One of the recent trends in loudspeaker design has been to incorporate dipole or open baffle alignments into the design. This has the obvious benefit of removing resonances within the body of air behind the diaphragm, but can this same result be achieved through another technique?
As far as I understand it, the behavior of the air within the enclosure and its effects on the loudspeaker can be thought of as a mass-spring system. The resonance or ringing due to the presence of modes within the enclosure space can be equalized out (by applying equal amplitude inversion signal processing of the resonances) because it is a linear phenomenon. The non-linear effects however can not. But where do the non-linear effects caused by the resonances arise? Is it because of nonhomogeneous pressure distribution over the surface of the diaphragm (ie higher damping in certain positions relative to lower damping in other positions) leading to erratic cone motion and thus non-linear distortion? If we managed to make the damping uniform over the surface of the diaphragm (by forcing the diaphragm to launch a 1 dimensional plane wave whose attributes only varied with distance from the diaphragm) wouldn't the observed non-linear effects due to the air vanish and become a linear phenomenon?
Thanks,
Thadman
As far as I understand it, the behavior of the air within the enclosure and its effects on the loudspeaker can be thought of as a mass-spring system. The resonance or ringing due to the presence of modes within the enclosure space can be equalized out (by applying equal amplitude inversion signal processing of the resonances) because it is a linear phenomenon. The non-linear effects however can not. But where do the non-linear effects caused by the resonances arise? Is it because of nonhomogeneous pressure distribution over the surface of the diaphragm (ie higher damping in certain positions relative to lower damping in other positions) leading to erratic cone motion and thus non-linear distortion? If we managed to make the damping uniform over the surface of the diaphragm (by forcing the diaphragm to launch a 1 dimensional plane wave whose attributes only varied with distance from the diaphragm) wouldn't the observed non-linear effects due to the air vanish and become a linear phenomenon?
Thanks,
Thadman
Re: Re: Re: Enclosure resonances, not a big deal?
I think so, I didn't experience a degradation since. My boxes are damped - reflex too - and modes were never measurable in the resulting soundfield. Of course non linear distortion was often measured but I never found anything else but rattleing from soft screws etc.
so long
thadman said:
I think so, I didn't experience a degradation since. My boxes are damped - reflex too - and modes were never measurable in the resulting soundfield. Of course non linear distortion was often measured but I never found anything else but rattleing from soft screws etc.
so long
Re: Re: Re: Re: Enclosure resonances, not a big deal?
What if pressure nodes were located along the surface of the diaphragm? Would it not be possible for the forces imposed by them to excite modes present in the diaphragm? I'm sort of thinking along the lines of aerodynamic flutter:
"Flutter is a self-feeding and potentially destructive vibration where aerodynamic forces on an object couple with a structure's natural mode of vibration to produce rapid periodic motion."
Would it be possible for pressure along the diaphragm to do something similar? Amplify structural modes that propagate non-linear vibration?
xpert said:
What if pressure nodes were located along the surface of the diaphragm? Would it not be possible for the forces imposed by them to excite modes present in the diaphragm? I'm sort of thinking along the lines of aerodynamic flutter:
"Flutter is a self-feeding and potentially destructive vibration where aerodynamic forces on an object couple with a structure's natural mode of vibration to produce rapid periodic motion."
Would it be possible for pressure along the diaphragm to do something similar? Amplify structural modes that propagate non-linear vibration?
I don't think enclosure resonances are easily solved by filtering. They're a form of ringing, so they'll keep going longer than whatever excited them. Better to build an enclosure that minimizes it.
Or be like the whackos that designed a speaker called the Adiabat, that made a "feature" of the lack of internal damping. The resonances could be clearly seen on the impedance vs frequency plot when a magazine (SGHT?) reviewed it. I'm surprised the reviewer didn't just slash open the nearest pillow and see how the speakers sounded with some stuffing.
Or be like the whackos that designed a speaker called the Adiabat, that made a "feature" of the lack of internal damping. The resonances could be clearly seen on the impedance vs frequency plot when a magazine (SGHT?) reviewed it. I'm surprised the reviewer didn't just slash open the nearest pillow and see how the speakers sounded with some stuffing.
Re: Re: Re: Re: Re: Enclosure resonances, not a big deal?
I've never seen things like that with speakers.
