Please Define Flare Rate Frequency

[1audiohack]

With regard to horns, what is flare rate frequency?

Examples, Steve Schell's "Big Ed" is a 15Hz flare rate, my pals Leviathan's are a 48Hz flare rate, not the LF cutoff, but flare rate in Hz.

I have scoured this and other sites, just bought the 2008 Handbook for Sound Engineers at the recomendation of a friend, and a week and $104.00 later, have not yet found it.

Its driving me crazy, the term is used like everyone learned it in grade school, I missed that somehow!

Thanks all.

[Hoerninger]

Cut off frequency <> flare constant, yes.
The flare constant has the dimension of a reciprocal length.
http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=28629&d=1190904530
____________
Peter

[4313B]

Its driving me crazy, the term is used like everyone learned it in grade school, I missed that somehow!They're just showing off. Only five guys really know what flare rate is, the rest just act like they do. ;)

BTW - The discussion on it was in 3rd grade on a Friday afternoon close to the end of the second semester. You were probably busy pulling the redhead's ponytail sitting in front of you, shooting spit wads at your buddy across the room, gazing out the window at a spectacular spring day or simply nodding off from shear boredom. It happens...

[Chas]

BTW - The discussion on it was in 3rd grade on a Friday afternoon close to the end of the second semester. You were probably busy pulling the redhead's ponytail sitting in front of you, shooting spit wads at your buddy across the room, gazing out the window at a spectacular spring day or simply nodding off from shear boredom. It happens...

:rotfl::rotfl:

[1audiohack]

Thank you kindly Peter. Now I need a math reference book!

OK 4313B, your known around here as a know it all but, how in the HELL do you know about the redhead?!? ;)

[timc]

Thank you kindly Peter. Now I need a math reference book!

how in the HELL do you know about the redhead?!? ;)



:rotfl::rotfl::rotfl::rotfl:



-Tim

[Ian Mackenzie]

[quote=4313B;228963]

You were probably busy pulling the redhead's ponytail sitting in front of you, quote]

As long as it was a female:eek:

[1audiohack]

There were no males with ponytails when and where I grew up, hell I was six when I saw my first black person!

[scorpio]

Flare rate, does that have anything to do with the red-hair bell-bottom pants? 1GHz I'd say...

[1audiohack]

Alright alright already! Everyone knows what I was doing in school and it didn't stop in the third grade.

Consequently I need a little more help with this subject.

When I look at what Peter sent me I don't see the key, it looks like all variables to me.

Peter, or anyone, could you please provide an example?

Thank you from the back of the class!

[Hoerninger]

I don't see the key. (http://I%20don%27t%20see%20the%20key)
There is no key, that is why the redhead's ponytail is always more interesting. :spin:
(It is only a compilation I made many years ago which ended up in a drawer.)

I will go through an example:
Assuming there is a driver with a throat diameter of 1.5 inches, it should be used with a round exponential horn from 800 Hz up. For frequency response linearity I choose a lower cutoff frequency of 400 Hz. With these data the calculations of the dimensions start.

The radius at the throat is (about) r0 = 2 cm = 0,02 m. (1 inch = 2,54 cm)
The flare rate (Formerly I called it flare constant) for 400 Hz is calculated by
<3> k = 4*Pi*f/c = 14,65 /m ,
the horn length by
<11> L = 2/k*ln(2/(k*r0)) = 0,262 m ,
the mouth area
<12> AM = 4*Pi/(k*k) = 0,0585 squaremeter ,
the mouth radius
<13> rM = 2/k = 0,136 m ,
For the volume there are calculated
the throat area
A0 = Pi * r0*r0 = 0,001257 squaremeter
and finally the volume
<15> V(L) = A0/k*(e power (k*L) - 1) = 0,00390 cubicmeter = 3,9 liter.

