Hi all,
I have a pair of BG RD75 planars.
They are crossed over with some Marchand XM46 line level passive crossovers driven by Conrad Johnson Premier 8XS' monoblocks. I have been using 3 pairs of Aurum Cantus G2Si ribbon tweeters but plan on replacing these with some 60 inch Magneplanar ribbon tweeters for a true matching line source. I imagine that these are a natural pairing. I was hoping that someone might have some suggestions re; crossover frequencies/slopes and designs.
Thanks in advance.
Cheers, Peter
I have a pair of BG RD75 planars.
They are crossed over with some Marchand XM46 line level passive crossovers driven by Conrad Johnson Premier 8XS' monoblocks. I have been using 3 pairs of Aurum Cantus G2Si ribbon tweeters but plan on replacing these with some 60 inch Magneplanar ribbon tweeters for a true matching line source. I imagine that these are a natural pairing. I was hoping that someone might have some suggestions re; crossover frequencies/slopes and designs.
Thanks in advance.
Cheers, Peter
I have a similar plan. I have collected some information which I will post later.
What are you using below the RD75's?
I have Magneplanar Tympani IVa's. I'll use the RD75s' to replace the mid panel. I hope to figure out how to remove the tuning pucks from the mid bass panel since the RD75's will cover that range.
What are you using below the RD75's?
I have Magneplanar Tympani IVa's. I'll use the RD75s' to replace the mid panel. I hope to figure out how to remove the tuning pucks from the mid bass panel since the RD75's will cover that range.
Hi Steve, nice to hear from you.
I think I have managed to integrate the tweeters very successfully with the RD 75's(far better match than the Aurum Cantus). I'm crossing over at about 3200hz at 12db per octave with a very simple cap and inductor. The RD's have been left running all the way up. I might experiment with rolling them off one day. I roll the RD 75 bass off at 200hz at 24db with a line level Linkwitz Riley filter. The bass/midbass consists of a pair of SEAS L26R04Y per channel in an open baffle configuration similar to the Linkwitz LX521. they are powered by an NCore 400 and I use a Mini DSP 10 for the crossover and room equalization but just for the bass. It works really well there but is definitely not good enough for full range use. I have a few subwoofers modeled on the big Genesis system. They provide the really deep bass. They are also equalized. This is all a result of nearly 40 years of playing around with hi-fi! I'll send some pictures later on. Do you have the RD 75's already as they seem to have gone out of production unfortunately? I've often wondered what I would do if they malfunctioned. Parts Express have BG NEO 10's(expensive) and also GR Research 10's which look almost identical and appear to be viable alternatives.
Anyway, lovely to hear from you and keep in touch.
Cheers,
Peter
P.S. Couldn't see pictures of your turntable but I'm impressed!
I got hooked on planars/ribbons after hearing a friends QRS1D about 35 years ago!
I think I have managed to integrate the tweeters very successfully with the RD 75's(far better match than the Aurum Cantus). I'm crossing over at about 3200hz at 12db per octave with a very simple cap and inductor. The RD's have been left running all the way up. I might experiment with rolling them off one day. I roll the RD 75 bass off at 200hz at 24db with a line level Linkwitz Riley filter. The bass/midbass consists of a pair of SEAS L26R04Y per channel in an open baffle configuration similar to the Linkwitz LX521. they are powered by an NCore 400 and I use a Mini DSP 10 for the crossover and room equalization but just for the bass. It works really well there but is definitely not good enough for full range use. I have a few subwoofers modeled on the big Genesis system. They provide the really deep bass. They are also equalized. This is all a result of nearly 40 years of playing around with hi-fi! I'll send some pictures later on. Do you have the RD 75's already as they seem to have gone out of production unfortunately? I've often wondered what I would do if they malfunctioned. Parts Express have BG NEO 10's(expensive) and also GR Research 10's which look almost identical and appear to be viable alternatives.
Anyway, lovely to hear from you and keep in touch.
Cheers,
Peter
P.S. Couldn't see pictures of your turntable but I'm impressed!
I got hooked on planars/ribbons after hearing a friends QRS1D about 35 years ago!
I would not try to remove the buttons! I think you should let the bass cover up to 200-250 Hz as the RD75 are not that good below that frequencies. I understand there are a few problems with the RD75 around 5-6 kHz and it may be a good idea to cross them over just below that. I think the Tympani ribbon is used to about 4 kHz acoustically.
