A new home for the BG ribbons?

[Brian Bunge]

Jon and Thomas,

I think Hank's real issue with the MCM driver is that he doesn't want to have to deal with having to flush mount 16 of those non-round frames! Can't say as I blame him there.

Brian

[ThomasW]

The drivers don't need to be flush mounted. Just cut round holes spaced so that the straight/flat sides of the frames are touching.

Remember we're only running these up to ~500-600Hz, not 1.2-1.3Khz.




theAudioWorx
Klone-Audio

[Brian Bunge]

Thomas,

So there's no problem surface mounting these huh?! That kicks ass!

Brian

[Hank]

J&T, I just e-mailed you the MCM driver's specs/CLIO plot, for two reasons: the time invested in scanning it and trying to post it, and also because it's so ugly .
Well tuning a bit below Fs...would you really count on someone being able to always place a speaker for optimal room lift and therefore count on it as part of system response, OR would you go ahead and tune Fb close to driver Fs? In my case, flat to 40Hz would be fine and I'd cross to my Adire Tempest sonosub at 60Hz. Yes, after reading about LS's, I'd try the power taper also, so that means three separate compartments and more weight. I would never have considered Baltic Birch ply for other than a subwoofer cabinet, but with the memory of manhandling those 250 lb Alpha LS cabinets, I might consider ply. What do you guys think?

Jon, if all you get for a plane ticket to London is temporary saw space in your girlfriend's garage, we need to have a little talk .
Maverick here as well - the three computers I bought for my kids and my new one are all AMD-powered. They make good chips here in Austin.

Airport security to Jon, Pete and Hank: "Sir, what are those weird looking object you're dragging in here?"
Us: "Just a pair of line source speakers ma'am. I have their seat tickets right here and I'm going to a speak-off in Denver".
Security: "You National Guard guys, get over here, quick!"

[Hank]

Guys, I hope you realize that Brian is just kidding. He and I both hate non-round frames. BUT, for a line source, I really LIKE the MCM frame! I would route a rectanglar recess for the stack of drivers, then do a through-hole route the appropriate distance inside the recess so that there would be a long rectangular baffle cutout the length of the driver stack. Since those driver frames are squared off on four sides, you can just lay them in edge-to-edge. I think they would look great recessed like that and surface mounted, Brian, would not look good. I'd have to of course build the three separate chambers onto the back of the baffle.

[PMazz]

Alright, what's the deal with power tapering the woofs? I thought that was only to compensate for higher freq distance to listener issues. Is it something to consider for a ~500 hz xover?

OK, Tom, the MCM it is! Your recommendation is good enough for me. Hell, with the amount we'll need, we could become a stocking distributor. I hear their packaging is pretty lame and they have a tendency to not survive the delicate handling practices of UPS.

Jon, when I said drawings, I meant the crude sketches I tend to scribble when I'm in design mode. I can probably come up with something, tho.

As for a fair, impartial way to decide who captured "the true essence of a line array", I think everyone can just send me their speakers for a good long listening test. Figure 6-8 months just to be sure.

And if you want to save money on airfare, just seal yourself inside the enclosure and ship it common carrier. No smoked almonds, tho.

Pete

[PMazz]

Hank, if you wouldn't mind....can you E-mail a set of specs on the MCM?

Pete

[JonMarsh]

Hi Hank,

Thanks for sending the spec sheet from them. I understand why you're concerned, but again, the test methodology is important. The measurements on this sheet are "swept" sine tests, with the measurements actually made at discrete frequencies, and line drawn connecting the dots. This is a short continuous sine wave test, and the problem with that is the influence of the measuring environment. In other words, if you don't measure in an anechoic chamber, the relfections from adjacent boundaries create re-inforcement and cancellation at different frequencies, due to the differences in path length.




Most of the frequency response plots you see published are either anechoic sine wave (say, from SEAS, Scanspeak, etc) or they are MLS (such as published by DIY guys in AudioXpress, etc). MLS uses a wide range digital test signal that's a bit like a wideband noise; the measurement receives through the microphone only for a defined interval (which can be set and adjusted; for example, in CLIO you set the start of the sample selection and the end, in milliseconds). This allows you to discriminate against the early arrivals directly from the driver, and room reflections. The problem with this is that unless you're in a very big room, you have to set the end of the window to a fairly short value, like 10 - 15 milliseconds. The lowest frequency you can measure this way is basically the window 1 over the window time. So, a 10 or 15 millisecond window makes it impossible to measure bass below 200 Hz. Otherwise, you have to put up with more reflections affecting the response, which is to create a lot of small ripples. And some people wonder why I think room treatment is important! Or speakers that minimize their interaction with the room (dipoles)!

