BG RD75 for line array

[Mazeroth]

PE has some buyout BG RD75s for $459 right now in OEM boxes in their new flyer, according to an email I received today. They say they can only ship them via truck, but luckily for me, they're only an hour away from here so I can pick them up myself.

LONG story short. Just found out my wife is pregnant with our first so now money is going to be tight for a while. She's still fine with me building the theater but the speaker budget is going to have to be diluted a bit. This is only for watching TV/Movies/Gaming so the absolute in SQ isn't necessary but high SPL and the intimidation factor are still required. :B

Original thought for the last few days was a line of 10-12 Silver Flute 5.5" mids or Dayton RS150s in a sealed array crossed to a single Vifa XT25 double magnet around 2.5khz. These would cross to a ceiling mounted quad RSS390HF IB sub (already have these drivers). Sensitivity would be around 92 dB after taking BSC into account. Not ideal, but for $500 in drivers (I'm getting a deal) I think they'll work well. I had a single ribbon line array for a while and thought it sounded great.

Now, the RD75 comes along and I get to thinking. Is it going to be worth it to upgrade to the RD75 or do I just keep it simple? I know it's only good down to about 600 hz. so I would still need a group of 4-6 woofers to cross it to and that the high end isn't as good as a true tweeter. Though, I could use a DCX2496 for the crossover and do a full dipole with dipole mids/woofers flanked to the side. Decisions, decisions.

Just figure I'd ask what you all think? Also, if I go the line array route do you think a center would be beneficial? I know most say no with arrays but I've read a few where the couldn't believe they lived so long without one.

Thanks.

[minkuni]

600Hz ? You can use it lower than that, but of course if ultra high SPL-levels are the goal it pays to be careful. I did some very quick tests on a pair of RD40's a couple of months ago and was surprised at how low they could go. 150Hz LR4 was no problem at moderate levels and 250Hz LR4 should be plenty if you plan to crank it.

The important thing is to keep the center of the line at about ear height, as the sound changes quite a bit as you move along the line (as can be seen from the polar plots in the data sheets). With the longer ribbon you should have a wider sweetspot than I experienced with the shorter types.

I did some simple tests with the RD40's horizontally as well to see how it could work as a centre channel. Using a single RD40 gave a way too narrow sweetspot. Using two RD40's end on end widened the sweetspot, but the transition between the ribbons (sitting right in the middle) was a little bit too audible for my hopes. A single RD75 could be quite good a centre channel, but the seating has to be positioned inside the beam-width of the ribbon.

One thing I noticed was that with the two drivers positioned end-on-end to form a long horizontal array was that as I walked along the line I could swear the sound was coming directly from the point on the line closest to me. It felt a bit strange that the sound source seemed to track my position Something to keep in mind if the goal is a virtual source located at the centre of the screen for all viewers.

[ThomasW]

If one has the patience the RD75 can be use as the basis for a long term very high end project.

Start by using them with a line array of woofers and use EQ to boost the top end roll-off of the planars.

When the budget permits add a line array of leaf/ribbon/planar tweeters.

Audio nirvana is reached when the cone woofers are replace with line of electrostatic elements... In smaller rooms this can be accomplished with Acoustat 1+1's, or stacked 36" elements purchased from Just Real Music. Those with larger rooms or wanting higher output levels can use Acoustat 2+2's.

A system built like this is virtually without peer until the price of admission at retail hits $75K.

[CraigJ]

Thomas,
I've been following the BG threads for years and found more RD75/50 ideas than owners. Do you have suggestions on a a solid design to build? Although expensive, I don't think the BGs go on sale often, and a $590 savings is something to think twice about.

Thank you,

Craig

[ThomasW]

Craig,

My post above wasn't fantasy, it's a path I basically followed

My current mains consist of RD75s with a line array of 16 leaf tweeters and dual Acoustat 1+1's

I reached the end point with a slightly different path. Started with the Acoustats, added the leaf tweeters and lastly added the RD75's

Questions?

[CraigJ]

Thomas,

Sorry, I didn't mean for my post to sound so blunt. Next time I won't be watching the Packers play, and posting at the same time. I've seen pictures, and read your reviews of your system and know it's very real and world class. What I meant to say, is there a completed speaker design using the RD75 and an array of drivers that you'd recommend. ;x(

Thanks for your understanding.

Craig

[ThomasW]

There's really not much to design per say...