@peter iles
Thanks for the helpful info! I am looking at the Pass 2-way crossovers and a simple crossover for the mid to tweeter is what I have in mind.
I actually have two pair of RD75's. One pair is in some rather large 'wings'. The other pair is new in the box from B&G. They were bought for a project that never materialized and sat around for years.
I will post some pix of the turntable. The speed controller is quite elaborate.
@RogerGustavsson
Thank you! As usual you are most informative and helpful. 4kHz should be high enough to take advantage of the RD75's and avoid the 5 kHz peak.
Thanks for the helpful info! I am looking at the Pass 2-way crossovers and a simple crossover for the mid to tweeter is what I have in mind.
I actually have two pair of RD75's. One pair is in some rather large 'wings'. The other pair is new in the box from B&G. They were bought for a project that never materialized and sat around for years.
I will post some pix of the turntable. The speed controller is quite elaborate.
@RogerGustavsson
Thank you! As usual you are most informative and helpful. 4kHz should be high enough to take advantage of the RD75's and avoid the 5 kHz peak.
An externally hosted image should be here but it was not working when we last tested it.
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Now I have the B&G RD75's paired with the Tympani IVa's. For now I am running the RD75's open ended, whatever they will do for high frequency.
I ordered new tweeters from Magnepan and have a DBX Venu360 coming to handle the crossover so I can biamp. I will build a passive crossover for the RD75's and tweeters. As Roger recommended, high enough to get the most from the RD75'a but under the 5 kHz peak. Got to order the parts this week as the tweeters should be here in a few days. I can mount them next weekend.
I ordered new tweeters from Magnepan and have a DBX Venu360 coming to handle the crossover so I can biamp. I will build a passive crossover for the RD75's and tweeters. As Roger recommended, high enough to get the most from the RD75'a but under the 5 kHz peak. Got to order the parts this week as the tweeters should be here in a few days. I can mount them next weekend.
Attachments
The crossover, actually two crossovers.
The box is the crossover between the Tympani IVa bass\mid bass and the mid\tweeter panels. The Tympani mid\tweeter panel has a crossover as well.
I used a terminal block to permit easy changes to different value components.
ClarityCaps and Solen Perfect lay inductors. In the Tympani Magnepan has a position for a resistor to be added to reduce the tweeter output which the terminal block can accommodate. The fuse is to protect the tweeter. The L-pad is to reduce the output of the B&G RD75 to balance it with the bass\mid bass panels.
I sent the Venue360 to Audio Science Review to be measured. When it I will change over to biamping.
The box is the crossover between the Tympani IVa bass\mid bass and the mid\tweeter panels. The Tympani mid\tweeter panel has a crossover as well.
I used a terminal block to permit easy changes to different value components.
ClarityCaps and Solen Perfect lay inductors. In the Tympani Magnepan has a position for a resistor to be added to reduce the tweeter output which the terminal block can accommodate. The fuse is to protect the tweeter. The L-pad is to reduce the output of the B&G RD75 to balance it with the bass\mid bass panels.
I sent the Venue360 to Audio Science Review to be measured. When it I will change over to biamping.
Attachments
BG RD-75s & custom 182cm (6') ribbons
Hello Peter,
A long time ago David Graebener helped me with my 6' true ribbon design. I've attached a photo of the 3-way tri-amped dipole line sources - which have fallen on hard times; and, are now being rebuilt. Back in 1997 I had a large website, Acoustic Line Source Research devoted to the "RD-75 Dipole Baffle Study." Sadly my website had been archived at the defunct "DIY Speaker" website ... gone with the wind.
The design is non-optimal: The ribbons were started in 1987, and began playing in January 2000. One of the Reynolds Wrap ribbons busted in December 2014 and haven't been playing since. The RD-75s were a third pair since David wanted me to have 'good ones' for all the measurements I was posting online. The rectangular shape of the panels is not the best; nor is positioning the RD-75s in the center of the panel. Practical needs (and the rest of life) drove a compromise solution.
Currently I'm in progress of recreating a 'cutting station' for a new pair of ribbons. I was never able to get my old corrugating machine to work right back then - and it was a real task to cut a straight ribbon about 6.5' long. The foil you can see in the photo is a dummy for now.
