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Old 21st June 2012, 09:07 PM   #11
pkitt is offline pkitt  United States
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If a tapered TL has a single impedance peak like you illustrated, it's had the life literally stuffed out of it with the result of absolutely no contribution from the terminus' output to the bass response. If you're going to do that, you might as well just make a big sealed box rather than wasting your time building a complex tapered line.
Paul

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Originally Posted by RockLeeEV View Post
Hmm? While ther are different ways to tune, as far as I can tell a Tapered TL should have an almost entirely damped lower impedance peak:

Click the image to open in full size.

resulting in a shallow knee response profile like this:

Click the image to open in full size.

An ML-TL will have a dual impedance peak
Click the image to open in full size.

resulting in a more efficient, but sharper knee response profile like this:

Click the image to open in full size.

The different between the two alignments results in a different amount of overlap between the terminus' and driver. The Tapered TL will have an excursion profile like this, where the line controls the driver lower in frequency:

Click the image to open in full size.

while the ML-TL will have an excursion profile like this, where the port starts to act against the driver:

Click the image to open in full size.

While I don't want to make claims of what's "right" and "wrong", i think that if the tapered TL (quarter wave) is getting the same response profile as the ML-TL (bass reflex) then you're probably modelling the Tapered TL... unusually.
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Old 21st June 2012, 11:22 PM   #12
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Quote:
Originally Posted by pkitt View Post
If a tapered TL has a single impedance peak like you illustrated, it's had the life literally stuffed out of it with the result of absolutely no contribution from the terminus' output to the bass response.
the model still shows 3db of lift over a wide bandwidth. The F3 compared to a sealed box of the same size goes from 90hz to 52hz, and the F10 also drops slightly from ~33hz to ~30hz. The stuffed line still shows reduced excursion near its tuning.

Beyond that, the more shallow rolloff can sound better in some rooms and placements vs a flat ML-TL, due to room modes and pressure vessel gain causing peaking in the 20hz to 50hz region, which is a big factor in slow perceived bass.

If you ask me, bothering with any kind of resonator - line or port or passive radiator - is a waste of time. Use 3 or 4 carefully placed, small, equalized multiple sealed 15" subs for accurate bass in real rooms below 100hz. Go dipole or cardioid above 100hz.

Last edited by RockLeeEV; 21st June 2012 at 11:40 PM.
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Old 21st June 2012, 11:28 PM   #13
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by RockLeeEV View Post
Hmm? While ther are different ways to tune, as far as I can tell a Tapered
TL should have an almost entirely damped lower impedance peak:
Hi,

No it doesn't. It has the same double peaks at lower stuffing densities.
It has to have double peaks for the line output to be significantly useful.

rgds, sreten.
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Old 22nd June 2012, 08:27 AM   #14
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I must give credits to Paul ( thanks ) for having inspired me to build
my first tapered TL . It was a lot of work , about two years ago , and the speakers are still in my room , so it mustn't be that bad
I didn't put any stuffing inside
but much use of constrained layers damping ...and when I found a pair
of rotten Altec Mod.300 and repaired the foam , those gray woofers
really match the vinyl gray finish I adopted

Tony
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Old 22nd June 2012, 10:52 AM   #15
cs is offline cs  United Kingdom
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Quote:
Originally Posted by RockLeeEV View Post
While I don't want to make claims of what's "right" and "wrong", i think that if the tapered TL (quarter wave) is getting the same response profile as the ML-TL (bass reflex) then you're probably modelling the Tapered TL... unusually.
Hi,

In my modelling, the MLTL was uniformly stuffed at 0.5 lb/cu ft, but the TL was only stuffed in the first half (from driver end) of the line at 1 lb/cu ft. The second half of the TL was left empty. I used a 5:1 taper, starting at 3.4*Sd and ending at 0.68*Sd. The driver was a 6.5" poly-coned unit from HiVi, although that may not be my final choice.

The attached plots show freq resp, impedance and cone excursion for each configuration. If I stuffed the whole of the TL, then the plots were very similar to yours, with very little bass reinforcement.

