The POOR man's Tannoy DMT - AKA "The PM-DMT"

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It seems most 12"-15" pa coaxials reguire large enclosures to reach low (100litres or more), including the beta 12cx. Highpassing coax-LF you would get smaller overall enclosure. If go three way, maybe use subwoofer driver instead of coax woofer to get even smaller enclosure.
 
I use the Beta8 CX with a subwoofer. Very pleased with results. HF driver is ASD10001 which performs well, but requires unusual and slightly complex crossover.

Being done with the Beta8 project, I might take a swing at the Beta 12, probably try the D202 HF driver. It looks much easier to deal with than the ASD1001
 

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Older = better, hmmm depends. We will go for NEW here :)

3 hands of Dammar varnish..... on a loudspeaker cone...:eek: Would you do THAT again?

Dammar can transform any cheap paper cone into a refined instrument. You only have to varnish during the hot season, one hand per year, to avoid long curing times. :eek:

Those old coaxials I mentioned have low resonant point, apparently.


Well my HF hearing is slightly but surely degrading, can't even remember during my whole life (64 now ) being capable of hearing a 20 kHz "tone". :confused:

Are the Autograph's hand build by yourself ? Look good, what's the horn shape bottom part of the enclosure ?

kind regards.

Yes. They took 4 months of my life. :D
What bottom part? Maybe you are looking at the 2:3 replica?

IMHO, if you want to make loud noise, go for the dual woofers + bass reflex. If you care about musical reproduction, go for single 15" coaxial plus parallel slit ports, like some Tannoy and Onken 360. Do not save on good quality plywood or better, real wood.

I adapted some heavy wood woofers to a kind of Onken 360 (previously bass reflex) and the bass is more correct. The original Onken can be modified to have extra wider bass horn and even a midrange horn, like the Autograph's one, could be added. :)

Good luck and have fun.
M.
 

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3 way, not some crappy 2.5 way. Gets the lower midbass out of the coax cone, drastically reducing excursion which is good as the coax cone is the WG for the HF. I find the Tannoy logic for driver choice/xover dumb at best.

I've actually done this before with things like JBL 18 below the Tannoy coax (a variety as I've owned most of them) and found it improved the midrange substantially.

I currently have 2 projects that include coaxes; my surrounds, a Faital 8HX200 + 15" midbass and a similar bedroom speaker using the 6HX150 and a 15. All active of course.
 
Hey Brett,

Just while I was thinking, if 3-way is the way to go, why on earth would they use a 15" for > 250 < 1500 Hz?. Then came your point, the cone is the " horn" of the coax HF. As I understand the circumference of the round horn (the cone at its surround) will determine the lowest frequency for correct horn behaviour.

For a 15", that would be 2*3,14*19 = 1,19 m. That would give 340 / 1,19 = 285 Hz. That's the lowest point for the HF, but we want to cross at around 1200 to 1500 Hz. 285 Hz is on the very very very safe side. So we don't need a 15" here. A 12" would give 340 Hz, a 10" would give 450 Hz and so on. It would take a 4" driver to support 1200 Hz (providing I can use a calculator...).

So, a 5", 6" or 8" coaxial with a 15" LF would perform just as well as 2x 15". Your projects make perfect sense. Price wise that would be beneficial :D

What was Tannoy's idea behind the DMT 215 and WHY are they still popular. Or is it just gobble gobble talk? I can see a 15" will produce a nice soundstage in a relative small room (like a studio control room or at home) so that's a logical LF choice. The coaxial however makes me wonder. :confused:

As always, it's just one reason to make up a decision. It's more like the principle of decision trees and the most beneficial use of it. Like in chess, for each step in the game there are numerous options, the person that can think ahead in as much decision trees as possible will most likely win.

So what's the decision tree for 2x 15"?

Any ideas, comments??

Hhmmm, so much for logical choices.
 
Why a 15" coaxial?

Puzzled by my previous post, I went to search the web.

