Aerius panels and woofer-induced vibrations

Hi,

I own a pair of Aerius mkI driven by a Jeff Rowland Model One amplifier, which appears largely suited to the task.

Touching the Aerius chassis and resistors during music reproduction, however, has revealed me that every woofer vibration affects the panels, likely due to the poor structure of these loudspeakers that cannot absorb woofer movements.

My three question are:

1) does this fact decrease the panels performance in an audible way at medium-high volume?

2) if yes, as I suppose, can I do something to minimize the problem?

3) does this problem exist for all ML loudspeakers?

Thank you very much for your help.

Luca

I would say yes, it could have a negative effect on the performance of the panel. The general thought is we try to stabilize the panels to have no movement other than the film between the sators. It would follow that the intense vibration from the woofer/woofers in the cabinet below would transfer through the panel above.

You can try to install some type of dampening material to the walls of the cabinet. Do a search here and you should find a few suggestions for brand name products that may work.
The major construction approach would be to rebuild the structure holding the panel to separate it from the woofer cabinet. Not sure it would be worth the effort but you won't know till you try.

To test the idea you might listen to a recording in mono with one speaker until you are quite familiar with it, then place the Aerius speakers side by side. Disconnect the woofer on one speaker and the panel on the other and listen to the same mono recording. See if you notice any difference other than a slight offset of the lower ranges.
This may or may not show anything but only one way to find out.

I would say any hybrid ML could have this issue but you would have to check each model to see for sure.

Good luck.

1) In an audible way? While I can feel it everywhere with my 'finger-tip accelerometer,' I don't think I hear it in my SL3, but it can be measured. Even the suspicion that it's audible might affect your enjoyment.
http://www.stereophile.com/content/martinlogan-sl3-loudspeaker-measurements-part-3
In Fig.7, you can see delayed energy.

2) Try soft spongy feet. Actually, try different kinds of feet, as the coupling with the floor can worsen or mitigate the cabinet vibrations. (More to be said about this)
Also, going active xo on the bass will clean up the bass, so it doesn't excite the cabinet as much.

3) Yes, and also for any other cabinet with an integrated woofer. Even the panel alone (with no woofers) will excite itself....

Thank you very much for your answers.

My questions arise from the fact that I clearly hear what I interpret as high-frequencies distortion when the volume rise at medium-high levels and woofer vibrations shake the panel. At medium-low volume, by contrast, the sound is wonderful. Yesterday a ML expert told me that in the '80s he built a special stand to fix the CLS panels to avoid their shake during music reproduction, with an audible increase in their performance. He also told me that this problem, obviously, largely increases if woofers are included in the structure as for hybrid designs and that I can either accept it or just choose a different loudspeaker.

I agree with Tosh that every loudspeaker suffer from woofer's vibration, but for different loudspeakers types it has been almost eliminated. As transparency and sound purity are characteristic of electrostatic loudspeakers, it could be expected that the panels would be tentatively isolated from vibrations in some way, e.g. fixing them to the structure using a Sorbothane frame (I not a technician...).

I have tried different feet and I'll try again, but my feeling is that Aerius structure is too light to obtain any result in this way.

Luca58 said:

My questions arise from the fact that I clearly hear what I interpret as high-frequencies distortion when the volume rise at medium-high levels and woofer vibrations shake the panel. At medium-low volume, by contrast, the sound is wonderful.

Click to expand...

Could you try playing only the bass and see if you still hear any sound from the panel, as you suspect? That might be difficult to discern as the sound from the woofer would mask most of any ESL panel vibrations.

Have you checked and repaired >every single< screw hole in the MDF cabinet? Rail mounts, pcb, xo, etc? I found several stripped out holes in my SL3, and yours are much older....

If you are keeping these Aeriuses, then I encourage you to use an active xo on only the bass. The original Eminence 8inch woofers in the early Aerius aren't that good (compared to what's available now, 25 years later!) combined with a high xo point (500Hz), and small gauge inductor in passive xo make the upper bass and low mids muddy.

The older style Martin Logans had very stiff frames, so if the woofer cabinet shakes, the panel will shake too. The only way to combat this is to have the cabinet either tightly connected to the ground, or to add a lot of mass there. Same for the panel.

Another thing I noticed in my speakers is that the crossover circuits are not very good and produce higher order distortion. For example, if I play a pure sine tone at 130 Hz, I can hear a higher frequency buzzing in the panel. I have a setup right now where the speaker is bi-amped, with additional active crossover filtering so that the panel gets extra attenuation at frequencies that it is not supposed to play anyway. This has eliminated the buzzing.

