"Micro-Beaming" (Of Tweeters)
 

I noticed with both my old Mission 752Fs, and now my jizzmatic Dynaudios,
that the position for optimum treble for each ear is _extremely_ narrow;
something like +/- 1cm laterally.

It seems not so easy to check vertically, but logically, I think the
situation ought to be the same.

And we're not talking big radiators here; in both cases, the tweeters
are about 2cm - 2.5cm diameter.

I'm always fidgeting to get the clearest, optimum treble. I move slowly
sideways, and suddenly one ear will "click" into a position of very clear,
perfect treble. The trick is to have them both so satisifed at the same
position, and it's _not_ easy!

(The effect arises from the radiation pattern you get when you plot
response versus angle from axis for high frequencies. There's a main
centre lobe which gets narrower as f increases. It also gets narrower
as the diameter of the radiator increases. So it's generally better
to have a smaller diameter tweeter to get a wider main lobe. If my
hazy memories of my acoustics degree serve me correctly.)

It's a pain, though.

Anyone else noticed this ultra-narrow-sweet-spot for high treble with
normal tweeters?


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

"Micro-Beaming" (Of Tweeters)
 

Fleetie wrote:

I noticed with both my old Mission 752Fs, and now my jizzmatic Dynaudios,
that the position for optimum treble for each ear is _extremely_ narrow;
something like +/- 1cm laterally.

Anyone else noticed this ultra-narrow-sweet-spot for high treble with
normal tweeters?

No.

Does your listening room have many undamped surfaces?
It sounds like standing waves rather than a very directional tweeter.

--
Eiron.

"Micro-Beaming" (Of Tweeters)
 

Eiron wrote:

Fleetie wrote:

I noticed with both my old Mission 752Fs, and now my jizzmatic Dynaudios,
that the position for optimum treble for each ear is _extremely_ narrow;
something like +/- 1cm laterally.

Anyone else noticed this ultra-narrow-sweet-spot for high treble with
normal tweeters?

No.

Does your listening room have many undamped surfaces?
It sounds like standing waves rather than a very directional tweeter.

Could be, although as a rule higher frequencies become more directional
anyway.

--
Andy Hewitt ** FAF#1, (Ex-OSOS#5) - FJ1200 ABS
Honda Civic 16v: Windows free zone (Mac G5 Dual Processor)
http://www.thehewitts.plus.com

"Micro-Beaming" (Of Tweeters)
 

"Eiron" wrote in message ...
Fleetie wrote:

I noticed with both my old Mission 752Fs, and now my jizzmatic Dynaudios,
that the position for optimum treble for each ear is _extremely_ narrow;
something like +/- 1cm laterally.

Anyone else noticed this ultra-narrow-sweet-spot for high treble with
normal tweeters?

No.

Does your listening room have many undamped surfaces?
It sounds like standing waves rather than a very directional tweeter.


No no no no no.

It's beaming, without doubt.

It's just that until I actually noticed it, I didn't expect the effect to
be so pronounced.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

"Micro-Beaming" (Of Tweeters)
 

Fleetie wrote:

"Eiron" wrote in message ...

Fleetie wrote:


I noticed with both my old Mission 752Fs, and now my jizzmatic Dynaudios,
that the position for optimum treble for each ear is _extremely_ narrow;
something like +/- 1cm laterally.

Anyone else noticed this ultra-narrow-sweet-spot for high treble with
normal tweeters?

No.

Does your listening room have many undamped surfaces?
It sounds like standing waves rather than a very directional tweeter.



No no no no no.

It's beaming, without doubt.

It's just that until I actually noticed it, I didn't expect the effect to
be so pronounced.


Martin

What is the effect like using just one speaker?
How big is your tweeter?
Have you looked at an analysis of directionality relating to
wavelength and driver size? There is a good one in Martin Colloms'
book 'High Performance Loudspeakers'.

--
Eiron.

"Micro-Beaming" (Of Tweeters)
 

On Thu, 28 Oct 2004 20:56:02 GMT, "Fleetie"
wrote:

I noticed with both my old Mission 752Fs, and now my jizzmatic Dynaudios,
that the position for optimum treble for each ear is _extremely_ narrow;
something like +/- 1cm laterally.

It seems not so easy to check vertically, but logically, I think the
situation ought to be the same.

And we're not talking big radiators here; in both cases, the tweeters
are about 2cm - 2.5cm diameter.

