Using diffraction slots over a cone transducer to achieve very wide horizontal coverage? Can anyone comment on or refer to experience, threads, papers, etc about this sort of thing?
The general consensus is that diffraction of sound is associated with bad sound quality - but in this case would that hold true?
I'm looking to explore the pros and cons of a full range speaker concept that would use a slot over a single cone to offset increasing directvity with increasing frequency.
The general consensus is that diffraction of sound is associated with bad sound quality - but in this case would that hold true?
I'm looking to explore the pros and cons of a full range speaker concept that would use a slot over a single cone to offset increasing directvity with increasing frequency.
Hi,
Take a look at a recent... not... posted simulation I made for B139B-small, i.e. not a FR but only presenting the outcome of a couple of HR screens.
b
PS : The referred thread this original simulation was meant for is:
http://www.diyaudio.com/forums/multi-way/238047-what-effect-hiding-b139-kef-concord.html
Take a look at a recent... not... posted simulation I made for B139B-small, i.e. not a FR but only presenting the outcome of a couple of HR screens.
b
PS : The referred thread this original simulation was meant for is:
http://www.diyaudio.com/forums/multi-way/238047-what-effect-hiding-b139-kef-concord.html
Attachments
Can't be all that bad seeing how the BBC used it on some monitors.
The Karlson has a similar effect too. I have not had as much time to try BBC-slots on fullrange drivers as I like, but keep meaning to get around to it.
http://downloads.bbc.co.uk/rd/pubs/reports/1979-22.pdf
I think a bit of constriction could be helpful at times with certain drivers too.
IG
The Karlson has a similar effect too. I have not had as much time to try BBC-slots on fullrange drivers as I like, but keep meaning to get around to it.
http://downloads.bbc.co.uk/rd/pubs/reports/1979-22.pdf
I think a bit of constriction could be helpful at times with certain drivers too.
IG
although I accidentally messed up the smoothing on these two graphs, they kinda illustrate what happened when an oval aperture was introduced in front of a 15 inch woofer
no lens
lens
no lens
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lens
An externally hosted image should be here but it was not working when we last tested it.
Hi eqjive,
i fear applicability - especially of a very narrow slot compared to
cone diameter - is restricted in usable frequency range.
This is because the volume of air behind the slot and the mass
reactance of the slot together form a helmholtz resonator.
The cone/volume/slot configuration can only be used considerably
below that resonance, also depending on the kind of lowpass filter
to be used (e.g. in a 2-way system).
The concept is hardly applicable to fullrange IMO.
What was known as a Kolster Brandes slot diffuser largely overcame the problems associated with the trapped air that LineArray has mentioned.I cannot find my original reference via Gilbert Briggs and so I can only suggest an arrangement that suited 8'' speakers that suffered from a rising response above 2kHz,if someone wishes to try the device.Four 50 mm D circles are removed from a sheet of three ply ( approx. 5mm thick)The centres of the circles are on a 50 mm radius from a central point that lines up with the speaker cone centre axis and each circle is spaced at 90 degrees from each other.A slot of 31 mm width is removed from the plywood sheet and this runs from one of the 50 mm circles to the opposite 50 mm circle to form what in useage will be a vertical slot.There will need to be some thought given to the clearance between the diffuser and the periphery of the cone and in some cases a protruding roll surround.I would also suggest that an application of Blu Tack could be used to both dampen the plywood and partially streamline the inner surfaces.
from my copy
An externally hosted image should be here but it was not working when we last tested it.
driver diffuser
A big thank you to VaNarn & freddi for their input on this subject.
I own a pair of Visaton B200's that I have a love/ hate relationship with.
I am sure that everyone knows the issue with these drivers.
I made a pair of the modified diffusers today and bugger me,they transformed the B200's.
Unbelieveable that such a simple mod can do this good.
Very easy to make and try, judge for yourself.
Regards,elb
A big thank you to VaNarn & freddi for their input on this subject.
I own a pair of Visaton B200's that I have a love/ hate relationship with.
I am sure that everyone knows the issue with these drivers.
I made a pair of the modified diffusers today and bugger me,they transformed the B200's.
Unbelieveable that such a simple mod can do this good.
Very easy to make and try, judge for yourself.
Regards,elb
I am sure JBL did a stack of perforated plates with circular frustrum.
But did they try perforated plates with slot frustrum? I think they had
some preference for a wavy maze of plates for horizontal dispersion,
so we never got to see perforated plates in that application.
I'm just saying the modified KB diffuser looks to work on the same
principle? But its only one perforated plate, and holes are silly huge.
I don't know how much we trade-off here by keeping it simple...
But did they try perforated plates with slot frustrum? I think they had
some preference for a wavy maze of plates for horizontal dispersion,
so we never got to see perforated plates in that application.
