Cheers Don, that would be interesting reading. I'm sure i posted something similar in another thread on here to the effect that i'll be sticking with rockwool in the main part due to its effectiveness.
It's also cheaper, far more easily available & fireproof to boot 😀
I'd enjoy the read if you happen to find it, don't spend too much time searching though 😉
It's also cheaper, far more easily available & fireproof to boot 😀
I'd enjoy the read if you happen to find it, don't spend too much time searching though 😉
It's in Martin's papers (pdf files downloadable from his website) that discuss how he developed his spreadsheet models.
Specifically, 'Section 5.0 : Derivation and Correlation of the Viscous Damping Coefficient':
"The same sets of measurements were also performed using long fiber wool. The wool was a much courser fibrous tangle with a larger fiber diameter than the Dacron Hollofil II. The number of wool fibers in a given volume, for the same packing density, was probably significantly less than the number of Dacron fibers. (...) it appeared that the wool might provide a little less viscous damping for the same packing density. If there are fewer wool fibers per unit volume, then it makes sense that the amount of viscous damping is lower. I concluded that there is no magic associated with a wool stuffed transmission line. (...) "
- Martin J King
Incidentally, in Section 2 he discusses the slight speed of sound difference mentioned earlier.
The series of papers are well worth reading. They match my layman's understanding of the physics involved.
I should mention that this is where I disagree with MJK, he lists the measured l/4 as 94 because he uses the impedance peak rather than minimum as an indication of l/4.
Next we want to find l/4 for Figures, 2.3 (100g stuffing) and 2.4 (200g stuffing), 2.5 is so far damped that it is difficult to determine.
A question for all the experts out there:
How would we distinguish Hemholtz resonance from transmission line resonance when we look at the measurements in Martin's paper?😀
How would we distinguish Hemholtz resonance from transmission line resonance when we look at the measurements in Martin's paper?😀
Hemholtz resonance is essentially a lumped effect, a cavity and a port. The excitation is usually simply blowing air over the port as with a bottle. The narrowed section acts as a mass, and the cavity as a compliance. Not much to it. Hemholtz resonance does not come into play in a simple transmission line where the effect is distributed.
You are saying that a long pip cannot be excited like a Hemholtz resonator? Based on what math model can you say that? Application in halls suggest that these can be excited acoustically as well. There are also many applications where tubes like Martin's paper are applied as Hemholtz resonators.
Look, Helmholtz is the name of the person who first discovered this type of resonance:
Hermann von Helmholtz - Wikipedia, the free encyclopedia
See also:
http://en.wikipedia.org/wiki/Helmholtz_resonance
As I see it your claims are entirely wrong, "application in halls" not sure what you mean by this. The room modes
of a hall are cavity resonance modes involving standing waves. Something like a TL in 3 dimensions, nothing like
a Helmholtz resonator.
To me Helmholtz resonance is only historically interesting, and it really doesn't matter to me what it is. I'm fairly
certain that my understanding of it is correct but why don't you go study Helmholtz and see if you can determine if
he did any research on TL resonance. As far as I know he did not, and the term does not refer to TL type resonance.
I seriously don't think you'll find it - good luck to you.
Are you equating Helmholtz resonance with parallel mode resonance in contrast with the series mode that I mentioned?
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Hi George
The fact is that the two systems will couple and make any clear seperation of one effect from the other difficult to meaningless. Consider a bottle with a long neck. The bottle will have a resonance due to the necks mass and the bottles compliance, but it could occur that the neck had a length such that it was precisely tuned to this same resonance. In that case the two things would be impossible to seperate because they are not seperable - they are tightly coupled - each one depends on the other.
Adiabatic to isothermal
Without being able to prove it, intuitively I don't think it would be possible with stuffing to completely change the thermal conditions from adiabatic to isothermal, or even close, without completely stuffing the life out of the TL, meaning there would be absolutely no contribution from the terminus for bass response. In fact, I'd suspect the "life" to disappear long before reaching a stuffing density of 1 lb/cu.ft. if the whole line is stuffed, IMO. Thus, whatever line-lengthening effect might occur from stuffing, I'd expect it to hardly be significant. While it may not be entirely analogous, the pressure-waveform experiment I described points me in this direction due to how much copper had to be used to achieve a truly isothermal condition.
Paul
Without being able to prove it, intuitively I don't think it would be possible with stuffing to completely change the thermal conditions from adiabatic to isothermal, or even close, without completely stuffing the life out of the TL, meaning there would be absolutely no contribution from the terminus for bass response. In fact, I'd suspect the "life" to disappear long before reaching a stuffing density of 1 lb/cu.ft. if the whole line is stuffed, IMO. Thus, whatever line-lengthening effect might occur from stuffing, I'd expect it to hardly be significant. While it may not be entirely analogous, the pressure-waveform experiment I described points me in this direction due to how much copper had to be used to achieve a truly isothermal condition.
