A new home for the BG ribbons?

[PMazz]

OK, I need a reality check here.

Why not 6.5" drivers? In a box program using 6 drivers I come up with 98 dB at 1W/1M. Inputting only 20 W, the SPL goes up to 112 dB with only 1mm excursion. These are fairly typical drivers with only 3mm Xmax in a vented enclosure.

What did I miss this time?

Pete

[PMazz]

Tom,
How much taper do you think the baffle should have? Actually, how little could it have to spread out the diffraction freqs?

Pete

[PMazz]

Hank,
Timing is a problem right now. This may be down the road a bit for me, as I have to recoup from moving the shop.

The price break isn't all that much from buying 2, tho.

If you can wait, tho, it'd be fun to do "dueling ribbons". We'd really have Tom and Jon's heads spinning!

Pete

[ThomasW]

Hank

The question should be how large should I make the baffle not how small can I make it.

The flare in the baffle should be as wide as possible to obtain the best baffle loading. It could be attached with a piano hinge to rotate it out of the way whey not in use.

Pete

Very few 6.5" driver have the ability to play both low and loud.

Guys

Jon and I recommend designs based on creating the BEST possible performance for the time, money, and effort invested. And we pretty much guaranty the performance of the designs we create. But if one desires lower cost, smaller baffles, or whatever then go for it with the understanding of what those compromises will do.

If lower cost and narrow cabinets are a priority then just copy Danny's LS speaker. The CSS 6.5's are available for $39ea from Creative Sound Solutions

The large B&G planars are world class transducers and in our opinion deserve to be mated with similar drivers. So we recommend using the Hi-Vi M8a (the Seas Excel's are a little too expensive for our budgets). The M8a will provide a seamless top end transition with the planars, have more than adequate bass extension, and are the single most transparent cone driver I've ever heard.




theAudioWorx
Klone-Audio

[Hank]

I don't understand this cabinet geometry. "Flare" - what do you mean? What I see in the photo is three sections that look lke they are not flat across the front. It looks like the woof baffle section is angled back a bit from the ribbon section, putting the ribbon section farther forward. Also, I do see the section on the other side of the woof baffle tapers in towards the top, making the whole baffle narrower at the top. Am I seeing correctly? Also, I don't understand the hinge idea. If I have a solid cabinet (remember, I'm talking monopole here, which you seemed to thinks is fine according to an earlier post), so are you saying to hinge the ribbon baffle section on the side of the enclosure so that it swings back along the side of the enclosure when not in use?
I aplologize for asking what to you guys are probably elementary, obvious questions, but this trapezoid and hinged baffle section have me floored h:

Pete: I can wait awhile, especially with this new cabinet info to digest. Also, T&J may be getting tired of my questions, so it might be best to give this a rest for a month or so. Keep in touch. Also, I don't understand the woof size issue. It looks like your modeling six drivers showed enough SPL capability. I'm lost too.

[ThomasW]

Hank

I should have said taper not flare. Yes the tapered section could be mounted separate from the main baffle and swing out of the way to make the speaker more narrow when not in use.

For this prototype baffle we angled the planar section 12 degrees. That way it aims directly at the listener.






theAudioWorx
Klone-Audio

[Lex]

Hank said:

that's made with the sun-dried butt skin of water buffalo that has zero cone modes

I said, hahahaha!

Lex

[Hank]

Thomas, okay, taper the woof baffle bottom to top ala Apogee. Got it. You angled the ribbon section 12 degrees. Okay, stupid question time: why not a flat baffle and just toe-in the cabinet?
I guess you could "hinge" the tapered section (which appears to be the narrowest section) to make the speaker a little less obtrusive, but it might not look too good. I guess the unobtrusive goal is pretty much toast at this time in the pursuit of best sound. Guess it's a good thing I don't have a WAF to deal with.

Lex: Thanks, I needed that. I'm glad someone appreciates my humor. Actually, one of my favorite things is to make people laugh.
I could probably write some really obtuse "high-end" component descriptions. I've just made my first custom power cords with Teflon insulated silver-plated 12 gauge solid conductors and jacketed with Teflon, hospital grade male plugs and Schurter IEC connectors. I call them the HF Soundwerks model SO series power cords. Guess what the SO stands for.

[JonMarsh]

that's made with the sun-dried butt skin of water buffalo that has zero cone modes

You know, that's one of those popular speaker building legends going around (kind of like Urban legends), but unfortunately that dog don't hunt. The UV involved in sun-dried water buffalo butt skin results in excessive polymerization of collagen radicals, causing a system of "micro-cracks" to form, which degrades the stiffness over time with a classic inverse guassian bathtub curve.

The correct way to implement wafter buffalo butt skin cones is based on a sand drying process (similar to floral dehydration), using cyrogenically treated and freeze dried refined silica; the particulate diameter of the silica should not exceed 100 um, and for best results the mean of the three sigma distribution for particulate diameter should lie in the 40-50 um range.

Then we're really talking maximum PRAT!


Best regards,

Johann




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[ThomasW]

why not a flat baffle and just toe-in the cabinet

Angling the planar makes the baffle narrower, it aims the planar dierctly at the sweet spot and looks cool




theAudioWorx
Klone-Audio

[PMazz]

Any idea how the bass box is designed in this speaker? The Xover is supposedly 12 dB-250 Hz. It sports a 10" driver, according to the site, but how is it positioned and how is it's output directed into the room?

Pete

[JonMarsh]

There's a review by John Kotches out their, but it's not entire unbiased, as he bought a set. He likes the sound of the ribbon, and has some issues with the build quality and the way it's put together.

