Open Baffle Planar servo sub speaker project

[HAL]

One design goal is a highly optimized stereo setup with these speakers. The design is optimized for a sweet spot. Since these speakers are DIY and just for my setup, see no need to worry about full room EQ for multiple listeners. If folks want to hear them, they just sit in my chair.

The cube is in work for measurement mic placement. Will see what happens.

Two more days until baffle pickup. It has been in build for over 1 year. Most of that time was just waiting for the BG planars to be available again.

[HAL]

Ugh! Baffle postponed until later.

[HAL]

Here is an interesting paper the author sent to me for input on line arrays. Putting it here for others to read if interested.

Attachments

nflawp.pdf

(305.42 KiB) Downloaded 925 times

[tomp]

Here is an interesting paper the author sent to me for input on line arrays. Putting it here for others to read if interested.

Comb Line Destructive Interferences
for Circular Drivers Line Arrays
[1], [2], [3],
[4]
§ Limit center to center spacing between
drivers to less than one wavelength
§ Use power tapering to reduce effect

From his paper this is what I was talking about with line arrays made up of individual elements. When you have individual drivers to make up the line you cannot get that spacing down to a level that will eliminate lobing at higher frequencies. With line drivers, it is more a factor of end to end spacing than center to center spacing which makes it better but unless the diaphragm is continuous you cannot eliminate it.

Tom

[HAL]

Tom,
From what I read, that effect can be mitigated by working with center to center spacing of 1 wavelength or smaller. He shows another graph of the pattern and the comb filtering at distance was not occurring any more.

I do not hear the effect with the knee bend test with the FPS planars and the beamformer running at my listening position. Since I listen at a single position, I am not really affected by it. Hearing other segmented planars over time, seems to be a very small effect. Just my take.

For larger planar drivers, the GT AudioWorks folks are building a planar/ribbon/cone speaker hybrid that is 4' tall. Greg has talked about larger planar/ribbon drivers. I have heard the GTA2.5's in three rooms and they can sound really good. So that is an option for folks buying speakers. Probably the best demo so far was at CAF2015.

[Stuart Polansky]

Here is an interesting paper the author sent to me for input on line arrays. Putting it here for others to read if interested.

Comb Line Destructive Interferences
for Circular Drivers Line Arrays
[1], [2], [3],
[4]
§ Limit center to center spacing between
drivers to less than one wavelength
§ Use power tapering to reduce effect

From his paper this is what I was talking about with line arrays made up of individual elements. When you have individual drivers to make up the line you cannot get that spacing down to a level that will eliminate lobing at higher frequencies. With line drivers, it is more a factor of end to end spacing than center to center spacing which makes it better but unless the diaphragm is continuous you cannot eliminate it.

Tom

Oron, a guy who has successfully implemented Neo8 line arrays, measured and listened extensively to them (as substitutes for Tympani IV midranges) told me that the comb filter issues don't apply to planar drivers since vertical dispersion is non-existent; rather that the problem is specifically related to sound being emitted perpendicular to the face of the cone or dome. Since the cone or dome has surfaces which are other than vertical, sound will be dispersed in those directions, which will, in turn, interfere with the emissions of adjacent drivers, causing the "destructive" effects and comb filtering of which you speak.

But, I've been given to understand, the planar drivers in the Neo series, have no vertical dispersion component at all, except for random internal reflections between the membrane and the face of the housing. Those reflections also cause the 12kHz peak seen in the Neo8. The use in a line array causes the same "destructive" cancellation, meaning that the 12kHz peak is knocked out and the notch filter not needed in a line array. So, in the case of the Neo planars, the comb filter is a positive effect without causing lobing.

Now, I could be full of it, but Oron (who can hear, measure and who's opinion I trust) as well as Bohlender Graebener, who wrote about it in their product notes, believe it.

Bottom line is that I don't think there is a negative issue with planar line arrays. But heck, I'm just a "worker".

Stuart

Attachments

264-712-bohlender-graebener-neo8-specifications-44294.pdf

(333.74 KiB) Downloaded 912 times

[HAL]

Stuart,
I have heard a open baffle line array of 16 - Neo3-PDR's and 6 - Neo10 planars mated to two 3x12" servo subs.