Read this (in an article about the Tannoy Buckingham and the start of Tannoy's coaxial);

"Drawing from his knowledge of high efficiency products made for the high quality public address market, the Chief Engineer, Mr. Ronnie H. Rackham combined a high frequency compression horn drive unit concentrically with a 15" direct radiating bass driver. His skill in designing wide band horn systems married the two drivers together so that the flare shape of the 15" bass unit continued the flare rate of the high frequency unit.
It was this important part of the design process that conceived a very low coloration horn device. Because the HF horn had a very large mouth diameter it had an inherently low cutoff frequency. The crossover point from the bass to high frequency was selected at 1kHz; nearly a whole octave above the natural horn frequency lower cut off point, leading to previously unheard of low levels of coloration".

So there we have it, although way to large, it's the benefit of low coloration that makes these Tannoys sound so "neutral". That's also what I like about my Tannoys.

Looking at the Tannoy Buckingham, that's a configuration that maybe is more to my liking. 2x 12" to around 300 Hz and a 6" (or 8") coaxial for mid and high. Proper 3-way with large impact and point source.

To be continued.
 
Then came your point, the cone is the " horn" of the coax HF. As I understand the circumference of the round horn (the cone at its surround) will determine the lowest frequency for correct horn behaviour.

For a 15", that would be 2*3,14*19 = 1,19 m. That would give 340 / 1,19 = 285 Hz. That's the lowest point for the HF, but we want to cross at around 1200 to 1500 Hz. 285 Hz is on the very very very safe side. So we don't need a 15" here. A 12" would give 340 Hz, a 10" would give 450 Hz and so on. It would take a 4" driver to support 1200 Hz (providing I can use a calculator...).
Not quite. The cone depth isn't sufficient to support anything like the level of LF loading for the HF driver to get down to the numbers you suggest from a raw circumference calculation. I don't have directivity numbers for the Tannoy drivers, but many of the modern pro coaxes often do. Use similar frame sizes as a guide.

So, a 5", 6" or 8" coaxial with a 15" LF would perform just as well as 2x 15". Your projects make perfect sense. Price wise that would be beneficial
It could potentially be; how it turns out will depend upon the totality of the design decisions around the project.

What was Tannoy's idea behind the DMT 215 and WHY are they still popular. Or is it just gobble gobble talk? I can see a 15" will produce a nice soundstage in a relative small room (like a studio control room or at home) so that's a logical LF choice. The coaxial however makes me wonder.
I ignore pretty much anything manufacturers post on their products as I've read far too much self serving rubbish over the years. Stick to the physics.

My reasons for the two projects I mentioned were to heep as much of the bandwidth as possible on the coaxes, and get all of the midbass onto a dedicated driver to get the coax cone moving as little as possible to keep the mids clean and give me lots of SPL capability when and if I need/want it. Plus I already own all the drivers.
 
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I got it, I think

With the input I got from y'all;

- Coaxials BUT avoid the low-mid bass
- Go 3-way
- Active wins over passive

My own preference;

- Sonically in the Pro range
- Loud enough to make you rock (if anything else)
- Cheap as possible (affordable for most)
- 2x LF (I'll come back to that) both play the same notes.
- Be able to handle (in size and weight)

I came up with the following (yes I'm a bit comprehensively ;) );

The configuration would be 2x LF (hold your breath, I'll come to that) and 1x Coax.

Side note:
For the LF's, years ago I just by accident found that there's a logic behind the diameter (or it just happens to be). A 15" has the same Sd / Vas (give or take) as 2x 12". A 12" has the same Sd / Vas as 2x 10". Etc.
From my experiments with subs for my "PA in the boot of your car" I found that a smaller LF driver sounds tighter, more direct because of its smaller cone (defraction / cone break-up issues). Of-course, 1 smaller driver can't keep up with the bigger one, but 2 of them can. Adding to that, it's 2x the magnet, ½ the power to handle per speaker, could be cheaper (sometimes not, but mostly +- 10%).


So IF our PM-DMT would be 2x 15" (which started this whole shebang), with our (see above) choices, it would become a 2x 12" for the LF (= one 15") and a Coaxial to replace the other 15" (doesn't have to be 15" as it plays from around 250Hz). Could also be 4x 10", w'll see. It would make the box somewhat bigger.

