Porsche 928 Ground Zero Premium Speaker Upgrade 1983-1995 | Restomod

A beautiful upgrade for your Porsche 928's audio system, allowing you to enjoy your drive even more. Say goodbye to those crackling speakers with limited frequency response and low power, and treat yourself to this upgrade. Everything fits in the original positions and consists of high-quality speakers from Ground Zero, a German specialist in car audio systems. 

The old original speakers had a power rating of just 14W (door) to 25 watts (bass). Due to age, the paper cones are often torn. It's time to replace them. We did all the work of finding a replacement set and checking the fit, spending almost a year on it. 

Modern alternative speakers often have their own grilles, which do not fit the classic interior of the 928. We therefore set out to assemble an attractive set of speakers with high-quality drivers and developed a mounting kit based on this, with grilles that closely follow the original design and therefore fit well in the interior of the Porsche 928.

The system has a modular design. You can start with just the door speakers and bass speakers and later expand it with a 4-channel power amplifier and/or one of the active subwoofer options.

Background information about this design.

A few years ago, we designed replacement rings for the door speakers and also reproduced the housing of the bass set. We always wanted to offer an attractive replacement grille as well. We still have a large box full of prototypes, none of which looked right. Eventually, we succeeded and continued by looking for other speakers, for which we developed a mounting kit that matched the original as closely as possible.

There are two versions of the speaker rings that hold the grilles: a threaded ring (1983 - 1988) and, later, a ring that clipped into place (1989-1995). With both systems, the ring can sometimes break during removal. Due to production issues, we ultimately developed an improved system for mounting the rings for this product. Therefore, you must always use our new rings when purchasing this set.

Choose your configuration

• Door set: 4 Ground Zero speakers, 60 W RMS / 100 W max., for both doors
• Bass set: 2 Ground Zero speakers, 100 W RMS / 150 W, for behind the seats
• Power amplifier: compact Ground Zero 4-channel amplifier, 4 × 65 W RMS at 4 Ω
• Seat subwoofer: compact active subwoofer, 120 W RMS, placed separately behind the passenger seat
• Separate subwoofer: active 8-inch subwoofer, 250 W RMS, with quick connect in the luggage compartment 

All components can be ordered and added separately.

Benefits of this upgrade

• High-quality Ground Zero speakers
• Specially assembled for the Porsche 928
• Installation in the original speaker positions
• Precisely fitting mounting plates
• Attractive speaker grilles
• Grille mounting rings and screws included
• Expandable with a power amplifier
• Choice of two active subwoofers
• System can be built up step by step

Ground Zero door set

The door set uses Ground Zero 2-way component speakers: 2 tweeters and 2 midrange drivers.

• Model: Porsche 928
• Model years: 1983-1995
• Position: both doors
• Number of speakers: 2 + 2

Mounting kit consists of

• Precisely fitting mounting plate
• Attractive speaker grille
• Grille mounting ring
• Matching screws

Key speaker specifications:

• Diameter: 100 mm / 4 inches
• Power: 60 W RMS / 100 W max.
• Impedance: 4 Ω
• Sensitivity: 89 dB
• Frequency response: 70 Hz-20 kHz
• Tweeter: 19 mm silk dome
• Mounting depth: 30 mm
• Ground Zero GZIC 400FX

Thanks to its shallow mounting depth, this speaker is very suitable for the limited space available in the Porsche 928 doors.

Ground Zero bass set

The bass set is a 2-way component system: 2 bass speakers and 2 tweeters. Their higher power handling and sensitivity make these speakers a good complement to the door speakers. When used in a 6-speaker system, the second tweeter can be omitted because there is no space for it. 

