Transparency

[LineArray]

Hello, here is a strange but simple question and i'd like to
hear your opinions:

I am wondering in how far a loudspeaker - especially a transducer
with large membrane area like an ESL - sounds "transparent" by
really letting sound go through it which comes from reflections
in the room.

An ideally transparent loudspeaker would be no obstacle for
sound at all and would not cause diffraction.

A very small box might not cause much trouble because of being
small and having some distance to the listener.

A speaker with a large baffle area is a "non neglegible object" near
the listener. It must be detectable by reflection and diffraction,
simply by being there. No ?

Imagine the sound coming from a source behind or in front of
the loudspeaker under question ...

Given there is some effect, should a loudspeaker be acoustically
"transparent" preferably ?

What is the expectable difference in being transparent or not due to
imageing e.g. ?

Is "typical" ESL sound - besides being dipole - also characterized by
being "really" transparent to some extent ?

Kind Regards

[andyr]

Originally Posted by LineArray

Hello, here is a strange but simple question and i'd like to hear your opinions:

I am wondering in how far a loudspeaker - especially a transducer
with large membrane area like an ESL - sounds "transparent" by
really letting sound go through it which comes from reflections
in the room.

An ideally transparent loudspeaker would be no obstacle for
sound at all and would not cause diffraction.

A very small box might not cause much trouble because of being
small and having some distance to the listener.

A speaker with a large baffle area is a "non neglegible object" near
the listener. It must be detectable by reflection and diffraction,
simply by being there. No ?

Kind Regards

Interesting question ... but surely an obvious answer?

As you say, "An ideally transparent loudspeaker would be no obstacle for
sound at all". And yet both ESLs and Maggies have a large sheet of mylar which, surely, acts as a sound barrier (as I would've thought that air pressure cannot pass through the mylar?).

But whether this large sheet influences the sound by being a source of sound wave reflection is an interesting concept.

I think the "transparency" of ESLs (and Maggies) is due to them having neglegible driver mass, so they don't exhibit the kind of overhang which some cone drivers do, which can cause muddiness (the opposite of "transparency").

Regards,

Andy

[LineArray]

Hi Andy,

yes i also think a clean decay contributes to the notion of transparancy.

But as was shown in the

ESLs have bad decay plots

thread, being an ESL does not mean to have a smooth and fast decay automatically - it is not builtin with the ESL principle of operation.

And there are pretty good conventional speakers too, concerning decay spectrum and step response.

Surely a mylar foil e.g. is airtight and won't let air pass through. But i think
sound can pass through a mylar foil which is stretched over a frame to
some extent and dependent from frequency.

I guess someone who is talking to you while standing behind streched
mylar will sound different to you, than someone ho is hiding behind a
chipboard baffle of same size.

I am asking myself if this makes a difference and what the consequences
would be ...

Kind Regards

[kavermei]

Some commercial ESLs, most notably the QUADs, have dust screens made out of stretched mylar on both sides. So obviously such a screen must be quite transparent.

Kenneth

[LineArray]

Good point kenneth,

i knew that, but was not aware of it in this context.

So some speakers in fact seem to be acoustically rather
transparent.

Does it contribute to the ability of disappering subjectively
during performance ?

Hypothesis would be that it is an advantage if a speaker is either
small and well shaped to minimize diffraction
( and minimizes "casting shadows" for high frequencies e.g.)
or being acoustically transparent or semi transparent for wavelengths
smaller than its dimensions.

A flush mounted speaker also would circumvent the effect by
mimicking a piece of wall. A bookshelf speaker can also
simulate flush mounting, when placed well.

But for floorstanders standing in front of a wall with
some distance this might be worth discussing.

[kavermei]

Thinking some more about this, I think that

- in my experience, for the speakers to "disappear", placement would be very important. The stereo image must be correct or it will not happen.
- dipoles should never be placed parallel to and close to a wall anyways. So any wave hitting the speaker's front or back plane will already have bounced several times off the wall. Therefore it may not be that important whether or not the speaker is actually acoustically transparent
- in my experience I never heard a point source (electrodynamic) speaker that could "disappear" as easily as a very large panel speaker (such as a large ESL). But I think this has more to do with having a single large plane moving in unison, than with the panel speaker being transparent or not. (This is just a theory I have, I can't prove this.)

Kenneth

[LineArray]

Hi,

i agree with all your observations and do not believe, that
acoustical transparency is the one and only essential thing.

But maybe a "underestimated co factor" ... and if it changes
the listening experience i would be interested in "how" or towards
which direction it may change the subjective experience.

[a.wayne]

Very interesting topic on the simple speaker and it's complexities ....

Transparency as we are discussing is a function of time coherency IMO, direct vs reflected . try getting a speaker to image or appear transparent outside in a field or in a highly over damped (absorptive ) listening room ...

The bigger the baffle the more it becomes a problem , Point source speakers are easier to design and setup to control this field and achieve good transparency and imaging than big full range planers or dipoles, even when planers have an advantage due to there rear energy a bonus in creating this sound field.

IMO this happens because most designers (planers ) tend to go for size ( obvious reasons ) and in doing so , get a big open sound , but lose out bigtime on imaging , necessary in getting the speakers to be transparent ( leave the room) by not paying much attn to baffle control , shape, size et al.......


.

[Calvin]

Hi,

while not beeing completely acoustically transparent -the comparably massive stators introduce a fraction of damping (in the sense of reflection)- the damping and absorbability (in the sense of tranmission) of the diaphragm is very low, at least below several kHz.
This interesting feature made it possible for Quad to use a very thin film as protective cover as mentioned before.
It also allows to use stacked films to increase SPL.
The effectiveness of the SPL-increase (theoretically +6dB, in practise I gained up to +4dB) depends on frequency range and distance of the films towards each other and has been proven mathematically as well as in practise. The effect has been known for many decades but was and is seldomly practised.
This feature would be impossible if the diaphragm weren´t acoustically transparent enough.
At least with ´open´, transparent panel designs You can do the following experiment. Listen to the panel in very close distance. Now wave slowly with Your hand behind the panel. You will hear the difference which stems from the rearside reflections from Your hand!

jauu
Calvin

[LineArray]

Originally Posted by a.wayne

Very interesting topic on the simple speaker and it's complexities ....

...
The bigger the baffle the more it becomes a problem
...

so there would be a "small is beautiful" advantage for massive
open baffle and box type speakers ... at least in the context
of acoustical transparency.