@justin zazzi
I read a great discussion a few posts back and wanted to revise the topic of Loud Speaker Design and innovation.
Just curious on your thoughts/opinions on why we haven't seen anything like the phoenix gold cyclone or CV Strokers in today's car audio? I don't know what the PG performance was but CV did really well with that design.
Sorry to hijack - I happen to own two PG Cyclones (one broken), and had the honor of making pen-pals with Tom Danley back in the early '00s, with the goal of making my own rotary servo subwoofer (NOT to make a product to sell, just a fun one-off, for engineering bragging rights). Unfortunately my business partner (fellow audio tech geek) and I burned out the motors that Tom Danley personally had suggested to us, and we put it on the shelf to focus on other things... that would have been fun though. Basically I'd taken a flat bar stock for the center, and had my buddy CNC machine some motor mount adapters - I mounted one motor on each end, unlike the Cyclone with had one motor at one end. The motors were each about double the size of the Cyclone's, so I made a center vane out of foam core and kevlar, hollowed out with stiffening channels, and then vacuum-bagged it for a super light vane. Instead of a screw shaped wave guide, I was just going to build it into a quad-chamber box that would manage the wave phases. Would be fun to pull tat project off the shelf, but it was becoming an expensive experiment...
Anyway, I'm not seeing the similarity between the PG Cyclone and the CV Stroker:
The Cyclone was a remarkable one-of-a-kind joint effort between PG Cyclone, specifically licensing Tom Danley's patented servo-drive technology - interesting for that rotary implementation that ServoDrive doesn't even sell. It was a one of a kind.
I can tell you from my experience with the Cyclone, that it is good for about 40hz and down (way down), but basically then you need another more traditional subwoofer to pick up the 40hz and up to wherever your midbasses really pick up. It was also very expensive, to not do everything that a subwoofer of today can do. And the real advantage was displacement - this was before "high excursion" subs really existed. I'd have to find the specs again, but this was before subs like the W7 or XBL^2 existed, so they were advertising the Cyclone had 3x the displacement of a standard 12"... which is about what a W7 does, or a CSX-12, and even a W7 is less expensive.
View attachment 10757
The Cerwin Vega Stroker is basically just a traditional subwoofer. It had a unique little gimmick, but it isn't really wild or radical IMO: in place of a dustcap, they used a second spider, that clamped onto a rod that poked forward of the pole piece. I say "clamped" because there was a set screw that allowed you to slightly adjust the center "at rest" position of the cone unit in the magnetic gap - some say that was to compensate when you mounted the subwoofer horizontally, to actively avoid cone droop... but that's really solving something that isn't usually a problem anyway. It did make the suspension quite unique, because really there was both an upper and lower spider, and even the surround was spider-like. But essentially, it was a big, heavy SPL sub with a fancy dustcap. Definitely not as far-out as a Cyclone.
View attachment 10758
Do you mean "Why aren't there more unique subwoofers"?
There are, if you look past the kids who only care about "power handling" (despite the trade-offs in efficiency that imparts) from their salad-bar contract manufactured subwoofers, there's lots of unique geek stuff - that's the stuff I love.
I'd suggest reading up on:
- underhung vs overhung subwoofers (just as a baseline on motors - but underhung are far less common)
- optional components like shorting rings and sleeves (seeing DUMAX measurements of BL curves will help understand that topic - as well as the ones below: )
- the JBL GTi DDD motor - which had two separate magnetic gaps, and two opposite-wound windings on the former, to not only give it linearity, but a braking force if driven to over-excursion.
- the XBL^2 motors - essentially a groove in an underhung-sized top plate, with a voice coil winding length perfectly balanced so that as coils leave magnetic field 1, they enter magnetic field 2, keeping BL linear - but in a MUCH simpler way than JBL did
- Side note for googling: check out where the W7 is cross-drilled in it's long excursion motor, and it's winding length. Some say that's to create an XBL^2-like effect, without running afoul of the XBL^2 patents.
- Speaking of the W7 - it's own front suspension is very innovative, and allows for a larger cone - therefore more cone area, and a larger surround - therefore more excursion capability, previously somewhat mutually exclusive.
- Shallow subwoofers - some of these stuff the motor inside where the cone used to be - well done ones are interesting engineering, and worth looking into the trade-offs on excursion and how they overcome them.
If it's not just unique subwoofers you are interested in, search out:
- plasma tweeters. In pursuit of the lowest mass possible, it's literally sound from an electrical flame.
- Electrostatic drivers, and magnetic-planar drivers. It's a panel suspended in either a massively high-voltage static field, or a magnetic field, rather than a cone.
- Distributed Mode Loudspeakers. It's literally just a motor, designed to vibrate something that otherwise wouldn't be a speaker
- Even - phase plugs and whizzer cones on midranges. That search will get into a great discussion on speaker directionality.
- which also makes me think of compression drivers - in the late 80's and early 90's they were morphed into "waveguides" that dominated IASCA SQ competitions back then
I'm sure I could come up with others (I own a dome subwoofer with a 10" voice coil but that was never on anyone's radar), but if you are researching to understand them personally, and then to understand why these aren't all commercial successes, that list above will keep you busy for a couple years.
Usually though, commercial failure comes down to two things:
- Relatively unproven technology is uncomfortable to most people. That's a barrier to sales and to adoption rates.
- Low volume sellers, and complex assemblies, both add to cost. Expense is always a barrier. Even me - I'm personally a "bang for the buck" fan way more than I'm a "geek engineering" fan.
...and that always should make an engineer ask themselves:
- What is the goal we're trying to achieve? Speakers simulate air - is there something different you are trying to achieve? Why?
- Is there an existing way to achieve that goal, that reaches the limits we want, for less money? Then why engineer a more expensive way?
Sorry - /hijack.
(EDIT for visuals: )
JBL GTi - really two opposing motors folded into one - you can see both coils, both magnetic gaps - which are opposite wound, because those gaps are opposite phase:
View attachment 10759
XBL^2 motor cutaway - showing "at rest" position, but as the cone moves in either direction, coils leave one gap and enter the other, leaving BL constant (linearity) while making huge excursion:
View attachment 10760
Compare that to those baseline "overhung" and "underhung" cutaways.
And the best I can find of the W7 internals... see that sneaky pole vent cross drilling in there? It's right at the center of where the coil is "at rest", having the same type of effect as XBL^2 [as that would weaken the field at that spot]... but also that innovative basket, suspension, all custom parts that the little guys just can't do:
View attachment 10761
EDIT edit: (apologies)
I can't mention ServoDrive and how different the Cyclone is, without showing what they actually sell:
View attachment 10762
It's interestingly a rotary servo motor at the top (blue, mostly hidden - looks like a shop tool motor) with a shaft that goes to that proprietary belt mechanism, which converts the rotary motion to linear motion - pushing two shafts that move two "traditional" 15' cone units in a linear way.
. Anyone remember the old Bob Carver amps that put out hellacious power in a tiny rack mount chassis? This was before the class D amplifier days. How did he do this? Regulated variable tracking power supplies. The power supply adjusts its rail voltage rapidly in sync with the incoming signal. This kept power supply switching losses to a minimum.