Speed of sound is an interesting idea. At one point, I thought that by putting 2 litre jugs inside the speakers, the sound wave would enter the containers and speed up before exiting, therefore throwing the wave pattern off and create an interruption or even cancellation of the waves. Not sure if it actually did anything. Lost interesting in taking the idea further.
I also agree with SY on this one.
Keep in mind that water is a common material and that if there were anything to it, we would see them on the market.
I also agree with SY on this one.
Keep in mind that water is a common material and that if there were anything to it, we would see them on the market.
Hmmm.... I was thinking..... I read an article about see weed and waves.
When they removed all the see weed close to land the waves reaching land became much bigger.
Maybe you could make something similar.
Not sure if it works the same way in an enclosed space without air. You might need the air over the water to have it move as a wave.
When they removed all the see weed close to land the waves reaching land became much bigger.
Maybe you could make something similar.
Not sure if it works the same way in an enclosed space without air. You might need the air over the water to have it move as a wave.
I don't think the water will absorb so much as the interface with the panels will have greater internal reflection. Two impedance mismatches between inside and out. Someone mentioned using rough particles to make the water more dissipative, which sounds reasonable. I'd be thinking about things like kaopolite.
If one wanted to be REALLY over-the-top, one could use ferrofluid in a silicone carrier, then put field plates in the cabinet walls. The orientation of the particles could be tuned, and perhaps dynamically vary with the signal...
If one wanted to be REALLY over-the-top, one could use ferrofluid in a silicone carrier, then put field plates in the cabinet walls. The orientation of the particles could be tuned, and perhaps dynamically vary with the signal...
SY said:
mmmm I think this may be beyond my expertise
There is certainly room for a bit of research. I think the plan will be to design some translam enclosures which have pockets or a hollow in the walls to be stuffed/filled with whatever happens to be the winner of the sound deadening test... ahhh decisions decisions.
Thanks for all the useful input.
jacco vermeulen said:
If you're serious then you'll have to explain what that means first
I still have a lot to learn which is why I'm on here before I properly start my project in September.
The idea of gels with suspended particles sounds very interesting. If anyone has suggestions of gels or similar substances which may be worth a look I'd be very grateful to hear from you. I may do as someone has suggested and run a test with water as a comparison to everything subsequent.
One thought that had struck me was to to test how different materials reacted to different frequency ranges then create a mix of different substance particles - sand, lead, foam/plastics which would be most effective to cover a wide range of frequencies. Possibly suspend this in some kind of gel or liquid to damp their movement. I was, however, slightly worried that the most dense particles would eventually vibrate their way to the bottom of the mix.
Does anyone know whether currently used materials like sand, foam etc are more effective at specific frequency ranges?
Again, Thanks
Not really, i can do an FFT excitated wave ripple analysis but somehow i had the notion i ended up at Drole Patrol.
How about the "Wasser-Werke", a fully active multi-way transmission line DIY design from the late '80s.
A highly complex project, includes all the power amps and active XO's, by a German engineer named Mr Guido Wasser, likely will cost you both a house and a marriage before it's finished.
And yeah, there's even real Water involved in the Wasser-Werke.
"Wasser-Werke" is German for Water Works, btw.
How about the "Wasser-Werke", a fully active multi-way transmission line DIY design from the late '80s.
A highly complex project, includes all the power amps and active XO's, by a German engineer named Mr Guido Wasser, likely will cost you both a house and a marriage before it's finished.
And yeah, there's even real Water involved in the Wasser-Werke.
"Wasser-Werke" is German for Water Works, btw.
Hi all
I have used violin pick-up (piezo pick-up) to monitor the vibrations of speaker enclosures and it works very well.
Viewing it's output on the oscilloscope, listening to it through headhone amp. or recording on a wave.file for further analysis are all feasible. And it is cheap.
On wave file, you can feed the signal of the speaker leads on one channel and the pick-up signal on the other channel.
Then you look for amplitude, frequency spectrum and time delay of the pick-up signal in relation to the stimulus (speaker leads signal).
Regards
George
I agree up to a point.
Sound waves travelling in air within the enclosure will hit some boundaries of another medium.
For what happens at such a boundary, you may find the attachment useful.
But for the part of the acoustic energy that succeeds in entering the other medium, we have to consider the absorption of this energy into this medium (energy dissipation mostly in the form of heat).
Regards
George
PS. When you look at the tables of acoustic properties, for simplicity, you have to take into account only the "VL" velocity. This is the velocity of Longitudinal waves. Gaseous media (air) supports only longitudinal waves.
Thanks George! That was very kind of you to post. I was wondering about sound absorption with regards to this impedance mismatch. Presumable If the mismatch is large you wil just end up with huge standing wave problems because the waves will just be reflected back around the cabinet? However if the mismatch is not so great and the waves are able to propagate through the new material, presumably the next important step is to ensure that the material will absorb the wave energy rather than resonating along with them.
Maybe a graduated lamination from low impedance mismatch at the first boundary to get the waves in then laminations or layers of something which would absorb the waves further in so the cabinet does not resonate externally?
If the impedance mismatches where greater as you went through at least the reflected waves would have to travel back through more material before going back into the cabinet?