The 10" woofer, as you might guess from looking at the cabinet, is side firing. This is not a problem IF you're doing a crossover in the 100-125 Hz with a steep roll off. Then, the on axis integration and response up to 500-600 isn't an issue.

But, if you use a low order crossover, for the crossover to integrate properly throughout the transistion band, the drivers must have smooth extended response on the listener axis. Crossing over at 250 Hz with 12 dB/octave means you need good respnose on axis for the 10 up to 450-500 Hz, and it means the RD must hold up down to 150 Hz. With a side firing 10, you're going to have integration problems with this crossover.

Most every speaker I've heard with floor mounted side firing woofers operating above 125 Hz has problems with bass to mid integration; even the Joeseph Audio RM33si has some issues, and it's crossover is 125 Hz. In fact, two sets of samples which Stereophile tested showed they had substantially different crossovers. Maybe they've got that sorted out, now.

You're also going to have integration issues (I suspect) because of different wave launch patterns in the crossover region between the 10" point source on the floor, and the RD Ribbon.

That is purely speculation on my part. Heck, we could probably lash up something similar, and see what it sounds like. I don't know what 10" they use in this, how it performs in the low end and the midrange. The only "10's" we have on order or available are better suited as a dipole woofer, not a sealed box- designed for long excursion, and with a 6 dB/octave roll off above 75 Hz.









Regards,

Jon




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

[Lex]

Probably could, and would! LOL Wow, you guys made 100 posts now. I am impressed.

Lex

[PMazz]

Do you think it would be possible to mount x number of 8" drivers inside the rear of a tall, but deep enclosure housing the RD75, mounting them sideways, stacked vertically and firing into a manifold that opened thru the front baffle?

Maybe a 12" wide baffle that the RD75 would be mounted in with the manifold opening on one side, next to it.

Or am I thinking too much again!

Pete

[ThomasW]

Manifolds really only work well for subwoofers.

Any driver used with the RD planars needs to operate up well into the midbass. The midbass defiinition would turn to mush if the drivers were mounted in an manifold with a shared outlet




theAudioWorx
Klone-Audio

[JonMarsh]

Flip!

Though I'm not sure I'm visuallizing exactly what you have in mind with the manifold configuration, I agree with Thomas that it would likely make for some problems trying to take it up to a usable area for the RD75s. I'd further qualify his statement by saying that any lower bass system used with the RD75 needs to work up into the lower midrange- say, clean to about 600 Hz so that a 350 to 450 Hz crossover can be managed properly.

Note that Linkwitz has to equalize out resonances which arise in his folded H style push pull woofer assemblies, and he's only trying to use them up to about 150 Hz. There are both peaks and dips that arise. Even Thomas's IB manifold starts to show some issue in the 90-110 Hz region; small enough that we can equalize them out for the most part, but also great enough that even with that EQ, the best crossover point is still about 75 Hz.

Hey, Pete, there's no such thing as thinking too much, and I can easily tell from your posts that you're reading and thinking quite a bit about this! And thats a very good thing!

Now, as an investigational thing, it would be interesting to ponder whether doing a more conventional line column (sealed) with side firing 8's (I presume you have a real desire to minimize the front baffle width, probably because of placement limitations or esthetic concerns?) might not work tolerably well, depending on the crossover point- it would, in my opinion, work better than a single 10" crossed over at 250 Hz.

The question would be, how high up would the response at 90 degrees off axis hold up, and could one then implement, say, a 4th order L-R crossover, plus baffflestep EQ for the ribbon and 8's as necessary? Maybe even as low as 250 to 275 Hz the power handling (using the larger Ribbon like the RD75, not an RD50) would be OK with the 4th order crossover instead of the 2nd order. Then the ribbon is down 6 dB at the crossover frequency, and about 30 dB an octave lower. I'd still be happier (I think) with a 300 Hz crossover minimum, but with a Marchand or similar unit, it's easy to swap frequency modules and experiement. The new XM44 crossover can acccept additional functional modules for things like baffle step and LF EQ, so that might be the real ticket for the flexibility you need to optimize a system like this.

Regards,

Jon




Earth First!
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[Dennis H]

Hi guys,

Great thread. I just had to register to toss in my $.02. I haven't seen a WTW configuration mentioned for a narrow, high SAF, monopole system. I'd think an RD40 or 50 with a couple of 8" to 12" woofers could work well. You'd maintain a pseudo line array with the woofers if you kept the crossover low enough that the woofers weren't lobing too badly. You'd have to decide on your priorities re bass extension, vertical sweet spot and overall power handling to decide on the drivers, crossover and enclosure height, but it seems doable.

Dennis

[Lex]

Jon, you call that a flip? :LOL:

Dennis, welcome to the forum. Hope you enjoy your stay here.

This thread is sort of like TTP now, it's similar to a wreck, you just can't seem to turn away from it. Lots of good info and discussion though. Great job guys!

Lex

[JonMarsh]

While in the discussion of various ribbon/cone hybrids, I thought I'd bring up some of the Genesis models.

One of their "moderate priced" models (if you call $25K moderate? was the Genesis 350, shown below, using a combination of 8" metal cone woofers, emit type midrange ribbon drivers, and a few spiral cut ribbon tweeters.




Genesis 350

It was to be augmented (before their financial collapse) by the 350SE, a more interesting design and closer to what we've been discussing here. In place of the emit midranges, imagine an RD 48" Ribbon.

I don't have a jpg of the 350SE, but i have a picture from a trade show, and I'll stry to scan it in this week and post later. It's similar in configuration to the 350, obviously, but differs in using a 48/50" RD ribbon, and a full vertical line soruce of the spiral cut ribbons.

