Cicada Rebuild Stage 2: Adding DSP for Time Alignment and Crossover Control

Custom Build · Cicada Rebuild, Stage 2

A DSP processor is what turns separate amplifier channels into one tuned system. Stage 1 of this Cicada Rebuild established the two amplifiers, the Braille lithium battery and the power distribution, but no speakers were connected yet. Stage 2 adds a Cicada Audio DSP412PRO, a 4-input, 12-output processor, before the speakers go in, so that when the front, rear and saddlebag mid-bass stages are wired up they play through one controlled system from the first note, rather than being corrected after the fact. The DSP412PRO sets the crossover points, levels, EQ and time alignment for each amplifier channel and system zone.

Why the DSP goes in before the speakers

Stage 1's write-up flagged this as the next move. The SoundStream HDHU.V2 head unit gives the system a clean line-level source, but on its own it can't set the crossover points, levels and time alignment each amplifier channel needs across two amps. Putting the DSP in at this stage, ahead of the speakers, means the front, rear and mid-bass stages are commissioned through the processor the first time they play, rather than run on rough factory-style filtering and corrected afterwards. At highway speed, with wind and engine noise stacking up, that control is what a system pushing this much power needs.

A dedicated DSP gives three things the head unit alone can't: time alignment (delaying the nearer speaker channels so sound from each location reaches the rider's seat more closely together), independent crossover points per channel (so the 10-inch saddlebag mid-bass hands off cleanly to the front and rear component mid-bass drivers instead of overlapping them), and parametric EQ to reduce measured peaks and shape the response around the resonances the fairing and saddlebags introduce.

What does the DSP412PRO actually do?

The DSP412PRO takes up to four inputs and provides selectable four-, eight- or twelve-output operation, splitting the incoming signal into separate, individually tuned channels on the way to the amplifiers. On this build it uses all four inputs from the HDHU.V2, fed by the front and rear RCA pairs, and runs five processed outputs: four processed component-stage outputs for the FLX1400.4 (front left and right, rear left and right) and one mono output for the FLX1600.1 mid-bass, taken as a mono sum of all four inputs in DIALD. That leaves spare processed outputs for another amplifier channel, an active speaker section or a dedicated subwoofer stage later, without replacing the DSP.

Each of those outputs is its own zone in the tune: the four front and rear channels and the mono saddlebag mid-bass stage. Within each front and rear component channel, the supplied passive network filters and protects the tweeter and sets its level attenuation, so the DSP processes the component channel as a whole rather than controlling the mid-bass driver and tweeter independently; the component system's passive network and the driver's natural roll-off manage the upper-frequency transition to the tweeter. Control runs through Cicada's DIALD software on a Windows 11 laptop over USB-C, where each output gets its own crossover, time delay and EQ. Cicada's older smartphone DSP apps are no longer supported. It's an initial setup and measurement process, with the tune stored on the processor and revisited only when the system changes or needs further refinement, not something you touch on the side of the road.

Cicada Audio

DSP412PRO

Up to 4 inputs and 12 selectable outputs. DIALD software for time alignment, crossover and EQ across multi-amp systems.

$770 View Product →

How is the DSP wired into a two-amp system?

The DSP412PRO sits ahead of both amplifiers in the signal chain, not after them. The basic order on this build looks like this:

1. Head unit output from the SoundStream HDHU.V2: four line-level RCA channels, the front and rear pairs, into the DSP412PRO's four inputs.
2. DSP processes the signal and splits it into separate, tuned channels.
3. Front and rear channels run from the DSP to the FLX1400.4, which will drive the front fairing (14CXK65.4) and rear saddlebag-lid (CXK69.4) speakers.
4. Mono mid-bass channel runs from the DSP to the FLX1600.1, which will drive the two CMB10.S4NEO 10-inch mid-bass drivers, with its own crossover point set independently of the front and rear stages.

That gives five processed output zones from the DSP:

We'll publish the actual crossover frequencies, slopes, polarity, delay and level values once the speakers are in and the system is measured and tuned.

The HDHU.V2's remote output switches on the DSP412PRO, and the DSP's own remote trigger output then switches on both FLX amplifiers, so the processor is the turn-on point as well as the audio hub. Because the DSP handles the crossover and level work, the amps don't have to rely on their own built-in filtering: the repeatable signal-processing settings, routing, crossovers, EQ, delay and output levels, live in DIALD, while amplifier gain structure is still set at the hardware.

Before tuning, the HDHU.V2's 15-band EQ is set flat and its front and rear high-pass filters are disabled, or set to their lowest available frequency if the head unit has no true bypass, so the DSP receives the widest practical, neutral signal, with the head-unit volume and fader placed at reference positions for gain setting. Live fader control stays available afterwards, but moving the fader changes both the front-to-rear balance and the input mix feeding the mono mid-bass output, so the reference tune is set with the fader centred and positions away from centre are best treated as temporary preference adjustments rather than the calibrated system balance.

The FLX1600.1 also keeps its Dube's Custom Street Machines remote level control for day-to-day adjustment of the mono mid-bass, independent of the fader. The system is tuned with the Dube's control at its maximum intended listening position, and the DSP output level, the FLX1600.1 gain and the head-unit reference volume are set together so that position corresponds to the established clean maximum. Turning the control down reduces the mid-bass; returning it to the reference position restores the tuned level without exceeding it.

What changes once the DSP is tuned?

Once the system is measured and tuned, the difference shows up in a few places. Vocals and mid-range sit forward instead of getting buried under bass. The hand-off between the 10-inch saddlebag mid-bass stage and the front and rear component channels is set from measurement rather than guesswork, so excessive overlap is controlled and the mid-bass stage sums cleanly with the front and rear channels. And because each active output is time-aligned to the rider's seat, the front and rear stages integrate rather than arriving as separate sources.

None of this changes the amplifiers' rated output. What it changes is how usable that output is on the road. The system is set up and measured stationary, then road-tested: wind and engine noise still mask detail at speed, but a properly controlled system uses its available output more effectively than one running on rough filtering.

Is a DSP worth it on a single-amp Harley system?

It can be. A simple coaxial system can perform well on the head unit and amplifier controls alone, while a component, horn-loaded or acoustically tricky system gains a lot from EQ, precise crossovers, level control and time alignment. Cicada's PRO-series amplifiers, the FLX700.4PRO and FLX1400.4PRO, can handle a four-channel-plus-mono system themselves: their four amplified outputs power the front and rear channels, while their two processed line-level pass-through outputs can feed a separate mono amplifier for the mid-bass or sub. The standalone DSP412PRO is the better fit on this build because it already uses two separate non-PRO amps and benefits from up to 12 outputs, broader routing and room to expand.

What's next for this build?

With the DSP412PRO in and the signal chain built around it, the next stage adds the speakers: the front and rear component stages and the 10-inch saddlebag mid-bass drivers. Once they're in, the whole system gets measured and tuned in DIALD, and we'll put numbers to the result and compare it against the SoundStream build it replaced.

Frequently asked questions

Browse the full Cicada Audio range, or check out the DSP412PRO to start planning your own multi-amp build.