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Electrostats vs conventional drivers
Electrostats vs conventional drivers
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Old 9th February 2019, 08:08 PM   #121
tacit_tactix is offline tacit_tactix  Canada
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This is why you cannot EQ a electrostat in this particular frequency region. The stronger you make the front pressure, the back pressure will be equally as strong. So you can add as many db as you like and you will not gain any bass output at the lower frequency region.

The same is true of a woofer in free air, below a certain frequency the pressure waves diffract around the width of the woofer, and cancel eachother out, increasing low output may give some small boost directly on axis, where the diffraction is negligable, as you see in the dipole graph. But it wont help much or at all if you go low enough in frequency.

Last edited by tacit_tactix; 9th February 2019 at 08:15 PM.
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Old 9th February 2019, 08:13 PM   #122
tacit_tactix is offline tacit_tactix  Canada
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This radiation pattern (in the low frequency region) is a characteristic of all dipoles , and exists regardless of line source, point source, or plane.

The geometry of the source does influence the radiation patter at higher frequencies where pressure waves beam in a rectlinear fashion, as opposed to the bass region where they travel more like true waves and exhibit bending around objects.

Further you will have reflections from the back wave which meet the front wave at points in the room forming comb filtering. This also cannot be equalized out, because the time delay cannot be changed electronically, but is a physical characteristic of the room (specifically the path length differences from the source to the listener). Therefore, the only way to reduce those interactions, is with acoustic absorption, or building an enclosure for the ESL.

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Old 9th February 2019, 08:21 PM   #123
tacit_tactix is offline tacit_tactix  Canada
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The reason the response is different at varying distances is partially because of the diffraction from the rear wave to the front (near field , less diffraction ) , and due to the pressure squared fall off as the surface area of the spherical wave increases with distance from the source.

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Old 9th February 2019, 08:26 PM   #124
tacit_tactix is offline tacit_tactix  Canada
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Your solution to make the panel the width of the wall eliminates the rear pressure wave completely (it is an enclosure).
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Old 9th February 2019, 08:28 PM   #125
tacit_tactix is offline tacit_tactix  Canada
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Roger Sanders Electrostatic cook book was a good resource when I built electrostats and derrived the solutions of the damped driven harmonic oscilator from first principles of a spring , and demonstrated that the high frequency response was inversely proportional to the mass of the oscillator back in 2005 at bay area science and engineering fair.

All the cases are covered in this book. Highly recommended.
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Old 9th February 2019, 08:38 PM   #126
tacit_tactix is offline tacit_tactix  Canada
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You can read Roger Sanders description of ESL bass suck out in his book here, on pg 18, where he clearly describes the pressure waves from front and back of the panel canceling eachother out.

http://www.introni.it/pdf/Sanders%20...ook%201995.pdf
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Old 9th February 2019, 09:41 PM   #127
tacit_tactix is offline tacit_tactix  Canada
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a line source, will radiate energy in a more focused way than a point source, and the fall off in acoustic pressure as a function of distance from the source is actually less for a line source, than point source, because the surface of the wave front has less area. The acoustic energy is spread across a sphere as opposed to a plane, and the surface area of the sphere grows with distance, the surface area of a line source does not grow spherically, but only the plane gets larger in one axis only with distance from the source. This is of course only applicable in mid to high frequency range where sound travels in a straight line from source, and low frequency pressure waves will radiate spherically regardless of the source geometry.

Considering this, your explanation for why ESL have reduced output in the low end , is incorrect and is actually an explanation for why they have greater output in the high end.

Last edited by tacit_tactix; 9th February 2019 at 09:47 PM.
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Old 9th February 2019, 09:49 PM   #128
tacit_tactix is offline tacit_tactix  Canada
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In conclusion, there are a few real solutions to the thin bright sound of an ESL.

Build the ESL with a rear wave enclosure.

Make the ESL pannel about 2 feet wide to minimize the diffraction.

Cross over the the ESL panel with a steeper slope, and / or at a higher frequency.
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Old 9th February 2019, 11:41 PM   #129
tacit_tactix is offline tacit_tactix  Canada
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Curving the front panel will also decrease the high frequency energy at far distances, this can make the tonal balance seem less bright, but it won't bring back the lower mid to bass area that is cancelled from dipole radiation.
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Old 10th February 2019, 12:33 AM   #130
golfnut is offline golfnut  New Zealand
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Quote:
Originally Posted by tacit_tactix View Post
a line source, will radiate energy in a more focused way than a point source, and the fall off in acoustic pressure as a function of distance from the source is actually less for a line source, than point source, because the surface of the wave front has less area. The acoustic energy is spread across a sphere as opposed to a plane, and the surface area of the sphere grows with distance, the surface area of a line source does not grow spherically, but only the plane gets larger in one axis only with distance from the source. This is of course only applicable in mid to high frequency range where sound travels in a straight line from source, and low frequency pressure waves will radiate spherically regardless of the source geometry.

Considering this, your explanation for why ESL have reduced output in the low end , is incorrect and is actually an explanation for why they have greater output in the high end.
Read the Baxandall chapter. The effect you speak of gives the membrane mass at low frequencies (via the radiation impedance), which in turn causes the membrane resonance (mass on a spring)- this is the low frequency limit of an ESL. Above this frequency, the SPL is nominally constant with frequency. At frequencies much above the resonance, the membrane is essentially massless.

Remember too that ESLs are a pressure source, not a volume-velocity source like conventional divers - the behaviour is quite different.
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