I am trying to understand the difference, if any, of cabinet vibration at the 1st modes (first breathing modes of loudspeaker cabinet resonance) if it is within the pressure frequency region. For a smaller cabinet the frequency band-width where sound acts in pressure mode is wider. So if the first resonant modes fall in this region is more of the energy (back wave of driver) transferred to the vibrating cabinet walls than if this first resonance was further up and passed the pressure zone? I guess this question would be similar to the concept Room Gain/Car Gain and if there is an effect caused by the walls/doors/panels of the room/car vibrating at frequencies where room/car gain comes into play. What would the consequences be?
Now to complicate things what if we also have a port/passive radiator present (open window, or car door to the outside).
What I have read is that if a port is present on a cabinet, lets say tuned to 50hz, there is only a depressurisation of the cabinet at frequencies up to twice the tuning frequency. So past 100hz (and if the loudspeaker is small enough) pressure is maintained above said frequency. So if a cabinet had its first mode below the 100hz, lets say 80hz, it could affect the port output. I would assume it would act like another mass spring system (another port)? Would the presence of the port mitigate the cabinet vibration so that it is less prevalent than if no port was present?
Any insights would be helpful.
Now to complicate things what if we also have a port/passive radiator present (open window, or car door to the outside).
What I have read is that if a port is present on a cabinet, lets say tuned to 50hz, there is only a depressurisation of the cabinet at frequencies up to twice the tuning frequency. So past 100hz (and if the loudspeaker is small enough) pressure is maintained above said frequency. So if a cabinet had its first mode below the 100hz, lets say 80hz, it could affect the port output. I would assume it would act like another mass spring system (another port)? Would the presence of the port mitigate the cabinet vibration so that it is less prevalent than if no port was present?
Any insights would be helpful.
I do not understand your first paragraph and consequently the question/s being asked.
Cabinet vibration is driven by 1) the internal air pressure and 2) the drivers shaking the baffle. The former is only large enough to be of significance at low frequencies normally well below the frequency of the lowest cabinet resonance. Consequently it is common to ignore it when designing a cabinet to radiate low levels of sound and consider only the drivers to be forcing the cabinet resonances. For woofers/subs in tiny sealed cabinets it may be wise to check the cabinet motion is OK in terms of stresses, strains and loading the driver even though irrelevant to cabinet resonances.
Cabinet vibration is driven by 1) the internal air pressure and 2) the drivers shaking the baffle. The former is only large enough to be of significance at low frequencies normally well below the frequency of the lowest cabinet resonance. Consequently it is common to ignore it when designing a cabinet to radiate low levels of sound and consider only the drivers to be forcing the cabinet resonances. For woofers/subs in tiny sealed cabinets it may be wise to check the cabinet motion is OK in terms of stresses, strains and loading the driver even though irrelevant to cabinet resonances.
I don't really understand your terms, but I think you are referring to standing waves? It seems to me that standing waves by nature can't ever overlap with the simple pressure zone because a simple pressure zone is due to wavelengths much larger than any internal dimension, so constructive/destructive interference cannot happen at any point in the air volume. Whereas standing waves have wavelengths on the same order of the internal dimensions. so there can be internal interference. This can impact port response, so adequate lining and possibly additional damping at the center of the air volume are required.
Simple flexing of walls in the simple pressure zone is resolved with bracing.
Panel resonances aren't related to either of these things, and driver isolation and CLD panels work best in this area.
Simple flexing of walls in the simple pressure zone is resolved with bracing.
Panel resonances aren't related to either of these things, and driver isolation and CLD panels work best in this area.
I've isolated machnical vibration by mounting drivers in a box, inside the main enclosure (supported by foam gaskets), and the main enclosure STILL vibrates (I can feel the vibration when my hand is on the speaker). I've also bolted 4.5 Kg of cast iron to speaker magnets, and still the enclosure vibrates. I tried back to back drivers, coupled together and floating in the main enclosure, and still it vibrates (in this case I think there's flex caused by bass pressure, but I could be wrong). It's my ambition to make a speaker enclosure that has no vibration whilst playing music.
So all the energy of the inner mvt of the cone is diseaparing(ing) thanks to the bracing ? really ? Pression left not dosspated in heat, no ? Or all is backed on the inside cone and all is solved (forget heavy dense and losy cabinet walls ?)
Mass Spring Mass attenuation does not exist anymore ?
Hello Andy,
This is what I was getting at. "The former is only large enough to be of significance at low frequencies normally well below the frequency of the lowest cabinet resonance". What if the frequency of the cabinet is at these low levels. That is what I was trying to get at.
Hello diyiggy.
Yes. The idea is to understand the pressure force and how it affects Cabinet resonance. More specifically if the Fundamental Frequency is low enough to be in the Simple Pressure Zone how it is affected, vs if it is not within the Simple Pressure zone.
