Dipole or Monopole?

[JonMarsh]

Hi Pete! Thanks for the welcome, I'm glad to be back!

Your measured plot doesn't look too bad at all, especially considering you're at 3 dB/div.

Just to see what they're capable of, I'd experiment with pulling them out a little further from the back- any chance of some rear wall damping to kill some of the back wave in the upper midrange/lower highs? This may smooth things out further and sharpen up the imaging. Of course, I realize my reputation as "Mr Speakers out in the middle of the room" does tend to precede me.

I'm jealous that you've got your RD50's already. But hopefully I won't be too far behind you. It depends on how many nickels and dimes I have left over paying bills at the middle of the month.

BTW, where did you by the OW703 fiberglass? I've been looking for a local source in Northern CA. It's good stuff for acoustics work.

Keep us posted!

Regards,

Jon




Earth First!
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We'll screw up the other planets later....

[ThomasW]

Pete

I've bought a ton of amps off Audiogon. I always ask for the serial number and a photo if possible. I always call and talk with them on the phone too.

Then I only pay by COD (cashiers check or money order). Frequently the buyer will be concerned about getting burned for shipping of the pkg if somehow gets returned. If that's the case I send the buyer a check in advance for one-way shipping.

PayPal offers no protection for the buyer. The escrow services are good but $$$, and many sellers don't like the hassle




theAudioWorx
Klone-Audio

[PMazz]

Tom, thanks for the COD advice. I'll give it a try.

Jon,
I'll play with "out further into the room", but it won't be long for this world, if you know what I mean. I stuffed some 703 into the rear cavity of the dipoles. You can just see it on the side shot above. I'll try some other treatments too. I got the OW703 from a local sheetrock/insulation distributor. They happened to have the unfaced 703 because a builder ordered it and then renegged. I got it for ~ 1/2 price, $.86/ft. 2'x4' tiles. Foil faced is more common usually. I use it around the shop for sound absorption.

Pete

[Hank]

Atta boy, Pete! You took the plunge and ponied up for some RD's. I'll vicariously enjoy your experimentation since college costs for two of my offspring have two IV's sucking the contents out of my wallet. It's $30 8" Chinese subwoofer drivers for me for now...sigh

Those are dipoles, right? It looks like you did a baffle with side boards for a U-shape with no back, and some high density fiberglas stuffed between the side boards. So far, do you think you'd want to supplement the RD's with tweeters like the Grand Poobahs seem to recommend?

[PMazz]

Hi Hank, thought we lost you there for a minute. College kids, huh? Ugh. Sister went thru that a couple years ago. Still mumbling to herself.

Before I played around with some top end EQ, I would've said absolutely. Not so sure now. All those years around power equipment may be taking their toll. I'll hold off till I get them properly set up. Still want to give a sealed enclosure a try, too.

Pete

[ThomasW]

Actually if the area behind the RD50 is filled with rigid fiberglass insulation the speaker is much more like a monopole than a dipole




theAudioWorx
Klone-Audio

[Hank]

Yeah, Thomas, I skipped over the word "rigid" I guess. Who knows, I'm mumbling to myself these days. It may be Jan - Feb before I can order some RD's. sigh...
Or maybe I can start selling my BoseBusters and make some extra coin.
(background laughter from crowd at the mention of the illusion of making money building speakers)

Hey, I noticed a post from the designer from the south of France that BG is developing a NEO 10 that will have lower extension.

[ThomasW]

Hank

After living with the black dipoles in the family room for a couple of months now, I'm going to whip up a pair of Arvo's for that room.

I need the speaker to have the ability to have good sound over a larger area of depth. The black dipoles sound good but the output levels have to be changed if I move to a different listening position. That won't be a problem with the Arvo design.

Personally I don't see much benefit to a Neo 10.




theAudioWorx
Klone-Audio

[Dennis H]

Hi Thomas,

Interesting. What do you think is going on with having to change the levels when you move? Is the midwoof line acting as a point source at lower frequencies so you have to boost them as you move farther away?

[ThomasW]

Dennis

Yeap the drop-off rate from the RD-75 planars is different from the cone driver line array.

So the output level and toe-in must be changed if I'm seated at the main listening position ~11' away, vs the sofa ~7' away, vs the dinette area ~16' away. There is no 'happy medium' When optimized for any one place, that causes a loss of focus, definition, soundstage at the other areas




theAudioWorx
Klone-Audio

[Dennis H]

Sounds like the ideal room for a line array would have a flat ceiling so you could go floor to ceiling with the LF drivers. The reflections should simulate an infinite line and keep the -3dB per doubled distance at all frequencies. It might even be a good idea to have hard floor and ceiling surfaces and run the HF drivers floor to ceiling. I'm wondering if that would eliminate that nasty notch you get at about 1.5K when you measure an RD75 from about 6 feet away. The simulated infinite line might fill that in and make the frequency response much less distance dependent.