Paul
You could stuff an acoustic suspension speaker to test your intuition, I have done this and informally tested different materials. I also linked to MJK's experimental data. You might want to have a look. I also have to wonder how you chose copper and while it might have been a good choice for your application I doubt that it has the right characteristics for speaker applications. What were the characteristics of the copper material?
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Using copper for the intended purpose of creating a calibrated isothermal "lung" to then use to calibrate the output of a ventilator that would be "breathing" for a patient, is the only way it can be done correctly. As I said, while it might not be entirely analogous to using polyester fill to stuff a speaker, we are talking about doing the same thing, changing the thermal conditions from adiabatic towards isothermal. I know that it's generally considered that stuffing a sealed box will increase the box's effective volume by up to ~20%, thus lowering Qtc. Does that automatically mean the same percentage increase will occur in a TL but just in its length? Why, if there is an increase, is it not to all dimemsions, not just length? IOW, the effective volume contained in the line would be increased by 18% (to use your original "ideal" factor) but would happen by each dimension, width, depth and length, increasing 2.62%, thus making the line-lengthening effect almost insignificant?
Paul
Paul
Changing the cross sectional area changes the characteristic impedance of the line Zo, and yes Zo also changes with damping material; I prefer to view the Zo change as the compliance per unit length changing but I believe that you could also view it from the cross sectional area change as you suggest. Look at the equation for the speed of sound, the adiabatic constant changes:
http://hyperphysics.phy-astr.gsu.edu/HBASE/sound/souspe3.html#c1
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Hi,
One must ask who is the "self proclaimed expert" or claiming to be.
Having read the referenced paper at best I'd say its turns you into being
basically informed, and if you believe its the last word on the subject I'd
suggest it is a case of belief rather than knowledge.
High End 3 Way ? not without baffle step compensation for a start ...
Some of do know the difference between TL's and vented boxes
and even know what a MLTL really is, or not as the case may be.
I have only replied because I have bothered to read the referenced paper.
/sreten.
So, you're agreeing that adding stuffing causes an effective volumetric change by changing the thermal condition, rather than a uni-directional (one dimension only) change? And if you are, then I assume you're also agreeing that the change would affect all three dimensions more are less equally (I don't see how they could not)? Going from there, then, each dimension would be changed the same percentage in order for all three to be equally affected, thus, the effective increase in line length, as well as the effective increases in line depth and width, would be at most 2-3%? If you agree to all this, then the line length increase is not very significant.
Paul
Paul
I feel like I am on trial here. No, simply put the adiabatic or isothermal factors in the equation for the speed of sound. It is that simple. You might also take a look at MJK's data if you were interested in what happens in real life rather than trying to imagine the answer.
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No, you're not on trial here but I would like you to provide adequate support for your claim that adding stuffing to a TL increases the effective line length by 18% (ideally). I don't need to take a look at Martin's work as I'm very well versed in it and use his worksheets almost every day either for myself or for others in modeling TLs, not to mention building numerous TLs and measuring their performance. Martin's work does not show anything to support the magnitude of change from stuffing you claim. Yes, when I add stuffing or increase stuffing density and/or length, there is a slight lowering of the system's tuning frequency across the board (as shown in the frequency of the valley between the impedance peaks, the frequency of minimum driver motion, etc.) that might come from an effective increase in the line length, but nothing anywhere near 18%. On that basis I again state that any change in effective line length from stuffing is either insignificant or pretty small.
Paul
Paul
Well, I dont have your knowledge
On one side my experience is that acoustic material is without much effect when it comes to low frequency ressonance standing waves in tall slim box design
On the other hand, why does acoustic material affect a bassreflex tube
Not only when its placed inside the tube, but also when placed close to tube, inside the box
In fact, it can affect a BR tube quite a lot
On one side my experience is that acoustic material is without much effect when it comes to low frequency ressonance standing waves in tall slim box design
On the other hand, why does acoustic material affect a bassreflex tube
Not only when its placed inside the tube, but also when placed close to tube, inside the box
In fact, it can affect a BR tube quite a lot
Let's see if we can get on the same page here as they say, this is one of the reasons I ask about people's background. It is a reasonable question contrary to what others think here. Do you agree that there is an analogy between a vented system where the behavior is similar around l/4 and Fb in the vented system. Let me mention that this analogy was suggested by Professor Wadesworth at WPI to aid in the understanding not as the suggested model for my project. Wadesworth taught the transmission line course at WPI at one point in his career:
3pNS3 Circumaural hearing protector development at the WPI Acoustics
It is also a standard analogy used in microwave design involving TLs or cavity resonators.
Do you agree that l/4 is indicated by the minimum input impedance as I have previously mentioned?
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The support is that if you understand the analysis of a TL loudspeaker you will see that l/4 is a minimum in the input impedance. From MJK's data which is convenient being online:
fl/4
Unstuffed: 65 Hz
100gm: ~58 Hz
200gm: ~50 Hz
fl/4
Unstuffed: 65 Hz
100gm: ~58 Hz
200gm: ~50 Hz
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