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Tobias Tosin Partridjent

PE-Dayton Audio CBT24 Epique Build Log

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Hey Everyone, 

 

First time posting here but long-term audiophile since I was in high school.

 

Back in about July 2017 I purchased this speaker kit from the USA, this is a Dayton Audio / Parts Express kit jointly designed by Don Keele, Jr.

I've always been very interested in this technology as the ground plane version that these are and the version before use the floor reflection as an advantage instead of a destructive influence. 

 

The kit is called the CBT24, "Epique" I purchased the kit as the difference in price is about 500USD, I thought I could save a lot on painting and assembling myself (and I did).

 

The kit comes with premade wiring harness for both, all major wood working assembly already done, wiring binding post input cup, bolts, drivers, screws, name plates and sound deadening. 

24 x 2-inch Dayton Audio ND64-16 2-1/2" Full Range drivers are what these are designed around, each are 16 ohms DC, with the harness a 4-ohm load total is what is seen at the amp.

 

The wiring in the CBT24 is such that the loudest output are at the floor and quietest (12db approx.) down at the top, only two massive resistors are needed for the attenuation/padding of the last couple of drivers, more on the technology and the shading maths behind it can be found on Dons website : http://www.xlrtechs.com/dbkeele.com/

 

Below is a timeline of photos from the start to finish:

 

The padding resistors I added a little zip tie to remove the strain on the resistor leads, there are two in each speaker, so this is added insurance the resistor wouldn't break in two :P

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The MDF boxes as delivered, I test fitted the drivers and noted that the side walls were a little tight on the outside basket of the drivers, especially at the ends of the boxes, I noted this and sanded those MDF edges heavily, this is something I did tell the supplier about, even just 1 mm wider would have been nice to reduce the chance of scratching the paint/finish.

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Here are the Dayton Audio ND64-16 2-1/2" Drivers, very well made for how cheap they are, especially when there is 48 x of them :)

I did discover however that the metal frame vents do get blocked off quite a bit on the MDF cut-outs as the thickness and proximity of the MDF is almost the same height, I left the boxes un modified due to the amount of work to correct this. Chamfers on the rear inside edges of all the driver cut-outs would be a nice change in future versions to release the pressure, this choking does affect the TS parameters of the woofers from reading I’ve done.

 

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After receiving the kit, I did research on MDF preparation etc, I settled on the following procedure sticking to Oil Based paint the whole way through:

1) Sand RAW MDF with White 180 Grit Sandpaper

2) Seal with Dulux Prep coat 1Step Oil Based Primer, Sealer & Undercoat, I rolled this on with roller and a fine good quality brush.

3) Sanded Undercoat with 220 Grit Sandpaper

4) Apply Base/Final coats: Rust-Oleum 2x UltraCover Paint+Primer with light sanding between.

5) Apply Clear coat: Also Rust-Oleum Branded Gross finish.

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I first painted the bases completely to get a feel for my ability, I did work out my approach to sanding the undercoat was not enough, I did get a slight orange peel look to it, I fixed this in the tower painting by sanding the under coat with 180 then 220 Grit to first get the levels all correct and then sand further to smooth it.

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Once I was happy with the bases (halted at clear-coat stage) I stared on the towers, these took about a day to sand ready, I also filled in gaps like the one below with some putty :)

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Next, I coated everything in one go so that the panels that would be seen the most, two sides, top and front where well connected and consistent finish. I rolled on this undercoat and brushed on small tight areas too to make sure even coverage. I did fail to seal the bottom thick enough the first time haha, I fixed this later by just using the roller.

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This was both towers fully coated and drying (no picture of rear panel and bottom being finished)

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Next, I sanded them with 180 then 220 grit sandpaper, and cleaned them thoroughly before the main black paint, here I laid them down on one side, this method seemed to work very well for the base black paint as I could get nice even application. Each coat on each speaker was recorded so i could track where i was up to, I alternated between sides, back and front to get even coverage.

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Once all the main paint was done I proceeded to attach the towers to the bases, in hindsight this was a mistake for the clear coat, I worked out with the clear coat that actually almost flooding the area of application instead of a thin coat resulted in less over-spray or chemical dust getting on the bases and other panels. I instead disassembled them and made some temporary feet from scrap MDF I had, this allowed clear coating of the bases and towers to be down separate which resulted in a much more professional look. In the end I ended up using approx 2litres of clear coat in spray-can form to coat these o-o

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I left them to dry for approx 8 days to make sure as much of the fumes was gone, I then blew all the dust out ready to bring inside, I settled on not even sanding or polishing the finish as it was already butter smooth.

 

I attached the base temporarily and sat both upright to install the wiring harness in both through the top hole. A recommendation I read was to leave the speaker input cup until last instead of connecting it first, as fly leads outside the box were much easier to connect instead of reaching in.

 

I then laid them the towers on their side, removed the base and used a little hot glue gun and glued the harnesses in place in both boxes, making sure each labelled connection came out the correct baffle hole number and that the wiring and resistors were far back as possible from each driver, without being to far for the cables not to reach.

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Once wiring was done I inserted and left loose the Polyfil sound deadening.

