CBT build thread - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 30 Old 05-23-2019, 09:25 PM - Thread Starter
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CBT build thread

Wanted to try a pair of CBT arrays as a possibility for home theater. The only commercial offerings are the PE kits. I like the CBT36 but thought a little more displacement would be helpful for theater duties, so I designed a cousin using the slightly larger Dayton ND105 vs the ND91 Keele uses in his kit, 16 per array. The tweeter will be a peerless frameless 3/4 fabric dome, 48 per array.

To simplify wiring and decrease losses through voltage dividers needed to achieve the Legendre shading of driver output I'm going to use two amplifier channels for midbass and two channels for tweeters per array with DSP to make appropriate filters. Voltage dividers will still be needed but the upper half of each tower will be down -3dB digitally to start.

Based on expected seating height the array will need to be at least 60" tall. I'll keep the 36 degree arc of the PE kits as the shading drops output so much beyond that there isn't much point in continuing it further.
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post #2 of 30 Old 05-23-2019, 09:29 PM - Thread Starter
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I briefly looked into having panels CNC but the cost seemed too high. I may change my mind about that later!

I did have a router template CNC to simplify creation of the front panels and make sure I kept everything uniform.
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post #3 of 30 Old 05-23-2019, 09:36 PM - Thread Starter
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The aluminum template is indexed down the panel one position at a time, first routing through hole the after another index the recess for driver flange. Tweeter holes routed three at a time, they overlap at each index and are used for local alignment. I marked the panel with parallel straight lines the width of the template to ensure global alignment

Excess material removed first with 3" hole saw and 1" forstner bit before routing. Clamp when aligned, center punch the two mounting screw locations (which will later serve to mount front panel to enclosure) then secure with flat head screws into a chamfered hole in aluminum plate (which is a self centering combination).
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post #4 of 30 Old 05-23-2019, 09:41 PM - Thread Starter
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Front panels are mostly done. This is working from the back side as the ND105 drivers will be rear mounted to keep high surround flush with panel and decrease diffraction issues especially from the tweeter line.

Still need to drill and countersink all the driver and panel mounting holes. 94 per panel I think. I plan to flush trim the edges after mounting to enclosure. I hope I can pull that off on a curved face.
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post #5 of 30 Old 05-23-2019, 09:45 PM - Thread Starter
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The line of holes looks wobbly in that pic... maybe camera lens distortion or maybe shadow effect. They are perfectly straight.

I decided to make a template for the enclosure side (instead of using the first side made as template for the others) in case I want to make more of these in the future. Didn't want to use an assembled speaker or worse yet have to disassemble it for a pattern.

Tip: curved rough cuts are 100x faster with a skillsaw than a jigsaw. May leave some blade paint and burn marks on the wood but big deal. Just need to get close enough to make flush trim routing easier.
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Last edited by Bigus; 05-23-2019 at 09:52 PM.
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post #6 of 30 Old 05-24-2019, 04:48 AM
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It's refreshing to see a build like this going together! Thanks for sharing your progress.
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post #7 of 30 Old 05-24-2019, 09:01 AM - Thread Starter
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Speed of progress greatly increased by help from my minion.

Remember, safety first. Proper eyewear is a must!
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post #8 of 30 Old 05-24-2019, 09:07 AM - Thread Starter
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Hate that the forum insists on turning all my pics sideways?
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post #9 of 30 Old 05-24-2019, 09:16 AM
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Interesting build. I am a fan of the CBT concept. I listened to them at Cedia last year and love what they do. I showed Arrow these as something that could possibly work for large microled installs.

Did you consult with Rick Craig about your design? I know he worked with someone on a build a couple of years ago using a tweeter and IIRC a 5" driver.


Found the project.
http://techtalk.parts-express.com/fo...c-40-cbt-array

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post #10 of 30 Old 05-24-2019, 09:28 AM
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Very nice! I love line arrays in general, never heard the CBT but I am sure they are fantastic. Small driver arrays lack that midbass of bigger drivers or that fuller deeper sound, so integrating them into the subs does wonders.

