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Old 15th July 2019, 05:53 PM   #881
mbrennwa is offline mbrennwa  Switzerland
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Ok, this was a long break. I have done a bit on wood working and ordered x-over parts for the second prototype (Mundorf seem to be out of stock, though).

The CNC shop also sent me a bunch of circular augerpro* waveguides that fit the Scan Speak tweeter. There are now three waveguide candidates for the Monkey Coffin (1 :

- The WG148, which I used until now in the Monkey Coffin design. The WG148 is a cheap plastic part, but it works very well. The issue with the stock WG148 is that it does not fit the Scan R2904 tweeter. I managed to modify the WG148 to match the Scan tweeter, but it's not so easy.

- The augerpro* circular Scan waveguide. This is the same diameter as the WG148 and almost the same depth. It fits the R2904 Scan tweeter like a glove.

- The augerpro* 5" version A. This elliptical waveguide theoretically allows mounting the tweeter a bit closer to the midrange driver. However, the magnet of the midrange driver used in the Monkey Coffin is so big that this does not work.

(*Augerpro designs superb waveguides and publishes the 3D files for them. Simply send these files to a 3D CNC service and off you go! I used 3Dhubs.com, and they were great.)

I made a few measurements comparing these three waveguides (results in the the attachment):
- Scan R204 tweeter in waveguide, mounted in the Monkey Coffin baffle
- Anechoic measurements: on-axis and off-axis at 10 increments (-90 to +90), both horizontally and vertically
- Microphone 100cm away from the baffle surface. Rotation axis was on baffle surface, passing through the x/y center of the tweeter
- Red curves: "inside" (horizontal) or "upwards" (vertical), blue curves: "outside" (horizontal) or "downwards" (vertical), black curve: on-axis

As I see it, the circular augerpro waveguide performs pretty much the same as the WG148. It will therefore work in the Monkey Coffin design as it is, without any modifications to the x-over. This is not surprising, since the dimensions are identical to the WG148. The elliptic waveguide is also good, but slightly different above 8 kHz or so.

Given the aim that the Monkey Coffin should be easy to make on a kitchen table, the circular augerpro waveguide seems to be a good replacement for the WG148, which requires difficult modification. Flush mounting the elliptical waveguide is a bit more difficult, beause it's not so easy to make the cut-out with a router. Oh, and CNC parts look so much better than the cheap plastic WG148!
Attached Images
File Type: png dispersion_waveguides_in_OSMC_baffle.png (553.8 KB, 481 views)
File Type: jpg 20190715_164507.resized.jpg (328.3 KB, 478 views)
File Type: jpg 20190715_192330.resized.jpg (270.5 KB, 472 views)
File Type: jpg 20190715_192344.resized.jpg (229.5 KB, 479 views)
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Group buy for augerpro waveguides for Scan Speak tweeters -- elliptical version -- circular version

Last edited by mbrennwa; 15th July 2019 at 06:04 PM.
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Old 19th July 2019, 11:12 AM   #882
mbrennwa is offline mbrennwa  Switzerland
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X-over partsssss!!!

This will be a busy weekend.
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File Type: jpg 20190719_112937.resized.jpg (320.7 KB, 384 views)
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Group buy for augerpro waveguides for Scan Speak tweeters -- elliptical version -- circular version
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Old 19th July 2019, 12:34 PM   #883
Paul Vancluysen is offline Paul Vancluysen  Belgium
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Always exiting moment, hopefully with good results. This is the first time a stereo set then.
I would not be surprised it wil give other impressions than a mono speaker.
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Old 21st July 2019, 01:05 PM   #884
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by Paul Vancluysen View Post
Always exiting moment, hopefully with good results. This is the first time a stereo set then.
I would not be surprised it wil give other impressions than a mono speaker.
Short summary: no (bad) surprises!

I finished building the second prototype. Since I didn't have a stereo amp in the workshop, I went to the basement and came back with an old class-D amp that refuses to die, no matter badly it is treated. That's always good to have in the workshop. I hooked everything up and listened to some music. Sound was good, but... well, is that everything!?

After a while I went back to the basement and came back with an F5 that was built by Nelson Pass himself. I guess that should do in terms of street credibility. And no, what came out of the Monkey Coffins with the class-D amp was not everything. I never heard my F5 as good as this!

Don't hold your breath for more measurements and data. I am busy with listening to music, even though the acoustics of my workshop are not exactly great (I tried using the skateboard as a diffuser, but no luck).
Attached Images
File Type: jpg DSC09278.JPG (975.5 KB, 137 views)
File Type: jpg DSC09279.JPG (709.0 KB, 201 views)
File Type: jpg DSC09280.JPG (632.0 KB, 202 views)
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Group buy for augerpro waveguides for Scan Speak tweeters -- elliptical version -- circular version

Last edited by mbrennwa; 21st July 2019 at 01:07 PM.
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Old 21st July 2019, 01:09 PM   #885
6L6 is offline 6L6  United States
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This is looking excellent!!!! Well done!
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Old 21st July 2019, 07:11 PM   #886
Paul Vancluysen is offline Paul Vancluysen  Belgium
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Good progress!
What are the findings now if you compare the stereo with the earlier mono setup? Are the timbre and tonal balance still ok? I think it could be different.
Like you are mentioning also, you need a good listening environment and set for the final tuning now.
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Old 21st July 2019, 07:18 PM   #887
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by Paul Vancluysen View Post
Good progress!
What are the findings now if you compare the stereo with the earlier mono setup? Are the timbre and tonal balance still ok? I think it could be different.
Like you are mentioning also, you need a good listening environment and set for the final tuning now.
Timbre and tonal balance is pretty much the same as with the mono setup.

I am amazed how much of a difference I could hear between the two amps. I knew the F5 sounds different (better) than the old class-D, but I never heard it so much. I guess these speakers are quite revealing. And they do really well with a smallish amp like the F5.
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Old 24th July 2019, 07:39 PM   #888
mbrennwa is offline mbrennwa  Switzerland
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I just started a separate thread with a group buy for the circular augerpro waveguide for the Monkey Coffin tweeter. It's here.
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Old 25th July 2019, 07:09 AM   #889
cbueche is offline cbueche  Switzerland
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Good morning,

I'm following this project since the begining, I would be interested in building a pair of these, but im waiting for some more info to participate in the GB. Maybe its a bit too early for the waveguide gb ?

Things like driver list, XO components list, etc. I guess this is coming up at some time ? And of course the construction plans 😏

Thanks to all for your efforts!
Charles
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Old 25th July 2019, 08:55 AM   #890
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by cbueche View Post
Good morning,

I'm following this project since the begining, I would be interested in building a pair of these, but im waiting for some more info to participate in the GB. Maybe its a bit too early for the waveguide gb ?

Things like driver list, XO components list, etc. I guess this is coming up at some time ? And of course the construction plans ��

Thanks to all for your efforts!
Charles
Well, the group buy can be repeated at any time. Or you can just order the waveguides directly.

You are right that documentation is not yet very well developed. You can take a look at the current documentation here.

Some quick pointers:
  • The current box dimensions are slightly different than shown on the earlier drawing, because it does not have the bass reflex port on the front. I do have an updated drawing, but I need to double check this. I'll post it once I think it's right.
  • Drivers: tweeter = Scan Speak R2904 / midrange: Volt VM752 / woofer: Faital 12PR320
  • The documentation linked above shows the current version of the x-over (elliptic filters), including a detailed parts list
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