By: Vance Dickason, Car Audio and Electronics Magazine

Original link here.

Earthquake Sound designs, manufactures, and markets high performance audio systems for use in home, automotive, and pro-sound audio systems. Located in a 60,000 square foot facility in Hayward, California, Earthquake exports to over 50 countries worldwide and in 2010 opened a European warehouse in Denmark, so suffice it to say, that Earthquake is a fairly substantial car audio manufacturer.

The company was founded in 1984 by Joseph J. Sahyoun, a music freak and Aerospace Engineer, which as the story goes, was unhappy with the existing loudspeaker technology and performance, and decided to put his advanced engineering knowledge to use.  Earthquake quickly created a name for itself in the car audio industry and became well known for its powerful subwoofers and amplifiers.  In 1997, using his existing expertise in the car audio industry, Joseph Sahyoun expanded his company to the home audio industry.

After reviewing the Ascendant Audio 18” monster 94 lb. SMD subwoofer the last go around, Ben emailed me and asked if I would do another subwoofer review. He didn’t really tell me what it was, just a 15” subwoofer from Earthquake Sound. So OK, another sub, no problem. Then it arrived. Holy s**t!!! What I got was the HoleeS 15, Earthquake’s 15” competition subwoofer, weighing in at 112lbs. No rest for the wicked, I guess.

Obviously, this is not your basic entry level car subwoofer, and at a MSRP of $2499, this design is really intended for the serious car audio competitor, or maybe just someone who wants the loudest woofer possible. Like all Earthquake subs, this is a beautifully crafted product, but let’s start with the frame. Given the total weight of 112lbs. that this frame has to support, this cast aluminum fame is a very substantial 9.5 inch deep 16 spoke design with a chromed finish. The HoleeS is intended for front mounting only and incorporates a chrome fitting over the eight hole mounting flange plus a rubber mounting gasket.

Like virtually all high-powered car subwoofers the frame is part of the convection cooling system. The area below the first spider mounting shelf (there are two mounting shelves for the four spiders) is very open and has twelve 95mmx35mm vents, each covered by chromed screen material. Additional vents are located at the junction of the frame and the 37mm thick chromed front plate (the HoleeS has more chrome than the front bumper of a ’57 Chevy!) with an additional sixteen 35mmx5mm vents that enhance airflow across the front plate and voice coil.

Horsepower for this gonzo subwoofer is provided by FEA (Finite Element Analysis) computer designed motor structure that includes four 19mm thick 275mm diameter stacked ferrite magnets sandwiched between the 38mm thick front plate and the chromed 20mm thick shaped T-yoke (a T-yoke combines the backplate and the polepiece to complete the magnetic circuit and focus all the magnetic energy in the front plate gap) with a 7mm deep bumpout to prevent the voice coil from “bottoming” (hitting the backplate on a rear stroke). Additional convection cooling is provided by a 20mm diameter pole vent and eight 9mm peripheral vents surrounding the pole vent and located on the bottom of the T-yoke bumpout. All in, this gives the HoleeS a total mounting depth of 14.25”.

The business end of the HoleeS (the cone assembly) is likewise rather feature laden. HoleeS’s cone is made from thick pressed pulp paper with a fiber fill material, making this cone extremely stiff. If you look at the photo, the cone looks like is made of metal, but this is actually a silver colored poly injected dust cap that covers the entire cone surface. This also adds stiffness to the entire cone assembly, plus contributes to the total chrome look of this subwoofer.

The voice coil attached to the cone assembly is also pretty amazing. This is an extremely long voice coil and measures 127mm (5”) long and 76mm (3”) in diameter. The voice coil former material is black anodized aluminum and wound with an 8 layer (two 4 layer 1 Ohm windings) flat copper wire coil. Flat wound voice coils (the wire cross section is rectangular rather than round) are often used in high powered handing pro sound drivers. While Earthquake has this coil wound by a company specializing in this type of design, Earthquake actually uses their own in-house proprietary “baking” process to glue the coil to the former in such a way that the usual problems with out-gassing and high temp bubbling do not occur. The two 4 layer coils are terminated to the proprietary and patented “PSP” fused terminal that will allow up to 8 gauge speaker wire to be connected to the HoleeS 15.

Given the 38mm gap height, the 127mm coil height results in an overhung format motor with a impressive 44.5mm Xmax number. This means the cone can travel up to 44.5mm either forward or to the rear and always have the same number of turns of voice coil wire in the gap area. In reality, since the magnetic field in the gap area extends above and below the gap for some small distrance, the coil can actually travel somewhat further and still deliver the same Bl (magnetic horsepower).

Suspension for the cone and massive voice coil is provided by a 40mm high and 40mm wide either drawn composite poly foam surround. Remaining compliance is provided by an array composed four 10” diameter linear black Nomex spiders, two located toward the top of the frame, and two located at the lower part of the frame. That pretty much describes what makes up the HoleeS 15, so now let’s look at the performance.

