The B-G RD-75 Dipole Baffle Study 1997-1998 - diyAudio
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Old 9th September 2014, 01:08 AM   #1
diyAudio Member
Join Date: Feb 2010
Location: Long Beach, California
Default The B-G RD-75 Dipole Baffle Study 1997-1998

About a month ago I discovered that my very large website "Acoustic Line Source Research" dating back to 1997 when the B-G Corporation offered the RD-75s to the group for $400 each, had been archived by the follow-on organization to the old "Bass List" forum (see below).

I had Bill Waslo's IMP/MLS FFT measurement tool, and a couple friends who assisted with clandestine measurements at a local high school gymnasium and auditorium. This was "The RD-75 Dipole Baffle Study."

ALSR - The RD75 Dipole Baffle Study - Table of Contents

I'd like to name-drop David Grabener for his support and assistance. B-G ultimately gave me a third pair of RD-75s for my study, since the first two pairs (ahem!) were not operating exactly as B-G wanted for an online publication.

David provided me computer modeling assistance for my unusual magnetic circuit design large True Ribbon tweeters (1cm x 182cm). Information about them can be found elsewhere on the ALSR website.

I'd like to tout the virtue of all the measurement plots seen at the website as being 'splices' of both high resolution low frequency and high frequency measurements. With the old IMP/MLS few mastered the splicing technique ( with phase being a critical issue).

I rather precisely defined an operational definition for what I termed a "Flat Dipole Baffle" - and you will see measurements on a number of variations of a 'flat baffle.' In the end, what was independently found at the end of the Study was that a 'flat baffle' doesn't cut when a '3-Dimensional baffle' is available. No great revelation nowadays, eh?

ALSR - The RD75 Dipole Baffle Study - The Auditorium Measurements

Of course the conceit of the study was using an RD-75 as an almost full-range driver - which would mean a certain limitation of maximum SPL.

I don't believe you'll ever see greater range of comparative FR measurements on the RD-75 in very large venues.

And finally, sheez, after getting the true ribbons playing in 2000 I finally broke a ribbon (manually) about a month ago. Now I've got to come up with another ribbon cutting methodology (as the old one was trashed in 2000).

Hope there's food for thought to be found in "The RD-75 Dipole Baffle Study."

Click the image to open in full size.
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Old 9th September 2014, 06:58 PM   #2
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Join Date: Feb 2010
Location: Long Beach, California
Default The Near Field

To belabor a point about measurements you'll not often see:

ALSR - The RD75 Dipole Baffle Study - Theory: You are in the Nearfield

High-resolution (2Hz below approximately 300Hz) plots at 1m, 2m, 4m and 8m distances. At 0.75m, 1.0m and 1.25m height. Taken in a very large gymnasium.

Interesting to see how theory plays out in reality.

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