Anders Buen

How the air and body modes combine

Recommended Posts

In a normal violin the main air resonance, A0, lie close to c#, 270-280Hz, and the first main body mode may lie around 440 Hz ish, close to open A.

Below the A0, these two resonances will cancel and the response quickly becomes weaker for lower frequencies. But between them they do add, not much but still. Above the first body mode they will cancel again contributing to the deep valley typically found around 500 Hz.

What happens if the A0 and first body mode exchanges and the A0 lie higher in frequency than the first body resonance? Maybe a child violin have such a relation.

How does the A0 and main body resonance sum up then? Will it be the same as in a normal violin or what?

Share this post


Link to post
Share on other sites

I'm not totally sure what you mean by the modes "cancelling"... as in opposite phase, or just that they are both declining at the same time?

Between A0 and B1- there is the CBR, which I don't think you can ignore.  I don't often see it on impact hammer results, but it is usually much stronger bowed.  One of my recent violins had the CBR much stronger than B1-, and I'm not sure why.

I think it would take a huge change in concept to get the A0 frequency higher than the B1- frequency, such as making huge F-holes.  That would kill off any body mode at lower than A0 frequency, as air from the inside would be cancelling the outside volume change.  That doesn't happen if the A0 is the lowest frequency.

Share this post


Link to post
Share on other sites
4 hours ago, Anders Buen said:

In a normal violin the main air resonance, A0, lie close to c#, 270-280Hz, and the first main body mode may lie around 440 Hz ish, close to open A.

Below the A0, these two resonances will cancel and the response quickly becomes weaker for lower frequencies. But between them they do add, not much but still.

What is the mechanism of this cancellation and addition?

Share this post


Link to post
Share on other sites

Hi Anders, Don

Could you go the other direction and make the A0 frequency real low towards the G at 196 Hz to avoid cancelling the out of phase B1-?  Sort of like a viola with violin pitch strings.

But I think it is important that the B1- frequency isn't an octave above A0 in order to avoid having a strong fundamental and a strong first overtone which might cause a wolf note.

Share this post


Link to post
Share on other sites
14 minutes ago, David Burgess said:

What is the mechanism of this cancellation and addition?

A0 is blowing out air through the f holes while B1- is trying to suck air in.  Or vice versa.

Share this post


Link to post
Share on other sites
6 hours ago, David Burgess said:

What is the mechanism of this cancellation and addition?

I think it is related to what WeiNreich called the «toothpaste effect». Below the A0 the air will pump out of the holes if the body is squeezed, and above the A0 the air will have turned phase so that it pumps in at the same time as the body is squeezed. Then the air and body work in the same direction and their effects add with  the same sign for the «monoplole». 

The squeesing is sort of thought of as the effect of the first «breathing» body mode driven by the bridge.

Share this post


Link to post
Share on other sites
8 hours ago, Don Noon said:

I'm not totally sure what you mean by the modes "cancelling"... as in opposite phase, or just that they are both declining at the same time?

Between A0 and B1- there is the CBR, which I don't think you can ignore.  I don't often see it on impact hammer results, but it is usually much stronger bowed.  One of my recent violins had the CBR much stronger than B1-, and I'm not sure why.

I think it would take a huge change in concept to get the A0 frequency higher than the B1- frequency, such as making huge F-holes.  That would kill off any body mode at lower than A0 frequency, as air from the inside would be cancelling the outside volume change.  That doesn't happen if the A0 is the lowest frequency.

It is opposite phase between air flow and body motion.

Agree on the CBR, which may also give some net volume change too. But a more complicated vibration. Some good violins do have a radiating CBR. 

If the f-holes were made larger than normal and we had a small body the swich of position might happen? I suppose even small insturments do have the A0 as the lowest resonance anyway.

I am asking the question because floating floors with venting of the void beneath may have a «A0» that might influence the performance of the floor. I have a scale model for it, a 3l ice box with some resilienat layer (rubber foam) and a fllor surface of harboard with a slit in it on top of that. That slit and airspace should give an A0. No one seems to have thought this through for floors and nothing can be found on it. 

