bohlender graebener rd50 dipole eq ?

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Yes, I use the RD-75 as a dipole with a very minimal baffle, in fact just some foam tube to round off the edges.

The low end response depends very much on the listening distance. For large distances (several meters) there will be a slow roll-off starting at approx 1 kHz. This is because the RD-75 is line-source above 1 kHz only, and will gradually shift from 3 dB loss per doubling of distance, into 6 dB loss at lower frequencies.

I listen at very short distance, where there will be little or no low-end roll-off.

Hi StigErik,

Sorry if already asked :

If yo add more Rd75 by speaker can we supress the line array limits or multiple rd75 will trouble each others in a same plane baffle ?

Can we imagine a V baffle with a Rd 75 at each side and the edge of the V toe in to the listener ?
 
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It has to do with wavelength.
It remains line-source (cylindrical sound radiation) where the wavelength of the sound is many times the length of the line. Somewhere around four full wavelengths, the line will gradually become omnidirectional (spherical radiation). For a 2 meter line that means approx 700 Hz.

The only way of increasing the low frequency line-source behavior, is to increase the length of the line. If we stack three RD-75's on top of each other for a 6 meter long line, we have line-source behavior to approx 200 Hz.

I suggest you read this article on line arrays. It explains it to some degree:
Line array - Wikipedia, the free encyclopedia
 
Thanks for the link and explanation.

I supose too if the line is 6 metes but you go back thre times to the initial listening position the result wil be the same or maybe the large radiation of bass frequence help with the room to keep a position behind near the initial listening position.

Well the V baffle is a bad idea ! And with the drivers in the width of the room : each side of the listener at 1 meter ? Is there a cancelation of the sound when the right/left waves meet together at the center position?

When i see your acoustic filter behind the B&G i uppose you think at all the placement possibilities and try many for see how work a dipole line array !
 
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you should get to count the floor reflection as doubling the line length if you don't have excessive absorption - which you won't for the low frequency

if your line reaches floor to ceiling, both having flat parallel reflective surfaces, then it looks like an "infinite" line
 
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The 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?

See:
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.
levels.

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."

John
 
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