richie00boy said:
No it wouldn't, that's like saying that when light passes through liquid or glass it changes color.
Assuming the waves slowed down in the fill, if you looked at the waves in air vs in the fill the physical spacing between them would be reduced in the fill, but the time spacing would be the exact same, so the frequency would be the exact same. Same reason why light bends when it goes through liquid or glass, but it still stays the same color, in the slower medium the wavelength changes but the frequency doesn't.
Either way, I'm not sure if the waves actually slow down in the fill. I had simply heard that somewhere and since my specialty isn't acoustics I just accepted it and went on with my life. Bottom line is it will change the Q and F3 to reflect a larger enclosure, but it won't have the added efficiency of this larger enclosure. What we're talking about has nothing to do with standing waves, so the whole wavelength being longer than the largest dimension in the box is a moot point.
Bill Fitzpatrick said:
What's detair and whay?
The Adiabatic-isothermal concept has been often referenced, but never conclusively proven. That it is used in many books is no proof of its veracity. Blind belief and repetition of the conventional view is not necessarily helpful.
A thesis by Gavin Putland - do your own search - basically debunks the idea, although it offers no experimental evidence.....
Yes wavelength is directly related to frequency, but the constant of proportionality is the speed of sound/light in the medium you're talking about. If you change the medium, you change the speed of sound/light, and you change the relationship between the wavelength and the frequency.richie00boy said:
soongsc said:
The reason it doesn't change color is because the frequency doesn't change. The frequency IS the color, not the wavelength. Yes you're right it changes while in the medium and then changes back once it leaves, but what if it never leaves? If you're swimming underwater and you look at a blue object, it will still be the same color blue as out of the water. Same with sound....the speed of sound in air is roughly 344m/s and the speed of sound in water is roughly 1483m/s, over 4 times faster. If what you guys are saying is true, then if you heard anything underwater its pitch would sound 2 octaves higher than it does in air, but it doesn't, it sounds pretty much the same. The reason it sounds the same is because the frequency is the same, the frequency is independent of the medium.
sr20dem0n said:
Sorry! We're applying the wrong physics!
In speaker stuffing, the media remains air. Since the way sound travels through air is a series of continuously change of air pressure, thus there is airflow between the areas of different pressure. Stuffing acts like a resistor and inductor on electrical signals. So more stuffing is like increasing sereis R and L, since the sound wave is attenuated, it's like the sound wave travelled though more distance.
oops clarification
Sorry what I forgot to include was the different frequencies I was using for the different wavelengths. My bad I didn't notice that. The formula i used is as follows for a appoximation. Elevation above sea level is not accounted for and humitity may change the density also.
v = 331.5m/s + 0.6T using 24 deg c
Frequency(Hz) wavelength(m)
20 17.295
21 16.471
22 15.723
23 15.039
24 14.413
25 13.836
26 13.304
27 12.811
28 12.354
29 11.928
30 11.530
31 11.158
32 10.809
33 10.482
34 10.174
35 9.883
36 9.608
37 9.349
38 9.103
39 8.869
40 8.648
41 8.437
42 8.236
43 8.044
44 7.861
45 7.687
Material Speed of Sound (m/s)
Air 343
Steel 6100
Timber 5260
Brick 3650
Speed of sound through materials at 20 °C.:
wavelength would change as the speed of sound does but that wasn't part of my error.
wavelength(Frequency)=speed of sound
soongsc said:
Sorry what I forgot to include was the different frequencies I was using for the different wavelengths. My bad I didn't notice that. The formula i used is as follows for a appoximation. Elevation above sea level is not accounted for and humitity may change the density also.
v = 331.5m/s + 0.6T using 24 deg c
Frequency(Hz) wavelength(m)
20 17.295
21 16.471
22 15.723
23 15.039
24 14.413
25 13.836
26 13.304
27 12.811
28 12.354
29 11.928
30 11.530
31 11.158
32 10.809
33 10.482
34 10.174
35 9.883
36 9.608
37 9.349
38 9.103
39 8.869
40 8.648
41 8.437
42 8.236
43 8.044
44 7.861
45 7.687
Material Speed of Sound (m/s)
Air 343
Steel 6100
Timber 5260
Brick 3650
Speed of sound through materials at 20 °C.:
wavelength would change as the speed of sound does but that wasn't part of my error.
wavelength(Frequency)=speed of sound
There's a lot of confusion above in this thread.