I hope to find the time tonight to transfer and post what I measured. This is one of those rare times when what I measure is nicer looking than the company's data sheet! Usually it's the other way around. I've generally found Focal to be quite accurate about their curves, and the repeatbility. Eton is pretty good, too, except they don't publish impedance curves. Accuton has been one of the worst offenders regarding actual's versus published.

I'm not selling MCM drivers, so I don't want you to feel like I'm pressuring you to use them; part of the fun of DIY is making and developing your own choices. I have just kept talking about this particular MCM driver, because it seems to offer a lot of value for the money, for SOME applications. Maybe this one. I imagine the CSS driver is pretty nice, though without tech specs, I sure wouldn't buy it at 2X the price of the MCM. Since I've examined the MCM, and I like aspects of it's construction (spider, rear spider venting, cast metal frame, Xmax, etc) it seems like a relative bargain- I haven't been ablet to find anything else that looks as good for significantly less than 2X. And while I don't mind spending money when it's justified, I'm also not into spending it unnecessarily.

BTW, I'm ordering some more of these today.

Just sit back, relax, let me be the guinea pig....




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

[JonMarsh]

Alright, what's the deal with power tapering the woofs? I thought that was only to compensate for higher freq distance to listener issues. Is it something to consider for a ~500 hz xover?

Good point from Pete- I haven't run the numbers yet, (you wouldn't believe how swamped I am with real work right now!), so there's more than a chance that for this size line and crossover frequency it's unnecessary. The truth hurts but it will set you free!

Maybe I'll get enough to do nine per side, just in case....

BTW, you've got mail.

The ones I first received were packed decently, in individual boxes. They weren't *overpacked* by any means, but no problems with them or any other MCM's received to date.

Hey, on the airlines I fly these days I don't often get the smoked almonds, either! What a contrast when I got bumped up to first class coming back from my trip to Colorado last month... talk about how the other half (no, more like 5%) lives....


Best regards,

Jon




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We'll screw up the other planets later....

[JonMarsh]

Well tuning a bit below Fs...would you really count on someone being able to always place a speaker for optimal room lift and therefore count on it as part of system response, OR would you go ahead and tune Fb close to driver Fs?

This is a factor for almost any speaker- excepting wide range dipoles. Why? The room lift is a physical phenomena based on the distance from adjacent boundaries. It is directly related to the wavelength, so setting the corner frequency is a function of distance from the walls and floor/ceiling. I have a MathCAD doc I created eons ago for doing this calculation.

Classically, if you make a ported or sealed speaker (say, medium size bookshelf like my M8 monitor) and if you design it to be flat to the Fb and roll off below, in room it will be getting some lift already by the time it hits Fb, unless it's located well out from the walls. Even for the M8, which we deliberately roll off some, some folks building this design say it's too strong in the bottem end. And theyr'e right; it is, where they put it in the room, fairly close to a wall, and lift kicks in about 60 Hz.

In reality, room placement is inextricably linked to the fundamental speaker design. Understanding that, you can balance the two off, and get them to work together. Not undertanding it, you wind up with designs that don't sound right with the placements people usually try, or that don't reach their potential.

Done properly, you have two choices:

1. Place the speaker flush to a boundary, and design keeping the other adjacent boundaries and their contributions in mind.

2. Design for a golden mean ratio, with a smooth lift kicking in to compensate for an initially shallow roll off; this allows the greatest bass extension and subjective detail, plus the perception of a deeper low end without boom than is possible anechoically.

I'll try to post a chart tonight shoing how it works.

Note the difference between the Cardas recommended room placment for speakers versus what most people try off the bat....





You don't necessarily need placement that is this WAF hostile, but you have to consider the placement as an integral part of the speaker design. Seriously.

Even using my MathCAD calculations, you'll still wind up following the Cardas suggested golden mean for ratio's of wall/floor distance- 1.618:1 . I was doing this long before I ever heard of George Cardas, but he's codified the concept into most of his products. Good stuff....

Regards,

Jon




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We'll screw up the other planets later....

