Any theoretical or sonic advantage to a sealed versus T-line enclosure??

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Just curious for the hardcore experts here. Besides *size* is there any advantage either sonically or in "theory" that a sealed sysem (infinite baffle) beats a TL in the 100Hz-20Hz range??????

Not looking to start a war either way, just asking for either "scientific" or "subjective" thoughts.......

Thanks!
 
If your really talking infinite baffle this will be better quality wize but you will need more displacement to get down as low as a port assisted TL.

If your talking regular sealed compared to TL then i'm wondering the same thing actually.

With a TL you will always have two outputs (driver and port ) firing into the room. It will always have an overlap frequency wise which you may or may not hear.

Ive had a large TL to listen to a few years ago for about a week and it was amazing ( my hearing has improved much since then though so i cant say i can back it up presently.. :) )

TL also has the benefit of improving the midrange because the rear waves are "transported away from the driver" so i suspect that this should sound better maybe even with a closed port ? so its really still a sealed system.

Please fill in here guys, we need to know :)

Coolin
 
For sealed, I mean a system that would, say, have a 12" driver in a large 100-150 liter cabinet versus something comparable in a TL enclosure. All I know about sealed system types is this:

There are two types of sealed enclosure systems: the infinite baffle (IB) system and the air suspension (AS) system. The IB system normally uses a large enclosure where the compliance (or "springiness") of the air within the enclosure is greater than the compliance of the driver suspension. The AS system normally uses a small enclosure where the compliance of the air within the enclosure is less than the compliance of the driver's suspension by a factor of 3 or more.

So then most likely a 12"er in that large a cabinet sealed would most likely be an infinite baffle, no?
 
OK then, forget the infinite baffle sealed system aspect, my bad there.

How about regular sealed versus T-line.

Let's say you were in a 2-way debate with someone on the merits of each technology, and you were representing the sealed system. Would you even have a leg to stand on in any aspect of performance over the T-line? Objective or subjective?

Opinions or thoughts from anyone??????

I personally own 1 design of each as "subs" and want to know what others think for fun.
 

GM

Member
Joined 2003
Greets!

The performance goal of a 'classic' TL (i.e. heavily stuffed, or ~aperiodic) is to get a near IB response in a much smaller package, which it does. It also has the potential advantage of lowering the system Q to < the driver's Qts, which an IB can't do enough to be audible. For instance, I've critically damped (Qtc = 0.5) drivers with a Qts as high as 2.45 when the driver was placed at the proper point along the length of the pipe. The trade-off is that it 'sucks the life' out of wide BW drivers, so best IMO to limit this extreme damping to the midbass/LF BW.

Another plus is that it highly damps the Fs impedance peak if properly designed, so its acoustic phase is flatter. If you're willing to accept a higher F3 to get a flatter phase response, then design the pipe based on Fp = Fs/Qts.

When you compare a typical T/S max flat sealed cab to an equivalent Vb TL, it all falls apart though since you will wind up with a higher F3 to get an aneochoic flat response in such a short 'pipe'.

The IB OTOH has theoretically greater gain at the lowest frequencies and requires no stuffing, but unless a wide BW driver is used and/or it has the mechanical displacement and electrical power handling to drive it this low it's a moot point. Last, but not least, a driver wants to 'feel' an equal pressure on both sides of its diaphragm, so this is reason enough IMO for the IB to be the default choice of the two where practical, which for most folks is unfortunately strictly a 'pipe dream'.

GM
 
GM, always using your knowlege for the good :)

If you forget all the numbers and size issues can you say which SOUNDS better and in which way (detail/dynamics etc.)
Same size driver though.

jjkozlow, whats your opinion based on your two subs ?...
There probably too different to really say?
 
Well, I have this Fried TL sub with twin 10" Kef woofers:

http://www.t-linespeakers.org/classics/friedH/fried_H.html

And I have this home brew sealed job (2 of them obviously) with a total of 4 Peerless 10" 850146's:

http://img18.imageshack.us/content.php?page=done&l=img18/7759/grandconcertopic0170do.jpg

Both are "excellent", and I woulda tried to do my home brew as a TL (the monitor on top of it is), but size and the 2 driver look prevailed.

