In this guide: The short answer · What a processor does · Use the maker’s presets · Comparison table · Linea Research · Martin Audio DX · NEXO DTD · Install DSP · Amplifier gain and limiters · Popular picks · FAQ

The short answer

A passive speaker has no brain. A loudspeaker processor (also called a system controller or loudspeaker management system) sits between the mixer and the amplifiers and does the jobs a powered speaker does internally: it splits the signal between tops and subs, lines up the timing, corrects the response and limits the level so the drivers survive.

Pick the processor that carries the speaker maker’s presets for your boxes, with enough outputs for every amplifier channel you will drive:

• Martin Audio speakers: a DX0.4 or DX0.6 for most BlacklineX and CDD systems, or the DX4.0 when you need four inputs, eight outputs and AES3 (the DX4.0-DANTE if you also need Dante).
• NEXO speakers: a NEXO DTD with amplifiers of your choice (NEXO lists a DTD with its DTDAMP amplifier as an optional powering solution on its P+ and ePS datasheets), or a NEXO NXAMP, which combines the amplifier and controller and is NEXO’s recommended powering for P+ and L-series systems.
• Mixed brands, hire stock or a system you want to tune and network seriously: a Linea Research ASC48 or one of the smaller NSC models.
• Installed buildings with zones, paging and control panels: an install matrix such as the Allen & Heath AHM or BSS Soundweb London, which can also handle speaker processing.

If your speakers are powered, you usually do not need any of this: the processing is already in the box. Our Blackline XP vs BlacklineX guide covers the powered-or-passive decision itself.

What a loudspeaker processor does

Martin Audio’s description of its DX0.4 is a good summary of the whole category: routing from inputs to outputs, equalisation, input and output delay “to time align components in a system”, crossover filters, and “a two-stage limiter; program and peak”, which “will protect your speakers from damage due to excessive power”. Each of those does a distinct job.

Crossover

The crossover sends low frequencies to the subs and takes them away from the tops. That lets the tops play louder and cleaner. NEXO puts the trade-off plainly in its DTD manual: running the mains in crossover mode “will increase maximum output level of the Main speaker while producing less low end”. In a bi-amped box, the crossover also splits the signal between the low and high drivers of the same cabinet, each on its own amplifier channel.

Filter types and slopes vary. The Martin Audio DX0.4 and DX0.6 offer Bessel, Butterworth and Linkwitz-Riley filters from 6 to 48 dB per octave. Linea Research uses its own LIR linear-phase crossover filters, which it says have less latency than FIR filters.

Delay

Output delay time-aligns parts of a system that sit at different distances, for example a sub on the floor and a top on a pole, or a delay speaker halfway down a long room. Input delay shifts a whole feed. On the DX0.4 and DX0.6 there is up to 600 ms on each input and 200 ms on each output.

EQ

Output EQ belongs to the speaker preset: it corrects the cabinet’s own response and normally stays locked. Input EQ is for the room and the occasion. Keeping the two separate means a quick tweak for a bad room never touches the protection settings. The DX4.0, for instance, has high-pass, shelving and parametric filters on every input and a separate crossover-plus-EQ section on every output.

Limiters

Limiters are the reason most passive systems need a processor at all. A peak limiter catches fast transients, while an RMS or program limiter watches longer-term power, which is what overheats voice coils. The better processors go further. Martin Audio and Linea Research both describe limiter suites with peak, RMS and excursion limiting, plus multiband limiting for passive two-way boxes; Martin says its VX limiting “gives a passive enclosure the same protection as a fully active unit”.

Why the speaker maker’s preset matters most

The processor is a toolbox. The preset is the work, and the people who designed the cabinet have measured it. That is why makers point you at their own settings.

• Martin Audio says the passive CDD12 “should be used with a compatible controller with appropriate limiter settings to provide system protection”, and that with a DX controller or iKON amplifier, “enhanced DSP and FIR-based presets” get the best from it. For BlacklineX, a folder of presets comes with the free DX0.4 and DX0.6 control software, and Martin also publishes a parameter spreadsheet for use in other processors.
• NEXO quotes its P+ speakers’ performance “with NEXO processing” and provides a dedicated preset for every horn and flange option on each P+ cabinet. The DTD runs NEXO’s own setups, phase-compatible across the PS and LS ranges and other NEXO speakers, and new presets are loaded over USB.
• Linea Research processors are brand-neutral. Linea offers factory preset downloads for several other loudspeaker brands, including Martin Audio, RCF, JBL, Funktion One, dB Technologies, TW Audio, Fulcrum Acoustics and Pioneer Pro, with the instruction to “verify the preset and limiter configuration on the intended system”.