When you think about how little those tweeters cost at wholesale, and how much the original 350 was asking, they should have been in the design from day one. $32K was the proposed price for the SE version.

Arnie Nuddel has always been a fan of servo woofers, and they do allow one some lattitude in tailoring the response of a small woofer box with a lot of drivers- however, they still don't get around Hoffman's iron law, and sometimes I wonder if he wouldn't have been more successful ditching the servo electronics, investing in driver quality instead, and using a plain simple Linkwitz transform. Speculation on my part, as someone who didn't have to walk the walk.

For the DIY enthusiast, the available drivers and design tools make it possible to own a true state of the art speaker for an outlay of a few thousand dollars, a fair amount of "sweat equity", and some careful thought and planning...

Regards,

Jon




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

[PMazz]

Jon, my problem is my room. I have a 14' wall in front that has a left side wall, but opens to a short hallway on the right. To position my RPTV on the wall far enough into the room for furniture, and the equipment rack next to it, leaves only about a foot, although I could encroach into the hallway area a little. Here's an old pic.



I've been putting off building an entertainment center to house everything (not speakers), but haven't gotten it finalized yet. Integrating the speakers, looks wise, is in the equation, tho.

I've been tempted by the Marchand stuff for a while now, but keep reading and hoping that the digital Xovers would get cheaper faster. Having a digital xover with parametric EQ, time and phase control and the like sounds too good to be true. So far it's been to expensive to be true!

As for the ideas I come up with, I just wish some of them were actually any good!

Pete

[ThomasW]

Too much talk and not enough building.

After we measured the drivers in the test baffle other priorities can to the front, and I never bothered to assemble the black baffle. So while waiting for a pr of RD075's to arrive I started putting it together.

For those interested it's 31" wide at the bottom and 80" tall



There are all sorts of speakers using the bigger planars one of the more interesting approached is the Panga from Davidson with it's TL loaded woofer



And the new plex baffle design from Meadow Song Labs






theAudioWorx
Klone-Audio

[JonMarsh]

Yup, the rooms and living layouts we have to work with often do present some serious contrainsts!

That's a "suspended" subwoofer behind the RPTV, I presume? The plate amp is the clue... I think I remember your original posts about constructing it, too.

One thing that helped me a bit was a decision years ago to go with FPTV; though I've bought one RPTV since then, it's now in my daughter's bedroom and I consider it "hers"; when ever she moves out to her own place (other than her mom's) it will hopefully go with her. You can't beat the depth and stealth factor of a screen, particularly a pull up, though I favor fixed installations now.

But I have a weird gig anyway, now having a roll around screen on a custom stand.. and no projector! I do have power amps at the front on stands off the floor, but the rest of the gear is on two Salalmander racks out of the ways away, and shortly I'm going to (hopefully) convert my pasive preamp to an active balanced design, possibly with Jensen transformers like the one I used in my X1 crossover, to allow longer runs on the interconnects; if there's an active crossover, it'll be up front with the amps.

Thomas W has a more ideal (from convenience and hiding stuff) setup with just preamps and one crossover in a low shelf in the living room, and power amps in a dedicated "coat closet"- a luxury many of us lack!


If I was tasked to do something SOA but still fitting into your room, my head scratching would probably lean towards a nearfield line array for the bass/lower mid. The general disadvantage to most 6's is low Xmax (it's a tradeoff with sensitivity, due to the smaller cone). If you have enough of them, then the Xmax is less important, of course. Perhaps very unimportant if you have a dedicated sub, as you do.

I'm not a "dealer" or re-seller like Danny at GR, so Hank may have access to some good prices that way- looking at off the shelf, if I had to go with 6-1/2's on a budget, I'd try the MCM carbon fiber 55-2321. I bought four to evaluate early this year. I'll take some pics and post- it's a very decent design for the money- extended pole peice, good overhang on voice coil, a flat spider with rear venting (as with ScanSpeak, Seas, and the other better brands). With a 400 - 600 Hz crossover to an RD ribbon, should work cool. Let's say, um, 8 6-1/2's is 52", so 8 of these with an RD 50, if you don't like the imposing height of an RD75.

Maybe I'll have to build this just to know if this can really work- I've got four of them, so I'll just need four more (for mono), plus the RD. Gee, I don't think Yvonne will go for that for my birthday, though.... :LOL:

Would need baffle step comp in the crossover for the 6's; also in the RD if the crossover was as low as 400 or so.


Somewhere around here I've got the T/S parameters for these drivers; if I remember correctly, Qts is around 0.38 or 0.4, so there's some flexibility; they can be used sealed with good results (Q of 0.5 in largish box) or in a low tuned reflex. Have to check the paper catalog.









This side view picture doesn't show as well what you can see looking at one of these close up; judging by the overhang, Xmax is about 4 mm, which is pretty solid for a six.

Note the flat spider and rear venting of spider/voice coil area. Pretty good for a $18.50 driver...


So, a budget array could be 8 of these per side. Round it up with shipping and it's $320 for both sides. That's only a teensey bit more than what two ScanSpeak 7's would cost.

To wire for power tapering, I'd wire the top three in series, and the bottom three in series, and the center two in series. Then I'd connect all three series connection in parallel. Net impedance would be about 6-1/2 ohms, a pretty reasonable load for most solid state amps.

I would build the cabinet with sepearte chambers for the top and bottom three and the center two. I'd probably elevate the bottom of the line between six and eighteen inches from the ground; this would make the net height in the range of 60 to 72" - not short, but smaller than many of the other line arrays cabinets proposed. Place the RD 50" either centered or toward the top- esthetics would indicate centered, acoustics (for standing reproduction) suggest toward the top.

