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Multi-Way Conventional loudspeakers with crossovers

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Old 26th December 2012, 12:17 PM   #931
Pano is offline Pano  United States
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Quote:
Originally Posted by Barleywater View Post
Plus is that wavefront formation is coherent even up very close, and may be listened to up close as nearfield monitors.
Yes, very much so.
Kudo's to your buddy and his woodwork, those are very pretty.
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Old 26th December 2012, 12:23 PM   #932
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Thanks Pano, Jeremy does very nice woodwork indeed!
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Old 26th December 2012, 07:14 PM   #933
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Originally Posted by CopperTop View Post
I can't help but reproduce this quote from Rod Elliott when talking about baffle step effects:
If the driver is crossed over below its baffle step the issue is reduced, if low enuff no issue at all. 4" pipe, BS -3dB ~1140 Hz, 5" 912 Hz.

dave
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Old 27th December 2012, 01:22 PM   #934
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The piston doesn't have a baffle stop. Baffle may me considered to start at effective edge of radiating surface. In case of SEAS Prestige L16RN-SL (H1480) 6" driver, SD is given as 104 square centimeters, which is effective diameter of roughly 4.5", and in my case this is centered in a pipe with OD of 6.75", leaving a baffle that is 2.25". Radiation aperture at 1kHz is much closer to a sphere than to a flat plane. Thus why it is described as omnidirectional below 1kHz. When the physics in space immediately behind the driver are understood, it becomes clear that no lateral wave transmission occurs below 1kHz in a 6" ID pipe. Think inside a box 6" on a side, 1kHz is single mode.

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Old 27th December 2012, 05:49 PM   #935
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Quote:
Originally Posted by Barleywater View Post
The piston doesn't have a baffle step... in my case this is centered in a pipe with OD of 6.75"
Your speaker is immune to the laws of physics?

On-axis response will look something like this (with a 6.75" baffle -- frequency scale multiplied by ~3.5). Since thr real driver is not a point source, actual response will be more complex (more ripple, less amplitude)

Click the image to open in full size.

Now in this instance the listening axis is at 90 degrees which will affect things.

dae
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Old 27th December 2012, 06:06 PM   #936
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maybe he was talking about the other orientation?
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Old 27th December 2012, 08:04 PM   #937
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Originally Posted by planet10 View Post
Your speaker is immune to the laws of physics?
Law's of physics on which planet?

Nice cartoon. How about reality:

SEAS 0 and 90 degree.gif


Above are measurements of woofer mounted in pipe pointing at ceiling. Woofer has been equalized on listening axis as used in 2-2way set up. Yellowish trace is listening axis, blueish is vertical axis above woofer. Tweeter arm is not present. Measurements are gated to about 6ms.
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Old 27th December 2012, 09:07 PM   #938
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Quote:
Originally Posted by Barleywater View Post
Law's of physics on which planet?

Nice cartoon. How about reality:

Attachment 319948


Above are measurements of woofer mounted in pipe pointing at ceiling. Woofer has been equalized on listening axis as used in 2-2way set up. Yellowish trace is listening axis, blueish is vertical axis above woofer. Tweeter arm is not present. Measurements are gated to about 6ms.
Well, well. Your actual measures show pretty much what the "cartoon" from Olson (real world studies done at RCA in the lates 40s. early 50s) would predict given the realative size of the membrance in the pipe, but worse than i would have expected in the sense that the baffle-step ripple is extending lower in frequency than expected.

You have to be careful dissing giants like Harry Olson. "Acoustics" is one of the must reads for anyone designing speakers. The graph is from page 23, and represents a real-world measurement -- no screen grabs in those days.

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Old 27th December 2012, 10:49 PM   #939
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Cartoon shows +/-5dB. Results are likely for tiny radiator, and is just the kind of stuff that leaves potentially great approach unexplored till the 21st century.

And yes, always something has to give. I'm sure narrow baffle towers with thin skinned full range drivers show more interesting response. The display FFT is 8192 point, so low end shows a little more ripple.

Mind this is quick setup, and a real live result. Pick at it all day.


We are all working with the same physics.

zoom 60-300 FFT65k.gif

Same listening axis measurement, no gate, 65k point FFT spectrum. Wall, floor, and ceiling reflections are clearly seen in IR, and contribute to the result.

As infrequent as real results of current designs are on this, and other audio forums, I've seen many that look a whole lot lumpier:

Click the image to open in full size.

The above result is considered promising. Even with heavy stock, internal bracing, and more damping, low end response will likely remain like this. But maybe some published results exist for an optimized version/variation of this.

Nobody seems in a rush to post up, likely because nothing fundamentally has changed in decades.

Linkwitz offers up something a little different, and with DSP techniques it is taken further.

I've no disrespect for Olson and the other giants, quite the contrary. I show great respect in repeating and duplicating experiments, demonstrating scientific approach, and learning from hands on reality.

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Andrew
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