Large Format Driver Geometry

[bfish]

I need some help with my geometry homework.

Part 1; Does anyone know the included angle of the conical WG used in large format drivers?

Part 2; (presumably needs the answer to part 1 to complete) If a new mounting flange was made of 1/4" stock, and the mating side had a 1.4" hole, what size would the "exit" hole be to continue the conical expansion uninterrupted?

(should be fairly obvious to see where this is leading...)

[Earl K]

Hi Brad,

Part 1; Does anyone know the included angle of the conical WG used in large format drivers?

- Here's what I know .

- FWIW ( to your project ), Clifford A. Henricksen states that the flare rate ( Fpg ) for the Altec 288, JBL 2440/1, & the TAD 4001 / is 225 hz / for all 3 .
- The TAD 2001 is listed as 350 hz . I'm inclined to assume that the other "classic" small format drivers use this same figure .
- This info is published in the chapter that Henricksen authored ( chapter 14 ) within the "Handbook for Sound Engineers / The New Audio Cyclopedia" .

- From time to time, I've seen other numbers bandied about as the flare rates for these drivers. Typically the stated numbers are close enough to this 225hz figure ( that I'll avoid a pointless argument ) . I'll continue to believe that C.A. Henricksen(s)' numbers are correct the ones .

I need some help with my geometry homework.

- As best as I can measure a 2441 ( using one of those carpenters angle finders ( bevels ) shoved down the drivers' throat & then overlaid onto a large protractor ) it looks to these older eyes to have a throat angle of 4 degrees ( off the 90 degree perpendicular ) . This ought to be close to the 288 ( though they are different points taken along an exponential curve /which approximates a conical for the first portion )


<> cheers

ps;
C.A. Henricksens' "Tangerine" Phase Plug Patent ( for Altec ) .
Bruce Howze & C.A. Henricksen (s)' Loudspeaker Horn Patent ( for Community Light & Sound ) .

[bfish]

Thank you very much Earl!

When I get around to "making the cut", I'll post my results. My initial plan to whack off a beat/broke pair of 511s at the 1.4" mark didn't allow for 1/4" of plate between horn & driver, so I want to continue the flare thru the plate and then make the cut at the plate exit diameter. At first I thought that I'd just go 1.4" round to square in the 1/4" thickness, which would continue expansion, but at an unknown (to me) rate. Now I feel that a flared, round plate opening followed by tapered fill in the square corners would be smoother.

[Panomaniac]

3? is the figure I see quoted the most.

I've been thinking of stuffing some putty down there to make a plug and then measure it. Put some saran wrap at the bottom to keep the putty out of the phase plug. That would not sound nice!

[Earl K]

3? is the figure I see quoted the most.

Hmmm, while searching for Altec references within the "Beyond the Ariel" thread I came upon this ;

Simulations

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Here is Bjorn Kolbrek's simulation of the radiation impedance of a 420 Hz Le Cleac'h horn with a T = 0.707 and profile optimized for an Altec 288. The green curve on the right is the power factor, or the power admitted into the horn. The red curve on the left is the reflection coefficient, the power reflected back towards the diaphragm. I see this as similar to a VSWR curve for an antenna, showing the transmitted power versus power reflected back to the transmitter.

Now, it is a simulation, and I treat all simulations with a degree of skepticism. But still, it is interesting to look at, and other simulations by Bjorn Kolbrek showed strong reflections when the throat flare of the horn did not match the internal flare of the 288 driver (which is 8 degrees). Very slight mismatches between the compression driver and the throat flare of the horn create surprisingly large ripples in the 500 Hz to 3 kHz response region.

FWIW, 6 or 8 degrees is likely not that huge a difference for what Brad is intending to do ( carving up a 511a into a 511E ) .

<>

[Panomaniac]

I think you're right. And what is the flare rate inside the 511 throat? Do we know?
Would be nice to get it right, if possible.

And speaking of modified 511s, have a look at these odd puppies:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=290369292030

[Earl K]

And speaking of modified 511s, have a look at these odd puppies:
eBay

- Those modded 511s on eBay belong to an LHF poster named ( sbjacob ). He hadn't talked about them on the forum / so I'll assume they just weren't that successfull for him .
- He may have been inspired by a thread authored by another LHF member named Lars.
- His thread was called " 511b Massacre " . He had an interesting project going utilyzing twin 414s / though I think he was trying to shoehorn ( abuse ) them into working as OB speakers .
- Again, this was another project that didn't get a final report .


Here are a few pics of Lars "handiwork" .
]

The location in the horn bell where Lars made his cut-through is pretty interesting. The resulting slot looks to be almost small enough ( in horizontal height ) to warrant an attempt to make a constant directivety style horn from parts . This would use the 511 bell mated to an Altec 34503 throat adapter ( the cast metal diffraction slot piece, scavenged from an early MantaRay series horn ) .

And what is the flare rate inside the 511 throat? Do we know?

- No, but what's a little diffraction amongst friends.

<> cheers

ps ; Here's Lars website ; reVintage

[bfish]

...And what is the flare rate inside the 511 throat?...

Actually, there are 2 in the initial square section. The photo is of a 511B half section laid flat on a scanner. I added a few lines for reference. Note the nearly imperceptable flare increase (yellow added lines on lower edge)... hard to see here, but really noticeable with a straightedge;



I'm afraid my laptop may be dying... took me ~3 hours to get this posted...

I have a few emails to some of you I need to answer, be patient please...

[Panomaniac]

Beautiful, man! Thanks for posting!
From your lovely scan it seems that the very start of the throat is 3~3.5? then going to 5?, then to 8? before the major flare.

So depending on where you cut it, you'll get a different flare rate. It does seem that it is made to match a CD with a 3? flare.

[bfish]

You're welcome. Guess I should add that I took several measurements with a micrometer at various points, and in each case, the initial section proved "square", i.e., the horizontal and vertical inner dimensions were equal.

It appears by the time a 1/4" mtg plate is added that the remainder will be entirely in the wider flare section. By copying the original post-transition, round-to-square smoothing, it should prove a good transition. Now you can probably see why I wanted to flare the mtg plate accordingly.