Simple answer, by the way this is basic physics/chemistry:
Stuffed box = approximately Isothermal condition (a system where the temperature is held constant by the "thermal inertia" of the stuffing)
Unstuffed box = approximately Adiabatic condition (a system that retains the heat of compression and therefore the temperature changes with pressure)
Here's a discussion of the theory:
http://farside.ph.utexas.edu/teaching/sm1/lectures/node53.html
I wrote this on another forum about closed box systems and it might help:
Yes sealed systems do boil down to a simple parallel mass spring system. Fc, Qtc, and passband efficiency define the low frequency, small signal performance. They're simple second order high pass filters from the electrical analogy perspective and this is what Thiel and Small theory use to leverage their analysis.
Interesting that you mention the stuffing, because I notice that most older acoustic suspension systems have so much stuffing that it's pushed right up against the back of the driver. Stuffing deep in the box acts to dampen standing waves or box modes, and to also take the system from adiabatic to a nearly isothermal condition causing an increase in effective volume. However, damping right up against the back of the driver adds an acoustical damping component essentially in parallel with the others in the driver. There are two damping components the mechanical resistance in the spider and outer edge as Rms or Qms, and the electrical damping component due to motor braking Res or Qes, these in combination define the total system Q or Qts in free air, or Qtc in box. It's interesting that the power radiated should provide some damping, but remember these systems are less than one percent efficient thus the power radiated can be ignored with little error being introduced into the model, isn't that ironic? However, damping right up against the back adds additional acoustical resistive loss that can be modelled as a reduction in Qms and can be significant thus lowering Qtc. It's cheating, since if the target is a lower Qtc, a system with higher efficiency results when it is obtained through a stronger motor (more magnet)or lower Qes. There's one positive aspect of using acoustical damping which is to make the system less sensitive to source impedance. If the majority of the damping comes from the motor then the system Qtc is very sensitive to source impedance or damping factor. The Peerless 1727 has a fairly strong motor so I pushed the damping material further away from the driver. Sealed systems are really pretty simple, moving mass sets Fc once a box size is chosen and provided Vas is much larger. Motor strength establishes Qtc if Qms is high and acoustical losses are low as they should be. This is what establishes the volume/bandwidth/efficiency tradeoff. Make the motor stronger and passband efficiency goes up, but Qtc goes down and the output at Fc is reduced (bandwidth loss). Make the moving mass higher to lower Fc and efficiency also goes down as a result. In quality control and value engineering we like to look at how sensitive a final performance characteristic is to a particular component in the system. A properly done acoustic suspension system is dominated by the air spring, so system performance is nearly independent of Vas as long as it is much higher than the box volume, yet many worry about Vas error in drivers that they purchase. The important value is moving mass which unfortunately is only indirectly indicated through Fs and Vas, but it can be computed. It's also unfortunate that most of the other Thiel and Small driver parameters will be off simply if there is some Vas error. It's possible to recompute them by applying a correction to Vas and then see if they're correct. Motor strength is important since it primarily determines Qtc when Qms is very high as it should be. Motor strength also effects passband efficiency which is obviously important.
Link to original thread: [http://www.classicspeakerpages.net/...opic_id=4930&mesg_id=4930&listing_type=&page=
Simple answer, by the way this is basic physics/chemistry:
Stuffed box = approximately Isothermal condition (a system where the temperature is held constant by the "thermal inertia" of the stuffing)
Unstuffed box = approximately Adiabatic condition (a system that retains the heat of compression and therefore the temperature changes with pressure)
Here's a discussion of the theory:
http://farside.ph.utexas.edu/teaching/sm1/lectures/node53.html
I wrote this on another forum about closed box systems and it might help:
Yes sealed systems do boil down to a simple parallel mass spring system. Fc, Qtc, and passband efficiency define the low frequency, small signal performance. They're simple second order high pass filters from the electrical analogy perspective and this is what Thiel and Small theory use to leverage their analysis.
