CHR70 Pensil boxes: anechoic measurments - Page 3 - diyAudio
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Old 18th December 2012, 11:59 PM   #21
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Hi Tux, Bob (fellas).
Following on from the 2 previous posts, you might want to read my last post again as you've sort of "overlooked" the fundamental factor, which is the operation condition of a long stroke, single cone, low mass, single point-source driver. Tux, Bob (et al other experienced Diyers), please remember that many members don't always have your long experience and my email bag grows ever longer.

Its important to better understand the operation of the power-train in this type of driver, as a dual simultaneous output operation; Oscillation (mostly LF) and resonance (MF-HF). These emittance functions can't be isolated from each other. Any potential inference (particularly return wave LF - counter pressure) acting on the rear of the driver, will affect its entire bandwidth output. Micro-resonance emissions with a main carrier wave passing across the cone surface substrate risks being interrupted throughout in the entire output spectrum; And mechanical compression/de-compression of the power-train is also likely to result.

Large thin walled (15-mm MDF) unbraced boxes of the type deployed by Evan and Mr Ning, can affect the operation of the driver. The box will generate a counter oscillation that risks affecting driver operation and No amount of damping will save the box from this lack of stability.

Remember, Markaudio drivers are unusual. They are low mass, long stroke designs with soft compliant suspensions, more bass (LF) capable than most other full-range makes, and a fair number of woof-mids for that matter. Therefore, they are potentially more sensitive to external influences of the types being discussed. For those of you who wish to look at recent independent assessment of this performance aspect of Markaudio drivers, take a look at Matsumoto san' work:

Alpair 10 Gen. 2 Low range performance

As a Mech Eng of some 35 years+ and as a designer maker of drivers, its my job to know what potential external factors can impact on driver operation. Should you want a Markaudio driver to work cleanly within its operational spectrum in a large box of the types deployed by Evan and Mr. Ning - Add some bracing!. I have 4+ years worth of test data relating to counter effects on driver power trains functioning inside sealed and vented boxes. Its commercially sensitive material, maybe next year (when time permits) I could re-work it to make a paper that would be of interest to members.

Bob's point about not using bracing in smaller boxes is reasonable. In mechanical engineering circles, principles of strength and rigidity are well understood, being relative/proportional to size/scale. Small boxes (bookshelf) are usually much less in need of bracing.

Tux, regarding combing, I can appreciate that this phenomenon is audible in the case of several drivers (line arrays for example), but for 2 drivers, its simply not an audible issue for typical room listening situations. I'm with you on keeping to the "purist" side of Full-Rangers. For example, My living room system is pure single point source for 5 boxes (5.0 system -no sub, I get nice bass from the Pensils). But we have accept that Full-Rangers are limited in their power output and twinning CHR's did work really well. Power handling was really decent, so it a great option for those guys wanting to keep their builds simple, while giving themselves a bit more "juice" so to speak. As a maker, I have to do what I can to satisfy the many needs of Diyers as possible.

Naturally, for those members (Diyers) operating FAST and multiple OB systems, assuming the CHR/P or Alpair is somehow isolated from other drivers, counter influences on the Markaudio unit of the type discussed here shouldn't be a issue.

There's always a danger for me, as a maker when publishing tests of the sort that Evan and Mr Ning made. They are simply experimenting and understand the limitations of the MDF material. These guys treat the data from these tests as only "indicative". They use these early tests as a stepping stone to further development. In this instance, I published their work to encourage members and Diyers to experiment. In doing so, we should accept that variations in outcomes is part of the process and results don't always meet expectations. Evan so, I was much encouraged by the potential of these boxes. Scott has I think sent me data for a optimal alignment for a twin driver Pensil design (must search through my email). I'm confident these types of boxes, built properly will work well.

Got to go chaps, ton of work to do.

Merry Christmas

Last edited by markaudio; 19th December 2012 at 01:36 AM.
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Old 8th January 2013, 03:10 AM   #22
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Any more word on the dual CHR box? That one had me a bit interested.

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Old 22nd January 2014, 04:00 AM   #23
JoeyGS is offline JoeyGS  Philippines
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Hi Mark,

With the twin driver, did you use the R70.3 Pensil plans as-is and just added another driver?


Originally Posted by markaudio View Post
Hi Mario,
Re the twin driver set-up, there was no audible combing effect from the test boxes. The listening distance was around 3.3 metres. Combing should not be an issue on 2 driver close mount set-ups of this type with listening distances greater than 2 metres.

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.

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Old 28th January 2014, 05:27 AM   #24
Tom V is offline Tom V  United States
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It's nice to know you can throw a pair of $40 drivers in a crappy mdf box (*) you hacked together in an hour and have flat response from 50-30K. It's a nice century we are living in.

(*) Crappy well-designed mdf boxes...
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Old 28th January 2014, 10:12 AM   #25
hajj is offline hajj  Lebanon
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That's the first time I see these measurements, and must say, they are impressive!
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