CHR70 Pensil boxes: anechoic measurments

[tuxedocivic]

Cool to see this data. Thanks. Interesting to see the top end rise. Definitely audible IMO.

Originally Posted by markaudio

Specifically in the 15-kHz to 20-kHz range, its not possible to specifically identify this effect as the boxes used only 15-mm MDF and weren't braced. However, I'd normally expect to see a flatter response from set-ups of this type, making it useful for those with bigger rooms and/or requiring more power-handling.

Thanks
Mark.

What does the box construction have to do with the 15khz+ region, let alone comb filtering. I do think this setup will comb, as low as deep notches around 2khz at 45 degrees vertical. But I agree it may not be audible if sitting on axis as the combing will be in the reflected sound (ceiling and floor).

Was the mic on axis with one of the drivers, or centered?

Thanks again. Would really like to one day try a bipole or top firing variant of something like this.

[chrisb]

Originally Posted by tuxedocivic

Thanks again. Would really like to one day try a bipole or top firing variant of something like this.

you know where you can hear "something like this"

[boxdiycast]

Can only say!!!

Wanna have some plans of the hybrid boxes!!!!

YES YES YES, please!!

[chrisb]

Originally Posted by boxdiycast

Can only say!!!

Wanna have some plans of the hybrid boxes!!!!

YES YES YES, please!!

Which hybrids exactly? Unless I've missed it (certainly not impossible ) we could all be talking out of our assets about an enclosure that hasn't even been "designed" yet

As Mr Atkinson might opine - imaginating you know what you're doing is one thing, but proper engineering is quite another, and definitely requires credentials (and an advertising budget )

let the mud fly boys

[Scottmoose]

A proper twin-driver version has already been done; I had no involvement with the hybrid enclosures above, so I preferred to do one myself to the target alignment. Whether there is sufficient interest to justify having it drawn up & released is as-yet unclear.

[skeeter99]

Originally Posted by Scottmoose

A proper twin-driver version has already been done; I had no involvement with the hybrid enclosures above, so I preferred to do one myself to the target alignment. Whether there is sufficient interest to justify having it drawn up & released is as-yet unclear.

Scott,

I would definitely be interested in the twin diver CHR Pensil design. Been kinda missing building anything lately and this woud be a great addition to my setup. Plus I'd like the excuse to try the CHR's

Scott D.

[markaudio]

Originally Posted by tuxedocivic

Cool to see this data. Thanks. Interesting to see the top end rise. Definitely audible IMO.

What does the box construction have to do with the 15khz+ region, let alone comb filtering. I do think this setup will comb, as low as deep notches around 2khz at 45 degrees vertical. But I agree it may not be audible if sitting on axis as the combing will be in the reflected sound (ceiling and floor).

Was the mic on axis with one of the drivers, or centered?

Hi Tux,
I'm in Jakarta killing time between flights.

I'm a bit surprised you don't have the answer to your box influence question. Most certainly large thin walled un-braced boxes of the types being tested will inevitably create interference with driver back-wave generation (as illustrated in the graphs). Markaudio drivers are long stroke compliant designs with low profile , low mass cones. Any force coming back toward the rear emitting surface risks contamination of the resonance patterns crossing the material surface of the cone substrate, resonance compression/decompression can result.

Hence why Dave (et al) I understand for this reason and other factors, spend allot of time bracing their boxes.

Regarding combing, as said, it isn't an audible issue. There's plenty of boxes using multiple drivers on the market with no complaints about this effect.

Interestingly, measurements were taken in 3 positions (top driver, between drivers and bottom driver centers @ 1 metro). Only an average 0.5dB variation on the results between all 3 mic positions.

Cheers
Mark.

[Bob Brines]

Originally Posted by markaudio

Hi Tux,
....Any force coming back toward the rear emitting surface risks contamination of the resonance patterns crossing the material surface of the cone substrate, resonance compression/decompression can result.

Hence why Dave (et al) I understand for this reason and other factors, spend allot of time bracing their boxes.