Such floors can be mounted on springs e.g. But if the airspace under the floor is not vented it will be stiffer than wanted, and the performance becomes impaired. Venting creates an A0, but hwi does that affect the performance?

I think my model box floor has a high A0 and the floor resonance lower, which would be equivalent to the situation I ask about in terms of bowed instrument bodies.  

May be relevant for bass reflex loudsdpeaker designs too.

Share this post


Link to post
Share on other sites

If you make a violin out of infinitely stiff material so there is, in effect, no B1- mode, then A0 will have a certain frequency. 

If you put a typical violin in a vacuum so there is, in effect, no A0 mode, then B1- will have a certain frequency.

Once you have a violin made out of regular material in an atmosphere, the modes become physically coupled to each other and their characteristic frequencies change based on that coupling. There is no inherent cancelling or reinforcing based strictly on observed frequency of vibration. Cancelling or reinforcing of air movement is a rather complicated function of the driving frequency (note being played) relative to the frequency of each mode and the internal sound damping of the air for the air mode and the wood for the body mode.

When playing notes on the G string, I would expect the A0 mode to be moving most of the air for the lower harmonics and the B1- mode doing almost nothing. For the higher harmonics, the A0 would see very little excitement while the B1- would spring into action. For notes played on the A string, the reverse would be true.

Share this post


Link to post
Share on other sites
8 hours ago, Anders Buen said:

I think it is related to what WeiNreich called the «toothpaste effect». Below the A0 the air will pump out of the holes if the body is squeezed, and above the A0 the air will have turned phase so that it pumps in at the same time as the body is squeezed. Then the air and body work in the same direction and their effects add with  the same sign for the «monoplole». 

The squeesing is sort of thought of as the effect of the first «breathing» body mode driven by the bridge.

Thanks, Anders.

When I have superimposed two frequencies, I often found that they could reinforce or cancel each other, within very narrow ranges like one or two hertz, and could have various effects like generating lower sub-harnonics or "tartini" tones or "beats", well below the frequencies which violins are conventionally thought to emit.

Share this post


Link to post
Share on other sites
9 hours ago, Anders Buen said:

It is opposite phase between air flow and body motion.

Agree on the CBR, which may also give some net volume change too. But a more complicated vibration. Some good violins do have a radiating CBR. 

If the f-holes were made larger than normal and we had a small body the swich of position might happen? I suppose even small insturments do have the A0 as the lowest resonance anyway.

I am asking the question because floating floors with venting of the void beneath may have a «A0» that might influence the performance of the floor. I have a scale model for it, a 3l ice box with some resilienat layer (rubber foam) and a fllor surface of harboard with a slit in it on top of that. That slit and airspace should give an A0. No one seems to have thought this through for floors and nothing can be found on it. 

Such floors can be mounted on springs e.g. But if the airspace under the floor is not vented it will be stiffer than wanted, and the performance becomes impaired. Venting creates an A0, but hwi does that affect the performance?

I think my model box floor has a high A0 and the floor resonance lower, which would be equivalent to the situation I ask about in terms of bowed instrument bodies.  

May be relevant for bass reflex loudsdpeaker designs too.

Being a former floorguy I wonder what you mean by "influence the performance of the floor" ?  Are you talking about sound deadening and absorption for inner floor construction? or are you talking about influencing it's effects and how it works in a space like a concert hall? trying to incorporate a floor system into acoustic parameters of the space? Or are you talking about sports floors when you talk of "too stiff" or stiffer than wanted? 

Share this post


Link to post
Share on other sites
42 minutes ago, jezzupe said:

Being a former floorguy I wonder what you mean by "influence the performance of the floor" ?  Are you talking about sound deadening and absorption for inner floor construction? or are you talking about influencing it's effects and how it works in a space like a concert hall? trying to incorporate a floor system into acoustic parameters of the space? Or are you talking about sports floors when you talk of "too stiff" or stiffer than wanted? 

