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Old 13th August 2012, 05:06 PM   #671
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Default Mark audio chp-70

I received a pair of chp-70s from Madisound last week with the intent of trying them in folded Tabaqs, but after reading this thread and listening to the drivers in some old BR enclosures, lined with 1/2" cement board, I will be making a pair of FHs using my plentiful supply of oak boards.
The chp-70s sound absolutely gorgeous in their temporary housing driven by my Starfish pre and Pass F5 clone. Initially,I tried them with my MF B200 integrated and they were so-so. Maybe they are breaking in rapidly?
Has anyone here made their FHs with hardwood and/or used hardibacker lining?
Peter
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Old 13th August 2012, 05:19 PM   #672
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There is at least one hardwood build, with cherry IIRC. No hardi backer or similar, that should not be necessary since they have specific stuffing details. In fact, I believe cement board lining in the FH3s would be a huge mistake. Lots of satisfied builds, to the specs, why mess with that?


Quote:
Originally Posted by pjblakey View Post
I received a pair of chp-70s from Madisound last week with the intent of trying them in folded Tabaqs, but after reading this thread and listening to the drivers in some old BR enclosures, lined with 1/2" cement board, I will be making a pair of FHs using my plentiful supply of oak boards.
The chp-70s sound absolutely gorgeous in their temporary housing driven by my Starfish pre and Pass F5 clone. Initially,I tried them with my MF B200 integrated and they were so-so. Maybe they are breaking in rapidly?
Has anyone here made their FHs with hardwood and/or used hardibacker lining?
Peter
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Old 13th August 2012, 05:32 PM   #673
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by pjblakey View Post
I received a pair of chp-70s from Madisound last week with the intent of trying them in folded Tabaqs, but after reading this thread and listening to the drivers in some old BR enclosures, lined with 1/2" cement board, I will be making a pair of FHs using my plentiful supply of oak boards.
The chp-70s sound absolutely gorgeous in their temporary housing driven by my Starfish pre and Pass F5 clone. Initially,I tried them with my MF B200 integrated and they were so-so. Maybe they are breaking in rapidly?
Has anyone here made their FHs with hardwood and/or used hardibacker lining?
Peter

slow typing this post, as I'm donning my kevlar vest and flame proof jumper, but I'd like to offer the opinion that hardibacker cement board, or any very high density material intended for enclosure damping should be reserved for other projects

edit: fastbike beat me to it


if you're confident enough with your fabrication / assembly skills to build these with solid hardwoods, by all means , but keep a couple of things in mind;

- The Mark Audio drivers will need some break in time ( at least 100hrs), and adjusting the final damping fill for acoustic tuning of bass response, or for that matter any passive or active EQ, should await completion of that period

- Damping fill level to apex (behind the internal divider) remains the same for all drivers, but the area immediately above, and below the driver can vary depending by system, and access to these areas can be very tight once the enclosure is buttoned up. More than a couple of builders have fabricated with a removable top panel to allow access - a brilliant solution - keep in mind that this needs to be airtight.
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Old 13th August 2012, 05:34 PM   #674
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Quote:
Originally Posted by pjblakey View Post
Has anyone here made their FHs with ...hardibacker lining?
For the love of heaven don't do that Peter. You'll push the panel Fs right down, slap bang into the middle of the cabinet's operating BW. You'd also need to redesign the cabinet, thanks to the loss of internal volume.
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Old 13th August 2012, 08:26 PM   #675
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Thanks for the response, guys.
It seems like hardibacker is a no-no!!
However, I have enough oak to build many speakers and will certainly provide access to the top portion, either removable top or upper baffle.
Peter
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Old 13th August 2012, 08:27 PM   #676
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Quote:
Originally Posted by fastbike1 View Post
In fact, I believe cement board lining in the FH3s would be a huge mistake.
+1

dave
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Old 19th August 2012, 07:01 PM   #677
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Default Half way there!

I have planed the oak, cut, assembled and sanded the first of my FHs - the second will be finished similarly this week.
The CHP-70s have been playing 10 hours+ a day for a week in some lashed up BR boxes. I transferred one of the drivers to a folded Tabaq that I finished last month, and, with it playing the left channel, and the FH the right, I had a quiet session while indulging in a bottle of merlot.
The only known construction deficiency in the FH is a lack of felt lining behind the driver. I live very close to the carpet capital of the world, but unable to find felt locally, except under the carpet of my F-150. I used some polyester batting instead, recognizing that it wouldn't perform the required duty, but maybe better than nothing.
My room is such that the left speaker is 3 feet from the side wall, and the right speaker 6 feet from its' side wall. Both baffles are 2 - 3 feet from the front wall.
There seemed to be quite a disparity in the bass performance of the Tabaq(in the corner) to the FH on the right.
So, this morning, I got my Radio Shack SPL meter out and ran through the Stereophile test CD2 warble tones.
Using the C scale, I set my reference level(6ft from the speaker) to 60db at 200Hz(the first tone in the bass seqence) and determined the following:
In the corner(left), the Tabaq sound pressure level was +/- 3db from 200Hz to 40Hz(63db), whereas the FH suffered a bump between 100Hz and 50Hz peaking at 74db(80Hz) dipped to 61db at 50Hz and finished 63db at 40Hz. Nothing audible below 40Hz.
Comparing each speaker in the right channel(non-corner) location, they performed within 2db of each other, albeit, with much reduced low bass output(53db@40Hz).
This is the first horn type enclosure I have built - since both the Tabaq and the FH apparently benefited(?) from room corner loading, is there something peculiar about the FH that would cause the bump in the 50-100Hz octave when in the corner, or possibly lack of felt damping?
Completing the warble tone tests, both speakers played within 2db all the way up to 10kHz(limit of my hearing).
Looking forward to completing the other - thanks guys for a beautiful design.
Peter
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Old 19th August 2012, 07:43 PM   #678
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The MA units don't really require corner loading in FH3 (as you've just discovered), and are mostly content with just a front wall and floor for boundary conditions. What you describe is almost exactly what I'd expect them to do in such conditions, i.e. produce substantially more gain. You'll need to add more damping to that channel to bring it back into line. Avoid too much near the driver or you'll mass-load the cone.

Very nice looking build BTW.

Last edited by Scottmoose; 19th August 2012 at 07:46 PM.
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Old 19th August 2012, 08:08 PM   #679
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Thanks, Scottmoose. When I have the other one assembled, I'll play with the damping. Hopefully, by that time I will have found some felt, too.
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Old 19th August 2012, 09:24 PM   #680
mightym is offline mightym  United States
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A suggestion for the felt.

Try the local automotive interior material supplier.

I've found all cotton felt that was used for trunk lining/underlayment at one.

John
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