Off the top of my head, I think the narrowest you could make this cabinet would be 16" to 18". The depth would be in range of 24" to 28", in order to absorb rear wave of planar as well as cones adequately. This wouldn't be light, even if you went with Baltic Birch ply, perhaps layerd with 1/4" hard board, and solid hardwood corner edges. Baffle step would occur about 800 to 900 Hz. RD would need some EQ in crossover, or you could just crossover at 800 Hz, and LF response of 6-1/2" drivers would be tapered for Baffle step.

These 6's are rated for 70 W each; even with the power tapering, a realistic rating, figuring normalizing to 140 watts for two in series at 16 ohms, and about 1/3 the impedance with three sets, that's about 420 watts at 6 ohms. Do you think that might play reasonably loud, since the aggregate sensitivity should be at LEAST 90 dB?

If one watt = 90 db,
10 watts = 100 dB
100 watts = 110 dB
400 watts = 116 dB

Aw, gee, we better build four, two for surrounds, just to make sure we can hit reference levels.... :LOL:

Hope your sub has some cajones...





-Jon




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

[PMazz]

Tom, I agree, let's make some dust! Much more rewarding.

Did you ever get to finish those? They certainly look impressive.

I will fit something like those into my room if I possibly can. Height isn't the problem, except for the left main. I've only got 79" under that soffit to work with. The rest of the ceiling is 94" high.

My original thought, based on a line array, was to possibly incorporate them into "decorative" columns flanking the entertainment center. I was thinking of extending the soffit across the top of the ent ctr to house a subwoofer. It could only be 14" high to match the drywall soffit, so maybe 4 or 6 12" drivers? Or maybe some sort of manifold in the front with a couple of Adire's new Tumults.........Still have that in the works.

Along those lines, I thought maybe line arrays would fit in as "columns" suspending the soffit overhead. Depth could be ~30" if need be, although some redesign of the left wall would be needed, as I intended to extend the DVD storage around the corner under the existing soffit (along the back wall on the left).

Of course this would pretty much lock me in to living with these for a while. Not exactly a good thing for someone like me who's designing the next latest greatest speaker system that I just HAVE to build. And usually before the current latest greatest is even finished!

Pete

[Victor]

What a great thread! It is super interesting to me as I am right in the middle of my own super speaker project. Jon, Thomas, perhaps you guys would remember our all but brief discussion of my 2-peace system, that Thomas called a “Chinese menu”?

Anyway, I just finished the ‘wings’ that house my RD-75 driver, They do look like an airplane wings, really. I will try to get the picture for you to see. There is a 6-inch diameter half-round used on the slopping side. So the front of the baffle is flat 12 inches on top and 18-inches on the bottom and then this flat portion is glued to this 6-inch half-round. So overall dimensions are about 15 inches on the top and 21 inches on the bottom, the height is 77 inches. The baffle has no sharp discontinuities in the front or in the back. So, it does look like a swept airplane wing.

Right now I am deep into the crossover for the RD-75. It looks that I am going to go with 4rth order L-R at 300 Hz, active 8.5 dB notch (Q=3) at 5 kHz and high frequency boost above 14 kHz. I have the circuit done up and am currently using SPICE to ring out the details. It looks good on paper so far. I know from J. Whittaker measurements that RD-75 is nearly flat till 15 kHz. Also I am not using any baffle step compensation, as I think none will really be necessary with 300 kHz cross-over.

I am very interested in what you guys will end up doing. My “Chinese menu” calls for the aforementioned ‘wings’ to be placed right next to two W-frame Linkwitz woofers with a total of four12-inch drivers and a column of four 10-inch Scan Speak 25W/8565 positioned on top of the stacked woofers. All dipole!

Regards,
Victor

[ThomasW]

Victor

Hi welcome back. Yes I certainly do remember your project

How about some pictures of your project. Curious mind want to see!

John Whittaker did some measurements of RD-75. He posted his data to the DIY B&G forum. Here are the average HF responses

AVERAGE: (6 drivers)
15,060 Hz 0.00 dB
16,705 Hz -3.00 dB
17,385 Hz -6.00 dB

I originally set mine up with no supertweeters but found the top end response lacking. This may be a function of being 'spoiled' by having the column of Technics leafs for so iong. So after a few days of listneing I put them back in the system. The imaging isn't quite as precise with the additional array, but the top end response is smoother and certainly more extended.

Pete

I built the black baffle (there's only one, it's a prototype) more than a year ago. But got side tracked with other projects and sort of lost interest. After hearing the RD-75's as mids in the ESL array I thought it might be a good idea to drop some drivers in and give a listen. A pair of RD-75's will arrive from PE sometime this week.

You certainly have a problematic room. Suggest RD-50's and a line array of midwoofers. Not usre about the 'built-in' idea. You'd need some test equipment to fine tune the XO




theAudioWorx
Klone-Audio

[Hank]

Thomas: "...and looks cool." Aha! I knew it - angled for looks.

Jon, I finally received the specs from MCM for that 6 1/2" driver:
Re 6.1 ohm
Fs 42.3 Hz
Zm 37.2 ohms
Qms 2.59
Qes .51
Qts .42
Vas 26.64
SPL 89.13
Cms 1.15
Bl 6.62
No Xmax given
Have you seen the response graph? It is one of the worst I've ever seen, with sharp peaks and valleys of up to 9 dB from 200 to 1,500 Hz. I can fax it to you. Recently Thomas wrote in an e-mail:
"It seems that even the smallest irregularities in the FR plots can have a noticable impact on the performance. Previously we thought that avoiding the main cone breakup mode was the most important consideration. But that's now changed. This unfortunately means that only certain drivers that operate within a pistonic window are the best ones for accurate playback. Because the if smaller 'bobbles' in the FR plots are a function of cone breakup, then those frequencies must be kept out of the drivers passband." This driver wouldn't pass your new standard. I can fax the spec sheet to you. Would you give me your opinion of Danny's GR165 (4.5mm Xmax and smooth curve) versus this MCM unit?