It is two or three factors: 1. the sound insulation between floors, 2. the impact sound insulation between floors, and 3. the "drum sound" we experience in the same room as the floating floor is mounted. For the noise from dropped weights in gyms, the best technology according to suppliers and some acousticians are spring supported heavy floating floors. In theory it is possible to get very low resonance frequencies by choosing soft springs and a fairly large distance between them, e.g. 2x2 m. A similar solution is to use other types of material like rubber blocks or technical PUR foams distributed in a similar manner, but they tend to be a bit stiffer. Next step is to use continuous layers of mineral wool, glass wool, PUR foam, or elasticised EPS.  

The sound insulation, and particularly the impact noise reduction, is much determined by the main resonance frequency of the floating mass and stiffness of the springs or supports. A simple mass-spring-dashpot system. For higher freqencies than the main resonance we get an insulating effect, quite steep with increasing frequency. This is similar to classic vibration insulation. Around the main resonance we get a worseing of the response compared to no floating floor present, and for frequencies below, not much happens. 

However, many suppliers disregard the stiffness of the enclosed air. And I am pretty sure not many do know how the Helmholz resonance may influence the response of a floor. If we have 20mm of ventilation slit around a 4x5m heavy floating floor on springs, the Helmholz resonance should be around 60 Hz ish using a bass reflex model calculator. We know a violin and a guitar, or an empty plastic bottle responds pretty lively around the Helmholz resonance if we tap it or simply handle them. I would believe that a floor could do so too. And it may impair the super duper insulation effect of the expensive spring supported heavy floating floor, with theoretical resonance frequency of say 5 Hz. The question is how? 

I do have a simple model for it, but it is difficult to decide what is the Helmholz resonance and what are other responses. It is also difficult to figure out the effect if the Helmholz resonance if above the main floating floor resonance. 

A closed airspace of some 30 mm would give a resonance without springs at ca 20 Hz, so if no venting is used, some 25 Hz is what we get for the theoretical spring floor of 5 Hz. And then the floor does not perform better than a cheaper point supported floor using e.g. rubber blocks, glass fiber cubes (Kintetics KIP), or technical PUR like Sylomer. With a lower airspace it may not perform better than a traditional concrete on mineral wool floor, the most usual solution for e.g. rehearsal room floors for amplified music. 

This is nerding and off violin acoustics. But the models from there can be used, I think, as well as for loudspeaker designs. E.g. a port resonance for a bass reflex loudspeaker is probably always lower in frequency than the loudspeaker element resonance, which by the way also is much dependant on the air stiffness of the loudspeaker volume. I could e.g. play with this on a loudspeaker with varying port depth. However, my loudspekaers are pure pressure types. 

Share this post


Link to post
Share on other sites
17 hours ago, Marty Kasprzyk said:

Hi Anders, Don

Could you go the other direction and make the A0 frequency real low towards the G at 196 Hz to avoid cancelling the out of phase B1-?  Sort of like a viola with violin pitch strings.

But I think it is important that the B1- frequency isn't an octave above A0 in order to avoid having a strong fundamental and a strong first overtone which might cause a wolf note.

Thans Marty. I guess you describe one of your violin designs with a very low and strong A0 we have heard in Oberlin. It sounded more like a viola or even a cello for the lowest notes on the G string. :-)

I guess what you say about the A0 and B1+ frequencies may be smart.  

Share this post


Link to post
Share on other sites
2 hours ago, ctanzio said:

Once you have a violin made out of regular material in an atmosphere, the modes become physically coupled to each other and their characteristic frequencies change based on that coupling. There is no inherent cancelling or reinforcing based strictly on observed frequency of vibration. Cancelling or reinforcing of air movement is a rather complicated function of the driving frequency (note being played) relative to the frequency of each mode and the internal sound damping of the air for the air mode and the wood for the body mode.

When playing notes on the G string, I would expect the A0 mode to be moving most of the air for the lower harmonics and the B1- mode doing almost nothing. For the higher harmonics, the A0 would see very little excitement while the B1- would spring into action. For notes played on the A string, the reverse would be true.

I enclose a graph from Shellengs classical article The Violin As a Cirquit from 1963 explaining the A0 and B1- modes and how they influence the resulting response. The resonances have skirts that may play a role also at distances from the resonances, especially if there are nothing else going on in those regions. I think the model for a loudspeaker port (A0) and the main loudspeaker cone resonance (B1-) is acting similarly.

