Cerwin Vega Stroker Pro 15 Users Manual CAEP 051000p068 73 CVSTROKER

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2015-02-03

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MOBILE AUDIO

For moreinformation, visit us at www.cerwin-vega.com.

Since 1954,

Cerwin Vega, one of the

oldest speaker companies around,

has had a major reputation for building speakers

that allowed everyone to be “loud and proud.”

Therefore, it’s no surprise that Cerwin-Vega has

introduced one of the most outrageous car sub-

woofers I have reviewed to date, the Stroker Pro

15. At 68.3 lbs., they have the “Where’s the Beef?”

award in the bag. Even more impressive than its

physical size is this product’s technology.

The Stroker Pro cast aluminum frame acts as

both a giant heatsink (an old but good trick) and a

highly effective Faraday

shield or shorting ring (a new

patent-pending trick). The cut-

away drawing (Fig. 1) shows that this woofer not

only has two separate magnets (actually, the lower

magnet is two magnets stacked together, so tech-

nically three magnets), but also two gaps, a tech-

nology known as Multiple Magnet Air Gap (MMAG).

Because of the physical layout of the MMAG motor

format, CV could mount the lower magnet system

to the back of the frame, like a normal woofer,but

turn the frame’s inside diameter upward to form a

shorting ring.

In addition to attenuating nasty eddy currents

produced by the woofer motor and lowering distor-

tion, a large shorting ring also reduces motor tem-

perature by decreasing inductive heating. Figure 2

reveals what an outstanding thermal pathway this

frame makes with the upturned section directly

adjacent to the naked voice coil. The Stroker has

four other thermal pathways: two in the spider-

mounting area and two at the rear of the motor.

There are two sets of vents integrated into the

lower-spider mounting shelf (this woofer has two

mounting shelves for three spiders). A 1/8” gap

goes around nearly the entire perimeter of the

CERWIN-VEGA

STROKER

PRO 15

TEXT: VANCE DICKASON &

ERIC HOLDAWAY

PHOTOS: COURTESY OF MANUFACTURER

THAN A ONE

NOTE WONDER —

A FRONT-RUNNER FOR

SOUND QUALITY AND SPL

shelf’s 10 1/4” diameter except for the six 1/2”-

diameter mounting posts that it suspends from.

This gives substantial venting area for the airflow

generated by the lower spider motion to move air

past the exposed voice coil and top plate. For the

air caught between the two spiders, there are an

additional six 1/4” x 2” vents. At the back side of the

motor you have a series of six 3/32” diameter

peripheral vents that move air from between the

pole piece and the voice coil out the back of the T-

yoke. Lastly, an aluminum-sleeved 1 3/4” diameter

pole vent powered by the large, moving clear plas-

tic dustcap supports the third spider at the top of

the woofer. Because of this, the sleeve extends to

about double the height of the pole, and thus acts

as another heatsink.

The real heart is the MMAG motor structure.

Since the voice coil is shorter than the combined

length of the two gaps, it appears similar to a con-

ventional underhung voice coil motor. In the con-

ventional motor, as the short coil rides out of a sin-

gle large gap in either direction, the total number of

voice coil turns in the gap decreases and so does

the total Bl, or total horsepower, of the motor.

However with the Stroker Pro dual-gap motor, the

situation is more like hav-

ing two gaps working in

unison. As the number of

turns starts decreasing in

one gap, the number of

turns in the other gap

increases so that the num-

ber of voice coil turns of

wire in the gap stays con-

stant. The cool part is that

it operates in a way that

the two gaps are always

working in conjunction

with each other such that

the number of turns does

not begin decreasing until

the voice coil starts to

leave just one gap. (See

sidebar on pg. 73 for more

information on dual-gap

technology.)

Other features for the Stroker Pro motor include

a forged and CNC-milled single piece T-yoke that

includes an extended pole piece with a pole vent.