I play the system as a 2-way now. I've not heard any problems previously with uncorrugated tensioned ribbons (at least up to 2014 when I stupidly broke one of the ribbons). I was able to post a frequency response measurement of the ribbons to the old "Dipole Forum (Yahoo?)" which didn't show any resonance problems - and, get this, at very low amplitudes the ribbons were 'flat' to below 20Hz. It didn't take much low-frequency amplitude to 'blow' the ribbons out of the magnetic gap.
Surely the true ribbon Magnaplans must exhibit the same 'microphone' behavior?
For years I used a pair of the rather lame Behringer 3-way active crossovers (24dB/octave) at about 300Hz (woofers to RD-75) and 5.5kHz (RD-75 to ribbons). I've since acquired a pair of MiniDSP 4x10HD digital crossovers and can find nothing wrong with their sound quality compared with the Behringers. In fact they sound quite superior to the old and cheap Behringers. I always used the factory supplied notch filters with the RD-75s. I intend to to implement the notch filters in the future via the MiniDSP units.
The dipole woofer line arrays became operational in 2003 - when I 'glued' the three elements together. The large curvature edges (~6" diameter) are a 'pool noodle' covered with 1" thick foam and painted many times with a stucco-like mixture of elastomer paint heavily loaded with 80-grit sand. I believe that the woofer arrays have a nominal area equivalent to an 18" subwoofer. I'm not currently using subs but you can see one of four 10" subs (swarm array) to the left of the panels - just waiting to be implemented.
All this in a rather small living room. Dipoles really need breathing room. Lucky I don't have pets, children or cleaning ladies to damage anything. With an open an exposed ribbon you don't even look sideways at it!
So, here's the punch line: After about 14 years of visual operation of the ribbons it became clear (in further context of the dummy ribbon in the photo) that the ribbons are modulated by external sound input ... after all, they can be considered microphones too. The dummy ribbon is only attached at the top and it sure does flap around as I drive the now two-way to loud amplitudes.
Being old now my enthusiasms wane but I've got the calibrated mics and REW and hope to get onto 'tweaking' the crossovers as soon as I get a new pair of ribbons installed. The cutting bench is newly made, I have a dual-rotary cutter fabricated, a new corrugating machine. All that is left is needing the motivation to get on with it.
John
Hello Peter,
A long time ago David Graebener helped me with my 6' true ribbon design. I've attached a photo of the 3-way tri-amped dipole line sources - which have fallen on hard times; and, are now being rebuilt. Back in 1997 I had a large website, Acoustic Line Source Research devoted to the "RD-75 Dipole Baffle Study." Sadly my website had been archived at the defunct "DIY Speaker" website ... gone with the wind.
The design is non-optimal: The ribbons were started in 1987, and began playing in January 2000. One of the Reynolds Wrap ribbons busted in December 2014 and haven't been playing since. The RD-75s were a third pair since David wanted me to have 'good ones' for all the measurements I was posting online. The rectangular shape of the panels is not the best; nor is positioning the RD-75s in the center of the panel. Practical needs (and the rest of life) drove a compromise solution.
Currently I'm in progress of recreating a 'cutting station' for a new pair of ribbons. I was never able to get my old corrugating machine to work right back then - and it was a real task to cut a straight ribbon about 6.5' long. The foil you can see in the photo is a dummy for now.
I play the system as a 2-way now. I've not heard any problems previously with uncorrugated tensioned ribbons (at least up to 2014 when I stupidly broke one of the ribbons). I was able to post a frequency response measurement of the ribbons to the old "Dipole Forum (Yahoo?)" which didn't show any resonance problems - and, get this, at very low amplitudes the ribbons were 'flat' to below 20Hz. It didn't take much low-frequency amplitude to 'blow' the ribbons out of the magnetic gap.
Surely the true ribbon Magnaplans must exhibit the same 'microphone' behavior?
For years I used a pair of the rather lame Behringer 3-way active crossovers (24dB/octave) at about 300Hz (woofers to RD-75) and 5.5kHz (RD-75 to ribbons). I've since acquired a pair of MiniDSP 4x10HD digital crossovers and can find nothing wrong with their sound quality compared with the Behringers. In fact they sound quite superior to the old and cheap Behringers. I always used the factory supplied notch filters with the RD-75s. I intend to to implement the notch filters in the future via the MiniDSP units.
