DIY multicell horn

[HiFiPlayer]

Thank you guys, you let me find that web page again. I was lost this website path too long.
His opus still makes me feel wonderful. A real expected horns builder.

[Mirrophonic Sound System]

Hi Larry & B.A.Carr

Larry to see a Western Electric 24A horn, click on "rate member" to the
left and it will give a blow-up of the photo.

I made the copy 24A out of sheet metal damped with glued on rubber with cast alloy throat coupler
but it is for 2" drivers - not altec. Tomorrow I'll change the picture to show this homemade horn.

For 288's I once made Edgar's 300 hz wood horns and adapted
Altec alloy throat couplers to them - sounded great !
This Edgar horn project was in Speaker Builder magazine 1/86.

BA Carr: Your CNC ideas are good I think Edgar's 300hz round Tractrix horns are
produced this way. They seem to be machined from a solid
piece of a glued stack of hardwood sheets.

[Mirrophonic Sound System]

Now the picture is of the cloned 24A horn without internal 'multicells'
- which are unnecessary for home systems.

It has the exact same dimensions, flare-rate, cut-off freq, etc.

[joejoe723]

Hi Mirrophonic Sound System, i think that you are a very good horn player. Now, i have a lot of questions.
From other topic, you mention that
Western Electric 24A: 35.5" x 26" = 923 sq in =120HZ cut-off
JBL 2390: 35" x 7.5" = 262.5 sq in = 235HZ cut-off (use adapter for Altec drivers)
Altec 511 is 23" x 9" = 207 sq in mouth area = 265HZ cut-off frequency
If i know the mouth area. How to know/calculate the cut-off frequency?
I wondered that i saw a vitavox 220Hz horn before and the cell mouth is so small(around 8"x 8"). Why the vitavox horn can have a such low cut-off frequency?
On the other hand, Can you explain why the internal 'multicells' is unnecessary?

Thanks

[Mirrophonic Sound System]

The picture at left now is a home constructed 300hz Tractrix-contour wood horn
designed by Dr Bruce Edgar - details of construction are in Speaker Builder 1/86.

Construction is super easy and design was truncated towards throat end
to match exit of Altec 288 throat coupler.

It is sitting atop an Altec 620 enclosure with a 416 for bass -
crossover was 400hz 24db/oct bi-amp

[thevott]

My home-made 1505, may it rest in peace.

Years ago I constructed a replica Altec 1505 out of paperboard and tape! Now wait, this thing actually worked like a charm because I filled it with beach sand. The horn was easy and fun to build using 60 identical panels (modeled after one cell of my existing tar filled 1505) which resulted in 15 cells that all converged at a plaster-cast throat assembly. I then enshrouded the horn in the same heavy-gauge paperboard and filled the unit with sand for non-resonant mass, adding duct tape here and there to stop the handful of sand leaks that ensued. The finishing touch was the addition of my trusty 902 drivers (adapted of course) to the two 1505s. The result was excellent. Unfortunately the more I hauled the 'sand monster' around the the more it collapsed under its own weight springing numerous leaks. I don't think a day went by when I wasn't applying duct tape and/or sweeping up sand! Nonetheless, that horn found its way into a number of live music productions performing valiantly and it always proved to be a good conversation piece as well. At last, though, the horn was beyond any help that duct tape could offer and the unmanageable beast was eventually buried in the back yard like an expired pet. This seemed appropriate since it was mostly sand anyway. The thing that really amazed me about the horn, even in it's last days of applicable life, was that even in its physically distorted state the sound quality was still excellent and in A to B comparison it seemed identical in sound to its tar filled brother.

Someday sombody is going to dig that thing up and scratch their head.

MP

[joejoe723]

Hi Mirrophonic Sound System
Thankyou, very detail explaination ^_^. I saw the Vitavox horn in the Vitavox web site. Sometimes, it can be found in the ebay(Of course, the brand is Dukane). I think that Vitavox horn structure is similar with the early Altec horn and seems no other maunfacturer produce the 220Hz horn.
Hi thevott, I am very interested on your homemade 1505. I understand that you can copy one cell from the original 1505 and so you can make all 15 cells with paperboard. But, I wondered that the part between the 15 cells and the throat, how can you made it??? I think that a leakage will be happened at that part. On the other hand, i heard that when the 1505b is filled with sand, the resonant will be reduced

[thevott]

LarryLarry,
The short section between the cells and the plaster throat was also paperboard and was permanantly fastened to the throat by duct tape. The sand cavity extended to the throat as well. Duct tape is very effective at sealing up leaks and once the sand is present there is virtually no absorption of sound energy into the light weight paper and tape materials. The whole thing was mounted to a plywood skid which prolonged it life by months I'm sure. This was obviously a fun (if not laughable) experiment that proved surprisingly successful, however a more permanent assembly could be easily made of hardwood (throat assembly) and perhaps thin flexable plywood panels for the cells and outer shell. The unit could then be filled with concrete. But don't plan on taking it anywhere, that's what 511Bs are for!

[Mirrophonic Sound System]

Vott:
Is that drawing depicted in your avatar represent an actual system
or just a fantasy drawing ?

I'd like to hear one of those monster concrete bass horns that
you read some experimenters have actually built !

[Mirrophonic Sound System]

Larry:
It's funny that you mention the 220 hz Vitavox horn as I
have one of these ! It says DuKane model SA-325 - made by
Vitavox for DuKane of St Charles, IL. (St Charles is where
they have the big jukebox & antique shows - 40mi W of Chicago)

Is the other DuKane/Vitavox a single or pair ? I would like
to sell this one or buy another to make a pair.

The cells of the Vitavox are indeed 8"x8" but the cut-off freq
is the TOTAL or SUM of the cells in a multicell.

To find the cut-off frequency then we take the total mouth
area and find the radius of an equivalent circle :
which is the square root of area/pi= R
Now divide the speed of sound,13500,by 2.pi.R

With an eponential horn, the higher frequencies will tend to
beam. Western Electric solved this problem in the early 30s
by making the horn a composite of many smaller horns (with
higher cut-offs)that would direct the higher sounds in a
wide arc required for those 5000-seat movie palaces.
For home listening we don't mind having a little HF narrowing
(511's narrow the HF because they are exponential)
because it is a "sweet spot" listening situation and we
might also be using a supertweeter . Just like projection TV
screens beam light - OK for home but unsuitable for public exhibition.