This vent gives access to a patented adjustable spi-

der bias system for the top or third spider. All the

original Stroker woofers

had this adjustment sys-

tem; however, it was set

at the factory for maxi-

mum linearity. Stroker

owners found that tweak-

ing this setting enabled

the woofers to play even

louder. Biasing a spider

toward the front side and

causing the voice coil to

be deliberately off-cen-

tered toward the front of

the gap area creates high-

er amounts of even-

ordered distortion (2nd

and 4th harmonics to be

exact). Besides the warm

tones caused by the

biased spider, the

increased even-order distortion also increases the

bass due to a psycho-acoustic phenomenon called

the missing fundamental (which produces percep-

tion of low bass from notes an octave higher). So, if

you want to go from very clean linear bass to an

altered warm bass sound quality, Stroker Pro

woofers come with a tool that allows the user to do

that.

One of the key features to good subwoofer per-

formance is a solidly stiff cone, and the cone in the

Stroker is about as stiff as it gets. Built from layered

carbon graphite and thick paper, the cone is further

reinforced by the large 7 1/2”-diameter clear poly-

carbonate dustcap. Long excursion in a subwoofer

requires the suspension to move long distances.

One solution is incorporating a wide surround that

allows the cone to move further. However, this

decreases the cone area, which in turn requires the

cone to move further! Cerwin-Vega’s patent-pend-

ing solution is SdMaxx (Sd is an engineering abbre-

viation for the area of a cone). Rather than being

low and wide, the polyether foam surround is more

of an ellipsoid shape, tall and narrower. The result is

the same excursion ability, but a greater cone diam-

eter and area. The other part of the SdMaxx system

is an attachment design that allows the entire cone

Figure 1

Figure 2

assembly to be quickly removed and replaced.

The rest of the assembly consists of the three-

polycotton/conex blend spiders. The two lower spi-

ders (mounted inverted to each other to cancel out

some of the non-linear behavior) are 8 1/2” in diam-

eter while the top spider is about 7” in diameter. All

three are progressive, which means they increase in

stiffness the further out they move in either direc-

tion. The dual four-layer voice coil is wound with

high-temperature copper wire on a black anodized

100mm (3.9”) diameter aluminum former. Voice coil

tinsel leads are connected to dual connecting

blocks on opposite sides of the frame. Each termi-

nal block has two sets of hex screw terminals that

accept up to 14-gauge wire, allowing the Stroker

Pro to be easily configured with the voice coils in

series or in parallel.

IN THE LAB

Part 1 of the objective measurement consists of

large signal analysis followed by the LEAP 5 analy-

sis. Using the Klippel analyzer (on loan from Klippel

GmbH), Pat Turnmire, CA&E reviewer and CEO of

Redrock Acoustics, performed the large signal

analysis and provided the Bl (X) curve shown in

Figure 3. The black curve is the Bl curve and shows

the motor strength of the woofer as it moves in

both directions from center rest position. The lighter

curve is a type of displacement curve, and if both

curves were identical, the motor system’s motion in

and out of the frame would be perfectly symmetri-

cal. When a woofer is totally linear (linear would

mean that the woofer motion matches the input

signal exactly with no distortion), the Bl curve

should be centered on the 0mm point (where the

cone is positioned when there is no signal) and

symmetrically decrease with the same slopes in

both directions of voice coil travel. When a woofer

exhibits a forward or rearward offset it may indicate

the magnetic and mechanical systems are not

absolutely optimal. If the motor strength decreases

more rapidly in one direction (usually the outward

direction) than the other, the result is increased lev-

els of distortion at high operating levels. It is not

uncommon, however, for a woofer voice coil to be

deliberately offset a few millimeters in order to keep

the motor more linear in the 90-110dB SPL range,

which exactly describes the situation with the

Stroker Pro.

