MCM 55-5670 Bandpass Sub
It turns out the MCM 55-5670 woofer models pretty well as a 4th order bandpass sub. I set about building a pair using 10" concrete forms and so far it's turned out pretty well.
The sim gives an F3 in the upper 20's.
I cut the concrete tube to length for the sealed chamber.
I made the ported chamber from Baltic birch plywood with a removable panel to mount the woofer and port with. I routered a slot in the top panel and the ported box to set the tube in and glued the sections together.
I put a MiniDSP in front of the test amp with a 12db/oct 200hz low pass filter to make this measurement. I plan to use a pair of the $35 Foster plate amps from a previous thread to drive them with.
The plan is to put a panel on the port side to mount the amp with and cover the other 3 sides with fabric. You can ignore the inductors in the picture. I hooked them up before I hooked up the DSP for measurements.
Ron
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I finally got around to hooking up one of the Foster plate amps I plan to use and I took some measurements and then tried to do a little listening. I cranked the level up a bit with a scope connected and saw a weird spike on the scope and the woofer went dead. The amps have been sitting around for a long time so I thought maybe it just died. I tried the other plate amp and nothing. I hooked up DATS to the woofer leads coming out of the port and it showed that it was shorted. In the picture above the woofer is upside down with the driver face up. I didn't have leads on the woofer and just used some clip leads to connect the driver to the wires in the box which worked perfectly fine using a test amp with the box upside down. When I tried the plate amp I'd turned the box right side up with the woofer face down and when I cranked things up the clip leads got pulled into the magnet shorting them together. I put the amps on the bench and fortunately they survived having their output shorted. Now I can get back to doing some measurement and listening. If I can get them together I'll be bringing them to Ankeny where they will probably be unfinished.
Ron
Are those the Foster amps Jack Hidley was clearancing after the NHT buyout? If so, they have a pretty big boost by default.
They are the clearance amps that were so cheap I bought 4 of them. They have been modified to remove the boost.
Ron
They were $25 each in 2010.
"Foster subwoofer plate amplifier. 115W into 4ohms, 80W into 8ohms. 4th order (24dB/octave) low pass adjustable from 50-200Hz. 0-180 degree phase switch, RCA and speaker level inputs, volume control. Unit has a 3rd order (18dB/octave) high pass filter at 29Hz with a Q of 0.707 built into the subwoofer section."
This thread has the modifications.
https://diy.midwestaudio.club/discussion/comment/30492
Ron
I modified my pair as well.
I have them together but unfinished and ready to go to Ankeny. This is the nearfield measurement. The little blip in the middle is at 60Hz so you can ignore it.
-3db of 29 on the low end and -10db of 22.
-3db of 116 on the high end which should be a pretty good match for the Krystals.
Ron
The LR Mains speakers I'm bringing could use a sub
You're welcome to try them. I've got them set up to run off the speaker inputs and I'm wondering if the plate amp has enough gain that way. When I ran them off a receiver with sub outs I didn't have to turn the level all the way up like I have it now. They should make OK speaker stands.
Ron
It wasn't too hot today so I thought I'd try out my new Wagner Flexio 5000 paint sprayer. Happy to say it works well. The clean up was a bit tedious but now that I know what I'm doing it should go much faster next time. Here's a short demo video.
https://youtube.com/watch?v=XwtBmMahUFk
I plan to wrap the speakers in a stretch knit and trim the tops and bottoms out in cherry so there's still a bit of work to do. I painted them with Latex flat black because I don't want the birch to show through.
These would have been a PITA to paint with a brush. I probably spent 15 minutes actually painting with the sprayer. There was very little overspray.
Ron
I've got a Wagner Control Spray MAX, the predecessor to yours. I find it relatively easy to clean up for water based stuff. Especially in a tub. Oil based stuff is quite the pain to clean.. Though blowing mineral spirits flames makes it a little more fun.
. Not that I'd suggest it.
Try water based poly with it. Satin works really well.
After a lot of procrastination and other stuff to do I'm back at these. I put couple of coats of black Duratex on the bottoms and backs. I had my wife sew up a tube of stretch knit fabric that I could slide over the box and staple. Next up is a wooden topper and base.
Ron