Hello Cracked Case,
Energy has to go somewhere. I would assume by adding more mass to the isolated driver more mechanical energy is converted to acoustic energy. And this acoustic energy has to go someplace. If it isnt being absorbed completely inside the cabinet (stuffing) or shunted out of the cabinet (speaker stands, feet..etc.) the enclosure will vibrate. The way it vibrates is the complicated part to understand (hence my initial questions). If the cabinet is made of flat panels you can research transmission loss through plates and get a better idea of how this transmission works (resonant frequency, critical frequency) in the different regions (stiffness controlled, mass controlled and damping controlled regions). All these regions change according to materials used, thickness, stiffness, youngs modulus..etc. I would try to understand at what frequency you are getting resonance at. What is your cabinet made of? Then you can understand how to best control the acoustic energy that leaves the back of your driver.
Augerpro, the cabinet I am using is sufficiently small as to have the standing waves much higher in frequency (so this is not my problem). I was interested in the area where the wavelengths are much longer than the cabinet, in my cabinet up to 500hz. So if I had a cabinet resonance anywhere under 500 hz I wanted to know the affect it would have.
This is what I was getting at. "The former is only large enough to be of significance at low frequencies normally well below the frequency of the lowest cabinet resonance". What if the frequency of the cabinet is at these low levels. That is what I was trying to get at.
Hello diyiggy.
Yes. The idea is to understand the pressure force and how it affects Cabinet resonance. More specifically if the Fundamental Frequency is low enough to be in the Simple Pressure Zone how it is affected, vs if it is not within the Simple Pressure zone.
Hello Cracked Case,
Energy has to go somewhere. I would assume by adding more mass to the isolated driver more mechanical energy is converted to acoustic energy. And this acoustic energy has to go someplace. If it isnt being absorbed completely inside the cabinet (stuffing) or shunted out of the cabinet (speaker stands, feet..etc.) the enclosure will vibrate. The way it vibrates is the complicated part to understand (hence my initial questions). If the cabinet is made of flat panels you can research transmission loss through plates and get a better idea of how this transmission works (resonant frequency, critical frequency) in the different regions (stiffness controlled, mass controlled and damping controlled regions). All these regions change according to materials used, thickness, stiffness, youngs modulus..etc. I would try to understand at what frequency you are getting resonance at. What is your cabinet made of? Then you can understand how to best control the acoustic energy that leaves the back of your driver.
Augerpro, the cabinet I am using is sufficiently small as to have the standing waves much higher in frequency (so this is not my problem). I was interested in the area where the wavelengths are much longer than the cabinet, in my cabinet up to 500hz. So if I had a cabinet resonance anywhere under 500 hz I wanted to know the affect it would have.
Yes, the energy has to go somewhere. I am trying to find out how this energy moves around. The bracing will just push up the fundamental resonance frequency unless it is a damping brace that doesnt change strength of cabinet (like kef does). The mass spring attenuation is what I am getting at. Since room gain and car gain create such high increase in volume I would assume that more force is at play here when compared to frequencies that are not in the Pressure Zone. This force puts into movement a passive radiator and the air in a port so I would assume it can put into motion a lot more easily a fundamental resonance if it is low enough. If this is the case I would also assume that it would affect port performance.
To be honest, I'm tempted to just cheat, and have an extra enclosure (like an acustic hood) over the speaker, with an opening for the drivers, that has an air gap between the two (I hope to do this with my quad cube speakers).
I'm also tempted to have really thin walls with lots of dampening applied; it would be prone to flexing from internal pressure because of the lack of rigdidity, but so heavily damped that it would be to dead to resonate.
I'm also tempted to have really thin walls with lots of dampening applied; it would be prone to flexing from internal pressure because of the lack of rigdidity, but so heavily damped that it would be to dead to resonate.
No competently designed conventional cabinet will be close. A non-conventional one using very thin panels and weak bonding between the panels just might but what would be the reasoning behind such a design? It also might end up being well damped and not much of a problem.
What is a simple pressure zone? The force from the internal air pressure on the cabinet at the frequency of normal cabinet resonances is usually negligible compared to the force on the cabinet from the reaction to the acceleration of the cone/coil assembly.
The work done compressing the air inside the cabinet by the cone is largely returned to the cone when the air is expanded. There is a small amount of energy transferred overall but not much. When the internal dimensions approach a quarter wavelength internal stuffing will be effective at dissipating sound. There doesn't seem to be an issue of significance.
We're mixing different sources of energy, and different mechanisms, and talking about it like it is one source and one mechanism. The reason you hear what you hear sitting inside or car, or even inside a speaker box, are due to different mechanisms that what you would hear standing outside the car or speaker box. Also, the mechanisms at play change with frequency, due to changes in the wavelength versus certain dimensions. Internal air mass dimensions in the case of standing waves, and panel dimensions in the case of panel resonances. These are different mechanisms with different causes.
