TL vs vented: transient issues
- Thread starter crazyhub
- Start date
Vented can be designed with good transient response if one designs the low frequency rolloff to be more gradual, like a Bessel function, instead of a sharp knee. In my experience this does take a larger box than other approaches. The trick is to play around in WinISD (or whatever) to get the gradual rolloff.
My intuitive understanding of a TL cabinet design is that it reduces the spill of music streaming out of the porting. Imagine that you stand deep inside of a labyrinth and scream. The person in the door way to the labyrinth will not hear you, but if he has an instrument that measures air pressure he will read a fluctuation in the door way. Music streaming out from a traditional porting pipe is a problem because makes the music experience muddy, ghost sounds.
A closed box design gives a better transience because of the air pressure speeding up the reset of the cone. If you imagine an infinite TL design where the sound "never" reaches the air gap, to the driver the cabinet is closed, which gives better transience. A TL cabinet doesn't need an air gap if the path of the sound is muffled by dressed walls and the volume is big enough to produce the sought roll off of the low bass. That is my understanding.
A closed box design gives a better transience because of the air pressure speeding up the reset of the cone. If you imagine an infinite TL design where the sound "never" reaches the air gap, to the driver the cabinet is closed, which gives better transience. A TL cabinet doesn't need an air gap if the path of the sound is muffled by dressed walls and the volume is big enough to produce the sought roll off of the low bass. That is my understanding.
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Hi Crazyhub,
Here is an interesting review of the differences between the TL and VB --
http://www.linearx.com/files/pdf/EncShopApp_01.pdf
Peter
Here is an interesting review of the differences between the TL and VB --
http://www.linearx.com/files/pdf/EncShopApp_01.pdf
Peter
I think what Planet 10 is saying is that modern TL theory (King and Ausberger(?)) are more complete models that take into account the box shape. BR consider the box to be a perfect Helmholtz radiator, which it is not. TL theory includes the box cross section, its length and degree of stuffing. A BR can be modeled as a TL, the reverse is not true.
TL vs Reflex
A TL can never be as good as a reflex because it requires damping material to quiet the resonant pipe sounds, which drastically reduces efficiency. In addition, once a TL is built, the length of the line cannot be changed to optimize tuning. A TL will rapidly go out of tune as the drivers break in. The only real advantage TL's have is that the enclosure is stiffer due to all the wood required to build the thing.
A TL can never be as good as a reflex because it requires damping material to quiet the resonant pipe sounds, which drastically reduces efficiency. In addition, once a TL is built, the length of the line cannot be changed to optimize tuning. A TL will rapidly go out of tune as the drivers break in. The only real advantage TL's have is that the enclosure is stiffer due to all the wood required to build the thing.
I'll have to disagree totally.
A TL is pretty tolerant of T/S changes. A BR is not, and even thou you can change the tuning as a driver breaks in, that does not deal with the dynamic shifts in T/S caused by the dynamics of the music and how much wick you are giving the system.
dave
I think it is already clear (theoretically and sound-wise) that transient-wise TL sits there between bass reflex and sealed.
I agree that one of the problems of TL is the efficiency. It kills sonic. But most of high end speakers are even worse. It sounds "alive" only when driven by high power high damping amplifiers. So It cannot be said that "TL can never be as good as a reflex" from normal perspective. From my own perspective (where I have always tried very hard to relate every things with "enjoyment factor", e.g. may be it is the group delay issue), I think I'm agree
Intuitively, I think the better one should have port properties that change with spl etc. May be passive radiator is on the right track.
I disagree about TLs being less efficient and killing sonics. Unless you over-stuff a TL, thus killing all of the output from its terminus, there will be no loss of either efficiency or sonics. The efficiency is primarily dependent on the driver itself, not the line.
Paul
Paul
I think it is already clear (theoretically and sound-wise) that transient-wise TL sits there between bass reflex and sealed.
I agree that one of the problems of TL is the efficiency. It kills sonic. But most of high end speakers are even worse. It sounds "alive" only when driven by high power high damping amplifiers. So It cannot be said that "TL can never be as good as a reflex" from normal perspective. From my own perspective (where I have always tried very hard to relate every things with "enjoyment factor", e.g. may be it is the group delay issue), I think I'm agree
Intuitively, I think the better one should have port properties that change with spl etc. May be passive radiator is on the right track.
If you model a reflex properly, and that assumes whatever program you use can do so, you will find resonant "pipe" sounds in it, too, particularly if the box is a tallish, floor-stander. But most, maybe no software programs for reflex/vented boxes take into account the effects of those "pipe" resonances and you will most likely end up with a (far) less optimized design. Also, driver break-in is way over-stated, needing very little time to do so, which you should have done before making your final and design reference TS measurements. All of the long-term driver break-in that people claim is necessary is really their ears breaking in and getting used to the different sound of their new speakers.
Paul
Paul
Exactly. By trading off parameters, a vented enclosure can be made to have transient response very close to that of a sealed box.
Really? OK, some general points. For a start, what does 'as good as' mean? Until you properly define it, and eradicate any erroneous assumptions, it doesn't mean anything. Which brings us to the next point. What do you mean by TL? It's become a catch-all phrase which can be and regularly is used to describe cabinets that are almost the functional opposite of each other.
If the term is applied in its strictest sense, a 'pure' acoustic transmission line is a pipe that is stuffed to provide the flattest possible impedance load. Period. End of story. No other considerations. Whether you agree with the principle behind it (viz. whether or not you believe creating the flattest impedance load is useful) is irrelevant: that's what it is (and completely dissimilar to a BR -they would naturally be unlikely to be used for the same purpose). The vast majority of boxes described as TLs do not conform to this; most deliberately use the pipe fundamental to provide some LF output, while a modest quantity of stuffing is applied along with careful driver offset in the line to eliminate the unwanted harmonic modes. This does not mean that such cabinets cannot produce useful LF gain. If they do not, the designer was either incompetent, or somebody enforced a compromised variation of the box for xyz reason.
As for driver break in, as Paul said, this should be done before a box is designed, whatever the cabinet may happen to be. You may want to factor the amplifier output impedance into that if relevant, room acoustics &c. too. Since T/S values obtained also tend to vary depending on the measurement conditions, this ideally needs to be accounted for also; again, this applies to any enclosure type.
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