I prefer the midbass slam of the sealed system and the pitch definition of the TL sub as a "general" comment. Not to say there is a lack of pitch definition with the sealed system, quite the contrary, it is great. The TL is about 5-10% "better" in that area to my ears though. Both go down into the low 20's response wise, with the coffin TL flat to 20Hz in my room, but otherwise a wash in extension.

The homebrew is relatively "new" to me, I've had it up and running for about 2 months now. I guess my biggest astonishment is really how good and close it comes to my coffin TL. I thought I would be giving up some performance by going sealed, but, to my amazement the sealed system just about equals it and in midbass, I believe it betters it . Although the Peerless drivers are "newer" by, oh about, 20 years, so I'm sure much of what I'm hearing are the difference between the drivers themselves.

So anyway, I was curious as to what the experts here thought. As a longtime Fried speaker nut, I have been "born and raised" transmission line. I guess the bottom line is there is less difference between the 2 types then what I had previously been "trained" to believe.

Joel
 
Greets!

Best I can anyway. ;)

In the <100 Hz BW they should 'sound' identical for a given driver/alignment/room location, but as I noted, once you move up into the driver's non-pistonic BW the IB will sound more 'open'/'dynamic'/'detailed', though it may not be as 'accurate' as the better damped TL. Most folks appear to prefer the former since some of the signal gets lost in the recording process, but some of us prefer the more highly damped presentation of a low Qt driver or compression horn, so the TL usually gets the nod.

At one time I had ~the best of both, a 300+ ft^3 false wall IB loaded with a 'stereo' matched pair of Altec 15" midbass horn drivers which have a measured 20 Hz Fs/0.16 Qts. They now reside in a pair of highly damped 20 ft^3 corner loaded ML-TL cabs tuned to 16 Hz, and frankly they sound as good to me as the IB, but with the bonus of more gain, so as always YMMV. :)

GM
 
jjkozlow, this sounds about like i would have expected. You are comparing two TL drivers to 4 Sealed drivers though if i understand correctly though..

Like i said earlier the port of your TL is partly out of phase with the driver which messes with the sound. Your dual TL's only complicate this even more. Mabey you could close the ends off and make them sealed a see how they sound. I'd like to know what you think about it this way.

GM, Thats good to know. You do need big boxes to get this quality sound though.

Ive also noticed the tighter (beter damped) your drivers are the the worse alot of recordings get because of the lack of added colorations.
Too bad the recording guys dont all have quality speakers....
I think in 20 years time it will have improved a bit :(
 
Like i said earlier the port of your TL is partly out of phase with the driver which messes with the sound. Your dual TL's only complicate this even more. Mabey you could close the ends off and make them sealed a see how they sound. I'd like to know what you think about it this way.

You lost me there coolin. How is my port partly out of phase with my driver in the coffin? Here is an internal view of it:

http://www.t-linespeakers.org/classics/coffin/index.html

Just curious....
 
The port output will always be delayed compared to the direct radiating driver. The levels of each will vary depending on freqency but with an overlap in the low end.
A regular sealed sub does not have this "disadvantige"

I have read that not everyone is sensitive to this kind of "distortion" so test it for yourself.

If tuned low enough its probably not audible.
 
Gotcha. Not noticable with this TL sub. Anyway, you are correct, 4 drivers sealed versus 2 drivers in a TL in 2 different rooms, different equipment, etc. Comparing apples to oranges.....

BUT

I will say this for the plain old "sealed" supporters---the overall difference is not what I was led to believe previously between sealed and the TL designs. They are very close in absolute terms in all measured performance. That the sealed enclosure was much "easier" to design and build, I just find it interesting. YMMV.......
 
Over the years of reading various comments (on boards like this) and studies (including multiple articles in Speaker Building and "now" Audio Express), and listening to other's designs (comercial and non-comercial) as well as my own I've come to these conclusions:

1. As GM has noted, practically speaking TL's can be grouped into two distinctly different categories -

A. Pure Sub TL's (i.e. less than 40 Hz), these are pretty rare.. and I don't think I've ever seen a comercial version of one (that wasn't at least incorporated with a speaker).. even the pro stuff typically extends higher than 40 Hz.

B. Designs that are not in category "A" above. Most of these designs are not true TL's - and again as GM noted when the driver utilizes a TL (or a quasi-TL) AND extends higher in freq. from the bass (32 Hz up to 80 Hz) into the midrange (80 Hz and up) audio quality in the upper bass and lower mid's through the middle of the midrange often suffer. In most cases though I do dispute the notion that the TL is portraying a more "accurate" response in this region.