The Stroker Pro Bl (X) curve shows the woofer

voice coil is offset by a fairly trivial 2.5mm rearward

(inward) from its rest position. This Bl curve is a very

symmetrical, broad and flat plateau with nearly

equal slopes in either direction. The displacement

at operating SPL near Xmax is nearly 0mm, so this

is about as good as it gets. Bl can decrease to

approximately 70% of its small signal value and the

driver will still function in a satisfactory manner, only

with an elevated level of distortion (about 20%).

Since this is not really perceivable, it’s really not a

subjective problem. The 70% of maximum Bl dis-

placement limit for the Stroker Pro is 36.3mm,

4.8mm more than the physical Xmax of 32mm.

This subwoofer’s Kms(x) or Stiffness of

Suspension curve (see Fig. 4) likewise exhibits very

good symmetry in both directions of travel. The off-

set is a negligible 0.5mm rearward at the rest posi-

tion and transitions to about 2mm of also not-so-

significant forward offset as it reaches the physical

Xmax of the woofer. The compliance limit for the

suspension when it drops to 50% of its rest value is

greater than 38.1mm. Both “limit” numbers, Bl and

compliance, represent the level at which distortion

climbs to 20%, which is a realistic criteria for sub-

woofers given the ear’s lack of sensitivity to distor-

tion at low frequencies.

Next I generated the T/S (Thiele/Small) parame-

ters for the Stroker subwoofer. Following my usual

speaker geek test procedures, I used a LinearX

LMS (Loudspeaker Measurement System) analyzer

and VIBox for measuring dynamic impedance

(impedance at different voltages). Testing is accom-

plished by performing a series of voltage and cur-

rent sweeps that are later converted to multiple

voltage impedance curves. With the driver clamped

to a rigid test stand, measurements were made at

1V, 3V, 6V, 10V, 15V, 20V, 30V and 40V. Rather than

use an added mass or test box method to find the

Vas (volume of air equal to the driver compliance) of

this driver, the measured weight of the cone body

(with 50% of the surround and 50% of the three

spiders removed) was used instead. This group of

multi-voltage impedance curves was copied into

the LEAP 5 software and the parameter model

derivation utility was used to produce the T/S para-

meters shown in the data chart. These numbers

were then used to generate the computer box sim-

ulation data provided in the Data Chart.

The Stroker Pro Thiele/Small parameters shown

in the Data Chart were used to produce computer

box simulations using the Leap 5 Enclosure Shop

software. The software was configured to simulate

the woofer’s low-frequency performance in the

same size boxes recommended in the Stroker Pro

manual, a 2.7ft3sealed box with no fill material and

a 3.0ft3ported box tuned to 36Hz with two 4” diam-

eter vents and also with no fill material. The LEAP 5

graph curves in Figure 3 show the SPL at 2.83 volts

(black curves) in half-space, 2.83 volts in an aver-

age 154ft3car compartment (blue curves), and at

the SPL at a power level required to get maximum

linear excursion (red curves, also half-space). The

sealed box curves are solid lines and the ported

enclosure curves are the dashed curves. The 2.83-

volt results produced an F3 of 43Hz for both box

types. Increasing the simulated input voltage for the

2.7ft3sealed box computer simulation to 150 volts

increased excursion to the Xmax +15% level and

pushed the SPL to a seriously devastating 126dB.

The 3.0ft3vented box computer simulation took

126 simulated volts to drive the Stroker Pro to just

beyond Xmax (Xmax + 15% or 36.8mm for the 15”

Stroker woofer) and resulted in an SPL of an

extremely loud 128dB! This monster definitely

Figure 3

Figure 4

Brand:Cerwin-Vega

Model:Stroker Pro 15

MSRP: $1,699.00

Warranty:1 year parts and labor

MECHANICAL SPECIFICATIONS

Weight 68.3 lbs.

