Pictures of GM MLTL-48?

[PrimaLuna]

Very soon, I am going to build the GM MLTL-48 on the Jordan site. I am going to build the triangle version.

Does anyone who has built this very have a few pictures to post. I would love to see them.

Thanks

 

[abpea]

Hello PrimaLuna,

I just finished these two weeks ago. This is my third pair I've built. I love this speaker and I can't give GM enough thanks and credit for developing such a wondeful speaker.

I ** HIGHLY ** reccommend this speaker! Sounds fantastic and has huge WAF. Build it, I promise you won't be sorry.

Here is my left GM MLTL48er:

 

[abpea]

Here's the right one:

 

[PrimaLuna]

Thanks. Just what I was looking for. A few questions if you don't mind.

How did you round the corners?

And, is that an equilateral triangle or did you give them a wider front side?

Beautiful. Good job. I can't wait to get started.

 

[Dumbass]

Whoa, nice woodwork!

Looks like isosceles right triangle. One neat thing about that, besides fitting perfectly into a corner, is that you get reflections of the rear-wave that effectively cancel each other, without interfering with the pipe action (Ron Clarke's back horn designs use this strategy).

I'll bet those books on either side work as nice diffusers/absorbers.

I'll just add one comment: those cones are really fragile, and the shiny driver attracts the fingers of children of all ages. Rich Drysdale's got a dent thanks to a toddler nephew. You might want to consider some sort of grille.

 

[ulfheden]

Whoa, nice woodwork!

Looks like isosceles right triangle. One neat thing about that, besides fitting perfectly into a corner, is that you get reflections of the rear-wave that effectively cancel each other, without interfering with the pipe action (Ron Clarke's back horn designs use this strategy).
...[snip]

Cancelling reflections?

This is something I don't understand. Can anyone please explain to me how this works?

/Peter

 

[abpea]

Here are the dimensions for GM's MLTL 48"er that I use:

(All dimensions internal)

Baffle = 11"
Sides = 7.75"
L = 48.0"
XO = 15.45"
Vent = 2" wide x 2.75" long (center of vent is 4" above bottom)
Stuffing = 0.54lb

I used a 3/4" round over bit in my router to do the edges. I still need to put the mahogany cap and base on them when it warms up a little more and I get some more time.

We are moving those book cases and the speakers will eventually be in the corner next to both walls but for the moment they sound wonderful right where they are.

This is my third set of these speakers I've built and everytime I listen to them I am amazed at the sound that comes out of them. I had a friend over this weekend who works in a high end audio shop in town. I played them for him and he got down and put his ear up to the port, turned them around and really checked them out. Then he started looking under and behind the other furniture in the room. Said he swore I had a bigger driver stashed in the room somewhere!

I have measured these down to 35Hz which is amazing when you think about it and just shows what a great job GM did when he designed them.

I enjoy these speakers tremendously, I'm sure you will too.

Bruce

 

[abpea]

Here's a picture of the top of one of the speakers.

Internally each side is 7.75" wide and the inside width of the baffle is 11". The external width of the front baffle is 13.5".

I used 1x (which is actuall 3/4" thick) #1 clear white pine for the sides, top and bottom. I doubled the tops and bottoms meaning I used two tops and bottoms on each cabinet. I know solid wood isn't stable, it moves and can split, etc. and I should have used 3/4" plywood... I'm experimenting here so just go with me on this

The baffle is a full 1" thick piece of African mahogany with some other African hardwood whose name I can't remember right now. I found this plank on the junk pile at my lumberyard and grabbed it. It has a very nice reddish color, is very dense and hard. Looks good with the mahogany!

 

[PrimaLuna]

They are striking.

One more question if you are willing: What is the benefit of deviating from the equilateral triangle design to the isosolese triangle? Is is purely aesethic? Or does it enhance any aspects of driver performance?

I understand the idea that if you keep the speaker box volume consistent, you can adjust the design to your liking.

Thanks

 

[abpea]

Hey PrimaLuna,

The shape of the triangle doesn't have anything to do with aesethics. GM designed the speaker with a specific cross-section area (~30 square inches).

You can make your cabinet an equalateral triangle if you like as long as the cross-section area equals ~ 30 square inches. Be sure and draw it out first, measure the dimensions of the speaker and check to be sure the speaker will fit in the cabinet you design. When you have the choice GM recommends using a wider baffle for this cabinet than not.

Have fun and I hope that helps.

Bruce

 

[PrimaLuna]

I will have fun.

I know initial design of a triangle didn't have anything to do with aesthetics. My question is, why did YOU change the shape of his triangle?

Or, asked a different way: You said that GM recommends a wider baffle if possible. Why does he recommend this?

Sorry for nitpicking. I am new to this. Just trying to get all of the info. I can get.

Matt

 

[Dumbass]

Cancelling reflections?

This is something I don't understand. Can anyone please explain to me how this works?

I'm trying to find the posts where Ron explains it with much more specificity than I could.

