the ancient urge to build a dual-woofer three-way

Pat McGinty

Senior Member
One of my favorite advantages of designing for DSP is how much simpler bass system design is, and how much better the end result is. Back in the day we needed to experiment with box volume, port specifications (length, crossection and flare, both ends) and, very tricky, internal baffling. The possible combinations were endless and the process of getting to the target took an adjustable mule and lots of hot glue and time on your knees. If you couldn't judge each iteration in a snap you were dead. And if you found yourself talking yourself into liking the end result, yup, dead.

Now we merely characterize each driver by observing what box volume results in best transient behavior - read: rise and settle times - then use that number each time we use that driver. We just manhandle the amplitude response in the processor to 'buy back' bottom end. So it' a clean process without relying on resonance to puff things up.

The idea is a breakthru for custom work because we can pretty much just cut-and-paste a build together from our stable of characterized drivers.

The volume layout of this four-driver three-way pretty much just falls into place with some consideration of economy of material. Barely a high school geometry project. There's plenty of room for a streamer bay at bottom.

You can see that we can pack a lot more transducer onto the baffle because the volume requirements are so much lower.

layout screen grab.jpg

And, very nice, we can isolate the two woofers covering the same band. With a vented alignment, dividing the box volume in half like this results in about for times as much port, so the overall box dimensions so suffer badly that you just put up with the issues of two woofers sharing the same load.

Not a bad size. About what we had with Blue Heron, but much, much, much more speaker.

Testing for proof of concept was easy, if a bit silly looking. Two 9.5" Satoris in their proper volumes, one 7.5" Satori and, just for giggles, we toggled in and out a 'weak sister' bottom octave system that really couldn't keep up. So, no, we couldn't hit the target in the bottom half of the bottom octave - but we sure could convince ourselves that the 4x10" 1KW idea will hit a walk-off home run. Half that much is probably more than fine.

There's an FA252 hiding behind, driving the LF pumps.

With just the mains playing, a nifty range of bandwidth/amplitude trade-offs was apparent. And we're enjoying the kind of LF resolution we've come to expect. A little more because they're twins. And the midrange seems quite comfy rolling in at an arbitrary 120Hz with a five pole Butterworth. That's a fine point we'll worry about later. Anyway, we're both at 'thumbs up'.


20190828_140644.jpg


Next, make some sawdust. Important not to get too attached to an idea - not to invest too much, not to make the proto's too pretty. We'll make a raw set that can we can launch into the dumpster without a second thought if they don't measure up. Just me, it's Murphy's Law upside down, make 'em pretty and, of course, they'll suck. I'm not superstitious, but you can doom your own project by getting too in love with it.
 

Prime Minister

Site Owner
Staff member
This sounds very interesting. Numerous upgrades for mine pending? Hmmmm.

Btw, I like what you are saying about speed of transients. And now that I've lived it, it would be hard going back.
 

Pat McGinty

Senior Member
This sounds very interesting. Numerous upgrades for mine pending? Hmmmm.

Btw, I like what you are saying about speed of transients. And now that I've lived it, it would be hard going back.
The Hypex and minidsp are sonically equivalent. For guys who have spent decades pursuing vanishingly small increments in amp performance, it's gonna be hard to accept that the current modules are damn near ideal.

I merely cut-and-pasted the biquads from minidsp to Hypex for Kite - and you'd be hard pressed to differentiate between them. The comparisons of interest happen on the business side and app side.

The USD is killing the EU.

On the app and features side it really is a mixed bag. I think that if we laid out a point by point scorecard, it'd be draw. They take sorta opposite approaches on many of the important points.

At issue for us is that we wish to prosecute our "modular" system concept, which requires being able to daisy-chain at least four units. Minidsp and Hypex both handle that fine with one teeny exception that has just now come to light. A customer tripped over the problem before we did: with minidsp a 24/96 signal will drive two, four or six units, no problem. But at 24/192 the limit is three. I figured "Bah! who cares?", but that does seem to hold the potential to be a problem in the market. I'm a little miffed, really, there's no doubt that some artist will publish in, say, 32/384. Then, what does that mean? Your streamer and your speakers are passe'? The situation kinda makes one appreciate the beauty of the Sony/Phillips standard for CD - digital audio would have gone nowhere had there been a free-for-all.

Anyway, Hypex does indeed pass the test at 24/192 so that sorta makes the choice. And their expanded line of eight plates - including four three channel models - that can be configured fourteen different ways up to 1KW is quite liberating. Our LF systems really like the extra juice. So we'll be happy and carry on.

Transients? Yes indeed. The effect is even more remarkable in the low bass where you've never enjoyed quick signal tracking. Well worn recordings take on new dimensions and, funny funny, with LF resolution that apparently exceeds that available to the recording guys, you'll occasionally hear things that were not intended like footsteps or a door closing. Let's just say that there is instrumental timbre in the bass that has always been masked by your resonance at roll off. So, yeah, one step closer. I know what you mean - there's no going back.
 