Rear Mounting Clearance 9.75”

Woofer Magnet Dim. (dia. X ht. in mm) 260 x 20 x 2,

200 x 20

Voice Coil Diameter 100mm (3.93”)

Voice Coil Winding Layers 2x2 (two, two-layer coils)

MEASURED T/S PARAMETERS

Nominal Impedance (ohms) 4

Revc (ohms) 3.65 (both 1.83-ohm voice

coils connected in series)

Sd (cone area in square meters) 0.087

Bl (motor strength in Tesla Meters) 22.2

Vas (in liters): 40.0

Cms (micrometers per Newton): 37.4

Mms (grams): 468.1

Fs (Hz): 38.7

Qms: 4.47

Qes: 0.83

Qts:0.70

POWER AND EXCURSION DATA

Sensitivity (2.83V/1M in dB): 86.1 series/92.1 parallel

Continuous Power Handling (watts RMS): 2,500

Peak Power Handling (watts): 5,000

Xmax ([coil length – gap height]/2 in mm): 38.6

COMPUTER SIMULATION DATA

Enclosure size for simulation (cubic feet)

Sealed: 2.7 (0% fill)

Vented: 3.0 (0% fill) tuned to 36Kz

-3dB (F3) at 2.83V

Sealed: (Qtc=0.93): 43.0Hz

Vented: (Qtc=0.93): 43.0Hz

Voltage to achieve Xmax + 15%

Sealed: 150V

Vented: 126V

SPL at Xmax + 15%: (36.8mm)

Sealed: 126dB

Vented: 128dB

DATA CHART

needs to be

treated with respect.

The Stroker Pro is an amazing exercise in max-

imum potential, and while I don’t think this is every-

man’s subwoofer, for those who want to join the

Cerwin-Vega “loud and proud” tradition, it’s a very

serious piece of equipment. The engineering

integrity of the product is impressive and it has the

features required for producing extreme SPL in a

car (something to be very careful with if you value

your hearing). Given the ability to modify the sound

quality with the spider-adjusting tool, my guess is it

will come off well in the listening test. I’m as curious

as everyone else to know if a woofer that measures

this well sounds as good as it looks. —VD

SUBJECTIVE

The Cerwin-Vega Stroker Pro 15 arrived on my

doorstep in an Anvil-type case with steel flip-up

handles, just like those used to carry concert gear.

Opening the box I was blown away—the sub-

woofer itself looks fantastic. It’s tall, massive and

damn near 70 lbs.! But it’s the clear dust cap that

captures your attention, allowing you to view the

front spider and the carbon-fiber cone structure

beneath. Beautiful!

Once I got the sub out of its case (with a little

help), I quickly pulled out the instruction manual to

see what the power handling was. I damn near fell

off my stool when I read the 2,500 watts RMS

power figure and the mind-bending 5,000-watt

music rating! But this technological wonder doesn’t

come cheap. As a matter of fact, the Stroker Pro 15

is the most expensive subwoofer I have put through

its paces on these pages with a stag-

gering retail price of $1,699.00.

INSTALLATION

A quick call to Cerwin-Vega got me to

Bob Diamond, CV’s senior design engi-

neer. He recommended I use a sealed

enclosure with an internal volume of 2.7ft3

for the best overall sound quality. Jayson

Olson, master installer at Speaker Works,

was enlisted to build this special enclosure.

The enclosure would be constructed out of two

layers of 3/4” MDF with internal bracing to add

strength and minimize flexing of the enclosure

walls.

Connecting the wires was fairly simple. The Pro

15 uses heavy-duty metal blocks with Allen head

set screws to lock the wires in. The subwoofer’s

dual 2-ohm voice coils were wired in parallel for a

1-ohm load.

Mounting the subwoofer into the enclosure was

a bit tricky. First, you are dealing with a front panel

on your enclosure that is twice your regular thick-

ness and Cerwin-Vega supplies these threaded

steel plates and cap screw bolts to hold the Stroker

in. My guys predrilled the holes in the box’s face

and then glued the threaded steel plates into posi-

tion. Remember, this is a large and heavy enclosure

at an estimated 70 lbs. Combine that with the Pro

15 and we’re dealing with approximately 140 lbs.

