Nat P TL?

[Mornlith]

Hi all -

I was lurking again gathering more ideas and was playing around in the Nat P thread. I saw all the discussion regarding the use of a MLTL, but then it looked like the TL portion of the convo fizzled out.

Has anyone tried doing something Scottmoose's parameters? Has anyone built the NatP MLTL? Or is the general concensus "don't bother/this is silly"?

[ThomasW]

Has anyone tried doing something Scottmoose's parameters?

Not that I'm aware of ..

Has anyone built the NatP MLTL?

See above answer

Or is the general concensus "don't bother/this is silly"?

More or less.

Even in the standard ported PE box the NatP has pretty solid output to ~32Hz.

But IMO it doesn't matter what you do with a pair of 7"s they'll never qualify as a 'fullrange' speaker. So why bother hassling with anything more complex than a ported box?

If/when you want to explore the lower octaves build a sub. That can be a separate device that sits somewhere else in the room, or it can be bass bins that serve as stands for the NatP

[Mornlith]

Thanks for the quick response. I will probably do a ported Nat P once the funding drain that is my bathroom remodel goes away and I know I will definately add a sub when I start my HT revamp. However....

The practicality of doing a TL does seem dubious, but "coolness" factor of doing something like a TL is intriguing to me since I am a newb. I was looking at Curt's pages and his revamped Tritrix/Triune TL design and after reading the Nat P discussion, I thought it would be kind of neat to see a "bigger brother" to the Tritrix TL.

[---k---]

I could have sworn that I've seen a NatP TL. I agree that using a sub is a better way to get full range, but there are a lot of people who aren't super huge bass heads like Thomas who would likely be 90% satisfied by either ported or TL NatP. A lot of comercial designs offer up even less! So, I wouldn't say it is a bad idea. Especially if you are like me and often to lazy to turn the sub amp on, except for movies.

If you still are intriged by TL design. I bet if you ask on the PE board someone will either point to a build or be willing to model it for you. There are a bunch of TL people over there - especially Paul K. I know people claim that they sound better than a ported. I don't know, I could see it being possible. Worth the effort? Who knows.

[Dennis H]

If you dig deep enough in the NatP thread, Scottmoose dropped by and whipped up an MLTL for it. It looks a lot like a lightly stuffed ported box to me, both in construction and frequency response, but I guess there must be a difference if the TL experts say so.

http://www.htguide.com/forum/showthread.php4?p=238657#post238657

[Paul K.]

Just couldn't resist the challenge!

Okay, I did a fairly quick ML-TL model with Martin's worksheets for a TL version of the Natalie P. My box has internal dimensions of 7.5"W x 11"D x 40"H, resulting in a gross volume of about 54 liters, which should give a net volume of around 50 liters after taking into account volume consumed by the RS180s and bracing. I used a stuffing density of 1 lb/cu.ft. in the top 21 inches of the cabinet. I also arbitrarily modeled with 0.4 ohms in series with the paralleled RS 180s. The center of the mass-loading port is 2" from the bottom of the internal height and can be located on either the baffle or rear panel. This port has a diameter of 3" and a length of 4". The resulting F3 is ~33 Hz, and F6 is just a hair above 30 Hz. The port air velocity with a 2.83-volt input was 1% of the speed of sound. You could, of course make the cabinet deeper, having more volume, shorten the port a bit, and end up with a lower F3, but I was trying to keep the net volume around 50 liters for comparison. While a true tapered TL is not a good fit for the RS180, there is a variation that works well but would take a bit more work on my part to model. This is best described as a coupling chamber with a tapered line appended to it. I will now try to attach the system response graph for the ML-TL I modeled (I hope I'm successful).
Paul K.

Edit: I forgot to state that I used John Krutke's T/S measurements for the RS180s.
Paul K.

[Mornlith]

Thanks Paul! I was real curious to see what it would be like...but it sounds like it really is like a highly stuffed bass reflex. If I get some time over the next few days, I might try to draft some drawings for the hell of it.

Out of curiosity, why is a tapered TL a bad fit for the RS180s? Is it only bad for the 180's or is it for all RS drivers?

[Paul K.]

Thanks Paul! I was real curious to see what it would be like...but it sounds like it really is like a highly stuffed bass reflex. If I get some time over the next few days, I might try to draft some drawings for the hell of it.

Out of curiosity, why is a tapered TL a bad fit for the RS180s? Is it only bad for the 180's or is it for all RS drivers?

The RS180 just happens to not work out particularly well in a true tapered TL when you look at its overall response and the resulting F3, but in a hybrid sort of tapered TL, it works much, much better. OTOH an RS225 works really well; I used one in an 18:1 tapered 3-way and was really pleased with how it turned out (I'll attach a photo of that speaker, the Alicante).

As you state an ML-TL is similar to a highly stuffed vented system, but it does take advantage of the 1/4-wavelength resonant frequency that's established by the line's length, in this case the height of the cabinet internally. Also, the stuffing density and location really goes a long way towards eliminating any kind of "boxy" sound in the midrange.
Paul

[Mornlith]

Out of curiosity, what do you mean by hybrid tapered TL? What made you decide to go that route? Science, intuition, for the hell of it, or all of the above?

[Paul K.]

Out of curiosity, what do you mean by hybrid tapered TL? What made you decide to go that route? Science, intuition, for the hell of it, or all of the above?

I just happened to try it out specifically for both an RS180 MTM and as a cabinet variation for the Dr. K's MTM designed by Darren Kuzma and detailed in the PE Showcase of speaker designs. This hybrid has the first ~1/3 of the line's length without any taper and the last 2/3's with typically a 10:1 taper. The modeling I had tried for the RS180 showed an ML-TL was a better choice as compared to a tapered TL all things considered but I wanted to see if I could achieve some of the attributes of a tapered TL, and this hybrid did that. The only downside of the hybrid TL is that it takes a larger cabinet to get the same F3 as would be obtained in an ML-TL. I've done a LOT of TL modeling, and continue to do so, and simply from repetition, I've gotten reasonably good at it and can usually determine pretty quickly if a TL is a good choice for a specific driver, and what type of TL is best.
Paul

[Paul K.]

"Hybrid" Tapered TL responses

Just for comparison, I modeled what I've been calling a hybrid tapered TL for the Nat P. As I stated, it takes a bit bigger box to achieve a similar F3 as compared to the ML-TL that I modeled, but if it's important to anyone, this hybrid is more TL-like in the shapes of its response graphs and impedance graph, plus the terminus air velocity is lower. I modeled with a box of the same width (7.5") and height (40") but increased the depth to 13" (from 11"), and because of the way this hybrid tapered line is configured within the box, not all of the box's volume is utitlized in the line (but it does create a neat area for mounting the crossover). Anyway from this modeling I've attached the same two response graphs that I did for the ML-TL modeling above for comparison. F3 and F6 are both 1-2 Hz higher than for the ML-TL and it's fairly easy to notice the detailed differences in the response curves. So it boils down to how big a cabinet one is willing to build and whether one is concerned about a particular configuration being called a TL or just a heavily stuffed vented system.
Paul

[ThomasW]

Bumping this up to attach a TQWP spreadsheet