Pictures of GM MLTL-48?

[ulfheden]

Regarding reflections inside triangular cabinets, Bailey explained it quite well in his original TL articles. Instead of one loud pulse from the rear wall, the triangular cabinet gives a series of diminishing pulses, all of which are at a much lower volume than the single pulse. Same amount of energy but distributed in frequency rather than amplitude. It's a neat solution. (Alternatively, I suppose you could make a rectangular box and place a triangular shape inside but you'd end up with a bigger box.)

Do you have any pointers to to the articles you mention?

The distance to the point of reflection would be constant no matter which way the waves travel as long as the wave propagating backwards is flat. But perhaps this is not the case considering the cone shape and higher frequencies?

I'm still shaking my head at this.

/Peter

 

[GM]

Greets!

There's two basic speaker design 'camps', those who only want to reproduce the signal and those who want a 'musical' system. I quickly realized that I preferred the former, so spent my DIY 'career' trying to find the right balance between adding/subtracting to the signal that netted as neutral as practical for the amount of acoustic gain I required for the app, which I concluded that in general WRT cab design meant a high aspect ratio rigid cab with just the right amount of acoustic gain with minimal internal damping. The original (short) MLTL design I did using at least 19 mm BB ply theoretically 'fills the bill', but I've never built/auditioned either the short or long version, so as always YMMV.

The theoretical max length version that ya'll prefer is in theory way too 'musical' for me unless heavily stuffed as even an MJK one dimenional sim shows strong resonances. Per Bailey (FYI, he just restated decades old prior knowledge), triangular construction combined with minimal internal damping negates the other axes contribution as long as included wall angles are > ~12 deg, so plenty of cab shape flexibility.

Anyway, glad folks are still enjoying these, I haven't been able to do hardly any DIY audio beyond 'bench racing' for over a decade now, so have to get my 'fix' vicariously through the efforts of others, so thanks for the continuing interest, kind words, and feedback! And of course, 'hats off' to TJ for all his decades long efforts to create a driver and publishing 'accurate enough' specs that makes designing a successful speaker without measurements, or even auditioning it, a simple procedure with just an absolute minimum knowledge of speaker design (i.e. Vb = Vas, Fb = Fs).

GM

 

[Dumbass]

OK, I understand what you say. Perhaps I put foot in mouth, but I don't think it works.

First of all, I can't see how colliding sound waves gets converted to heat. If that was the case we wouldn't have any propagating sound waves at all. Yes, I admit that gasses get hot when preassurized but that heat gets converted back to motion of the air molecules when the wave propagates and the preassure drops.

I'd say, when the sound waves collides the preassure just gets up and you will end up with a plain reflection.

Secondly, I can't see how the 45 degree reflector chamber would work differently if it was divided in in two symmetrical halves by a horizontal piece of thin solid material.

Consider the line where the sound waves collide. There must be a thin line of air molecules that don't move because they see equal pressure from both reflections. If we would replace that line of molecules that doesn't move with something solid, it wouldn't make any difference. Right?

In this case there is just a series of reflections. The first reflection is at 45 degree back. The second is at the centerline where the molecules don't move. The third is at the same 45 degree back again.

As I originally stated, my explanation was fatally imprecise.

I finally tracked down one of Ron's explanations:
http://gainclone.com/phpBB2/viewtopic.php?t=628

Read the entire thread.

 

[ulfheden]

As I originally stated, my explanation was fatally imprecise.

I finally tracked down one of Ron's explanations:
http://gainclone.com/phpBB2/viewtopic.php?t=628

Read the entire thread.

Yes I've read it several times now and I think your explanation was not at all imprecise.

What still remains an issue for me is that two sound waves of equal phase would cancel if they meet.

If you don't want to comment on my explanation in the previous post why this does not work, please at least consider the case when you have 2 speakers closely facing each other, playing in phase, in mono. Would those waves cancel? Will you have silence?

Then putting thermistors in styrofoam is a very bad idea itself. In order to measure the resistance of a thermistor you have to put a small current through it. That current will of course generate a small amount of heat in the thermistor. Normally the heat will dissapate to the air and the temperature of the thermistor will be very close to the temperature of the air, but when you stick it into styrofoam it will be insulated and the temperature of the thermistor will rise because the heat has no where to go. Some heat will still dissapate through the leads though, but you get the picture.

 

[Dumbass]

Yes I've read it several times now and I think your explanation was not at all imprecise.

What still remains an issue for me is that two sound waves of equal phase would cancel if they meet.

If you don't want to comment on my explanation in the previous post why this does not work, please at least consider the case when you have 2 speakers closely facing each other, playing in phase, in mono. Would those waves cancel? Will you have silence?

Then putting thermistors in styrofoam is a very bad idea itself. In order to measure the resistance of a thermistor you have to put a small current through it. That current will of course generate a small amount of heat in the thermistor. Normally the heat will dissapate to the air and the temperature of the thermistor will be very close to the temperature of the air, but when you stick it into styrofoam it will be insulated and the temperature of the thermistor will rise because the heat has no where to go. Some heat will still dissapate through the leads though, but you get the picture.

If you are really interested in pursuing it, you could track Ron down on the fullrangedriver.com forum. You should also check out his designs (plans, plus several builds) in the photo gallery of the site.

 

[ulfheden]

If you are really interested in pursuing it, you could track Ron down on the fullrangedriver.com forum. You should also check out his designs (plans, plus several builds) in the photo gallery of the site.

I've already been there, but I have not asked Ron since it has not come up in any thread and I think it might be a bit, umm.... say unpolite to just step in there and question his claims.

At least I still know that two facing speakers makes no silence

/Peter

 

[GM]

Greets!

Two like phases sum, not cancel, they must be 180 deg apart to cancel, otherwise dipoles would be all we'd need. WRT Ron's linked explanation, scroll down to see where he clarifies his misuse of the word 'cancellation'.

GM

 

[soongsc]

180 degree cancellation only applys in specific regions where the original and reflected waves meet. So this gets a little complicated in the higer frequencies.

As GM mentioned, the MLTL is a balance between a musical instrument and realistic reproduction, I was wondering whether it is possible to add an acoustic filter to damp the internal resonances other than the tuned frequency, which remind me that there's still an old box that hasn't been tested yet.

 

[Colin]

Some years BMC (Before MathCad), a quarter-wave design appeared in HiFi News which had problems with overheavy bass (it used a Kef B200, I think). The solution was to introduce an acoustic filter, consisting of a panel blanking off one of the line sections. The panel had a network of holes drilled in it, so it acted like the aperiodic vent that Scanspeak and others manufacture. I don't know if this is something that could be modelled in Martin's worksheets. Any thoughts, anyone?

Re the musical instrument aspect of the MLTL: This doesn't bother me and seems a valid trade off for use in a domestic environment. I'm not aware of any audible resonances (and it has proved to be cleaner in the bass than my sealed cab for the JX125). That said, I use the enclosures away from corners and the room has partition walls - it will doubtless sound different in a brick or stone built room.