TL vs Overdamped BR - Opinions?

dnewma04 said:
For all intents and purposes BR and PR are one in the same.
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Only for small signals.

"What is a small signal?" "Well, that's where the linear model applies." "Oh, OK. What's the linear model?" "That's a dynamic approximation built up from the small signal parameters."

-k
 
dnewma04 said:
If I were to guess, I'd say that sreten's were more based on your criticism of other enclosure types. There are plenty of very natural ported enclosures just like there are natural and detailed TLs, AS, aperiodic, etc. I've heard a lot of TLs and some of them have been very impressive but none have convinced me they are the best option.
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FWIW:

In the process of designing some TL's, I read much the seminal work, talked to Martin, Fried and others. I'm still not convinced anyone has a clear idea of how TL's work, why they should have any advantage, or why they should even be called, "transmission lines." In this kind of situation, everything falls on the skills and ear of the designer, which leads to a wide variety of final results.

-k
 
Ken I would assume that you are well aware of the different design parameters.. I have followed the research and broke down the design parameters by the formulas I found from the common denominators in many commercial designs. Besides the proven testing methods which are found through discovery which becomes evidence by the results. No one can prove each persons hearing perception. All an audiologist can prove is a hearing test by an audiogram interpretation. Listening to the same drivers in differnt types of cabinet loading and testing the response is what it comes down to in the proof of evidence. I would also like to know what sreten is referring to in articles HN and RR by the way.
 
Sure, I am aware of the design parameters and commonly accepted formulas. I don't want to play grump here. I've heard some very fine TL's, although none that categorically outperformed other approaches. Properly designed transmission lines readily hold their own among the options available.

I jumped in here to try and explain Tom's comment about substantial inconsistencies in the performance of serious TL offerings, an observation with which I agree. To me, this suggests that at least some key behaviors remain unmodelled, which in turn leads to greater design improvisation as compared to the more comprehensively understood approaches.

Finally, a few rhetorical questions:

-how does TL tuning and damping vary as a function of signal level?

-what are the acoustical and perceptual effects of a residual, comb-filtered and delayed rear wave being injected into the listening room?

- Acoustically, what theoretical advantage does a TL offer over an infinite baffle?

- What characteristics of a driver particularly optimizes it for use in a TL?

- Sure, it's a cool name, but has there been even one loudspeaker in all of history that actually meets the definition of a "transmission line"? Any that even come close?


-k (this last one is not really a question)
 
This is just opinion- but I've always been prone to go with something I can readily calculate (or at least know most of the parameters I'm working with), than something with variables that are at best, sort of hit-and-miss.

This is why I tend to use vented/reflex or PR alignments, or horns, and not transmission lines. The math is much more precise and predictable. Last thing you want, is to put a ton of work into building something, and have it NOT work. At least with a vented box, it's much easier to re-tune (and to tell HOW to re-tune) if it's not perfect "out of the box", so to speak...

Also, I've always been wary of the comb-filter/time delay/interference related issues regarding integrating the output of a TL or rear-horn, with the front output of a driver. Sure, a reflex box also has SOME delay- but MUCH less than a long horn or TL. The errors in both frequency response (comb filtering) and time response (group delay and such) due to the travel time within the chamber, are daunting for TLs and rear-horns, IMHO...

Regards,
Gordon.
 
Some of the theoretical advantages over infinite baffle a I have stated in earlier posts. The lower frequencies exiting line terminus do make them an expanding sound source unlike other types of enclosures. Drivers with low Qts. and large Vas out perform others being highly compliant. I have had many people that are so called experts on another forum claim there is no time delay from the sound leaving line terminus. A reverb if if only so slight by miiliseconds must occur in the delay. The use of damping material flattens the signal level response like a closed box Q of .7 . It still comes down to each drivers frequncy response and impedance curve. There is a reason some drivers used as subwoofers are crossed over as low as 100 hz due to impedance peaks at higher frequencies. The amplifier also sees a more resistive load .
 
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Hannibal.
GordonW makes some good points.
As mentioned ealier, if your are trying to make a AMT3 clone, or a 3-way Heil speaker I would either clone the cabinet dimensions etc of the AMT3- (perhaps increase it from 2.5 cuft bare to 2.7 cu ft) axe the port and used a sealed enclosure. Add 3 lbs of acostistuff per cab, fill the mid enclosure, and your good to go!
Use the 1040'SFs and Alpha 6A's. Or find yourself a AMT Tower with the transmission line-use a AMT3 crossover and add a midbox between the Heil and the main cabinet.
Each will give you the transient response that will match up well with the AMT Heil. The 1040SF's really shine when sealed in the AMT3 cabinet, and would highly recommend it to any one that has them in a ported AMT3 cabinet, as they are just palin outstanding!:music:
Spend the money you save on a nice amp with enough power to do the speaker justice.
Or perhaps you could adapt a Madisound kit, they aren't cheap though.
 
