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Old 21st May 2007, 11:12 PM   #361
Geoff H is offline Geoff H  Australia
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Hi John, thanks for the charts. I expected to see more of a difference.

The problem with a f/r chart is it needs to be compared with distortion figures. A rise of 3 dB for example, may be due to a resonance of some sort, and not a huge issue to most.

It could also be due to the harmonics of a sub multiple of that frequency. A trap with software testing.

Real results need a manual sweep and a tuned filter, not just measuring the wideband output from a swept sine wave or pink noise.
That takes more gear and time.

Geoff.
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Old 22nd May 2007, 12:24 AM   #362
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Hi Geoff.
The whole point of the exercise was to show the audible difference between materials. Using the same drive unit in each box takes away the only possible variable.
To be honest, I expected more of a difference also, especially between the two higher grade materials (BB and MDF), and spruce sheathing.
I tried to be as scientific and consistant as possible with these tests. To my way of thinking, that means using an accepted measurement method, and removing as many variables as possible. The program uses an MLS signal at a high sample rate, repeated 7 times then averaged. I can't see how the method you descibed would be more accurate.
I took the time to run these test to satisfy myself as well as to post here. If anyone else knows of a more detailed study, or if someone with a better test procerdure and equipment would like to run the tested, thats fine.
But for me at least, the question is answered - there's no signicant difference in the sound quality of a box built with either baltic birch or MDF.
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Old 22nd May 2007, 12:33 AM   #363
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Quote:
Originally posted by MJL21193
But for me at least, the question is answered - there's no signicant difference in the sound quality of a box built with either baltic birch or MDF.
Did you listen to the different boxes? Or are you going to let the graphs tell you what they sound like?

I don't think your tests are conclusive.

I have a whole crowd of people who heard a difference between 2 otherwise identical pairs of speakers made with MDF & plywood -- they couldn't agree which they liked better, but what they heard was consistent.

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Old 22nd May 2007, 12:45 AM   #364
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Quote:
Originally posted by planet10


I don't think your tests are conclusive.

Without looking into my crystal ball, I could see this coming.

How much more could I do? The boxes were not for listening. I heard the MLS signal, but honestly, listening is too subjective. It's coloured by any number of variables, such as mood, time of day, stress level, preconceptions. It's not a reliable, consistant measure of a materials quality.
How seriously would you take me if my results were based on my 41 year old ears?
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Old 22nd May 2007, 12:59 AM   #365
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Quote:
Originally posted by MJL21193
How seriously would you take me if my results were based on my 41 year old ears?
I don't have to -- you are the only one who matters for your speakers. I already have my own results. Besides individual sessions, a group test with some 20-odd people and at least a couple sets of really well trained ear/brain systems. A post test scrutiney showed that what people heard was generally consistent.

Listening tests are fraught with potential problems, but no more than a mic, SW & a sound-card. And in the end it isn't the computer listening to the speakers.

"In all things audio, the ear is the final arbiter."
Harry Olson

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Old 22nd May 2007, 01:08 AM   #366
tinitus is offline tinitus  Europe
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MJL... its good work you have done ... but I also think that music is much more complex than a test signal .... maybe that does make a difference somehow
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Old 22nd May 2007, 02:57 AM   #367
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Quote:
Originally posted by tinitus
MJL... its good work you have done ... but I also think that music is much more complex than a test signal .... maybe that does make a difference somehow

Thanks Tinitus.
Music is complex, so why is it that a favourite track is not used for acoustic measurements? The following is a quote from PureBits.com:
"MLS in a nutshell...
MLS is an abbreviation for Maximum Length Sequence. It is basically a pseudo-random sequence of pulses.
Nowadays Maximum Length Sequence measurements are quite standard in many different application fields. One of them is acoustics.

Using MLS techniques, it is possible to perform quasi-anechoic measurements of a loudspeaker without having to place it inside an anechoic chamber (a room free from echoes and reverberations). The impulse response can be easily windowed in the time domain, in order to analyze the signal and reject the reflections from the walls of the room. Moreover the room impulse response itself (and all the related parameters such as reverberation time) can be measured.
The MLS method can also be used to analyze and obtain information about the impedance or the absorption coefficient of a surface. "

Fairly straight forward - a signal tailor made for testing acoustics.
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Old 22nd May 2007, 03:20 AM   #368
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Quote:
Originally posted by planet10

I don't have to -- you are the only one who matters for your speakers. I already have my own results. Besides individual sessions, a group test with some 20-odd people and at least a couple sets of really well trained ear/brain systems. A post test scrutiney showed that what people heard was generally consistent.
I have sold speakers, traded them for other things, and even given them away. I've not heard any complaints.
Earlier in this thread (i think) we discussed the validity of the listening test detailed above, and my opinion still stand.
The whole reason for this thread in the first place was your advice not to use MDF - use anything except MDF, even solid wood (and softwood at that). Yet in the face of all of the evidence presented here (and also by ShinObiwan, on another thread), you refuse to concede.
What more can I say?

Quote:
Listening tests are fraught with potential problems, but no more than a mic, SW & a sound-card. And in the end it isn't the computer listening to the speakers.

"In all things audio, the ear is the final arbiter."
Harry Olson
[/B]
What do you use to simulate a speakers response? Pen and paper? An abacus? Trial and error? Pretty sure you use a computer for this complex analysis. I do, and I generally trust the results. Same goes for measurement.
In the end the ear is the final judge, but IMO a million other factors are more important to good sound quality than the kind of wood used.
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Old 22nd May 2007, 08:24 AM   #369
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Quote:
Originally posted by MJL21193
(and also by ShinObiwan, on another thread),
Which when analysed further supported my contention...

As i've said before, you don't have to prove anything to me, i've done my own tests and the proof is in the product. Not that that is going to stop me from getting even better at it.

Quote:
What do you use to simulate a speakers response? Pen and paper? An abacus? Trial and error? Pretty sure you use a computer for this complex analysis. I do, and I generally trust the results.
The analysis only gets you into the ballpark. There are many things that the computer doesn't tell you, and one has to rely on experience & actually building the things & tweaking from there.

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Old 22nd May 2007, 04:37 PM   #370
Geoff H is offline Geoff H  Australia
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"The analysis only gets you into the ballpark. There are many things that the computer doesn't tell you, and one has to rely on experience & actually building the things & tweaking from there."

That can work the other way too. If I can hear a possible problem, I may use a computer to identify the problem in order to find a fix.

What we are trying to establish is what may be a better material to build with. One thing I know for sure is MDF is worse than particle board.

BB Ply is out of the equation here in Oz. If you can find it, it's very expensive - some went on e-bay a while back at well over $100 a sheet, plus freight.

John, your testing has been interesting. It means we need to keep looking, who knows, we may find something better than what we are using now, if we are not satisfied. The swept sine wave I described earlier is only useful for frequency response, and as I demonstrated in another thread, only shows a small part in how a speaker sounds.

Regards,
Geoff.
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