10" MTM with NeoPro5i Ribbon - Build Thread

[opc]

Hi Everyone,

I've spent the last few months researching drivers, alignments, bass loading and several other things, and I'm finally far enough along to start this thread.

This is where I'll document the design process, the construction process, and hopefully soon, the finished result.

I think a little background is in order first...

My current set of speakers is a very nice pair of Lynn Olsen's Ariels. These took a few years to build, and several more years to tweak to their current status. I love them, but I've been longing for the much larger and more dynamic sound that only a larger pair of speakers can offer.

The Ariels are reasonably efficient, at about 92dB but I'd like that figure to go up. They're also light on bass, and for some reason, they're quite difficult to integrate with a subwoofer. My last few attempts have ultimately ended in me not using a subwoofer at all.

The desire for "big" speakers started several years ago when I was lucky enough to come across three Altec "Voice of the Theater" speakers. I used two of them in my main system for a few months, and then sold all three because they were so bloody big. During those months though, I became completely obsessed with the incredible dynamics and "huge" sound that they were able to produce. The bass and midbass, although not incredibly low, was so powerful that it just captivated the listener, and demanded your utmost attention. Unfortunately, the rather mediocre horns turned out to be a let-down, and ultimately resulted in a rather fatiguing speaker.

What I hope to achieve with these new speakers is the best of both worlds. I want the detail and easy listening qualities of the Ariels, along with the dynamics and presence of the VOtT's.

So far, here's what I've got:

- NeoPro5i Ribbons.
- Either AE Lambda TD10M or B&C 10NW64 midbass.
- MTM arrangement.
- Independent transmission lines for each 10" midbass.
- 1600Hz - 2200Hz crossover point.

I want very high efficiency, so the NeoPro5i is pretty much set in stone. I've listened to and measured three different compression drivers in a variety of horns and waveguides, and I didn't like any of them. The NeoPro ribbons both measure and sound better than anything I can find in the 100+ dB range.

The midbass drivers are still a toss up. I've ordered 4 of both, and I plan on auditioning both to see which of the two is best. The B&C drivers fit in a smaller TL than the TD10M drivers do, but they're also tuned 5Hz higher at 50Hz in place of 45Hz. I'm seriously concerned about the claims of the TD10M drivers, as no FR graphs can be found anywhere. I'll reserve judgment until I can measure them properly and compare them to the B&C drivers. I'm hoping they're as good as claimed.

The crossover point is a little up in the air as it's a trade-off between the increased beaming of the 10" driver at higher frequencies, and the increased distortion of the ribbon tweeter at lower frequencies. I'm pretty sure that only listening to both extremes will tell me which of those drawbacks is easier to live with. Like all things, the final compromise will probably fall somewhere in between.

The TL loading is also set in stone, as it's by far my favorite bass loading design. The taper for both drivers will be 0.2 and the lines were designed using MJK's TL worksheets. The TD10M's seem to work best in a 45Hz line, and the B&C drivers seem to need a 50Hz line. I'm not looking for huge deep bass, but I do want these to integrate well with a larger format (18" or larger) subwoofer in the future. I also need them to stand their own ground above 40Hz so they can be used as a true standalone speaker without ever needing a sub.

The finished efficiency of the speaker will hopefully be right around 100dB and should reach easily down to 35-40Hz and up to 40kHz.

I'll welcome any suggestions, comments or criticisms, and I hope to hear from anyone who has any previous experience with either of the 10" drivers mentioned above.

I'll attach a few details over the next few posts, but for now, let's start with the box design for the TD10M midbass drivers.

Cheers,
Owen

[GK]

I think a pair of 10" woofers spaced at that distance crossed over so high will have undesirable vertical dispersion characteristics / lobbing?
Maybe a WWT in a 2.5-way for BSC would be better, but that’s of course a completely different speaker.

Cheers,
Glen

[infinia]

Originally posted by opc

The crossover point is a little up in the air as it's a trade-off between the increased beaming of the 10" driver at higher frequencies, and the increased distortion of the ribbon tweeter at lower frequencies. I'm pretty sure that only listening to both extremes will tell me which of those drawbacks is easier to live with. Like all things, the final compromise will probably fall somewhere in between.

Hi
Do you have offaxis responses of the tweeter near your target Xover frequencies? The data sheets don't show any.
IMO it's good to match the directivities at the xover region.

[LineSource]

A 3-way with the Neopro and Lambda 10" + 15" looks attractive. Avoids MTM spacing issues with 10" midbass, allows sealed box midrange, and 25Hz deep bass from mass loaded transmission line with a port on the bottom of a raised-leg cabinet.


Neopro5i ribbon LR4 at 1,400

AE Lambda 10M in sealed well stuffed and braced box LR4 at 80Hz
----read AE Lambda Midbass 10 Project? thread

AE Lambda 15S or 15H in ML TL down to 25Hz www.quarter-wave.com

[opc]

Hi Guys,

Thanks for the early comments, very much appreciated!