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In a closed box the listener does not hear the back wave of the cone except in the form of distortion, time smear, cone reflections back and forth. I would rather hear a reverb from line terminus then distortion. The sound from the back wave of the cone is trapped inside the box. No damping material will eliminate this completely, foam wool, fiberglass etc.
 
@ken kantor:___________________________________________________
- What characteristics of a driver particularly optimizes it for use in a TL?
*
That is an interesting quest, wait, never mind, I see sm19422 is already on it.
Jeez, I can't type fast enough. :smoke:

@automojo:____________________________________________________
"...axe the port and used a sealed enclosure. Add 3 lbs of acostistuff per cab, fill the mid enclosure, and your good to go!"
*
'Mojo, I may end up trying that, but I usually don't like a sealed box sound,
it rarely appeals to me. After decades of working clubs and concert venues,
I'm burned out on certain types of bass sound in the same way I'm
burned out on horn-loaded anything. Now the idea of cloning the AMT Tower
has a lot of appeal. Better yet if I could just drop a 1040 into it and
have it work without too much tweaking. Which kind of relates to my
question below. Oh, for amps BTW, trust me I'm already covered.

Now if anyone can school a T&S noob about what, aside from Mms, are the
best predictors of cone driver "speed", I'd be much obliged. I need something
pretty zippy to keep up with a Heil. I can use the Eminence 1040 SF, but there
may be a proven design already out there built around some other driver that
can save me grinding through a lot of extra R&D - BUT it would have to be a driver
that's lively enough to match well with a Heil AND be able to reach down to 30Hz
or so like the Eminence can. So if anyone knows of such a design, or how to search
for one based on T&S parameters that promise good speed in the driver involved,
that would be sweet. Many thanks to all who are chiming in with all this
good information.
 
hannibal said:
@ken kantor:___________________________________________________
- What characteristics of a driver particularly optimizes it for use in a TL?
*
That is an interesting quest, wait, never mind, I see sm19422 is already on it.
Jeez, I can't type fast enough. :smoke:

@automojo:____________________________________________________
"...axe the port and used a sealed enclosure. Add 3 lbs of acostistuff per cab, fill the mid enclosure, and your good to go!"
*
'Mojo, I may end up trying that, but I usually don't like a sealed box sound,
it rarely appeals to me. After decades of working clubs and concert venues,
I'm burned out on certain types of bass sound in the same way I'm
burned out on horn-loaded anything. Now the idea of cloning the AMT Tower
has a lot of appeal. Better yet if I could just drop a 1040 into it and
have it work without too much tweaking. Which kind of relates to my
question below. Oh, for amps BTW, trust me I'm already covered.

Now if anyone can school a T&S noob about what, aside from Mms, are the
best predictors of cone driver "speed", I'd be much obliged. I need something
pretty zippy to keep up with a Heil. I can use the Eminence 1040 SF, but there
may be a proven design already out there built around some other driver that
can save me grinding through a lot of extra R&D - BUT it would have to be a driver
that's lively enough to match well with a Heil AND be able to reach down to 30Hz
or so like the Eminence can. So if anyone knows of such a design, or how to search
for one based on T&S parameters that promise good speed in the driver involved,
that would be sweet. Many thanks to all who are chiming in with all this
good information.
Click to expand...

Sure-I understand.
I can give you the parimeters. With twin 10" 1040's you are looking around 5+ cu feet.
 
sm19422 said:
In a closed box the listener does not hear the back wave of the cone except in the form of distortion, time smear, cone reflections back and forth. I would rather hear a reverb from line terminus then distortion. The sound from the back wave of the cone is trapped inside the box. No damping material will eliminate this completely, foam wool, fiberglass etc.
Click to expand...

I totally agree. A well designed ported or TL enclosure will usually out perform a sealed enclosure in those parimeters.
The key is well designed. And in this respect my taste is a bit on the opposite side to yours, as I feel most lower cost vented speakers seem more full in the bass then detailed in sound, a sound I don't really prefer. Same with some poorly designed TL's I have heard-which may have, and looked to possibly be home made, or modified, over dampned etc.
There are exceptions of course, as it's hard to generalize with speakers because there are always ones that will surprise you.
This may be a compromise in my AMT3 case, but it sounds good, very musical and detailed, and matches up with the Heil, and is non fatiguing to listen to. They way it "pressurizes" the listening space, similiar, to a lesser extent of course, as the Heil.
To me that's more important then ultimatley reducing certain types of distortions, as all speakers have those to a point anyway.
Detail dynamics and musicality are perhaps more important to me, but of course your taste may vary, as it's a flavor thing anyway- as much of audio is.
Zlich's LA Econowave also sounds pretty good to me for a 2-way horn speaker-with a few minor adjustments. I always liked the bass of the Large Advent, but hated the tweeter. IMHO Zilch found a good, fairly inexpensive way to harness this Advent quality.
The 1040's are more detailed and have more output, and can handle power and higher levels then the single Advent woofer.
As far as damping, in theory a well designed speaker and cabinet shouldn't require damping material., or perhaps a minimal amount seems more realistic.
But it can give you the chance to tune the response of the speaker to your taste/goals, help smooth out some peaks etc.
Regardless I find it fun and entertaining to play around with serveral configurations/ damping etc and see the results you come up with.
I don't think there is any right or wrong here. There are very nice speakers, sealed and vented, some with damping and some without , some with large amounts, some with a minimum amount, that sound very good.
 
