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Some questions about the Frugel Horn design


2016-05-02 10:12 pm

I'll build a FHXL for a pair of Alpair 10.3.
I already have the plans (thanks, Dave!).

But I'd like to know how (and why) they work!;)
I think it's better to build something when you know -a little bit- why you are doing it that way.:rolleyes:

What's the function of the "closed horn"/pyramid part (marked in red) ?
Why do it has to be filled in with isolation material (whool, pillows...) ?

What's the function of the curve of the lateral pannels (marked in green) ?

Where is it better to place the speaker connector?

Thank you!
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One of the design goals of the FH family was to keep them as compact as possible while benefiting as much as possible from the gain below driver's mass corner provided by the rear horn load (Scott / Dave, did I word that more or less right?) Hence, as with many other BLH / labyrinth designs, the folding of the closed section that is acoustically above the driver.

The curved mouth was derived from some very elaborate fluid dynamics modelling performed by Ron Clarke with industry proprietary software, and was used on several other of his own designs, and which has been incorporated in many of Scott Lindgren's Woden and Spawn series of enclosures. After comparing our own builds of other small BLH designs such as Buschhorn, borrowed Hornshoppe horns, and at least one of the Fostex "recommended" designs - several of which have rather compromised final flares / mouth sizes for the intended bass extension - we've been convinced that the curve is not just aesthetic.

As I replied in a previous post on the same question, we put the inputs near the top of the rear panel to keep the length of internal wiring as short as possible, and use terminal cup that are externally mounted, which make for a very easy dressing of wires tucked between seams of felt lining as shown on the drawings.


2016-05-02 10:12 pm
Thank you very much for your answers,

It's just that in my mind, a horn starts with the speaker in one end, and finishes with the mouth in the other end. Here the speaker is in the middle of the horn.
That's why I don't understand how the "pointy part" (red) can work, if its not by resonance :)

Thanks again,
I'm learning lots of things in this forum!
Think of the sub-class of loudspeakers designed to operate on quarter wave principles (as opposed to accidentally doing so) as a continuum from the several varieties of "TL" - transmission lines, through TQWP (a la Voigt) to some of the more recent tapped horns - including the FH designs. All of them "work" by using resonant behavior - or at least attempting to do so.

If it's not already been recommended, spend a few lost days consuming and attempting to digest Quarter Wavelength Loudspeaker Design

While their individual approaches / targeted design goals may vary, many of the advanced amateur / small commercial speaker builders frequenting this forum use Martin's worksheets as a fundamental tool in their design kit.


2014-05-12 7:47 am
Hence, as with many other BLH / labyrinth designs, the folding of the closed section that is acoustically above the driver.

Could you please give some more info regarding difference between other BLH designs where we have a series of straight barriers on the back of the speaker like a maze / labyrinth , expanding from the back of the speaker driver and opening at the back or front of the speaker box?

From the above reply from Dave, i could relate the closed pyramid (marked in red in above picture) as a folded half of BIB design, which is above the speaker driver.. is my understanding correct?
The taper of the FHs is more complex than a BIB, and they have the choke before the big mouth, the curve of which makes it look more like a square than it is. It is similar to the BIB in that they are taped horns with the driver placed partway along the horn.

The other kid of horn has an air-cavity which loads into a restricted mouth and expands towards the mouth. The horn can be smooth, which allows greater frequency response, or stepped (Olson/Nagaoka) where every fold acts as a low pass filter reducing the HF coming out the mouth.