[Hank]

Jon, yes proximity to room walls is very important as is proximity to objects. The local customer for the AV3's called me after he initially set them up - he couldn't get a seamless horizontal soundstage and it was lacking in depth. I went over and he put on a trio and the girl singer was just to the right side of the left speaker, and there was little depth. He had a stuffed wing chair off to the right of the couch and since it wasn't directly in line with the speaker, thought nothing of it. I moved the chair two feet. The singer was center stage, stage spread and deepened. He st in the sweet spot and three seconds later was beaming. Happy customer.

My only point about the flat Fb was would you always design, counting on a specific room lift, like 5 dB or maybe just a couple of dB knowing that people will end up with all sorts of placements, some of which you wouldn't tolerate, but here again is the WAF and physical room limitations. Yes, the room treatment topic is very, very important. At a recent Austin HT meet, we had a seminar and discussions, than at a later working session meet at my house, we built some room treatments. Interesting stuff.

Pete, I thought power tapering applied down lower, but if not, then we have no sub enclosures to worry about!
Now, how are you going to power-taper your RD75 high frequencies? Did Jon e-mail you the rest of that spec page that has the specs and T-S parameters? I have the second sheet, which is the drawing print. I can get it scanned and forward it to you.

[JonMarsh]

If you look at the effects of three boundaries (floor, rear wall, and side wall, you will always get at least 5-6 dB of room gain; the distance from the boundaries determines at what frequency this kicks in for each boundary.

Part of the problem is that you have to spread these effects, or you can wind up with some bad peaks and dips from effects in concert. The ratio of the distances is 1:618 to 1, so if you have the woofer of a speaker 0.8 meter off the floor, then try the side wall at 1.618 times that, and the rear wall at 1.618 times the side wall- this is the design distance for the M8 system, by the way.

If you design for flat anechoic to the LF cutoff, unless you're in a very big room well away from the nearest wall (3 meters or more) you will have problems in the 40-50 Hz region. I'll post a few charts tonight and you'll see what I mean.

Many people like these problems; they call it "slam" or "punch", but it's not flat, it's not real.

Regards,

Jon




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

[Lex]

Guys, working on a new design, I think you might find interesting. Thought I would get your input. One problem, it's going to take a crane to move them once I get them built. Jon, can you spec these out for me? I al really an idealist, not so much on details.

I don't want to interfere with you guys work, but I think this design has merit! :B

[PMazz]

Lex, I have a set of those in my car.....they're OK.

Hank, I've got a copy of the spec, thanks. I decided to buy 3 RD 28s so I can power taper them.

Anyone know who manufactures the MCM units?

Pete

[Dennis H]

THX anyone?

Pete got me thinking about the Peerless drivers. If you used a line of 12 of the CSX 5.5's next to an RD-75, I think you could fit the whole thing in an enclosure with a footprint of about 12"x12". Sealed, with some stuffing, it could be tuned to an Fb of about 80 Hz with a Q of about .6. Use the THX crossover (4th order lowpass, 2nd order highpass, at 80 Hz) on any pre/pro and you would be all set. Should be good enough to make ol' George Lucas proud.

[ThomasW]

Lex

Nice design, BTW ever heard of comb filtering? :B

Pete

I'm pretty sure most of the MCM drivers are built by one of the several huge OEM speaker companies in the far east.

Dennis

The little Peerless like the little SS Revelators are nice drivers for nearfield monitors. The problem with any driver that size even when used in multiples is that the swept volume is so small that radiation resistance issues come into play. It's better to go with a larger driver and bigger baffle.

It's also a good idea to have a driver that easily goes an octave or more below the XO point to the sub. That way there's no hole in the FR.

Just my opinion of course......

BTW what's a THX?




theAudioWorx
Klone-Audio

[Dennis H]

Hi Thomas,

Yeah, in a perfect world we could all have huge speakers. But, I'm looking for something I can place 8 of in a room..... 7.2 with twin centers. A 12" square line array wouldn't take up any more floor space than mini-monitors. :LOL:

Those little 5.5 suckers add up. 12 of them have an Sd bigger than a Tempest and a p-p Vd of about a liter. Should handle 80 Hz no problemo.

I've had good luck crossing sealed boxes to a sub using the THX/Linkwitz concept of combining the acoustic 2nd order highpass of the sealed enclosure with a 2nd order electrical highpass to get a 4th order combined response. The octave rule works well for most speakers because they are being asked to work pretty hard down low. But, with 12 little drivers, 4.5 mm Xmax at 80 Hz would be deafening in any normal sized room.

