Long Horn Question

[progressor]

How would you comment on the following:
Corner placement back loaded horn, folded, using some full range driver (e.g. Lowther), mouth area corresponding to 56 Hz cutoff frequency (i.e. Am=3754 sq.cm), hyperbolic-exponential contour (M=0.6), and horn length equal to 1/2 wavelength for 28 Hz (i.e. 614 cm). Additionaly, the driver shall be front-loaded with a short tractrix horn of appropriate size.
Thank you very much for your comments.
Regards,
Teodor

[Nelson Pass]

Perhaps you want to look up the Yamamura horn, which
resembles that description.

[progressor]

Dear Nelson,

thanks for Yamamura 'connection'. Yes, I've heard previously of his Dionisio Horn. However, all I've seen are some pictures.
Regarding the specific horn construction in my question - during the previous month or two, I had the chance to listen to such a horn. In fact, it is a little bit longer - about 7 m (!). There are some pictures of these horns in a Bulgarian DIY forum, however since it will be hard for you to navigate through it (it's in Bulgarian only) I allowed myself to upload some of them here:
http://diy-audio.atspace.org/alnhorn1.jpg EDIT: Linking from this site is not allowed./ peranders
http://diy-audio.atspace.org/alnhorn2.jpg
http://diy-audio.atspace.org/alnhorn3.jpg
I did not hear any time delay. And I'm not the only guy (excluding the happy owner) that had listened to them in several sessions. The sound is beautifull and amazing and ...!!
I know what the theory says, and I too am wondering as to what extent generally known formulae apply to such an unusually long construction.
Since the end of September'2004 I've been working on my own project of similar parameters. Spring'2005 shall be the starting date for construction works.

Knowledge not shared is knwoledge dead:
Dinsdale, Edgar articles - www.volvotreter.de
Leach articles - http://users.ece.gatech.edu/~mleach/ (thanks, Zobsky !)

Regards,
Teodor

[Nelson Pass]

In case you haven't seen it, I wrote an article called
"The KleinHorn pt 1" which is currently available at
www.passdiy.com and will soon appear in AudioXpress.
Part 2 is nearly ready for publication.

I say this in reference to the audibility of the delay of rear
versus front waves in long horns, mine being about 20 feet,
which is comparable to your case, but I do not front load
the driver with a horn.

It's an interesting phenomenon - you can hear it, but under
the right circumstances, nobody seems to mind. Partly this is
a function of the suprise of hearing a 5 inch Lowther kick some
butt, but also the importance of the effect may not be what you
would assume.

I find that the issue seems to revolve heavily around how much
of the midrange is allowed to be amplified by the horn, in other
words, its low pass character. I find that as I stuff the horn more
and filter out more midrange from the rear, the delay becomes
more objectionable, and the less I stuff the horn with absorbent
material, the better it sounds.

I'm at a loss to explain this satisfactorily, but a number of astute
listeners confirm this, and I speculate that the front/back
transition frequency is important, or alternatively, the speaker
sounds so lively without the stuffing that no one cares.

[progressor]

Yes, I've read your KleinHorn article about month ago. Impressive look ! I like it !
Unfortunately, I can't aford myself mouth openings of 152x183 cm (60x72 in.). I'll have to keep up a more manageable size like 75x100cm (30x40 in.) which is roughly the area for 40 Hz and corner placement.
However, there is one thing I'm not quite certain yet. And this is the horn length - should I obey the theory and make it ~349 cm (~137 in.) given the throat area is 70 sq.cm (27.5 sq.in.) and flare rate M is set to 0.6, or go down with cutoff frequency e.g. 33 Hz and make it ~423 cm (~170 in.) keeping the a.n. mouth area, or even go further using 20 Hz which shall lead me to a length of ~697 cm (274 in.) !? Note that the length in 33 Hz 'scenario' is very close to the half wavelength for 40 Hz, and this way the horn will probably operate in a more 'velocity-controlled' manner.
Regards,
Teodor

[Nelson Pass]

Of course with corner loading (1/8 space) you want to try
to use the room as the mouth, so you adjust your flare rate
and length to best mate with the character of the corner.
This isn't rocket science, but you shoot for the best you can
get.

For a given frequency cutoff, remember that this is the point
at which the output drops way off, and you will figure on using
it down to 1/2 above that frequency. For length, you want to
somewhat arbitrarily decide what size your corner mouth is, and
you can add the length from that to the length of the horn at the
mouth of the box and see if it makes for at least 1/4 wave at the
frequency you really want to still hear (1/2 oct above flare cutoff).

[AndrewT]

Hi,
Nelson can you clarify?
Set the Fc at about half an octave below lo end usable response. Then fix mouth area and length at half octave above Fc??
Allow a distance and an area for the effect of corner reinforcement? or just distance since corner area is already taken account in the 1/8 space calculation?
What distance?
Q. Is the effective speed of sound changed in the horn either at the throat end where pressure is very high or throughout the length? It might affect the delay.
Could the midrange effect you talk about be due to some midrange arriving with the bass in time due to similar delay and then masking the phase difference?
But this prompts the next question; surely the midrange delay and phase errors will be worse further up the frequency range? No, I don't think this is the answer.
regards Andrew T.

[progressor]

Recently I had a talk with a friend of my friend. He makes his own drivers (magnet, voicecoil up to the diaphragm) ... I had already been listening to them .... I'll just say they are 'similar' to Lowther's and AER's (MK-I) ones ...
During the conversation I wasn't able to understand much of his words, most probably I'll have to go back and read some more on acoustics basics. But he mentioned something interesting - it is important what is the air volume 'enclosed' by the horn, and it is possible to make the mouth smaller, keeping that volume - thus increasing the length.
Regards,
Teodor

P.S. One of my previous posts contains links (I hope at least some of you would be able to open them) to some pictures. The a.n. drivers can be seen there.