Offer to fund driver purchase for FAST design with ASR rigor

[Ilkless]

The Von Schweikert Unifield 3 uses a similar concept. I attended the 2009 RMAF with Albert Von Schweikert who was featuring the Unifield 3 at the show. He called it an augmented full range speaker. The full range speaker he employed was a 5” Fostex driver. It was crossed over to a 7” woofer at 100Hz and a ribbon tweeter at 8kHz. It is a wonderful sounding speaker which has all the benefits of a full range speaker with bass and treble extension most lack. I often played with the idea of building something similar with a larger woofer (maybe 12”) to give more bass extension and impact.

Martin

A supertweeter crossed high is only detrimental. Crossing so high causes severe vertical lobing issues and even more unpredictable and disjointed dispersion.

The point of the proposed design is to have near-coaxial coherence in a large woofer 2-way, without having to add a tweeter, or a coax driver, as all DIY coax drivers (SEAS etc) are compromised vs the proprietary ones vs Genelec and KEF.

 

[jaakkopetteri]

Don't really have anything to add here, other than agreeing that a sensible design should be possible within the constraints presented. A good widebander candidate I recently came across is the Kartesian Wib120_vHE (https://www.kartesian-acoustic.com/wib120-vhe). It has very nice large-signal parameters for the application (very linear and symmetrical Le(x), and very linear BL(x) within +-2mm) which should imply low intermodulation distortion. It also extends quite cleanly to 20kHz with an off-axis response that looks passable until 10kHz at least.

The most obvious negative of the driver is the cost, which is about 150 euros per driver from TLHP. It's also on the larger side, so it will naturally be more directional than some other alternatives.

I'm also excited about this driver. Directivity doesn't seem that bad, or at least on par with the 8414. The Klippel results just seem way better than anything else offered.

For a small widebander in a waveguide, I would consider the Wib50 or NE65W in addition to the SB65. Not sure if even a 10" WG would load these under 1kHz or so, but would love to see (and hear) the improvement above that

 

[hdspeakerman]

https://www.diyaudio.com/community/threads/10f-8424-rs225-8-fast-waw-ref-monitor.273524/

 

[Rick Sykora]

Sounds interesting but is not in my wheelhouse and behind on Directiva too...

Pretty sure @ctrl has some applicable experience, but he has other projects too.

Lol about Singapore. I took a cohort from Singapore to Parts Express (we were visiting a nearby customer) and he was flabbergasted. I think he bought a half dozen HDMI cables. He said they would cost 10 times more in Singapore. Have some fond memories of the island but thankful most of it was on the company tab.

 

[Timcognito]

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[hex168]

This may help narrow the field. Lots of measurements, including off-axis and distortion:

Timothy Feleppa's Pages: Speaker Measurements - Midrange/Fullrange Speakers 4" and smaller

The Dynavox LY302, the TC9 and the TC7s look interesting. As does your project!

 

[Rick Sykora]

A supertweeter crossed high is only detrimental. Crossing so high causes severe vertical lobing issues and even more unpredictable and disjointed dispersion.

The point of the proposed design is to have near-coaxial coherence in a large woofer 2-way, without having to add a tweeter, or a coax driver, as all DIY coax drivers (SEAS etc) are compromised vs the proprietary ones vs Genelec and KEF.

If you would consider a coax to handle the top end, there was a Sica that @ctrl had found. If interested, will dig it up. Looked promising but Sica lacked distribution here and so it was shelved.

There is also an inexpensive SB coax, but has a on-axis notch around 13 kHz.

 

[Wolf]

There is a new TB coming, the coax w4-2315:

W4-2315 - 4.5” Paper Coaxial Full Range - TB SPEAKER CO., LTD.

www.tb-speaker.com

 

[Ilkless]

If you would consider a coax to handle the top end, there was a Sica that @ctrl had found. If interested, will dig it up. Looked promising but Sica lacked distribution here and so it was shelved.

There is also an inexpensive SB coax, but has a on-axis notch around 13 kHz.

Not convinced DIY coaxs are worth the additional trouble of a 3-way XO and cost, given how tweeter response is modulated by the midrange cone's movement, and the roughness in the top octave. Having dealt with a widebander that rolled off from 5kHz (Mark Audio CHP-70) and finding it quite pleasant, IMO a smooth rolloff (even if steep) above 10kHz is less trouble than wrangling with a coax.

There is a new TB coming, the coax w4-2315:

W4-2315 - 4.5” Paper Coaxial Full Range - TB SPEAKER CO., LTD.

www.tb-speaker.com

Tangband makes some of the coolest looking drivers out there. The nulls at 8 and 10kHz are concerning to me.

 

[Ilkless]

Yes, also the change of the slope is important, ideally smooth and as far away as possible from the mid band.

To be sure I understood you correctly, you mean a polar response like the one drawn in red (which looks like KEF, Genelec or JBL LSR 7xx) is preferable to, for example, the one is blue (which should roughly be what a well-designed FAST with a wider baffle and lower baffle step looks like).

Directivity control via a large woofer and large baffle is not terribly practical. Speaking from experience using a 27x49" baffle for the front L/R in my main setup.