Below is the first test baffle



Below is a prototype baffle using the Apogee style baffle. The tall alu strip is the first line of planar tweeters I used with the Acoustat 1+1's. These were the only reasonably priced planar tweeter available in the mid 1980's. They were later replaced by leaf tweeters.

This design was abandoned since it was physically too large for the available space.



Just on note regarding the cone drivers. This array used 8-8" Etons. They were overkill since their output eclipsed that of the RD75's. 6.5" drivers would likely work fine in this application

Below are links to gallery pages with more RD based systems...

https://web.archive.org/web/20081122011026/http://home.comcast.net/~thomasw_2/

https://web.archive.org/web/20151002132903/http://home.comcast.net/~thomasw_2/page2B&G-Gallery&Links2.html

[Mazeroth]

I'm going to throw a bunch of questions at you, Thomas! :B

What do you feel you gained by adding the RD75s to your Acoustats? By chance do you know of any distortion measurements done on the RD75s? Or, do you have measurements of your RD75s in practice? Any pics of your latest speakers? Lastly, how do your arrays compare to the Isiris speaker you built?

Thanks!

[ThomasW]

Using the RD75's as pure mids took the entire system to a new level of performance.

Haven't measured distortion. It's so low one doesn't notice how loud they're playing. This is sometimes problematic since it's too easy to toast one's ears with high SPLs because the normal irritation associated with a system being overdriven isn't present..

They started out looking like this...

Image not available

Years ago Jon took a pic when we first set them up to see how they would sound. Now days the RD75 are mounted on alu angle and centered on the Acoustats...



The Isiris sounds like a very good speaker system. More often than not the array sounds like live music.

[Hank]

A couple of years ago, I suggested to Jon that he do a design using the RD-75's, thinking that might be my ultimate speaker with them and a line of ribbon or planar tweets and a pair of sealed subs. He bought a pair, but many other projects took precedence, so I've been thinking that as the 75's got more and more expensive, maybe I'd just go to electrostats, as in Thomas' Just Real Music link. It seems an expensive route to do the 75's and add a line of comparable quality cones, then a line of ribbon tweets, then eventually replace the cones with JRM electros. Those electro panels are actually surprisingly affordable, given the last few years of material inflation.
Thomas, what do you think about Rd-75's and stacked 36" JRM's (no ribbon tweets)? Not enough sparkle? This is very intriguing.

[augerpro]

Tom are those RD75s run dipole? What are some good options for ESL panels tweeters today?

[ThomasW]

Thomas, what do you think about Rd-75's and stacked 36" JRM's (no ribbon tweets)? Not enough sparkle? This is very intriguing.

The RD series get 'beamy' above ~5kHz so augmenting the top end is IMO important. If the listener sits directly on axis with the radiating element of the RDs then this isn't as big an issue.

Tom are those RD75s run dipole? What are some good options for ESL panels tweeters today?

Yes I run the RD75s dipole

If a good condition pair of Acoustat 1+1 panels can be found they're the best option (they're the only virtually bullet-proof ESLs ever made. 20yr old Acoustats sound as good as new).

Other than that the only option I'm aware of that will give a tall narrow panel is stacking the 36" units from JRM. Stacking the 48" tall elements is an option for those with ceilings taller than 8'.

Another option for those with tall ceilings is to stack a pair of Magnepan MMGs. At ~$1200/2-pr these would provide both the midwoofer and tweeter, probably eliminate the need for the RD75.

I know a few people are running RD75 as replacement mids for the old multi-panel Magnepan Tympani speakers

IIRC Martin-Logan had a tall narrow panel that was a special order. I saw one pair 15+yrs ago and have seen nothing since...

Tweeters are dealers choice. Pricing is the killer since dozens are needed. The cheapest are the B&G Neo3, then Fountek or AC ribbons.

[Johnloudb]

Thomas,

Thanks for sharing your designs. I've been following this and I'm still trying to figure out how to use my two B-G RD50s. I also have 4 Usher 8137A drivers. I'm thinking I might buy 4 or 8 more and make it a full range dipole similar to the design you had with the 8 Etons per side. I'd use 4 or 6 per side to limit cost, if that would work well.

Do you think the Usher would work in this type of application? Did your design require much equalization in the low frequencies? I'll be using a subwoofer with it, so I don't need a lot of extension. F3 of 60Hz would do.

[ThomasW]

I'd make a single test baffle and play with the 4 you have, that maybe enough for one channel.