It was time to see if we could fit this behemoth

into my Scorched-Earth Black Ford F-350 truck.

There was no way to place it in my normal location

on the floor, so we placed it carefully on the rear

seat. We tried the Stroker facing up and forward,

pointing left and right, but it did not sound correct.

With the enclosure on the rear seat, my seating

location was in a null point and the bass response

was pitiful at best. If I put my head up by the steer-

ing wheel, bass level increased exponentially. I

flipped the polarity of the Stroker, which did not

help, so it was back to the drawing board. Our

solution was to pull the rear seat out of the Ford.

This would allow us to get the Stroker into the loca-

tion that generally works best for most subwoofers

MUSIC SELECTION

Music Points Cerwin Vega

Artist Title Type Possible Stroker Pro 15

Tracy Chapman “Heaven’s Here on Earth” Folk/Rock 12.5 11

Diana Krall “Love Scenes” Jazz 12.5 10.5

10,000 Maniacs “Peace Train” Pop Rap 12.5 11

Usher “Intro” & “Yeah!” Pop Rap 12.5 10.5

Total 50 43

Ratings: 01 Poor 06 Average 12.5 Superior

CERWIN-VEGA

STROKER

PRO 15

in my truck.

The acoustic

match greatly

improved and

now we had a

great-sounding sub-

woofer (what I won’t do for

CA&E magazine, jeez!).

To power the Stroker Pro 15, I installed a Zapco

C2K-9.0XD amplifier to run it. The 9.0XD features a

24dB-per-octave crossover. With the 1-ohm

impedance of the driver, this Zapco will deliver

2,000 watts of power. The front half of my reference

speaker system consists of a pair of USD Audio B-

72Pro WaveGuide separates. I power these with a

Zapco C2K-6.0X amplifier at 150 watts per chan-

nel. The built-in highpass crossover filter was used

to block the bass to the component system. These

amps are fed via Zapco’s Symbilink balanced line

driver SLB-U. There are no other signal processors

in the signal path.

LISTENING

After four hours of break-in time I inserted a

favorite track—Tracy Chapman’s “Heaven’s Here

on Earth.” This subwoofer goes from very low fre-

quencies all the way up the scale smoothly without

drawing attention to itself. The bass imaging was

extremely good. The bass line always stayed up

front and did not pull to the rear of the vehicle at any

point. The bass drum was tight and the bass guitar

smooth and proper. That’s what’s so intriguing

about the Stroker Pro. There is nothing faint about

the looks of this subwoofer, indicating that it could

not be anything less than a brute, yet it had an artic-

ulate and delicate reproduction quality when the

music called for it. And, it had no trouble replicating

layered bass lines. Overall, each instrument stayed

well defined and taut.

On Diana Krall’s Love Scenes album, the stand-

up bass note changes were clear and well defined.

The note-to-note levels were equal and at no time

were they out of proportion to each other. The bass

plucks were very punchy and taut. This subwoofer

is no one-note wonder. It accurately reproduces the

frequency changes up and down the scale from the

string bass to the guitar and the drum kit. It was

very snappy and tight with excellent control. The

Pro 15 exhibited no blooming in the upper bass fre-

quencies like many of the other subs I have tested.

A great benefit to using a large diameter sub-

woofer like this one is how well it energizes the inte-

rior of your vehicle at really, really low frequencies.

Case in point, I had to remove my garage door

opener and sunglasses from their usual perch over-

head at far lower volume levels because they were

rattling almost instantly.

I played the 10,000 Maniacs remake of “Peace

Train” next. It opened with a bass drum kick that

was very low in frequency. Many subwoofers will do

an adequate job on this passage, but the Stroker

Pro 15 really got the job done. Each kick of the bass

drum was sharp, solid and deep. This track illus-

trated the performance gains that large format sub-

woofers have over smaller subwoofers.

