Beyond the Ariel

[soongsc]

Originally posted by Baseballbat
Hi,



the input changes, from maybe a single sine to zero, and this change is also an input, and the system reacts to it. The reaction is dependant of the complex frequency response, so on the group delay.

Bye


Baseballbatboy

So what difference will it make when you stop the input at 0 of a sine wave vs peak of a sine wave?

[gedlee]

Originally posted by mige0



You don't necessarily have to put yourself down, Earl

– looking at the bright side –
I'd say you have developed confidence in your *subjective* power of judgment and found the courage to express *without* asking for proof of the scientific world (or even the scientist in you)


Michael

Michael

I don't think that I put myself down. I just don't see any point in getting into the subjective "it sounds good to me" domain. And the reality is quite the contray to what you express - I have absolutely no confidence in my own subjective opinion, and actually, no one elses either. I have done so much subjective testing both myself and with other subjects to know how totally pointless most subjective impression are. I have seen "golden ears" who's opinions changed 180 degrees overnight and others who couldn't repeat a listening test blind if their life depended on it. I myself have made outrageous errors in listening when mistakes were made and not caught. No - as far as subjective evaluations go I have no confidence.

On the other hand, as I have made my speakers better and better objectively, virtually all of the subjective opinions over a large number of listeners and time have tracked the improvements perfectly. I have never been fooled by the numbers.

In that situation, would you bother with anything subjective?

[gedlee]

Originally posted by soongsc

So what difference will it make when you stop the input at 0 of a sine wave vs peak of a sine wave?

Soongsc

There is a great deal of difference spectrally in these two things. It has to do with "spectral leakage". When a sine wave fits exactly into the FFT window - at the zero crossings - then there is no "leakage" and the spectral peak will be exactly as it should be - on the sine wave frequency. However, if the sine wave does not fit exactly from zero to zero then the spectral peak will leak into the bins on either side. The greater the "bad fit" the greater the leakage.

[Rick Miller]

We have talked about the influence of cabinet material in the past, and I wanted to share a link to some measurement data from Wilson Audio. It shows the different “signatures” of material used to make speaker enclosures. It’s interesting to see how the walls of your speakers react to stimulation. A thanks goes out to Wilson for posting the measurements on the web. http://www.wilsonaudio.com/sasha/science.html

[pjpoes]

I believe the debate over cabinet materials was never whether measurements of their characteristic resonances could be done showing significant differences, but rather, what to make of those differences. First, there seems to be debate over the source of the vibrations. Is it sound transmitting from the speaker into the cabinet's internal air cavity, and then back into the cabinet materials itself, or is it a more direct path from the speaker through the frame, and then into the cabinet.

Then you have the issue of the audibility of differences. Wilson contends, like many other builders of very expensive speakers, that a material which has no ringing or strong modes when measured directly (such as through direct contact, accelerometers, etc.) reflects a very big impact on the sound of the speakers. That minimizing these modes, as they have, will make their speakers sound better. That is debatable, there is no definitive tests to show this. Lot's of subjective opinions exist, but I've seen nothing to indicate that we know reducing cabinet modes through exotic materials, as measured by these methods, will correlate to perceived improvements in sounds.

I think one problem is the measurement system that's used. I don't see that a contact measurement like that necessarily is a good analogue to how these modes might impact things audibly. If I was to look for the impact of cabinet modes as having an audible impact on the speaker, I would for the effects in the free field measurement of the speaker as well as the impedance trace. If you don't see the same resonance in the speakers output and a corresponding glitch in the impedance curve, I don't see how less cabinet noise will change the sound of the final speaker in any way.

However, after extensively talking with others on this subject around here, performing my own measurements and listening tests, etc. I've come to the conclusion that, of all the things to worry about in speaker design, this is not a major one. I think that a basic well constructed enclosure can be had by use of decent creative bracing, CLD panels in key locations, and thats about as far as it needs to go. If everything else has been made perfect on the speaker, and the only thing left is ensuring that the cabinet is resonance free for that last .000001% difference, then I could see putting money into better cabinet materials. However, I just don't see it contributing a significant amount of the final speaker sound. I have numerous measurements of test cabinets made with different materials, different dampening, bracing, etc, and I can show huge differences in the side measurements. However, I can't show any difference in the impedance plot without making a terrible enclosure (paper thin unbraced walls), I typically show no correlation to wall modes and FR measurements that I feel comfortable attributing to cabinets resonances, and I have never felt I could reliably hear a difference. Again, unless I made the cabinet so poorly as to be completely unrealistic.

[gedlee]

Nice post Matt - well said.

[xpert]

Originally posted by pjpoes
I believe the debate over cabinet materials was never whether measurements of their characteristic resonances could be done ...

Hmm,

DIY tends to over emphasize things that are at hand. In this case, the housing of the speakers. From wood over concrete to lead (in last consequence) is anything affordable for the hobbyist including the neccesary craftsmanship. Excellence is the minimum ...

Sound that transmitts through cabinet walls is not distortion in its own. In most cases it wouldn't add to distortion at all. No intermodulation. Just some little ragged amplitude response on +/-0.2dB level. And consequently some micro seconds of group delay. Harmless.

Good speaker design is about linearity, directivity, distortion. May be Wilson is through with that. From the graphs I've seen published I'm not to sure.

so long

ps: I took a glance at Wilsons "science" page. Great misuse of Cummulative Spectral Decay pictures, isn't it? Really catchy.

[ScottG]

Originally posted by gedlee


In that situation, would you bother with anything subjective?

Of course - its a part of life.

..and you can always add "others under control testing either do or don't support this position". (perhaps even offering limited but specific data if you desire.) You can use subjective excerpts from others (on the particular issues being argued), as you have done in the past (..though again, better to quote those statements to the specific issue discussed with a link for the rest). (..and of course you can compare and contrast such opinions to measurements.)

The goal isn't to preach "this is the way it is", rather it's there to say:

"hey, you might find this interesting enough to explore for yourself and perhaps share your own experiences".

[soongsc]

Originally posted by gedlee


Soongsc

There is a great deal of difference spectrally in these two things. It has to do with "spectral leakage". When a sine wave fits exactly into the FFT window - at the zero crossings - then there is no "leakage" and the spectral peak will be exactly as it should be - on the sine wave frequency. However, if the sine wave does not fit exactly from zero to zero then the spectral peak will leak into the bins on either side. The greater the "bad fit" the greater the leakage.

Thanks. I was expecting Baseballbatboy to respond. There were some following questions related with Group Delay and Cumulative Spectral Decay.

[soongsc]

Originally posted by Rick Miller
We have talked about the influence of cabinet material in the past, and I wanted to share a link to some measurement data from Wilson Audio. It shows the different “signatures?of material used to make speaker enclosures. It’s interesting to see how the walls of your speakers react to stimulation. A thanks goes out to Wilson for posting the measurements on the web. http://www.wilsonaudio.com/sasha/science.html

I kind of think we need to look at how this stimulation compares against speaker driver decay and room decay characteristics to determine whether effort in this area is well spent or not.