It's been a very long time since the black baffles were operational (6+yrs), so I don't remember what EQ settings were used.

[Hank]

I've read many times that the RD's are IT for midrange clarity/openness/low distortion, so I'm wondering why the electro panels are needed if one does RD75 and a stack of Neo3's, IF they're augmented of course with a pair of good sealed or OB subs crossed at ~200Hz.

[ThomasW]

Jon and I conducted listening tests of the RD planars at numerous frequencies (150Hz up to 650Hz). They really sounded significantly better with higher XO points.

When I had the separate forum for the B&G planars, people running similar tests confirmed this observation.

[CraigJ]

Just Real Music makes custom sizes; wonder if it's worth investigating sizes and prices. Say 72" by......

Craig

[ThomasW]

Probably depends on the custom pricing vs the cost for their stock panels

[augerpro]

That Just Real Music place has some decent (I think) prices. Anyone familiar with their performance? Not that ANOTHER experiment right now...especially one that will cost thousands of dollars. But having heard Tom's I think I would like to try something along these lines in the future.

[ThomasW]

That Just Real Music place has some decent (I think) prices. Anyone familiar with their performance?

Unfortunately they're a complete unknown.

For 10+years I've tried to find a supplier of smaller/shorter panels for stacking. To date JRM is the only supplier I've found that offers what's needed.

The nice thing is that using the panels as woofers means their performance isn't as critical as if they were being used fullrange..primarily we need something that's tough, not something with a great deal of finesse...

Not that ANOTHER experiment right now...especially one that will cost thousands of dollars

Yeap the price of admission is steep for this kind of system. I have about ~$5K invested in my speakers and a lot more than that in electronics driving them...that $5k was invested over a period of 20yrs...so it wasn't nearly as painful as plunking it all down at once....

I started with one pair of 1+1 panels run fullrange (that's how they were sold). After a couple of years I added the arrays of leaf tweeters. Next a second pair of 1+1's became available. And finally I added the RD75's.

For those wanting to take advantage of the RD75 sale I think a system using a line array of woofers is the best bet. They don't need to be high-end drivers since they're only running up to 650Hz max....using the cone line array will give the system more 'punch' than a single line of ESL panels. and the cone array can also be played harder/louder.

[Janosko]

B&G RD 75's augumentation

Howdy,
I've wanted to create the "biggest bang for the buck" high-end planar loudspeakers ever since the dawning of the CARVER. Stunning STAR WARS appeal~ It bowled me over, the first time I heard it in 1987. So clean and tempered, the bongo drums were s-o-o-o real sounding, voices were delineated palpable as the sound staging window was huge! Sound propagation, now a much different transfer function. Sure required tons of power to achieve realistic live levels though.AMAZING.
As the B&G RD75 was born (best midrange transducer I've ever heard) I thought, h-m-m-m... maybe these would work extremely well in conjunction with a local used pair of MG111a's!($700) Walla! As the midrange, they are awesome for the money invested.
The speaker now consists of:
2 bass panels per side x-vr; 300 @18/db.
RD75's x-vr; 400 @ 12db/oct./ 28oo @ 24/db.
MG ribbon X-vr; 28oo @ 24/db.
Face amp FS~12oo @ 800wts. per channel sounds very good - they sound really "alive " now that the power has increased from 350wts. per channel.
The bass is so good , on two channel listening I really don't need the 4 Maelstrom X~18'' 's... Planar or Infinite baffle.
Have fun!

[Hank]

For those wanting to take advantage of the RD75 sale I think a system using a line array of woofers is the best bet.

I just noticed this truncated frame RS woof in the new PE flyer:

http://www.parts-express.com/pe/pshowdetl.cfm?&partnumber=295-342&sf=08f-14&destination=295-342

I've always been fascinated by electrostats as well as the RD midrange, so if an RD75 and a pair of the 36" H electro's would be the cat's meow (again, with "stereo" subs), I'd rather spring for the money now than have that nagging feeling in the future that I'd need to replace a line of cones with electro's. What do you think, Thomas?

However, this might be the deciding factor:

Unfortunately they're a complete unknown.

I've never heard of the company, so would be concerned about the panels' robustness/longevity. Anybody know anything about them?