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post #11 of 30 Old 05-24-2019, 10:55 AM - Thread Starter
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Quote:
Originally Posted by Ericglo View Post
Interesting build. I am a fan of the CBT concept. I listened to them at Cedia last year and love what they do. I showed Arrow these as something that could possibly work for large microled installs.

Did you consult with Rick Craig about your design? I know he worked with someone on a build a couple of years ago using a tweeter and IIRC a 5" driver.


Found the project.
http://techtalk.parts-express.com/fo...c-40-cbt-array
I did shoot Rick a message. He offers a CBT that sounds identical or at least very similar to the design you linked to. I thought about going that route but wanted to keep baffle width down so 4" instead of 5" driver, and didn't like the largish CC spacing of tweeters in that build so went with a similar (maybe same?) tweeter without faceplate.

This first pair is to see if those design choices pan out or not. Hoping so!
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post #12 of 30 Old 05-24-2019, 11:00 AM - Thread Starter
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Originally Posted by MKtheater View Post
Very nice! I love line arrays in general, never heard the CBT but I am sure they are fantastic. Small driver arrays lack that midbass of bigger drivers or that fuller deeper sound, so integrating them into the subs does wonders.
I'm curious as to how these will do in that critical for theater midbass range. They have pretty decent combine displacement... these little Daytons really can move. I will have room for whatever overkill sub solution I decide on. But will I be missing that impact from 80-150Hz or so?

If so one option might be using a midbass module at the base of each CBT array. I have a Dayton reference 12 HF lying around so may experiment with that if needed. Another option would be to relegate these to surround duties and go for an even more capable design up front using something like the Anarchy 5.5". Or maybe the little tangband minisubs but I don't know if their upper range would be sufficient to mate with tweeter.
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post #13 of 30 Old 05-24-2019, 11:12 AM
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PE sent me an email with their new dual magnet drivers. Not sure if that would be better than the NDs for mid bass or not
https://www.parts-express.com/promo/...51076647214948

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post #14 of 30 Old 05-24-2019, 12:23 PM - Thread Starter
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PE sent me an email with their new dual magnet drivers. Not sure if that would be better than the NDs for mid bass or not
I saw those, look like really interesting drivers. Square flange would certainly simplify routing. Wonder how the distortion compares?

They are a little displacement challenged compared to the ND series (as are most other 4" drivers!), 2.5mm vs 4mm with an even greater xmech discrepancy I would think as the ND is at 10mm.
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Anyone have experience listening to a multichannel setup using a combination of CBT and non-CBT speakers for LCR vs surround (or vise-versa)? Other than at the MLP it seems generally the relative balance between the LCR vs surround would shift more noticeably.

@Bigus Your build looks great, I look forward to your impressions.
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post #16 of 30 Old 05-24-2019, 01:34 PM - Thread Starter
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Anyone have experience listening to a multichannel setup using a combination of CBT and non-CBT speakers for LCR vs surround (or vise-versa)? Other than at the MLP it seems generally the relative balance between the LCR vs surround would shift more noticeably.
This is my first foray into CBT. But I will comment generally speaking that CBT follows a similar -3dB per doubling of distance as linear line arrays do vs the more typical -6dB.

Arrays all around give less variation in spl among seating positions and rows due to variable distances from each speaker. But even arrays up front and conventional in the rear will see some of that benefit as the LCR would have relatively less variation even if surrounds varied more tylically.

Ad for tonal balance I can't say. CBT has a more well behaved horizontal response and thus better power response than a straight line array. Seems you'd want to match to a similarly well behaved surround, like a waveguide perhaps.

I may face that decision as well because I don't see using this design for overhead atmos speakers even if I really really like it!
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post #17 of 30 Old 05-24-2019, 11:00 PM - Thread Starter
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Four side panels template routed and sanded to an exact match.
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post #18 of 30 Old 05-25-2019, 02:37 PM - Thread Starter
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Bracing clamped and gluing.

I tried aligning one standing, the other lying on side. If I decide to build more of these I think I'd want to work on a traditional woodworking table that was perfectly flat, have some right angle jigs to ensure the two panels were perfectly aligned, and clamp to the table.

