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Multi-Way Conventional loudspeakers with crossovers

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Old 7th July 2013, 10:50 PM   #9021
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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.
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Old 8th July 2013, 03:00 AM   #9022
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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.

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Old 8th July 2013, 03:03 AM   #9023
Pano is offline Pano  United States
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Originally Posted by jzagaja View Post
We wil test 50Hz hypex t=0,3 soon - for 8, 12 or 15".
That's a lot of horn!
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Old 8th July 2013, 04:13 AM   #9024
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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 T-factor 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. Jean-Michel?
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Old 8th July 2013, 05:51 AM   #9025
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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.
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Old 8th July 2013, 06:36 AM   #9026
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Originally Posted by Kindhornman View Post
T=0.5 is exactly the same as a standard exponential expansion rate.
Hi Kindhornman,

I think you will find that a hyperbolic-exponential horn with T = 1 has a standard exponential expansion rate.

(The expression describing a hyperbolic-exponential horn simplifies down to that of an exponential horn when T = 1).

Kind regards,

David
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Old 8th July 2013, 06:39 AM   #9027
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I've found T=0,3 better for let say Beyma 12p80nd.
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Old 8th July 2013, 07:11 AM   #9028
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Originally Posted by Kindhornman View Post
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.
Hi Kindhornman,

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)

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Old 8th July 2013, 07:59 AM   #9029
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Would you not recommend the 288/400 to be crossed at 650, like Lynn has done with the Azura 425?

Pano,
If i ever get around to finishing the Altecs and putting the 288 on the jmlc400, you are welcome to have a listen. It wouldnt hurt to have an experienced Altec ear
Of course you can xo the 288 at 650, by all means - what we did here was just to see the potential of the various drivers and horn combinations. The 200T horn apparently Works well Down to 350 hz, so did the 288 (at least with 12 dB). This was, as I said earlier, done to check the limits of both drivers and horns at the very frequency Extremes. The one thing responsible for more bad horn sound than anything else is the stretching of frequencies too far.

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 TM-1201, and the New AutoTech J-horn fitted With GPA 515-8G (a very promising combo BTW).
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Old 8th July 2013, 09:01 AM   #9030
jeno is offline jeno  Norway
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Autotech always use T=0,8 except JMLC-200 which uses T=0. JMLC-200T uses T=0,8 as well. JMLC-350 has half angle of 7 degrees. It's good for tweeter application especially with new Radian 475-Be that we just received.
Do you have any more information on the 475-Be? Would be interesting with listening impressions, measurements, or info on availability. Thanks.
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