Glen,

The spacing of the 10" drivers is a pretty big concern for me, but I'm going to build up a mock baffle and measure it with all the drivers in place to see how bad it really is. Apparently with the very limited vertical response of the ribbon, there's not much to worry about as far as ribbon to midbass interaction goes, but between the two 10" drivers is another concern.

As of right now, it looks like C-C spacing of the 10" drivers is going to be about 18.25" with the B&C drivers. the TD drivers will be a little farther apart.

Infinia,

I've attached a .pdf of the tweeter measured in the baffle I'm planning to use, with flat plates over the midbass holes. No smoothing, and measured at a 1m distance. These are gated measurements, so ignore anything below 500Hz and above 20k (microphone limit)

The ripples in the midband are either from the tweeter not being flush mounted, or the sharp edges on the mock baffle. In the finished speaker these would at least be rounded over, and the tweeter would be offset and flush mounted to mitigate the impact.

Off axis response is really quite good for the tweeter, so it looks like I'll have to see how the midbass units do before making the call.

LineSource,

I've been following a few of the threads with the AE drivers very carefully. Part of me keeps hoping for someone to post some measurements, but there never are any for the TD10M.

I see where you're coming from, but I'm not sure it's quite my cup of tea. You'd have to pad the tweeter down by over 6dB to get it to the level of a single 10", then even worse you'd have to pad down the 15" as well. Your final system would sit at a little less than 94dB and it would be larger than the MTM I'm looking at.

If I find this light on bass, then I'd probably look into a pair of B&C 21" drivers in folded TL's to fill in strictly from 40Hz down to 10Hz or so. I'm not really all that bent on getting response that low, as most of what I listen to doesn't have much going on down there. Just the same, this is kinda cost-no-object, so I'll see where it goes.

Keep it coming!

Owen

[opc]

I should add:

Black trace = On Axis
Red trace = 30 degrees horizontal
Blue trace = 60 degrees horizontal

There's no scaling, but it looks like about 100dB @2.83V and 2kHz with a decent SPL meter at 1m away.

I've attached a modeled tweeter response with a 1800Hz 3rd order crossover and a little correction on that rise between 8k and 15k

I'm currently building this crossover for testing... results will follow.

Cheers,
Owen

[brucemck2]

OPC -- I like where you're headed. I'm on a search for high(er) efficiency too.

Do you have measurements of the actual efficiency of the ribbons? I've seen other's claim it's closer to 96db than 100+ and the difference is make or break for me.

[infinia]

Originally posted by opc
I should add:


I've attached a modeled tweeter response with a 1800Hz 3rd order crossover and a little correction on that rise between 8k and 15k

Hi
Thanks for the off axis data. I wonder why the large peak in response.. it almost looks similar to breakup in a cone. How did you tame it? Seems it would take a major correction to get your final response.

Edit> I doubt the peak is breakup related. My speculation.. mostly because off axis follows on axis closely. Is there a resonance nearby on the raw impedance charts?

[opc]

Hi Guys,

Brucemck2:

The high efficiency thing is really a big part of what I'm looking for, so it was the first thing I checked when I got those ribbons. I'm not sure if there was some differences between production runs, but mine are absolutely between 100 and 101 dB at a one meter distance with a 2.83 volt RMS sine wave at 2kHz. The SPL meter was flickering between 100 and 101, and it's an accurate enough meter to be trusted. You can use that to scale the graphs, and you'll see they're definitely at or above 100dB for the whole range.

If the efficiency thing was less of a big deal, I would have gone with RAAL ribbons, but at 94dB, they're not quite there.

infinia:

That peak is present on the published datasheet, but the one I measured is a good 2 or 3 dB higher in level relative to the rest of the response. I don't think it's a resonance as the impedance is perfect in that region. I've attached the raw impedance data, and I measured this three or four times, along with re-measuring a few known drivers to be sure. My impedance measurement correlates quite well with the published spec, except they cut their graph off at 600Hz, which is where mine gets a little confusing.

It looks like the actual ribbon resonance is the little bump between 700 and 1K, but I have no idea what the 40 ohm spike is at 200Hz. I had the ribbon directly connected to the impedance jig, so there was no cap or anything else between to cause that.

I'm guessing it has something to do with the transformer, but I really don't know.

Fixing the bump in the FR just requires a parallel notch with a wide band. The simulated values are 60uH, 3.2uF, and 10 ohms. I'll be testing them in the next few days with the filter in place.

Cheers,
Owen

[opc]

Hi Guys,

Just a quick update... the B&C 10" drivers arrived today, and initial impressions are very good!

I haven't had time to measure these yet, but that's what I'll be doing over the weekend. I have listened to them with a rudimentary crossover and I was very impressed. Looks like they're plenty efficient to keep up with the tweeter, so I think the finished efficiency will actually be 100dB if all goes well.

I have attached a picture of the drivers sitting on the floor, and one of the back side of the B&C driver.

They're quite well built, simple construction but excellent quality.

Cheers,
Owen