[ThomasW]

I just noticed this truncated frame RS woof in the new PE flyer:

http://www.parts-express.com/pe/pshowdetl.cfm?&partnumber=295-342&sf=08f-14&destination=295-342

I've always been fascinated by electrostats as well as the RD midrange, so if an RD75 and a pair of the 36" H electro's would be the cat's meow (again, with "stereo" subs), I'd rather spring for the money now than have that nagging feeling in the future that I'd need to replace a line of cones with electro's. What do you think, Thomas?

Those are cute, the Fs is a little high and the Sd a little low. I think 6" drivers are a good choice in this situation.

I've never heard of the company, so would be concerned about the panels' robustness/longevity. Anybody know anything about them?

One thing going for them (actually him) is that he's been in business for quite a while. I do recall reading something about his designs on DIYaudio

[JonW]

A system built like this is virtually without peer until the price of admission at retail hits $75K.

Using the RD75's as pure mids took the entire system to a new level of performance.

More often than not the array sounds like live music.

Haven't measured distortion. It's so low one doesn't notice how loud they're playing.

Thomas,

These are some pretty strong words to a forum full of speaker junkies. They make me really want to hear your system running full tilt. Unfortunately none of my planned work travel is taking me anywhere near your neck of the woods. But if/when it does, I’d love to hear that system.

Trying to think about it for a moment… What is so special about the type of setup you are running? Maybe some of it comes from the fact that you are running lots and lots of drivers within any given frequency range. And so distortion is really low because none of them are working much at all. For example maybe 16 tweeters doing the work of, typically, only one. Might that be a factor? If that’s the case maybe one could use, say, 16 dome tweeters (or cone woofers) to the same effect. There might not be any reason they need to be ribbons (or electrostatics, etc)?

And geometry of the whole setup must be a big factor, I’d think, but I don’t really understand that aspect of it either.

Another question: How do you make a crossover? Are there any special considerations in the design? I’d think it would be tricky. For driver measurements, well, if you place the microphone 1 meter from the center, some drivers will be 1 meter away and others might be almost 1.5 meters away. Maybe there’s something about running the system active. Just trying to understand the implementation of such a high-end design.



By the way Thomas, I recently saw this quote. I can’t find who said it originally:
“Youth we have enough of. How about a Fountain of Smart?”
I considered using it for my signature. But then thought it might be much more appropriate for you. :P :W

[ThomasW]

Jon,

I've heard the big SoundLabs, the Magnepan 20.1's, the Fullrange Apogee's, and other extremely $pendy systems. And my DIY arrays are certainly very strong competition for any speakers in this league.

The system has always used active crossovers (4th order L/R filters). In it's current incarnation it's a 4-way. In the next week or so it will get a new active crossover (and a conversion to every active element starting with the pre-amp backward running balanced). This is a project Chasw98 and I have been working on for a couple months...

You are correct about having a TON of radiating surface. That combined with the operation of each radiating element only in it's 'sweet-spot', goes a long way toward making these speakers sound so good.

All the drivers are pure line sources. So there's no concern about comb-filtering as there is with multiple point sources like dome tweeters.

In addition to the speaker drive elements, the system's performance is enhanced by playback electronics that are a bit above average....

[CraigJ]

Sorry, but as of 3:30 p.m. Central time, the OEM RD75 is OOS.
:boohoo:
Craig

[ThomasW]

I don't know if they haven't updated their computers or if they found more units, but they show as in stock as of 5:00PM MDT today (friday).

[JonW]

Hi Thomas,

OK, so the large radiating area does help. As do the fancy electronics. And using each driver where it performs best. And you’re running active crossovers. All of those points could apply to any speaker design, in general.

But it sounds like the specific drivers being line sources may be the unique feature here. Such that it allows you to use the many drivers. Otherwise things might get muddy with so many dome/cone drivers. OK that makes more sense if I understand it correctly. Thanks. :T But I still want to have a listen.

A related question: Does the use of line source drivers allow you to run very simple crossovers, like a 4th-order LR? Or are you using the active crossover to account for the standard issues like zobels, notch filters, BSC, etc.




Oh, and sorry about the news, Craig.

[ThomasW]

Jon

Using active crossovers makes these things easier...

There are no zobels, or BSC.

These particular planars have a cavity resonance that produces a peak ~5kHz, I use passive notch filter for that. I could take out the peak with active EQ, but I prefer not to have an equalizer in the midrange circuit.

[Johnloudb]

Hi Thomas,

OK, so the large radiating area does help. As do the fancy electronics. And using each driver where it performs best. And you’re running active crossovers. All of those points could apply to any speaker design, in general.