My position is that some of these cannot exist at the same time, they are mutually exclusive. For example, regarding the internal air mass, any behavior at frequencies that are in the simple pressure zone cannot have anything to do with behavior at higher frequencies where standing waves form. For the reason I mentioned above, you are talking about a different relationship of wavelength to internal dimension, on the one hand very large wavelengths compared to internal dimensions, and on the other, wavelengths on the order of the internal dimensions.
Then you have the behavior of the panels themselves, which having nothing in common with internal air mass behavior I just described. For example, stuffing in the middle of the internal air mass will damp the standing waves, but will do nothing for the panel resonances. Different mechanisms at play.
Your port example is simply about the internal air mass. Properly damp the standing waves, and the problem can usually be solved. Port placement makes a difference too.
As for where the energy goes when you brace, into the material of course. You add a stress to the structure, but if strain is lower, sound radiation will be low too. This applies in the simple pressure region, NOT the panel resonance region, which again, cannot ever be the same region.
If you are looking at the panel resonance region specifically, it is the result of the particular panel dimensions. Nothing to do with standing wave of the internal air mass. Now simple transmission of sound through the internal air mass and then into the panels can supply the energy for the resonances (Andy might disagree here), and also through direct vibration of the driver attached to the panel. But neither of these have anything to do with standing waves, or the simple pressure region of the internal air mass. Here you will have to use damping of the panels themselves. I think CLD construction is best, or application of aluminum-backed butyl sheets.
My position is that some of these cannot exist at the same time, they are mutually exclusive. For example, regarding the internal air mass, any behavior at frequencies that are in the simple pressure zone cannot have anything to do with behavior at higher frequencies where standing waves form. For the reason I mentioned above, you are talking about a different relationship of wavelength to internal dimension, on the one hand very large wavelengths compared to internal dimensions, and on the other, wavelengths on the order of the internal dimensions.
Then you have the behavior of the panels themselves, which having nothing in common with internal air mass behavior I just described. For example, stuffing in the middle of the internal air mass will damp the standing waves, but will do nothing for the panel resonances. Different mechanisms at play.
Your port example is simply about the internal air mass. Properly damp the standing waves, and the problem can usually be solved. Port placement makes a difference too.
As for where the energy goes when you brace, into the material of course. You add a stress to the structure, but if strain is lower, sound radiation will be low too. This applies in the simple pressure region, NOT the panel resonance region, which again, cannot ever be the same region.
If you are looking at the panel resonance region specifically, it is the result of the particular panel dimensions. Nothing to do with standing wave of the internal air mass. Now simple transmission of sound through the internal air mass and then into the panels can supply the energy for the resonances (Andy might disagree here), and also through direct vibration of the driver attached to the panel. But neither of these have anything to do with standing waves, or the simple pressure region of the internal air mass. Here you will have to use damping of the panels themselves. I think CLD construction is best, or application of aluminum-backed butyl sheets.
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My own definition is the region below the primary panel resonances (and standing waves for that matter), where the movement of the panels is not due to their resonance frequency, but lower in frequency, and due to simple flexing from air pressure changes inside the box.
It's worth remembering, while chasing this particular rabbit down the hole, that a significant proportion of the backwave is re-radiated through the cone. In my experience this is often mistaken for enclosure panel resonance as that energy is strongly coloured by the modes inside the box.
Those very long wavelengths won't energize the panel resonances. Only wavelengths equal to the wavelengths of the panel resonances will (obviously). So at those long wavelengths, or better said, at those low frequencies, panel resonances are not your concern. Simple flexing of the panel is the problem. Bracing is the solution here, ignoring any other considerations. I doubt CLD or lining on walls will do much because the mechanisms are different.
Maybe through the rubber surround, but how much really goes through the cone itself? It is not acting like a piston up until its breakup mode? And if it does vibrate it would be in pace with the actual original signal I would assume, but I can see how standing waves could affect this. This cone stiffness would be equivalent to the stiffness area Simple Pressure Zone definition by aguer (which I wrongly used before), most commonly know as the stiffness controlled region. Past the cone breakup mode I can understand how the sound can transmit more easily.
There is indeed a subject...sealed and vented are not the same, hence the more stuffed sealed cabinet.... does not mean that stuffing is enough btw.
I had only ever heard it referred to as the stiffness controlled region when referring to something vibrating: a low frequency stiffness controlled region, a high frequency mass controlled region and an interesting bit in the middle possibly referred to as the dampiing/resistance controlled region depending on what is going on.
Yeah that was just my own description, I didn't know what the engineers called it. Thanks.
Probably the only way to achieve that is to make a sphere that has 2 drivers, mounted opposite each other and with mechanically coupled magnets, wired in push-push mode. I have built such subs in metal and you cant feel anything even if the bass drivers go at full pelt.
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