Car Audio Crossovers, EQ, Time Alignment and Presets
A DSP (digital signal processor) lets you set the crossovers (where one speaker hands over to the next), the EQ (turning some pitches up or down), the time alignment (small delays so every speaker's sound reaches your ears together) and the phase (whether speakers push and pull in step). Peter Steinbacher of Pssound sets each one from what the speakers really do in the car, because below about 300 Hz the ear hears phase more than anything, and a cancellation can never be EQ'd back. One tune can't suit a quiet judging lane, a motorway at 70 mph and a badly mastered record, so he gives every car several presets.
The short version
Set each crossover from what that driver does in your car, and never copy someone else's numbers.
Fully active gives the most control, but semi-active works well when the mid and tweeter sit close together.
Peter's EQ is mostly cuts, and left and right are matched before timing is set.
EQ cannot fill a cancellation or fix poor aiming, so fix location, timing and phase first.
Tune linear from about 250 to 300 Hz up, add a bass rise below that, and don't roll off the top end.
Delay the nearer speakers, time each pair against the next, and flip polarity to prove it all adds up.
Keep a clean base tune and a daily tune with more bass, plus party, all-seat or doors-open presets if you want them.
Active, semi-active or passive
A passive crossover is a fixed filter between amp and speaker, with points the maker chose. Peter's complaint is that the same speaker set sounds very different from car to car, because speakers sit in different places and at different angles. A DSP lets you set every driver's high-pass and low-pass from what it actually does in your car. For the hardware, see our guide to DSPs and sources.
Fully active means one amp channel per speaker (six for a 3-way front), so every driver gets its own delay and EQ.
Semi-active means a passive crossover only between mid and tweeter, with the midbass on its own channel. Peter finds this perfectly good: you still time the midbass to the mid, and at the mid-to-tweeter handover the ear cares more about level than timing (watch). It works best when the two sit close together, as in the Mercedes W213. With factory speaker locations he advises going at least semi-active.
Choosing crossover points and slopes
The numbers you type into a DSP are only a start. What counts is the acoustic crossover point, where two drivers actually meet when measured in the car. So Peter says not to copy anyone's crossover points, his included: the 6GT's mid-to-tweeter handover is around 4 kHz, but you can't repeat that in another car (watch).
Basic starting points: sub up to 60–80 Hz; midbass from 60, 80 or 100 Hz; a 3-inch midrange from 250, 300 or 400 Hz (a soft-dome midrange won't play that low, so start it at about 600–800 Hz); tweeters from 2 kHz, or 4, 6 or 8 kHz.
Let measured cancellations decide. In the Golf mk8 a cancellation in the driver's-side midbass set the crossovers, so the owner got two presets: midbass handed to the sub at 60 Hz, or at 80 Hz for daily use. At 80 Hz the problem area isn't supported by the rear sub, a sacrifice Peter accepted in a daily car (watch).
Cross for the level you actually play. Low tweeter crossovers are fine at 85–90 dB, but at concert levels of about 100–110 dB cross higher, for safety and lower distortion. One owner had tweeters at 1 kHz and got away with it only because his gains were so low (watch).
A slope is how steeply a filter cuts sound beyond its crossover point. Peter's choice is Linkwitz-Riley 24 dB per octave: already 6 dB down at the crossover point and 24 dB down an octave beyond it, which he calls ideal for blending drivers (watch).
EQ the slope too, at least an octave past the crossover point. A peak there still plays alongside the neighbouring driver and spoils how the two add up (watch).
How Peter uses EQ
Peter calls the EQ job probably the most important thing in any car. His EQ screens look like a rollercoaster, but the curve only mirrors the speaker's measured response: take out the peaks and treat the dips as far as you can. Measuring is covered in our tuning guide.
Use fully parametric EQ, where you pick each filter's exact frequency, width and amount. If the problem is at 721 or 717 Hz, the filter belongs there, not on a fixed band at 700.
Don't fear many filters. The old advice to use few because many ruin the phase is a myth: response and phase go hand in hand, so without a linear response the phase will never be right (watch).
Mostly cuts. A 6 dB boost isn't scary, because everything is relative to the target line (the curve you aim for). If you do boost, lower the output levels so the DSP doesn't clip (watch). Don't drag levels so low that you crash the dynamics, and don't boost more than 3–5 dB unless you have to.
Harshness is usually the cabin. A tweeter can measure about 10 dB hot at 2–4 kHz in the car and get blamed. On pink noise (a hissing test signal) a mid without filters sounded very harsh, and with them on it was fine (watch).
