A Back Wave Baffle for Martin Logans

[Andersonix]

Thanks Jer. Do you also have pics of your complete desktop ESL assembly and set-up? (IOW, could you expand on the meaning of your phrase "I used the corner of the little woofer box as a beam splitter and that worked very well for my nearfield situation."?)

[geraldfryjr]

I am at this very moment getting them set back up, now that I have finished the power supply.

I had blown up one panel so I am working on it right now as we speak.
I have resealed it where one screen had gotten ripped and gave it another coat of clear acrylic.
The other panel is fine and takes every thing my supply can produce.
The supply produces 13.8Kv and the meter shows 5.2Kv so it is leaking some where but at least it is not profusely arcing.

It just sits there nice and quiet like it is supposed to do.
It is funny as I turn up the voltage it just stays about 5.4kv to 5.2kv like it hit a brickwall like a zener diode acts.
I believe that this is the point where the the air is starting to conduct and works out to be around 70v to 75v per mil for my D/S spacing .072" to .075".

I will see if I have some better photos in my archives and if not I will make some new ones.
This will be the first time I have been able to fire them up again(he,he,he, pun intended) since october of 2010 when the one exploded into flames, and will be in stereo as well.

I already fixed the frames and the diaghpram is fine,So all I have to do is paint on a new charge ring and bolt it back together as long as the stators pass the arc tests to at least 6Kv to 7Kv.
Most of the panel already does except for a few spots that is why I had to give them another shot of clear acrylic.

Basicaly what I did was lean the little panel against the corner of the little sony speakers that I used as woofers only (duct tape on the tweeter works good) and shoved them back in the cubby holes where the upper shelves are and is wide open.

Right now there is a monitor in one of those spaces so I may have to move the monitor or change it out for one of my smaller ones.


jer

[geraldfryjr]

Here are the pictures that I had posted but couldn't find.

I was working on three things here,
1# Canceling the back wave,but no pictures of the fiberglass insulation or top baffle.
2# The effect of multiple panels and their angles.
3# how many panels it took match the same output level of the 5.25" woofer box at the same power level,it took 2 but 3 was even better.

This was before I had gotten my big amps back from Florida.

The frequency response curve are no EQ and EQed for one open panel.

The measurements were done with a Peavey PVM-520TN and a Phillips PSC706 16bit card.
The irregularities I am sure where from room reflections as later I had gotten a ruler flat response with no EQ with the panel at a different position in the room and added some room treatment to dampen the mid and high frequency reverberations.

I will be doing this measurement again as I now have a Gina24 24bit 96khz card and a Dayton measurement microphone with the calibration data as well as a SPL meter.


jer

[Andersonix]

Thanks again, Jer, the fifth pic explains what you meant by 'beam splitter.'

[geraldfryjr]

Yes,that is the technique that Charlie has incorporated in his design.

Hopefully tomorrow I will find out how well it will work in stereo with the little panels, as I have only used them in mono so far.

When I did try it it seemed to have a better horizontal dispersion with less refraction of the rear wave reflecting off of the back panel of my desk.
Since I listen to them near field I may not notice any difference at all.

The proof will be when I move them out in front of my mixer or towards the middle of the room in a more open area.

I will start a new thread on these as not to clutter up this one.

I will be doing a lot of retesting on these with my new measurement tools as the tests that I posted almost 2 years ago were the best that I could do without any reference standard to go by.

I have been wanting to try some sort of acoustic lens or a small horn flare as well to finally put light on that idea as if it would be a benefit or not work at all for a small sized driver like these.

These things can and do get really really loud with an amplifier that can deliver the goods.



jer

[geraldfryjr]

Sorry about this repost But I didn't realise that I was in edit mode and I went over the 30 minute limit.

jer




Yes, That is the technique that Charlie has incorporated in his design.

Hopefully tomorrow I will find out how well it will work in stereo with the little panels, as I have only used them in mono so far.

When I did try it it seemed to have a better horizontal dispersion with less refraction of the rear wave reflecting off of the back panel of my desk.
The midrange hump in the frequency curve was most likely the refelctions off of the monitor as that distance is roughly the same as when they were set back into the cubby hole listening position.
As well as the early high frequency roll off may have been caused by the measuring devices limits.
Since I listen to them near field I may not notice any difference at all.

But it sure will be nice to listen to them again.
I was just absolutely floored listening even in mono.
So it is going to be a real treat now that I have the proper equipment to drive them now.

