Enclosure resonances, not a big deal?

[badman]

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....

[gedlee]

Originally posted by badman
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....

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".

[gainphile]

Try to stick your head/microphone into a loudspeaker cabinet and hear what's there . These are things OB lovers can live without

The best measured rear-wave attenuated box speakers is the Pluto I think, it's like 40db down reflected rearwave. It also still audible.

[planet10]

Originally posted by gedlee
These resonances DO occur, sure, but are they a significant factor to the sound quality

Both box resonances & air space resonances can have a very significant effect.

As the counterexample that shows they do, the quarterwave resonance in boxes like transmission lines & horns are counted on to have significant effects,

dave

[xpert]

Originally posted by planet10


Both box resonances & air space resonances can have a very significant effect.

As the counterexample that shows they do, the quarterwave resonance in boxes like transmission lines & horns are counted on to have significant effects,

dave

With the latter You intend to have resonances. You have to have 2 meters ++ of pathlength, and a port to let it out. Standard boxes have pathlengths of maximum 1 meter, segmented, well damped, no outlet.

Measure it yourself if You don't trust me. Any other wouldn't help.

[planet10]

Originally posted by xpert
You intend to have resonances

Of course you do... you are putting it to use instead of fighting it. It simply illustrates that resonances can have an effect,

You have to have 2 meters ++ of pathlength, and a port to let it out. Standard boxes have pathlengths of maximum 1 meter, segmented, well damped, no outlet.

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

[xpert]

Originally posted by planet10


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

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

[thadman]

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.

[gedlee]

Originally posted by thadman
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.

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.

[planet10]

Originally posted by thadman
determine whether or not a resonance could be equalized out using equal amplitude inversion signal processing. Brute FIR or something similar comes to mind.

They can, but not without throwing away the music that excites them.

dave