Cochlear Snail Horn

[schn0354]

Most back loaded horns expand in only on dimension, have many folds, and are a hybrid horn/TL/bass reflex design. I am experimenting with a pair of Fostex FE126E drivers in different enclosures and plan on building a relatively compact and efficient design for a small room listening environment.

The design would use the principle of the cochlea in the human ear, but operate in reverse with the driver replacing the "sensor" and be back loaded. It would essentially mechanically filter high frequencies and amplify low frequencies.

Why the Inner Ear is Snail-Shaped
Short article with scientific link
http://focus.aps.org/story/v17/st8

Coiled like a tuba instrument, it would expand exponentially. It could be made with paper mache with 20 gauge steel wire forming the skeleton. Wood glue would be used for strength. Damping should be similar to MDF, but it would need to be built up in layers. Has anyone tried this before? Also, how is the compression chamber volume and throat area determined for maximum efficiency?

Using the same principles, theoretically it could also be made into a 1/2 wave mass loaded transmission line with a sealed end like the B & W Nautilus. Not sure of the effectiveness of this though.

[Scottmoose]

Most back loaded horns expand in only on dimension, have many folds, and are a hybrid horn/TL/bass reflex design.

With some inevitable exceptions the majority of back loaded horns can be regarded as BR cabinet variations with gigantic vents. Most typically use a hybrid of QW & horn actions because a full-sized horn is gigantic. For e.g. at 40Hz, you'd need a mouth ~85in x 85in. Even corner loading, which nominally permits an eightfold reduction in mouth area, still demands a very substantial terminus area if full horn-loading is to be maintained. And that's without bringing other issues into play.

Folds are a double edged sword. They're the enemy of absolute efficiency; however, they can be useful too. A perfectly smooth expansion is not automatically going to be an advantage.

Most designs expand only in one direction a) because it's easier for most DIYers and b) given that they're bass-horns, the added potential distortion / standing waves aren't as much of an issue down in the LF where our hearing sucks, as it would be in the midband.

I am experimenting with a pair of Fostex FE126E drivers in different enclosures and plan on building a relatively compact and efficient design for a small room listening environment.

Good luck & let us know how you get on. Although the words 'horn' and 'compact' sit rather uneasily together. Assuming we're talking bass-horns here anyway.

The design would use the principle of the cochlea in the human ear, but operate in reverse with the driver replacing the "sensor" and be back loaded. It would essentially mechanically filter high frequencies and amplify low frequencies.

Could be rather attractive.

Coiled like a tuba instrument, it would expand exponentially. It could be made with paper mache with 20 gauge steel wire forming the skeleton. Wood glue would be used for strength. Damping should be similar to MDF, but it would need to be built up in layers. Has anyone tried this before?

Seems reasonable, although you might not find the exponential contour to be your best option. I believe paper mache has been used quite a bit by different people, so yes, it's been done.

Also, how is the compression chamber volume and throat area determined for maximum efficiency?

Ah. Something tells me you might want to read up about horn design before you start as these are rather basic factors. If you want maximum efficiency for example, an exponential horn is not going to be the best option. GM posed a plethora of sources in a thread here a couple of weeks back. Have a quick look through the last 3 - 5 pages of threads & you should spot it.

Using the same principles, theoretically it could also be made into a 1/2 wave mass loaded transmission line with a sealed end like the B & W Nautilus. Not sure of the effectiveness of this though.

Well, it would be a 1/2 wave sealed line anyway. How well that would work would depend on the eventual design. Fine for midrange duties, but the 126 really does need a horn if you want to keep excursion under control.

[schn0354]

Thanks Scott. I read some of the recent posts and read MJK's quarterwave website. I played with Hornresp software and even with instructions, could not understand it. Yes, a true horn action would be too large for even a very small room. I looked at plans on the Frugalhorn website, and it is difficult to know the advantages of each design other than looks and size. It seems few have built enough different designs for direct comparison.

Currently, the FE126E drivers are in 6.7L bass reflex enclosures tuned to 92Hz (-3dB at 90Hz). I am using this as a starting point for comparison. The Fostex recommended simple bass reflex design tuned for 61Hz seems very low, especially considering the average parameters measured by Planet10 (Fs = 92Hz). Overall, they sound very good from about 200 Hz to 15KHz. Beyond subjective listening, I do not have the equipment to do a frequency response measurement.

Would the best compromise be a 1/4 wave TL with some sort of horn action, i.e. flared mouth?

[Scottmoose]

FWIW, the best compromises for the FE126E (IMO) are either

a) a long path, high gain horn -but not taken too low. Or

b) Get it in either a baffle or sealed box, and support everything below about 500Hz with a suitable 15in HE woofer.

Yeah, the number of boxes on the FH site are a bit confusing -we'll have to have a bit of a tidy up at some point I reckon. Pick of the bunch on there for the 126, in no particular order are probably the Frugel-horn itself, Ron's A126, or the Saburo cabinets.

[loninappleton]

As a reminder, there was that one made of PVC-- not the seraphim at
the TL site --but another stand mount PVC horn made in sections....
there were even plans on how to make it, but I tried to find the
link and couldn't come up with it. Line length winds up to be about 81 inches or so. Very sculptural. I can't remember if the FE126 was used.

[stevodude]

Yea, I remember that one, http://tpluspod.com/rtl/fostex%20PVChorn.html

pvc horn. using fostex 108ez

[loninappleton]

Originally posted by stevodude
Yea, I remember that one, http://tpluspod.com/rtl/fostex%20PVChorn.html

pvc horn. using fostex 108ez

Thanks for finding it.

[schn0354]

Interesting application of pvc pipe for straight transmission line.

I suppose you could do all the length calculations and approximate, but could you also tune it by ear? I.e., mount the driver on a baffle at one end of a mass loaded Sonotube. Then make a sliding baffle with a 2" port at the other end. Basically three mdf discs, 1 slightly smaller than pipe with firm weatherstrip around the circumference for a press fit sandwiched between 2 discs same size as the pipe. Apply a signal to the driver one octave below Fs (or lowest possible) using a frequency generator and tune for maximum resonance by sliding the rear baffle.

Keep in mind I have yet to build a TL speaker, so this is theoretical. Seems very simple to do though. A friend tuned his piano by starting with a tuning fork as a reference and adjusting the strings successively along the music scale by listening to interference created when sounds were not at 1/2 octave intervals. However, he is an engineer and violinist with a good ear.

[planet10]

Originally posted by Scottmoose
Pick of the bunch on there for the 126, in no particular order are probably the Frugel-horn itself, Ron's A126, or the Saburo cabinets.

And a dark horse... Harvey. Just got an email from someone who was really thrilled with his Harvey with FE126eN ... and i don't take his comments lightly, as his main system has Feastrex...

Aangus says he is going to have his Harveys for us to hear at the upcomong diyFEST.

dave

[Scottmoose]

Really?!? Now that is surprising. In a positive way of course.