I wonder what happens if they change sequence. B1- first then the A0. Obviously that is not a good instrument design, or maybe it just cant happen for a wooden box with a hole in it instrument, as Don indicates. I would have guessed that his increasingly cut top plate instrument would be such a test and could have a higher A0 than B1- at some point, but then the design would be something complely different also affecting the response. Maybe the Hutchins "Swiss Cheese Violin" with corked holes in the ribs would get a high A0 at some point? 

Shelleng A0 B1- diagram.jpg

Share this post


Link to post
Share on other sites
7 hours ago, Anders Buen said:

It is two or three factors: 1. the sound insulation between floors, 2. the impact sound insulation between floors, and 3. the "drum sound" we experience in the same room as the floating floor is mounted. For the noise from dropped weights in gyms, the best technology according to suppliers and some acousticians are spring supported heavy floating floors. In theory it is possible to get very low resonance frequencies by choosing soft springs and a fairly large distance between them, e.g. 2x2 m. A similar solution is to use other types of material like rubber blocks or technical PUR foams distributed in a similar manner, but they tend to be a bit stiffer. Next step is to use continuous layers of mineral wool, glass wool, PUR foam, or elasticised EPS.  

The sound insulation, and particularly the impact noise reduction, is much determined by the main resonance frequency of the floating mass and stiffness of the springs or supports. A simple mass-spring-dashpot system. For higher freqencies than the main resonance we get an insulating effect, quite steep with increasing frequency. This is similar to classic vibration insulation. Around the main resonance we get a worseing of the response compared to no floating floor present, and for frequencies below, not much happens. 

However, many suppliers disregard the stiffness of the enclosed air. And I am pretty sure not many do know how the Helmholz resonance may influence the response of a floor. If we have 20mm of ventilation slit around a 4x5m heavy floating floor on springs, the Helmholz resonance should be around 60 Hz ish using a bass reflex model calculator. We know a violin and a guitar, or an empty plastic bottle responds pretty lively around the Helmholz resonance if we tap it or simply handle them. I would believe that a floor could do so too. And it may impair the super duper insulation effect of the expensive spring supported heavy floating floor, with theoretical resonance frequency of say 5 Hz. The question is how? 

I do have a simple model for it, but it is difficult to decide what is the Helmholz resonance and what are other responses. It is also difficult to figure out the effect if the Helmholz resonance if above the main floating floor resonance. 

A closed airspace of some 30 mm would give a resonance without springs at ca 20 Hz, so if no venting is used, some 25 Hz is what we get for the theoretical spring floor of 5 Hz. And then the floor does not perform better than a cheaper point supported floor using e.g. rubber blocks, glass fiber cubes (Kintetics KIP), or technical PUR like Sylomer. With a lower airspace it may not perform better than a traditional concrete on mineral wool floor, the most usual solution for e.g. rehearsal room floors for amplified music. 

This is nerding and off violin acoustics. But the models from there can be used, I think, as well as for loudspeaker designs. E.g. a port resonance for a bass reflex loudspeaker is probably always lower in frequency than the loudspeaker element resonance, which by the way also is much dependant on the air stiffness of the loudspeaker volume. I could e.g. play with this on a loudspeaker with varying port depth. However, my loudspekaers are pure pressure types. 

I assume your trying to invent a floor system for a project you are working on? Or are you and the guys at the gym getting tired of all that noise? 

Any sound deadening systems that I've done have been for between floor noise reduction for high end condos and stuff like that. It is my experience that the in room noise is a direct reflection of what the interior finished floor material will be, obviously harder surfaces are more reflective. 

Any of the systems I've done in the past have avoided creating air pockets and have usually relied on some type of laminated system of sound deadening under layments.

Any weight or gym rooms that I've done have had foam/rubber matting placed on top of the existing finished floor on top of the the sound absorbing subfloor. These have been primarily recreational in home type gyms

But I am curious as to why you are brainstorming on this one, I do feel that there is a market for a floating laminate flooring that is engineered to be quite that requires no excessive subfloor system. Basically a wear surface that is backed by a sound deadened backer that is robust enough be installed and retain dimensional stability. Perhaps the core could be manipulated with chambers to increase the effect, I would think cubed chambers with pin holes in an elastic material that would allow them to compress and slowly release air , yet be elastic enough to re expand, thus sucking the air back in after being compressed by stepping on the area.