[JonMarsh]

Boy, I'm glad I don' t have days like today too often! Seemed like I was either on a conference call or in a meeting all day, excepting lunch and mens room breaks.

Re the proposed MCM driver, here's the MLS response I measured, in a fairly tiny sealed box (just interested in looking at the midrange):







This test box isn't very deep (quite the contrary), so there may be some backwave interference with the front. I think these samples are a little different from the one measured in the spec sheet, because from the impedance curves and response plots on the ones I measured, first cone mode appears to be at about 900 Hz, rather than at the 800 Hz or so of the "factory" plot. Not that it's a significant difference in this application, crossing over somewhere like 450 to 500 Hz.

I ordered 12 more today.

I think Pete's suggestion of the Peerless CSX 7" sounds pretty good- not much bigger, excellent performance. Price is a bit higher-(well, more than a bit, more like 2-1/6 times higher) but it's a very safe bet- I'd be curious to see what one looked like up close and personal. The T/S parameters look right on the money for this application.

Hey, Lex, that's a pretty nice rig you've put together, but what's the load impedance? Do you have a plot you can share with us, I'm not sure one of my wimpy Aragon's will drive it... :LOL:

That little Peerless 5.5 might work out- a problem with many of the 5's is relatively low sensitivity- just a matter of lack of radiation resistance, as Thomas says- this one is better than average.






When are you going to build yours? I'd use one of my frequent flyer tickets to hear a 7.2 system with RD75's!


Regards,

Jon




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

[Lex]

Hey, Lex, that's a pretty nice rig you've put together, but what's the load impedance? Do you have a plot you can share with us, I'm not sure one of my wimpy Aragon's will drive it...

Yeah Jon, it's a helluva load. I expect to have something like 4 Krell Master Reference Amplifiers to drive it. :LOL:

Thanks for the complement there Thomas, let me know if you want the plans, lol.

Lex

[JonMarsh]

Boundary loading 101.



Using a layout my daughter suggested for placing the MkIV version of the bookshelf speaker, (high DAF), and not worrying about using the golden mean for staggering the boundary distances, this results:




Note that the MathCAD document plots the speaker LF transfer function based on the mathematical properties (Fb, Q, number of poles), the boundary radiation resistance/support, and the resulting composite room response.

I've heard a lot of setups that sounded like this- it's easy to see where the bass would be perceived as one note and lacking definition in the upper midbass; rock drum would be strong, but acoustic bass and other upper bass instruments would suffer greatly in definition.

For a "correct" layout, following the golden mean and optimized for the driver/box Fb, this results.




For any given speaker system with a given Q and cutoff, there aren't that many "correct" locations in the room.

You may not like those wiggles in the response, but if you get a real world response in a rectangular room with a monopole system that is this smooth over this frequency range, you're doing good.


Regards,

Jon




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

[Dennis H]

Hi Jon,

Don't cash in your miles just yet. I'm putting my house up for sale so the only sawdust I'm making these days is for all those little fix-up projects I kept meaning to do "someday." :LOL:

I did a quick power check on 12 of the Peerless 5.5's and it looks like a woofer section amp with 100 clean watts into 8 ohms would do the job pretty well. Of course more would be better for those into wretched excess. Anyway, if you were biamping, any stereo amp with enough power for the ribbons should handle the woofs just fine.

Speaking of amps and crossovers, has anyone tried the new QSC DSP-4? John Gordon claims it's more "transparent" than the DSP-3 but the proof is in the listening. Even if it didn't turn out to be good enough to use full time, with a street price of around $400, it looks like a great prototyping tool to test different configurations.

[ThomasW]

Dennis

I was all set to jump on a DSP-4 after early discussions with John Gordon. The initial specs were going to allow signal processing as low as 10Hz. Unfortunately that didn't happen. Due to some manfacturing considerations (they were in a hurry go get the product to market) the signal processing was limited to 20Hz like the DSP-3. I really wanted something with digital accuracy to add infrasonic boost to the big IB. Oh well maybe later......

We don't do much true XO prototyping these days. Jon's trick Cauer/Elliptical designs imported to LspCAD Pro have proved very accurate. A minor tweak here and there and the design can be frozen.

