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Old 12th April 2009, 08:35 PM   #5211
Telstar is offline Telstar  Italy
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Quote:
Originally posted by Rick Miller

Most of the readers of this thread are wanting to have the best sound possible and they are doing the work themselves to have better speakers and a lot of them are using the “no box” design. Other than having no box the only way to have less box acoustic output is to make it as dense and “dead” as possible.
Quoted for truth.
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Old 12th April 2009, 08:52 PM   #5212
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Quote:
Originally posted by Telstar


Quoted for truth.

Thank you Telstar.
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Old 13th April 2009, 03:00 AM   #5213
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Quote:
Originally posted by john k...
1) These are all near field measurement baffle dimension makes no difference, but it was the same in all cases.
What was the actual baffle size used?
Are the near field measurements presented totally unaffected by the baffle?

Quote:
The point here was to show what you have to deal with when building a U-frame or sealed box.
Assuming you make the worst possible design choices.

Leaving aside the issue of damping:
- the “U-frame” is the equivalent of mounting the driver on one end of an 8” long tube with the same diameter as the cone and leaving the other end open.
- the “sealed box” is equivalent to mounting the driver in a cube (7” x 7” x 8”) that is too small (volume wise) for the driver.

Both represent very poor design choices - which is easily seen when compared with the open baffle plot.
Also, if the baffle has no influence in the near field measurements, the absolute low frequency plot of the open baffle is not indicative of real world performance.

Cheers,

Alex
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Old 13th April 2009, 03:35 AM   #5214
dlr is offline dlr  United States
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Quote:
Originally posted by Alex from Oz


What was the actual baffle size used?
Are the near field measurements presented totally unaffected by the baffle?



Assuming you make the worst possible design choices.

Leaving aside the issue of damping:
- the “U-frame” is the equivalent of mounting the driver on one end of an 8” long tube with the same diameter as the cone and leaving the other end open.
- the “sealed box” is equivalent to mounting the driver in a cube (7” x 7” x 8”) that is too small (volume wise) for the driver.

Both represent very poor design choices - which is easily seen when compared with the open baffle plot.
Also, if the baffle has no influence in the near field measurements, the absolute low frequency plot of the open baffle is not indicative of real world performance.

Cheers,

Alex
You need to re-read John's posts carefully, as you've missed his points entirely.

Dave
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Old 13th April 2009, 07:14 AM   #5215
mige0 is offline mige0  Austria
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Quote:
Originally posted by gedlee

I had a long talk with Laurie Fincham of THX some time back about THD. He said that he is very close to elliminating it from all THX specifications because no one could PROVE its relavence to perception. This was enlightening since for the first time I found someone who saw the issue as it is. It's not the burdon of the sceptic to prove that THD isn't relevent, its the burdon of the believer to prove that it is. According to Laurie, THX has not been able to find any solid evidence that THD is meaningful. Only that its easy to do.



THX is a company of salesmen and for sure no reference when it comes to subtle effects of audio.

Years back, I measured the so called "THX crossover" cinema owners have to buy to proudly stick a THX logo onto their movie theatre.

Oh boy – what a hyperbole s**t they sell !

What THX *did* for us, was to address and make aware of audio related issues like
- air condition noise
- speaker rattling
- room acoustic (isolation and reverberation)
- FR equalising within a some tolerances over more than one seat

and last but not least with the points above they established kind of minimum standard for how to do cinema rooms.

But really - forget about their audio-equipment recommendations.- its all about making money (at best).

This is not to say you might be completely wrong about significance of THD measurements – but you really don't need a THX guy's opinion for that.


Michael
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Old 13th April 2009, 09:07 AM   #5216
FrankWW is offline FrankWW  Canada
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Laurie Fincham is not chopped liver:

http://www.malcolmsteward.co.uk/wordpress/?page_id=94

Does it not occur to you he may have gone to THX because they see need for improvement?
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Old 13th April 2009, 11:05 AM   #5217
mige0 is offline mige0  Austria
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With all due respect –
who ever – in the context of THX - anybody is "chopped liver" to me...


By the way – his admiration of Dolby (somewhere in the middle of that interview where I stopped continuing reading) is what tells us a lot about his preferences – mere power of industry heroes (one of which he'd like to be / become ?).

Same as I said about THX as company applies to Dolby as company – a bunch of salesmen backuped by a host of lawyers .

Have developed preamps for film – many times better regarding noise and distortion than any Dolby equipment - main difference – my design was based on solid rules "only" – nothing you could run for a patent... - been there, done that...
D:


Michael




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Old 13th April 2009, 11:29 AM   #5218
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Quote:
Originally posted by Graham Maynard


Maybe if you did a continuos recording in time over several sine cycles your trace would behave exactly as I claim ?
It is so long since I checked, but I believe Linkwitz observed amplitude responses in Time.


Cheers ........ Graham.
I believe you are talking about shaped burst testing the SL does (did). As I said, the FR I posted is the FFt of the system impulse. If you take that impulse (or take the IFFt of the FR to recover the impulse) and convolve the impulse with a burst signal you will get exactly the same thing as you do if you measure it. They are all one in the same. The system impulse defines its response.
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Old 13th April 2009, 11:54 AM   #5219
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Quote:
Originally posted by Alex from Oz


What was the actual baffle size used?
Are the near field measurements presented totally unaffected by the baffle?



Assuming you make the worst possible design choices.

Leaving aside the issue of damping:
- the “U-frame” is the equivalent of mounting the driver on one end of an 8” long tube with the same diameter as the cone and leaving the other end open.
- the “sealed box” is equivalent to mounting the driver in a cube (7” x 7” x 8”) that is too small (volume wise) for the driver.

Both represent very poor design choices - which is easily seen when compared with the open baffle plot.
Also, if the baffle has no influence in the near field measurements, the absolute low frequency plot of the open baffle is not indicative of real world performance.

Cheers,

Alex
This is about how enclosure resonances impact cone motion. Not what is a well or badly designed enclosure. Nor is it about what the free field response of any of these system are. But if you want to know how the low frequency response is related to the near field of an OB then please review
this.

Oh, and again, what would you like th U-frame dimensions to be?
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Old 13th April 2009, 12:50 PM   #5220
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A couple of days ago I said I would post some measurements at the rear of the U-frame with different damping. Here they are.

Click the image to open in full size.

The damping material is fiberglass insulation. The key is 40ZR = 4 ounces damping material (approximately 2 lbs/ft^3), 20ZR = 2 ounces, 10ZR = 1 ounce, 00ZR = undamped. 1 ounce fills about 2/3 of the u-frame with the insulation open and fluffy. 2 oz fills the u completely with little compression. 4 oz is pretty heavy damping and the insulation is starting to be compressed.
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