But it sounds like the specific drivers being line sources may be the unique feature here. Such that it allows you to use the many drivers. Otherwise things might get muddy with so many dome/cone drivers. OK that makes more sense if I understand it correctly. Thanks. :T But I still want to have a listen.

A related question: Does the use of line source drivers allow you to run very simple crossovers, like a 4th-order LR? Or are you using the active crossover to account for the standard issues like zobels, notch filters, BSC, etc.




Oh, and sorry about the news, Craig.

One advantage to line sources is that they have very little vertical dispersion. So ceiling and floor reflections become less of an issue. That's one reason I'm interested in a line source design. Our listening room fairly dead and has open ceiling (with beams, and floor above exposed). It does some bad things to the high frequencies.

[Saurav]

The Isiris sounds like a very good speaker system. More often than not the array sounds like live music.

In my limited experience at a couple of audio shows and a few friends' systems, and modulo my tastes in audio... I've found that Really Big Horns and Really Big Planars tend to have a presentation that Really Big Boxes with Cones don't. I can't say that I've heard the best there is, but I'd like to think that I've heard some pretty good speakers at CES/RMAF.

There's just something about the large horns and planars I've heard that I really enjoy. It's difficult for me to describe, but I mostly perceive it as a sense of effortlessness and ease to the presentation... which I think for me primarily comes from the high dynamics and SPL capabilities.

Thomas' speakers definitely fall into that category.

[CraigJ]

Oh, and sorry about the news, Craig.

I didn't really need to go from 45" to 75" . Besides, my wife will be much, much happier. Thomas, hope you are right, retail computers said 9 left in stock, wholesale person (Becky) said all were gone.......Did Hank purchased a pair?
Craig

[augerpro]

I think the dipole radiation had a lot to do with big soundstage too, don't you think Tom? At the least I did not perceive ANY box sound whatsoever, just a big, effortless soundstage.

[ThomasW]

I think the dipole radiation had a lot to do with big soundstage too, don't you think Tom? .

Line arrays either dipole or monopole tend to throw a wide sound stage.

Going dipole eliminates the effects of box coloration on the drivers and allows the speaker to load better to the room.

So a dipole line array is the best of all worlds... :B

Something we usually talk about in these threads but haven't touched on yet is those wanting a lot of midbass 'slam', should probably use dynamic drivers for their woofer section instead of ESL panels. It takes a really big ESL section to create the same amount of impact as can be obtained from a single line of 6"-8" midwoofers. (this is why my speakers use 2-of the Acoutst 1+1 panels per side...)

Also people considering ESLs need to know they're fundamentally a pure capacitive load, so they present a very challenging load for amplifiers.

[JonW]

Jon

Using active crossovers makes these things easier...

There are no zobels, or BSC.

These particular planars have a cavity resonance that produces a peak ~5kHz, I use passive notch filter for that. I could take out the peak with active EQ, but I prefer not to have an equalizer in the midrange circuit.

OK, thanks. Having just learned the basics of passive crossover design maybe it's time I learn about actives. All the little things that you can deal with in a passive crossover (BSC, zobels, notch filters, etc.), I'll be interestd to see how that's done actively. But here, in the case of your line array, it sounds a little different still. The array looks to eliminate the need for some of the complexity. Interesting. I'm glad this thread came up.

I didn't really need to go from 45" to 75" . Besides, my wife will be much, much happier.

:B
I remember really liking the sound of those (Newform?) speakers you had with that big, skinny, tall tweeter. There might be something appealing here in this line array approach. Maybe I need to check it out.

[Hank]

Did Hank purchased a pair?

I'm getting SO close to pulling the trigger - just still concerned that if I do a line of cones and a line of planar tweets that I'll always wonder if I shoulda done stacked electro's instead of the cones and tweets.
Thomas said he recommends 6" mid-woofs for this application. The truncated Dayton in the new PE flyer is 6", so I don't quite understand his saying their SD is a bit low. He did point out their highesh 59 Hz Fs, which doesn't bother me as I'd cross such a system to subs at ~100+ Hz.

http://www.parts-express.com/pe/pshowdetl.cfm?&partnumber=295-342&sf=08f-14&destination=295-342

$29 gets you this 6 1/2" TB driver with 11.5 mm Xmax 8O and 38 - 800 Hz FR:

http://www.parts-express.com/pe/pshowdetl.cfm?&partnumber=295-342&sf=08f-14&destination=295-342

For a line of planar tweets, the Dayton is on sale:
http://www.partsexpress.com/pe/showd...392262#reviews Cross over from the RD-75 at ~4500 Hz?
Hmmm...2 RD-75's + 18 PT-2C8's + 18 RS150T-8's = ~$2,144 8O
Boy, that would have to be my final speaker project. :E

[Dennis H]

For a line of planar tweets, the Dayton is on sale:
http://www.partsexpress.com/pe/show...2392262#reviews Cross over from the RD-75 at ~4500 Hz?