The dipole woofer line arrays became operational in 2003 - when I 'glued' the three elements together. The large curvature edges (~6" diameter) are a 'pool noodle' covered with 1" thick foam and painted many times with a stucco-like mixture of elastomer paint heavily loaded with 80-grit sand. I believe that the woofer arrays have a nominal area equivalent to an 18" subwoofer. I'm not currently using subs but you can see one of four 10" subs (swarm array) to the left of the panels - just waiting to be implemented.
All this in a rather small living room. Dipoles really need breathing room. Lucky I don't have pets, children or cleaning ladies to damage anything. With an open an exposed ribbon you don't even look sideways at it!
So, here's the punch line: After about 14 years of visual operation of the ribbons it became clear (in further context of the dummy ribbon in the photo) that the ribbons are modulated by external sound input ... after all, they can be considered microphones too. The dummy ribbon is only attached at the top and it sure does flap around as I drive the now two-way to loud amplitudes.
Being old now my enthusiasms wane but I've got the calibrated mics and REW and hope to get onto 'tweaking' the crossovers as soon as I get a new pair of ribbons installed. The cutting bench is newly made, I have a dual-rotary cutter fabricated, a new corrugating machine. All that is left is needing the motivation to get on with it.
John
Attachments
Hello @John ASLR and welcome to the discussion. How nice to hear from someone with such wonderful experience.
I had not heard RD75's before, only aware of their reputation. I managed to find two pair. One pair in the 'wings' in the pic and the other pair new in the box.
I am looking to build another baffle for the second pair so any input you may share with me would be greatly appreciated. I would like to incorporate the RD75 and a ribbon tweeter.
Since the pix I have attached the Tympani IVa tweeters to the side of the RD75 baffles and built a little crossover.
Do I understand correctly that you are intending to make ribbon tweeters?
I had not heard RD75's before, only aware of their reputation. I managed to find two pair. One pair in the 'wings' in the pic and the other pair new in the box.
I am looking to build another baffle for the second pair so any input you may share with me would be greatly appreciated. I would like to incorporate the RD75 and a ribbon tweeter.
Since the pix I have attached the Tympani IVa tweeters to the side of the RD75 baffles and built a little crossover.
Do I understand correctly that you are intending to make ribbon tweeters?
@Steve3J,
Thank you for the welcome. Your last question first "Do I understand correctly that you are intending to make ribbon tweeters?"
My research on "Current sheet" true ribbons began in 1987. In 1997 with David Graebener's intellectual assistance my pair of 6' (182cm) long ribbons changed design from a 'horseshoe" to "open circuit" magnetic design. Final fabrication of the ferrite/neodymium magnetic circuit was completed soon thereafter. But precision cutting of aluminum foil and corrugation considerations delayed playing inception until January 2000.
I'd also been consumed in a massive investigation by the Department of Labor as to Vietnam veteran discrimination in the California State University system. That took almost all my time from 1998 through 2001. Time flies when you're having 'fun.' Almost all my time was consumed leading the class-action veterans' group.
My ribbons played from January 2000 through December 2014 when a ribbon broke.
Hence my ribbons are built now- but need new ribbons due to a ribbon breaking in 2014. I am in process of redeveloping a ribbon cutting and corrugation system. Very non-trivial! I still carry a fantasy of demonstrating predicted frequency response variations using different thicknesses of aluminum foil (in much shorter line source configurations). I do not intend to make ribbons for others. I am old and cranky.
----[ Taking only one RD-75 example from the Dipole Baffle Study ]
What I write below is backed up by many frequency response plots previously posted to my "ALSR" website and the old Bass List, which are no longer in existence. If there is interest I can dig up the plots and possibly post them here?
Thesis: The RD-75 frequency response at both distance and height is not what you might think.
Measured in a very large gymnasium in 1997, using Bill Waslo's "IMP/MLS" system in order to test the thesis that a line source output drops by -3dB for every doubling of distance, the RD-75 was measured semi-anechoically on a highly reflective hardwood floor (worst case reflections) at both distances of 1m, 2m, 4m and 8m. And at heights above the floor of 0.75m, 1.00m and 1.25m.
What is seen both in distance and height are "rolling dips" in the frequency response seemingly due to floor reflections of sound. Hence the understanding that both Rudi Blondia and I came to at the time was that an RD-75 dipole baffle configuration would have to be 'tuned' for the distance and height at which it was to be listened to.