The config will be:
- 2x 12" LF and 1x 8" (or 10") Coaxial MF & HF.
- 3 Way active crossing depends on drivers 250 Hz & 3.5 kHz
- Bass reflex OR Transmission line. BR seems a "safe" choice and most suppliers provide all there data based on BR, I have little experience with TL. So maybe, that will be the next version.
- Coax in a sealed enclosure with a acoustic roll-off around 250 Hz.
- Target for around 100 - 150 liter cabinet, so select LF on it's capability to perform well in a small BR (which there are). That way, it's kind of easy to handle.
- Use 18 mm bitch BB quality plywood. (low weight, high strength).
- Solid bracing
:D

Side notes;
- Why 3.5 kHz? If we look at the whole sound scape we want to reproduce and find the "most important" sound area / human musical attention, it would be human voice and solo instruments. Looking at the frequency range, that's mostly between 250 and 3.5kHz (3.5 is the frequency that makes up for the "s, t, etc) in the words we pronounce. If we can't here would people say, a big part comes from this frequency that does not stand out enough (or the person just doesn't pronounce clearly but we can't make up for that). I don't want to cross in that area from one driver to the other, but leave this up-to only one driver (the MF of the coax).

- On Coaxials, maybe it's wise to look for a coax driver including it's HF (one kit) as opposed to what I so far did, find a low-mid driver which is the frame of a coax and look for a HF and bang them together. That way, we can forget about the issues we run into as a result of the technical connection. May still do, but why make it our selves complicated here.

Now, How's that for a start? :cool:
 
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To whom it may be of interest,

Depending on experiences and/or personal preferences we orient our projects. Usually, a frequency dependent approach is used... :(

My interest is towards dynamics (time domain) and transparency. I comment this because there is an aspect of reproduction that I have not seen commented: when only the tweeter is horn loaded there is a lack of coherence between HF and the rest of frequencies. The horn being an acoustic amplifier, it not only increases the sensitivity of the transducer (a technical question) but it produces an increase in the sense of musical dynamics (a perceptive question) so the sounds "jumps" at you. When the midrange and bass does not jump, there is a perceived difference, a lack of dynamic coherence, between tweeter and the rest. If you never heard it right you probably will not complaint, but there will be always something odd (like some Klipsh speakers) to the sound presentation. That is why I sold my Tannoy Definition 500 speakers when I first listened to my 2:3 Autograph replica with cheap full-range driver and that is why the GRF Autograph enclosure is so good; not only it has also midrange and bass horns but it does so in a "point source" more or less manner so there is coherence in time and space: a relaxing experience.

Take a look here for description of sound perception:

Rick's Tannoy Autograph Enclosures

While the Autograph can be considered a titanic effort, something comparable can be achieved with less complicated enclosures. Take a look to my quick drawing of the modified Onken 360 (this one is the Petit version) I talked before. I hate square boxes so mine wood be triangle (corner) or trapezoid in shape.

Dynamics. :cool:

Just saying...

Best wishes, M.

PS: sorry, I did not see your last post...
 

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To whom it may be of interest,

Depending on experiences and/or personal preferences we orient our projects. Usually, a frequency dependent approach is used... :(

My interest is towards dynamics (time domain) and transparency.....

Dynamics. :cool:

Just saying...

Best wishes, M.

PS: sorry, I did not see your last post...

Hey Max,

Thanks to bring this up.

I am a BIG Horn fan and have build some in the past. One of them was a "correct version" of the Electro Voice Eliminator 1. What I did not understand at that time is that commercial companies need to cut corners to build affordable loudspeakers. Now a days, asking 20 - 60 K-euro's is apparently not an issue, which I can understand, but was a reason for me to dive into this an see if we could come up with an alternative for those that cannot afford.