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@automojo:_____________________________________
"With twin 10" 1040's you are looking around 5+ cu feet. "
*
I want to make sure we're on the same page here. That's a good volume
for a TL cab for those drivers is what you're saying?

I think I may have goofed in my last:

"...there may be a proven design already out there built around some other driver
that can save me grinding through a lot of extra R&D - ..."

...I'd meant to say "proven design" - of a TL cab specifically.
Hope I didn't muddle things too much for everyone by not
phrasing myself more clearly.
 
No-that volume is for a ported enclosure with 2 1040SF in the same cavity. You would have to crunch the numbers for a TL
Madisound has a TL kit. You would have to use their bass driver, but I don't see a reason why you couldn't modify the upper end to incorporate the Heil.
Using the transition driver/mid would complicate things.
You may able to get by with just the two drivers-similiar to the tower.
Idealy the Great Heil works best with a transition driver, but the smaller woofer would minimize problems. The small Heil 2-ways with 6-8 inch woofer have little problems integrating with the Heil.
 
One nice thing about building your enclosures is being able to choose the thickness of wood. I have a Sears table saw. It required building tables just to support the one inch thick wood in order to rip it. Automojo stated the correct phrase well designed. Over stuffed lines response curve would be that of a closed box using a a very low box Q. Under damped enclosures will sound boomy. In my opinion one of the very musical ported designs are the 2 way Totem Columns. The Yahoo t-line group founder uses PA drivers in his t-lines. He is very happy to give members of his group advice. Being a teacher its in his nature to educate. This might be of interest to Hannibal after working decades in clubs and concert venues. My son is a bands tour manager [ TEXAS IN JULY] and sound engineer that has been exposed to PA systems all over the country and Europe. He has yet to see any that use t-lines. The size is a limiting factor for their use. Taper ratio, stuffing density, terminus area, line length, driver selection. Commercial designers spend a considerable amount of time perfecting their designs. It is a fun and rewarding hobby. Enjoying the music is the end result.
 
Tom Brennan said:
What is an expanding sound source? What are the benefits of one?
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Great question. I read the links hoping to find an answer without much luck. A google search only finds this thread. I've built 4 TLs since 1990 or so and it's the first time I've run across this terminology.

According to one of the links:

"The C/3-L retains the ideal front dimensions and rounded edges of the
C/3, the pyramidal shape that is nature' S "expanding sound source". A
folded, quarter ‘wave length line is added to the rear, terminating at the
top. The enclosure is now deep at the bottom, and 1235" deep at the top."

So, a pyramidal shape is an expanding sound source. Seems rather unsubstantial.
 
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Hey 'Mojo,
I see I could in fact have phrased myself better.
But it's good to have that 5 cubes for a design basis if I do decide to
go conventional BR.

"You may able to get by with just the two drivers-similiar to the tower.
Idealy the Great Heil works best with a transition driver, but the smaller
woofer would minimize problems."
*
Dave Dlugos AKA Planet 10, often to be seen at DIYA, did something like
that with a pair of 9" Fostex, push-push, in a TL that looks an awful lot like an
AMT 3 Tower clone. He said he liked it better than an AMT 1 he'd
shoehorned an Eminence Alpha 6A (IIRC) into, so yeah it can be done.
Fostex seems to have followers that see them as really fast. I looked at
a bunch of them and kept seeing some pretty heavy Mms on them. That's
another thing that has me wondering what I might still need to learn
in evaluating the speed of a driver via it's T&S parameters.
Myself, I don't want to go to all the trouble of building a TL (or any) cab
with an undersized driver and then STILL have to bring a sub to the poker game.
Odds are I'm going to go 3-way no matter what. Not necessarily,
but odds are.
 
The pyramid shape is used for imaging,diffraction, time alignment. Fried uses the term expanding sound source , enormous acoustic gain. There is a lot of info to read . Hard to keep track of where everything is on the IMF site. Some info was removed on the site as I earlier posted. Where the lowest frequencies exit line terminus on the subwoofer the sound expands due to the size of the wavelengths.


http://f1.grp.yahoofs.com/v1/oCgzTw...BKsLyStfcfug_0t8/Fried Studio V brochures.pdf
 
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