[PMazz]

I've been noticing some buzzing withthe RD50s. Even without EQ on the top end it's still there. Any ideas?

Pete

[ThomasW]

Pete

Do a low power frequency sweep.

I'd lay odds that the panels are buzzing around the 200Hz XO point. It's just too low for the shorter panels. B&G uses a 500Hz XO point in their systems that use the RD50




theAudioWorx
Klone-Audio

[JonMarsh]

This would be my suspicion also. What are the slopes on your HT Pre-Pro crossover, Pete? For 200 Hz, they definitely MUST be 4th order L-R at a minimum. Otherwise, I expect too much stress on the RD50's.

I'm planning a 600 Hz crossover, and undecided as yet whether to use a standard 4th order L-R or go with my "Hi-Finite" slope crossover, since the latter gives 48 dB/octave for the first 50 dB or so.... If I was to try 200 Hz or 250Hz, I'd definitely go with the high slope crossover.

Regards,

Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[PMazz]

The slope is 12 dB high pass/24 dB low pass.

I haven't done the sweeps yet, but the buzzing seems to be occuring at higher freqs. I'll guess ~3-4 KHz, maybe higher.

The xover and amp haven't gotten here yet. I picked up one of the Weller WES50 soldering stations for the xover project. What size tip is ideal for PCBs?

Pete

[ThomasW]

What size tip is ideal for PCBs?

Probably the smallest one you can find...it depends on the iron but the 1/32 conical tip is probably best

Unless something is goofy the panels shouldn't buzz at higher frequencies. What SPL is this buzzing occurring at? Does the buzzing go away if the fiberglass insulation is removed?




theAudioWorx
Klone-Audio

[PMazz]

Freq sweep sounds fine. Problem is there with or w/o fiberglass. 80 - 85 dB volume levels. Only hear it on two CDs (new). Sort of like a sibilance issue, but not it. Will hook up MTMs and have a listen.

Pete

[JonMarsh]

The slope is 12 dB high pass/24 dB low pass.

This is not good. Though the 12 dB electrical high pass will combine with the 12 dB or so acoustic high pass of the drivers around 200 Hz to make something close to 24 dB/octove low pass, the power feed at low frequencies would be higher than I would want to see with the RD50's. This would mean the electrical feed at 100 Hz is down only 12 dB- not very much. Maybe enough? I don't know.


-Jon




Earth First!
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We'll screw up the other planets later....

[PMazz]

This is not good

Not good as in sound or not good as in driver damage?

The Marchand XM9 will solve the problem, hopefully, if it's not doing damage now. Should be here this week. Amp by next week. Sucking solder fumes....who knows how long.

Pete

[JonMarsh]

Distortion not good, but unless you really "wail" on them, probably not any driver damage. I'd treat them gently, though. We found Thomas's RD75's really sang at 600 Hz, but crossed over lower lost their sense of ease and life.

YMMV.

Don't worry Pete, I'm just jealous 'cause you already have your RD50's to play with, and I'm still in the planning stage. Of course, Thomas would just tell me that gives me some time to get the Arvo Part's finished and work on my other back logged projects.

Face it, I just need a month off from work.

-Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[PMazz]

Yea Jon, but somehow I suspect yours will be done first.

I know what you mean about unfinished projects. My list is fairly long as well. Maybe not as creative or unique, tho. On top of all that, the wife is bugging me hard to build a new bedroom set. Seems as though some idiot promised her a surround system and wall unit when some new gear arrived a while back. :roll: She's now threatening to actually BUY furniture. ACK!

Wait till she sees me soldering the Marchand.....actually just listen for a "Now what the hell is this" scream. :LOL:

Pete

[JonMarsh]

Oh my.....


Sometimes I forget what an easy life I have ( ) with only an 18 year old daughter living with me....

Bro, I'd say you'd better get busy on that bedroom set! Priorities definitely have to be negotiated then followed through on! :LOL:

-Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[Dennis H]

We found Thomas's RD75's really sang at 600 Hz, but crossed over lower lost their sense of ease and life.

That's using them as dipoles, right? How much lower do you think you could go with a monopole enclosure? I notice Wisdom is crossing their monopoles really low but, of course, they are using a premium version of the driver.