Chris.
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File Type: jpg MLTL plots.jpg (63.1 KB, 42 views)
File Type: jpg TL plots.jpg (61.3 KB, 37 views)
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Old 22nd June 2012, 01:26 PM   #16
pkitt is offline pkitt  United States
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What I've found to be almost always the best stuffing configuration for the best overall system response coupled with optimum port/terminus air velocities and driver excursion considerations, is this: In an ML-TL only the first 50% of the line's length contains stuffing, while in a tapered TL it's typically the first 60-67% that's stuffed. If stuffing is added beyond those lengths, the detriment to F3 is usually too severe for whatever is gained anywhere else. Increasing the stuffing density, however, for the lengths I mentioned will provide improvements in response smoothness with a much smaller detriment to F3. Just a whiff of stuffing in the terminus of a tapered TL will completely kill its output. In a tapered TL I will use a larger taper ratio before increasing stuffing density or length because the larger taper also minimizes response ripples (I never use a taper ratio smaller than 10:1).
Paul

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Originally Posted by cs View Post
Hi,

In my modelling, the MLTL was uniformly stuffed at 0.5 lb/cu ft, but the TL was only stuffed in the first half (from driver end) of the line at 1 lb/cu ft. The second half of the TL was left empty. I used a 5:1 taper, starting at 3.4*Sd and ending at 0.68*Sd. The driver was a 6.5" poly-coned unit from HiVi, although that may not be my final choice.

The attached plots show freq resp, impedance and cone excursion for each configuration. If I stuffed the whole of the TL, then the plots were very similar to yours, with very little bass reinforcement.

Chris.
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Old 22nd June 2012, 01:35 PM   #17
pkitt is offline pkitt  United States
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I agree with you on one point; I would never recommend a TL of any kind for strictly subwoofer use, which is what you're really talking about in your last statement. It's a waste of time, but if someone wants to, that's fine. But since I don't use, want or need a subwoofer, all of my designs are for full-range systems, usually 3-ways. A TL is inherently a 4th-order system and its response shape can be tailored to have 4th-, 3rd- and 2nd-order rolloffs below F3, with obviously different effects on its impedance profile and how much bass contribution is provided by the port or terminus. Since there is very little, if any, content in most music (excluding special effects for movies, for instance) below 30 Hz, much less at 20 Hz, I consider it waste of abilities to force a 2nd-order rolloff because the improvement provided below 30 Hz is wasted, while at the same time, there is less output above 30 Hz where there is actual content to be heard.
Paul

Quote:
Originally Posted by RockLeeEV View Post
the model still shows 3db of lift over a wide bandwidth. The F3 compared to a sealed box of the same size goes from 90hz to 52hz, and the F10 also drops slightly from ~33hz to ~30hz. The stuffed line still shows reduced excursion near its tuning.

Beyond that, the more shallow rolloff can sound better in some rooms and placements vs a flat ML-TL, due to room modes and pressure vessel gain causing peaking in the 20hz to 50hz region, which is a big factor in slow perceived bass.

If you ask me, bothering with any kind of resonator - line or port or passive radiator - is a waste of time. Use 3 or 4 carefully placed, small, equalized multiple sealed 15" subs for accurate bass in real rooms below 100hz. Go dipole or cardioid above 100hz.
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Old 22nd June 2012, 02:42 PM   #18
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interesting. I always wondered what was the difference between a MLTL and pipe shaped Reflex....Im hesitant to say there isnt one, since Im no expert, but It makes me wonder...

How many of those 80's/90's 'tower reflexes' actually stumbled upon MLTL operation.

I used a taper ratio of 20:1 on the basis that in a reflex system the 'rule of thumb' i know is a min vent area of 1/7th Sd, which is what I have used in several reflex designs (eg 5" woofer, 2" ID vent).
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Last edited by mondogenerator; 22nd June 2012 at 02:53 PM.
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Old 22nd June 2012, 02:55 PM   #19
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It's just the air that acts as a 'mass ' that is coupled to the membrane till
a certain frequency , beyond that limit it's too slow to follow the higher cycles .
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Old 22nd June 2012, 03:05 PM   #20
pkitt is offline pkitt  United States
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I'm sure there have been a lot of accidental ML-TLs created over the years, and I'm just as sure most of them will be quite a bit removed from having an optimal performance that can be achieved by proper location of the port. I've used taper ratios from 10:1 to 26:1 with good success.
Paul

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Originally Posted by mondogenerator View Post
interesting. I always wondered what was the difference between a MLTL and pipe shaped Reflex....Im hesitant to say there isnt one, since Im no expert, but It makes me wonder...

How many of those 80's/90's 'tower reflexes' actually stumbled upon MLTL operation.

I used a taper ratio of 20:1 on the basis that in a reflex system the 'rule of thumb' i know is a min vent area of 1/7th Sd, which is what I have used in several reflex designs (eg 5" woofer, 2" ID vent).
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