Inakustik S25 BiWire Jumpers Review: Replacing the Weakest Link in Your Speaker Connection

Welcome to our Inakustik S25 BiWire Jumpers Review. If you own a pair of loudspeakers with bi-wire terminals, there is a good chance a small, overlooked component is holding your system back. It isn't your amplifier, your source or your speaker cable. It's the humble stamped metal plate bridging the high-frequency and low-frequency binding posts on the back of your speakers. In this review we look at how in-akustik's S25 BiWire Jumpers replace that compromise with a properly engineered, Made in Germany connection built on the technology of the respected S25 speaker cable series, and why this is one of the most sensible, cost-effective upgrades an audiophile can make.

Why the Bridge Matters: Damping Factor and the Weakest Link

For a loudspeaker to sound its best, the amplifier must keep the drivers firmly under control. That means accelerating the cones with precision and, just as importantly, bringing them to a controlled stop with equal authority. The measure of this control is the amplifier's damping factor.

Here is the catch that many enthusiasts miss: the damping factor quoted on an amplifier's spec sheet is not what your drivers actually see. Every element in the series path between the output stage and the voice coil adds resistance, and each of those resistances erodes the effective damping at the cone. Your speaker cable plays a part, the terminations play a part, and on a bi-wire speaker being driven from a single pair of amplifier outputs, the jumper bridge plays a part too.

In the majority of cases, that bridge is a simple stamped metal plate. It is an inexpensive piece of hardware with poor electrical properties and high contact resistance, designed for manufacturing economy rather than audio performance. In in-akustik's words, it actively limits the damping factor that your amplifier and speaker cable have worked together to achieve. You may have invested carefully in a well-matched amplifier and quality cable, only to have the signal funnelled through a sliver of plated metal for the final few centimetres. The S25 BiWire Jumper removes that weak point entirely.

"For many speakers, the standard bi-wiring bridges — often simple stamped metal plates with poor electrical properties — are the weakest link in the signal path. The S25 BiWire Jumpers replace this weak point with a high-quality connection based on the technologies and materials of the S25 cable series." — in-akustik

S25 Cable Technology, Distilled into 150mm

Rather than reinventing the wheel, in-akustik has taken the construction principles of its S25 speaker cable series, one of its most respected high-fidelity ranges, and applied them to the specific demands of a speaker bridge. This is a genuine piece of loudspeaker cable engineering, simply cut to a purposeful 150mm length and terminated for binding post duty.

4-Fold Multicore Architecture

At the heart of each jumper is a 4-fold multicore conductor structure with a total cross-section of 2 × 5.0mm². This is achieved through four individual 2.5mm² conductors, each comprising 50 × 0.25mm strands of high-purity OFC copper. That is a generous amount of copper for such a short run, and it is precisely what you want in a link whose sole job is to present the lowest possible series resistance between terminals.

The multicore approach also addresses the skin effect, the tendency of higher-frequency signals to travel towards the surface of a conductor rather than through its core. By dividing the conductor into multiple fine-stranded cores, in-akustik minimises this effect, ensuring the delicate high-frequency information destined for the tweeter terminals arrives with the same precision and completeness as the low-frequency energy delivered to the bass drivers. The intended result is a more detailed, more controlled and more dynamically coherent presentation across the full frequency range.

High-Purity OFC Copper and PE Dielectric

The conductors are made from high-purity OFC (Oxygen-Free Copper), chosen to minimise contact resistance and deliver a permanently stable electrical connection that does not degrade over time. The insulation is PE (polyethylene), a well-regarded dielectric in audio cable design. The finished cable measures 8.5mm in diameter and is dressed in an attractive dark blue jacket, with red and black colour coding to keep polarity straightforward.

Terminations Built Like a Precision Instrument

A great conductor is only as good as its termination, and this is where in-akustik's attention to detail really shines.

• Gold-plated brass cable lugs: The spade connectors are made from brass with gold plating. Gold's exceptional corrosion resistance means contact quality remains consistent for the life of the speaker, with no oxidation creeping in to raise resistance over the years.
• Pressure-grouted contacts at 1.5 tonnes: The contacts are assembled under 1.5 tonnes of pressure, the same connector assembly specification used on in-akustik's NF-404 Micro AIR interconnects. This creates a mechanically robust, electrically stable termination with the lowest possible contact resistance between conductor and lug.
• Stepped 6/8mm spade forks: The stepped fork design accommodates a wide range of binding post sizes, giving you a secure, high-contact-area fit on a broad variety of loudspeakers.

Quality control is equally serious. Every S25 BiWire Jumper undergoes individual continuity and short-circuit testing of all conductors before it leaves in-akustik's factory in Germany. That's the sort of assurance you want from something that will sit permanently at your speaker terminals.

Unsure whether the stepped 6/8mm spades will suit your speaker's binding posts? Give our team a call on 1300 308 711 and we'll happily talk you through compatibility.

Not Bi-Wiring? You'll Still Benefit

Here is the part that makes the S25 BiWire Jumper relevant to so many listeners. You do not need to be running true bi-wire speaker cables to benefit. In fact, the single-wire system is exactly where the jumper earns its keep, because that is where the factory bridge sits directly in the signal path to one set of drivers.

