Extremis6 Transmission Line

[BassAwdyO]

So today I decided I had a few extra bones to spend so I thought I'd build some new speaker enclosures. I was thinking of all the possible designs I could use and decided I would try out a TL for fun.

I have never made a TL before, so I did a bit of investigation and found some basic TL rules of thumb. Using those rules I designed a 46hz TL for Adire's Extremis6 midwoofer.

The design is simply a 6' line starting at 2(sd) tapering down to sd over the first 12 inches and then remaining constant. Total enclosure size is 12"x25"x8"

I havent finished yet, so I'm not sure how they will sound. From what I've read I'll probably have to play around with stuffing density a bit to get it to sound perfect.

How does my design look?

I'll post pics and results when I am completed!

[BassAwdyO]

Here's a pic of the stuffed TL with the side panel removed....

I'll post more pics soon!

[edjosh23]

Very nice, I was planning on doing an extremis TL this summer with a ribbon tweeter and a possible midrange. How do they sound?

Can we see pictures standing up?

Thanks,

Josh

[BassAwdyO]

I just got done playing around with the stuffing and I finally got it just right(to my ears anyway)

They sound great! Guessing from just listening in room I would say the f3 is around 35hz(in room) with usable response down to 30hz. When it gets down to that low it is pretty taxing on excursion, but I really dont need anything that low out of the mains because the sub(tumult) can take care of it.

Just listening a bit I can already tell a difference in how well they intregate with the sub. The bass is very defined and clean and sounds purely like it is coming from the mains. With the BR boxes I had the extremises in It just didnt intregate as well(I'd guess that the group delay is probably higher on those BR's and thats probably why)

I plan to add on some curved wings to eliminate baffle step and put some tweeter enclosures on the top(using a pair of Vifa DX25's I have)

I was thinking of simply making the curved wings out of some 8" PVC pipe cut lengthwise to create a 90degree arc. Will that work?

[bzdang]

Looks good. I was thinking that some hair netting could be placed across the woofer hole as you insert the woofer, and trimmed off around the rim of the woofer after the screws are tightened, to keep the stuffing out of the frame.

[BassAwdyO]

Yeah, I'm actually going to get some of the non-metallic window screen from work for that. I just used some aluminium window screen to retain the stuffing near the terminus, but thought it might rattle against the basket or something if I used it around the driver.... A peice of thin cloth would probably work well also.

[bwbass]

Why did you decide to tune it so high?

You'll get lots of output but it will be more "peaky" and not extend as low. I thought the point of a TL was to tune the quarter wave to the driver's Fs to control excursion and smooth out the impedance curve.

[BassAwdyO]

All of the reading I did indicated that the tuning should be a quarter wavelength of the Frc of a closed box using said driver of equivilant line volume. The line volume was near 1cubic ft which makes the closed box frc about 46hz. That gives a wavelength of ~25ft and a line of about 6ft

[GM]

Greets!

Interesting methodology. Where did you read this? Traditional wisdom says to tune it to Fs so that the dip above Fp will be boosted by the pipe's 1/2 WL pulse. Since a driver wants to 'feel' an equal pressure on both sides of its diaphragm, then in theory Vp = Vas, but the stuffing adds acoustic mass to the driver. This lowers Fs, ergo the effective Vas increases somewhat. Since the traditional performance goal of a TL is to get a ~IB response in a relatively small cab, Vb = 2*Vas and Lp (in) = 13560/6/Fp always performed extremely well for the few I did.

Not that yours looks bad in a sim, with 1.0 lb/ft^3 0f polyfil stuffing density down the length of the line it looks like a 'classic' TL should and since your effective line length is only a few inches shorter than what I calc (72" Vs 75.33"), both are tuned to ~Fs. My larger CSA (2.34 ft^3 Vs ~0.9752 ft^3) means it will have more gain though, so it's not surprising yours sims ~ -3dB/30 Hz compared to mine. Also, since the larger Vp increases damping, a lower stuffing density can be used.

At this low a frequency though, +3dB doesn't sound much louder so whether the extra size is worth it I guess would depend on the app/SAF/driver's Xmax.

GM

[Grahamt]

Originally posted by GM
Greets!
Traditional wisdom says to tune it to Fs so that the dip above Fp will be boosted by the pipe's 1/2 WL pulse.

GM

Just an FYI, you might want to measure the Fs if you haven't already. If I recall correctly I measured it at around 38 Hz.