In practice: load the maker’s preset, set the amplifier as the maker specifies, then do your room shaping on the inputs. If you cannot find an official preset for your speaker in a given processor, that is a strong reason to choose a different processor.

The processors compared

Linea Research ASC48 and NSC

The ASC48 is Linea’s flagship system controller: four inputs, eight outputs, analogue and AES3 connections, 96 kHz processing, LIR linear-phase crossovers and the full peak, RMS and excursion limiter suite. It stores up to 50 loudspeaker presets and 10 system-wide snapshots, and it is controlled from the front panel or from System Engineer 8 over Ethernet, with contact-closure ports for simple third-party control. The ASC48 Dante adds Dante networking, so a digital console can feed the processor without going through analogue.

The NSC Series is Linea’s more compact range, built on what Linea calls an “ASC48-derived architecture”. There are three sizes, each with analogue and AES3 inputs as standard and an optional 8 x 8 Dante version:

• NSC24: two inputs, four outputs. A stereo pair of bi-amped boxes, or stereo tops and subs. Also as the NSC24 Dante.
• NSC46: four inputs, six outputs. Tops, subs and a fill or delay feed. Also as the NSC46 Dante.
• NSC48: four inputs, eight outputs, for multi-way or multi-zone systems. Also as the NSC48 Dante.

Linea lists fixed installations, live venues, touring and rental, theatres, houses of worship, clubs and hospitality spaces among the NSC’s typical uses. Choose Linea when you run more than one speaker brand, want one software platform across several processors, or want the most control over a tuned system. Check that a preset exists for your speakers before you buy.

Martin Audio DX0.4, DX0.6 and DX4.0

Martin Audio describes the DX0.4 as “the ideal processing tool to partner the ADORN, CDD and BlacklineX ranges”. The DX0.4 has two inputs and four outputs, and the DX0.6 two inputs and six, all on balanced XLR. Both have a library of Martin Audio channel presets that you import output by output, so one processor can run, say, CDD tops and BlacklineX subs. Each stores 32 user presets and has password-protected user levels, useful when the system lives in a venue and staff should not touch the crossover.

For BlacklineX, Martin’s user guide says the X8, X10, X12 and X15 can run without a controller, provided their AES and peak power ratings are not exceeded and care is taken to avoid amplifier clipping. For maximum performance it recommends a DX0.4 or DX0.6, and it calls the DX0.4 or DX0.6 “the ideal system controller” to provide the active crossover for the X115 sub. Once there is a sub in the system, you need a crossover somewhere.

The DX4.0 is the larger controller: four inputs and eight outputs, analogue or AES3 (selected in pairs) and remote control through Martin’s VU-NET software. It adds the VX limiter suite and FIR filters for O-Line. Martin’s datasheet lists Dante, with automatic fallback to analogue or AES3, but the DX4.0 is also supplied as a separate DX4.0-DANTE model, and we list the two separately. If you need Dante, order the DX4.0-DANTE; do not assume the standard DX4.0 has it. Martin also partners DX processors with its VIA amplifiers, such as the VIA2004. Our Martin Audio vs NEXO guide shows how the speaker ranges line up.

NEXO DTD

The DTD takes the speaker processing from NEXO’s NXAMP amplifiers and puts it in a 1U box that works with amplifiers from other makers. It has two analogue inputs, an AES/EBU input and USB audio for direct playback from a laptop. Its three outputs are left and right mains plus a mono sub. The -N versions add a two-channel Dante input.

• Touring (DTD-T): connectors on the front, two knobs for sub and main gain, and a switch for wideband, crossover or user mode. Available as the DTD-TU and the Dante DTD-TN.
• Install (DTD-I): rear terminal-block connections and no hardware controls. Everything is set from a computer and can be locked against accidental changes. Available as the DTD-IU and the Dante DTD-IN.