Jon

Next time you drop in for a stay at Casa De' Tomas you can hear 4 channels of RD-75 :B

I got a call from Kevin this PM he's going to come by Thursday and help me move the black dipole upstairs now that it's fully operational




theAudioWorx
Klone-Audio

[Dennis H]

Thomas, my understanding is the DSP-4 works below 20 Hz but you just can't set corner frequencies or see the shape of the curve below 20. The workaround is to draw your filter at 200 and then change the frequency to 20. The shelf filters seem backwards (to me). The corner frequency is the end of the shelf, not the beginning. So, to shelf up below 20, you would use a high shelf and cut above 20.

[Hank]

Jon, thanks for the MathCad plots. You're correct, most people are clueless about speaker placement (the WAF is as immutable as Hoffman's Iron Law).
This Lex guy has lots of time on his hands, doesn't he?
5.5"? 12" baffle width? hmmm.....

[Lex]

lol Hank. I had just got home from work, and needed a release, haha. Did I mention the cable biz has been a bit slow, so I have time to waste.

Lex

[Hank]

Excuse me sir, I don't believe we've been formally introduced. What cable biz?

Hey Pete - look at this Stryke 7" driver. Intended for sealed application and they say works dipole. $10 each for 8 or more. Temptation lurks around every corner.

[ThomasW]

Dennis

Just color me greedy, I want a hinge point at 10Hz




theAudioWorx
Klone-Audio

[Lex]

allo Hank! Allow me to introduce meself. I am Lex, one of the 2 owners here at the forum as well as thecableforum.com. I also own the brand CAT Cables, in the banner at the foot of this page. I also own Quantum Cable, signature in this post, and yes, I am doing it 1 more time, I am starting a new cable brand "Zeus". Zeus Cable. The website is active, but no product for sale yet. Soon, very soon on that one I hope. I am waiting on a couple of things to make the first products there.

I guess someone should stop me soon, huh?

Nice to meet you Hank.

Lex (Doug)




Cable Guy DVD Collection

[PMazz]

Hank, good spot! Thanks!

Very tempting. 16 of these for $160!

Anybody have any real world experience with these?

Pete

[JonMarsh]

Do they have 12 step programs for people who start cable companies?



Do they have 12 step programs for people who build DIY speakers?

Good questions, all.


Re the Styrke 7" driver, here's the published raw response.







I wonder if their suggested fix with the felt ring for the 1 kHz dip actually modifies diffraction, or damps cone edge vibration? The impedance curve would tell....


I give up!
Unquestionably the low buck wonder of the week.




My only critical comments would pertain to construction - stamped frame, a conventional spider (increases even order distortion) and no venting of voice coil area behind spider. A lot of driver for $10, though!


Regards,


Jon




Earth First!
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[Hank]

Hot Damn! It's about time I contributed something to this operation!
Jon, when you get the impedance curve, please give us your opinion about the applicability of this lil' 7" puppy.

Lex, I'd ask why so many cable companies, especially when it's so hard to sell cables. I'm the competition, as my cohort Brian Bunge is. He has a selling web site but I don't - some day maybe. So many cable companies, so few potential buyers out there who haven't been "convinced" that Monster Cable is the ultimate.
But, I won't ask because you're obvioulsy into this as a labor of love. Best wishes in your new venture and nice to meet you too. You've got a couple of quality moderators in Jon and Thomas - they are an asset to the DIY community, generously sharing their knowledge and experience.

[PMazz]

Well, the more playing around I did with drawings the last couple days, the more I realized I will have to live with a straight baffle. The only alternative involves the amount of baffle that should be left next to the RD75. Figuring ~4" for the RD, and another 1" to a 7" driver and I'm already at 12". I can probably only get away with ~18" wide baffle, maybe 20".....maybe. Should I start thinking about those 5"ers?

I'm bummed!

Pete

[ThomasW]

The latest planar/hybrid design from Carver Audio



More pics HERE

Scroll to bottom of the page




theAudioWorx
Klone-Audio

[JonMarsh]

Interesting esthetics.... the looks almost make it a "klone-worthy" project, but I think we're basically looking at a single ported 12" driver on the low end, and a 175 Hz crossover. Hmmmm. Ribbon driver rated at 2 ohms... a special Radia version? It could sound pretty good... but I can't help but think it won't really reach the potential of the RD drivers. Not with that crossover and that LF configuration. But maybe I'm just being curmudgeonly again.






There really aren't all that many amplifiers that are truly happy with 2 ohms... it messes up the output stage trasfer linearity unless you use a pot full of transistors.... I feel bad enough designing an eight inch bookshelf speaker that's only a bit above 3 ohms in the minimum HF impedance.... except it sounds pretty d*mn good, and it's not my fault the Vifa tweeter is really a 3 ohm tweeter. I tell ya, it's not my fault- they made me do it!


