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Old 6th July 2005, 03:19 PM   #11
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Yes, I know the geometry is quite amazing and doesn't look like a standard BLH. That was just a simulation example and I wouldn't have built this thing anyway, due to its size.

Some little questions about the sheet :

Is it as accurate as your ML-TLs sheets, which work perfectly well, because you seem not to have really tried it according to your website ?

Is it interesting to consider the "sound pressure in time domain" graphic to adjust the geometry, because a horn seems to send back the impulsion through the mouth with a delay, but amplified too. Does it mean a horn always has some coloration, and is it possible to increase the impulse impact of the driver with a horn ?

Is it possible to model some damping in the horn, like in the coupling chamber ?
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Old 6th July 2005, 04:48 PM   #12
MJK is offline MJK  United States
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Quote:
Yes, I know the geometry is quite amazing and doesn't look like a standard BLH. That was just a simulation example and I wouldn't have built this thing anyway, due to its size.
Why present something for comment if you have no intention of building it? If you are going to post nonsense designs, looking for feedback, then I am not sure how long you will continue to get useful comments.


Quote:
Is it as accurate as your ML-TLs sheets, which work perfectly well, because you seem not to have really tried it according to your website ?
The BLH worksheets on my site use the same assumptions as the TL worksheets and produce the same type of calculated response. The BLH and ML TL accuracies are the same. However, for a BLH to be of reasonable size it needs to interact with the walls and floor so that the mouth size can be reduced. This capability is not included in the current worksheet and requires the user to recognize and adjust the design for this effect. My newer BLH models take this into account. To date I have not found a BLH design that I considered good enough to actually build and then correlate against the newer MathCad worksheets, I am still working on this project.


Quote:
Is it interesting to consider the "sound pressure in time domain" graphic to adjust the geometry, because a horn seems to send back the impulsion through the mouth with a delay, but amplified too.
I believe that a double pulse is an inherent property of a BLH. A TL does the same thing but to a lesser extent due to the fiber damping in the line. The key question, is it audible and does it degrade the BLH performance? I have heard strong opinions expressed both ways on this issue, my guess is that this is not a big problem. Secondary pulses will also be generated at room boundary conditions and if managed they are not huge issues.


Quote:
Does it mean a horn always has some coloration, and is it possible to increase the impulse impact of the driver with a horn?
The BLH horn's pulse will always be stronger then the driver's pulse, that is the whole point of horn loading. The only way I see of increasing the driver's pulse is to add a front loaded horn, I am still working on that simulation. The horn's pulse will always lag the direct pulse from the driver due to the extra distance is has to travel along the length of the horn.


Quote:
Is it possible to model some damping in the horn, like in the coupling chamber?
Yes, all of the models will accept up to 1 lb/ft^3 of fiber damping at any section. You will have to hand edit the input if you want a custom and optimized distribution of fiber damping.


You have a very good driver with the F120A, if you use it correctly I think that you could have a very good finished speaker system. My advice is to design and build a ML TL style of enclosure tuned to the driver's fs (using measured T/S parameters) and not chase something that stretches the driver's intended application too far based on incomplete input information. Adding an appropriate BSC filter, to get a balanced SPL response, and you should have a very high performance speaker system. Don't look for room shaking deep extended bass from a small driver, it cannot move enough air to replace a 10 inch or bigger sub.
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Old 6th July 2005, 05:27 PM   #13
Greg B is offline Greg B  United States
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Generally speaking, I've always found it a bit of a mistake to try and push a full range driver in a TQWT down too far. My preference with the FX120 would be a design that gets to 75 hz or so, with no peaking at Fc, and about 3 db of excessive gain 100-300 or so. Others prefer to design for dead flat FR and use a choke/resistor for BSC. Either way 'works'.

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Old 8th July 2005, 09:14 AM   #14
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I've played with all the parameters of the BLH worksheet and finally, I obtain something which looks correct and extends the FX120 just like I want, with a decent horn length that can be gently folded so it doesn't take too much place. (the first design geometry I showed was just the best thing I obtained at this time)

Greg D : I really cannot accept an enclosure that only extends down to 75Hz, because then I will miss half of the music. As I have no sub, I prefer more bass at the expense of maybe less dynamics, as I have a small room.

I found it a little astonishing to obtain the same results with a 12 and 19 in long coupling chamber, with the driver placed at different points. The 12in chamber would have been perfect, but due to the driver's size which cannot fit into it, I must use the 19in long chamber.

As the chamber has a small internal volume, how should be considered the interactions caused by the magnet's volume, which is quite big on the FX120 ?

Concerning the tapper, I suppose "linear taper" means it will look like a TL design = parallel sides and a constant cross sectional area expansion, making it look like a little like a triangle seen from the side of the horn isn't it ?

And in the worksheet, I do not understand how to enter the sections by hand, as there is no space visually defined for the 10 sections, like in the TL sections sheet (I'm not really a crack at maths, unfortunately )

Here are some screen captures of the best modeling I obtain. I took care of the impulse response to balance the whole work, and it seems like I will increase the impact of the driver with this geometry, a nice thing for a fullrange system

I prefer not to reduce the mouth size because the speakers might not be placed on the floor of my room, but maybe (maybe) on my desk (I know, it looks strange )
Attached Images
File Type: png fx120horn2.png (28.8 KB, 272 views)
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