 

 

Share this post


Link to post
Share on other sites

The width of the "skirt" about each peak, typically taken at -3dB from the peak, correlates directly with internal energy loss (damping) for that mode of vibration. 

The horizontal axis represents the frequency of the note relative to the natural frequency of the mode. So when the note frequency lines up with the mode natural frequency, the peak is the highest.

The dip between A0 and B1- is mostly due to the note frequency being "far" from the natural frequency of either mode, rather than any significant cancelling of air motion between the two modes.

In terms of the ability to generate raw acoustic power across the playing spectrum, you want a lot of natural modes crammed across the playing spectrum. In other words, figure out how to create more natural modes in that frequency range.

Simply switching the position of the A0 and B1- modes might not do much in terms of power or tone, assuming one could figure out how to do such a thing without a significant redesign of the basic shape of the violin.

 

Share this post


Link to post
Share on other sites
8 hours ago, ctanzio said:

>

The dip between A0 and B1- is mostly due to the note frequency being "far" from the natural frequency of either mode, rather than any significant cancelling of air motion between the two modes.

>

Referring to Anders' attachment of Shellengs' diagram:

Below the A0 peak the A0 tail and the B1-tail cancel because A0 and B1- are out of phase so there is little output

The phase of A0 changes above the A0 peak so the A0 and B1- tails add together and there is a large output between the A0 and B1-peaks.

 

Share this post


Link to post
Share on other sites
1 hour ago, Marty Kasprzyk said:

Referring to Anders' attachment of Shellengs' diagram:

Below the A0 peak the A0 tail and the B1-tail cancel because A0 and B1- are out of phase so there is little output

The phase of A0 changes above the A0 peak so the A0 and B1- tails add together and there is a large output between the A0 and B1-peaks.

 

A mathematical "circuit" is created for the A0 effects and numerically simulated, i.e., as if there is no B1-. That is the "air" line in the diagram.

A similar thing is done for the B1- effects. That is the "body" line.

The two circuits are then coupled and the new circuit simulated.

Because these are two complex, COUPLED motions acting simultaneously, there will be small time segments where the effects do cancel, and other time segments when they reinforce. For any driving frequency, the combined plot represents the TIME AVERAGE of these effects.

Phase variations certainly enter into the results, especially at driving frequencies between the natural frequencies of the two modes, but the dominant effect is the rapid decrease in the amplitude of each mode that drives the sound output that is observed in the uncoupled results.

It is not a simple case of "Oh, they are completely out of phase. That is why it drops off so rapidly."

 

Share this post


Link to post
Share on other sites
12 hours ago, ctanzio said:

Simply switching the position of the A0 and B1- modes might not do much in terms of power or tone, assuming one could figure out how to do such a thing without a significant redesign of the basic shape of the violin.

I disagree.  At these frequencies, sound is a monopole driven by volume change (and air resonance).  With the B1- being higher than the A0, there is not much coming out of the soundholes to cancel the external volume change (at the B1- frequency).

If the A0 is higher than the B1-, then the B1- will see significant cancellation from opposite-phase leakage from the soundholes.

In relation to Anders' floor situation, I think it is clear that at 5 Hz structure resonance and 60 Hz air resonance, the top and back side of the floor at 5 Hz will cancel each other out.  Think of a speaker in a 60 Hz ported enclosure driven at 5 Hz...whatever pressure is coming from the front will see nearly  equal and opposite pressure from the port.  You'd still get a resonance at 60 Hz, though.  Things would be different if we were talking about a huge floor where the dimensions of the floor become comparable to the air wavelength.

Share this post


Link to post
Share on other sites

I just saw in the «Why you hear what you hear» book that adding Helium gas into the violin body will move the A0 significantly upwards and make the violin sound tinny. However, I do not know if it would move enough to pass the the main body resonance. 

Share this post


Link to post
Share on other sites
17 hours ago, jezzupe said:

I assume your trying to invent a floor system for a project you are working on? Or are you and the guys at the gym getting tired of all that noise? 

