1/4 wave TL Sub

[planet10]

Planet10:

Trapeze! WAY COOL (not my bag though)

You actually know of Trapeze (it is a pretty obscure spreadsheet).

dave

 

[GM]

>How do you like the sound of ML-TL vs standard TL? Is it closer to a vented box, or does it retain all the qualities of a TL?

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~ the same as critically damped vented, i.e. close enough to TL that I've fooled many folks, except with way more SPL.

====

>GM had trouble attaching his spreadsheet so here it is... it only implements the basics (and for fiberglass i believe)

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?? What else is there? No, it has both, above the gray bar is for fiberglass and below is for polyfil, etc.. Plug in Qts, etc, and the rest is calculated.

GM

 

[qi]

Planet10:

Thanks.

I've been consulting in the PC business since 1978 (yes -- pre IBM PC (CP/M systems)). I haven't missed much as far as PCs go (even MACs)

GM:

Thanks, also.

Fireman:

I sure hope this is helping you also, and that I have not hijacked this thread. Clearly the way to go is GM's ML-TL or with Dave's calcs.

Regards
Joe

 

[planet10]

I haven't missed much as far as PCs go (even MACs)

I still find it amazing that this software, last realease in 1988, running on my 50/100 '040 runs circles around Excel (or any other spreadsheet) on my Dual 867 G4.

dave

 

[fireman]

gm:

ml-tl...

1. build 88" x 13" x 13" column
2. stuff with 1.7 lbs of fill
3. mount driver 30" from top
4. mount 5" diameter x 8" long tube at bottom of column

...am I close?

We're talking 1 1/2 4X8 panel here ! That's an awful amount of baltic birch for a 10" sub. At this very moment in time, I cannot go that way. Definitively not.

Fireman:

I sure hope this is helping you also, and that I have not hijacked this thread. Clearly the way to go is GM's ML-TL or with Dave's calcs.

I still have the leftover part of the sonotube I removed when I first built my "prototype" sub. If I reattach it to it's twin brother, I get a 72" long 12" diameter tube. Using the lenght alone, I figured I'd get it tuned to around 42 Hz. I still haven't figured the relationship with the diameter though but as far as I can tell, it doesn't have that big an influence on the whole design. That will have to do for now.

Later on this summer, I'll get my hands on some 3/4" baltic birch and build that monster. I'll let you guys know how it went when it's finally built.

 

[GM]

>If I reattach it to it's twin brother, I get a 72" long 12" diameter tube. Using the lenght alone, I figured I'd get it tuned to around 42 Hz. I still haven't figured the relationship with the diameter though but as far as I can tell, it doesn't have that big an influence on the whole design.

====

It's not about the diameter per se, but the total Vb of the tube (which does make a big difference in LF gain for a given Fb), ergo for a longer tube, the diameter will be smaller for a given Vb. Where the diameter affects Fb is in the end correction, where the actual measured Fb will be slightly lower than predicted based on its length.

With this extra Vb, you can get considerably more gain (though not nearly as much below 30Hz as the 'monster') by capping off the terminus and adding a 4" diameter x 7" long vent. This will tune it to ~22Hz.

GM

 

[qi]

GM:

That was going to be MY next question

In doing so, Fireman is creating a 72" sonotube ML-TL?

What does he lose by leaving the driver at the top and not placing it 30" (or so) down?

How much stuffing, and is it placed only in the upper portion of the tube?

 

[GM]

>In doing so, Fireman is creating a 72" sonotube ML-TL?

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If he caps it off and adds a vent.

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>What does he lose by leaving the driver at the top and not placing it 30" (or so) down?

====

More gain over a wider BW/lower F3, though with slightly more 'ripple' in the upper BW. ~25.2" yields the max gain/BW for this pipe's dims.

====

>How much stuffing, and is it placed only in the upper portion of the tube?

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0.2lbs/ft^3 for the ML-TL, ~1.0lbs/ft^3 for the 72" TL.

GM