The hornresp sim I posted earlier gives an idea of how strong the reflections at the open end are by looking at the magnitude of the impulse response. You have the direct sound, the inverted first reflection of the impulse, the inverted reflection of the reflection, etc. It also shows how the pipe acts as a lowpass filter -- the reflections get broader as they decay.
I use the 1 D wave equation to formulate all of my models, only 1 dimensional motion is used in the closed form solution. So the TL models I derived only consider motion of the air along the length of the pipe and the end boundary conditions. They do not include any reflections off of the side walls.
Then I go ahead and design TLs. I have double checked my models many times with a finite element solution for the specific geometry which includes all three directions of motion and shows me pictures of the pressure distribution along the pipe and calculates the resonant frequencies, the results match my simulations. I also do electrical impedance and SPL measurements of the finished speaker, the results match my simulations. So unless I am getting really lucky every time, I believe my modeling methods and there are no reflections off of the side walls.
I am certain that side wall reflections do not play a role in the first few TL resonances, the bass frequencies. At low frequencies this is purely air vibrating along the length of the TL, even around the bends. All of these modeling methods and some of the finite element solutions can be found documented in various places on my web site.
Hi Martin,
I have done a lot of reading on your site.
You mention a point I was holding as a hole card - the bends in the average TL.
I have done a lot of reading on your site.
You mention a point I was holding as a hole card - the bends in the average TL.
At low frequencies a bend or two plays no real roll in the response. For a once or twice folded TL the 1/4, 3/4, and even the 5/4 standing waves behave pretty much like a straight TL. Once the frequency gets up above say 500 Hz, then some standing waves will appear across the line but the fiber damping should kill them. The bass produced by a TL is all due to the first couple of axial standing waves and the end boundary conditions.
I suppose ripple has always been an issue with a TL used in a "standard" 3way
I need to say that my experience with genuine TL is from a time long before any kind of subs and plateamps
TL was really hot in the seventies, and a bit after, but since then a dead duck I never considered of any value
Im surpriced that its becoming popular again
Are new TL designs much better ?
Or are they really good used as subs only ?
I need to say that my experience with genuine TL is from a time long before any kind of subs and plateamps
TL was really hot in the seventies, and a bit after, but since then a dead duck I never considered of any value
Im surpriced that its becoming popular again
Are new TL designs much better ?
Or are they really good used as subs only ?
This analogy will probably cause more questions and yea buts then anything else I could offer, but it is the best I can come up with to try and describe what happens. Visualize a foamy whipped cream slowly injected at one end of the TL and expanding along a folded path starting at the driver end of the TL and moving towards the open end until it seeps out the open end. As it reaches a bend it will follow the path of least resistance which is to turn and go around the bend. Crashing into the bend and turning around to go back up the TL will not happen, it will progress along the easier path of life.
The bass wavelengths are so long in a TL, 4 times the length of the TL at the first resonance, that reflections are not going to happen. The first standing wave does not know the bend even exists.
TL's designed in the 70's were essentially based on trial and error, more error than not. TLs can be designed more accurately now so the results can be predicted, optimized, and are in general better performing. A TL has its own set of trade-offs and strengths and weaknesses. Some people believe in TLs and some don't, like everything else there are both good and bad examples and no one superior enclosure design.
Would it be fair to say that a tone of low frequency will reflect from a surface that is in close proximity to the source? Take a concrete wall for example and place a woofer 10 inches from it. I expect due to the short distance that no reflection will take place?
In general yes. Almost all due to having analytic tools which let us predict the TL response.
dave
Just a short note, but I have to say that people could do math back then too
Sometimes its as if it was like the stone ages
Even today many people are repeating what happened back then
So, it must have been quite a good time, in some respect
Even some quaterwaves from back then are getting new life, and becoming hot
Drivers too
I spent my entire youth with those things
I know exactly what they could and couldnt
Length could be calculated
But I admit, a commonly used rule was a start area alike the driver size, and ending in about a quater of that
Tho, the straight line was never in use, or at least not to my knowledge
But seems not that much different from Tony Gees well known 2way TL experiment
To me the most significant difference is measurements of the result
Only test magazines did that
I can also say that we had a pretty good one
The general spirit was much different
But its still the listening that decides, it seems
The big mistake made in the 70's was the myth that the fibers slowed the speed of sound in a TL. People calculated shorter TL lengths assuming the speed of sound dropped by 30% to 50% due to fiber stuffing which introducing a huge mistake right out of the gate. The moving fiber myth dominated TL design for many years from the 1960's up through about 2000. Some people still cling to that concept. In my opinion, the second biggest mistake was using the rule of thumb equation f = c / (4 x L) for every TL geometry (tapered, straight, or expanding) when it is only accurate for a constant cross-section TL.
Ok, that I have never heard about, so I suppose not the same issue in my country
Maybe we were lucky to be small, and far away from US 🙄
To be honest, US was not very hot in terms of good sound 😀
Altec was simply too big and expencive, and JBL took over, and my ears didnt like that too much either 😱
Well, better leave that, its old history
Maybe we were lucky to be small, and far away from US 🙄
To be honest, US was not very hot in terms of good sound 😀
Altec was simply too big and expencive, and JBL took over, and my ears didnt like that too much either 😱
Well, better leave that, its old history
Still waiting on a definitive, coherent answer - "just because" doesn't cut it. Anyone?
I get the distinct feeling I'm being ignored....
🙂
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