User mode, set in NEXO’s Dory software, unlocks speaker and sub selection, crossover frequency, delay, gain, user EQ and limiters. NEXO lists the DTD with its DTDAMP as an optional powering solution for P+ cabinets such as the P12, and for the ePS range. For bigger P+ systems with subs such as the L18, NEXO’s datasheets recommend an NXAMP, such as the NXAMP4x2mk2, which combines amplifier and controller. The P+ cabinets themselves are covered in our NEXO P+ series guide.

The DTD differs from the others in one important way: it reads the amplifier outputs. NEXO’s manual says all power amplifier outputs “must always be fed back to the DTD to ensure correct speakers protection”, and the unit shows a “NO SENSE” warning if that feedback is missing. NEXO also warns against amplifiers that add more than 10 ms of latency, and says any amplifier DSP should be bypassed (“Flat Mode”) so it does not disturb the DTD’s protection.

Install DSP: Allen & Heath AHM and BSS Soundweb London

In a fixed install, speaker processing is often one job among many: zones, paging, microphones and wall controls. An install matrix can do the lot.

The Allen & Heath AHM-16, AHM-32 and AHM-64 let outputs be set either as zones or as speaker processing, with 2, 3 or 4-way crossovers, PEQ, delay and limiter. Those outputs count against the same total, so plan for them. Our AHM-16 vs AHM-32 vs AHM-64 guide covers sizing.

BSS Soundweb London is open architecture: you design the signal path in HiQnet Audio Architect from a palette of processing and logic objects. The BLU-100 has 12 analogue inputs and 8 analogue outputs. The BLU-806 takes four I/O cards and adds Dante/AES67 with primary and secondary ports. Both link to other Soundweb devices over the BLU link bus. This is a system integrator’s tool. A dedicated processor is the quicker route for a PA that only needs a crossover, delay and limiters.

Processor, amplifier gain and why limiters can fail

A limiter in the processor knows nothing about the amplifier after it. Its threshold is calculated for a known amplifier gain. Martin Audio’s BlacklineX guide is blunt about this: if the amplifier has front-panel gain controls they “MUST be set FULL UP”. Turning them down does not add protection; it just means more input is needed for full power, which “will make the limiter in the system controller useless”. Use the maker’s preset with an amplifier of the gain the maker specifies.

Three practical points follow:

• Count outputs, not speakers. Every amplifier channel needs its own processor output: a stereo pair of tops and subs needs four, and a bi-amped box needs two per side.
• Do not double-process. If your amplifier has DSP, either use it as the processor or set it flat. NEXO says this outright for the DTD.
• Size the amplifier properly. Our matching amplifiers and speakers guide covers watts and ohms, and the subwoofer guide covers where the subs go once the crossover is set.

In a permanent installation, the design, installation and testing of the electrical side, including mains supplies to amplifier racks, is for a competent person.

Popular picks from the shop

Frequently asked questions

Do I need a speaker processor for passive speakers?

For a single pair of full-range passive speakers, not always. Martin Audio, for example, says its BlacklineX full-range boxes can run without a controller provided their power ratings are respected and amplifier clipping is avoided. Once you add subwoofers, or bi-amp a cabinet, you need a crossover, and a processor is the usual way to provide it, along with the maker’s EQ and limiters.

What is the difference between a speaker processor and a crossover?

A crossover only splits the frequency range. A loudspeaker processor includes the crossover but adds delay for time alignment, EQ for the speaker and the room, limiters for protection, routing, and stored presets, usually with remote control software.

Can I use a Linea Research processor with Martin Audio speakers?

Linea Research lists Martin Audio among the brands with factory presets for its controllers, and Martin Audio publishes parameters for some ranges, such as BlacklineX, for use in other processors. Whichever you use, check that the preset matches your exact model, and set the amplifier gain the preset assumes.

Can the NEXO DTD be used with non-NEXO amplifiers?

Yes. NEXO designed the DTD to be used with amplifiers from other manufacturers. The amplifier outputs must be fed back to the DTD’s sensing inputs for the protection to work, and the amplifier should not add more than 10 ms of latency or run its own processing.

Do I need the Dante version?

Only if the rest of your system is on Dante. With a digital console or stage box on Dante, a Dante processor keeps the signal digital from the desk to the processor and avoids extra conversions. With an analogue mixer and amplifiers, the standard version does the same speaker job.

How many outputs do I need?

One per amplifier channel that needs different processing. Stereo tops and subs need four; add one or two for front fills, delays or monitors. If in doubt, buy the larger model: a 2-in, 4-out processor with no spare outputs is full on day one.