Question about beaming with the CHN-70 - diyAudio
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Old 24th September 2014, 05:14 PM   #1
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Default Question about beaming with the CHN-70

I haven't seen any posted info about dispersion pattern of the CHN-70 yet. Is it something that I should just measure myself? I assume with a 7cm cone it won't be that bad?

A friend is asking about me building him a speaker that works for both mid-field and near-field listening and I was pondering putting two CHNs in each box (with a switchable cap across the second one). He had expressed concern about too narrow of a sweet spot with his old speakers, and this got me wondering what would happen if I put the two CHNs horizontally on the baffle and put a slight convex curve to the baffle (say 15deg)? Would this smear any centre image or would it help to widen the sweet spot? Obviously this wouldn't do much with the cap switched on, but with it turned off (so full signal gets to both drivers) what can I expect from this baffle arrangement?
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Old 26th September 2014, 02:05 PM   #2
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Yeah it's weird that Mark choose not to include off-axis curves in the data sheet as he use to do with the other drivers. But the off axis behavior should be pretty similar to the first generation CHP 70, seeing as the cone seems to be about the same size and shape.

I would just put two unrestrained CHN 70s in a regular 90 cab and be done with it.
Wall reflections and the good off-axis behavior of Marks drivers should take care of the rest for you.
Also at 90 the wavefronts won't cancel or interfere at the cabinet level because they are approximately perpendicular to each other.
The old Epicure Micro Tower just used that very same approached.

Last edited by Squeak; 26th September 2014 at 02:30 PM.
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Old 27th September 2014, 05:55 AM   #3
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Quote:
Originally Posted by Squeak View Post
Yeah it's weird that Mark choose not to include off-axis curves in the data sheet as he use to do with the other drivers. But the off axis behavior should be pretty similar to the first generation CHP 70, seeing as the cone seems to be about the same size and shape.
Thanks, that gives me a baseline. I may end up measuring it myself to be sure. The measurements alone would be a cool project.

Quote:
Originally Posted by Squeak View Post
I would just put two unrestrained CHN 70s in a regular 90 cab and be done with it.
Wall reflections and the good off-axis behavior of Marks drivers should take care of the rest for you.
Also at 90 the wavefronts won't cancel or interfere at the cabinet level because they are approximately perpendicular to each other.
The old Epicure Micro Tower just used that very same approached.
Sound waves at 90 angles of initial propagation do interfere with one another. They're spherical in nature.

I would assume a closer spacing between pairs of drivers would be preferable. From the CHP axis response graphs it looks like a 20 angle between the two drivers could be beneficial for widening the sweet spot. I'm just worried about it creating a region of confusion.

Really I'd love to hear from anyone who has listened to dual driver mark audio enclosures (I know multiple builds are out there) as to how they found it best arranged for critical listening at a variety of locations.
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Old 27th September 2014, 07:04 AM   #4
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Hi Stoch, Squeak, Guys

Its unlikely I'll publish off-axis responses for this driver and possibly others. I've come under attack from a small but extremely vocal number of members on Diyaudio who believe their home testing is superior. As the only driver maker on the forum, I'm a soft easy target for these few who wish to use the forum to force their ideas upon others.

However, there is sometimes a light at the end of the day when sanity returns when the more practical sensible members engage. For comparative performance to the CHN, please take a look at this thread and note its test results:

Markaudio CHP-70 Project

Thanks
Mark.
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Old 27th September 2014, 07:06 AM   #5
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That's sad news.
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Old 27th September 2014, 07:35 AM   #6
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Quote:
Originally Posted by stochastic View Post
That's sad news.
Hi Stoch,
Up to the time of my illness it was wonderful to have good debates, but for what-ever reason the climate changed, regular experienced Full-Range expert members got drowned out, or moved on.

An example of this sad practice is on the thread I've suggest that would help you, where an experience member is effectively being bulldozed by a new guy who believes he knows absolutely everything and doesn't do anything wrong.

My recommendation is to engage with those members who have the most experience, Planet 10, Chris, Bob Brines, Dr. Scott, Dr. Jim Griffin, Jim Shearer, more recently the Zia, the Burchells, Joseph Crowe and similar contributors. These guys regularly use Full-Range drivers and correctly know/apply the operational characteristics of Markaudio drivers into their projects.

Don't get hung-up on beaming or other similar issues. The CHN is a small driver, its not an issue. Most of whats written is rubbish and best ignored. Build a pair of nice boxes, a good number of plans will come about and there's advice on tap. Just Enjoy your project. You'll get a good result without getting bogged down in the snake-oil comment that spoils the hobby.

Thanks
Mark.

Last edited by markaudio; 27th September 2014 at 08:07 AM.
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Old 27th September 2014, 07:51 AM   #7
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Hi Stoch,
I've deleted your last post as its too vague, guys won't know which tests you're referring to. Please re-post quoting the EXACT set of tests to which you refer. Its best to make a link to the particular page(s) that you refer. Let's avoid confusing readers.