In the Lab

Part 1 of this objective measurement section consists of large signal analysis using the rather expensive (about $50,000 including all the software) but enormously effective Klippel analyzer followed by the LEAP 5 parameter creation and box analysis. Working with the Klippel analyzer (courtesy of Klippel GmbH), Pat Turmire, also a CAE reviewer and CEO of Red Rock Acoustics, ran the large signal analysis on the Earthquake 15” subwoofer and provided the BL(x) curve shown in Fig. 1. Please note that the curves in this review had to be done using a special simulation capability that the Klippel analyzer has built in to thesoftware. This was done because the 2500W amplifier Patrick was using did not have enough power to push the HoleeS to its limits and allow the analyzer to resolve Bl and compliance (to push this monster to its 44.5mm Xmax would take at least a 5kW amp!), however, these curves look reasonable and give us a good idea about the performance of the HoleeS 15 sub.

The black curve is the BL curve and shows the motor strength of the woofer as it moves in both directions outward from center rest position. The lighter curve is a displacement curve and if both curves were identical, the motor systems motion in and out of the frame would be perfectly symmetrical. When a sub is completely linear (“linear” indicates that the woofer motion exactly tracks the input signal perfectly with absolutely no distortion), the BL curve should be centered on the 0mm “rest” position (where the cone is positioned when there is no signal) and symmetrically decrease BL (as the number of turns in the gap decreases with outward motion) with the same slope in either direction 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 in the other, the result is increased levels of distortion at high operating levels.

The HoleeS BL(x) curve in Fig. 1 shows the woofer voice coil has no offset at its rest position, which is optimal, and only a small amount (as a percentage of the long voice coil) as it increases excursion. This BL curve has a moderately symmetrical broad shallow slope plateau with reasonably equal slopes in either direction, typical of high Xmax woofers. 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%). This is the amount of excursion where the Bl drops to 70% of the maximum at rest Bl. Unfortunately the Klippel analyzer was not able to resolve this subwoofer’s Kms(x) Stiffness of Suspension curve (again, due to insufficient watts), so I’m not going to display or discuss this part of the analysis. Please understand, this is nothing wrong with the Klippel analyzer, it's just that this woofer, like the previously reviewed Ascendant Audio SMD, require considerably more than 2500 Watts to drive the woofer to anywhere near its maximum excursion. Also, because we were not able to drive the HoleeS subwoofer hard enough, I cannot determine whether Bl or compliance contributes most to the 20% distortion level when Bl drops to 70%. However, I will say that from what I can determine from the Klippel Bl(x) curve, this woofer has sufficient headroom to produce volume levels adequate for dB Drag applications, and far in excess of safe SPL for music listening. This was verified by the LEAP 5 simulations below.

Next I measured the T/S (Thiele/Small) parameters for the Earthquake subwoofer. Using my typical speaker analysis procedures, I fired up a LinearX LMS (Loudspeaker Measurement System) analyzer and VIBox (VI for voltage/current) for measuring dynamic impedance (impedance at different voltage levels). Testing is done by performing a series of voltage and current sweeps that are later converted to multiple voltage impedance curves (this is just basic Ohms Law, where you divide Voltage by current and you get resistance, AC impedance in this case). After clamping the driver to a rigid test stand, measurements were made at 1V, 3V, 6V, 10V, 20V, 30Vand 40V. I chose to stop increasing voltage at 40V mostly because it just gets too loud, even with ear protectors, to be in the same room. As it was, the HoleeS in free-air looked perfectly linear at 40V and probably would have continued like that to beyond 70V or 80V and still been linear. Instead of using the standard added mass (delta mass) or test box method (delta compliance) 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, 50% of the spider, and 50% of the lead wire removed) was employed as this is significantly more accurate. The set of multi-voltage impedance curves was then transferred from LMS into the LEAP 5 CAD program and used to create the T/S parameters shown in the Data Chart. The calculated driver parameters were then used to create the computer enclosure simulations, with the results also listed in the Data Chart.

