Enclosure resonances, not a big deal?

[gedlee]

Originally posted by thoriated


Probably Gedlee considers a 10db difference 'a very small effect', since it would only result in a 1db amplitude disturbance or less.

The amount a 10 dB change in extraneous sound radiation makes to the amplitude response depends on how far down this radiation is in the first place. If its down far enough then a 10 dB change makes no difference at all. I was not able to detect any amplitude response changes that could be linked to structural changes. That IS a data point.

[planet10]

Originally posted by thoriated
A crude but useful way to get an idea of what any given panel is contributing to the overall sound is to, while music is playing, place one end of a pen, pencil or similar lightweight small diameter rod against the the portion of the panel in question and press the other end near the ear, closing off the air channel to the eardrum. This will use bone conduction to selectively filter for the panel contribution. MDF sounds awful using this technique in my experience.

A mechanics stethoscope works REALLY well.

dave

[planet10]

Originally posted by gedlee
The amount a 10 dB change in extraneous sound radiation makes to the amplitude response
depends on how far down this radiation is in the first place. If its down far enough then a 10 dB change makes no difference at all.

I'm not exactly sure what you are saying here.

But, i'm not overerlly concerned with anything that would affect the typical measured FR, of concern to me is any extraneous noise that will affect the signal 30-40-50 dB down. It is this delicate part of the signal that is important in giving the music greater reality and subtle imaging clues.

thoriated mentions "MDF sounds awful using this technique in my experience... tend to 'drone'"

This is exactly the continuous ouzing of delayed energy that obscures low-level detail. The prime (sonic) reason i stay away from MDF.

dave

[thoriated]

How's this? For audiophiles, MDF is the woodworking equivalent of the electrolytic capacitor.

[gedlee]

Originally posted by planet10

But, i'm not overerlly concerned with anything that would affect the typical measured FR, of concern to me is any extraneous noise that will affect the signal 30-40-50 dB down. It is this delicate part of the signal that is important in giving the music greater reality and subtle imaging clues.

dave

Hi Dave

This point is a guess on your part that is unsubstantiated and generally not in line with data regarding masking etc. If this IS your belief then I understand your position, however, you must understand that little to nothing in psychoacoustics would support this kind of conclusion.

[gedlee]

Originally posted by thoriated
How's this? For audiophiles, MDF is the woodworking equivalent of the electrolytic capacitor.

No, better would be "MDF is the woodworking equivalent of Oxygen Free Copper." Electrolytic problems are a real effect and I don't use them for that reason.

[planet10]

Originally posted by thoriated
How's this? For audiophiles, MDF is the woodworking equivalent of the electrolytic capacitor.

Good one. To be avoided if at all possible.

dave

[badman]

Originally posted by gedlee


Hi Dave

This point is a guess on your part that is unsubstantiated and generally not in line with data regarding masking etc. If this IS your belief then I understand your position, however, you must understand that little to nothing in psychoacoustics would support this kind of conclusion.

Have you done masking tests with music/dynamic content rather than overlaying frequencies upon a steady state wave?

Also, when the input ceases, if there's stored energy resonating in the enclosure but not the driver output to mask it, couldn't that be audible where it might be masked during the conditions that start it resonating?

"It's too low in level to be audible" is an excuse to be lazy in addressing known issues. That might have been said of HOMs, eh? But you found the ear-brain mechanism have some variability in its sensitivity, did you not? Much more sensitive at higher amplitudes, etc? Perhaps box resonance is something that we're sensitive too in a variable fashion and the tests performed did not emulate our sensitivities effectively. You of all people should be attuned to the fact that microphones and ears act differently.

[gedlee]

Originally posted by badman
You of all people should be attuned to the fact that microphones and ears act differently.

I am quite attuned to this, but I'm also not prone to jump at obscure issues that are obviously of minimal impact just because some audiophool claims that he "hears them".

IF, and that is a big "if", cabinet resonances were to be audible then it would be the tail of the resonance that would be the most audible. This is identical to the HOM situation (which, by the way IS completely consistant with psychoacoustic studies NOT contrary to them) since it is a group delayed effect which is not masked effectively. But, UNLIKE HOM, the enclosure resonances are likely to be much lower in level that the primary sound. HOMs can be nearly equal in level to the main signal in a worst case, and would always be greater in level than enclosures resonances. Hence, I cannot see the case for enclosure resonances being anything at all on par with HOM, especialy since, as I said, I tried to measure them and could not. I HAVE measured HOMs!

The entire side of this discussion which believes in "box effects" is without anything of support except for "beliefs". The real data is all on the other side.

[Pano]

Originally posted by gedlee
What you hear is what YOU hear, that is not data.

Indeed it IS what I hear. It could be "data" if compared to what other people hear.

When I hear differences that are super subtle and ephemeral I don't get too interested. But differences as big as box resonances, or the lack of them? Those are too obvious to ignore. The difference between 3/4 MDF and 3/4" Baltic birch? I don't know. But the difference between cheap 5/8" ply and 1" super dense marine ply? That I DO know. Ditto sand filled walls.

The question should be of "how much stuffing, bracing, damping is needed to get the coloration down to a level where they don't matter?" That level is going to be different for different folks. And the techniques used to get there will be different. But it can be done.

<rant>
Trouble is (for me, anyway) that this forum has become almost as useless as A-A. Ask a practical question about building, then get an endless argument telling you what you hear or how you approach the problem is useless, misguided, unscientific, not measured right, whatever. How the hell is anyone supposed to build anything? Real, practical experience seems to count for nothing.

Reading many threads on this forum one might conclude that any changes or improvements you make are useless, bogus, the result of an over active imagination, stupidity or voodoo. Apparently everything sounds the same and it's easy to build a perfect a perfect speaker, amp, DAC, whatever. “Just do it my way, cause everyone else is wrong.”

Talk about useless..... </rant>