Re your proposed anechoic testing. Make sure the baffle is correctly designed and fully tested for damping. Give the PRECISE baffle dimensions when quoting your results along with EXACT details of the test set up. Include the PRECISE specification and calibration of the mic, its position and the EXACT method of its alignment to the driver. Include pics (like Joseph Crow's blog) of the testing environment. Give everyone the opportunity to properly assess the quality of your work and make their own minds about the outcome from a driver in a free-air condition inside an anechoic chamber.

I literally live inside anechoic chambers allot of the time during driver testing sessions.

Thanks
Mark.

Last edited by markaudio; 27th September 2014 at 08:12 AM.
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Old 27th September 2014, 08:42 AM   #8
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Quite right Mark, I was on my phone and just typed an impulsive response to the sight of the various measurements in the thread you linked. I hadn't opened the mdat file Joseph Crowe supplied so I didn't see the mic calibration he has (though exact model still unknown). Still all of Joseph Crowe's measurements seem to be in-box, in-room (untreated - though a few of his measures are gated), with closed-cell foam sofa cushions for absorption on the floor.

spekr's measurements in that linked thread seem to have no situational information other than angle of measure.

The anechoic chamber I (may) have (limited) access to is primarily designed for wireless antenna measurements so wouldn't be accurate in low frequencies. Here's a pic: Click the image to open in full size.

The ring of microphones and the spinning centre table allow for rapid 3D dispersion pattern mapping. I'm not sure if those microphones pick up audio frequencies or not, but I'm very friendly with the prof in the photo and he'd happily spend some time showing that room of his off and trying some audio stuff in there.

I'm not trying to take up your time Mark, I'm much more curious about measuring precisely for my own enjoyment of playing with my Josephson C550 mic and a possibly useful semi-anechoic chamber. I'd also like free-air dispersion patterns of the speakers I plan to build with, which I'm not sure any of the linked responses are. Though after looking at spekr, Joseph Crowe, and your factory spec measures of the CHP, I'm sure this is more just a project that could help me understand measurement techniques better, than it is a documentation effort for the CHN. I would assume the rolloff would be similar in degree to those seen with the CHP.
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Old 27th September 2014, 09:13 AM   #9
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Hi Stoch,
No worries, its my doctors orders rest day. So I'm resting up and reading. Good to "chat" on the forum with you.

Joseph's efforts are pretty good for a home set up. He's given allot of info on his blog so others can better understand his approach. He's largely filtered out <500Hz responses due to significant room influences. Might have been interesting to see a non-filitered test comparison but I appreciate he's trying to assess his box design in relation to the CHP driver. My guess is Joseph is using a non-lab class mike, possible a cheap unit going to 20kHz. But he does appear to have positioned it fairly accurately given his off-axis results. Overall, I'd suggest his work will be comparable to the use of a CHN, as both CHP and CHN share a similar cone design. You might wish to send a message to Joseph. He's a descent helpful guy.

Alas member spekr makes allot of comment in various threads with little (if any) precise and verifiable explanation as to his methods, or his actual knowledge. He makes consistent errors when commenting on the design/operation full-range drivers and largely ignores the advisory posts of the experienced knowledgeable members.

Jim Shearer has made a start on using his new pair for CHN's so likely there will be some sharing of experience here:
CHN-70 breaking in

Bob Brines has also made a start. More sharing of information here:
Almost let the magic smoke out of a CHN-70

I hope you'l have time to feedback on your project. I get the impression you have much interest in acquiring higher quality accurate and verifiable data, commendable.

Re the anechoic chamber, very interesting and thanks for posting. Looking at the pic of this chamber, its quite specific in application. Not sure quite how you'd create a baffle to fit and align. Typically, for reasonably accurate responses for a driver mounted in fee-air, a baffle size of 1000cm X 1500cm would be needed. For your interest, I've attached the IEC standard baffle design/sizing information relating to use in anechoic environments. I guess the questions are: Can you make a suitable baffle, will it fit inside this chamber and can your (or a) mic be accurately aligned @ 1 metre in front of the driver.

Cheers
Mark
Attached Images
File Type: jpeg baffle.jpeg (933.0 KB, 170 views)

Last edited by markaudio; 27th September 2014 at 09:23 AM.
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Old 27th September 2014, 09:38 AM   #10
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Hi Stoch,
Re your C550 mic, not sure which model it is within this family. I had a quick look at the specs, range to 20kHz but I can't see any frequency charts. I notice the rated accuracy is +/- 2dB, I guess across its working range which is likely to be something around 50Hz to 16kHz. Expect either side of these ranges to increase in dB variance as many mics in this range class fall-off markedly in the LF and HF extreme bands.

Likely that the CHN is a ideal driver for using/testing this mic. Possibly why you selected the CHN?

Cheers
Mark.
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