DATA CHART

Brand Earthquake Sound
Model HoleeS 15
MSRP $2499.00
Warranty 30 days parts and labor

Mechanical Specifications
Weight 112 lbs.
Rear Mounting Clearance 14.25”
Woofer Magnet Dim. (dia. x ht. In mm) 275x19x4


Voice Coil Diameter 76mm (3”)
Voice Coil Winding Layers 8 (two 4 layer)
Measured T/S Parameters
Nominal Impedance (Ohms), coils in series 2
Revc (Ohms) 2.15
Sd (cone area in sq. meters) 0.0894

Bl (motor strength in Tesla Meters) 17.2
Vas (in liters) 124.2
Cms (micrometers per Newton) 129.5
Mms (grams) 398.5
Fs (Hz) 22.2
Qms 5.79
Qes 0.40
Qts 0.38

Power and Excursion Data
Sensitivity (2.83V/1M in dB) 87.1
Continuous Power Handling (watts RMS) 7000
Peak Power Handling (watts) 15,000
Xmax ([coil length – gap height]/2 in mm) 44.5

Computer Simulation Data
Enclosure size for simulation (cubic feet)
Vented 1 5.4 (no fill) tuned to 70Hz
Vented 2 5.4 (no fill) tuned to 43Hz
-3dB (F3) at 2.83V
Vented 1 67.8Hz
Vented 2 37.9Hz
Voltage to achieve Xmax + 15%
Vented 1 115V
Vented 2 120V
SPL at Xmax + 15% (51.2mm)
Vented 1 136.5dB
Vented 2 136.0dB

Box simulations were generated for two vented type enclosure volumes that were specifically recommended by Earthquake Sound for use in dB Drag contests (see Fig. 2). Both enclosures were 5.4 cubic feet, but the one intended for dB Drags was tuned higher to 70Hz in order to produce a peak in the response, so that when you pulse the speaker with a high voltage, you get maximum SPL, which of course is what dB Drag’s all about. The other box has a lower tuning which produced a lower F3 and would be more satisfactory for music listening. The LEAP 5 graph curves in Fig. 2 shows the SPL at 2.83V with the HoleeS mounted in SUV sized 250-cubic-foot car compartment, about the size Chevy Tahoe. This resulted in a F3 of about 67.8Hz for the 5.4ft3 box tuned for dB Drag competition and a –3dB (same thing as F3) of 37.9Hz for the 5.4ft3 reflex enclosure (vented box) tuned to 43Hz for music listening. I also included a 31Hz tuning example which I think might even be more satisfactory for music listening and has an F3 of 24.5Hz. Increasing the simulated input voltage for the computer simulation to 115V for the dB Drag vented enclosures pushed the sub’s excursion to Xmax plus 15% (51.2mm for the HoleeS 15) and increased the driver output to a really loud 136.5dB. For the same box tuned to the lower 43Hz frequency, 120V resulted in about the same SPL, 136dB.

The last objective test I performed on the Earthquake Sound subwoofer was to measure its distortion using the Listen Inc. SoundCheck analyzer. The setup for this test is to mount with woofer in free-air rigidly clamped to a test stand, and adjust the SPL using a noise stimulus to 94dB at 1 meter. I then put the microphone 10cm from the dust cap so that the ratio of direct to reflected sound is sufficiently high that the result is pretty much just the inherent distortion of the woofer. Fig. 3 shows the result. As you can see, while the woofer develops some fairly high distortion at this SPL above 100Hz, but it really doesn’t matter since the response will be band limited by an electronic low-pass filter, probably 24dB/octave at 80Hz-100Hz. At frequencies below that, the HoleeS looks well behaved. Again, you need to remember that your ear is very insensitive to distortion at 100Hz or lower.

By: Adam Rayner, Talk Audio

Original link here.

In a market that sees a slew of shallow styled subwoofers, Earthquake Sound have some corkers. Not for them the choice of a ten OR a twelve, no, they start with paired ‘woofer-designed’ sixes for those really skinny places you want to squeeze some bass out of, go up via a shallow eight and then also sell a mighty fifteen inch woofer above the ten and twelve sizes that is just so discoidal, it’s bonkers! Here’s a rip from their site. The coolest thing is the BMW direct-replacement eight:

Earthquake Sound Corporation is the original inventor of the Shallow Woofer System (SWS) that produces a lot of bass from a small space. Protected by three U.S. Patents, Earthquake Sound manufactures the SWS woofers in 5 different sizes (6.5in, 8in, 10in, 12in and 15in) with 4Ohm impedance.

Our most popular size is the SWS-8 due to the fact that it is designed to replace the BMW factory speakers that are located under the front seats. There is no modification required. Simply remove the seats and replace the factory woofers with the exact-fitting SWS-8 woofers to improve the sound quality of your mobile audio.

Since many OEM amplifiers are now coming with a 2-Ohm impedance, Earthquake Sound released the SWS-8Xi that has a 2-Ohm voice coil.

In addition to BMW cars, the SWS series are the perfect BASS solution for any car. Many factories are now using woofers in small areas. To improve your bass, simply replace the factory speakers with the SWS woofers.

Low profile mount for placement anywhere
2-Ohm impedance
Inverted style cone design for maximum excursion in shallow mount applications
High temperature voice with heat-sink attachment
NOMEX/ROMEX spider assembly
Protected by 3 U.S. patents
Aluminium Bobbin