Yes, there are too many parameters affecting good speaker design. Type of box plays almost insignificant role. It is probably better to understand what can be achieved (technically and sound-wise) from each of them.
Technically, TL gives flat impedance, period. Sound-wise, each of us know the sound of JLH 96 amplifier playing music at 50Hz, -50 degree out of phase, 5 ohm impedance (Or we have no idea?).
Technically, TL pipe creates time delay. Sound-wise, again, a lot of experience required to make a meaningful opinion.
I think, port noise of bass reflex is over estimated, while time delay is under estimated.
And it is relatively easy to enjoy music from a sealed box 😕
Any fiber in the line will restrict air movement and cause a loss in efficiency vs unrestricted. It is an inherent disadvantage of a TL.
I agree with your point. The more a BR cabinet resembles a TL, the more TL problems it inherits and the more TL band aids it will need (stuffing, etc).
As Colonel Potter on M.A.S.H. used to say, "BULL COOKIES". Whatever sensitivity (efficiency if you prefer) a driver inherently has, it will have that in any box, minus electrical losses from crossover and wiring resistances, down to any reasonably musical frequency unless you stuff the life out of it. Any losses from stuffing fibers are otherwise relegated to higher frequencies (above several-hundred Hz) because they act essentially as low-pass filters, which is what you want.
Paul
Paul
Cute, really cute. 🙄 TLs don't have unusual problems nor do they need band aids, no more than any other box design, including a BR. Like any box, they have pros and cons, and benefits and disadvantages, including like all other boxes that some drivers aren't suited or best for them.
Paul
Paul
A backside vented enclosure (TL, BR, PR, etc) is designed to use the resonance peak of the driver to increase efficiency in a bandwidth around that frequency. Ideally, the energy of the resonating driver should be resistively consumed by vibrating air outside the enclosure, not vibrating a half pound of fluff inside it.
If a driver is damped by resistance in an enclosure, there is less cone movement and less port or pipe air movement and therefore, the efficiency at those frequencies is decreased.
from my understanding is the up to 5dB gain that a vented design has over IB or sealed, is due to the 'vent' and as such that rule of thumb applies to TLs too. The benefit with TLs is the ability to lightly stuff to help kill the pipe upper modes. With a reflex it just messes the whole thing up (unsure about PRs tho).
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Not so. I stuffed a 10 ft ^3 vented cabinet with 15 lbs of Acousta-Stuf. The box Q went down a little, and the tuned frequency was more or less unchanged (28Hz). The bass is still very good, but the improvement in midrange was dramatic.
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What a coincidence!
I got an email from a guy for whom I had modeled a TL a few years ago. He was in the process of building a small, ported 2-way and asked me to determine the best location for the port, knowing my experience and success in designing TLs. The cabinet had internal dimensions of 6"W x 7.5"D x 12.5"H. Whatever software program had been used didn't even determine optimum port dimensions, much less an optimum port location. Bottom line? It doesn't really matter what the internal dimensions are in a BR cabinet. There will be resonances created from the internal cabinet dimensions and relative locations of driver and port. If your software program can't take those into account, you have just as good of a chance of ending up with bad stuff from your port/system as not.
Paul
I got an email from a guy for whom I had modeled a TL a few years ago. He was in the process of building a small, ported 2-way and asked me to determine the best location for the port, knowing my experience and success in designing TLs. The cabinet had internal dimensions of 6"W x 7.5"D x 12.5"H. Whatever software program had been used didn't even determine optimum port dimensions, much less an optimum port location. Bottom line? It doesn't really matter what the internal dimensions are in a BR cabinet. There will be resonances created from the internal cabinet dimensions and relative locations of driver and port. If your software program can't take those into account, you have just as good of a chance of ending up with bad stuff from your port/system as not.
Paul
Far more a problem with a TL. For most BR's the cabinet dimensions are small compared to the tuning frequency. BTW, we haven't even talked about the often large air path difference around the TL's folds. A wave travelling the inside of the fold will often have a 10% shorter distance than the outside, smearing the time and phase response. Not to mention the turbulence around a 1 board thick corner.
Now a BR doesn't have that problem because it doesn't rely on a delay line, it is a simple series capacitance (box) and inductive port. There is very little phase and time smearing. It reactively filters out frequencies outside of the passband with little need for resistive material.
Dome right, it is still on the order of 1/4 wl or less at any frequencies getting out the terminus so is moot.
A typical BR is usually fairly tightly tuned and therefore out of tune most of the time, TLs are typically much more tolerent of the dynamic changes of T/S parameters (rememvber, T/S are not scalars, they are curves, numbers given are a sample from the cutves)
dave
I was going through some late 90s HiFi World supplements with some of their speaker designs last night. They recommended running the speaker for a month before retuning the port to deal with T-S parameter shifts. These were unusually low Q designs, intended for near wall positions
There are T/S parameter shifts due to break-in, and there are dynamic shifts (depends on drive level) that occur always, and there are shifts due to changes in the "weather" (pressure, temp, humidity)
dave
there are ways to damp a line or a box to deal with internal resonances without stuffing the line. Gilbert Briggs came up with what he called a membrane absorber. a sealed system with fibrous damping material covered with a thin membrane the system must be air tight. These work very well I have used them in T-Lines and in box speakers. I hope that this may be of some interest here. Best regards Moray James.
Don't you need flow resistance to damp the pipe resonances in a classic TL design? I understand how membranes are valuable for damping the pressure wave at the walls in a sealed design, but not the secondary pipe resonances.
Damping is not the only tool for dealing with unwanted pipe resonances. Driver offset & restricted terminus are 2 of them. Some "TL" (in the broad sense) get away with very little damping.
dave
If I remember correctly the driver offset only removes odd resonances, leaving even ones mostly unaffected. When you say terminus restriction do you mean flow restriction or mass loading, i.e. a port?
Drew
Drew
Given that in a line open at one mode, IIRC, there are only odd order resonances. What resonances offset deal with depends on the offset. The one usually targeted is the 1st unwanted resonance as it is the one that would nee the most damping otherwise.
dave
dave
Dave,
One of the reasons I am asking questions at this this time is I am planning my first serious build using a transmission line design. It will use a AE TD12X and SEOS horn. I have been reviewing possible alignments and right now a folded ML Voigt pipe is at the top of the list. This configuration will allow the 1/3 offset of the driver and as you say the restricted terminus (port) will aid in the reductions higher order pipe resonances. Do you know any drawbacks to this configuration? The TD12X has a low Qts, is this an issue? Voigt's usually use medium Q drivers.
One of the reasons I am asking questions at this this time is I am planning my first serious build using a transmission line design. It will use a AE TD12X and SEOS horn. I have been reviewing possible alignments and right now a folded ML Voigt pipe is at the top of the list. This configuration will allow the 1/3 offset of the driver and as you say the restricted terminus (port) will aid in the reductions higher order pipe resonances. Do you know any drawbacks to this configuration? The TD12X has a low Qts, is this an issue? Voigt's usually use medium Q drivers.
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