Such large baffles come with a serious downside and that is resonance. To make mine tolerable, I have 1/2" plywood sandwiched with 3/4" MDF using green glue. The legs are 2x4 lumber triangles, and 80lbs of concrete blocks holding them down.

If you are willing to go through such effort, using a coaxial plus 3 way crossover just makes more sense than a 2 way FAST. It would be a shame to have nice low frequency directivity and then have it be uncontrolled at the high end.

Oh, I don't mean controlling directivity massively to 90° at 250Hz or something. I just mean a design with a lower baffle step as a consequence of the baffle width. As well as narrower directivity in the upper-end of the woofer passband.

I was wondering if the baffle width and large woofer directivity could allow a smooth blend to the widebander.

 

[Ilkless]

I'm also excited about this driver. Directivity doesn't seem that bad, or at least on par with the 8414. The Klippel results just seem way better than anything else offered.

For a small widebander in a waveguide, I would consider the Wib50 or NE65W in addition to the SB65. Not sure if even a 10" WG would load these under 1kHz or so, but would love to see (and hear) the improvement above that

Not necessarily for the loading on the bottom end, but to smooth out the beaming a little, and for the 2-3kHz loading.

https://www.diyaudio.com/community/threads/10f-8424-rs225-8-fast-waw-ref-monitor.273524/

Yes I reference this design in my OP. I just think the RS225 is not a competitive woofer now, plus there's the issue of its cone breakup. Moreover, I'm quite skeptical about fixating on phase and time-domain performance, potentially at the expense of directivity and FR.

 

[thewas]

To be sure I understood you correctly, you mean a polar response like the one drawn in red (which looks like KEF, Genelec or JBL LSR 7xx) is preferable to, for example, the one is blue (which should roughly be what a well-designed FAST with a wider baffle and lower baffle step looks like).

Yes, ideally the change of slope should be as low in frequency as possible.

 

[Ilkless]

Yes, ideally the change of slope should be as low in frequency as possible.

That's fair, I thought you were talking directivity mismatch between 2 drivers at first. IMHO if there's no mismatch, the narrowing will sound like lesser air that might be an acceptable compromise to some people (like me) in return for increased dynamics in the midbass, lower compression and lower baffle step than a smaller 2-way with waveguide. And with less directivity mismatch than a large woofer + dome tweeter 2-way.

I know a 3-way would help with wider horizontal directivity in the top 2 octaves, but it also means more vertical lobing, and significantly more complexity, unless a coax is used. And we both know the only really good coaxs on the market are all proprietary.

 

[DavidMcRoy]

This is all very interesting to me since I'm acquiring parts and materials for a DIY 2-way open baffle. On each speaker I'm using two MarkAudio Alpair 12P full-range drivers over and under a dipole planar tweeter in MTM/d'Appolito configuration on a rather large open baffle (50" H X 24" W/127mm H X 61mm W.) I've never built a dipole before, but I've been reading about pitfalls, dos and don'ts, etc. I'll be triamping and using DSP for crossovers, EQ, polarity, level matching and delay. There will be an active, sealed box sub involved. (I'll probably explore dipole bass down the road, and I know that'll have to be physically very large.)

 

[Ilkless]

This is all very interesting to me since I'm acquiring parts and materials for a DIY 2-way open baffle. On each speaker I'm using two MarkAudio Alpair 12P full-range drivers over and under a dipole planar tweeter in MTM/d'Appolito configuration on a rather large open baffle (50" H X 24" W/127mm H X 61mm W.) I've never built a dipole before, but I've been reading about pitfalls, dos and don'ts, etc. I'll be triamping and using DSP for crossovers, EQ, polarity, level matching and delay. There will be an active, sealed box sub involved. (I'll probably explore dipole bass down the road, and I know that'll have to be physically very large.)

FWIW I think Mark Audio's design direction is along the right track; well-ventilated baskets, highly optimised cone profiles for dispersion, purpose-designed components for wideband use. But I think Mark Fenlon is similar to Rob Watts (Chord) and Alan Shaw (Harbeth). They are all very competent engineers but apply their knowledge to build audio equipment based on dubious, pseudoscientific design goals they derive from anecdotal listening.

And because of this, the frequency response suffers due to an obsession over eliminating the surround, high sensitivity and light cones (because of the intuition that light cones = more detail) rather than nailing a smooth FR and dispersion hat's easy to work with, even if sensitivity is lower.

I have heard the Alpair 12P before in a Pensil box and it had a real problem with lacking coherence and treble raggedness. Narrowing dispersion to be expected. But uneven dispersion, even if wider than average for the size class, is really objectionable and makes the driver sound phasey. Which is a shame because that sky blue paper cone is one of the prettiest I have ever seen.

I would love to see an Alpair 7P that's designed with more power handling, smoother dispersion and smoother response.

 

[thewas]

That's fair, I thought you were talking directivity mismatch between 2 drivers at first. IMHO if there's no mismatch, the narrowing will sound like lesser air that might be an acceptable compromise to some people (like me) in return for increased dynamics in the midbass, lower compression and lower baffle step than a smaller 2-way with waveguide. And with less directivity mismatch than a large woofer + dome tweeter 2-way.

