Frame

The frames I've been using have never been totally successful but have been in use for 15 years. Time now to build some proper ones.

We have long thought that the vast majority of ESLs fail to reach their potential due to the limitations inherent in the frame design. This is especially true when the ESL is full range and is required to deliver substantial bass information.

What has concerned us is it seems the frame is usually only given a last thought and in most cases does not support the panel adequately. But what is adequate?

Adequate means to me supported evenly and rigidly over the whole length of the speaker panel without twist or bending in any plane. In a full range ESL, that means the panel is usually large. In the case of Acoustats that panel length is about 8 ft. As there is little or no information on this subject with respect to ESLs, I chose to look at how conventional speakers address this problem of rigidity and then try to apply it to an ESL.

Design aims:

1. Rigid and Square - to be maintained over time
2. Mass loading option
3. Bolt to frame or clamp to frame option
4. ability to slide around and spike (not at the same time)
5. bolted/screwed together to keep design flexible and to ensure squareness when assembling
6. able to experiment with compounds twixt panel and frame
7. able to experiment with edge treatment/wings etc
8. minimal stuff at rear and nothing (or little) in the way of the radiating surfaces reflecting energy back at the panel

A First Go

So what do they sound like? First I have to say I am even more impressed by Jim Strickland's panel design. I believe the plastic grid construction making the stators very rigid contributes to their quality. Why anyone would go to all the trouble of building an ESL (unless that's your thing of course) when a pair of 2's or 1+1s (or 2+2s) could be picked up for peanuts relative to today's prices. They have to be the best ESL speaker materials kit available.

For a summary of the 1 + 1s, check Hot Rod 1+1s

 

After full view of speaker, rear view of top half, rear spike detail, attachment of copper to wood frame and joint detail.

The thing that finally got me to replace the old frames was hearing Jack Bouska's awesome system (another LLDIY looney). The broadband power response that this system has is illuminating and thought provoking but my Acoustats are still the ones for me.

Update - April 9th 2002

Rocket Lauchers

The frames are now nearly a year old and have performed superbly. One day, I hung half a bag of sand over a rear stay to gauge tilting effects. I had assumed I would hear a tighter bass but no - the reduction in HF distortion was very noticeable as was the increase in focus. Bass was hardly altered. This indicated that maybe the frames were "buzzing" on the floor? The design always had the option to add mass due to it's tubular construction but I didn't want to add mass to the tube frame itself.

So back to the plumber supplier for some big tube - 4" / 100mm plastic waste tube seemed ideal so two 6'6" / 2m lengths were capped off (screw type), sand filled and clipped to the rear frame tube. Each tube weighs about 56lb / 25kg.

The previous cleaning up of "noise" now extended down into the lowest bass. Up to that point, I was not aware just how noisy the frames had been and these way quieter previously than any other ESL frame I've heard.

I removed the wooden frame completely and using the pipe clips, coupled the panels to the tube frame directly. This confirmed a number of things; the panels sound like the material they are attached to and that they need to be attached to something massive and well damped. The non-wooden frame speaker was making itself heard in comparison with more of the music camped on the speaker. Room for further development.

 

After full view of speaker, side view (looks like a Rocket Launcher to me) and detail of attachment to frame

Update - October 14th 2002

After spending some time with the heavier frames, I find the life has gone from the music. Sure I thought things had been "cleaned up" but it would seem "cleaned up" is not how I like things. The mass in the frame seems to have caused a storage and release mechanism of the frame's energy thereby messing with the musical message. This is not entirely obvious on first listen but became apparent over time. The vast open window that I enjoyed so much with the light weight frames disappeared, sanitised somewhat and so boring.

As an aside to the above, I'm revisiting some of the component recommendations - specifically the use of replacement resistors instead of the HF control, the HF capacitors (LV side), multiplier parts and a few others.

Update - December 10th 2002

Some of my assumptions in making the frames above - the requirement for static stiffness and mass to counter the energy in the frame may well have been misplaced. Experimenting with the frames and reading more about vibration measurement and control (very good tutorials here on the Newport site) led me to think a light and rigid approach may well be better if applied to the right area.

Adequate support for static loads is way different to providing support at audio frequencies. If the main mode of resonance is below that being produced by the speaker, then it will stay still. The frames may not be as statically stiff as the old ones but they are compared to most panels so seem to provide good support as the bass is very clean and goes deep while allowing other instruments to stand alone and not be swamped. This aspect alone leads me to think this approach may yield better long term results.

Accidently, the wooden frame is relatively light and quite rigid. The tripod support does not now provide stiffness; only support for the frame. In the future I may be able to make the frame stiffer and lighter as the two requirements of support and holding the panels are seperate.

Although it's early days yet, this is by far the best frame design I've had. The mass approach has benefits but this method is far more musical. I'm sure there are improvements I could make but it will be a while yet before I can get a fix on what. What is a sure thing - the panels sound more like the material they are suported by than anything else and so it will be this aspect that deserves development in the future.

Inspiration for further development may be based on the parallels in TT design. Both the speaker and cartridge are tranducers that convert movement to electrical energy or vica versa. The panel is like the cartridge, the headshell like the frame (support for the transducer), the tripod frame like the arm tube (lightweight, stiff support) and the TT base like some form of mass sink (currently the floor but could be added to) for vibration. How all this translates into a design will be the fun part.

 

From left - left speaker, right speaker, rear view bottom joint, rear view top joint and lastly, very important rear brace