If a layer which had a high impedance mismatch was placed at the most outside edge would this possibly have the effect of creating an enclosure which had a similar damping capability of double the material thickness due to the "return journey" of the waves as they travelled back upon reflection at this outer boundary?
These thoughts are not qualified by any expertise, just my application of what little physics/wave knowledge I have garnered so I may be way off. It's good to get the thoughts of those who know to keep me in the right direction
Thanks for the idea about a piezo pickup for measuring external cabinet resonance. I was considering putting sand on it and running a frequency sweep to see when it started to dance
Your idea sounds far more useful !!!
Maybe a graduated lamination from low impedance mismatch at the first boundary to get the waves in then laminations or layers of something which would absorb the waves further in so the cabinet does not resonate externally?
If the impedance mismatches where greater as you went through at least the reflected waves would have to travel back through more material before going back into the cabinet?
If a layer which had a high impedance mismatch was placed at the most outside edge would this possibly have the effect of creating an enclosure which had a similar damping capability of double the material thickness due to the "return journey" of the waves as they travelled back upon reflection at this outer boundary?
These thoughts are not qualified by any expertise, just my application of what little physics/wave knowledge I have garnered so I may be way off. It's good to get the thoughts of those who know to keep me in the right direction
Thanks for the idea about a piezo pickup for measuring external cabinet resonance. I was considering putting sand on it and running a frequency sweep to see when it started to dance
Your idea sounds far more useful !!!
Yes
Yes
Yes. This is what I think.
Yes, if you don't want to dissipate them as with the above sentence of yours.
Not exactly. At first, the effect of gradual impedance mathing is not the same as dissipation. Furthermore, for the return jorney, you have to apply the same formula, but now media 1 becomes media 2 and vice versa. This will not give you straight analogous results. Try it on paper.
Please note the following:
The final transition from one medium to another using intermediate layers of materials with progressivelly increasing impedances, is used in optics extensivelly for to reduce reflections, making for sharper image. The two media is air and lens. The intermediate layers are the coatings on the lens surfaces. I've seen up to 5 layers of coating on both sides of lenses. (There dissipation is not their target. On the contrary)
Regards
George
In Post #36 I was referring to “airborn” sound waves, i.e. sound waves originating from the rear side of the speaker cone, traveling into the air of the enclosure cavity and impinging on the walls of the enclosure.
How much of the speaker cone waves will reach the enclosure walls, is a matter of the intervening medium: air and amount of acoustic staffing. Then, for the acoustic waves that will reach the enclosure walls, we would do better to make them “damp” their energy onto the walls and guiding this damped energy into an energy converter, in order to:
Weaken the internal acoustic waves, so they do not hit back strong on the speaker cone and colour it’s sound
and
Reduce vibrations of the enclosure panels, so they do not become another source of sound.
In fact, there is another source of sound waves we want to get rid off.
This is the vibration that is transmitted from the speaker chassis to the enclosure walls through the speaker outer rim and the attaching screws.
May be this vibration (call it “landborn”) is more severe than the “airborn” one.
The remedy options are (at least ) two:
Either the speaker chassis is firmly attached to the enclosure, so the vibrations of the speaker are fully transmitted (“sucked”) into the massive or dissipative or massive and dissipative enclosure walls,
Or
The speaker chassis is attached to the enclosure in a mechanically lossy way (and no attaching screws), so the vibrations of the speaker are not transmitted into the enclosure walls. For this second case, I think that the speaker chassis has to be massive and well damped.
Regards
George
How much of the speaker cone waves will reach the enclosure walls, is a matter of the intervening medium: air and amount of acoustic staffing. Then, for the acoustic waves that will reach the enclosure walls, we would do better to make them “damp” their energy onto the walls and guiding this damped energy into an energy converter, in order to:
Weaken the internal acoustic waves, so they do not hit back strong on the speaker cone and colour it’s sound
and
Reduce vibrations of the enclosure panels, so they do not become another source of sound.
In fact, there is another source of sound waves we want to get rid off.
This is the vibration that is transmitted from the speaker chassis to the enclosure walls through the speaker outer rim and the attaching screws.
May be this vibration (call it “landborn”) is more severe than the “airborn” one.
The remedy options are (at least ) two:
Either the speaker chassis is firmly attached to the enclosure, so the vibrations of the speaker are fully transmitted (“sucked”) into the massive or dissipative or massive and dissipative enclosure walls,
Or
The speaker chassis is attached to the enclosure in a mechanically lossy way (and no attaching screws), so the vibrations of the speaker are not transmitted into the enclosure walls. For this second case, I think that the speaker chassis has to be massive and well damped.
Regards
George
gpapag said:
I feel this is an interesting problem to tackle...
remedy one- the speaker walls would have to be of sufficient mass in comparison to the signal applied to dissipate this energy in such a way as not to create further "non-complimentary" waves in a noticeable way... or at least how much dissipation is required for any unwanted sound not to be noticeable?
remedy two- something similar to most acoustic damping techniques applied to industrial machinery (I think) but this is inevitably going to lead to reductions in efficiency of the driver as presumably the force it reacts to to create sound is the resultant force it applies to whichever material it is attached to when displacing air... the old newtonian each and opposites etc....
I can only see the former working or ... ummm well maybe I'm out of my depth here and I need someone who knows more to interject... its late and thus bedtime
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