OK then, why the difference?

I think its due primarly to air flow resistance (not simply a system dampening effect which can be acomplished electrically to highlight the audible difference - though it is somewhat similar in sound). In otherwords the fundamental of the music is grossly distorted in TIME when the driver's diaphram is essentially "slogging through" the music it is trying to reproduce. The rise time will be effected to an extent, but more importantly the decay will be so "foreshortened" as to, (as GM and others including myself have stated), "suck the life out of the driver". Considering rise, decay, and rise again (or a dynamic model), the airflow resistance is cutting out decay to get to the next rise.. sort of an acoustic version of signal clipping. Conversly, soley system wide dampening is audibly more "uniform" in its effect. Note though that all of this is driver bandwidth, excursion/sd, mass, and force related. For instance IF the driver is operating higher in bandwith while also required to reproduce low freq.s and has a smaller surface area - then it typically has higher excursion levels, increased mass, and lower eff........................................................................................................all of which will limit the drivers capability to even produce a realistic decay (so with many drivers it could be a reduced or even moot point).

(Remember though that a TL does not require stuffing, its just that virtually all are created with it for various reasons depending on the design.)

Note that even with a true Infinite Baffle BOX (10 X Vas) that utilzes stuffing to achieve an increase in volume has this same "life sucking" sound depending on how much is used and where it is placed in the box.

Naysayers might contend that this is incorrect by looking at a traditional CSD plot (a favorite of mine BTW), typically by showing that the CSD is much "cleaner" in the respective freq. region for a "quality" TL design over a non-stuffed IB (or sealed). The problem is that this type of measurement and graphical display is not dynamic (whereas music is), and as a result will not show this gross distortion.

Remember though that I did put a qualifier, ("In most cases though"), on the question of accuracy of one desing over another. The most obvious from reading the above would be IF the other designs (IB, sealed, etc.) utilized stuffing that would effect air flow resistance, OR conversly if a TL could be made that significantly reduced this problem. But there is of course a LOT more to it than that.

First of all I don't think I've ever heard a true IB speaker that extended into the bass region (or have even seen a comercial one produced that provided acceptable output in the bass region). In fact the only designs I've seen that were true IB's extending in this region are DIY subs that are built into a home and "ported" into a large attic space or simply to the exterior of the home. Even a design that proported to be an IB in Audio Express was in fact a cardoid design that relied on stuffing. (..sure it was aproximating a IB higher in freq. but it wasn't a real IB.) So practically speaking this leaves us with quasi IB's that are really larger sealed boxes that still have at least some character of the "air spring effect". We can of course reduce this effect to some extent with a closed labyrinth design or an aperiodic design.

Now the closed labyrinth ("snail" design) still has problems with considerable pressure based "air spring" generated back emf and the myriad of distortions it creates along the "signal chain". In otherwords it does little to reduce overall box pressure, but it does reduce pressure near the driver to an extent - and more importantly it also reduces dynamically related pressure that would interfere with higher freq.s (i.e. the back pressure is more "averaged", "normalized", "steady", "constant" (etc.) and does not effect the upper freq. response of the driver as much.)

Conversly the aperiodic enclosure significantly reduceds this back emf by reducing the box air pressure, but not enough in a typical design that it doesn't interfere with the lower excursion potential of higher bandwidths that the driver might be used for (i.e. a bass driver that operates into the midrange). In otherwords though the aperiodic enclosure does reduce back pressure which ultimatly effects excursion, it rarely is enough to NOT interfere with driver excursion at higher freq.s because those higher freq.s rely on comparitivly small excursion levels which are more easily altered due to back pressure. (and again in a normal aperiodic box the back pressure is NOT "averaged" and is effectivly dynamically "related" which is more "distortive".)

(BTW, this is why B&W use a combination of these designs in their most impressive technical products - i.e. the Nautilus. Though they still have the problem of system-wide back emf because none of their bass designs utilize an aperiodic design, a serious oversight IMO.)

So Then..

With most domestically acceptable IB's that are NOT STUFFED you will sonically experience detrimental effects due to:

1. Increased system-wide back emf because of some box pressure.
2. Increased dynamically related distortion due to non-averaged back pressure as freq.s increase.