You can try this test yourself by playing a test tone at say 130-200 Hz and sending the signal to the panel only.

beanbag said:

The older style Martin Logans had very stiff frames, so if the woofer cabinet shakes, the panel will shake too. The only way to combat this is to have the cabinet either tightly connected to the ground, or to add a lot of mass there. Same for the panel.

Another thing I noticed in my speakers is that the crossover circuits are not very good and produce higher order distortion. For example, if I play a pure sine tone at 130 Hz, I can hear a higher frequency buzzing in the panel. I have a setup right now where the speaker is bi-amped, with additional active crossover filtering so that the panel gets extra attenuation at frequencies that it is not supposed to play anyway. This has eliminated the buzzing.

You can try this test yourself by playing a test tone at say 130-200 Hz and sending the signal to the panel only.

Click to expand...

The buzzing you are hearing may or may not be coming from the woofer grill. Mine had the same issue (I did not find the exact frequency, but 100-200 Hz sounds right) until recently. The problem was solved using some ML supplied foam tape. The top and bottom edges of the grills were free to rattle and annoy.

beanbag said:

The older style Martin Logans had very stiff frames, so if the woofer cabinet shakes, the panel will shake too. The only way to combat this is to have the cabinet either tightly connected to the ground, or to add a lot of mass there. Same for the panel.

Another thing I noticed in my speakers is that the crossover circuits are not very good and produce higher order distortion. For example, if I play a pure sine tone at 130 Hz, I can hear a higher frequency buzzing in the panel. I have a setup right now where the speaker is bi-amped, with additional active crossover filtering so that the panel gets extra attenuation at frequencies that it is not supposed to play anyway. This has eliminated the buzzing.

You can try this test yourself by playing a test tone at say 130-200 Hz and sending the signal to the panel only.

Click to expand...

Not likely, passive XO distortion should be minimal when driven within reasonable power.

You can try this test yourself.

beanbag said:

You can try this test yourself.

Click to expand...

I didn't but while measuring for room acoustics there is hardly any distortion to be seen or heard. THD and harmonics are generally low, showing readings in 0,XXX% range.



I don't see evidence of the crossover circuits are not very good and produce higher order distortion

To do my test, you'd have to turn OFF the woofer, else you are flooding everything with 1st harmonic. Then you either have to use your own ears to listen for the buzz (LOL, what level have I sunk down to), or else you will have to close mic the panel and then do a fourier transform of the signal.



I hear the same buzz even if I use notch filters on my DSP to cut out 390 and 650 Hz. I have noticed this with two different amps, two different DSPs, and two different DACs. However, I found out today that it doesn't seem to scale with volume, so I dunno about that. To make sure, I'd have to drag a lot of test equipment to my living room to really find out where it is coming from.

Hi Luca, I own a pair of the current generation Ethos and asked a similar question a while back and got very little response. If I rest my hand on the panel frame, vibrations are very easy to feel with each thump of the woofer and it seems pretty obvious that this would affect the sound emanating from the panels. I have not tried a fix yet but I thought maybe a sandbag on each woofer enclosure might help to dampen the vibrations.

I have to think that ML designers have thought about this situation and must not be too concerned about it. My Ethos sound great and I can't hear a specific distortion that I can attribute to the vibrating panel, so I guess that's why I haven't worked on a fix yet.

I think you may have a good idea. Decoupling the panel from the woofer box with sorbothane or some other material and putting a separate pair of spikes on the panel to couple it to the floor might eliminate from the panel much of the vibration caused by the woofer box.

Does anyone know why ML doesn't do something like this?

dh46374 said:

Hi Luca, I own a pair of the current generation Ethos and asked a similar question a while back and got very little response. If I rest my hand on the panel frame, vibrations are very easy to feel with each thump of the woofer and it seems pretty obvious that this would affect the sound emanating from the panels. I have not tried a fix yet but I thought maybe a sandbag on each woofer enclosure might help to dampen the vibrations.

Click to expand...

Some people here do use weights on their woofer enclosures.

Indeed, and it made a considerable improvement to my Spires; see my tweaks thread..

Sim suggests as long as you worry about (and dampen if necessary) the main ESL & sandwiched stators' own main resonances and self-excitations, you are pretty safe from anything being induced through the MDF.

Is this simulation done with the bottom of the cabinet fixed? I would have expected some overall cabinet movement that opposes the woofer.

MPS said:

I didn't but while measuring for room acoustics there is hardly any distortion to be seen or heard. THD and harmonics are generally low, showing readings in 0,XXX% range.

I don't see evidence of the crossover circuits are not very good and produce higher order distortion

Click to expand...

Which ML speaker are you measuring here?

Larry said:

Which ML speaker are you measuring here?

Click to expand...

Measurement is of ML CLX in my room. It presents response at listening position.

Thank you very much for your kind answers.