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Old 17th June 2013, 06:05 PM   #1
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Default Custom Celestion Ditton project - need expert opinions

I've been doing some serious brainstorming recently and, since I am going to have a fair bit of cash to play around with, I've been thinking I would like to embark on an interesting project.

Recently I acquired a pair of Celestion Ditton 25s, and while they are fantastic, my plan with them is to eventually turn them into a pair of Celestion Ditton 66s. But then, I got to thinking. What if, instead of doing that, I made an improved Celestion Ditton 66? I feel that the major flaw with the Ditton 66 is from the MD500 to the HF2000. It is crossed over at 5kHz and the HF2000 is really at its best above 10kHz. I think this is where the Ditton 25 is superior, but of course it lacks in the midrange bliss the Ditton 66 is known for. So, why not combine the two?

There are also some other improvements that could be made if the cabinets are going to be custom built. Such as totally isolated cabinets for the bass driver, midrange and tweeters. Separate crossovers could be used for each and allow for tri-amping. Also much better components on the crossovers could be used. And of course the cabinets could be made to be much nicer (although the 66s do look very nice as is).

I am able to get the schematics for both speakers, allowing me to combine the crossovers of both speakers and all I would really need is the cabinets built to specifications, which I can take from the cabinets of the 66 and 25, although of course I could make my own calculations and come up with a different sized cabinet that may be more suitable. But of course I think a lot of the groundwork has already been done in this department by Celestion which I can simply re-use.

So here's my design idea:

-Combine the Ditton 66 and Ditton 25 Drivers, that is use the 12" bass woofer with the ABR (or maybe without and instead port the 12", or in a sealed enclosure), the MD500 dome midrange, the two HF1300s from the 25, and the HF2000 for the top-end.
-Combine the Ditton 66 and Ditton 25 crossovers
-Separate and isolate into 3 sections for the bass, mid and tweeters
-Use better components for the crossovers
-Build nicer, stronger cabinets
-Allow for tri-amping

What I am looking for opinions on is the idea of this. I am a bit of an amateur when it comes to speaker design so that is why I am attempting this, by using the groundwork already done on the two speakers but somehow make a hybrid of the two while at the same time making some improvements.

I guess what I am really looking for is what areas of concern should I have from doing something like this? Is it even a good idea?

Any thoughts are welcome!
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Old 20th June 2013, 12:13 AM   #2
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I hear you. I have Celestion 44s and I love them. I have rebuilt the crossovers and replaced the HF2000s with Seas 19TFF1 19mm tweeters.

I also want to build an ultimate 3 way around the wonderful Celestion 12"

I also want to have each driver in its own cabinet, B&W 801/ Nautilus style.

Some points:

The 44s are a sealed box, and are in my opinion better than the 66s bass. The ABR allowed a lowed bass, down to 20Hz, whereas the 44s roll off a tad higher, but sealed cabinets produce a faster bass than ABR. A port would be a total mistake in my view. I have some ABRs here. They suck. Sealed cabinet is the best.

Definitely build better cabinets, from birch ply, instead of chipboard (yuck!)

Forget the HF 2000 - it is a lousy tweeter. 19TFF1 from Seas is the way to go - same resistance/ ohmage, much much better tweeter, and not overly priced. Lush!

THe MD500 is a mixed bag - limited range, old and often in need of complex repair, best of it's time. Crossing to these is going to be a compromise, as it was with the 66s. I think there are better options, both cone and dome, from modern designs.

What I plan to do is just what you are doing, but from the basis of the wonderful 12s, and taking nothing else from the 66s really. That's how to do the 66s but better!

Actually much simpler is to get the 44s - they are better than the 66s!

I hope I haven't pissed on your cornflakes, as they say.
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Last edited by LucasAdamson; 20th June 2013 at 12:19 AM.
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Old 20th June 2013, 12:17 AM   #3
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Oh, my top tip - sell the HF2000s - you might get more for them than the speakers cost you - I have several times!!! They pay for a lot of the restoration project - seriously they are deeply flawed tweeters from the very early days of tweeter design.
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Old 20th June 2013, 04:08 AM   #4
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I guess the only reason I wanted to work with the old drivers was to get the same flavor of sound.

I have read that the domes are a complicated repair and the response can vary depending on the state its in. This is starting to get me away from that.

Maybe I should use the 44 mids instead, as they do match the bass woofer in looks too, and maybe that with the Seas tweeter and do a 3-way. However I think one flaw is the midrange running up to 5kHz, I think it would be more suitable to run it down around say, 3.5kHz. I'll have to look into that Seas tweeter and see what its response is like. I agree that tweeters have come a long ways.
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Old 20th June 2013, 09:19 AM   #5
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Running the tweeters down to 3,500 is no problem at all as far as the graph shows.

http://www.phific.ee/138-294-thickbo...ge-19tff-1.jpg

The 44 mid is a very good paper cone driver that I am happy with, but there are modern dome mids that are considered to be excellent too if you'd rather go that route. Perhaps it makes more sense than the original dome mid that approaches its end of life. The 44 mid can certainly manage well beyond 5Khz with ease. Why are you keen to crossover lower?
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Old 20th June 2013, 12:56 PM   #6
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Well, I suppose it's because 5kHz seems like a high crossover point for a midrange driver. My thoughts were that they only used that crossover point because of the HF2000. 5kHz is already too low for the HF2000 and it seemed like they picked that high of a crossover point to work with its limitations. If the 44 mid can run up to 5kHz no problem though then I don't see why I wouldn't use that instead.

So I guess it's starting to sound like I'm going to be making an improved pair of 44s instead of 66s I was intending not to use the ABR anyways because I agree that the bass is a tad sloppy with it in there. I had a pair of 44s many months ago but the HF2000 domes were pushed in. However I recall the bass being very nice on those.
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Old 20th June 2013, 01:46 PM   #7
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Well, the 44s are excellent, but with improved cabinets, crossovers and tweeters, they would be sublime. I have done the crossovers and tweeters, and I'm very happy - the tweaking I am doing is now superficial in a way, but the cabinet can be improved I'm sure. The volume is correct, but sturdiness, damping, height are not optimal.
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Old 20th June 2013, 02:47 PM   #8
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Okay, I have pulled the trigger on a pair of Ditton 44 mids. Now I just need the crossover bits and to get cabinets measured to the right size.

Are you familiar with calculating cabinet sizes for drivers and what information I need for the calculations? I have a feeling I'm not going to easily find the internal volume and size of cabinet for the 44. It's also an odd size because the entire cabinet is open except for the midrange being isolated. I'm also going to have to calculate the size of the cabinet for the mid anyways.

I need the thiele small parameters I think right?
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Old 20th June 2013, 04:03 PM   #9
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I could measure I guess.

Give me a few days...
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Old 20th June 2013, 04:15 PM   #10
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Outside diameter of the 44s is 370mm wide x 260mm deep x 765mm tall. Wall thickness looks like standard 18mm, which would give inside measurements of:

370-36mm =344mm wide

260-36mm =224mm deep

765-36mm =729mm high

Now I realise that the box size and shape may have been partly a question of practicality, and that there is a mid box inside, which I can't measure right now, but that's something to be getting on with...
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