Any sound deadening systems that I've done have been for between floor noise reduction for high end condos and stuff like that. It is my experience that the in room noise is a direct reflection of what the interior finished floor material will be, obviously harder surfaces are more reflective. 

Any of the systems I've done in the past have avoided creating air pockets and have usually relied on some type of laminated system of sound deadening under layments.

Any weight or gym rooms that I've done have had foam/rubber matting placed on top of the existing finished floor on top of the the sound absorbing subfloor. These have been primarily recreational in home type gyms

But I am curious as to why you are brainstorming on this one, I do feel that there is a market for a floating laminate flooring that is engineered to be quite that requires no excessive subfloor system. Basically a wear surface that is backed by a sound deadened backer that is robust enough be installed and retain dimensional stability. Perhaps the core could be manipulated with chambers to increase the effect, I would think cubed chambers with pin holes in an elastic material that would allow them to compress and slowly release air , yet be elastic enough to re expand, thus sucking the air back in after being compressed by stepping on the area.

 

 

I am running a sort of semi private research project on gym noise. It is a problem when gyms are in the same building as apprartments. Impacts from dropped weights are very strong impact sources. And yes, thick mats can help. But even 70-80mm thick mats on 100-150mm concrete floating on 50-100mm mineral wool or something more fancy like point supports of rubber, EPDM, technical PUR or springs, still there will be annoying impacts heard in these appartments.

I do also lift weights and I am educated in physics. The problem is interesting and the suppliers of floors does not share the single numbers we need, the insertion losses. It is difficult as a consultant (my daytime job) to assess the different floors objectively, and not many in the field know much about what sources there are in gyms. 

I do have transducers, software etc for acoustic testing of violins. These are handy for scale tests of floors and how they behave eg In scale 1:10. I draw ideas from the violin acoiustics knowledge and try to incorporate this into the understanding of how a floor behaves if it is vented.

How the A0 of a floating floor influences the floor performance would be a new insight in the field. Maybe it is not so important for the performance, or maybe it is. I am sure the theory behind it is not very complex. 

It is quite easy to hear if there are say 100mm concrete floating floor in a gym versus just mats on the heavier floor slab of say 200-250mm concrete or something similar. If there were holes in the floor or slits around the perimeter for venting, I think we would hear it, but at a very low frequency. Bassy. That effect probaly also would act on the floor below, and thus carry on to the rest of the building. The main mass spring resonance does transfer in that manner. My idea is that the A0 also might be transferred as a significant contributor.

I do have ideas maybe we could utilize the A0 for improvement of the very low frequencies, add porous material to the ports to boraden or deaden the response, or have distributed ports with something in them. The helholz principle is used for absorption of sound in rools too, often with a porous material behind the slats or perforated polates. Somewhat like haveing a lot of violins in a room with cotton in their f-holes. Would be absorbers of sound around c#. 

Share this post


Link to post
Share on other sites

A0 is related to, but not the same as, the Helmholtz frequency of the ported box. A0 arises from the coupling between the breathing mode component of the B modes and the Helmholtz resonance. The frequency is a bit lower than that of the "bare" Helmholtz resonance. If you filled the box with helium, the helmholtz frequency would increase by about a factor of 3 (it scales with the speed of sound in the gas). The low frequency body breathing modes could then no longer couple to/drive the Helmholtz resonance, so A0 as we understand it wouldn't exist. There might be coupling with higher frequency  body modes, but that would be a different can of worms, I think.

That's what I reckon, anyway :D

For a definitive answer you'd need to ask the Goughmeister.

Share this post


Link to post
Share on other sites
4 hours ago, Don Noon said:

I disagree.  At these frequencies, sound is a monopole driven by volume change (and air resonance).  With the B1- being higher than the A0, there is not much coming out of the soundholes to cancel the external volume change (at the B1- frequency).

If the A0 is higher than the B1-, then the B1- will see significant cancellation from opposite-phase leakage from the soundholes.

