A little big Help

[JonFo]

It might be that your amplifier is reacting to the capacitive load in ways that significantly alter the response as the volume goes up.

One quick method of determining this is to put a 1 Ohm 60w rated resistor (it will be a big one) on the hot lead from the amp to speaker. That added resistance usually helps amps deal better with the reactive load of the ESL.
Anything between 50 and 100w rating is fine, so something like this works: uxcell 2 Pcs 100W 1 Ohm Screw Tap Mounted Aluminum Housed Wirewound Resistors: Single Resistors: Amazon.com: Industrial & Scientific

BTW- this is the entirety of the secret behind the Sunfire voltage vs. current source outputs, the current source has a 1 Ohm load inside the amp, right on the terminals (discussed in great detail here).

Or borrow an amp that is well-known for playing well with ESLs (see our amp thread) and try that.

 

[Brandon Hartwick]

Have you tried a sweep with Room EQ Wizard? I really have a hard time believing this is power related as usually if it's a problem like that equipment will either work or it won't.

 

[JonFo]

It might be that your amplifier is reacting to the capacitive load in ways that significantly alter the response as the volume goes up.

BTW- this is a major reason why bi-amping makes sense for ESLs, as the highly reactive load from the ESL might vary the distortion and response curves of the amp driving the panel.
If the woofer side is also being driven by that signal, it is also getting the distortion products and reflecting the changed frequency response.

This is a challenge for powered woofer models (like the 11a), as they are in essence already bi-amping, but are getting their input 'feed' from an impedance / level matching circuit connected to the same amp that is being modulated by the ESL. So no way to feed the woofer amps a 'clean' signal from the pre-amp.
This is why I think the OP is seeing the change in bass output as system volume is increased.

Suggestion to ML for future iterations (or for the savvy DIY person):
Add an XLR input connected to the woofer input internally. Users can use a Y-splitter to send the signal to the amp for the ESL panel, and then another goes to the speaker for the woofer amps.

But the easy answer is: just use an amp that does not radically change behaviour under load.

 

[ttocs]

BTW- this is a major reason why bi-amping makes sense for ESLs, as the highly reactive load from the ESL might vary the distortion and response curves of the amp driving the panel.
If the woofer side is also being driven by that signal, it is also getting the distortion products and reflecting the changed frequency response.

This is a challenge for powered woofer models (like the 11a), as they are in essence already bi-amping, but are getting their input 'feed' from an impedance / level matching circuit connected to the same amp that is being modulated by the ESL. So no way to feed the woofer amps a 'clean' signal from the pre-amp.
This is why I think the OP is seeing the change in bass output as system volume is increased.

Suggestion to ML for future iterations (or for the savvy DIY person):
Add an XLR input connected to the woofer input internally. Users can use a Y-splitter to send the signal to the amp for the ESL panel, and then another goes to the speaker for the woofer amps.

But the easy answer is: just use an amp that does not radically change behaviour under load.

Nice explanation. Thanks!

So if an amp reacts the way you explained, does it mean the amp is not stable enough for the stat panel?

 

[user 49888]

Thank you very much for the explanation and I think, as far as I can, that I bought the ML ESL 11a thinking my amp had no problems.
At this point, despite the help of everyone whom I thank, I think I am at a crossroads: looking for a suitable amp to try at my home (not an easy feat in Rome) or parting with the MLs and looking for other speakers.

 

[JonFo]

Nice explanation. Thanks!

So if an amp reacts the way you explained, does it mean the amp is not stable enough for the stat panel?

Yes, if the output signal varies a lot across a relatively narrow volume level, then definitely not stable enough.
The frequency distribution of the content also has something to do with it. If the recording leans towards lots of mid to high frequencies (say, a brass band), then the low-impedance dip the ESL has might drive the amp into oscillation, increasing the THD, which in turn generates more high-end harmonics, which make the oscillation worse.

 

[Tmort]

I’ve got the Anthem MCA 225 mk 2 powering my classic 9’s (400w at 4 ohms), it does a wonderful job. New they’re very fairly priced.

 

[user 49888]

Good morning
in the meantime I thank everyone for sharing their experiences and above all for the technical examinations related to the careful choice of the amplifier ...
I have looked at the thread related to the choice of the amplifier but I still kindly ask for some advice or experience regarding the interfacing with my ML Impression 11a.
A sincere thanks

 

[msimanyi]

I am not familiar with your amp, but I did an online search. On the surface, it seems it could or should be a good match.

Do you have any audio dealers near you who could loan a different amp to test? The discussion on this forum about amps should expose you to a number of brands and models you might consider.

 

[Garrett]

I have the 11a's and driving them with MC462 and when playing loud they sound even better. I have 1/4 " acoustic panel behind the speakers (4'x 3'). Have you looked at the amperage you're drawing off the circuit you are plugged into. Your amps should have the amperage they will draw and it may be at the upper limits that circuit will supply. If you have everything plugged into one circuit you will find maybe that is the problem. I have three circuits feeding my room so the amplifier in on one circuit by itself so I don't have to worry about exceeding the 15 amps. Each one of your amps can draw up to 1600 watts so if they are on one circuit you are going to have a problems.

 

[Russr]

It seems to me that this might be a more fundamental (electrical supply) issue.

Paolo, could you measure your supply voltage WHEN THE SYSTEM is exhibiting the issue (i.e. 75dB+) and you're hearing the issue. As Paolo mentioned, his AC supply is below-spec. I'm wondering if that is exacerbated under load, and if so, by how much? You have some beefy external amps, the internal Bass amp, etc.

Have you noticed the issue is more prevalent at certain times (for example, if you have heating on during winter, or if you're brewing a nice espresso?!

Just a thought, but my early days in Audio & PC trouble-shooting dictated to look for the simplest explanations and work your way "up"!

I'm trying to think what audible issues would manifest if the magnetic fields in the power amp power supplies start collapsing, and then separately, what would happen to the (I assume) switch-mode power supplies in the internal Class D amps if supply voltage dipped below a certain threshold...?

Good luck, let us know how it goes.

Russ