I was able to get this pair right but only after considerable time and frustration.
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post #19 of 30 Old 05-25-2019, 02:40 PM - Thread Starter
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Braces. These stop short of front face leaving plenty of clearance for drivers.
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post #20 of 30 Old 05-27-2019, 11:33 AM - Thread Starter
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Center punching all holes to be drilled and countersunk in face via the template jig.
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post #21 of 30 Old 05-27-2019, 11:35 AM - Thread Starter
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I tried using a hand drill on test piece since the locations are all center punched, but just didn't feel I was consistently enough perpendicular. Press is going to take a heck of a lot longer but at least I'll know they are done right.
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post #22 of 30 Old 05-30-2019, 07:44 PM - Thread Starter
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It's killing me that I haven't been able to make any progress the last few days. And headed out of town next week.

A test on scrap piece with quicky flat spray finish. Keep the square profile on midrange diver hole, or maybe add a tiny roundover?
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post #23 of 30 Old 05-30-2019, 08:06 PM
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It's killing me that I haven't been able to make any progress the last few days. And headed out of town next week.



A test on scrap piece with quicky flat spray finish. Keep the square profile on midrange diver hole, or maybe add a tiny roundover?

Tiny round over would be pretty cool.

Leave it at 8 ohms and call it a day :)
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post #24 of 30 Old 05-30-2019, 08:09 PM - Thread Starter
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I think I'll try that on the test piece and see how it looks.
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post #25 of 30 Old 06-13-2019, 12:04 PM
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Any updates?

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post #26 of 30 Old 06-13-2019, 01:59 PM
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Quote:
Originally Posted by Bigus View Post
I think I'll try that on the test piece and see how it looks.
I'd vote for the round over, but I'm a bit biased

Those drivers are going to look awesome in the array! Will the tweeters be mounted flush with the front baffle? They're press-fit correct?
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post #27 of 30 Old 06-13-2019, 04:40 PM - Thread Starter
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Any updates?
Week at the beach and then busy week at work. I managed to get all of one baffle drilled and a good start on the other. I'll have some time tomorrow evening and hopefully at other times this weekend and see how far I can get.
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post #28 of 30 Old 06-13-2019, 04:43 PM - Thread Starter
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I'd vote for the round over, but I'm a bit biased

Those drivers are going to look awesome in the array! Will the tweeters be mounted flush with the front baffle? They're press-fit correct?
Thanks. I had to order a new but... the countersink holes are very close to driver cutout so a max 1/16" roundover can be used. Smallest but I had was 1/8" radius. It will be here tomorrow, I'll see if I can get pics of the test piece up this weekend.

Tweeters are sort of pressfit. Aggravating. They have a ring slightly larger diameter than the face and little bumps the same size where terminals attach. Will be a tight fit mid tweeter but leave a tiny gap ring around the face. Hoping I can seal it carefully with some black silicone.
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post #29 of 30 Old 06-14-2019, 09:30 PM - Thread Starter
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Quick and dirty with 1/16" roundover.

Can't go any bigger because of screws.

I finished all the countersunk holes for driver and baffle mounting and did the 1/16" roundover on midrange cutouts. Not a big difference from square but I like a little better.

Tried a test bend of the faces without kerf cuts... close but not comfortable doing it without. Maybe if I steamed the wood but I think I'll just do the kerf bend instead. Been wanting to put my neighbors sawstop to use anyway.
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post #30 of 30 Old 08-12-2019, 01:42 PM - Thread Starter
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Man, been too busy lately between work and putting out fires with house construction. Not literal fires thankfully.

Have made a little progress thiugh. Faces are all countersunk and routed except from the side chamfers which I may do with chamfer template bit while mounted.

Finished the pattern for the base and rough cut the 4 pieces I'll need for this pair. Double thickness for each base, the bottom layer gets the cutouts to allow terminal mounting hidden under speaker and exiting at rear. Will get these template routed soon and then tackle the kerf cuts to bend faces.
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