I'm just saying the modified KB diffuser looks to work on the same
principle? But its only one perforated plate, and holes are silly huge.
I don't know how much we trade-off here by keeping it simple...
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You might want to see how a K-slot affects directivity in a simulation of the mini Karlsonator with and without a K-aperture here: http://www.diyaudio.com/forums/full-range/237948-speaker-kicks-butt-large-spaces-27.html#post3566993
It makes a big difference at mid range of 500 Hz.
It makes a big difference at mid range of 500 Hz.
500 Hz to 2000 kHz is seldom where there's problems with directivity IME.
I'd be much more interested in something that could give a bit more uniform directivity for the 5000, to perhaps all the way to 16000 kHz region.
The KB and Karlson slot looks to have much the same thing going on. IE they are straddling the line between doing a narrow opening to simulate a smaller driver and still allowing the other frequencies to "get out", without too much filtering and congested coloured sound.
The KB slot could be viewed as approximately the same thing as the Karlson slot only stylized.
I'd be very interested to hear whether they really work as intended. And how much colouration they cause.
I've been thinking of another variation and simplification/generalization on the theme, although not confined to mainly work horizontally: A torus (doughnut) shape suspended flat in front of the driver.
This would avoid any sharp edges, it would also avoid much of the sharply defined cavity and be stiffer.
It would still have a narrow central opening and a peripheral opening.
No doubt this has been done before. Anyone know about it?
I'd be much more interested in something that could give a bit more uniform directivity for the 5000, to perhaps all the way to 16000 kHz region.
The KB and Karlson slot looks to have much the same thing going on. IE they are straddling the line between doing a narrow opening to simulate a smaller driver and still allowing the other frequencies to "get out", without too much filtering and congested coloured sound.
The KB slot could be viewed as approximately the same thing as the Karlson slot only stylized.
I'd be very interested to hear whether they really work as intended. And how much colouration they cause.
I've been thinking of another variation and simplification/generalization on the theme, although not confined to mainly work horizontally: A torus (doughnut) shape suspended flat in front of the driver.
This would avoid any sharp edges, it would also avoid much of the sharply defined cavity and be stiffer.
It would still have a narrow central opening and a peripheral opening.
No doubt this has been done before. Anyone know about it?
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Squeak, I don't know if it's been done, but I gotta say I've thought of similar embodiments before. Getting better dispersion up to ~2kHz is good IMO, as it'll broaden an 8" or 10" woofer's dispersion to meet up a tweeter with similar pattern. Any higher and the slot gets tighter, too much choke, hence the "flying donut" lens idea.
Not exactly the same, but Altec had a "coaxial" driver that was a small horn suspended over the dustcap to try and amplify whatever came out of there. Of course throat coupling will be poor, as it might be with a diffusor, but it must have worked to a certain extent?
IG
Not exactly the same, but Altec had a "coaxial" driver that was a small horn suspended over the dustcap to try and amplify whatever came out of there. Of course throat coupling will be poor, as it might be with a diffusor, but it must have worked to a certain extent?
IG
I am a little confused as to the arrangement. The axis of the donut is coaxial with driver? And you mean a round donut like the type we eat not a flat disc with a hole in it?
Yeah. To reference something i can find a picture of, just like the cantilever support on the Axiom 80:
Only thicker and rounder.
Or it could be any toroid shape that is better suited. A torus is just close enough and relatively easy to find or make in styrofoam for example.
I've KTubed over the dustcap to some success, but its damn hard to make that
a permanent fixture... And it does need about 1/4 or more inches of clearance.
Not for want of hitting the cap, but just cause it sounds better that way.
Long ago I did some tests with diffraction slot on 8" fullrange driver. It was simple piece of thick cardboard which I encarved with knife
The result: It works.
However, be prepared for severe on-axis level drop at high frequencies. This is because the energy is redirected to wider angle than originally. Simple energy preserving law
So if you initially have flat on-axis at high freqs, after the slot it'll be down to -10 ... -20 dB. For a driver having heavily rising freq response, diffraction slot maybe a good idea.
Acoustic Lens
Hmm, reminds me of the Electro Voice Acoustic Lens, found on the Interface:A circa 1973
They had an equalizer that went with the set but I don't know if they boosted the highs as well as the bass.
It seems that to scale this up to a full range size, a non-rigid material should be used. How about a donut made of loosely-woven yarn on a needlepoint hoop? The yarn would be very fuzzy so as to block the highs yet the midrange would blow through.
Hmm, reminds me of the Electro Voice Acoustic Lens, found on the Interface:A circa 1973
They had an equalizer that went with the set but I don't know if they boosted the highs as well as the bass.
It seems that to scale this up to a full range size, a non-rigid material should be used. How about a donut made of loosely-woven yarn on a needlepoint hoop? The yarn would be very fuzzy so as to block the highs yet the midrange would blow through.
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