In gross layman's terms, imagine two particles shooting toward the reflector, symmetrically opposite from eachother. They each will hit a 45deg reflector, then collide directly head-on, right at the center. So now imagine the speaker driver, placed symmetrically w.r.t. the reflector, sending rearwave directly toward the back reflector. There is a cancelling effect, where energy gets converted to heat, from the rearwaves essentially "colliding" in the middle.

If I had a scanner nearby I could jot a picture that would make it much clearer.

Ron uses this technique in all (?) of his backhorn designs, he says that his designs require very little (if any) stuffing material in the chamber.

Here's one example, see how the back chamber has that right angle at the back, with the vertex directly in line with the driver.
http://fullrangedriver.com/gallery/albums/userpics/10044/1~0.pdf

 

[Colin]

Hi Bruce

Three pairs, eh? You have been busy. Nice cabinet work on the latest pair. (Mine are still - er - pre-production in appearance.)

I can second Bruce's opinion about this enclosure. I think it's a knockout design and is the best enclosure I've yet heard the JX92 perform in (I haven't heard the 31 MLTL but have listened to the VTL and various vented enclosures). The bass goes down to below 35Hz. I believe GM has commented that the bass might deviate from strictly neural, but it seems to suit these drivers, giving the sound a subtle warmth which is very alluring. And having holographic imagery which operates deep into the bass is fantastic.

I built mine as an equilateral triangle, as on the Jordan site, purely because I liked the shape. The triangle does the job of suppressing resonances.

Ref the drivers - yes they are VERY delicate. Mark Audio sells a neat perspex grill which attaches to the driver bolts via little magnets. Looks good in place. (You have to remove it for listening, of course.) It's already saved one of my drivers from a dent.

 

[Dumbass]

Or, asked a different way: You said that GM recommends a wider baffle if possible. Why does he recommend this?

Wide baffle makes baffle-step cutoff frequency lower. In other words, the front baffle more closely approximates an infinite plane.

With placement near wall, wide baffle not as important, because the wall acts as a baffle by proxy. My conjecture, though, is having wide baffle is still good because you have a uniform, completely flat surface, so driver radiates into half-space for a good portion of the freq spectrum.

Read "Sound Basics" and the FAQ from Ted Jordan's site, he states it in slightly different terms.

 

[Dumbass]

Ref the drivers - yes they are VERY delicate. Mark Audio sells a neat perspex grill which attaches to the driver bolts via little magnets. Looks good in place. (You have to remove it for listening, of course.) It's already saved one of my drivers from a dent.

I've seen people use those round fan-grilles from a PC, not a bad look IMO and don't think would hinder sound at all.

 

[PrimaLuna]

That's what I was looking for. Thanks.

 

[abpea]

Thanks Dumbass...

Good explanation as to why someone would want to use a wide(er) baffle!

Hey Colin! I figured you would show up sometime. Good to hear from you. Yes indeed GM's 48"er is my speaker of choice for the forseeable future.

They sound wonderful and my wife likes them... I'm a happy man!!

Bruce

 

[abpea]

PrimaLuna,

One other thing, I don't use any baffle step filter, tweeter or crossover of any kind on my speakers. I have my speaker cables soldered diretcly to the the speakers (yes it does make it sort of inconvenient if you move them around very much but I don't).

I was building a subwoofer to go with my system but stopped because I don't feel like I need one. This speaker puts out plenty on the low end and I'm not kidding you will be amazed by what you hear.

The only tricky part about this speaker if there is a tricky part is tweaking the stuffing. Stuff the speaker from just below the driver and go up. Start with about half of what you think you'll end up with and spend an enjoyable afternoon tweaking and listening and you will be rewarded generously!! Take your time, listen to an assortment of music you know well and when you've got it right you'll hear an incredibly lush, warm sound your ears won't believe.

Ok I have to stop... I've been accussed of *gushing* too much when I talk about this speaker!

All I can say is build a pair. They're easy to make and you'll be glad you did!

Happy listening -
Bruce

 

[ulfheden]

In gross layman's terms, imagine two particles shooting toward the reflector, symmetrically opposite from eachother. They each will hit a 45deg reflector, then collide directly head-on, right at the center. So now imagine the speaker driver, placed symmetrically w.r.t. the reflector, sending rearwave directly toward the back reflector. There is a cancelling effect, where energy gets converted to heat, from the rearwaves essentially "colliding" in the middle.

If I had a scanner nearby I could jot a picture that would make it much clearer.

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.

/Peter

 

[Colin]

Hi Bruce - Yes, my SO also approves the triangular design. I have been banned from building floor-standing speakers any other shape.

The MLTL feels at times more like a musical instrument than a speaker. That could be a bad thing with some designs but I think GM got the tuning just right on this one.

Re the stuffing - I used BAF, lining the cabinet walls from just below the driver to the top and then placing an extra roll in the centre (between the already lined walls). It isn't compressed and I have never experimented with the stuffing. I may have been lucky or it may be because BAF is designed to attenuate the mid-hf. (For USA readers, BAF is bonded acetate fibre - you can find it at www.wilmslow-audio.co.uk - I'm not sure if is similar to Acoustuff but it has different performance characteristics to long fibre wool.)

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.)