The proof will be when I move them out in front of my mixer or towards the middle of the room in a more open area.

I will start a new thread on these as not to clutter up this one.

I will be doing a lot of retesting on these with my new measurement tools as the tests that I posted almost 2 years ago were the best that I could do without any reference standard to go by.

I have been wanting to try some sort of acoustic lens or a small horn flare as well to finally put light on that idea as if it would be a benefit or not work at all for a small sized driver like these.

These things can and do get really really loud with an amplifier that can deliver the goods,in which BTW at the time I only had one stereo amplifier so one channel drove the ESL and the other drove the woofer.
Right now I am focusing on the fact that they sound so good rather than them being dipole drivers as my room is just not big (wide)enough for full blown dipole system to reach the sound levels I am trying to achieve.

But Sound quality does come first, although the I listen mostly to modern music(Rock-N-roll), I like all forms of music even orchestras ,everything!
This sometimes is a big undertaking for just one set or type of speakers.

How things sound is very subjective so I don't use fancy words to describe it as it either sounds good or something is wrong and needs to be fixed.
So therefore I won't criticize one for trying something new because it may be what works for ones particular application or situation for what ever reason.

I think that closing up the back of the ML is very interesting and is something that I and many others have been curious about and has been discussed over and over.
Hence the question "Can an ESL be put in a box or an enclosure?".

When I did my little experiment of filling of the back of the panel I did notice a little high end finesse was dampened a bit but not enough to destroy the sound of the panel or added any coloration as the sound quality was still there.
I have heard many dynamic tweeters and midranges that sounded much worse,in fact that is kinda what it sounded like.
Much like when I first powered them up after seven years and they were loaded up with extra mass form dirt and sand with the much thicker Licron original formula as the coating.
Had I been listening to them in stereo I might not have noticed it at all.

I had found that it must have been the added pressure behind the diagphram that was was causing this and as I moved the insulation back from the panel to about 8" the finesse started to come back.
This setup was fully open and the appratus became to large for my desk and become very messy to work with.

I did get more bass output though which was what I was after.

My conclusion was that, It may be quite feasible for a larger panel were the mass the of the diagphram is much greater to overcome the added back preasure but not for my little panels.



jer

[Andersonix]

I noticed that Sound Lab has another small ESL hybrid, the WallStat, in addition to their MiniStat, so perhaps the arrangement is not a dead end (so to speak)? Both seem to 'absorb' the rear wave (but then also use a lens on the front, which I don't care for, philosophically!).
How do these sound, and is it worthwhile to DIY something like this for a desktop ESL?

[geraldfryjr]

That is a very good question.
Those are some avenues that I had intended to explore.
To me the magic of the ESL is not because they are a dipole driver but because of the inherently low THD that they produce.
With the right materials and consideration of proper dimensions to me they blow away dynamic drivers in most respects for the costs envolved.
In the last 20 and even within the last 10 years the materials have taken quite a leap to be able to make DIY ESL's even a feasibility,namley coatings and especially transformers.

My very first listen of an ESL was the MartinLogans just before I had finished my 8" X 22" panels.
Then I built my little panels modeled after my very first panels made out of some perforated aluminium material that had a very low open area and poor performance because of it .
The idea between the two sizes was one was 4 times larger than the other and I wanted to see if this actually would be 6db more efficient.
But the struggle of not having some decent transformers had set me back a bit until two years ago when I got back into it.
But I did have a good coating system down as I had built two sets of little ones,one using spray paint (one of those got lost) and the other set used powder coating,and what a world of difference the extra open area made using the PC method not to mention being able to run a much higher bias voltage.

But all in all they all sounded the same as the ML's that I had first listened to.
With the exception of bass extension they added no coloration to the sound and are clean and crystal clear.
So much so that they even fooled my dog into thinking it was raining and storming outside and refused to go out because of it, When the moon was out and shining brightly with no cloud in the sky.

I was listening to a tape of forrest sounds,Yes, A cassette tape!
He,he,he you had to be there to see that one !!!
This completely amazed me for such a smal set of speakers.

And for what it is worth I liked the narrower panels more because they were less beamy than even my 8" wide panels.
In recent studies I finally found out why this is.

This was all back in the summer of 2003 before I had access to my big power amps that at the time were powering the same Appoge Duette's that I now have.

And even then although they were underpowered and no bass system they sounded better than those Duette's and I loved those speakers.
I still do but they are in sad shape and I don't have the room to properly set them up.

jer