Interesting that you mention the stuffing, because I notice that most older acoustic suspension systems have so much stuffing that it's pushed right up against the back of the driver. Stuffing deep in the box acts to dampen standing waves or box modes, and to also take the system from adiabatic to a nearly isothermal condition causing an increase in effective volume. However, damping right up against the back of the driver adds an acoustical damping component essentially in parallel with the others in the driver. There are two damping components the mechanical resistance in the spider and outer edge as Rms or Qms, and the electrical damping component due to motor braking Res or Qes, these in combination define the total system Q or Qts in free air, or Qtc in box. It's interesting that the power radiated should provide some damping, but remember these systems are less than one percent efficient thus the power radiated can be ignored with little error being introduced into the model, isn't that ironic? However, damping right up against the back adds additional acoustical resistive loss that can be modelled as a reduction in Qms and can be significant thus lowering Qtc. It's cheating, since if the target is a lower Qtc, a system with higher efficiency results when it is obtained through a stronger motor (more magnet)or lower Qes. There's one positive aspect of using acoustical damping which is to make the system less sensitive to source impedance. If the majority of the damping comes from the motor then the system Qtc is very sensitive to source impedance or damping factor. The Peerless 1727 has a fairly strong motor so I pushed the damping material further away from the driver. Sealed systems are really pretty simple, moving mass sets Fc once a box size is chosen and provided Vas is much larger. Motor strength establishes Qtc if Qms is high and acoustical losses are low as they should be. This is what establishes the volume/bandwidth/efficiency tradeoff. Make the motor stronger and passband efficiency goes up, but Qtc goes down and the output at Fc is reduced (bandwidth loss). Make the moving mass higher to lower Fc and efficiency also goes down as a result. In quality control and value engineering we like to look at how sensitive a final performance characteristic is to a particular component in the system. A properly done acoustic suspension system is dominated by the air spring, so system performance is nearly independent of Vas as long as it is much higher than the box volume, yet many worry about Vas error in drivers that they purchase. The important value is moving mass which unfortunately is only indirectly indicated through Fs and Vas, but it can be computed. It's also unfortunate that most of the other Thiel and Small driver parameters will be off simply if there is some Vas error. It's possible to recompute them by applying a correction to Vas and then see if they're correct. Motor strength is important since it primarily determines Qtc when Qms is very high as it should be. Motor strength also effects passband efficiency which is obviously important.
Link to original thread: [http://www.classicspeakerpages.net/...opic_id=4930&mesg_id=4930&listing_type=&page=
soongsc said:Post #2 says it's a vented box, how did we get to closed box?
You're right about the confusion.
Question #1 asks about stuffing, helps to understand it with regard to closed box systems. I've also written a lot over the years about stuffing vented box systems.
OK yeah he asks with regard to vented systems: "Is there a downside to stuffing in terms of sound quality?"
Yes too much stuffing near or in the port will lower Qp and reduce the bass output at Fb and the power handling due to increased excursion. There is an assumption of fairly high box Q (Qa, Qp, Ql)in T&S analysis of vented systems and therefore tradition has been to only line the walls to reduce cavity resonance or standing waves. However, this is not optimal if one thinks about min/max pressure/velocity in the box. I don't follow tradition when stuffing vented systems.
LOL, I think I'm more confused than then when I started.....
Ok, how about vented bass and how it plays in a room. I have noticed that in my room with hard wood floors speaker postioning can play a huge roll in bass output and perception.
Also in regards to this I know are speaker stands are important, and thier quality, (weight, build), but can anyone explain why this is?
Ok, how about vented bass and how it plays in a room. I have noticed that in my room with hard wood floors speaker postioning can play a huge roll in bass output and perception.
Also in regards to this I know are speaker stands are important, and thier quality, (weight, build), but can anyone explain why this is?
soongsc said:
Sorry! We're applying the wrong physics!
In speaker stuffing, the media remains air. Since the way sound travels through air is a series of continuously change of air pressure, thus there is airflow between the areas of different pressure. Stuffing acts like a resistor and inductor on electrical signals. So more stuffing is like increasing sereis R and L, since the sound wave is attenuated, it's like the sound wave travelled though more distance.
That all makes sense just fine, I was just trying to say that the frequency doesn't change as the medium changes, pretty much a completely different topic than that this thread is focusing on
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