[JonMarsh]

Hi Dennis,

I don't have any experience to make a case for a different crossover point monopole compared with dipole. Based on excursion issues as you get lower in frequency (and keep in mind, we were using a pretty good size baffle) I'd recommend no lower than 300 Hz in monopole- but that's a "seat of the pants" suggestion. And I might still prefer the higher point- I think it's something you'd need to investigate based on your SPL requirements and perhaps some careful distortion measurements. Also, don't forget baffle step may be an issue- if you use the RD75 or RD50 in a narrow baffle monopole, I expect there would be a drop off going from half space to full space radiation. But the only way to know for sure is to measure the setup you're considering/developing.

I'm staying with 600 Hz because even BG recommends a more restricted frequency range for the RD50 than the RD75.

Regards,

Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[ThomasW]

I'm staying with 600 Hz because even BG recommends a more restricted frequency range for the RD50 than the RD75.

And I'm sticking with a ~600Hz XO point with my RD-75's because I think they sound better with a higher XO point




theAudioWorx
Klone-Audio

[PMazz]

It's a shame the DPL12s can't be used that high, seeing as I have a few laying around.

Maybe I'll try the AV8s I have laying around.

Pete

[JohnR]

The Lambda dipole woofers can be used that high. I haven't been paying close attention so I'm not exactly sure what you'd be looking for, but we can talk about trading a pair of 12" Lambdas for some DPL12's if you're interested.

JohnR

[PMazz]

Thanks for the offer John, but I'll likely stay with double 8" or so drivers if this concept works out. I want to try a sealed "bass box" to go along with the RD50 and 12s would be too large for what I have in mind.

Pete

[ThomasW]

Pete

According to Dan Wiggins the DLP12's can go up to 450Hz.

It shouldn't be too big a deal to whip up a couple of plain dipole panels for an audition




theAudioWorx
Klone-Audio

[JohnR]

No worries, Pete. It was just a thought, I have my DPL12s in isobaric boxes, but eventually... IB, I hope. Figured a few more wouldn't hurt :-)

Here's my flat baffle prototype... as you can see, my prototypes are, ahm, a little less sophisticated than Thomas and Jon ... :LOL:



JohnR

[PMazz]

Didn't Tom Hanks build something like that in the movie Castaway?

Hey, that's why they're called prototypes. I've got a complete set, or two, of raw MDF and flakeboard speakers. They never get past the prototype phase before I'm off on another project.

Pete

[PMazz]

Tom,
I will give some dipoles a whirl, for sure. Does the breakup start at 450 or can they be crossed at 450?

Pete

[ThomasW]

Pete

I think Dan said the the break up was at 600Hz and as a result not to use the driver above 450Hz




theAudioWorx
Klone-Audio

[Hank]

Hey, I'm still here, just penniless. I thought I'd stir things up a bit.
Any comments on coaxial drivers? Here's a new one:
http://www.nuera-acoustic.ca/products/datasheets/W4-937S.jpg
$32.10 1-5 qty.

Let's see some more lively debate on RD's vs Newform Research.
Anything for action

[PMazz]

The RD50s seem to be sounding better day by day.

Am I imagining this or do the RD50s have a break in period?

Pete

[ThomasW]

Pete

Yes there is a break in period with the B&G's while the panel equalizes the stresses of the mfging process. Basically the same as any speaker

Hank

The B&G vs Newform isn't really a debate, more like an apple vs oranges situation




theAudioWorx
Klone-Audio

[Hank]

'sigh'...I tried.

Pete are you leaning towards dipole for your final design?

[Dennis H]

Yep. Hank, you're going to have to look elsewhere for a WWF brawl. Me, I like both apples and oranges (and grapes and berries and.......) :LOL:

[PMazz]

Too early to tell. I've only tried the dipoles so far. I'm still waiting for the Marchand xover to get here, be assembled, and then I need to do a proper bass box to complement these B&Gs. I will most definitely do a sealed enclosure and give a listen for a while. They are really sounding pretty good with just a high crossed sub, so I'm hopeful that I won't have to do a full blown LA.

Pete

[Hank]

Can't let this thread lay dormant too long.

Small, low-end, short-throw drivers get 100 dB in a narrow enclosure:

http://www.partsexpress.com/projectshowcase/Kuze3201/Kuze3201.html

Not quite hi-fi, but shows you can do something in a narrow enclosure.

Pete, how's the grand experiment going? Jon, did you get your RD50's? I'm living vicarously through you guys for now.

[PMazz]

Hi Hank, I saw those towers in the PE flyer. Pretty neat looking.

I updated the thread on my project. Sealed enclosures all around. Not for long, tho.

I've been waiting for Jon to blow us away with something. Tom has had them longest, but I guess he's integrating them into his ESL line.

