Frugel-Horn Mk3

[chrisb]

Originally Posted by Scottmoose

Group delay in a back horn is a function of axial length and its upper corner frequency. Nobody's complained about group delay yet, so make of that what you will. FH3 when used as intended should have a lower Fhm than the A126 though. Different designs, different priorities.

FWIW, some folks are / claim to be far more sensitive to group delay in BLH than others, and would recommend (multiple) front loaded horns instead - which are not without their own complications of design / implementation in smaller domestic situations.

[MJK]

Originally Posted by chrisb

by a perverse extension of that logic, an open baffle nested into a corner would be horn loaded as well?

What is your definition of horn loading?

At low frequencies, I don't think there are very many enclosures that can be classified as horn loaded. By my definition, the size of the mouth determines if an enclosure is horn loaded or a resonant (TL or TQWT) enclosure. By my definition, an expanding geometry does not automatically become the definition of a horn.

Martin

[Bob Brines]

Originally Posted by chrisb

....by a perverse extension of that logic, an open baffle nested into a corner would be horn loaded as well?

I will admit that I am way out of my element, but I would think that anything stuck in a corner will get some degree of horn loading. One of the things I want to try is a corner loaded woofer in a box that simply constitutes the back chamber. In other words a front loaded horn.

Bob

[ra7]

Martin has a valid point. The mouth of the FH is more like a slot. It is not really expanding like a horn should.

In a strict voight pipe, there is some horn loading because the expanding profile opens into a mouth that is consistent with expansion. There is also resonant action due to the nature of the tapered tube and the location of the driver.

[Scottmoose]

I think Martin was speaking generally. Either way, this subject has already been discussed / commented on at the start of the thread, but to briefly repeat, FH3 is expanding exactly as it 'should.' Inserting a choke into the flarepath of a back-horn certainly has precident: I refer you to Harry Olson. Which is a fairly good precident as far as I'm concerned.

Yes, a Voigt (no 'h': P. G. A. H. Voigt you know) pipe could be described as a chamberless tapped conical horn if you do not choose to define a horn by impedance matching to Fc, but by, for e.g., the presence of 1/2 wave behaviour. Both definitions seem perfectly sensible to me, so YMMV.

FWIW, FH3 is nominally impedance matched when corner loaded (as it was strictly speaking designed to be) to ~85Hz, about 1/4 octave above Fc.

[Scottmoose]

Originally Posted by Bob Brines

I will admit that I am way out of my element, but I would think that anything stuck in a corner will get some degree of horn loading. One of the things I want to try is a corner loaded woofer in a box that simply constitutes the back chamber. In other words a front loaded horn.

Bob

Well, if the corners & room dimensions are such as to provide the desired gain BW, you'll be in business. At the very least, baffle-step will become a non-issue.

[MJK]

I would not classify corner loading as horn loading. As you add boundaries you restrict the area that the source is radiating into (4 pi - 2 pi - 1 pi - 0.5 pi) and thus increase the resulting SPL output with each step down in pi space. Horn loading increases the efficiency of the output from a source in free space. Corner loading can be used to reduce the mouth size requirement to achieve a horn and raise the horn's SPL output even more.

Try the following exercise. Model the FH3 in your favorite software tool (MathCad is recommended), then model the FH3 without the end flare stopping at the restriction and compare the SPL responses. I have spent quite a bit of time studying the FH3 because it is such an interesting design.

The FH3 is a really elegant and simple design that is reported by many individuals to perform extremely well with several different drivers. Congrat's to the design team. But in looking at the simulations it appears to me to be a resonant mass loaded TQWT type of speaker and not what I (my definition of a horn which may not be consistent with somebody else's definition) would classify as a horn. There are a series of resonant peaks and valleys that help produce the bass output. When combined with a floor and rear wall boundary condition the bass produced matches the mid-bass and higher response, no BSC needed. Well done.

Martin

[Scottmoose]

Thanks, Martin, that's quite a compliment. Glad you like it.

Scott

[ra7]

Very interesting. I might give this a try. I have several drivers lying around which might fit this design.

Was the supra baffle ever designed for the FH3? That would allow quick mounting and dismounting of different drivers.

Thanks.

[Scottmoose]

No, primarily because it doesn't need one -not with the MA drivers at any rate. If the Fostex is corner loaded (should be noted strictly speaking FH3 is a corner-horn design) it should pass muster with a high output impedance amplifier & the assumption you're not expecting that combination to excel at playing Metallica.

Which isn't to say you can't try one if you wish. I believe Dave & Chris's prototype have removable / detachable baffles to allow precisely that, although they are not suprabaffles in the sense that they are not physically larger than the front baffle.

Just to stress again, FH3 is certainly not supposed to be the last word in back-horns. Far from it. It's a deliberately simple box offering that is easy to build, reasonably forgiving of different drive units, & hopefully a good footing for people new to the hobby and / or horn variations.

Scott