Zaph and Monte Kay both tested versions of that tweeter and found it to have very high distortion. I'd say you'd be better off just sticking with the RD75 all the way up unless you can afford some real ribbons like Fountek, etc.

[augerpro]

Dennis I hate to bring up your favoritist person in the world, but Thy has some good info worth being aware of on these Dayton planars. He was saying that Zaph tested a version of the early A version, which did have poor distortion. But the B and C versions have moved to push-pull magnets instead of just push and distortion is much lower. Might be worth looking into before writing them off completely.

[ThomasW]

Given the very low wholesale 10+ pricing of the RS150T those are probably worth it. I'd use the Neo3 over the Dayton planar tweets.

Another option are Maggie 1.6's for under $2K/pr...

[Mazeroth]

Dennis I hate to bring up your favoritist person in the world, but Thy has some good info worth being aware of on these Dayton planars. He was saying that Zaph tested a version of the early A version, which did have poor distortion. But the B and C versions have moved to push-pull magnets instead of just push and distortion is much lower. Might be worth looking into before writing them off completely.

Monte emailed me measurements of the newest C version about a year ago. At low power they perform decent at best. If you look at the 2.5k you'll see some subharmonics that show up. Very strange. However, if you cross around 4 khz. and keep the power low they may work well enough.

Frequency Response



2.5 khz. 1 watt



3 khz. 1 watt



4 khz. 2 watts

[Dennis H]

Yeah that does look better. 4kHz, 2W -- a bit under 1% 2nd and 3rd harmonics. It'd be interesting to see if a line of them is better than the RD75 at high frequencies.

[augerpro]

I know Tom uses his RD75's to 5khz. LR4 @ 5khz looks usable with those Daytons, and you could even go higher I'm sure. I think Tom's suggestion of the BG Neo3 is probably a good one from a cost standpoint too. Performance would be higher also, although I wonder if they have greater vertical dispersion-which you may not want in a LA-than the Daytons?

[Mazeroth]

I know Tom uses his RD75's to 5khz. LR4 @ 5khz looks usable with those Daytons, and you could even go higher I'm sure. I think Tom's suggestion of the BG Neo3 is probably a good one from a cost standpoint too. Performance would be higher also, although I wonder if they have greater vertical dispersion-which you may not want in a LA-than the Daytons?

I'm not an expert on line arrays by any means but I do know that a line of full range drivers (B3N) that I made a test baffle for had significant drop off in the upper octaves. I made a test baffle with four of those drivers and took measurements from 2 meters. In the center of the "array" it was almost perfectly flat out to 10 khz, then it began to drop off due to the comb filtering. Now, if I moved my microphone to the bottom of the bottom driver or the top of the top driver (I should note the baffle was placed so the center of the drivers was ~ 1 meter from the ground) I measured a drop off starting around 3 khz. The final measurements I took, both 1 foot under and 1 foot below the "array", showed a drop off starting around 1 khz. I think it's safe to say that Jim Griffin's white paper is correct in that arrays project a more cylindrical wavefront in the near field. This will help to mitigate floor and ceiling bounce. With that, I'd be pretty certain to say the same will hold true if using a line of the Neo3s.

[Hank]

Thomas, thank you for your continued input. I'm definitely not a line array expert, so let me ask this: is my number of 9 per side too many woofs and planar tweets? I'm not trying to get very close to the physical length of the RD's. I would think 6 or 7 woofs would be sufficient if the drivers had good Xmax, but what about the optimum number of planar tweets?

[ThomasW]

Hank,

In an ideal world you want a line array as tall as the ceiling. If that's not an option there should be enough woofers to have the same output level potential throughout the passband as the RD75's. And the line of tweeters should be as tall as you want the vertical dispersion to be, 4' or more IMO .