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Good 8" FR for Transmission Line
Good 8" FR for Transmission Line
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Old 16th January 2018, 02:51 AM   #21
planet10 is offline planet10  Canada
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Good 8" FR for Transmission Line
Quote:
Originally Posted by CLAD View Post
That photo is not the Voigt Pipe with an offset driver.
Its not. It is the TL project i mentioned from speaker builder. What we have learned about TLs since King and Augspurger released their TL models in 1999 means we can design something considerably more optimal.

Sure you can email me, but i am sure that readers will be interested in what happens.

dave
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Old 16th January 2018, 02:58 PM   #22
CLAD is offline CLAD  United States
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Yes, I see.

That is a true Voigt Pipe!

The 60" length, and the offset location of the driver is the critical component. The air does not necessarily need to travel the same direction down the full length of the line.

Hornresp automatically modeled that particular alignment for me, and I had to change it because I didn't recognize it as a TL. I'll switch it back and see what happens.
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Old 16th January 2018, 03:07 PM   #23
CLAD is offline CLAD  United States
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Hey Dave,

So the terminus you speak of; does it vent the outside concentric volume, or the one in the center, and does it make a difference?

Chris

BTW, that was another poster that wanted to PM with you. I'm fine with the discussion on the forum.
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Old 16th January 2018, 06:23 PM   #24
CLAD is offline CLAD  United States
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Hey Dave,

So if I do the two pipes like you showed in the drawing, and ad a third short pipe as a duct-terminus, does it then become an MLTL?

Also, What software do I need to model that terminus?

thanks,

hris
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Old 16th January 2018, 07:57 PM   #25
planet10 is offline planet10  Canada
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Good 8" FR for Transmission Line
If you vent the annulus section (the outside) of the concentric pipes, you have an expanding volume toward the terminus so it is a Voigt. If you vent the inner pipe you have a smaller end terminus. The latter will need to be much shorter. If your goal is to get about a 30” height, and given the 50% offset limitation i’d suggest the Voigt as being able to get you closer to optimum performance.

Mass-loading is accomplished by restricting the terminus which in the real worls looks like a port. I prefer slot vents, but a “plumbing pipe” (or a bunch of smaller ones in parallel) is also applicable.

Then you need to find a driver with Qt, Vas that works in your restricted enclosure. Fs can be tuned for by the exact length you end up with.

dave
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Old 16th January 2018, 08:15 PM   #26
CLAD is offline CLAD  United States
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Ok.

Thanks Dave, and others!

I have enough information to get to work.

I'm going to use the SEAS FA22-8. I'm not sure if it was recommended, but the recommendations and a little homework got me to Madisound, and steered me away from the PS220 and the Betsy.

It's going to be a 24" pipe inside a 30" pipe, like the image you showed me Dave. Driver will fire out the top, port will fire out the bottom. (hornresp, from my modeling actually looked a looked a little better when I fired the port out of the small pipe???)

I'll post pictures when I have them.

Cheers!

Chris
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Old 16th January 2018, 08:22 PM   #27
planet10 is offline planet10  Canada
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Good 8" FR for Transmission Line
FA-22 is a nice driver, but i have only considered using it sealed (50-60 litres is good). Any quarter-wave line will likely need to be bigger. You have a gross volume of about 55 litres… i’d consider just abandoning the TL idea.

dave
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Old 16th January 2018, 09:16 PM   #28
CLAD is offline CLAD  United States
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That was the conclusion I came to when I modeled the typical bass reflex as a comparison. The FR was very close to the same for both simulations.

What I am going to do, just for kicks, Is build it first as a Bass Reflex, but make it modular so I can take it apart and add the inside pipe afterward, to see if it has any effect at all.

I kind of doubt it will do anything. It might control the modes a little bit, and it will give me the option to stuff half the enclosure at a time, which did produce slightly varying results on Hornresp.

That's the plan!
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Old 16th January 2018, 09:32 PM   #29
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Good 8" FR for Transmission Line
If you are doing th eFA22 BR is a bad move IMO.

dave
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Old 16th January 2018, 10:27 PM   #30
CLAD is offline CLAD  United States
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I didn't really see any problems with it, other than it wasn't great, but BR put me back to the possibility of using PS220, (which is a little cheaper), and a10" pipe.

That one doesn't really impress me that much either, but I'm just experimenting with the "Omni" idea, so it just has to be relatively acceptable.

I might stick with BR, but to stay in line with my philosophy of trying to do something a little untypical, I might put a 10" pipe inside a 12" pipe, and fill the gap with concrete, or sand.

Any other High Mass enthusiasts out there??
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