slot over speaker to offset increasing directvity? - diyAudio
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Old 1st July 2013, 08:00 PM   #1
eqjive is offline eqjive  United States
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Default slot over speaker to offset increasing directvity?

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.
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Old 1st July 2013, 09:13 PM   #2
bjorno is offline bjorno  Sweden
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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:

What is the effect of hiding the B139 in the Kef Concord?
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File Type: jpg KefB139-small-KefKit2_DI.JPG (415.4 KB, 526 views)
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Old 2nd July 2013, 09:05 PM   #3
eqjive is offline eqjive  United States
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I'm a bit surprised there is not more comments here given how passionate folks can be about horns and waveguides.

Thank you for the post and data shown - care to provide any commentary on it?
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Old 3rd July 2013, 01:54 AM   #4
IG81 is offline IG81  Canada
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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
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Old 3rd July 2013, 03:53 AM   #5
freddi is offline freddi  United States
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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
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lens
Click the image to open in full size.
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Old 10th July 2013, 12:11 AM   #6
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Quote:
Originally Posted by eqjive View Post
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 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.
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Old 10th July 2013, 06:58 AM   #7
VaNarn is offline VaNarn  Australia
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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.
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Old 10th July 2013, 09:53 AM   #8
freddi is offline freddi  United States
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from my copy
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Old 10th July 2013, 01:16 PM   #9
IG81 is offline IG81  Canada
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Never seen that one before, pretty neat! Thanks for mentionning and posting the article Vanarn and freddi.

IG
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Old 15th July 2013, 11:44 AM   #10
elb is offline elb  Australia
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Default 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
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