Horn Mouth Diffraction

[mefistofelez]

Dear all,

It is rather well understood that a finite aperture of a horn/wave-guide causes diffraction effects, [1]. However, neither this reference nor another paper [2], which at least tangentially touches on this issue, gives any insight on computation of a mouth shape that would give an optimal (whatever the criteria) diffraction.

I am also aware of the work of Jean Michel Le Cleac'h [3], but this appears to be concerned with the entire horn contour, and not only the mouth shape. As such, it appears inapplicable to a situations, where a horn contour is pre-determined, e.g., constant directivity.

I would appreciate if anyone, who aware of any theory/papers/software dealing with this issue, could post references.

Thank you,

M

[1] Geddes, E., R.: "Sound Radiation from Acoustic Apertures." JAES., vol. 41, pp. 214-23 (April 1993)
[2] Henwood, D.J.: "The Boundary element method and Horn Design, JAES, vol. 41, pp. 485-496 (June 1993)
[3] http://ndaviden.club.fr/pavillon/lecleach.htm

[al2002]

The best reference, in fact the only reference I know of, on this topic is Geddes' book, "Audio Transducers". I strongly recommend it.

It can be ordered directly from his site: www.gedlee.com.


A sample calculation may be seen here:

http://gedlee.com/downloads/Appendix_A.pdf

Hope this helps.

[mefistofelez]

Dear al2002,

thank you for the reference.

However, it seems to me that we are micommunicating because the link that you have posted treats calculation of a wave propagation throug a wave-guide assumed to be conical; therefore, without mouth flare.

The only comment related to my inquiry is on p. 302: ". . . waves reflected . . . can be reduced by radius'd (flared) mouth treatment as we discussed in Sec. 6.6."

Could you tell me if Sec. 6.6. contains any theoretical derivation of the flare or just states to do so?

M

[Cloth Ears]

Is this (http://www.users.onaustralia.com.au/...phd/thes.ps.gz) along the lines of what you're looking for? I haven't read it yet as I haven't been able to grab the printer for long enough.

[jomor]

Originally posted by mefistofelez
Dear all,

It is rather well understood that a finite aperture of a horn/wave-guide causes diffraction effects, [1].
.
.
.

I would appreciate if anyone, who aware of any theory/papers/software dealing with this issue, could post references.

http://www.nutshellhifi.com/library/...r-design1.html

Look at the Horn paragraph. In fact, the whole article is a "must read".

[pooge]

http://db.audioasylum.com/cgi/m.mpl?...pooge&session=

[al2002]

Originally posted by mefistofelez
Dear al2002,

thank you for the reference.

However, it seems to me that we are micommunicating because the link that you have posted treats calculation of a wave propagation throug a wave-guide assumed to be conical; therefore, without mouth flare.
M

No miscommunication. The link was only given to illustrate the standard of the book. It does not, of course, show a diffraction calculation.

The only comment related to my inquiry is on p. 302: ". . . waves reflected . . . can be reduced by radius'd (flared) mouth treatment as we discussed in Sec. 6.6."

Could you tell me if Sec. 6.6. contains any theoretical derivation of the flare or just states to do so?

M

Yes, it does.

[454Casull]

Originally posted by pooge
http://db.audioasylum.com/cgi/m.mpl?...pooge&session=

"Earl, in your waveguide paper you dealt with a radius at the baffle, but didn't specify its curvature. Can you eloborate on this?" The radius should really be as large as a wavelength of the lowest frequency, but a rule of thumb says that it should be no less than 1/4 wavelength at the lowest frequency of waveguide use. This will diffract a lot less energy, but still a significant amount at the lowest frequencies.

[pooge]

Earl Geddes uses a 2" radius on his waveguides

[al2002]

Originally posted by pooge
Earl Geddes uses a 2" radius on his waveguides

I believe it is the cabinet edge radius which is 2". The waveguide itself has a 4" flare at the mouth.

Also, in response to an earlier post, Geddes' recommends a lambda/2 flare at the mouth.