Your topic;

1 - We could incorporate a modern version (the tapped horn from Tom Danley) for the low range. That would make it bigger (you need to have a ¼ wavelength of the lowest freq. to play within the cabinet so to speak) and difficult, but not impossible to do. It makes the horn way shorter and still behave like a horn. No matter what, you need to squeeze a complete horn (or better the most importent part and enough of it) into a box and use the surrounding to make a complete again. They will always be kind of "little" monsters. The tapped horn front AND back loads the driver making a much better coupling (equal both ways of the cone movement) of the driver. The tannoy's have a low freq. back load and a mid frequency front load. Different animal partly.

Draw back of the corner loaded folded horn you mention here, is just this fact, it MUST be corner loaded (it's folded from the driver point to squeeze the length into a rather small cabinet (ahummm) and at the end of the horn path, use the wall to extend the horn. Since it's a trick used to make a smaller (part of the horn) version of the real thing (which would be immense). ADDING the fact that I aim for Studio control room ONLY here, where they will be placed some 2 meters form the console (flush mounted in your face so to speak) makes that It's not the same target. The tapped horn could be placed anywhere, although corner loading would make it LOUDER, not run LOWER.

Talking of the devil, while I write this down, THAT's a Synergy horn. :D horn loading ALL drivers, with the LF tapped, the MF front load and the HF at the start of the horn. I added a drawing of the animal.

2 - We could mount the coax in a mid range horn (conical or exponential) within the cabinet, that would not add up this much in volume (details to be seen). I haven opted for a coax as it acts like a point source in the MF to HF domain, so no acoustic cancelation, comb filtering issues. NOT the fact that the HF will be horn loaded, which is a kind of draw back as you correctly point out.

Come to think of it, then a Transmission Line would maybe be a better option, which is also a ¼ wavelength monster, but only back-loads the driver. a 12" would require at least a 100 liter cabinet to start working. Also does not require corner loading. Charles did that for the LF in combination with a 12" Tannoy coaxial.

So maybe no Bass reflex and horn load the coax. But, no offence, now we need to do apples by apples. A wrong designed horn will sound AWFULL, so will a bass reflex. A correctly designed horn will sound loose and natural, may out perform a correctly designed BR but a correctly applied BR could turn out nicely. They just completely different animals. It's also our ears that come into play here, our perception of sound works very odd in our brain.

But hey, lets first there to get an idea on paper.


You're on the radar... specifically for dynamics :nod:

kind regards.
 

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Come to think of it, then a Transmission Line would maybe be a better option, which is also a ¼ wavelength monster, but only back-loads the driver. a 12" would require at least a 100 liter cabinet to start working. Also does not require corner loading. Charles did that for the LF in combination with a 12" Tannoy coaxial.

Good. I've also thought about that, Like a PMC-coaxial. :lickface:

MB2-A SE (Active) | PMC Loudspeakers
 
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First Version

OK,

Just a rough sketch

Using Faital's (because I have them in store) 12PR300 & 8HX200.

This is the bass reflex version. I feel a strong urge in getting a TL version as well.

30 - 20.000 Hz +- 3 dB. Don't mind the x-max warnings here, the Faital can handle this with ease, xlim = 14 mm.

Note the Coaxial hardly moves at 1,6 mm @ 250 watt. Need some eq'ing as to be expected.

See attachments for details, drawing in pdf NOT TO scale (yet). Gives a first idea.

KInd regards.
 

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Side notes;
- Why 3.5 kHz? If we look at the whole sound scape we want to reproduce and find the "most important" sound area / human musical attention, it would be human voice and solo instruments. Looking at the frequency range, that's mostly between 250 and 3.5kHz (3.5 is the frequency that makes up for the "s, t, etc) in the words we pronounce. If we can't here would people say, a big part comes from this frequency that does not stand out enough (or the person just doesn't pronounce clearly but we can't make up for that). I don't want to cross in that area from one driver to the other, but leave this up-to only one driver (the MF of the coax).

- On Coaxials, maybe it's wise to look for a coax driver including it's HF (one kit) as opposed to what I so far did, find a low-mid driver which is the frame of a coax and look for a HF and bang them together. That way, we can forget about the issues we run into as a result of the technical connection. May still do, but why make it our selves complicated here.

Now, How's that for a start? :cool:

I'd be more concerned about getting a smooth dispersion than not crossing between 250Hz - 3.5k.
 
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