Some claim the horn is smoother at the low end when the opening angle is not 45 degrees but 43 degrees. The results are
horn length
<9> x(43 degrees) = 2/k*ln(2*tan 43 degrees/(k*r0) = 0,253 m
mouth area
<10> A(43 degrees) = 4*Pi/(k*k)*(tan43 degrees)power 2 = 0,0509 squaremeter
and the volume
<16> V(43 degrees) = 0,00339 cubicmeter = 3,39 liter.

These calculations are best done in a spreadsheet. This time I used a pocket calculeter, I hope it is all correct.

Btw. where is blondie in the second row last week? :thmbsup:
____________
Peter

[1audiohack]

Thank you Peter, you are a great help. This will keep me busy for a while.



Btw. where is blondie in the second row last week? :thmbsup:



At home with my children of course.:)

[hmolwitz]

Ignoring all of these valuable and pertinant formulae, the Flare Rate that Steve Schell was referring to was the growth in size of the horn, if you have a trapezoid imagine one side with a 15 degree angle, has nothing to do with Hertz or Helmholtz.
I actually built something approximating his horn and found it fairly successful at producing large quantities of low bass. however my construction methods and materials were fairly insufficient to the task.
The basic concept behind his device is a rectangular horn that expands at that 15 degree number on one axis, you could construct such an item fairly simply if you incorporate no folds or splits, however it would be fairly cumbersome at around 16 ft long.
You can use the standard horn calculators to calculate the mouth size for frequency desired.
I would recommend OSB board in the heaviest thickness you can manage, thoroughly braced.
I used a pair of Altec 3156 drivers I had laying about, opposed and compression loaded into the throat, each in about a 1.75 cu ft box.
If I crank it near 150 watts it is fearsome, but it is also a bit buzzy as I used largely random bits of scrap to construct it and was careless in my joinery, and wanted to be able to disassemble and move it.
It is also missing the last segment for now as I am short of cubic footage.

pics (http://picasaweb.google.com/harry.molwitz/Sub#5275774020910382386)
Harry

[1audiohack]

OK I must have missunderstood Steve.

And the flare rate in degrees for a conical horn is relatively easy to conceptualize, calculate and build.

What I am working / struggling with is the ability to math model a conical flare, (one dimension at a time, BiRadials later!) so as to correctly create one.

Conceptually I still don't get how or why flare rate is described in Hz. I never told anyone I was smart!

I currently have a couple of LF horns and concur that they can't be too rigid! At higher levels the panels contribute significantly, and adversly to the sound. Its amazing what a couple of ratchet straps and bricks for mass will do for testing! Even more that all the anomalies show up in high resolution impeadance measurements, throat leaks, panel resonance, all of it.

Have fun with yours, thank you for the pic's.

Barry.

[Hoerninger]

Conceptually I still don't get how or why flare rate is described in Hz.

Steve Schell gave an example in this forum:
http://audioheritage.org/vbulletin/showpost.php?p=152815&postcount=3

Recalculating of " 50" doubling of cross sectional area " gives a cut off frequency of 15 Hz which he states. Steve speaks of 15 Hz exponential flare, which is easy to understand. This means that it is an exponential horn and the flare rate corresponds to 15 Hz.

But the flare rate itself is expressed in a reciprocal length. The cut off frequency and the flare rate are proportional:
100 Hz : 3,66 x 1/m = 0,0931 x 1/inch
200 Hz : 7,33 x 1/m = 0,1861 x 1/inch
300 Hz : 10,99 x 1/m = 0,2792 x 1/inch

There seems to be a problem with the conical flare? For the moment I am more interested in Blacky ... :bouncy:
____________
Peter ;)

[1audiohack]

Thank you Peter. This is now making some sense.

I hope to get some real time to work on this, this weekend. I am sure more questions will follow.

Thank you all for your patience! Folks like you make this a great place.
Barry.

