First 2-way (T-Line)

[BoyQott]

Hello,

I've designed my very first two way. but I want to ask you a couple just-to-be-sure questions before I buy the components and build the speaker.

first some info:
- it is a 2-way, TMM
- M: Midrange woofer "Visaton W 130 S - 8 ohm"
- T: Dome tweeter "Visaton SC 10 N - 8 ohm"
- Crossover: 3000 Hz at 12 dB / Oct

One woofer is a vented box tuned to 44 Hz
One woofer is a T-Line.
- T-Line is approx 26L -> woofer gives 65Hz
- T-Line is approx 1.3m -> 1/4 wave gives 66Hz
- T-Line starts at 111mm, next bend is 90mm, next 80mm, 70, 60, & 50. (easier to build)

Questions:
1. The T-Line is tapered, but in not smoothly, so every bend makes the line smaller. Is this okay?
2. The woofers are rated at 50W, the tweeter at 100W and the crossover at 100W. Can these components work together? How strong amp do I need?
3. Am I forgetting something important? Will this (probably) work?

Thanks in advance!
I hope that I'm understandable with the questions. I'm kinda new to this.

 

[pkitt]

Yes, you can create a smoothly tapered line in effect by using multiple segments, each with a smaller area than the preceding segment. The more segments you have, the more it will emulate the performance of a smoothly tapered line with the same taper ratio. That said, you show the actual length of the line to be ~51" and that, indeed, would create a 66 Hz 1/4-wave resonant frequency, but only if the line was not tapered, having the same area along its whole length. Your line is tapered at a bit more than 2:1, which will makes its effective length be ~59" and create a 1/4-wave resonance of 57 Hz. That may or may not be appropriate for your woofer's Fs and Qts, however. What are those values and are they published values or actual measured values?
Paul

Hello,

I've designed my very first two way. but I want to ask you a couple just-to-be-sure questions before I buy the components and build the speaker.

first some info:
- it is a 2-way, TMM
- M: Midrange woofer "Visaton W 130 S - 8 ohm"
- T: Dome tweeter "Visaton SC 10 N - 8 ohm"
- Crossover: 3000 Hz at 12 dB / Oct

One woofer is a vented box tuned to 44 Hz
One woofer is a T-Line.
- T-Line is approx 26L -> woofer gives 65Hz
- T-Line is approx 1.3m -> 1/4 wave gives 66Hz
- T-Line starts at 111mm, next bend is 90mm, next 80mm, 70, 60, & 50. (easier to build)

Questions:
1. The T-Line is tapered, but in not smoothly, so every bend makes the line smaller. Is this okay?
2. The woofers are rated at 50W, the tweeter at 100W and the crossover at 100W. Can these components work together? How strong amp do I need?
3. Am I forgetting something important? Will this (probably) work?

Thanks in advance!
I hope that I'm understandable with the questions. I'm kinda new to this.

 

[BoyQott]

Yes, you can create a smoothly tapered line in effect by using multiple segments, each with a smaller area than the preceding segment. The more segments you have, the more it will emulate the performance of a smoothly tapered line with the same taper ratio. That said, you show the actual length of the line to be ~51" and that, indeed, would create a 66 Hz 1/4-wave resonant frequency, but only if the line was not tapered, having the same area along its whole length. Your line is tapered at a bit more than 2:1, which will makes its effective length be ~59" and create a 1/4-wave resonance of 57 Hz. That may or may not be appropriate for your woofer's Fs and Qts, however. What are those values and are they published values or actual measured values?
Paul

So, you are saying that making the line smaller in segments is fine?
But that the line should be shorter? (btw, how does that work? calculating the 1/4 wave freq of a tapered line?

Woofer Fs = 52 Hz
in speaker approx 65 Hz
Qts = 0,47
the Fs and Qts are data from the website.

Thanks!

 

[pkitt]

Yes, just as I said, you can make a "tapered" line using multiple segments with each succeeding segment have a constant but smaller area than the preceding segment. I've done it and got very good results with 7 segments.

When a line has an area that decreases as you go from the closed end of the line to the open end of the line, the tapering has two effects. One, it makes the line's effective length longer than its actual length and, two, it reduces the magnitude of the response ripples that naturally occur at the odd harmonics of the line's 1/4-wave resonance. The larger the taper ratio, the shorter the line needs to be for a specific 1/4-wave resonant frequency, and the more the response ripples are reduced in amplitude. It's just plain physics and acoustics.

Using the published Fs and Qts for your woofers, I estimate the line's 1/4-wave resonant frequency needs to be on the order of 45-47 Hz (because Qts is higher than 0.4) in order to achieve a flat response from the knee in the response curve on up. For instance, using 46 Hz as the desired 1/4-wave frequency, a non-tapered line would need to be ~74" long, and if tapered at 2:1, ~55" long. I can't determine, however, the exact optimum frequency without modeling the line with a number of the other T/S values along with Fs and Qts.

For a desired 1/4-wave resonant frequency, you can calculate the required length for a non-tapered line just as you apparently did. Then, for it to be tapered, here are some line length multipliers to apply: Tapered 2:1, multiply by 0.866; tapered at 4:1, multiply by 0.75, tapered at 7:1, multiply by 0.663; and, tapered at 10:1, multiply by 0.615. I almost never use a taper ratio of less than 10:1, and have also effectively used 16:1 and 25:1.
Paul

So, you are saying that making the line smaller in segments is fine?
But that the line should be shorter? (btw, how does that work? calculating the 1/4 wave freq of a tapered line?

Woofer Fs = 52 Hz
in speaker approx 65 Hz
Qts = 0,47
the Fs and Qts are data from the website.

Thanks!

 

[pkitt]

I looked at all of the T/S values for your woofer on Visaton's site, then did a quicky 2:1 tapered TL model for it which shows a 1/4-wavelength resonant line frequency of ~41 Hz to be optimum. I used a starting line area of 36in2 (6" x 6") with an ending line area and exit area of 18in2 (6" x 3") in a line length of 60". This gave an F3 of just over 50 Hz but with a taper of just 2:1, the response was unacceptably lumpy to say the least. Changing the taper ratio to 8:1, with a starting area of 6" x 8" and an ending area/exit of 6" x 1" in a line length of 45" gives the same 1/4-wave resonance and F3 but with a far smoother response (not a smooth as I would prefer for a personal build but still okay). In both models the first 2/3 if the line was stuffed with polyester fiber at a density of 0.75 lb/ft3. Again, this was a couple of quicky modelings and used the published specs which may not be appropriate.
Paul