Of course floor damping would be expected to mitigate the rolling dips; but, it was highly interesting to see the outcome of the overlaid plots. In some cases the elements of the frequency response were of greater amplitude at distance. The 0.5m difference in height measurements also produced significant rolling dips in the frequency response.
This was 'boy science' at its best.
And then there was the matter of the 'Virtual line source" signals coming off the baffle edges to bemuse one.
Let me know if you're interested in seeing the distance/height plots and I'll dig in my archives. I was recently contacted through the DIY Audio by a Polish individual who had purchased a pair of NOS RD-75s in Poland. I was able to send him a copy of my entire "Acoustic Line Source Research" website. So I should be able to find the data?
John
Thank you for the welcome. Your last question first "Do I understand correctly that you are intending to make ribbon tweeters?"
My research on "Current sheet" true ribbons began in 1987. In 1997 with David Graebener's intellectual assistance my pair of 6' (182cm) long ribbons changed design from a 'horseshoe" to "open circuit" magnetic design. Final fabrication of the ferrite/neodymium magnetic circuit was completed soon thereafter. But precision cutting of aluminum foil and corrugation considerations delayed playing inception until January 2000.
I'd also been consumed in a massive investigation by the Department of Labor as to Vietnam veteran discrimination in the California State University system. That took almost all my time from 1998 through 2001. Time flies when you're having 'fun.' Almost all my time was consumed leading the class-action veterans' group.
My ribbons played from January 2000 through December 2014 when a ribbon broke.
Hence my ribbons are built now- but need new ribbons due to a ribbon breaking in 2014. I am in process of redeveloping a ribbon cutting and corrugation system. Very non-trivial! I still carry a fantasy of demonstrating predicted frequency response variations using different thicknesses of aluminum foil (in much shorter line source configurations). I do not intend to make ribbons for others. I am old and cranky.
----[ Taking only one RD-75 example from the Dipole Baffle Study ]
What I write below is backed up by many frequency response plots previously posted to my "ALSR" website and the old Bass List, which are no longer in existence. If there is interest I can dig up the plots and possibly post them here?
Thesis: The RD-75 frequency response at both distance and height is not what you might think.
Measured in a very large gymnasium in 1997, using Bill Waslo's "IMP/MLS" system in order to test the thesis that a line source output drops by -3dB for every doubling of distance, the RD-75 was measured semi-anechoically on a highly reflective hardwood floor (worst case reflections) at both distances of 1m, 2m, 4m and 8m. And at heights above the floor of 0.75m, 1.00m and 1.25m.
What is seen both in distance and height are "rolling dips" in the frequency response seemingly due to floor reflections of sound. Hence the understanding that both Rudi Blondia and I came to at the time was that an RD-75 dipole baffle configuration would have to be 'tuned' for the distance and height at which it was to be listened to.
Of course floor damping would be expected to mitigate the rolling dips; but, it was highly interesting to see the outcome of the overlaid plots. In some cases the elements of the frequency response were of greater amplitude at distance. The 0.5m difference in height measurements also produced significant rolling dips in the frequency response.
This was 'boy science' at its best.
And then there was the matter of the 'Virtual line source" signals coming off the baffle edges to bemuse one.
Let me know if you're interested in seeing the distance/height plots and I'll dig in my archives. I was recently contacted through the DIY Audio by a Polish individual who had purchased a pair of NOS RD-75s in Poland. I was able to send him a copy of my entire "Acoustic Line Source Research" website. So I should be able to find the data?
John
I hope you will be able to re-create this page, ACOUSTIC LINE SOURCE RESEARCH - Table of Contents
Hello @John ASLR
Very interesting. I hope your tweeter project goes well!
You discerned correctly that I was wondering if you would make tweeters for others.
Guess I will have to be satisfied with the Maggie ribbons.
Seems as though I ran across someone that is making ribbon tweeters. Have to see if I can find that again.
I would be most interested in your research. I am new to live source speakers and very impressed with the RD75's and would like to know more about them.
I am planning on making some baffles for an RD75 and Maggie ribbon tweeter. Any light you could shed on baffle width and shape would be greatly appreciated.
Thanks!
Very interesting. I hope your tweeter project goes well!
You discerned correctly that I was wondering if you would make tweeters for others.
Guess I will have to be satisfied with the Maggie ribbons.Seems as though I ran across someone that is making ribbon tweeters. Have to see if I can find that again.
I would be most interested in your research. I am new to live source speakers and very impressed with the RD75's and would like to know more about them.