I know a 3-way would help with wider horizontal directivity in the top 2 octaves, but it also means more vertical lobing, and significantly more complexity, unless a coax is used. And we both know the only really good coaxs on the market are all proprietary.

Yes, like always it is a individual compromise, personally I rather have a narrow beaming with a non-coaxial at the crossover region than this beaming in the last octaves. I think everyone must make his own experiences with such, I also experimented with similar projects in the past as like you I thought it would be a better compromise for an own DIY project but unfortunately they didn't work out as I expected. I also think it is no coincidence that none of our here known the state of art loudspeaker engineering companies offer FASTs but even non-coaxials instead.

 

[DavidMcRoy]

FWIW I think Mark Audio's design direction is along the right track; well-ventilated baskets, highly optimised cone profiles for dispersion, purpose-designed components for wideband use. But I think Mark Fenlon is similar to Rob Watts (Chord) and Alan Shaw (Harbeth). They are all very competent engineers but apply their knowledge to build audio equipment based on dubious, pseudoscientific design goals they derive from anecdotal listening.

And because of this, the frequency response suffers due to an obsession over eliminating the surround, high sensitivity and light cones (because of the intuition that light cones = more detail) rather than nailing a smooth FR and dispersion hat's easy to work with, even if sensitivity is lower.

I have heard the Alpair 12P before in a Pensil box and it had a real problem with lacking coherence and treble raggedness. Narrowing dispersion to be expected. But uneven dispersion, even if wider than average for the size class, is really objectionable and makes the driver sound phasey. Which is a shame because that sky blue paper cone is one of the prettiest I have ever seen.

I would love to see an Alpair 7P that's designed with more power handling, smoother dispersion and smoother response.

Thanks for the observations. I tend to think that asking a "full range" to actually handle everything up to 20kHz is non-optimum. It's one of those "pitfalls" I've read warnings about, many of those precautions in threads right here on ASR. My hope is that the Alpair 12P will excel from the midbass through the midrange, crossed over to a dipole planar tweeter that itself is claimed to be rather wideband as tweeters go at 500Hz to 20kHz. And I take that 500Hz figure as fantasy in actual operation. My design goal is about 3 or 4kHz or whatever turns out to be the best compromise. I'll be using 24dB/octave slopes and I'll be EQing resonances. Hopefully that'll push any HF shenanigans from the Alpair 12P down sufficiently. We'll see. This is basically a DIY active speaker. I don't think I'd even attempt this with passive crossovers. I don't think they make sense anymore.

 

[thewas]

Just out of curiosity I made a quick and dirty simulation model with similar sized decent drivers (10" & 4") and the baffle dimensions that were given to me from the OP:

(Grey curve is sound power)

(Horizontal and vertical angle plots - links = left, rechts = right, oben = up, unten = down)

(Directivity index)

The slight directivity narrowing in the lower mids could be improved with a further optimised crossover and baffle size but it also shows the inevitable and in my experience unfortunately audible problem of the high beaming and low sound power in the last 2 octaves.

 

[Ilkless]

Thanks for the observations. I tend to think that asking a "full range" to actually handle everything up to 20kHz is non-optimum. It's one of those "pitfalls" I've read warnings about, many of those precautions in threads right here on ASR. My hope is that the Alpair 12P will excel from the midbass through the midrange, crossed over to a dipole planar tweeter that itself is claimed to be rather wideband as tweeters go at 500Hz to 20kHz. And I take that 500Hz figure as fantasy in actual operation. My design goal is about 3 or 4kHz or whatever turns out to be the best compromise. I'll be using 24dB/octave slopes and I'll be EQing resonances. Hopefully that'll push any HF shenanigans from the Alpair 12P down sufficiently. We'll see. This is basically a DIY active speaker. I don't think I'd even attempt this with passive crossovers. I don't think they make sense anymore.

Have you considered the Alpair 12PW instead?

Are you using the BG NEO8? Planar, dipole, 500Hz is a very very small niche.

And yes, 20kHz is fantasy, but if one is fine with 14-16kHz, quite doable for a good 3.5-4" driver.

 

[DavidMcRoy]

Have you considered the Alpair 12PW instead?

Are you using the BG NEO8? Planar, dipole, 500Hz is a very very small niche.

And yes, 20kHz is fantasy, but if one is fine with 14-16kHz, quite doable for a good 3.5-4" driver.

I'm using the GRS PT6816-8, which reputedly performs similarly to the BG but with different materials. It appears to be a clone/knockoff. If it falls short, I'll return it and get the BG.

I haven't really looked into the Alpair 12PW. Might it have any significant advantages?

I'm also curious about MarkAudio's rather Byzantine driver break-in regimen. I intend to follow it. Is there something unusual about the design or materials used that calls for such specific procedures? I'm skeptical but I'm left with the impression that I'd be quite remiss if I didn't follow it to the letter. It involves so many hours of elevator music before cranking it to 11. Not a big deal to do, of course, but they're not shipped halfway around the world to me here on the US Pacific Coast in a vacuum, they get jostled around.

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