Earlier in the thread I'd suggested an RD50 with a stack of 6.5"ers, assuming they would move enough air, so maybe there's hope?

Make some sawdust

[JonMarsh]

I've measurements of this driver myself; it's biggest "problem" is a cone mode at 1 kHz which is a fairly steep notch. Below that my own measurements show smooth response in the midrange.

It's not a driver for a first order crossover (what driver with a stiff cone is? :LOL: ), but for a 400 Hz to 600 Hz crossover to a ribbon, it should work well. With a 4th order L-R at 500 Hz it would be down 30 dB at 1 kHz where the first cone mode occurs.

I don't have a copy of a published response curve from MCM, and I don't know how they measure- baffle type is important; notice how "crummy" the Seas Excel plots look, because they measure anechoic using small test boxes, whereas most folks measure their 6", 7", and 8" drivers on large IEC baffles.

Another matter about how "pretty" drivers look in the published FR curves is smoothing- many companies (Adire and others included) use 1/12th or 1/6th octave smoothing, which smooths over the ripples that arise from diffraction effects in a test baffle, etc.


From inspection of the voice coil overhang (which is quite visible due to the flat vented rear spider construction), the linear Xmax appears to be in the range of 4-5 mm. That's in the same range as the top Seas parts, and better than their standard offerings.

BTW, Danny doesn't use his own drivers in the line array; it's a different part from another source.

-Jon




Earth First!
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[ThomasW]

Hank

Neither Jon nor I have seen Danny's driver so can't comment regarding a comparison. But Jon has 4 of the MCM carbon fiber drivers and has measured them in his test baffle. He feels that the plots aren't a problem. The only real bobble is at 1Khz and that's well above the XO point.

Also we tend not to trust anyone's published specs. That's why we both have stacks of drivers sitting around gathering dust. These were brought in for testing and didn't measure well enough to warrant using. The only way to do a fair comparison is to measure one of Danny's drivers in the same baffle and see what's there.

For a under $20 driver one choses the driver with the fewest problems in the passband.

I find it interesting that Danny's is using the CSS midwoofer instead of his own designs in the line array he's selling.

Regarding my statement: it was predicated on a speaker that had little if any compromises in the design. If given the opportunity the drivers chosen should have a very flat impedance curve, and few 'bobbles' in the FR plot. But unfortunately that usually means an expensive driver.




theAudioWorx
Klone-Audio

[Hank]

Thanks guys.
Jon, thanks for clarifying the buffalo butt skin driver cone issue. No wonder my cones dissolved before the surrounds :LOL:

Yeah, I know Danny had CSS design that stiff 8" he uses in his line source. He wanted an 8" for that huge speaker and he doesn't have one of his own. As soon as I hit the submit button, I said to myself, "self, I wonder if the GR driver plot has been smoothed". Afterthoughts are great aren't they?
Well, why not ask Danny to send you a driver to test. If it belongs in the "gathering dust" pile, I'll have an answer. If by chance, it's a winner, and better that the MCM, then that's good info also.

So with an RD and 6.5" drivers, are we takling a baffle that's 16 - 18 inches wide at the bottom, taper to say, 12 - 14" wide at the top? Wow, that's wide! I can't imagine the width using 8" woofs. Also, you're recommending three separate chambers for the woofs. I was planning on a common chamber for all the woofs, venting out the cabinet back, and a shallow chamber for the RD. That could maybe result in a much shallower cabinet?

[JonMarsh]

Hi Hank,

Yeah, those buffalo butt skin cones are a tricky bunch to work with...

My understanding is that the new GR Research M-130 is a nice driver; it's getting some very positive comments over at the Madisound forum. And with your connection to Danny, I'd expect you can get a good price. It has a higher free air resonance, (50 Hz versus 42 Hz), and a slightly lower Xmax (3mm versus ~ 4.5 mm) than the MCM 6.5 carbon fiber model I'm interested in. The measurement for the M-130 on the web site looks like it's made on an IEC baffle, but not with smoothing. It's probably a great driver for a compact two way with a 1st order series crossover; the cone profile appears to be optimized to keep the direct on axis response as smooth as possible, and quite successfully so. It would probably be a super mid-woofer in a three way system, with something optimized more for LF kicking in below 100 or 125.

BTW, Danny is using a CSS six inch driver , not eight inch driver, according to his web site. The CSS driver is a nice looking paper cone driver, but there's absolutely zilch tech info on it at the CSS site. Odd. Don't know if it has a 2:1 advantage in performance over the MCM six. It probably goes higher cleaner, but crossing to the RD ribbon, that's not important. I imagine Danny can get you a good price on that one, too.

If you're buying at retail and selecting based on cost (for me, retail $23.95 vs. 18.50), the MCM wins- but also the MCM may have an edge in LF utility, given it's lower Fs and seemingly higher Xmax. If you're doing one of the typical Madisound 6.5" two ways with a vifa or whatever tweeter, the GR-Research should be king, and worth the extra money. Crossed over to a big ribbon at 400 - 600 Hz, I'm not sure it would have any advantage. I'll run some numbers at lunchtime.