BTW, prefiltering does the job. I'm amazed again every time when people try to tear others into doubt about such. Yes we can! Prefiltering is absolutely O/K against spurious resonances. There is nothing behind.
thadman said:
I've never seen things like that with speakers.
BTW, prefiltering does the job. I'm amazed again every time when people try to tear others into doubt about such. Yes we can! Prefiltering is absolutely O/K against spurious resonances. There is nothing behind.
Re: Re: Re: Re: Re: Re: Enclosure resonances, not a big deal?
It does nothing to remove the resonance. The problem is still there. If there was energy in the music to excite it, you have now removed it from the music by pre-filtering. A band-aid at best,
Much much better to just cure the problem at the source and the only way to do it properly.
dave
xpert said:
It does nothing to remove the resonance. The problem is still there. If there was energy in the music to excite it, you have now removed it from the music by pre-filtering. A band-aid at best,
Much much better to just cure the problem at the source and the only way to do it properly.
dave
Guys, when can argue about the effect a butterfly flapping its wings in South America has on the sound, but is it really worth it? You have to scale these effects to put them in context or the real problems. These resonances DO occur, sure, but are they a significant factor to the sound quality - NO!. Move on!
Then why'd you bother doing a better job on the composite Summa cabs than the MDF you're selling now?
Most of us who've built loudspeakers believe/are aware that the solidity and internal resonances within a cab are readily audible. I think you know this too and just are happy to ignore it because it's one of the more expensive problems to solve....
Most of us who've built loudspeakers believe/are aware that the solidity and internal resonances within a cab are readily audible. I think you know this too and just are happy to ignore it because it's one of the more expensive problems to solve....
badman said:
Except it was the other way arround! I did the Summa first, and then the MDF enclosures. The fact that the MDF sounded as good was pretty convincing for me that the enclosure resonances were not that big a deal.
"Believe" is the key word above!! You believe its true, but its not. I've got the data, and you've got your "beliefs".
. These are things OB lovers can live without 
xpert said:
Of course you do... you are putting it to use instead of fighting it. It simply illustrates that resonances can have an effect,
The half wavelength transmission line in the B&W Nautilus tweeter is far less than 2m and does not have an outlet. The quarterwave TL in my Tysen design is less than a quarter meter long and has significant effect (as designed).
A 1m tall sealed box will act as a half-wave resonantor at ~170 Hz with harmonics at multiplies of that.
Personally i am more concerned with box panel resonance thou.
dave
planet10 said:
dave,
Don't let us argue about the most significant inch. Of course resonances could occure and they will. BTW: the B&W item is heavily stuffed and build up for the purpose to eliminate the whole sound on its pathway down the pipe.
As Mr. Geddes told You right away, the quest referres to the severity of unintended resonances, or, in this thread non linear effects are questioned. The latter would be rattling, the former, namely linear resonance can be measured on a regular basis but most often it is well below the threshold of perceptability.
To really know what happens You just measure it. There is no use in speaculations or debating some exemplary items or whatever without OWN measurements. From that You would simply know. If You can't measure, what does it lead to to talk that much without knowing?!
so long
I think a lot of you are missing the point of this thread. Acoustic resonances (standing wave, quarter wavelength, whatever you want to call them, etc) are not being debated whether audible or not. They are measurable and real in loudspeakers using enclosures. Dipoles lack them, but can the same effect be achieved in enclosure loudspeakers?
The point of this thread is to determine whether or not a resonance could be equalized out using equal amplitude inversion signal processing. Brute FIR or something similar comes to mind.
The point of this thread is to determine whether or not a resonance could be equalized out using equal amplitude inversion signal processing. Brute FIR or something similar comes to mind.
thadman said:
Well if that is the point, the answer is yes and no. The internal modes that affect the cone as a lumped mass can be exactly controlled, but any enclosure modes in the enclosure itself cannot. Basically any EQ is a single dimensional control scheme and can only ever control things that occur in only one dimension -"lumped parameter" effects. Box internal modes are basically lumped parameter, but the box stuctural modes are distributed. If EQ is used on any structural modes then it will affect the results differently at different locations. It can be shown that some locations will get better but some will get worse and that no EQ control can correct the problem globally.
The more important question is "What is SIGNIFICANTLY audible?". I don't agree any of the discussion here. If enclosure effects were audible then my speakers should sound terrible because they are nothing substantial in this regard. That's not the review that they get however. Of course enclosure resonances are a factor - it's just that they are a very small factor.
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