Horns theoretical question

[johninCR]

I'm trying to gain an understanding what makes Mr. Takenaka's spiral horns tick. Detailed descriptions and measurements are located at http://www3.ocn.ne.jp/~hanbei/eng-intro.html .

All the designs boil down to rear loaded horns with larger than typical compression chambers and a relatively short horn that has equal area entrance and exit. The entrance tapers rapidly down to a throat that gradually expands to the mouth.

I've tried to model these horns, if that's what they are, in HornRESP, but it won't allow the reverse horn flare before the horn itself. Modeling only the horn from the throat to the mouth shows the low end portion of the response he get, there are huge response spikes occuring above 100hz or so that are the result of a short small horn.

My question is, what is the effect of a reverse horn or flared entrance to a horn mouth? Does it in effect work as a high frequency acoustic filter which eliminates the response spikes? Is there an easy way to model this effect?

[John Sheerin]

Hi,
Doesn't look like a horn to me - looks like a vented box or some variation, maybe similar to what Martin King has done. What would be interesting to see would be the impedance curve. His measurments look like maybe his vents have tons of resonances, thus the broadband output?

[johninCR]

Thanks for the info John. Did you ever get your unity horn clone perfected?

Any ideas on what the effect would be on a horn's response with a significantly large flared entrance to the mouth?

[BillFitzmaurice]

Those definetely are not horns since there is no expansion. They are similar to pipe/reflex hybrids, so-called MLTLs, but likely far less susceptible to resonant modes above the fp due to the lack of any parallel walls within the pipe.

[johninCR]

Bill,

At the the interior end of the pipe, the cross sectional area starts as the entire area of the pipe end then rapidly constricts to the throat that is formed where the between the entrance end of the spiral and the first full turn. Then the cross sectional area expands gradually as the distance between the spirals increases until the other end of the pipe where the cross sectional area becomes the entire pipe again.

For example, let's use the linear model L150, since I have a pair of FE206E's on the way. Both ends of the spiral open to a cross sectional area of 23". The interior end constricts down to a throat area of 8.1"sq in a distance of 4.6". Then over a straight line distance of 13.1" containing 2 full spirals it expands back to 23"sq. The horn length over this straight distance is much longer due to the continuous folding resulting from the spiral. I don't know how to compute that effective length, but it contains the same air volume as a conical horn 23" in length.

Modeling such a short "horn" (throat to mouth only) shows just severe response peaks, obviously not what Mr. Takenaka is getting, so I'm back to my original question. What is the effect of a flared opening to the throat of a horn? Aren't there some bullet plug entrances to horn throats?

[BillFitzmaurice]

From the diagram the expansion didn't look obvious, it appeared to be a constant section. The flared opening to the horn throat isn't going to do much to the response.

[johninCR]

Thanks Bill,

I had hoped the entrance was the key. I'll defer to your experienced opinion. I guess it's the spiral motion and different lengths of travel that perform the magic. I was hoping a simple wooden duct of the same dimensions might work, but I guess I'll have to construct the spirals after all.

[BillFitzmaurice]

Going deeper into the site, and adjusting the mind's eye to see what he did, those are conic horns with a final exponential flare section, and could be dupicated without using the spiral section, the main key having no parallel walls, ie, a rounded cross-section, so still not an easy build. The large driver chamber isn't unlike a typical rear loaded horn config, it just looks different because of the overall package.

[johninCR]

With a lathe you could quickly build a tube insert that would give a remaining donut shaped area that would exactly follow his contraction and expansion. It wouldn't be as efficient space wise as his spiral, but it would still be more compact than typical rear horn enclosures, plus really simple (if you have a lathe). Make the tube removeable and you could quickly try different horn lengths and flares.

Nice idea don't you think? I should patent that one.

[BillFitzmaurice]

In all likelihood a patent search will find prior art from 1927.