Pete

[ThomasW]

I have 2 pair of RD-75s. One pair is the mids in the ESL array, the other pair are the mids in the black dipole baffles

Jon's RD-50s were delivered today




theAudioWorx
Klone-Audio

[Hank]

Jon's RD-50s were delivered today

Let the games begin! Or should I say, "continue"?

[JonMarsh]

Yup, got home from my trip, and besides my smiling daughter there were a pair of RD50's waiting for me.

In some available time sitting in airports and what not I've been working on the enclosure design in AutoCAD, drawing both an "optimum" alignment for deep bass for the MCM drivers and experimenting with some compromises.

Then I had either an epiphany or a Brain Fahrt (only time will tell!). :?

ThomasW will remember a system I built in the mid 80's to placate my wife re esthetics and to make it sort of easy to move around and to modify. We called this the "Modula" system, and there were sort of two incarnations, mostly due to crossover changes. It was literally assembled in a modular fashion, so that it was easier to move, and easier to modify.

The bass of it (literally and figuratively) was "sub cube" of sorts using a SEAS 13" driver, in a ported arrangement. On this set a frame which held a line array of 8 Panasonic leaf ribbon tweeters- (the big ones), and helped support two column like cabinets on the right, each of which contained an MTM array with Seas P17REX and an MB titanium dome midrange.

So, what I'm thinking of doing now is reviving this concept, but keeping the esthetic planned for the line array cabinet with 1-1/2" round overs, and the upper section (ribbon plus two four driver arrays stacked) would be about 60" tall, and would work in concert with a similarly styled bass cabinet, drivers not yet decided. I've got choices, with a pair of BPD1203's availalble, as well as a quad of DPL12's. This would even allow for adding a slice of some tweeter array in the middle as an experiement, since I'm planning for replaceable top and bottom panels and will make the woofer portion three or so inches wider.... Then, the risk for trying out tweeters is minimal; if it doesn't work as I like, I can go back to the original configuration with minimal hassle.

As I get this concept fleshed out in the 'puter, I'll post some drawings and renderings- maybe by the end of the week. 8)

It would be easier to build, and much easier to move around than a single monolithic cabinet. The upper range crossover, at 600 Hz, will be passive (external box), either a conventional 4th order L-R or my Hi-Finite Slope crossover, and the bottom end initially will be done with my Sumo Delilah II, which has a non loop feedback buffer for the high pass output, and variable crossover frequencies for both LP and HP (independently).

Unfortunately, tomorrow I get back on a plane for biz, so their won't be much accomplished this weekend.... :cry:


-Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[JonMarsh]

OK, a quickie update before I run for my plane today.

Below is a concept rendering for the initial three piece upper section, you can just see the demarcation between the ribbon cabinet and the two 6-1/2" line cabinets, but you can just barely see the split on those cabinets....





This will sit on a woofer cabinet... if the upper range isn't expanded with a tweeter strip, then the woofer doesn't have to be any wider than the 16" total shown here- think BPD1203, perhaps, in a smalled sealed box, with a hellacious amp.

Another possibility is two DPL12's per side, one firing front, one rear (this costs less than the BPD1203 did, which is no longer available); this might be in a little wider cabinet (19") to permit the add on of a tweeter ribbon array in the future; sides with same 1-1/2" round over..., with a black inset rectangular grille.

Finish either dark honey oak, or teak.

Ribbon module covers 600 Hz and up, doesn't operate in baffle step region.

Midwoofers cover 75 Hz to 600 Hz, with baffle step compensation, distance to wall set for room gain to kick in at about 100 Hz where six's start slow roll off in this size cabinet. If planned as a three way with "integral" sub cabinet, then volume per each 4 driver midwoofer cabinet would be reduced to about 50 liter. Then, it is still ported, and tuned to 32 Hz. Why? This models as producing a very flat response to 100 Hz, and has a 6 dB slope going below 100 Hz down to 32 Hz, down -3 dB at 75 Hz (intended crossover point). With the typical inductive roll off of high travel sub woofer drivers above 85 Hz, both LP and HP have a single pole function built in at 75 Hz. These are matching and complementary.

If used with my Sumo Delilah II electronic crossover in 2nd order mode, net acoustical crossover between bass cabinet and midwoofer line array will be 3rd order. If used with my XE electronic crossover (personal custom design, as used with the SLAMM's), electrical slope of 3rd order will add to driver pole/zero to produce net 4th order crossover.

Woofers boundary loaded, EQ depending on type of driver. Since located on one main boundary (floor), only slight room gain from walls (3 dB?)

Sounds good in theory (so far), let's see how the practice works out.

-Jon




Earth First!
_______________________________
We'll screw up the other planets later....