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Once all the wiring was done I unpacked all the 48x woofers and tested all for similar resistance and for mechanical noise - all passed :) 

I then screwed in all the drivers by hand, I strongly suggest test fitting each and pushing them down first as some of the spade input terminal areas of the woofers had a tad to much solder, rubbing up against the MDF cut-out. Finally the bases could be attached for the last time completing the build.

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I then spent a whole heap of time setting them up.

Nice little arty picture here:

 

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The system they are now apart of consists of the following:

2x CBT24

1x NAD C245BEE 4 channel amp (only two channels used as 4ohm load)

1x Custom made digital Preamp (pictured below), USB Streamer, Optical/Coaxial SPDIF input, MiniDSP branded 2x4 + MiniDigi combo, running left and right active sub-woofers in stereo or 2 in 4 out.

2x Yamaha NS-SW300 sub-woofers in stereo (not summed mono)

1x Marantz CD32 CD Player.

 

No room correction on the MiniDSP at this time, only a phase flip on the subs, crossovers are 100hz @ LR 48db/Octave.

 

The system sounds awesome even without E.Q. and is well worth the time put it.

Thanks for Reading, please leave a comment :)

 

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:)

 

 

 

 

 

 

Edited by Tobias Tosin Partridjent
spellcheck

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13 hours ago, Al.M said:

Nice work, how do they sound?

Hey AI.M, 

 

Thankyou, they sound very interesting indeed, I am using them in a carpeted room at the moment, I haven't had a chance to setup my RTA microphone but from the initial listening they sound as claimed - the frequency response sounds almost exactly the same whether standing, sitting and no change in distance from front of room to the back of the room, the best way I can describe it is its like a hologram or like those old films where the eyes follow you/look at you from the painting. The next thing which is known is as they are like a massive CD horn they will need slight correction of high frequency, the drivers apparently already have a slight rising response to account for this, but more might be needed for particular room and because of the tweeter-less design.

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Very interesting design and great work!

Do the many small drivers generate sufficient bass down to the 100Hz Xover to the subs?

Is there enough cone radiating area and Xmax available with 12 drivers each side to reach down to 100Hz at reasonable volume?

 

cheers

Mike

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Very impressive kit mate. You've been able to finish them to a very high standard too which must be hugely satisfying. Well done!

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1 hour ago, Upfront said:

Very impressive kit mate. You've been able to finish them to a very high standard too which must be hugely satisfying. Well done!

Thanks Upfront haha, Yeah I was super worried, it was the first time I've ever painted MDF to a finish of that calibre so I'm really happy, it was surprising easy when I just took the time and patience.

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1 hour ago, almikel said:

Very interesting design and great work!

Do the many small drivers generate sufficient bass down to the 100Hz Xover to the subs?

Is there enough cone radiating area and Xmax available with 12 drivers each side to reach down to 100Hz at reasonable volume?

 

cheers

Mike

Yeah they are have a about 4-5dB down response at 100hz, so flat to 150, so the crossover is not too bad of choice, I may end up raising it but, that being said the Yamaha NS-SW300 subs actually sound amazing and noise free even up high so i've got some room to work, i put the steepest I could digitally to protect them from the really low stuff to reduce box vibrations and wasted power.

Second question Im not quite sure, even with all the surface area effectively it probably adds up to a 8 inch woofer or something.

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23 hours ago, Tobias Tosin Partridjent said:

Yeah they are have a about 4-5dB down response at 100hz, so flat to 150, so the crossover is not too bad of choice, I may end up raising it but, that being said the Yamaha NS-SW300 subs actually sound amazing and noise free even up high so i've got some room to work, i put the steepest I could digitally to protect them from the really low stuff to reduce box vibrations and wasted power.

The great thing about your setup is that with MiniDSP and stereo subs you can tweak until you hit the optimum.

I had a quick look at the Yamaha subs - the spec says up to 160Hz, but they're a 10" driver, so you shouldn't hit cone breakup issues till much higher.

 

I'd be experimenting with the crossover point between 150 - 200Hz and hear what sounds best.

160Hz would have the sub covering 3 octaves - which is a reasonable target for an individual driver.

The array would still need to cover 7 octaves, which is a lot, but that's what your array is all about.

 

Taking away 100Hz - 160Hz or 200Hz from the full range Dayton drivers will take a lot of excursion load off, and excursion equals distortion - keep in mind they only have 1.9mm Xmax.

 

As much as it's fun watching drivers move (well maybe that's just me) - but as a guide, if you can see the Dayton drivers moving, then you've either got the wick wound up too much or you need to sneak the crossover up higher.

 

I realise it's a stupid comparison in this context, but I've had numerous people listening to my stereo asking if my 18"s were working - they could hear great bass but they couldn't see the cones moving (they were moving, but just a little bit :))

 

You can't "hurt" the Yamaha subs by running them higher - it's all about how cleanly the Yammies can play up high (I run my 18"s to 300Hz).

You can sure hurt the Dayton drivers by running them too low at elevated volumes and exceed Xmax and/or thermal limits.

 

Just love your project - well done!

Keen to see your updates as you tweak/tune the setup.

 

cheers

Mike

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