In the case of the dipole speakers we very much want to use tapered baffles. In making a suggestion for Pete and his room layout, contructing a tapered sealed enclosure would add greatly to the complexity. Dealing with the fixed diffraction/baffle step issue is probably simpler than building a more complex sealed enclosure. So, considering you have to allow for rear wave absorbtion and mounting area for the RD and 6's, plus internal bracing and chamber seperation. The RD driver is about 5" wide. Allow 7" for the ribbon, and 8-9" for the mid-woofers, you've got a 16" wide cabinet. The depth will derive from the need to absorb the rear wave and tune the 6's to a Q of 0.5, roughly around 50 Hz. This will give very good articulation and damping in the bass, and the ability to flatten in room with a combination of boundary loading and perhaps a slight amount of passive EQ. Details to follow-


For doing power tapering, you should have seperate encosures for the drivers operated at different power levels- otherwise, the ones being driven with more power will counter the others to varying degrees in the low frequencies. If you really don't want to have seperate sealed sections, then perhaps consider forgetting power tapering, and use nine drivers, three sets of three in series, all paralleled. This would result in an 8 ohm nominal impedance. Nothing wrong with that....

The attractiveness of this whole idea (to me) is how small and how inexpensively can we put together a decent RD/line array combo, so that folks could get into the benefits of the RD midrange-presense range performance and dynamics at a "reasonable" price. I wasn't really considering building something like this until this discussion got going, but I now I think it's a fun idea, and the dollar exposure isn't much- (since the RD50 could always be re-cycled into a more elaborate project). Basically, the potential "throw-away" part is just $300 bucks worth of drivers (for stereo) and the materials to construct the test boxes. That's a cheap experiment by my standards- the parts just to build a new DAC experiment run well over that- just the cheapest approach for low volume PCB's may cost $300 for the analog portion and $300 for the digital.

So, let's say we're looking at $1,030 for the RD-50's at retail. Can probably improve on that a little. MCM six's or Danny's driver's for you at special price, I'm rounding up/down to $20 each, which for an 8 driver line array is $320, nine driver array $360. Be generous, plan on maybe $300 or so for crossover components... plus wood, glue, hardware... realistically, about $1700. Plus sweat equity.... lots of sweat....

Not too much different in price from the LS array, but it would use an RD ribbon to an octave or more lower than the Neo8's in the LS array. That oughta be worth something....

Utlimately this would probably be used with a good sub, but with a small amount of passive EQ, a version using the MCM 6's should be flat in room to 40 or slightly below, with a gradual roll off (Q of 0.5). 8 six inch drivers per side is about the same radiating area as 4 - 8" drivers. It could be interesting.

-Jon




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[JonMarsh]

Hi Victor!

I remember some earlier discussions about your project- where are you at in the construction phase? Any picture's you'd like to share with us yet?

What you may or may not need for baffle step depends on the performance in the baffle you're building, of course. The RD's have some rise in the low end as well as their dipole behavior which modifies what you may expect to see- the only way to know for sure is to measure.

Are you doing your own active crossover from scratch, or modifying an existing unit? The Marchand 44 looks custom made for experimenters who prefer active crossovers and need the added EQ circuitry. I might not have built my custom active crossover for the X1 klones if the Marchand XM44 had been out, but then I can adapt my own boards to dipole apps easily also.


Do you have an estimated date of completion- or first listening? Keep us informed on how it's coming along- with the "nerve" this thread has struck, maybe we should have a DIY dipole forum section at HT Guide....

Best regards,

Jon




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[Hank]

Jon, no, not that new GR driver. The one I mentioned earlier in the thread:
"I was thinking about Danny's 6.5" driver, #GR165. It's Xmax is 4.5mm, not too shabby and the curve looks pretty good.
FS 39.5 Hz
RE 10.85 ohms
Qms 2.52
Qts .53
Qes .67
Xmax 4.5mm
L (1k) .34 mH
L (10k) .62 mH
Vas 36.26 Liters
Ms 11.91 grams
Cms 1.374 mm/newt
Bl 6.89 Tesla-M
SPL 87.5 db
Area 137.07 sq cm

Better Xmax and lower Fs than Danny's new driver. Please check this GR 165 at lunch.
Okay, I stand corrected on Danny's CSS driver, but it's actually 6.5".
Now I know that 6.5" will deliver the dynamics and SPL. The Alpha LS's were playing in my large living room (open to loft above and other rooms) with various music playing, from a capela quartet to "Gladiator" soundtrack. BIG sound.

I'm thinking RD50 monopole, inner MDF enclosure lined with dampening vinyl and filled with AcoustaStuff. Then, common chamber for the woofs with say, three 3" dual flared vents on the back (ala the LS). Why would that need to be more than 12" deep?

Heh-heh, glad I got you hooked :twisted:

[ThomasW]

Hank

Well, why not ask Danny to send you a driver to test

Jon and I had a rather interesting interaction with Danny on another forum. It ended with the moderator editing Danny's post because he was aahh.... shall we say less than politically correct. So I doubt that he be all that willing to provide a driver for us to test




theAudioWorx
Klone-Audio

[Hank]

Heh-heh, I know. Brian Bunge, my bud in Georgia, sent me a link and told me in person the, ah, unfortunate comment. Too bad that artistic-types get too defensive about their own styles, let their feelings overpower an intelligent exchange of ideas. I've noticed some designers posting generalizations that they have adopted as dogma, like cone material X is no good, or absolute minimum crossover count is the only way, or exotic capacitor materials/construction is a waste and doesn't contribute to better sound, etc, etc, etc. From the outside, I observe that speaker designers aren't pure engineers, but are part creative artist. I suppose that's where the artist temperament comes in.
Anyway, I try to learn from everyone, especially you and Jon, since I value your many years of experience. And again, thanks for both of you taking the time to educate me about line sources in this thread. The result may just be that I'll build something!
(pssst...maybe I'll buy a GR165 and send it to Jon)
p.s. An array of 6.5"ers can pump out sufficient SPL! :P :LOL:

[JonMarsh]

Well, I think I have a clear idea why Danny used the CSS in his line array.