BTW, now I know what they mean by a garage shop.... this makes the old Innersound facility look like a tour of the Revel digs in Canada...

~Johann




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

[Lex]

Thanks Hank. Well, I truly enjoy the development process. I love the challenge. As to my multiple brand/product concept, well if each brand can learn to crawl, eventually walk, and someday jog. Well, I am in the business full time. Sure, it's highly competitive. But you believe in yourself, and your products, and just make it happen. Every business I know of is competitive, some more so than others. But hey, somebody is going to sell higher quality cables, might as well be me.

I have made a lot of progress in about a year and a half. If it continues, I may just have something here for the future...

Yeah, Jon and Thomas are amazing DIY gods, I mean guys, I mean gods. They really command a lot of respect for the way they pave for the rest of us. Kudos guys.

Lex

[PMazz]

Funny, that's sorta similar to the lines in one of my scribbles. Shape is nice, but how the hell do they mount the grill? I couldn't see any mechanical connectors.

I'm still baffled about how wide to make these. This may have to be a wait and build one and listen and measure situation for me. I got so frustrated with my design I started thinking about a RD75 and a bass box again.

Pete

[Hank]

I'm with you, Pete. The wide baffle that T&J recommend has me thinking also. That's why I declined the 8" drivers and was concentrating on 6.5"ers. But that Stryke 7" I found sure has an attractive price! I just dunno. I kinda like the Apogee look, so at least the baffle won't be quite as wide at the top?
J&T: What would be the minimum baffle width, bottom to top, that would be acoustically acceptable?

[ThomasW]

Baffle width should be as wide as possible.

At a mininium you're got 4.75" wide for the B&G, combined with the width of the chosen woofer. There must be an inch or so for the sides of the box, and some space between the B&G and the woofers.

'Optimal' performance is going be obtained with a tapered wing given the fact that it spreads the baffle loading out over a wider frequency range.

Putting the 'wing' on a hinge would give the best loading and allow the wing to pivot out of the way when not needed. A piano hinge combined with the supports used for drop-leaf tables would do the job.

If anyone wants to figure out the size for a certain frequency look HERE. Some other interesting audio/physics stuff can be found HERE




theAudioWorx
Klone-Audio

[David Meek]

Jeez, those new Carvers are georgeous! :T

I'm still trying to figure out how that funky little workshop produced THOSE cabinets. Does not compute.




David - HTGuide flunky
Our "Theater"
Our DVDs on DVD Tracker

[JonMarsh]

There are ways with coping with any baffle width, but it has to be taken into account in the crossover design. Issues are different with regards to monopole and dipole, but we've been mostly talking monopole re the line arrays with small drivers.


With a baffle width of 12", for example, the baffle step transition occurs around 1 kHz; there's some on axis peaking at that point from the edge diffraction, then a 6 dB shelving over about a 2 octave span. A 16" wide cabinet would push that down to about 700 Hz. To me, it makes sense to plan the crossover and baffle size so that only the woofer has to be compensated for baffle step; otherwise, the ribbon crossover becomes a bit more complex- not unmanageably so, but still we're talking about modifiying inductor and capacitor values and adding at least an additional R/C network.

-Jon




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[Hank]

El flippo!
Okay, 16" baffle width. I assume that's with the MCM 6.5" drivers?
Thomas, a folding wing might help a bit for someone with the WAF to deal with - good idea to keep in mind if I happened to get a customer for a line source someday.
Are you guys saying that a dipole implementation would result in a narrower baffle? If so, how much narrower?

David: one of the linked photos looks like that might be part of a cabinet shop - there's a guy working on some doors. You can make just about any shape with MDF. They may even have an N.C. routing machine, which would make quick work of a stack of glued up MDF sheets. I've seen one slice and dice Magnepan frames at their plant. Also, the cabinets may have been sent out to an auto body shop for painting, although some big cabinet shops have their own spray booths. Careful sanding, priming and painting will produce a professional looking cabinet.

[Dennis H]

Are you guys saying that a dipole implementation would result in a narrower baffle?

I should let Jon and Thomas speak for themselves but what the heck.....

I think they are saying the opposite. A dipole depends on a wide baffle to make bass. You can read all about the theory on Linkwitz's page but, in general, if the baffle is too narrow, the front and back waves will cancel too much and efficiency will suffer.

