Frugel-Horn 2v0 - A diyAudio Reference Development Project

[planet10]

Note: the diyReference horn has co-opted development of the Frugel-Horn 2. Quotes represent the good stuff from the pre-amble

Originally posted by rjbond3rd I hope there's some interest in a collaborative diyAudio reference project on how to design a BLH / BVR.

Is anyone interested in puzzling out how the variables and trade-offs fit together (driver, required cutoff frequency, throat, mouth, expansion, chamber etc.)?

If we could formulate some general solutions / tradeoffs / sizing relationships, maybe newbies like me could eventually design and build one in a weekend for a variety of common drivers. If one made a mistake, one could just rip out the "inner box" and start over.

Any pointers from the gurus? Any interest from the newbies?

Originally posted by rjbond3rd
What driver(s) would you guys like for that?

Originally posted by planet10
For the FE126 there already exists Saburo, Austin A126, Frugel-Horn. The 1st 2 are very good in their class, the Frugel-Horn we know could use some massaging...perhaps this project can co-opt FH 2v0? Scott and i already have done some very preliminary work on that,

It does need to work within some constraints to full-fill its original design goals. But i think it is possible to get more/better bass, smoother response, and to simplifier the build (make it more elegant)

Frugel-Horn was always a collaborative project... mostly me with help from Scott, a bit from Martin, and Ron'd flourishes at the end, that really put the icing on the cake,

We should retain the FE126 as driver of choice.

Constraints:

1/ needs to remain petit and corner loaded as an ode to the original inspiration
2/ optional deflector & sBaffle. I think that the option of a non-curved mouth (ie Level 0) build should not even be considered.
3/ i'd like to keep the full height rear mouth (but not fixed in stone), but it does expand faster than it should to be really useful. Besides acting as a deflector, it increases the horn length & mouth size.

Things i'd like to incorporate
a/ a bit wider (tentatively 10mm). The inspiration is 130, the FH 140. One of Ron's remarks was that even that little bit made for an improvement in the shape of the mouth exit curve and the shape of the deflector. There is probably a combination of widths & other factors that could allow for the deflector to be made with 45s. It also takes the width out to where, we have found from other projects, reflections off the side walls becomes less of an issue.
b/ a minimum of pieces.

The attached sketch shows my 1st pass idea of the folding (it is far from set in stone, just a simplification i came up with -- the current is ghosted in in the background). As drawn it is 4 conical sections. It does represent a bit slower taper at the end (and could be slowed even more by legthening the bottom angled piece (allowable due to the last part of 2 above) , and allows for a longer horn with fewer pieces. It also has fewer parallel sides in the air cavity, yet allows for playing with volumes.

dave

[rjbond3rd]

Hi Dave, wow, that is a thing of beauty.

[Scottmoose]

That was something Dave & I chatted about during the original FH design process. I reckon it could make a good basis for the FH MK2.

Without going into specifics here, FWIW, I'm going to throw this out for the sake of debate:

I don't think we should pursue maximum LF extension with these. If that is desired, the slightly larger A126 (or other cabinets) will serve the purpose better. I think a more sensible goal for this design, assuming it's decided that an FH MK2 should be the DIYaudio reference horn (the FH is supposed to be a community project, so it seems logical to what passes for my mind) would be to aim for a more modest tuning frequency -say, 70Hz, or around that area, & aim for gain / efficiency, and minimising both distortion & driver excursion. The 126 doesn't have much of the latter, so keeping this down is essential to maintaining a clean sound. Going for high gain in the horn's operating BW will also, as Paul Klipsch pointed out, help reduce distortion.

Just my thoughts -any other ideas, agreeing or contrary?

[planet10]

Originally posted by Scottmoose
to aim for a more modest tuning frequency -say, 70Hz, or around that area, & aim for gain / efficiency, and minimising both distortion & driver excursion. The 126 doesn't have much of the latter, so keeping this down is essential to maintaining a clean sound. Going for high gain in the horn's operating BW will also, as Paul Klipsch pointed out, help reduce distortion.

Just my thoughts -any other ideas, agreeing or contrary?

I totally agree. It gives us a chance to get full horn loading when the corner is used. If someone needs more bass, the deflector can be turned into a stealthWoofer(tm).

dave

[Scottmoose]

Sounds like a good plan to me.

[rjbond3rd]

Random observation:

The BLH is a sexy intellectual challenge, but a tough one. So maybe a project goal could be this: if you follow along, work your brain and do the build, you will gain an insider's understanding of how it all works and why.

It reminds me of the excitement in college when you got into a study group with the smart kids.

[rcdaniel]

I totally agree.

Me too Quality over quantity.

[Scottmoose]

OK, so, I reckon we can now state that we have two initial stipulations for this DIY Audio reference horn.

1/ The chosen driver is the Fostex FE126E
2/ We shall aim for bass quality, rather than bass quantity. Ergo, we shall limit our aims & aim for a more modest tuning frequency, with the goal of keeping efficiency up, and driver displacement / excursion down, to minimise distortion on several fronts.

Are we all agreed on this, or any other thoughts?

rj -you started the discussion, so it's naturally your call: would you like to employ this debate as a MK2 Frugel-horn development thread? Based on your previous posts, you seem positive on the idea, and it's probably opportune, as good as the existing box is, I think we'd all agree it could be usefully improved upon. However, as you are the thread starter, we should defer to yourself.

If you / everyone is happy about this idea, can I suggest to Dave or any of the other moderators that the thread is made a sticky, and MK2 Frugel-horn added to the title? Even if it goes down a different track, making it a sticky would probably still be useful.

[rjbond3rd]

An auspicious beginning! I naively tried to calculate the mouth of a ~70Hz corner horn, using this classic equation:

Am = 1/(SF*4pi) * (c/F0)^2

Where Am = mouth area, SF = 8 (corner radiation, 8pi), c = speed of sound and F0 is the cutoff.

However, I get .6269m^2. Here's how:

Am = (1 / 12pi) * (340^2 / 70^2)
Am = (1 / 37.68) * (11560 / 4900)
Am = .02653 * 23.59
Am = .6258m^2

If a 70Hz wavelength is approximately 4.9 meters in diameter (not sure if that's right!), and we're using the 8-fold reduction in mouth size (due to the corner), then the mouth would be about 4.9/8 = .6125m^2. So this figure seems to check out.

However, wild-guessing the mouth is ~12cm wide by ~74cm high, I get about .0888m^2, rounding up to account for the RonC-style mouth radius, we can say about .09m^, or even more roughly, a tenth of a square meter.

Assuming any of this is accurate, any hints on the disparity? I'm not lazy, I'm stuck.

[Alex from Oz]

This being a reference horn and all, why not incorporate some cabinet EnABL into the design?

Cheers,

Alex