A twist on the Smith Horn...

[Earl K]

I think that Earl K mentioned somewhere that the vanes were used to better spread mid frequencies.

- Yes, I have mentioned that the inclusion of vanes appear to help the loading ( & directivety ) of the lower frequencies ( ie; the first couple octaves above crossover ) / more than being there to help in the dispersion of the HF.
- Since I have no Smith style horns here to measure / my opinion is strictly conjecture at this time.
- My opinion is derived from a visual study of info ( on pg. 51 ) in Harry F Olsons' book, "Acoustical Engineering". Here , his studies depict the horizontal response of a horn which he classes as a "parabolic". The pictured horn is clearly of the same class as a Smith type except that it lacks the internal vanes. It is 1/2" entry, with the top and bottom plates also spaced 1/2" apart. The side-walls form a 90° angle. The bell lips are 12" deep
- The picture shows a very "beamy" horn from 1100 hz to 4400 hz. This is shown to be clearly related to the radius of the horn ( 12" depth in this case ). Olson chooses frequencies of study that are multiples of "R" ( or the primary bell depth referenced against a wavelength, in inches ).
- 8800hz to 17600 hz shows an increasingly smooth and wide horizontal spread, as frequency is increased.

By the way the HF mini smith horn used in westlake studio monitors do not have vanes.

Yes, it becomes a matter of choosing your poison . One such compromise is to go the Westlake route and use 2 Smith style horns ( one with vanes for MF and an another HF horn that's lacking in vanes ).

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[ChopsMX5]

Alright, so if I build the horns like I said earlier with the flat lips, and put the vanes in, does the shape of the vanes make a difference? IOW, if I build the horns like a triangle with the side walls perfectly flat from the horn entry all the way out to the lips, do the vanes have to be smooth and rounded, or can they be thin, sharp and edgy like a stretched out diamond to match the horn's walls? Like so...

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Also, since my Altec 902 drivers are 1", I take it the horn entry and top/bottom plate spacing should also be 1", correct?

Apparently, for a first time build with limited tools and woodworking skills, I'm trying to make things as simple as possible to get an idea of what to expect and general impressions on the horns' sound.

Thanks!

[yggdrasil]

Yes, you can try with a diamond shape.

It might be like two conical sections in stead of one exponential.

Again - Do you have some measuring devices?

[ChopsMX5]

The only thing I have for measuring is TrueRTA, a Behringer ECM8000 mic and a dbx mic preamp. I don't think any of those will help with meauring the horn in the way you are speaking of.

[yggdrasil]

You are very close with that equipment.

Look at Winairr (http://www.audioxpress.com/bksprods/...s/sof-airw.htm) or Speaker workshop (http://www.audua.com/).

Speaker workshop is freeware. Winairr has a trial version, but you will very soon want the full version.

If you chose to look into speaker workshop I can find the links to a very comprehensive manual.

I prefer winairr for measuring midrange and UHF because it is easyer to isolate room modes.

[ChopsMX5]

You are very close with that equipment.

Look at Winairr (http://www.audioxpress.com/bksprods/...s/sof-airw.htm) or Speaker workshop (http://www.audua.com/).

Speaker workshop is freeware. Winairr has a trial version, but you will very soon want the full version.

If you chose to look into speaker workshop I can find the links to a very comprehensive manual.

I prefer winairr for measuring midrange and UHF because it is easyer to isolate room modes.

Do you know if those programs have versions that work on Windows XP Pro 64-bit?

The reason I ask is because that's the problem I ran into with TrueRTA on my main PC. It won't install on a 64-bit platform. The only thing I could possibly do is install these programs on my 32-bit laptop, but the built-in soundcard tends to add a bit of noise into the signal. However, that was right after I bought TrueRTA and I may have not had something set up correctly. I'll have to try it again. If I can get it to run with minimum noise interference, then I should be fine with those other programs as well.

[yggdrasil]

I have no experience with Windows XP 64 bit.

I just checked TrueRTA's homepage. If you have the 1/24 octave version, it should be sufficient.

Laptops tend to create noise on the internal soundcards.

I have a Soundblaser live 24 USB soundcard for my laptop. At $50 it is a very reasonable solution. I compared the sine waves on my oscillosope, and the built-in soundcard was shocking.

[ChopsMX5]

I just checked TrueRTA's homepage. If you have the 1/24 octave version, it should be sufficient.

I have a Soundblaser live 24 USB soundcard for my laptop. At $50 it is a very reasonable solution. I compared the sine waves on my oscillosope, and the built-in soundcard was shocking.

Yes, I have the 1/24 octave version. You say it should be sufficient, but I wouldn't be using TrueRTA for what we're talking about, right? What would I be measuring from a DIY horn? Of course the frequency range of it, since it needs to load the driver to 500Hz. But as far as midrange dispersion, it wouldn't help me any. That's where I'd need one of those other programs mentioned above.

Also, keep in mind that I am running my 902 drivers all the way up to 20kHz... a.k.a. - no tweeters. So these horns I build need to cover the entire range from the xover point (somewhere between 600-760Hz) on up. The reason I am limiting the xover point to 760Hz is because that's where Usher crosses over their D2 loudspeakers at. I'm assuming that's to get the most out of the 15HM drivers without getting them near their upper limits.

[yggdrasil]

Measuring should be done at ~1 meter. Right in front, at 30 degrees off center and 60 degrees off center.

The resulting graphs will show your driver and horn combo's frequency response. The goal is flat, with no dips or peaks.

Regarding frequency range: A Smith horn for 1" driver will not be practical down to 500-750 Hz due to size. Remember that the 2397 was usable 800Hz, and halving the horn height will approximately double the width. At the other end both the 2397, and the 1200Hz Smith horn rolls off at 12-14K.

You could probably make a network that compensates for the HF rolloff.

The need to play below 1KHz does not favor Smith horns.

[ChopsMX5]

Regarding frequency range: A Smith horn for 1" driver will not be practical down to 500-750 Hz due to size. Remember that the 2397 was usable 800Hz, and halving the horn height will approximately double the width. At the other end both the 2397, and the 1200Hz Smith horn rolls off at 12-14K.

You could probably make a network that compensates for the HF rolloff.

The need to play below 1KHz does not favor Smith horns.

Even if the 1" Smith horn is 25" wide and 25" or more deep, it still won't support 500-700Hz loading? If that's the case, I might as well forget about the Smith horn altogether and just stick with my Altec 511B's.

And you do know that I am referring to the hybrid Smith horn that I drew up on the first page of this thread, correct? I'm not talking about a typical, rounded Smith horn.

[yggdrasil]

Here's a suggestion for you to try out.

Page 1 contains 750Hz horn data/definition.

Page 2 contains the normal scaled Smith horn.

Page 3 contains a suggestion for "cutting" down on the horn.

You can easily try it with diamond shaped vanes. Use L and V4 for length and center width of the vanes.