Extending the Exponential Straight 4-3 Horn

I'm really loving my Victor 4-3 and am thinking about adding an extension to the horn that will make it a six foot or eight foot non-folded length to achieve the low end response of the folded horns of the Credenzas without the drawback of loss of high frequency clarity that those folded horns exhibit. Has anyone out there done this kind of thing? I'm thinking that I could take the opening measurement of a Credenza horn and extend some flexible plywood from the mouth of the 4-3 horn, try to duplicate the extending taper and then make some sides to follow this curve. It could be connected airtight with something like blue-tack and be removable, since I don't have that much room here.

Can someone please provide an opening measurement for any of the Credenza horns that might be on hand?

The 4-3 has such a nice illusion of low frequency response perhaps a 1, 2 or 3 ft extension might be all that is needed for improvement. Any thoughts or experience out there?

Cheers,
David

It sounds like you are in for a lot of trouble, or a lot of math. You can't just add on to acoustic devices without carefully calculating things.

Also, the bass must be in the record in the first place. Most acoustic records cut off at around 300 to 400 Hz.

RC is right. In order to create an effective horn extension and have it perform at maximum efficiency, you'd have to know the "taper formula" used by Maxfield and Harrison, who designed the original tone chamber. Keep in mind, the Orthophonic Victrola was designed to function as a unit. Everything--including the weight and mass and size of the needle-bar and the diaphragm, the distances between the needle-bar pivot and it's connection to the diaphragm and to the tip of the (standard size) needle, the flexibility of the diaphragm, the length of the horn, the horn's expansion rate, and the size of the mouth of the horn--was factored into the design.

I actually tried something like this years ago when I owned a Consolette, which was missing its grille. I constructed a horn extension, which measured about five feet long, out of paper-mache, braced internally with chicken wire. The small portion of the horn fitted directly into the cast-iron elbow inside the Consolette's horn's mouth. I simply guessed at the expansion taper, based on some generic illustrations I found for exponential horns.

The end result was similar to this, in principle -- http://www.youtube.com/watch?v=pF22AS3F ... r_embedded

While the bass was, indeed, enhanced to the point where I could hear the pedal action of some organ recordings, overall, I was disappointed with the results--not quite up to the performance of a Credenza. Within a few days aft it was completed, the horn began to crack and crumble, so I gave up on the idea. But, had I the facilities to construct a more permanent type of horn, I might have tried it again. (It's always fun to experiment.)

The thing to keep in mind is that, in lengthening the horn to six or more feet, you will have to re-do its overall taper to compensate for the additional length. In other words, the taper of the horn will have to be more gradual than that used for the Consolette. Simply adding an extension, onto the mouth of the Consolette, will not produce the best results. There may be slightly more bass, but there would also be added resonance and distortion.

I assume that the math could be contained in the patents, but I don't have time to research those now. Also, I've tinkered with audio components in the past and even am using my own homemade unipivot wooded tonearms in both my 33 1/3 and electric 78 playback set-ups and they blow away anything I've owned and just about everything I've heard except in very highest endest of set-ups of a few good friends. I also do fine tuning of saxophone bore tapers and tone-hole modifications for a living.

Thanks again Joe for your feedback. I kinda thought you might have tried something like this. That link is cool.

I'm going to start from the assumption that Victor got it right all the way to the mouth to the horn so I'll start extending from there. I think I'll start with trying to add 4 ft pieces to the existing horn with something thin but stiff and smooth like masonite. These can be easily be pre-cut from my lumber yard from 4' by 8' sheet and if that length doesn't show a promising result then why bother with anything smaller. I can make an adjustable height frame for the top piece using my adjustable height bicycle repair stand to hold the open end. Once I am satisfied with the look of extending the expanding taper of the existing wooden horn, I'll move on to the bottom piece and just let this go to the floor smoothly. The sides will be left parallel for this experiment but will be stiff plywood and sealed to the top and bottom pieces with silicone so as to be airtight. I have some industrial silicone that cures in 5 minutes and also is easily removed, so I can experiment with top and bottom tapers if the first experiment yields any glimpse of improvement to the low end.

I won't get around to any of this for a few weekends, but this thinking out loud about it will help me refine the process before I attempt anything. Hopefully I'll also get some tips from folks out there.

Cheers,
David

wilsaxo wrote:...I'm going to start from the assumption that Victor got it right all the way to the mouth to the horn so I'll start extending from there. ...

Hi David:

It's true that for the Consolette's horn, which is about three feet long, the taper is correct. But, that was designed to have a specific cut off frequency--about half that of the Credenza--and the size/area of the horn's mouth was factored into the equation for the overall taper in order to minimize reflection.

For an exponential type horn of say, six or seven feet in size, the taper would likely be more gradual, so for instance, at the three foot or half-way point, it may well turn out to be about 1/2 or less of the size used for the mouth of the Consolette.

Though not to scale, and perhaps a little exaggerated, this illustrates what I mean:


(What appears as a parallel bore in the thin part of the six foot horn, would, in fact, be an extremely gradual taper. My PC's image software's pixels are not fine enough to enable me to draw this accurately.)

BTW, there are actually a number of sites that list formulas, etc., concerning the designs of exponential horns with specific cutoff frequencies -- for instance --

http://www.snippets.org/LDSG/HORNS/design.html
http://www.rocketsciencecanada.com/rock ... eShape.asp
http://www.angelfire.com/nc3/talkingmac ... lhorn.html

I have to confess, the math is well above my head.

In any event, it sounds like you have plenty of room for trial and error, and it should be fun to hear about the results of your experiment(s). Please keep us posted.

JDS

There was a major discussion about this subject (including formulas) in "UK&European Gramophone & Music Forum. Might help you caculate scientifically
Regards
John

john46 wrote:There was a major discussion about this subject (including formulas) in "UK&European Gramophone & Music Forum. Might help you caculate scientifically
Regards
John

Hi John:

You mean this one? -- http://www.ukgramophones.proboards.com/ ... thread=266

No, it´s this. The other one has been closed down.
http://ukgramophones.proboards.com/index.cgi
Have fun!
John 46