Cerwin-Vega stroker Pro 15 User Manual

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MOBILE AUDIO

USA: Cerwin-Vega!, Inc. • 9340 De Soto Ave. • Chatsworth, CA • 91311 ©2005 Cerwin-Vega

Phone: [phone] • Fax: [phone] • Cerwin-Vega! is a division of the Stanton Group

Cerwin-Vega! reserves the right to make changes to product specifications and design at any time

CERWIN-VEGA

STROKER

TEXT: VANCE DICKASON &

ERIC HOLDAWAY

PHOTOS: COURTESY OF MANUFACTURER

PRO 15

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 sub­woofers I have r

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 pr

The Stroker Pro cast aluminum frame acts as

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

eviewed to date, the Stroker Pro

oduct’s technology.

A FRONT-RUNNER FOR

SOUND QUALITY AND SPL

highly effective Faraday

shield or shorting ring (a new

patent-pending trick). The cut­away drawing (Fig. 1) shows that this woofer not
only has two separate magnets (actually, the lower
magnet is two magnets stacked together, so tech­nically three magnets), but also two gaps, a tech­nology 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
turn the frame’s inside diameter upward to form a
shorting ring.

, but

MORE

THAN A ONE

NOTE WONDER —

In addition to attenuating nasty eddy currents
produced by the woofer motor and lowering distor­tion, a large shorting ring also reduces motor tem­perature 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

-

Figure 1

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 T­yoke. Lastly, an aluminum-sleeved 1 3/4” diameter
pole vent powered by the large, moving clear plas­tic 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 con­ventional underhung voice coil motor. In the con­ventional motor, as the short coil rides out of a sin­gle large gap in either dir

ection, 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 Str

oker Pro dual-gap motor, the

situation is more like hav­ing 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 num­ber of voice coil turns of
wire in the gap stays con­stant. 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 spi­der bias system for the top or third spider. All the
original Stroker woofers
had this adjustment sys­tem; however, it was set
at the factory for maxi­mum linearity. Stroker
owners found that tweak­ing 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-cen­tered toward the front of
the gap area creates high­er amounts of even­ordered 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 percep­tion 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 per­formance 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 poly­carbonate 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-pend­ing solution is SdMaxx (Sd is an engineering abbre­viation 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 diam­eter and area. The other part of the SdMaxx system
is an attachment design that allows the entire cone

e 2

Figur

Figure 3

assembly to be quickly removed and replaced.

The rest of the assembly consists of the three­polycotton/conex blend spiders. The two lower spi­ders (mounted inverted to each other to cancel out
some of the non-linear behavior) are 8 1/2” in diam­eter 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 direc­tion. 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 termi­nal 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 analy­sis. Using the Klippel analyzer (on loan from Klippel
GmbH), Pat Turnmire,
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 symmetri­cal. 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 lev­els 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 of
(inward) from its rest position. This Bl curve is a very

CA&E reviewer and CEO of

fset by a fairly trivial 2.5mm rearward

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 dis­placement 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 off­set is a negligible 0.5mm rearward at the rest posi­tion and transitions to about 2mm of also not-so­significant 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 sub­woofers given the ear’s lack of sensitivity to distor­tion 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 accom­plished 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

Figure 4

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 para­meters shown in the data chart. These numbers
were then used to generate the computer box sim­ulation data provided in the Data Chart.

The Stroker Pro Thiele/Small parameters shown

in the Data Chart wer

e 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

3

manual, a 2.7ft

sealed box with no fill material and
a 3.0ft3ported box tuned to 36Hz with two 4” diam­eter 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 aver­age 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 2.83­volt 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

DATA CHART

rand:Cerwin-Vega

B

odel:Stroker Pro 15

M
MSRP: $1,699.00

arranty:1 year parts and labor

W

MECHANICAL SPECIFICATIONS

Weight
Rear Mounting Clearance 9.75”
Woofer Magnet Dim. (dia. X ht. in mm) 260 x 20 x 2,

-

Voice Coil Diameter 100mm (3.93”)
Voice Coil Winding Layers 2x2 (two, two-layer coils)

MEASURED T/S PARAMETERS

Nominal Impedance
Revc (ohms) 3.65 (both 1.83-ohm voice

Sd (cone area in square meters)
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:

POWER AND EXCURSION DATA

Sensitivity
Continuous P
Peak Power Handling (watts): 5,000
Xmax ([coil length – gap height]/2 in mm): 38.6

COMPUTER SIMULA

Enclosure size for simulation (cubic feet)

Sealed: 2.7 (0% fill)
Vented: 3.0 (0% fill) tuned to 36Kz

-3dB (F3) at 2.83V

(Qtc=0.93):

Sealed:
Vented: (Qtc=0.93): 43.0Hz

Voltage to achieve Xmax + 15%

Sealed:
Vented: 126V

SPL at Xmax + 15%: (36.8mm)

Sealed: 126dB

ented:

V

(ohms) 4

coils connected in series)

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

ower Handling

TION D

ATA

(wa

tts RMS):

68.3 lbs.