Wrapping up, I put in Usher’s latest album and

cranked up the “Intro” track that leads into the track

“Yeah!” “Intro” uses mostly acoustic instruments

with super dynamics and at 0:23 secs into it, the

Stroker punched out a super tight, loud bass line

that was still very realistic sounding. On “Yeah!” it

simply laid down powerful, pumping bass that went

down to the lowest bass notes clearly. Even on this

repeating boomfest, the bass image stayed up

front, solid and fixed.

CONCLUSION

The more I listen to the Cerwin-Vega Stroker Pro

15, the more I like it. It is the best all-around large-

format subwoofer that I have tested by a large per-

centage. It did not matter what type of music I

played, the Stroker Pro 15 made it sound correct

and good. It does its job at all volume levels and

can handle fantastically high amounts of power.

This thing is very expensive, but its performance is

exceptional! Looks like I am going have to do some

begging to get a couple for our VW Beetle show

car. Hey, Mr. Diamond! We need to talk. —EH

SUBJECTIVE SCORE CHART

Points Cerwin-Vega

Possible Stroker Pro 15

Overall Sound Quality 50 45

Tonal Balance 10 08

Low-Frequency Extension 10 09

Clarity at Low Volume 10 08

Clarity at High Volume 10 09

Impact 10 09

Total Subjective Score 100 88

Ratings: 00 Poor 05 Average 10 Superior

CERWIN-VEGA

STROKER PRO 15

If you were to look at the Stroker’s motor in

conventional terms, and consider the distance

from the outside of one gap to the outside of the

other, a distance of 44mm, as one long gap and

figured Xmax based on this and the voice coil

length (remembering that Xmax is voice coil

length minus gap height and that number divided

by 2), which is 38mm for the Stroker Pro, then

the Xmax would only be a silly 3mm. However,

when you consider the dual 12mm gap aspect of

this motor, the Xmax number is really 32mm. And

if you consider the actual Bl curve of this monster,

it’s really more like 36.8mm, which is the manu-

facturer’s Xmax specification for this woofer.

There are a number of positive aspects to this

dual-gap technology, the biggest being the enor-

mous excursion potential. For a given coil length,

the dual gap motor will have 2.5 times more

Xmax than a conventional single gap motor. For

example, a 38mm voice-coil length with a single

12mm gap would have an Xmax of 14mm, com-

pared to the 32mm of the Cerwin-Vega dual-gap

woofer. The other benefit has to do with how

constant Bl is at high SPL levels. Many conven-

tional woofers have a more or less “bell” shaped

Bl curve, which means that as they start operat-

ing at maximum SPL levels, the Bl or motor drive

level will begin decreasing rapidly. This coupled

with the elevated voice coil temperatures mean

that the effective box Q and F3 numbers are gen-

erally higher than at low SPL levels. Effectively,

this suggests that the really low bass tends to go

away somewhat when you get extremely loud

with most subs. With the Stroker Pro, the Bl

curve is very flat and extended and the result is

that the motor does not exhibit as much box Q

and F3 shift as is normally experienced at high

SPL levels. While this extra high output stability

is primarily due to the flat Bl characteristics of the

Stroker Pro, some of this stability can be attrib-

uted to its excellent thermal cooling characteris-

tics.

SPL in car measurement at 2.83 volts, 1 meter – with

Bruel & Kjaer Type 2231 Level Meter set to Un-weighted,

SPL and Fast.

20Hz > 90.6dB

40Hz > 93.4dB

80Hz > 94.6dB

Max SPL > 136.3dB

The Max SPL measurement was taken using only 2,000

watts. At 5,000 watts, a gain of 3-5dB is conceivable.

XMAX AND DUAL-GAP TECHNOLOGY

For more information about reprints from Car Audio and Electronics, contact Wright’s Reprints at 877-652-5295

Cerwin Vega Stroker Pro 15 Users Manual CAEP 051000p068 73 CVSTROKER

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