[Steve Schell]

The flare rate (or flare constant) of a horn refers to its rate of expansion, which determines how low in frequency it will load the driver for efficient output. Theoretically, at the calculated flare frequency the output has dropped by 3dB and falls off rapidly below that as the horn no longer loads the driver effectively. At frequencies much above the flare frequency the loading provided by the horn is essentially constant, though the response of a horn/driver combination will eventually droop higher up due to several things working in combination, mainly the driver's moving mass overcoming the motor strength.

There are many types of horn flare expansions, from conical (straight sided) to exponential to hyperbolic. Exponential has long been thought to be a good compromise for bass horns, and I have found them to work very well. In a pure exponential horn the cross sectional area will continue to double, i.e. 1,2,4,8,16, etc, in a given distance. The equation I use to calculate the flare constant (Fc) in inches of an exponential horn goes like this:

4 x Pi(3.1416) x Fc... divide the result by 13,200... take that answer and divide .7 by the answer to obtain the Fc.

Using Big Ed as an example, 4 x 3.1416 x 15 = 188.496

188.496 divided by 13,200 = .01428

.7 divided by .01428 = 49.0196

So, the cross sectional area of Big Ed (the horn, not my brother whom it is named after) doubles every 49 inches. It begins with a 66 square inch throat, has expanded to a cross section of 132 square inches after 49 inches, has expanded to a cross section of 264 sq." after another 49 inches, and so on.

If you run the numbers, you will find that a horn with twice the Fc of another horn will have half the doubling distance, same as the wavelengths of the frequencies involved.

There, that's more than I know about the math involved, never a strong subject of mine. Calculations of other flare types get more complicated, which I think is reason enough to avoid them. Main points to consider are that in general the longer horns are, and the larger their mouths are, the better their performance will be. Whenever a room corner can be exploited for a bass horn the performance is improved due to the 1/8th space loading provided; sort of an acoustical free lunch.

[whizzer]

A. To determine throat area: At = (2Pi)(Fs)(Qts)(Vas)/c
where At = throat area in sq. ft.; Fs = driver's resonance frequency in Hz;
Qts = driver's total Q factor; Vas = compliance as equivalent volume of air in cu. ft.

B. To determine mouth area: Am = [1/(SF)(4Pi)](c/Fc)(c/Fc)
where Am = mouth size in sq. ft.; SF = Size Factor (SF1 is free space--like hanging above a cornfield; SF2 is half space--on a floor; SF4 is quarter space--on a floor and next to a wall; and SF8 is 1/8th space--in a corner); c = speed of sound in feet per sec. (1130); Fc = desired cutoff frequency (-3 dB).

The horn length should be at least 1/4 wavelength--in practice, the distance from the throat to the calculated mouth size using the contour formula below.

C: To determine contour (flare rate or flare frequency): Ax is equal to At times e raised to the power of 2x divided by xo.
where Ax is the area of the expansion at distance x from the throat; xo is equal to 2/k where k = (4Pi)(Fc)/c, where Fc is the desired cutoff and c is the speed of sound; e = a constant (like Pi, or 3.1416....); e = 2.71828....

So, for an example, using a Pioneer 10-inch instrument loudspeaker, A25GC40-51-F-Q, with an Fs of 30 Hz, a Qts of 0.15, and a Vas of 5.08 cubic feet, and figuring an exponential horn with a cutoff of 50 Hz with a size factor of 8 and a cabinet width (internal) of 16 inches, we find a throat area of 24 square inches, a mouth area of 730.4 square inches, a length of 73.6 inches; the distance in which the cross-sectional area doubles is about 14.94 inches.

[1audiohack]

You all have been a great help! I think I've got it.

I have modeled some of my old simple JBL horns in David McBeans HORNRESP program and need to set up the TEF and check myself against reality.

Steve I also finally swept your old corner horns in "The Big Corner" (38 feet tall, 50+ foot long walls of 6 inch thick concrete, outdoors) I will PM you when I get it off my laptop if your interested.

I am dying to cut wood!!! :D

Thanks again,
Barry.