Bass set (square version)

• Model: Porsche 928
• Model years: 1983-1988
• Position: behind the front seats
• Number of speakers: 2 + 2
• Version: for the square original speaker housings

Mounting kit consists of

• Precisely fitting mounting plate
• Attractive speaker grille
• Matching screws
• Reuses the existing housing

Key speaker specifications:

• Diameter: 165 mm / 6.5 inches
• Power: 100 W RMS / 150 W max.
• Impedance: 3 Ω
• Sensitivity: 91 dB
• Frequency response: 75 Hz-20 kHz
• Mounting depth: 65 mm
• Ground Zero: GZIC 165.2HE

Bass set (round version)

From 1989 onward, Porsche developed a round speaker for the bass set instead of the square speaker version. A splitter was used for the 4 additional speakers in the rear panel. We are still developing this round mounting kit. The bass speaker used will be the same as in the square version.

10-speaker system

Porsche 928 models from 1988 onward may have the original 10-speaker system. Therefore, check in advance which version is installed in the car. This version always has the round bass speaker housing, which we are still developing.

Power amplifier

The speakers can be used without a power amplifier. But for more power, the system can be expanded with a compact Ground Zero 4-channel power amplifier. It provides the speakers with more power, dynamics, and control than when they are driven only by the radio, simply because a radio always has less power than a power amplifier. Ground Zero describes this model as a compact Plug & Play 4-channel ISO amplifier. 

This is especially worthwhile when using the system at higher volume or when you want to build a more complete audio setup. Thanks to its small size, it fits in several positions: behind the radio, under the cover next to the passenger seat, or even in the storage compartment between the rear seats. 

Key specifications:

• Channels: 4
• Power: 4 × 65 W RMS at 4 Ω
• Power: 4 × 75 W RMS at 2 Ω
• Bridged: 2 × 150 W RMS at 4 Ω
• Technology: Class D
• Frequency response: 10 Hz-22 kHz
• High-level input: yes
• Auto-on: yes
• Plug & Play ISO connection
• Dimensions: approx. 82 × 185 × 40 mm
• Model: GZRA 65.4-MICRO

Subwoofers

For extra low end (deep bass), you can choose from:

• a compact active subwoofer (120W RMS) that can be placed behind the passenger seat
• an even more powerful separate active 8-inch subwoofer (250W RMS) for the luggage compartment

A subwoofer primarily supplements the low-frequency range, which the limited dimensions of the original speakers make difficult to reproduce fully.

A subwoofer is connected to the radio's Pre-amp Out output, or, if there is no such output, to the speaker outputs, and also has its own power cable.

Ground Zero GZCS SW-800A behind the seat:

• Diameter: 200 mm / 8 inches
• Power: 120 W RMS / 180 W max.
• Frequency response: 30-150 Hz
• Low-pass filter: 45-150 Hz
• High-level input: yes
• Auto-on: yes
• Phase control: 0° / 180°
• Housing: cast aluminum
• Dimensions: 315 × 235 × 80 mm
• Bass remote: included

Ground Zero GZCS 20SUB-ACT in the luggage compartment:

• Diameter: 200 mm / 8 inches
• Power: 250 W RMS / 340 W max.
• Low-pass filter: 50-150 Hz
• High-level input: yes
• Phase control: 0° / 180°
• Operating voltage: 9-16 V
• Cone: aluminum
• Housing: sealed wooden enclosure
• Dimensions: 270 × 393 × 160 mm
• Quick-release power connector

Frequently asked questions

Does the door set fit all Porsche 928 models?

The door set is suitable for Porsche 928 models from 1983 through 1995.

Which model years is the bass set suitable for?

The bass set is suitable for Porsche 928 models from 1983 through 1988 with the square rear speaker housings.

Is mounting hardware included?

Yes. The speaker mounting kit consists of a precisely fitting mounting plate, attractive speaker grille, grille mounting ring, and matching screws.

Do I need a power amplifier?

No. The speakers can also be used without a separate power amplifier.

Can I expand the system later?

Yes. The power amplifier and subwoofer can be added later.

Will the interior retain its original appearance?

Yes. The speakers are installed in the original positions, and the grilles provide a neat Restomod look.