Pat McGinty

Senior Member
The mules have been running for a couple of weeks. While the protos are being built a set of mules can enter the twilight zone of impending disassembly but, this time I keep going back, experimenting with the filters, but mostly to listen.

Yesterday evening they got an unexpectedly vigorous workout when the 'usual suspects' crashed my shop. Rockers, every darn one of them. Apparently word had gotten out that the beer fridge was in a fine state of readiness. Men, dogs, a yellow '69 Dodge Dart drove across on the lawn.

I'll cut to the chase: we rocked the stuff most guy's can't play, at realistic levels anyway. Roger Waters The Wall Live 2010-1013, Beck Live at the Hollywood Bowl and plenty of classics. The empties piled up, we passed the tablet around so every guy could pick his tunes, a sing along to Tangerine, Zep III. Like a bunch of kids.

It's a damn good thing we don't have neighbors.

Anyway, the system surprised me - and that just does not happen. It's so vibrant and immediate. Breathtakingly forceful with quick, silent resolve. Guitar timbre in SPAAAADES. Hours of going all-out and nothing but a light happy feeling. Very pleasant.

Sorry, I sat down to write about the tech issues of five pole Butterworth bandpass filters, passive v.s. dsp, and that came out instead.
 

Prime Minister

Site Owner
Staff member
The mules have been running for a couple of weeks. While the protos are being built a set of mules can enter the twilight zone of impending disassembly but, this time I keep going back, experimenting with the filters, but mostly to listen.

Yesterday evening they got an unexpectedly vigorous workout when the 'usual suspects' crashed my shop. Rockers, every darn one of them. Apparently word had gotten out that the beer fridge was in a fine state of readiness. Men, dogs, a yellow '69 Dodge Dart drove across on the lawn.

I'll cut to the chase: we rocked the stuff most guy's can't play, at realistic levels anyway. Roger Waters The Wall Live 2010-1013, Beck Live at the Hollywood Bowl and plenty of classics. The empties piled up, we passed the tablet around so every guy could pick his tunes, a sing along to Tangerine, Zep III. Like a bunch of kids.

It's a damn good thing we don't have neighbors.

Anyway, the system surprised me - and that just does not happen. It's so vibrant and immediate. Breathtakingly forceful with quick, silent resolve. Guitar timbre in SPAAAADES. Hours of going all-out and nothing but a light happy feeling. Very pleasant.

Sorry, I sat down to write about the tech issues of five pole Butterworth bandpass filters, passive v.s. dsp, and that came out instead.
Well damn.
What part of it makes it so surprising?
 

Pat McGinty

Senior Member
Well damn.
What part of it makes it so surprising?
Well, you'd expect 500W into twin 9.5" Satoris to make dandy mid bass. What's surprising is just how much fun that is. It's really the combination of resolution and dynamics we've been missing all along. I mean, there's a lot of music that's always been lost, blurred.

The trick is high passing the mid bass system, then doing the heavy lifting at the bottom with a separate system. That keeps it clean and quick, cooler, more centered coils for better dynamic expression, better timbre. It is a bit of a luxury - money wise - but, for me anyway, it satisfies a longing that's drawn me thru this for so long. When you get it right it's such a happy thing.

Glue Saturday:

20190907_085249.jpg
 

Prime Minister

Site Owner
Staff member
Well, you'd expect 500W into twin 9.5" Satoris to make dandy mid bass. What's surprising is just how much fun that is. It's really the combination of resolution and dynamics we've been missing all along. I mean, there's a lot of music that's always been lost, blurred.

The trick is high passing the mid bass system, then doing the heavy lifting at the bottom with a separate system. That keeps it clean and quick, cooler, more centered coils for better dynamic expression, better timbre. It is a bit of a luxury - money wise - but, for me anyway, it satisfies a longing that's drawn me thru this for so long. When you get it right it's such a happy thing.

Glue Saturday:

View attachment 16243
Very interesting!
You have talked more about heat then any other speaker designer I have read. It's a very logical concern. Especially at the kind of power you like to use!

When you say luxury, money wise, what do you think the cost will be? Twice a kite?
 

Pat McGinty

Senior Member
Very interesting!
You have talked more about heat then any other speaker designer I have read. It's a very logical concern. Especially at the kind of power you like to use!

When you say luxury, money wise, what do you think the cost will be? Twice a kite?
Yeah, roughly twice. Then about twice again for the quad pump kilowatt bottom octave arrays. I figure at flat to fifteen we should use very little excursion and quite coolly even at max pressure. So it should sound like a cool easy breeze.

And, yep, heat is trouble. Impedance varies linearly with temperature. But heat generated is the square of current, so it's an especially nasty problem. The longish time constant makes it that much uglier.

Maybe on an "ordinary" system you don't notice it so much with polite music having lots of space between the notes, but big music with lots of energy will bring the thing to its knees with congestion and glare. I hate that, don't you?
 

