Effect of Lens on Mid Horn Frequency Response?

[Beowulf57]

Does anyone have information on the effect of the addition of a lens to a compression driver/horn combo? I recall a post which showed the effect of adding a lens to the frequency response curve, but can't locate it now. Examples would be adding the 2308 lens to an LE85/2420 using the 2307 or 2312 horn, or adding the same lens to a 375/2440 using the HL93 horn. I am particularly interested in the effect on the lower end of the response curve.

[Fred Sanford]

Does anyone have information on the effect of the addition of a lens to a compression driver/horn combo? I recall a post which showed the effect of adding a lens to the frequency response curve, but can't locate it now. Examples would be adding the 2308 lens to an LE85/2420 using the 2307 or 2312 horn, or adding the same lens to a 375/2440 using the HL93 horn. I am particularly interested in the effect on the lower end of the response curve.

I tried searching the site for "acoustic lens". Here's a couple links, hope they help:

http://www.jblpro.com/pub/obsolete/A...ns_Family1.pdf

http://www.lansingheritage.org/html/...nical/lens.htm

[Beowulf57]

I tried searching the site for "acoustic lens". Here's a couple links, hope they help:

http://www.jblpro.com/pub/obsolete/A...ns_Family1.pdf

http://www.lansingheritage.org/html/...nical/lens.htm

Thanks Fred...I have looked over those items. I'm hoping someone has actually done some frequency sweeps that provide an indication of the effect of adding the lens on the low frequency response, i.e., does it extend the low end compared to the horn alone?

[louped garouv]

according to page one of the article linked above written by George Augspurger, “The lens introduces NO tonal coloration and can be designed to give almost any desired directional pattern.”


is that the answer?

[Beowulf57]

according to page one of the article linked above written by George Augspurger, “The lens introduces NO tonal coloration and can be designed to give almost any desired directional pattern.”


is that the answer?

Hmm...getting closer but still cigar.

I wish to find out if there is any change to the low end rolloff when you add a lens to one of these or a similar horn. I :dont-know

[Robh3606]

Well for what it's worth here is a 2307 measured in my 4344 with and without the lense. My lense is the H94 serpentine not the 2308. I don't see any significant differences. Looks to me like the horn is the determining factor.

Rob

[Hoerninger]

Rob's measurements encourage me to formulate my thoughts:

A horn gives a "charging" to the diphragma which is obsolete when the sound travels into free space. Then the sound distributes freely in space. But the higher the frequency the higher the directivity. The aim of the lens is to distribute more divergent (although just like in optics there can be made more directivity otherwise).
So the lens distributes wider in free space which contradicts any horn effect. There is no enhanced charging at lower frequencies.
____________
Peter

[Chas]

I think I would agree with Peter. It is likely to be transparent at lower frequencies. Just gut feeling being expressed...

[Beowulf57]

Well for what it's worth here is a 2307 measured in my 4344 with and without the lense. My lense is the H94 serpentine not the 2308. I don't see any significant differences. Looks to me like the horn is the determining factor.

Rob

Thanks Rob...that helps! Also most useful to see another example of a sweep with the H91/2307. Anyone got a sweep of the 2312 horn?

[Beowulf57]

Rob's measurements encourage me to formulate my thoughts:

A horn gives a "charging" to the diphragma which is obsolete when the sound travels into free space. Then the sound distributes freely in space. But the higher the frequency the higher the directivity. The aim of the lens is to distribute more divergent (although just like in optics there can be made more directivity otherwise).
So the lens distributes wider in free space which contradicts any horn effect. There is no enhanced charging at lower frequencies.
____________
Peter

Good thinking...makes eminent sense.

[Ian Mackenzie]

Without the horn it honks badly.

Depending on the resolution of the test method you can make it look as smooth or messy.

I think the lense adds a bit of noise but the benefits outweigh any negatives. The low end response isidentifcal on axis.

I did some off axis response curves once but cant find them. You may well find the low end response has better dispersion. I think that is what helps because on the 4345 baffle the 2307 honks without the lense using a 10 inch mid cone.

[Maron Horonzakz]

IAN ,,,,What kind of noise???

[Beowulf57]

Without the horn it honks badly.

Depending on the resolution of the test method you can make it look as smooth or messy.

I think the lense adds a bit of noise but the benefits outweigh any negatives. The low end response isidentifcal on axis.

I did some off axis response curves once but cant find them. You may well find the low end response has better dispersion. I think that is what helps because on the 4345 baffle the 2307 honks without the lense using a 10 inch mid cone.

Oh yeah...without the lens, the sound bores right through my head. Good point about the graphed sweep resolution giving a smooth or messy appearance to the frequency response curve. I wonder how low the lens' dispersion is effective?

[Ian Mackenzie]

Noise, as in response noise ripple depending on the resolution of the measurement set-up.

Someone would need to run some off axis measurements, I no longer have the 2307/2308 or the 1 inch compression drivers.

Ian

[Beowulf57]

Thanks for all the help: results posted here: http://audioheritage.org/vbulletin/s...028#post222028