Jon raises a good point about making a monopole baffle wide enough that all the baffle step compensation can be done on the woofers. It would make passive crossover design much easier. I keep thinking in terms of active crossovers so, in that case, it's no big deal to EQ the whole signal before you split it into woofer and tweeter lines.

[JonMarsh]

With a dipole you have to plan and deal with the dipole cancellation/reinforcement effects, wihch is another level of complication. The 6 dB/octave roll off towards the bass starts at a frequency which is a funciton of the baffle size- the large the baffle, the lower it is. The smaller, the higher. Per your previous inputs and discussion, my impression was that a dipole setup was too big for you, and required too many drivers for the SPL you want (remember 4x rule- so 8 6-1/2 sealed would require the equivalent aire moving of 32 - 6-1/2" or 16 - 8". )


Re driver T/S parameters for the Stryke driver.

It doesn't look to good, for making a small system. The Qes is highish, at 0.65 (low electrical damping), and the reuslting Qts of 0.53 is on the high side for a ported system. It can be done, but there's a trade off. (as usual, the devil is in the details).

The ideal box for extension, output, and flat response for the 7" Stryke is my M8 bookshelf- internal volume 32 literes, and tuned to 32 Hz, well below the driver free air resonance. That's a pretty big box for a 6-1/2/7" driver.

With that size, you can get some fairly smooth, strong output down to that range, up to about 96 dB down to the mid thirties. Xmax is the main limitation, and because of this, bass power handling is a little low, but hardly surprising for a 7.

However, the problem is the size of the box. 32 liters is almost double what the MCM can work fairly well with. Any smaller box for the Stryke driver and it turns into a boom box, with substantial peaking, unless you tune the Fb so low that you don't get any useful port reinforcement in the mid low bass, which limits output level and raises distortion considerably in the 45-75 Hz range. Essentially, it's converting it to a sealed box that unloads below the port tuning. This is another driver who's electrical parameters are better suited to a typical sealed system. Otherwise, it requires a large box, and has little tolerance for over load (10 watts below 80 Hz is pretty much the limit).


The MCM will work well in cabinets from 16 to 24 liters. For flattest in moderate size room and smallest box, a 16 liter alignment tuned to 36 can be flat in room to 40, and down 3 dB at 35. This alignment has a slower roll off than the typical 4th order ported. Transient response is cleaner. Maximum output down to 35 Hz is 98 dB. Per driver. For an 8 driver array, 107 dB. 8) That's not counting room gain, so you can tack on another 6 dB if you wish, and for a stereo pair, another 3 dB. That's about 113 dB in the low bass range. Of course, above 100 Hz it can play louder, as it's not Xmax limited. :LOL:

For larger rooms, a 24 liter alignment tuned to 36 Hz will be flat in room down to about 35 and -3 dB at 30. This alignment will be "weightier" in the bottom end but require more room from the walls to tune the room gain to the right frequency range. Maximum output for one driver down to 33 Hz is 98 dB.

For either of these alignments, I would compartmentalize the woofers (probably two per space) and use a 3-4" diameter flared port for each, to keep air velocity under control.



-Johann




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

[Hank]

Okay gents, I was thinking a dipole needs to be wider, just got confused...whew!
Thanks for looking at the Stryke 7" Jon. Since it's new, John must have had a purpose in mind and I think the clue is in the description, which says something like it works in a dipole arrangement. Do I smell a line source project over at Stryke?

Well, I think I've taken enough of the dynamic duo's time, and Jon is about to leave for vacation/work trip, so I propose that I not ask any more questions for a while. The plan I'm considering for a couple of months from now is a monopole implementation of RD50s and Jon's recommended MCM driver, baffle width about 16" and the woofer baffle tapered in bottom to top. Pete, when are you going to buy drivers?
Hmmmm...how am I going to wrap veneer around an angled cabinet corner...hmmm....got some thinking to do....

Thanks folks, it's been a very interesting, educational, fun experience and I'm going to quit bugging T&J for a while.
Makin' sawdust

[Dennis H]

A question for you dipole experts. Can one side of the baffle be sealed to a side wall or do both sides need to have air around them? I'm thinking (only thinking) of the possibility of building big dipoles into the two sides of an architectural feature such as an arch or a framed opening separating two rooms or two areas within a large room. Done right, it could be pretty invisible.