When you connect a single run of speaker cable to one pair of terminals, the signal for the other section of the crossover must pass through the bridge. Swap a stamped plate for the S25 BiWire Jumper and that path gains better electrical properties, lower contact resistance, more controlled signal distribution and a construction built for audio performance. in-akustik describes this as a meaningful and immediately audible improvement over the standard metal plates supplied with most speakers.

What should you listen for? Given the design goals, the areas to focus on are the qualities most influenced by driver control and coherent signal delivery: tighter, better-defined bass with cleaner stops and starts, fine high-frequency detail that integrates seamlessly with the midrange and low end, and a sense of dynamic ease when the music swells. Put on a well-recorded track with a walking double bass or a crisp drum kit and pay attention to how decisively notes begin and end.

Who Are the Inakustik S25 BiWire Jumpers For?

• Owners of bi-wire speakers running single cables: The most obvious candidate. If your speakers came with stamped plates or flimsy links, this is a direct, targeted upgrade.
• Listeners who have invested in quality speaker cable: You have already paid for low resistance and quality terminations along the cable run. The S25 jumpers ensure that investment isn't undone at the final junction.
• Enthusiasts chasing amplifier control: If you care about damping, bass grip and dynamic precision, minimising series resistance at the terminals is fundamental good practice.
• Anyone seeking a low-risk, high-value tweak: No new components to match, no system rebalancing, just a better connection in the place that needs it most.
• in-akustik and S25 cable owners: Pairing S25 cable with S25-based jumpers creates a consistent conductor philosophy right up to the crossover.

The 4-pack format makes sense for a typical stereo setup, giving you a red and black bridge for each speaker. If you're running a more elaborate system, or want to plan cable and jumper choices together, reach out to us at sales@theaudiotailor.com.au and we'll help map out the best approach.

Installation Tips

Installing the S25 BiWire Jumpers is refreshingly simple:

1. Switch off and, ideally, unplug your amplifier before touching the speaker terminals.
2. Unscrew the binding posts and remove the factory stamped bridges.
3. Fit the S25 jumpers, red to red (positive) and black to black (negative), using the stepped spade forks to suit your posts.
4. Tighten the binding posts firmly for maximum contact pressure, without overtightening.
5. Connect your speaker cable, power up and enjoy.

A popular question we hear is whether to connect your speaker cable to the high-frequency or low-frequency terminals when using jumpers. The answer can depend on your speaker and system, and it's well worth experimenting. Our team is always happy to share insights from experience, so feel free to call us on 1300 308 711.

Specifications at a Glance

Application	HiFi bi-wire jumper / speaker bridge
Quality	Exzellenz
Technology	Multicore
Design	4-fold multicore
Conductor Design	50 × 0.25mm per conductor
Cross-Section	2 × 5mm² (4 × 2.5mm²)
Conductor Material	High-purity OFC copper
Dielectric	PE
Cable Diameter	8.5mm
Length	150mm
Connector	Cable lug (spade)
Fork Width	Stepped 6/8mm
Contact Material	Brass
Contact Enhancement	Gold-plated
Connector Assembly	Pressure-grouted contacts (1.5 tonnes)
Colour Coding	Red / Black
Colour	Dark blue
Individual Inspection	Continuity and short-circuit testing — all conductors
Conformity	CE, REACH, RoHS
Made in Germany	Yes

Pros and Cons

Pros

• Replaces the stamped metal bridging plates that limit effective damping factor
• Built on in-akustik's respected S25 speaker cable series technology
• Generous 2 × 5.0mm² cross-section via 4-fold multicore OFC construction
• Multicore design minimises skin effect for detailed, coherent high-frequency delivery
• Gold-plated brass spades for long-term corrosion resistance
• Pressure-grouted contacts assembled at 1.5 tonnes for minimal contact resistance
• Stepped 6/8mm forks fit a wide range of binding posts
• Every conductor individually tested for continuity and short circuits
• Beneficial with or without true bi-wire speaker cables
• Made in Germany, CE, REACH and RoHS compliant
• Simple, tool-free installation in minutes
• Handsome dark blue jacket with clear red and black polarity coding

Cons

• Only relevant for speakers with bi-wire terminals, though that covers a huge number of models
• Once you hear the difference, you may start eyeing up an S25 speaker cable upgrade too

The Final Word: Small Upgrade, Big Return on Control

It's easy to overlook a 150mm bridge between two binding posts, yet it sits at one of the most critical junctions in your entire system. The in-akustik S25 BiWire Jumpers take that forgotten compromise and replace it with genuine cable engineering: 4-fold multicore OFC conductors, a substantial cross-section, gold-plated spades, 1.5-tonne pressure-grouted contacts and individual factory testing in Germany. Whether you bi-wire or not, it's a logical, elegant way to give your amplifier the control over your speakers it was always capable of.

As in-akustik puts it: "A simple upgrade. An immediate improvement." We couldn't agree more.

Ready to remove the weakest link? Explore the Inakustik S25 BiWire Jumpers on our website, or have a chat with Gabby, Nathan, Vaughan or Stuart on 1300 308 711 or sales@theaudiotailor.com.au. As Sound+Image's HiFi Retailer of the Year in 2021 and 2022, our team loves helping listeners across Australia fine-tune their systems, and we ship nationwide from Brisbane.