Two things jumped out at me about the GR165 before running any numbers on it.

One, the Re is 10.85 ohms. Let's call this what it is- this is for all intents and purposes a 16 ohm driver- not necessarily a bad thing, just that it will require different wiring arrangements. Actually, you could wire them as I described above, but it wouldn't suck much juice from the amplifier. This is a good driver for an MTM that you want to be SET friendly, for example... , whereas I tend to build speakers that like Aragon's and Ayre's for dinner. 8)

The other thing is the T/S parameters- Qts of 0.53, Qes of 0.67- this is a driver for sealed box applications, and not small ones at that, because of the relatively low cone mass. This means you need a big sealed box to get the best bass- a ported enclosure will be a boom box, I'm afraid. No way to avoid peaking over the nominal response- unless you tune it so low (say, 10 Hz) that there's no useful port output in the meat of the audio band.

For a sealed box, if you want a reasonable Qtc, (say, 0.577, Bessel alignment, not critically damped, but close) the numbers say you'd need a physical box size (per driver) of 122 liters. Yes, that's right, I said 122 liters. Yes, that is three times the size of the interior volume of the MkIV M8 monitor I showed a pic of much earlier in this thread, which uses a HiVi Research 8" woofer.

For a "Butterworth" alignment, with a Q of 0.707, the required size is 32 liters, exactly the interior volume of the M8A cabinet with the 8" woofer. Fb is 57 Hz. Not deep bass, but nothing wrong with that for a six.

So, if you use 9 of these in a line array, the cabinet volume reuqired (for Qtc of 0.707) is

9 x 32 liter = 288 liters. For the six's - excludes the ribbon.

That's 10.17 cu. foot. Ouch.

Let's say interior front panel space of portion of cabinet for 6's is 58" X 8". That's 20 cm X 147 cm. We need a volume of 288,000 cm2. That's an internal depth of 97 cm, (excluding volume required for drivers), which is, uh, 38".

You know, I think I know why Danny didn't use his GR-165's. :LOL:

It's a question of the T/S parameters. Light cone, low B/L product, low electrical damping, relatively high Qts. Good for a moderately sensitve largish sealed box. Or a smallish sealed box with a mini-monitor lift to the upper bass, a la BBC LS35a.


Are the MCM's I picked any better for this application? If you go for a sealed box with a Qtc of 0.577 (Bessel alignment) you need 19.8 L per driver. That's a little easier than 32 liters; it means the enclosure, for the same front panel, would only be about 2/3 as deep, or about 22". Qtc of 0.707 would be even smaller, but you're intersted in ported for the extra LF power handling.

How about ported?

"Optimal" response (if you mean flat anechoic) would require 30 liter per driver, with a port tuning of 40 Hz. Considering room lift, which can be in the 4-6 dB range with reasonable placement, an overdamped alignement should be used, with a 15 liter volume per driver, tuned to 38 Hz; this would extend the deep bass, and with room gain and positioning could be flat to 40 Hz with a -3dB point in room of 35 Hz. That seems fairly acceptable for something which may be used with a sub, but should have good overlap range with a sub, and resonable extension on it's own.

Then, we wind up with 15 liter per driver,

9 X 15 = 135 liters net for the MCM CF sixes,

and an internal cabinet depth of 45 cm, or 17.75". Overall depth probably about 20".

That could be a usable design, gott in himmel!



-Johann




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[Lex]

I hope all you guys buying from PE remember to use the "click through" at the top of this page when ordering. It's important for the forum, as PE is a top advertiser. No pun intended. Get it, at the top?

Thanks, and carry on! Whew, what a thread!

Lex

[Hank]

WOW!! Thatsa lotta cubica inches!
Yeah, the 165 has an EBP of 58.96 - sealed it is.
The MCM's result in a big (in my mind) cabinet. I see why Danny had CSS design the Alpha LS drivers. I forget the cabinet depth - my drawings are at home - but it's nowhere near 20" He did the woofs in a common space and there are, as I recall, four 3" dual-flared ports on the back.
Shoot, I'm stuck with a big, wide, deep cabinet. Hoffman, I'm gonna get you someday! :evil:

Lex, I bet your a top admin, but leave the humor to us.

[PMazz]

Hank, I've been looking at a lot of 6.5" drivers too. I was thinking sealed enclosure, but if you want what looks like a good 6.5" for cheap, check out the Dayton at PE #295-305. I'm just going by the listed specs, but it looks pretty good on paper.


8 drivers in 6 cu ft, tuned to 37 Hz. Only ~3mm Xmax, but looks like it'll get you there.

Pete

[PMazz]

I was looking at the Peerless 850122 CSX 6.5" in a sealed enclosure. From the Peerless site:



8 of these in 6 cu ft might work.

Pete


BTW, Jon, no worries about enclosure complexity....that's the easy part. I would still be leaning toward the RD75 vs the 50, tho, unless you foresee a problem in my room. I was drawing some baffles and think maybe, instead of a straight taper, something curved, top to bottom or even wider at top and bottom and narrower towards the middle?

[JonMarsh]

Interesting ideas, Pete.

