Want to build a TL subwoofer - driver advice needed

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I'm reading through the section now on geometries with changes in cross-sectional area. Placing speakers with hefty mounting depths - like subs - can be hard to accomplish with a constant cross-section.

I'm wondering if it's better to use more small subs in a T/L, to increase the cross-sectional area of the pipe?
 
I'm reading through the section now on geometries with changes in cross-sectional area. Placing speakers with hefty mounting depths - like subs - can be hard to accomplish with a constant cross-section.

I'm wondering if it's better to use more small subs in a T/L, to increase the cross-sectional area of the pipe?


You can do what I did with the Boom Unit and the POC, and arrange the layout of the TL so that where the driver is located, there is enough clearance for its magnet structure.

Simple bass unit using the Dayton PA310

The Boom Unit...
 
So, with the picture that I posted... How does that fit into the scheme? Assuming one followed the "classic" rules - Low Qts drivers, T/L cross-sectional area proportional to the Vas of the drivers, etc, etc... Could this be used to achieve the goals of a T/L? Or is a T/L rigidly defined by the number, and orientation of the folds in the chamber?

FWIW, 'Classic' rules were derived back when amps had a high output impedance, which added as much as 8 ohms for an 8 ohm system, nearly doubling the driver's effective Qts [Qts'] or nearly halving its effective motor strength the way they looked at it and Vas was high to offset this loss of efficiency since high power was only available to the favored few.

Factor in that stuffing lowers the effective system Q [sysQ] and to get a transient perfect 0.5 Qtp requires a somewhat higher driver Qts if driven with a typical high DF amp [< ~0.5 ohm].

Of course if you prefer an over-damped response that clips the transients, then yes, use a < 0.5 Qts driver and if < ~0.4 Qts, designing based on Fs/Qts yields the TL ~equivalent of a damped/stuffed sealed alignment.

BTW, the picture shows a ducted port vented alignment, not a TL per se, though I forget what moniker they are more commonly known as, so can be designed as one in WinISD or similar.

edit: Got sidetracked and forgot that another 'classic' theory is a pipe area = driver Sd, which when properly damped results in the theoretical ideal of a 2:1 CR and actually works well with low Qt drivers if one wants the 'heart attack fast' sound of a compression horn or low Qt OB complete with the same downside, i.e. limited to only 2-3 octaves unless there's plenty of room/boundary gain, so best for mid-bass up in multi-ways IME.

Anyway, with today's simming programs you can quickly compare the basics of the various combinations.

GM
 
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You can do what I did with the Boom Unit and the POC, and arrange the layout of the TL so that where the driver is located, there is enough clearance for its magnet structure.

Simple bass unit using the Dayton PA310

The Boom Unit...

I was just looking at the modeling that you did on Dayton PA310. First question - what was the spreadsheet that you used? (your first photo, from the left)

What is percentage of Sd that is used to simulate the pipe size in Hornresp?

I'm not really getting that to work right now. I only have a (ridiculous) Mac at home.
 
I was just looking at the modeling that you did on Dayton PA310. First question - what was the spreadsheet that you used? (your first photo, from the left)

What is percentage of Sd that is used to simulate the pipe size in Hornresp?

I'm not really getting that to work right now. I only have a (ridiculous) Mac at home.

Answers:

The spreadsheet is a workbook (well, one of the workbooks) I've put together to describe a particular design. You basically enter a few parameters, hit the Optimize button, and it optimizes the layout and generates the Hornresp parameters. Hitting the Export button will then create a Hornresp data file which can then be imported into Hornresp for analysis. The workbook takes a little while to put together (a lot less time now that I know a few shortcuts), but it significantly decreases the design time afterwards. They are all available on my website, The Subwoofer DIY Page - Horn Folding

I didn't use a % of Sd for the design. I chose a box size and mouth size for the vent, then adjusted the dimensions in the workbook until the Hornresp sim showed me something I'd be happy with.
 
Oh, I see them. Basically, you have some pre-defined configurations.

That's cool.

Next question - is there a limit to the number of times that you'd want to fold the pipe? Or is it only important to respect the cross-section of pipe, through said folds?

I'm asking because I really don't like the aspect ratio of some of the designs. I was a longer horizontal layout, not a taller vertical.

Regarding multiple drivers - if I wanted to do (2) drivers per chamber, do I simply need to adjust the impedance and Sd values?
 
Oh, I see them. Basically, you have some pre-defined configurations.

That's cool.

Next question - is there a limit to the number of times that you'd want to fold the pipe? Or is it only important to respect the cross-section of pipe, through said folds?

I'm asking because I really don't like the aspect ratio of some of the designs. I was a longer horizontal layout, not a taller vertical.

Regarding multiple drivers - if I wanted to do (2) drivers per chamber, do I simply need to adjust the impedance and Sd values?

The limit on the number of folds tend to be a practical rather than theoretical one.

Impedance should be halved (parallel drivers) or doubled (series drivers). Sd should be doubled. Hornresp can do this automatically by selecting the right options when using it to sim.
 

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A simple 62 cm offset driver driver pipe with a Ap = Sd x 294 cm [~237 L] lightly stuffed full length to 'taste' or accept HR's 668 g of polyfil [~25 Hz Fp] is good for a < 100 Hz/4th order XO. Different tapers or even a MLTL didn't help much due to its high inductance.

GM
 
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