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Multi-Way Conventional loudspeakers with crossovers

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Old 3rd January 2007, 09:41 PM   #21
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Quote:
Originally posted by Tenson
Actually, I think they use the foam to change the phase of the sound and improve vertical dispersion limiting destructive interference.

I have no idea how you would use foam to change phase response.
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Old 3rd January 2007, 10:24 PM   #22
Tenson is offline Tenson  United Kingdom
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Hi,

Sound travels slower through an absorptive material, so the relative phase would change. Quite how much delay there is I couldn't tell you. I know of someone who did some measurements but in the end it was pretty inconclusive, except that there was a small delay.

Add that to the change in amplitude and you will have an effect on the vertical dispersion.

I'm sure I have an email somewhere with Aleksandar explaining what the foam did exactly and it was along those lines but I can't find it.
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Old 3rd January 2007, 10:25 PM   #23
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We all know open cell foam will attenuate/absorb from a given frequency and upwards depending upon its thickness. If we look at the RAAL's foam pads we can see a distinctive profile. This profile gradually increases in thickness towards the extreme length of the ribbon thus attenuating progressively more of the high frequency content as you move towards these extremes. The effect of this is concentrating the high frequencies toward the center of the driver and allowing the lower end of the frequency spectrum that the driver covers to pass virtually unaltered.

This all contributes to shaping the vertical dispersion beyond that of a normal ribbon.
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Old 3rd January 2007, 10:32 PM   #24
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They look dead ugly though...
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Old 3rd January 2007, 10:37 PM   #25
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Quote:
Originally posted by pinkmouse
They look dead ugly though...
What if I dyed them pink?
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Old 3rd January 2007, 10:38 PM   #26
Tenson is offline Tenson  United Kingdom
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Pink ribbon tweeters in a white and black speaker.. OH YES!!!


So, after going through all my emails from RAAL I found the info I remeberd reading, on the website - Duh!

"The dispersion pads are working as an acoustic lens, by slowing down the velocity of sound and thus shaping the sound wave front from cylindrical to spherical. The parasitic effect of partial sound absorption is inevitable, but acceptable. The pads are magnetic and they can slide on the front plate. By adjusting the distance between the pads, sliding them toward or apart each other, it is possible to shape the on-axis linearity vs. wide angle vertical polar response. In this way anyone can adjust the high frequency output by his-hers own liking. If the pads are completely removed, 15 kHz on-axis response is increased in level of about 7 dB."
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Old 3rd January 2007, 10:49 PM   #27
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Cheers Simon, much better description than our waffling

Also I was considering the 70-10 but it doesn't seem make quite as nice a fit as the 140-15. The new 70-20XR looks perfect as a compromise between those two, unfortunately its OEM only
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Old 3rd January 2007, 10:58 PM   #28
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And here's the Pinkmouse edition:

Click the image to open in full size.

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Old 3rd January 2007, 11:02 PM   #29
Tenson is offline Tenson  United Kingdom
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Well I love it!
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Old 3rd January 2007, 11:24 PM   #30
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Shin:

Have you recently had some really positive experiences with ribbon tweeters that helped you make this decision or are you going for something completely new? I actually don't ever think I've heard a system using ribbon tweeters, but after reading the information of Zaph's website where he reviewed a good number of them my initial reaction to them is "why?". Respectfully, Zaph did not review the tweeter you are talking about using and I really don't know anything about it in particular.
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