Black Beauty 2013 - a compact monitor with the CHR70A

Back in 2009 I made a compact monitor for the CHR70 gen1, the Black Beauty. This design also worked for the gen2, but the gen3's parameters differ too much to just drop them in.

So it was back to the virtual drawing board... I set for myself as a goal, to not only have a similar compact design, but to be able to offer all those who built the original Black Beauty the possibility to upgrade with minimal mods. After fiddling with LspCAD for a while, I came to a low tuned, well damped BR alignment that had the potential of sounding rather nice in the bass department:
PP2013 - BB BR - simulatie.png
It does not extent as far down as the original BB, but has a small raise in the response just above 100Hz, which should give it a nice "commercial" sound. The low tune helps in keeping the cone excursion down in the bass drum area.

So this Easter weekend (yes, this is this year's Easter Project) I started building the cabinets, of course also from black MDF:
BB2013 - hout en demping klaar om te lijmen.jpg
The MDF ready to be glued together. As you see, I have attached high density damping material ("Bondum 800") to the walls, there will be some normal Sonofil/Accoustastuff in the centre

more work in progress
BB2013 - gelijmd.jpg BB2013 - kastjes klaar.jpg

And ready for testing:
BB 2013 met testfilters.jpg

After running them in (Vivaldi's winter on repeat) for as long as my patience allowed :D I hooked them up to my PC for a first impression. That was not good, for the small cabinet gives a big hump in the midrange response.... but I expected that, so a quick correction with the VLC mediaplayer's graphic equaliser made the tonal balance OK, so I could test it a bit with some of my playlists. Long story short: great sound, passed the gate to further work on a filter. :cool: Bass sounded as expected, not deep but good presence and punch. All other qualities as I know them from Mark's drivers, so no need to repeat how good they sound :)

[to be continued ..... ]
Hi Mark, you're up early again :D
Thanks to you and your team for the driver in general, and for the effort to get this pair to me in time for Easter :cheers:

I have done some development of the filter and listened some more :sax: , but I'll write that tomorrow, it's past midnight here...

Are the dimensions of the new box similar to the original Black Beauty?
they are identical, the main difference is 1 extra hole for the BR tube
I would love to see some unsmoothed frg for the high frequencies.
what I measured looks prety much in line with the datasheet and measurements I saw in for example the Hobby Hifi, so an on-axis rising high with 2 peaks above the 10kHz. What is it specifically you are looking for that cannot be seen from the graph in the datasheet? Maybe Mark can help out here, since his measurements were done with a lot better gear than mine :cool:
....they are identical, the main difference is 1 extra hole for the BR tube
so here is the dimensional drawing:
the material used is 16mm black MDF

And this is the BR tube I used:
This results in a tune of somewhere between 50Hz and 55Hz, dependent on the amount of stuffing used. This particular tube requires a precisely drilled hole of 48mm diameter (49 is the max tolerable).

I placed the port on the back of the cabinet, and I advise this to do this always when making a BR for a full range (or classic 2way; with a 3way of FAST where the bass does not have to do also the mids there is no problem with the BR port in the front) to avoid the mids coming out of the BR tue messing up the response and imaging.
After the test on the PC, I did some quich measurements followed by a few sims to get a good starting point for a correction filter:
BB gen3 - 2 opties voor sperkring 2.png
so, 1 option is a single RCL, the other a correction using 2 RCLs

On listening I found little difference, so I did a check measurement:
BB gen3 - metingen 2 verschillende sperkringen.png
which explains why I did not hear much difference, because there is not much difference in the response....

So back to the 1 RCL, changed the R to 12ohm (so now a 0.68mH coil, 11.5uF (6.8+4.7) capcitor, and 12ohm resistor) and listened some more.... placement was not optimal (a bit too high), but had to do for the moment (I was not in the front when they handed out patience :D )

First impressions: I am very pleased with how the sound already, I could have these how they are now and be happy with them as my only speakers. Excellent imaging, neutral sound (not a hint of sharpness), beautiful details in the music, decent bass response. yes, I miss the deep bass in some recordings, but that was to be expected (I am a bit spoiled, in both my normal sets I have 10" woofers taking care of that).

So, for the moment I can already recommend the design in its current state: BB cabinet (well damped), BRHP35 tube, CHR70A, and a correction of a 0.68mH coil, 11.5uF (6.8+4.7) capcitor, and 12ohm resistor is enough to enjoy music, all else is luxury :D

I might post more updates later as I listen and test more, but that will take some time...
Have you listened to them before judging them?

The measurements I made are to help in developing the filter, nothing else. you can't judge any driver on just 1 curve. A rise at higher frequencies on-axis is what you see with most full range drivers, and this is not an error but is often actually required so the power average and/or off axis response is neutral.