I'm always fidgeting to get the clearest, optimum treble. I move slowly
sideways, and suddenly one ear will "click" into a position of very clear,
perfect treble. The trick is to have them both so satisifed at the same
position, and it's _not_ easy!

(The effect arises from the radiation pattern you get when you plot
response versus angle from axis for high frequencies. There's a main
centre lobe which gets narrower as f increases. It also gets narrower
as the diameter of the radiator increases. So it's generally better
to have a smaller diameter tweeter to get a wider main lobe. If my
hazy memories of my acoustics degree serve me correctly.)

It's a pain, though.

Anyone else noticed this ultra-narrow-sweet-spot for high treble with
normal tweeters?

I think you'll find that it has nothing whatever to do with the
tweeters, it's just a sign of a *good* speaker. I have always noted
that when you have really top-class speakers in a good environment,
the image 'snaps' into sharpest focus on the exact midpoint of the the
speaker position bisector. Moving your head sideways by an inch makes
a significant difference. IME, if you have a big 'sweet spot', that's
because it's fuzzy *everywhere*.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Micro-Beaming" (Of Tweeters)
 

"Eiron" wrote
What is the effect like using just one speaker?
How big is your tweeter?
Have you looked at an analysis of directionality relating to
wavelength and driver size? There is a good one in Martin Colloms'
book 'High Performance Loudspeakers'.

Did it in my degree.

(Well, at least to 1st order, anyway.) Forgotten the formulae now,
but not the basic concepts.

The tweeters are average size; a bit less than 1 inch diameter.

Must admit, don't have the book but have obviously heard of MC. Used to do
measurements for "Hi-Fi Choice" too, didn't he? I think that's where I
first encountered his name in the late 80s.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

"Micro-Beaming" (Of Tweeters)
 

In article , Fleetie
wrote:
"Eiron" wrote
What is the effect like using just one speaker? How big is your
tweeter? Have you looked at an analysis of directionality relating to
wavelength and driver size? There is a good one in Martin Colloms'
book 'High Performance Loudspeakers'.

Did it in my degree.

(Well, at least to 1st order, anyway.) Forgotten the formulae now, but
not the basic concepts.

Just found the simple formula for a 'piston' speaker in my copy of the
Newnes Audio and HF handbook. Too complicated to write in plain text
easily. :-) Can put it on the web if needed, though.

Put very approximately, you seem to get a half-power beamwidth of the order
of 45-90 deg across when the wavelength is similar to the diameter.

The tweeters are average size; a bit less than 1 inch diameter.

Must admit, don't have the book but have obviously heard of MC. Used to
do measurements for "Hi-Fi Choice" too, didn't he? I think that's where
I first encountered his name in the late 80s.

Still does reviews for HFN.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"Micro-Beaming" (Of Tweeters)
 

Put very approximately, you seem to get a half-power beamwidth of the order
of 45-90 deg across when the wavelength is similar to the diameter.

Hmm! 45-90 is a bit of a range. So diameter~=25mm, c~=344m/s, so
f~=13.7kHz.

I'm surprised. I'd have thought at that kind of frequency, the central
lobe would be considerably narrower, but I can't contradict you at the
moment.

That seems not to explain the extremely noticeable "micro-beaming" effect,
but maybe there are other things coming into play. I mean as I said, the
"sweet spot" is 1 or 2 cm at about 3 or 4 metres from the tweeter, which
is considerably less than ONE degree.

Thanks, anyway.


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

"Micro-Beaming" (Of Tweeters)
 

On Fri, 05 Nov 2004 18:50:40 GMT, "Fleetie"
wrote:

Put very approximately, you seem to get a half-power beamwidth of the order
of 45-90 deg across when the wavelength is similar to the diameter.

Hmm! 45-90 is a bit of a range. So diameter~=25mm, c~=344m/s, so
f~=13.7kHz.

I'm surprised. I'd have thought at that kind of frequency, the central
lobe would be considerably narrower, but I can't contradict you at the
moment.

That seems not to explain the extremely noticeable "micro-beaming" effect,
but maybe there are other things coming into play. I mean as I said, the
"sweet spot" is 1 or 2 cm at about 3 or 4 metres from the tweeter, which
is considerably less than ONE degree.

Get a copy of Martin Colloms 'High Performance Loudspeakers'. If you
care at all about music reproduction, it's an essential buy, and has
all that classic stuff in it. Akin to the Radiotron Handbook, I freely
admit! :-)
--

Stewart Pinkerton | Music is Art - Audio is Engineering