Actually, there's only ONE drawback to the RD75 I can think of-- cost. If cost and the esthetics of the size are not an issue, then by all means go ahead- the vertical pattern control of the big ribbon is fine, I think, even with a standard or lowish ceiling.

Are you thinking in terms of asymmetrical baffle layouts or symmetrical? (laterally and/or vertically) Might be some interesting possibilities. I do like how the Apogees look; but maybe that's a little dated in esthetics. Are you making any sketches (CAD?) you could PDF and we could post to talk about?

I'm attracted to the idea of seeing how well I can make a "baby" line work, now, after thrashing these ideas around with Hank. The Alpha LS is fairly tall, with it's 8 Neo8's; the idea of something a little more "petite" appeals to me- something in the 60 - 64" area. If I try it, I may find there is some particular flaw with the concept that annoys me- but maybe not. Oughta be killer on vocal and ligher classical, even without a sub. My girlfriend has one of those California maseter bedrooms that's big enough to put something like a line array tower in. Well, at least I think so; she probably woudn't! :LOL:

Regards,

Jon




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[ThomasW]

Jon

I don't know what it's going to take to get these guy to seriously consider the MCM 55-2321 @$18.50ea...... 8)




theAudioWorx
Klone-Audio

[Hank]

Jon, hot dog, you're hooked! Keep going.
Pete, why do you want your woofs sealed? Is it so you can do power tapering?

Whatever the best shape is for acoustics, I'm like Pete - I'll do it. Actually, personal taste-wise, I like the Apogee look.

Thomas, I am considering the MCM driver. I don't have to have the absolutely lowest-priced woofs. I might try to scan the spec sheet in - I'd like for you guys to see the Alps(mountains, that is) response profile. If I'm going to ante up the cost of RD50's, I want the woof sound quality to match - I just don't want to spend in the area of those Hi-VI's you guys like so much.

[PMazz]

Tom, it must be the wealth of information MCM has on their site. Hell, half the time I can't even find what I'm looking for there.

Hank, You know you're probably right. I should hold off passing judgement until I do a mock up in a box. I have always liked the sound of sealed speakers, tho, and tend to think in that direction first.

Pete

[ThomasW]

Hank

We're really not concerned with the plot from MCM. Jon has a Clio-Win setup and a $5000+ Labratory Standard B&K 4133 mic. He's run a complete set of measurements on the 55-2321. As long as he's happy with the performance I'm sure others will be too.

As a matter of fact he's so pleased with the driver and the price I fully expect him to create a 8 driver line array with the 55-2321 combined with a RD-50. I think he need to wait for the next pay period to order the drivers.

Pete

Yup finding anything without the part number the MCM site is problematic, and speaker specs are nonexistant

Does anyone know if MCM has a 'dealer' program like PE does?

To all the lurkers

I received a pr of RD-75's yesterday and have one mounted in the black dipole prototype baffle. As soon as I get a notch filter made, and can find some assistance to get them out of the basement I'll post some impressions and data




theAudioWorx
Klone-Audio

[JonMarsh]

As I said, Hank, there's a lot of variation in measurement technique- and measuring in a test box anechoic (as Seas does- look at their curves for the Excel Magnesium series, some of the finest drivers made), and if you don't know the conditions or equipment, you can be left hanging to make a meaningful evaluation.

I have made my own measurements, including 6" nearfield which swamps out baffle and mounting issues; from below 100 to about 900 Hz they look fine, just a very slight rise in the response- the sort of thing easily dealt with in the crossover. I'll try to bring those over to my desktop at home from the measurement PC, and post in the next day or so.

Actually, it's kind of cool that no one knows about or takes the 55-2321 driver seriously- a line array with them will definitly have that "Pipe Dream" look, and at the price they go for, it's an affordable experiment. I still favor a power tapered array; I'll setup the center two and the top and bottom three in their own enclosure spaces, and probably individually port them- the proposed alignment is similar to the M-8 bookshelf tuning, and also the Avalon Eidelon- which doesn't sound like a ported box either. The key is being a bit over damped, and tuning the Fb a little below the point that would yeild the flattest response before roll off, so that at the nominal driver Fs the system is down about 5 dB, which is compensated by positioning for room gain (so that the room lift, which is a function for frequency dependent on distance from walls/floors) with max port output tuned a half octave lower than that. This produces clean, tight bass with good extension without boominess in the midbass.

I'll just have to see if I can con my girlfriend into letting me setup a saw in her garage for a weekend.... :LOL: after getting her a free air ticket to England to see her mom this September, that shouldn't be out of the relm of possibility...

I think I'm just the maverick of LF driver's guy- hence the HiVi M8a in my bookshelf project, and now these MCM drivers proposed for a line array. Maybe it's a character flaw- probably has something to do with why all but one computer I've built or bought in the last 3 years has an AMD CPU.

The Dayton 6-1/2" woofer does have good T/S parameters for a reasonable cabinet size and alignment. It's only obvious drawbacks are a stamped frame with conventional spider arrangements and lower Xmax. This may affect power handling and LF distortion. Price is very reasonable. There are several projects with it for two way systems.

BTW, MCM makes some really g*wd awful tweeters, too- I've bought and tested a number of their speaker drivers, most I've tossed in the bin, but I think (for this application) the 55-2321 has the right characteristics. And I can't touch anything else similar for the price.

Hey, we could have a "build-off"! Everyone build their own favorite design for their line array, then we do a "rendevous in the desert" (Thomas and I did that a couple of years ago)(or somewhere more convenient) and have our own "DIY2003 Line Array" competition. Thomas's will be the real bear to pack up and move, and with the Acoustat's and all, he's got a bit of an unfair advantage.... well, no one ever said life was fair!

-Jon




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