I am beginning to be convinced that bracing in a small, low power speaker has little affect on the overall output of the driver/box combination. What is more important is damping. I ran some tests on a 15L BR loaded with an A10.2. The baffle was 24mm BB and all other panels 18mm TigerPly. The panel under test was unsupported 9"x15.5". I tested the panel unbraced, with a 1/4"x2" brace top to bottom (2" dimension standing away from the surface) and finally tying the braces together across the box. There was very little difference in the sound coming through the panel.

What this told me is that bracing makes little difference in such a small box. Bracing is probably only significant when the box is big enough and the sound pressure strong enough to case the panels to breathe.

Damping is another issue. The test box was lined on all surfaces with 1" Owens Corning 703. I did not test the effect of this damping, but I presume that is satisfies your concern about reflections impinging on the back of the driver. (Maybe not!) I also did not test the effect of the internal damping on the sound passing through the test panel. However, I believe that any significant reduction on the transparency of a plywood panel will required mass loaded damping on the internal surface or some constrained layer construction.

Bob

[tuxedocivic]

Originally Posted by markaudio

Most certainly large thin walled un-braced boxes of the types being tested will inevitably create interference with driver back-wave generation (as illustrated in the graphs). Markaudio drivers are long stroke compliant designs with low profile , low mass cones. Any force coming back toward the rear emitting surface risks contamination of the resonance patterns crossing the material surface of the cone substrate, resonance compression/decompression can result.

Hence why Dave (et al) I understand for this reason and other factors, spend allot of time bracing their boxes.

Not to be confrontational, but I'm not convinced box resonances have anything to do with 15khz, thus bracing wouldn't be a consideration here. And a 15khz backwave would be easily killed by almost any amount of stuffing in the box. If there isn't stuffing in the box, and the results are affected by this, then the results are not much use. Were the tests done sine swept or noise/RTA? If sine sweep, then the only noise in the box at 15khz would be 15khz. Unless a very fast sweep there could be delayed sound from say 10khz bouncing around in there.

Despite all this, it's still unrelated to combing. But I agree if there is a rear wave coming through the cone, it could attenuate the high frequencies. Unless I'm missing something though, not related to the box material

Originally Posted by markaudio

Regarding combing, as said, it isn't an audible issue. There's plenty of boxes using multiple drivers on the market with no complaints about this effect.

Full range though? Or low passed below where combing can become an issue?

Again, not trying to be confrontational. I build plenty of multi driver systems. But with your VERY good drivers and the whole concept of full range. Running 2 drivers full range seems against the grain of pure point source. I mean, the best thing about full range is zero inter-driver interaction. There's no cross over. As soon as you introduce a second driver, even if it doesn't have a cap or coil on it, you've corrupted that very thing.

Again, the advantages of 2 drivers may outweigh any combing and lack of point source, but then I'd suggest to any builder of this design to whack a 1.5mH coil in front of one of the drivers. Solve baffle step and combing and only sacrifice about 0.3ohms of DCR from the coil.

Originally Posted by markaudio

Interestingly, measurements were taken in 3 positions (top driver, between drivers and bottom driver centers @ 1 metro). Only an average 0.5dB variation on the results between all 3 mic positions.

Cheers
Mark.

Well that's good to know. Thanks.

And thanks for answering my questions.

[Bob Brines]

I am convinced that panel resonances have very little to do with the overall sound of a speaker. I would be very interested to see FR, THD or CSD plots that demonstrate panel resonance. I suspect that wood product speakers with panels of 18mm or greater are sufficiently internally damped that resonance will not be a problem. Sure, you can rap on a panel and it will give you its resonant frequency, but how much of that will be detectable in the real world with music exciting the panel?

I think the discussion goes a bit far of field with internal reflections are mentioned. Panel resonance is one issue, reflections are another. Any speaker with decently applied damping will keep the driver's cone from being violated by extraneous reflections.

Unless the panels are very large, the primary benefit of bracing is to reduce the in-out movement of the panels due to the internal pressure. With this in mind, my current bracing scheme is a single longitudinal brace on each panel. The brace probably need not be the entire length of the panel, and could probably be some curved shape, but I don't pretend to be a mechanical engineer. I also use window braces above and below the driver, but these serve to 1) break the pipe up into sections for stuffing and 2) square the cabinet during construction.

Bob