I heard no comb filtering effect with vertical height. Probably the best sounding pair of speakers I ever heard. They rank with the Infinity IRS Reference V's in sound quality. Just not the same amount of bass power, but the open baffle subs sound great and mated perfectly as well.

I am convinced this is the way to make progress.

[tomp]

Tom,
From what I read, that effect can be mitigated by working with center to center spacing of 1 wavelength or smaller. He shows another graph of the pattern and the comb filtering at distance was not occurring any more.

I do not hear the effect with the knee bend test with the FPS planars and the beamformer running at my listening position. Since I listen at a single position, I am not really affected by it. Hearing other segmented planars over time, seems to be a very small effect. Just my take.

For larger planar drivers, the GT AudioWorks folks are building a planar/ribbon/cone speaker hybrid that is 4' tall. Greg has talked about larger planar/ribbon drivers. I have heard the GTA2.5's in three rooms and they can sound really good. So that is an option for folks buying speakers. Probably the best demo so far was at CAF2015.

10KHz has a wavelength of 1.35 inches.

Tom

[HAL]

Well I just have to build it and see.

Already have the drivers and after hearing speakers that are similar, it is a non-issue for me.

Now to get the baffles.

[tomp]

Here is an interesting paper the author sent to me for input on line arrays. Putting it here for others to read if interested.

Comb Line Destructive Interferences
for Circular Drivers Line Arrays
[1], [2], [3],
[4]
§ Limit center to center spacing between
drivers to less than one wavelength
§ Use power tapering to reduce effect

From his paper this is what I was talking about with line arrays made up of individual elements. When you have individual drivers to make up the line you cannot get that spacing down to a level that will eliminate lobing at higher frequencies. With line drivers, it is more a factor of end to end spacing than center to center spacing which makes it better but unless the diaphragm is continuous you cannot eliminate it.

Tom

Oron, a guy who has successfully implemented Neo8 line arrays, measured and listened extensively to them (as substitutes for Tympani IV midranges) told me that the comb filter issues don't apply to planar drivers since vertical dispersion is non-existent; rather that the problem is specifically related to sound being emitted perpendicular to the face of the cone or dome. Since the cone or dome has surfaces which are other than vertical, sound will be dispersed in those directions, which will, in turn, interfere with the emissions of adjacent drivers, causing the "destructive" effects and comb filtering of which you speak.

But, I've been given to understand, the planar drivers in the Neo series, have no vertical dispersion component at all, except for random internal reflections between the membrane and the face of the housing. Those reflections also cause the 12kHz peak seen in the Neo8. The use in a line array causes the same "destructive" cancellation, meaning that the 12kHz peak is knocked out and the notch filter not needed in a line array. So, in the case of the Neo planars, the comb filter is a positive effect without causing lobing.

Now, I could be full of it, but Oron (who can hear, measure and who's opinion I trust) as well as Bohlender Graebener, who wrote about it in their product notes, believe it.

Bottom line is that I don't think there is a negative issue with planar line arrays. But heck, I'm just a "worker".

Stuart

Stuart:

It is not true that line arrays do not have vertical radiation. Their radiation is only cylindrical with frequencies shorter than one wavelength. The NEO8 has a length of 7.88 inches overall with a radiating element that is probably shorter. Even with the 7.88 inches the driver will start to radiate vertically at 1,715 Hz. The RD75's with their unbroken diaphragm go down to 180 Hz before vertical radiation starts to increase.

I am just trying to dispell some misconceptions, not saying that this is not a fantastic project. The benefits of the long dipole line array will vastly swamp any negatives of not having one continuous diaphragm. The sound from this will kill most dynamic driver speakers in the area of less floor and ceiling bounce, transient response, and dynamic range. The benefits of using the NEO8s also include much higher sensitivity than the RD75s. I have great results with the RDs but I'm driving them with a Crown Macro Reference that can put out over 1 KW into each 6 ohm driver. If you work with the lower sensitivity of the RD75s you have to use that kind of power. Then to protect the drivers against a glitch you have to have a protective circuit or you will destroy them if you do something stupid before you even realise that you did a bonehead move like pulling a cable with the power on. Everything is always a compromise.

Tom