200 x 20

0.087

0.70

2,500

43.0Hz

150V

128dB

SUBJECTIVE

needs to be

treated with respect.

The Stroker Pro is an amazing exercise in max­imum potential, and while I don’t think this is every­man’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

MUSIC SELECTION

itle

ge

12.5 Superior

T

s Here on Earth” Folk/Rock 12.5 11

ven’

“Hea

& “Yeah!” Pop Rap 12.5 10.5

“Intro”

Artist

pman

y Cha

rac

T

Diana Krall “Love Scenes” Jazz 12.5 10.5

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

Usher

Total 50 43

Ratings: 01 P

oor

06 Avera

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 sub­woofer 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

Music Points Cerwin Vega

ype

T

ossible Stroker Pro 15

P

CERWIN-VEGA

STROKER

PRO 15

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 2.7ft

for the best overall sound quality. Jayson

Olson, master installer at Speaker W

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 thick­ness 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 posi­tion. 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 steer­ing wheel, bass level incr
flipped the polarity of the Stroker, which did not
help, so it was back to the drawing board. Our
solution was to pull the r
This would allow us to get the Stroker into the loca­tion that generally works best for most subwoofers

eased exponentially. I

ear seat out of the Ford.

orks,

3

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

SUBJECTIVE SCORE CHART

Points Cerwin-Vega

Possible Stroker Pro 15

verall Sound Quality 50 45

O

Tonal Balance 10 08

equency Extension 10 09

Low-Fr

larity at Low Volume 10 08

C

Clarity at High Volume 10 09

Impact 10 09

Total Subjective Score 100 88

Ratings: 00 Poor 05 Average 10 Superior

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 B­72Pro WaveGuide separates. I power these with a
Zapco C2K-6.0X amplifier at 150 watts per chan­nel. 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 fre­quencies 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

SPL in car measurement at 2.83 volts, 1 meter – with
Bruel & Kjaer
SPL and Fast.

20Hz > 90.6dB

40Hz > 93.4dB

80Hz >

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.

ype 2231 Level Meter set to Un-weighted,

T

94.6dB

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 artic­ulate 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
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 fre­quencies like many of the other subs I have tested.

A great benefit to using a large diameter sub­woofer like this one is how well it energizes the inte­rior of your vehicle at really, really low frequencies.
Case in point, I had to remove my garage door
opener and sunglasses fr
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

Love Scenes album, the stand-

om their usual perch over-

Pro 15 really got the job done. Each kick of the bass
drum was sharp, solid and deep. This track illus­trated the performance gains that large format sub­woofers 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 large­format subwoofer that I have tested by a large per­centage. 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

XMAX AND DUAL-GAP TECHNOLOGY

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 Str
the Xmax would only be a silly 3mm. However,
when you consider the dual 12mm gap aspect of

, the Xmax number is r

this motor
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 enor­mous 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

oker Pro, then

eally 32mm. And

woofer. The other benefit has to do with how
constant Bl is at high SPL levels. Many conven­tional woofers have a more or less “bell” shaped
Bl curve, which means that as they start operat­ing at maximum SPL levels, the Bl or motor drive
level will begin decreasing rapidly. This coupled
with the elevated voice coil temperatures mean

fective box Q and F3 numbers are gen-

that the ef
erally higher than at low SPL levels. Effectively,
this suggests that the really low bass tends to go
away somewhat when you get extr

,

with most subs. W
curve is very flat and extended and the r
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 attrib­uted to its excellent thermal cooling characteris­tics.

-

ith the Str

oker Pro, the Bl

emely loud

esult is

Posted with permission from the September 2005 issue of Car Audio and Electronics ® www.caraudiomag.com. Copyright 2005, PRIMEDIA Inc. All rights reserved.

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