Prime Minister

Site Owner
Staff member
Yeah, roughly twice. Then about twice again for the quad pump kilowatt bottom octave arrays. I figure at flat to fifteen we should use very little excursion and quite coolly even at max pressure. So it should sound like a cool easy breeze.

And, yep, heat is trouble. Impedance varies linearly with temperature. But heat generated is the square of current, so it's an especially nasty problem. The longish time constant makes it that much uglier.

Maybe on an "ordinary" system you don't notice it so much with polite music having lots of space between the notes, but big music with lots of energy will bring the thing to its knees with congestion and glare. I hate that, don't you?
So is this speaker planned for production? It would be damn impressive.

I wonder what a Pat McGinty designed, low spl Jazz speaker would sound like. A speaker for folks who always listen to small groups, vocals, etc at moderate volume. A speaker that will never play Highway to Hell at concert levels. The original Kestrel would do that pretty well. But I'm thinking of a bigger, low mass driver, with no crossover (DSP, of course) , that is totally alive at 75-80 db. Maybe even less!

Just ruminating on a rainy day.
 

Pat McGinty

Senior Member
So is this speaker planned for production? It would be damn impressive.

I wonder what a Pat McGinty designed, low spl Jazz speaker would sound like. A speaker for folks who always listen to small groups, vocals, etc at moderate volume. A speaker that will never play Highway to Hell at concert levels. The original Kestrel would do that pretty well. But I'm thinking of a bigger, low mass driver, with no crossover (DSP, of course) , that is totally alive at 75-80 db. Maybe even less!

Just ruminating on a rainy day.

That'd take a driver especially good at small signal work, like this ultra symmetrical, ultra low reflection, underhung jobbie with a soft suspension, segmented cone.

20190907_141737.jpg

I'd place an emphasis on getting an over-the-top spacial presentation; height, depth and extra width. For that, there's nothing more beautiful than a dipole AMT. Not even close.

My last passive design was pretty much that but I couldn't figure out how to sell it. It seems like the brands doing extra pricey two-ways are pretty much stuck with large 'critical mass' ad budgets - not exactly my idea of a happy time. Anyway, best I can figure, for that idea, my interest ends at design.
 

Ernie

Activated
Oh. HELLO!

NOW you have my undivided attention!

(This discussion could be hazardous to my wallet.)

Can you elaborate on this for a moment? Please?
 

Prime Minister

Site Owner
Staff member
That'd take a driver especially good at small signal work, like this ultra symmetrical, ultra low reflection, underhung jobbie with a soft suspension, segmented cone.

View attachment 16247

I'd place an emphasis on getting an over-the-top spacial presentation; height, depth and extra width. For that, there's nothing more beautiful than a dipole AMT. Not even close.

My last passive design was pretty much that but I couldn't figure out how to sell it. It seems like the brands doing extra pricey two-ways are pretty much stuck with large 'critical mass' ad budgets - not exactly my idea of a happy time. Anyway, best I can figure, for that idea, my interest ends at design.
How about custom one offs? :)
 

Prime Minister

Site Owner
Staff member
That'd take a driver especially good at small signal work, like this ultra symmetrical, ultra low reflection, underhung jobbie with a soft suspension, segmented cone.

View attachment 16247

I'd place an emphasis on getting an over-the-top spacial presentation; height, depth and extra width. For that, there's nothing more beautiful than a dipole AMT. Not even close.

My last passive design was pretty much that but I couldn't figure out how to sell it. It seems like the brands doing extra pricey two-ways are pretty much stuck with large 'critical mass' ad budgets - not exactly my idea of a happy time. Anyway, best I can figure, for that idea, my interest ends at design.
How big a driver were you going to use with that "extra pricey two way"?
 

Ernie

Activated
It has escaped your notice that you described, exactly, my listening habits. Your speakers, and this dual-woofer model, are fascinating looks into the design and build of what is arguably a paradigm shift in speakers. Living, as I do, in a semi-detached home, realistic levels of orchestral music, or Highway to Hell, have never been a concern of mine. This latest set of design parameters, however, have my complete attention.

So, the list of customers for a speaker that hasn't even landed on a piece of paper, sits at two.
 

Prime Minister

Site Owner
Staff member
It has escaped your notice that you described, exactly, my listening habits. Your speakers, and this dual-woofer model, are fascinating looks into the design and build of what is arguably a paradigm shift in speakers. Living, as I do, in a semi-detached home, realistic levels of orchestral music, or Highway to Hell, have never been a concern of mine. This latest set of design parameters, however, have my complete attention.

So, the list of customers for a speaker that hasn't even landed on a piece of paper, sits at two.
Hey, I know exactly how you listen. And I know that something like this will work perfectly for you also. Perhaps a smaller woofer then I would want, but otherwise a lot of overlap. Plus, you and I have spent enough time listening together, for me two know are tastes are not dissimilar.

Basically, I was just having some fun with ya! :)
 
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