In contrast true TL's will have a greater reduction with both categories. Practically speaking though an IB that has an aperiodic "vent" can actually surpass a TL with respect to system wide back emf, AND this design feature is very easy to add to the "box". As to problem numer 2.. well an IB with a closed labyrinth is more difficult to construct than a true TL. (practically speaking though most TL's are not "true" TL's with a constant cross section.. i.e. most have a decreasing crosssectional line (i.e. "tappered") which has the same construction difficulty as a closed labyrinth.)

Of course all of the above concerns less commonly appreciated aspects of the differing desings.
 
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MJK said:


I don't understand. What is a true TL and what is not a true TL?


;)

methinks you would provide a far better explanation then I.

In this case though my use of the word "true" would be related to line length and driver resonance with a line diameter similar to that of the driver (tapered or not.. though I thought that the genesis for this design was specifically a constant cross-section, prob. mistaken though).

Of course this isn't to state that other designs utilizing an open line are not transmission lines, but rather not as transmission lines in the traditional sense within the context of loudspeakers.. In fact under the traditional sense I don't think that your tappered and port "aligned" line exactly meets the common notion either, but thats not to say that it isn't better.

In any event, I'm not sure that the use of the modifier "true" really has any significant bearing on what I wrote. I'm sorry if it was a stumbling block to comprehension, it wasn't intended.. (my writing can be obtuse at times):rolleyes:
 
In this case though my use of the word "true" would be related to line length and driver resonance with a line diameter similar to that of the driver (tapered or not.. though I thought that the genesis for this design was specifically a constant cross-section, prob. mistaken though).

Ok I understand your definition, I use the word "classic" to denote a TL that uses strictly a 1/4 wavelength standing wave to augment the bass of the driver. This could be straight, tapered, or expanding geometry(although expanding starts down the road of TQWTs and eventually ends up as horns). I think most of the original commercial TL designs were tapered to make the box smaller. I have not seen many commercial designs that use a straight line geometry

Of course this isn't to state that other designs utilizing an open line are not transmission lines, but rather not as transmission lines in the traditional sense within the context of loudspeakers.. In fact under the traditional sense I don't think that your tappered and port "aligned" line exactly meets the common notion either, but thats not to say that it isn't better.

I can't argue with you on these points. I gave up trying to strictly classify TL designs and now just refer to the entire spectrum as quarter wavelength designs. This includes "true" or "classic" designs, TQWT's, ML styles, and horns. The definition differences can be very subtle. When I first atrted in TL theory I used to generate some heated arguements over the definitions of TL's and in the end there was always disagreement resulting in a lot of wasted time and energy.

But to get back to the original topic, I think that a particular driver can be used to its best advantage in a sealed design or a TL design but probably not both. If you go back and look at the arguements for and against acoustic suspension vs bass reflex (and subsitute TL for bass reflex) I think most of the same pros and cons exist. A TL may be a little better damped, due to the fibers, then a bass reflex producing tighter bass and better transients. In my opinion, bass reflex and TL's have a lot more in common then most TL purists would like to admit.
 
MJK said:


But to get back to the original topic, I think that a particular driver can be used to its best advantage in a sealed design or a TL design but probably not both. If you go back and look at the arguements for and against acoustic suspension vs bass reflex (and subsitute TL for bass reflex) I think most of the same pros and cons exist. A TL may be a little better damped, due to the fibers, then a bass reflex producing tighter bass and better transients. In my opinion, bass reflex and TL's have a lot more in common then most TL purists would like to admit.

I find myself both agreeing and disagreeing here..(strange).

I agree that some driver parameters are better suited to TL's to achieve increased output lower in freq., but I don't think freq. extension is the only reason for utilizing a TL.

In otherwords even a driver with a qts of .15 could benefit from TL over another loading scheme for reasons having nothing to due with extending the freq. response over another design. I find this is particularly true with carefull placement of stuffing or a complete lack of it (..provided higher freq.s can be attenuated from the line through other means). As for the reasons, IMO pretty much what I wrote originally (though I neglected to mention the increase in cabinet bracing which is a usefull by-product of the TL). Perhaps its a bit of an oversimplification, but I find TL's to be usefull with energy storage problems that other designs (even domestically acceptable "normal" IB's) cannot offer.
 
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