I am planning on making some baffles for an RD75 and Maggie ribbon tweeter. Any light you could shed on baffle width and shape would be greatly appreciated.
Thanks!
@Roger & @Steve,
Still recovering from oral surgery and the horrors of doing my own taxes. I've located my archived "Acoustic Line Source Research" website files. Apparently I'll be able to extract text and photos from it without too much effort.
I've been mostly a lurker and not up-to-speed on the nuances of posting. With the implied effort to reconfigure the materials for posting I'm not sure the forum would want the materials? I just gave away about $2500 worth of ultrasonic cleaning kit, and got kicked out of the "Everything Else" forum to the "Swap Meet"?
I'm inclined to start a series of numbered post do 'isolate' the materials from being buried in this thread. A thread title such as "The BG RD-75 Dipole Baffle Study #1" and so forth might be best?
I'll make an effort to post something in the next two days, we'll see what happens?
Thanks for your interest.
John
Still recovering from oral surgery and the horrors of doing my own taxes. I've located my archived "Acoustic Line Source Research" website files. Apparently I'll be able to extract text and photos from it without too much effort.
I've been mostly a lurker and not up-to-speed on the nuances of posting. With the implied effort to reconfigure the materials for posting I'm not sure the forum would want the materials? I just gave away about $2500 worth of ultrasonic cleaning kit, and got kicked out of the "Everything Else" forum to the "Swap Meet"?
I'm inclined to start a series of numbered post do 'isolate' the materials from being buried in this thread. A thread title such as "The BG RD-75 Dipole Baffle Study #1" and so forth might be best?
I'll make an effort to post something in the next two days, we'll see what happens?
Thanks for your interest.
John
The Moderators approve!
@Roger & @Steve,
Very good news! The moderators have approved my bringing the "The B-G RD-75 Dipole Baffle Study" to this forum. It will be a monster task. First thing is they have to teach me how to "insert images" (rather than "attach") since having images in context of the explanatory text is critical.
As a teaser I'm going to "attach" a couple photos and a plot - without explanation except to say the plot is all about the 'near field' of a big, long line source like the RD-75. Can you 'see' the "Moving Dips" in the FR plots. I hope you get a WTF moment like I did back in 1997-98 when the "Moving Dips" showed up in all the 'near field' plots.
It is going to be a while before the rest of the 'meat' comes online here.
Ad Astra per Ardum
@Roger & @Steve,
Very good news! The moderators have approved my bringing the "The B-G RD-75 Dipole Baffle Study" to this forum. It will be a monster task. First thing is they have to teach me how to "insert images" (rather than "attach") since having images in context of the explanatory text is critical.
As a teaser I'm going to "attach" a couple photos and a plot - without explanation except to say the plot is all about the 'near field' of a big, long line source like the RD-75. Can you 'see' the "Moving Dips" in the FR plots. I hope you get a WTF moment like I did back in 1997-98 when the "Moving Dips" showed up in all the 'near field' plots.
It is going to be a while before the rest of the 'meat' comes online here.
Ad Astra per Ardum
Attachments
Hello @John ASLR
I hope you well.
How is your project to bring "The B-G RD-75 Dipole Baffle Study" to DIYAudio coming along?
I am moving forward, slowly LOL, with my second RD75 project. I'm thinking Rythmik FM8's for woofers as I won't have a large enough room for Maggie bass panels and I'm looking for some Maggie tweeters for the high end. I am using Maggie with my main system now.
Steve
I hope you well.
How is your project to bring "The B-G RD-75 Dipole Baffle Study" to DIYAudio coming along?
I am moving forward, slowly LOL, with my second RD75 project. I'm thinking Rythmik FM8's for woofers as I won't have a large enough room for Maggie bass panels and I'm looking for some Maggie tweeters for the high end. I am using Maggie with my main system now.
Steve
No RD-75 Dipole Baffle Study
Hello Steve,
I'm sad to report that after several consultations with Forum moderators that the practical inability to insert images (photos & plots) in a text stream led to suggestions to create a series of small PDF files which could be 'managed' as elements of a larger whole ... hopefully to be linked in single forum thread.
The projected 'overhead' of labor to restructure the Baffle Study data as PDF files squelched the project. Apparently the 'inline' insert method requiring image storage at another website doesn't work well at all?
