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

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]

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

 

[GM]

'GIGO' applies here, ergo you got the wrong answer.

WL circumference = ~13560"/F
WL diameter = ~13560"/pi/F
WL area = ~(diameter^2*pi)/4

Am = 1/(SF*4pi)*(c/F0)^2
Am = 1/(8*4pi)*(13560/70)^2
Am = ~0.009947184*37525.22449
Am = ~373.2703105"^2

FYI: 8*4pi = 32pi = ~100.5309649, not 37.68

Well, that pretty much used up all my higher math skills......

GM

 

[rjbond3rd]

Hi GM, thank you, I appreciate it. (Your correctly calculated mouth is still much bigger than the FH's could possibly be, so I'm still missing something interesting.) Thank you again!

(OT but GM, a pair of minty Alec VOTT's were just sitting in a building near my office, and today forum member Monte Verdi snapped them up, and will let folks hear them tomorrow. Minty!)

 

[GM]

You're welcome!

Yes, horn design is about as simple as a F1 racer's fully articulated front suspension, i.e. lots of design variables adjusted to the needs of the app.

GM

 

[rcdaniel]

When trying to get a feel for possible project outcomes (and the stuff that gets us there), I like to strip stuff back to fundamental purpose (needs, wants...), objectives, principles (moral & ethical), and constraints* blah blah blah…

So, when I read this:

1/ needs to remain petit and corner loaded as an ode to the original inspiration

... something does not quite sit comfortably with me*. I agree with the corner loading and maintaining small footprint, as these are practical considerations. However, I am not convinced of keeping the design arbitrarily petit (as an ode) at the cost of having a possibly more suitable driver height.

I guess it depends on the sentimental value versus the value of (possibly) more suitable driver height. That seems obvious to me as a outside observer, but I readily admit I don't really understand the relative values (or other compromises) of both options. The sentimental value may outweigh some (small?) benefit of raising driver height. Just putting it out there for consideration.

Cheers

* This my neediness and takes nothing away from the amazing contributions of folks here!

 

[planet10]

.. something does not quite sit comfortably with me*. I agree with the corner loading and maintaining small footprint, as these are practical considerations. However, I am not convinced of keeping the design arbitrarily petit (as an ode) at the cost of having a possibly more suitable driver height.

We are fitting within a niche here... that defined by the inspiration for the Frugel-Horn... the Hornshoppe Horn.

If you want a larger & taller horn Ron Clarke has already designed a proven reference... the Austin A126.

dave

 

[planet10]

(Your correctly calculated mouth is still much bigger than the FH's could possibly be, so I'm still missing something interesting.)

I'm not going to double check the math right now (i would have done the original calc at least twice), with the deflector and the corner loading, i calculated a theoretical cutoff of 75 Hz.

Remember that with the deflector in place , the mouth is defined by the back edge of the deflecor and the sides of the horn.

In FH 2 i imagined making this more explicit by doing a full height deflector and having the option of extending the top of the horn such that it is also the top of the deflector with the intervening space covered.

Without the defletor the horn cutout of FH 1 is about an octave higher, and the rest is TL action.

dave

 

[planet10]

having a possibly more suitable driver height.

PS: if you want to have the driver firing at your head, it doesn;t take much of a footer at the front to accomplish that.

dave

 

[rcdaniel]

We are fitting within a niche here... that defined by the inspiration for the Frugel-Horn... the Hornshoppe Horn.

So, is this more of an academic engineering challenge with arbitrarily self-imposed constraints of the original design 'brief'? That's fine for what it is - a learning experience, challenge, desire to better an existing design - as long as potential builders recognise it for what it is, along with its limitations etc. Seems like an investment of considerable resources for something that is arbitrarily compromised.

As for building the A126, I am sure it is a great design, but unless the design has been simplified and the drawings improved, I am thinking it a somewhat difficult build; it has been a while since I have looked tho.

Again, none of this is intended to detract form the contributions you guys have made to this forum and the broader DIY community.

Cheers

 

[chrisb]

So, is this more of an academic engineering challenge with arbitrarily self-imposed constraints of the original design 'brief'? That's fine for what it is - a learning experience, challenge, desire to better an existing design - as long as potential builders recognise it for what it is, along with its limitations etc. Seems like the investment of considerable resources for something that is arbitrarily compromised.

As for building the A126, I am sure it is a great design, but unless the design has been simplified and the drawings improved, I am thinking it a somewhat difficult build; I could be wrong tho.

Again, none of this is intended to detract form the contributions you guys have made to this forum and the broader DIY community.

Cheers

As some might be aware,I had participated in the development process of the original FH project, including the design and production of the first run of flat-pak kits and supra-baffles. I have built at least 3 pairs of the FHs, as well as one pair of the A126. Leaving discussion of your first paragraph to others, I'd like to address the second.

While there were some minor discrepancies in dimensions of the version of the drawings for the A126 that I started with, and we did report on revisions made to the chamber based on our initial listening sessions, the actual build was no more difficult than the Frugelhorn, or for that matter the 2 pairs of Buschhorn MKI that we built as a benchmark. I have built several designs before and since that were more difficult / time consuming than any of these BLHs.

Full disclosure - I generally redraw all plans to produce DXF files compatible with cut-planning and CNC machine programming - luxuries to which I realize not all DIYers have access. This affords me the opportunity to fine tune discrepancies that occasionally crop up in drawings.

 

[rjbond3rd]

Originally posted by rcdaniel So, is this more of an academic engineering challenge with arbitrarily self-imposed constraints of the original design 'brief'? That's fine for what it is - a learning experience...

Hi rcdaniel, I think it would be amazing to understand how to design a BLH, because then you could go and design another. And another.

It's true that you can aim the drivers at practically any height. (I'm using a chunk of 3/4" wood but a couple spikes would be better obviously.)