Simplified FLH's?

[leadbelly]

Forgive me if this is a stupid question to the front loaded horn crowd, of which I certainly cannot myself amongst
Let me just ramble off some thoughts and see how far off I am

I think I could DIY some FLH's I would be happy to use if I simplified and made a rectangular horn with 2 flat sides and only 2 sides curved. This could either be a rectangle or a square. If it helps define the question let's say a tractrix horn somewhere in the 100-200Hz region.

Now I don't see many examples of this, although there are some out there. I take it there are some negatives. What are these negatives? Cosmetics? Awkward dimensions? The flat sides affect directionality adversely? FLH design is an inexact science and the published models don't cover those cases?

[GM]

Greets!

Any shape other than round distorts ('colors') the sound to some extent.

?? Two sides flat/two curved is probably the most common due to the need to normally control the horizontal plane to a lower frequency, dating back to Bell Labs/W.E.'s widely copied early designs and all their variants over the decades: http://www.audioanthology.com/images...13%20copia.jpg http://www.audioanthology.com/images...t3%20copia.jpg

Both flares have directivity BWs, with the curved flare changing with frequency.

AFAIK, all 'retail' horn programs assume a straight round horn.

Where you can run into 'problems' is at the square or rectangular throat since the BW approaching its (Fh) cutoff will distort enough to cause standing waves and reflections (aka HOMs). These can be further aggravated by reflections back to the throat from the mouth if it isn't properly terminated, but these are a problem with any non-optimized horn flare if its BW isn't limited enough by the XO.

Bottom line, for wide BW apps, the throat needs to transition from round to square over a long enough distance to satisfy the HF BW requirements and the mouth needs to be terminated such that it doesn't cause any acoustic impedance mismatch when it releases the pulse wave (same concept as flaring a vent).

Typically though in the LF, midbass, lower mids BW, these are ignored in the interest of keeping it as small as practical and limiting its BW: http://www.volvotreter.de/pics_plans.htm

GM

[leadbelly]

Thanks GM, for your thorough-as-usual reply

[Colin]

John Greenbank produced a Wireless World design in the 70s which did just this for a horn which covered 400Hz up. It tried to compromise the Klipsch design, so the edges were cut away - what should have been a 19" wide horn was reduced to 12" across and the mouth height was around 6". The sides were curved, the top and bottom straight (but converged towards the driver). Driver was a 4" Eagle fullrange unit. It was mated to a similarly compromised bass horn based on the Klipsch corner horn.

It later went on to be used commercially in a Lecson model and the same idea cropped up again in the UK Impulse horns in the 1980s, even down to the cutaway sides. The Impulse speakers got some good reviews at the time.

Enough history, I built a pair. Bass (in the room I had at the time) was awful. Mid and up was surprisingly good. I've only heard imaging as good since moving to fullrange. This was 20-odd years ago and I wonder how they would compare to modern designs and drivers.

Around the same time, in the same magazine, Dinsdale was recommending circular horns as being far better, so I often wondered why the design appeared in the first place. (And what possessed me to spend 18 months of my life building the thing instead of buying some Lowthers.)

[Colin]

More on Impulse here

[jamikl]

I too played around with similar horns to the wireless world one mentioned on this thread back in the seventies. I loved the clarity and ease. Have missed that. Am now thinking of going that way again. The link with the impulse information whet my appetite. Have any of these been cloned. What would be a suitable 100mm driver for the mid. How about a wave guide high as well. Obviously I am a bit out of touch but learning again through this site. Big thanks to you all!!

[Colin]

If you get really keen, I can dig out the original article. However there are better designs out there now. Have a look at some of Ron's designs on the fullrange website. There will also be a lot of information elsewhere on this forum.

[jamikl]

Thanks Colin. I have those plans and the Dinsdale ones back in New Zealand. Also the Klipsch papers. Am really just thinking of something other than all the fostex designs which is why the Impulse horns caught my eye.

[Colin]

The Impulse designs are a funny mix. The original models had a so-called bass horn which looked suspiciously like some form of quarter-wave loading. So there are probably a few MLTL designs on the forum which could substitute.

It was the low (400Hz) crossover point to a single mid-HF driver which I liked about the original Wireless World design. This led me on to explore Jordan drivers as their original 50mm module did the same thing. Nowadays there's a range of options, horn loaded or otherwise.

The Impulse boxes do look neat, however.