A twist on the Smith Horn...

[ChopsMX5]

Just a quick question...

When I go to build my Usher D2 or JBL K2 "clones", I may want to try building a pair of Smith Horns for them just for fun. I'm thinking that because that design is much thinner than my Altec 511B's, the Smith's will allow the dual 15's to be closer together.

What I'm thinking about doing is have the Smith horn extend all the way from the front to the back of the speakers. This would have the Altec 902-8B drivers just past the rear of the bass enclosures, allowing the 15's that much closer together. Also, this horn would be over-built to support the weight of the upper bass enclosure as it would NOT have an enclosure of its own.

Now on top of that (this is where the question comes in), I thought that I could have the front of the horn perfectly flat and even with the front of the bass enclosures, instead of having them rounded in the front like traditional Smith horns and sticking out past the enclosures.

Would this be alright to do or is there a reason why the front of the Smith's are rounded?

Many thanks in advance! ;)

[subwoof]

The distance from the throat to the horn edge(s) should be constant for the "radial" derivative horns as compared to the constant-directivity ( CD ) types.

Look at JBL's tech sheet library to compare them:

http://www.jblproservice.com/navigation/pdf_nav_tech.html

Somewhere is a "tech-note" that compares the horn types.

Think of the horn as a slice of a pie - 90 degrees is 1/4 of a circle and is the accepted norm for standard listening environments.

You could always cut away the sides of the cabinet where the horn sides exit to maintain the curve in front but be sure to use an electronic crossover to correct for time delays.

sub

[Zilch]

Smiths want lips:

http://www.jblpro.com/pub/obsolete/2397.pdf

Add 6" to the horn height to achieve the "standard" 60° vertical beamwidth.

I have no clue what it is without those.... :dont-know

[ChopsMX5]

I was referring to something like this. It would be as wide and deep as the bass enclosures (somewhere around 24"W x 16-20"D).

http://charlest.zenfolio.com/img/v2/p778967903-4.jpg

[Maron Horonzakz]

Yes i have made Smith horns simmiler to that drawing....Bob Smith in his Audio mag article shows a illustration but the septa vanes are closer to the lip front.. Both curved and straight illustrations are shown.

[Steve Schell]

ChopsMX5, horn design is endlessly fascinating and shrouded in mystery, and it takes a great deal of study and experimentation to determine what is happening with a given design or change to a design. With every little change, usually several characteristics are changed at once- directivity, driver loading, diffractions and reflections among them.

Bob Smith designed his DSH in the mono era, principal goals being to maintain exponential loading for the driver while providing a wide horizontal spread of sound. This allowed for good response from the driver while avoiding the effect that all the sound was coming from a single point in space.

As you have drawn your design, it will be pretty much a classic exponential DSH to the point where the torpedos end, then become a conical (straight sided) flare to the mouth. This will certainly have different characteristics than the usual DSH with radiused mouth lips, and it might be really good! You will have to build it to find out.

One theoretical limitation of the classic DSH design is the abrupt termination at the mouth where the lips end. This should result in severe reflections and diffraction at the mouth, causing both ripples in the driver loading down near cutoff and secondary radiation at the mouth, resulting in multiple arrival times for the listener. Using a flat rather than radiused mouth as you have drawn may be a very good thing, as the distance between the driver and any point along the mouth is constantly changing, reducing the severity of any effects that occur as they will be distributed over a range of frequencies. Since DSH horns are so easy to build, perhaps you could knock together versions with both flat and radiused mouths and evaluate the differences.

The Emilar bowtie horns were basically exponential radial horns that were cut off flat at the mouth. Many people like the sound of these horns.

DSH designs have been discussed a lot on these forums, and there are many pictures of really nicely done horns. Search the forum threads for "distributed source horn" and "Smith horn" to find many of the threads. Dr. Smith's original article on the DSH is provided on this thread:

http://audioheritage.org/vbulletin/showthread.php?t=9148&highlight=smith+horn

[SMKSoundPro]

I am also considering making this 2397 horn for my own boxes and wondered where to find the drawings, or plans. Can anyone share the plans and details with me, please?

Scott.

[ChopsMX5]

Ah... So it seems as though I may be onto something here with this design. I may do this before even starting my "clone" project. If these work and sound really good, then I wouldn't have to waste time and money building enclosures for the Atec 511B's I have.

The main reason I'm looking to do a design like this is because these style horns are so low profile compared to the Atecs and would allow the 15" drivers to be that much closer together in the MTM fashion. Plus I could build my matching center channel about 6" taller and still fit under the projection screen. Hmm... Food for thought. :D

There's still a couple of things I need to know before starting on these horns.

1) Since I will be using Altec 902-8B (mains) and 902-8T (center), these are 1" drivers. I assume that the full height opening of the horn itself will also be 1", correct?
2) What determinds the low-end extension of the horn, the width, or depth, or both? Like I said, they'll probably be 24" wide at the mouth and between 16-20" deep, maybe even 24" deep, from the mouth to the driver mount.

As you can tell, I've never really ever done any research on horn design before. :o:

[grumpy]

here's a start for your research:

http://audioheritage.org/vbulletin/showthread.php?t=9601

http://audioheritage.org/vbulletin/showthread.php?t=5454

[ChopsMX5]

Just curious...

Are the vanes absolutely needed or are they just more or less used to disperse the HF more evenly?

[yggdrasil]

The vanes are a part of the original construction.

There are no vanes in the small Westlakes.

Anyway the final measurements will give you all answers..

[ChopsMX5]

??

Hate to say it, but that didn't tell me anything.

[Hoerninger]

Hi Charles,

in other words:

The Smith horn has a simple construction and by this way this type of horn gives a vertical sound distribution by defraction. The latter is the only thing what can really be predicted.

Considering horn construction most of all attemps make some assumptions which do not hold in daily life completely. So there are so many types of horns that "work".
The traditional attemp is to give the cross section an exponential growth which is tried to mainain by the vanes. But the classical approach uses round horns and no flat horns as Smith did. So omitting the vanes might be a way (Westlake variant).

You said you are new to horn building. There are mainly two ways to learn. Copy a proven horn or by try and error. Ok, some theorie should be the first step but that is not the whole story. A finished horn can only be checked by measuring and listening. The theorie before helps to predict some but not all aspects. (Computing with finite elements is fairly new.)
__________
Peter

[yggdrasil]

Short answer: No the vanes are not absolutely necessary.

Q: Do you have any tools for measuring the results?

[pos]

Just curious...

Are the vanes absolutely needed or are they just more or less used to disperse the HF more evenly?
I think that Earl K mentioned somewhere that the vanes were used to better spread mid frequencies. In fact the vanes might even be bad for HF: look at the polar responses in the original Dr. Smith article: it seems you can see this vanes on the graph!
By the way the HF mini smith horn used in westlake studio monitors do not have vanes.

[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". http://www.audioxpress.com/bksprods/media/b/bkpa1b.jpg (http://www.audioxpress.com/bksprods/products/bkpa1.htm) 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 ).

<> :)

[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...

/\
\/

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/products/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/products/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.