In relation to Anders' floor situation, I think it is clear that at 5 Hz structure resonance and 60 Hz air resonance, the top and back side of the floor at 5 Hz will cancel each other out.  Think of a speaker in a 60 Hz ported enclosure driven at 5 Hz...whatever pressure is coming from the front will see nearly  equal and opposite pressure from the port.  You'd still get a resonance at 60 Hz, though.  Things would be different if we were talking about a huge floor where the dimensions of the floor become comparable to the air wavelength.

So a loudspeaker with the A0 above the B1- (cone resonance) would be much weaker in the lows than the opposite traditional design then?

Floors usually are 4-5m or more in both directions. @60 Hz the wavelength is 6m-ish comparable to the floor dimension. But often the mockups tend to be smaller and without the «Ribs», just open at the sides. There will be resonances in the air anyway, like inside the violin, but I assume not an A0 before there are some sort of port involved. 

Share this post


Link to post
Share on other sites
8 minutes ago, JohnCockburn said:

A0 is related to, but not the same as, the Helmholtz frequency of the ported box. A0 arises from the coupling between the breathing mode component of the B modes and the Helmholtz resonance. The frequency is a bit lower than that of the "bare" Helmholtz resonance. If you filled the box with helium, the helmholtz frequency would increase by about a factor of 3 (it scales with the speed of sound in the gas). The low frequency body breathing modes could then no longer couple to/drive the Helmholtz resonance, so A0 as we understand it wouldn't exist. There might be coupling with higher frequency modes body modes, but that would be a different can of worms, I think.

That's what I reckon, anyway :D

For a definitive answer you'd need to ask the Goughmeister.

Yes, Colin Gogh. :-) But 3 times is enough to reach far above the B1-. Must find party balloons or gas. :-)

Share this post


Link to post
Share on other sites
49 minutes ago, Anders Buen said:

I am running a sort of semi private research project on gym noise. It is a problem when gyms are in the same building as apprartments. Impacts from dropped weights are very strong impact sources. And yes, thick mats can help. But even 70-80mm thick mats on 100-150mm concrete floating on 50-100mm mineral wool or something more fancy like point supports of rubber, EPDM, technical PUR or springs, still there will be annoying impacts heard in these appartments.

I do also lift weights and I am educated in physics. The problem is interesting and the suppliers of floors does not share the single numbers we need, the insertion losses. It is difficult as a consultant (my daytime job) to assess the different floors objectively, and not many in the field know much about what sources there are in gyms. 

I do have transducers, software etc for acoustic testing of violins. These are handy for scale tests of floors and how they behave eg In scale 1:10. I draw ideas from the violin acoiustics knowledge and try to incorporate this into the understanding of how a floor behaves if it is vented.

How the A0 of a floating floor influences the floor performance would be a new insight in the field. Maybe it is not so important for the performance, or maybe it is. I am sure the theory behind it is not very complex. 

It is quite easy to hear if there are say 100mm concrete floating floor in a gym versus just mats on the heavier floor slab of say 200-250mm concrete or something similar. If there were holes in the floor or slits around the perimeter for venting, I think we would hear it, but at a very low frequency. Bassy. That effect probaly also would act on the floor below, and thus carry on to the rest of the building. The main mass spring resonance does transfer in that manner. My idea is that the A0 also might be transferred as a significant contributor.

I do have ideas maybe we could utilize the A0 for improvement of the very low frequencies, add porous material to the ports to boraden or deaden the response, or have distributed ports with something in them. The helholz principle is used for absorption of sound in rools too, often with a porous material behind the slats or perforated polates. Somewhat like haveing a lot of violins in a room with cotton in their f-holes. Would be absorbers of sound around c#. 

I do feel at a certain point there is only so much one can bend the psychics within the one parameter and that solutions for the problem you are dealing with come from not only designing and engineering a gym flooring system but to also start looking at the weights themselves and what can be done to dampen and lower output when they are dropped, such as being coated with something like this stuff, and to have poly bushings and and washers 

Beyond being quieter, if the weights were covered in something like this it may be more safe by reducing injuries from dropping them on fingers and feet. A material like this could also be used as a core for the flooring.

Another solution may be to set up wire harness's for the free weights that don't interfere with the lifting but "belay" down the weights softly on the way down, thus preventing any slamming down. This also could be a backup safety feature.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.