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   Home » Horn-Loaded Speakers» Constant directivity = constant wavefront center? (6 posts, 1 page)
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  »  New  Engaging the David Haigner’s ideas..  The degree of disagreement correction...  Horn-Loaded Speakers Forum     7  88581  08-30-2009
10-29-2007 Post does not mapped to Knowledge Tree
el`Ol
Posts 225
Joined on 10-13-2007
Post #: 1
Post ID: 5758
Reply to: 5758
Constant directivity = constant wavefront center?
Hello all!

Some people call omnidirectional spekers "Hallsoßenwerfer" (reverb sauce throwers), some people even accept price and sensitivity of an MBL 101. While I find the MBL too diffuse, I still find there is something special about a speaker being radial. In my experiments with fullrange drivers placed at the height of my ears I found they have to face the ceiling very close to 90° to produce that magical image, so it`s not just the ratio of direct and reflected sound, but there has to be something about being radial.
My attempt to explain this is the following: In a pistonic direct radiator there is not only more beaming in the higher frequencies, but also the center of the wavefront is moving backwards, resulting in a different wavefront radius at the listening position, which results in different interaural time delays.
My question: Is it sufficient for a horn to have constant directivity in order to have constant wavefront center over its frequency range, or how else would a "constant wavefront center horn" have to look like?


Regards,
Oliver
10-30-2007 Post does not mapped to Knowledge Tree
CO
Posts 37
Joined on 11-18-2005
Post #: 2
Post ID: 5767
Reply to: 5758
This is also true for horns
Hello el`Ol

Can you better describe "the center of the wavefront is moving backwards" ? You mean the sound wraps around the speaker differently dependent on the wavelength compared to the baffle ratio i think ?

This is also true for horns (not only for constant directivity) only this point is much lower in frequency dependent on the mouth area and i think is mainly out of the usable bandwidth.

Gr, Collin
10-30-2007 Post does not mapped to Knowledge Tree
el`Ol
Posts 225
Joined on 10-13-2007
Post #: 3
Post ID: 5773
Reply to: 5767
Cone size and wavefront center
I mean for low frequencies that radiate omnidirectionally the wavefront center estimated from the wavefront curving at a point a bit away from the speaker would in fact be the center of the cone. For the more beaming frequencies it would be estimated behind.
10-31-2007 Post does not mapped to Knowledge Tree
CO
Posts 37
Joined on 11-18-2005
Post #: 4
Post ID: 5774
Reply to: 5773
Center of soundwave

The speed of the soundwave coming towards you will not change even if the lower frequencies are more omnidirectional so there will be no shift.

The SPL of these different frequencies will change though depending on distance because of this effect.

That’s why low and mid drivers ‘need’ reinforcement from the walls in a traditional loudspeaker arrangement.

So speakers are made to be listened to at certain listening distance. Wall reflections also have a large influence on the sound because they receive mainly off-axis sound which has less high frequency content.

Rgs, Collin
11-02-2007 Post does not mapped to Knowledge Tree
el`Ol
Posts 225
Joined on 10-13-2007
Post #: 5
Post ID: 5787
Reply to: 5774
Wave propagation simu
Here is a simulator for wave propagation:
http://www.falstad.com/ripple/
Choose setup = single slit.
Select mouse = edit walls.
Broaden the slit.
See what happens in the far field if you change the source frequency.
The simu is not high quality, but I believe to see that the wavefront is less curved for higher frequencies.
11-05-2007 Post does not mapped to Knowledge Tree
CO
Posts 37
Joined on 11-18-2005
Post #: 6
Post ID: 5801
Reply to: 5787
Simulation
Hi Oliver,

Thie single slit model is definitely not the correct model to be judging these effects. Even the other model baffled piston is iffy.

Rgds, Collin
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  »  New  Engaging the David Haigner’s ideas..  The degree of disagreement correction...  Horn-Loaded Speakers Forum     7  88581  08-30-2009
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