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MultiWay Conventional loudspeakers with crossovers 

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7th July 2013, 10:50 PM  #9021 
diyAudio Member

From all my work on exponential and hyperbolic horn lenses the most useful T value has always been 0.6 0.5 is simply a standard exponential expansion rate. The change in T value changes the slope of the output curve.

8th July 2013, 03:00 AM  #9022 
diyAudio Member
Join Date: Apr 2008

Looks beautiful  should sound great. I did a simple all plywood 50Hz design for a friend with GoTo drivers, based on my own horns but eliminating the fibreglass section. I think a short 'L' 50Hz 1/4 wavelength is a good compromise, particularly if one uses a long horn on top to give a lower cross over point to suit the bass horn upper roll off. This all goes to illustrate the strengths of Lynn's solution  time alignment, control of the cross over, living room dimensions.

8th July 2013, 04:13 AM  #9024 
diyAudio Member
Join Date: Apr 2008

I used T=0.6, after playing around with HornResp, but with no great understanding. I understood from Earl G that cut off is mostly just about throat size, mouth, and length. Basically from measurement with a 50Hz 1/4 WL horn you get 80  100Hz that's reasonably in control and everything below is room dependent disaster. Perhaps T factor has a greater influence on how the driver is loaded at the top end. I have never really understood on what basis Tfactor should be be selected in the Le Cleac'h expansion. Or indeed why it is selectable at all if there is an optimum for constant driver loading. JeanMichel?

8th July 2013, 05:51 AM  #9025 
diyAudio Member

Truetone,
In classical horn design you will find that the T factor is used to load the lower frequency with a slower expansion rate as the T value is increased. The initial throat size does not change, the expansion rate is what is changing. The length and the mouth size stays the same, only the expansion rate is changing. If you look at the expansion rate of an exponential horn you use a factor called M which is the flare rate in that equation, the length that the area doubles is equal to M. T adds another factor to the equation, in other words in a hyperbolic equation you get an extra term which is T which varies this expansion rate. T=0.5 is exactly the same as a standard exponential expansion rate. With a t= 0.6 the rate of expansion in the initial horn flare, the expansion is slightly slower increasing the low frequency loading and only slightly changing the upper frequency response. Increasing the T value makes the rate of change slower in the beginning and faster there after. The high frequency response will become more beamy on axis with the higher values of T. 
8th July 2013, 06:36 AM  #9026  
diyAudio Member
Join Date: Jun 2007

Quote:
I think you will find that a hyperbolicexponential horn with T = 1 has a standard exponential expansion rate. (The expression describing a hyperbolicexponential horn simplifies down to that of an exponential horn when T = 1). Kind regards, David
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8th July 2013, 06:39 AM  #9027 
diyAudio Member

I've found T=0,3 better for let say Beyma 12p80nd.
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8th July 2013, 07:11 AM  #9028  
diyAudio Member
Join Date: Jun 2007

Quote:
For an exponential horn: m = Ln(S2 / S1) / L12 or m = 4 * Pi * fc / c In each case the unit of m is length ^ 1. m is not equal to the area doubling length. Area doubling length = Ln(2) / m or Area doubling length = Ln(2) * c / (4 * Pi * fc) (where c = velocity of sound in air, fc = horn flare cutoff frequency) Kind regards, David
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8th July 2013, 07:59 AM  #9029  
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Join Date: Nov 2008

Quote:
There are of course many factors that come into play when it comes to choosing the final xo frequencies; driver, horn, personal preferences and not to forget what will be used BELOW the driver. Right now I am changing back and forth between single/dual GPA 414 Alnicos and similar TAD TM1201, and the New AutoTech Jhorn fitted With GPA 5158G (a very promising combo BTW). 

8th July 2013, 09:01 AM  #9030 
diyAudio Member
Join Date: Apr 2006
Location: Way up north

Do you have any more information on the 475Be? Would be interesting with listening impressions, measurements, or info on availability. Thanks.

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