What I would emphasize at this late date is that in an extended series of 'worst case' hardwood floor bounce measurements in the gymnasium the prediction of the average loss of only -3dB in SPL per doubling of distance was documented.
Measurements were made in full at distances of 1m, 2m, 4m and 8m. Height measurements were made at 0.75m, 1.0m and 1.25m at each distance. A lot of measurements!
What is seen in the overlaid plots are frequency responses which *change* with height/distance in sometimes significant ways. In some cases the FR in different ranges was of greater amplitude at greater distance compared with closer. There were "Moving Dips" of significant amplitude variation which 'rolled' through the overlaid FR plots - at both height and distance.
One assumes that trigonometry of the floor bounce (from a line source!) explains much of the FR variations.
Hence it became my opinion that integration of the RD-75 with other drivers required FR measurement at the actual distance/height to be favored in critical listening in order to account for distance/height FR variations by informed design of the crossovers.
Clearly the hardwood floor of the gym provided a better 'mirror' for floor bounce leading to the observed FR variations due to constructive and destructive amplitude interference effects. Overall, the RD-75s met the -3dB average fall of amplitude per doubling of distance out to 8 meters! Which I suspect is farther than most 'favored listening positions'.
It seems that the 'wisdom' that line source dipoles (of sufficient size) don't have floor/ceiling bounce issues should be considered with some skepticism.
Sorry about the matter - it is just fundamental to be able to have photos/plots with explanatory text surrounding. Sadly the forum's message reply system only allows for "attached" photos/plots at the end of the message.
Best wishes on your projects.
John
Hello Steve,
I'm sad to report that after several consultations with Forum moderators that the practical inability to insert images (photos & plots) in a text stream led to suggestions to create a series of small PDF files which could be 'managed' as elements of a larger whole ... hopefully to be linked in single forum thread.
The projected 'overhead' of labor to restructure the Baffle Study data as PDF files squelched the project. Apparently the 'inline' insert method requiring image storage at another website doesn't work well at all?
What I would emphasize at this late date is that in an extended series of 'worst case' hardwood floor bounce measurements in the gymnasium the prediction of the average loss of only -3dB in SPL per doubling of distance was documented.
Measurements were made in full at distances of 1m, 2m, 4m and 8m. Height measurements were made at 0.75m, 1.0m and 1.25m at each distance. A lot of measurements!
What is seen in the overlaid plots are frequency responses which *change* with height/distance in sometimes significant ways. In some cases the FR in different ranges was of greater amplitude at greater distance compared with closer. There were "Moving Dips" of significant amplitude variation which 'rolled' through the overlaid FR plots - at both height and distance.
One assumes that trigonometry of the floor bounce (from a line source!) explains much of the FR variations.
Hence it became my opinion that integration of the RD-75 with other drivers required FR measurement at the actual distance/height to be favored in critical listening in order to account for distance/height FR variations by informed design of the crossovers.
Clearly the hardwood floor of the gym provided a better 'mirror' for floor bounce leading to the observed FR variations due to constructive and destructive amplitude interference effects. Overall, the RD-75s met the -3dB average fall of amplitude per doubling of distance out to 8 meters! Which I suspect is farther than most 'favored listening positions'.
It seems that the 'wisdom' that line source dipoles (of sufficient size) don't have floor/ceiling bounce issues should be considered with some skepticism.
Sorry about the matter - it is just fundamental to be able to have photos/plots with explanatory text surrounding. Sadly the forum's message reply system only allows for "attached" photos/plots at the end of the message.
Best wishes on your projects.
John
Realize time has passed, wondered if you ever finished this and how it turned out? Are you still using the RD-75'S and magnepan ribbon tweeter? Very interested to hear how it turned out as I am looking to do the same...Thanks.
Thanks for the info.
Surprised you aren't using these in an open baffle. Have you considered a dsp crossover with active amplification?
I couldn't find a suitable pair of rg-75's so I decided to use a pair of 30" ribbons from a Carver Amazing speaker set for the mids with the Magnepan ribbon. Waiting to pick up the Carvers- will post here when I have something. Thanks again.
Surprised you aren't using these in an open baffle. Have you considered a dsp crossover with active amplification?
I couldn't find a suitable pair of rg-75's so I decided to use a pair of 30" ribbons from a Carver Amazing speaker set for the mids with the Magnepan ribbon. Waiting to pick up the Carvers- will post here when I have something. Thanks again.