Match left and right first. A +6 dB peak at 1 kHz on the right mid pulls everything to that side when a female vocalist sings in that band. If one side dips where the other peaks, even perfect timing never gives proper imaging.
EQ cannot fill a hole. Adding 12 dB into a dip of about 20 dB won't bring the curve back; as Peter puts it, "once it's cancelled out, it's cancelled out" (watch). Nor does it cure poor aiming.
Subs need EQ too. In one car the boot boosted the sub by about 8 dB over a wide band; in another, cutting about 8 dB near 44 Hz meant the sub needed less than a quarter of the power.
The bass rise and the top end
Linear is not the same as flat. Hearing is less sensitive at low frequencies, so a system tuned perfectly flat sounds short of bass. Peter's rule: tune linear from 250 Hz (or 300 Hz) up, then let the level rise by at least 3 dB per octave below that. A sports car may need 4 or even 5 dB (watch). His advice has moved: in May 2020 he wouldn't raise it more than 3 dB an octave for pure sound quality, but by 2025 he treats 3 dB as the minimum.
The rise depends on the car. Loud engine noise calls for more, or the bass disappears; parked with reference recordings you need less. The Golf mk8 ended at roughly 4 dB per octave under 200 Hz, which would be a little boomy in a competition car.
Don't roll off the top. Sloping the sound down above 2 kHz at 3 dB per octave or more loses detail and sounds dull; it only suits people listening at 120–130 dB (watch).
A 1–2 dB dip across 2–6 kHz is fine and can be more relaxing.
Time alignment
You sit about half a metre nearer the driver's side, so that side is louder and arrives first. At home, 4–6 m from the speakers, midbass, mid and tweeter timing is practically identical, but in a car every driver is a different distance from your ears, and even a 2 cm gap between tweeter and mid matters. Time alignment delays the nearer speakers so everything lands together. Done well, the speakers seem to vanish and mono material sits in the centre of the stage.
Time each pair against the next pair, not only left against right. When the midbass pair plays in time with the mid pair they sum and follow the curve, and in the Golf mk8 the midbass sat up on the dash (watch).
A 50-second rough start: after a quick measurement and basic crossovers, group the driver-side speakers if your DSP allows it and delay that whole side by about 1.2–1.3 ms, depending on how wide the car is. Verify left/right polarity first (watch).
Don't fake the centre. Pulling the image in front of the driver with false delays is not correct, in Peter's view: the stage turns narrow on one side and very wide on the other, and instruments blur. For people who like it, he offers it as an extra preset.
Phase and polarity
Below about 1 kHz, and especially below 300 Hz, long sound waves bend around your head, so the brain locates sound by phase (the timing of each side's wave) (watch). Both sides need the same phase response. When drivers are in time and in phase they blend and vanish as separate sources, and impact appears; a midbass pair or a sub alone has little punch, but together they add up to far more.
The polarity test. If you aren't sure two drivers are in phase, flip the polarity (swap positive and negative) on the midbass pair or the mid pair. If the timing is right you should see a huge cancellation dip on the measurement, and you can hear the lower midrange vanish (watch).
A sub out of phase can cancel far above its crossover. The Golf mk8's sub was crossed at 60 Hz, yet out of phase with the front it cancelled everything from 45 to 120 Hz. In phase and timed to the front, it summed beautifully (watch).
Tweeters are often the ones to flip.
Presets and the sub-level knob
Peter's view: "You can't have just a single tune" (watch). Mastering varies so much by genre that most rock can sound harsh and thin on an accurate tune. The car changes too. When judged, road noise is out of the equation, so you need less rise below 200–300 Hz; on the road the same tune lacks bass.
The daily tune always gets more bass, because at 70–80 mph road, engine and exhaust noise drown it out. He usually adds a wide 2–3 dB cut between 2 and 5–6 kHz too, which is more relaxing at high levels (watch).
A daily car such as the Mini Clubman gets three presets: SQ (clean, for parked listening), Daily, and All-seat (the daily tune with the rear doors playing normal stereo). Daily presets often switch on fill speakers, which add body and life; see our rear fill and staging guide.
A party preset lets the midbass play as much kick as it physically can and pushes the subs hard. A loud preset also crosses the midbass and sub higher, so less energy pumps into the door. Integration may suffer, but the system can be pushed harder.
Leave the right preset selected. At the finals he made a morning preset with slightly raised bass, left it on, and EMMA marked the bass down straight away. Keep the car's original preset too, so you can show before and after.
A sub integrates perfectly with the front at only one volume level, so the controller needs a visible reference. Peter prefers a numbered scale, such as the Helix Director, to an endless knob (watch). Turning the sub up moves the effective crossover and breaks alignment with the midbass.
Common mistakes to avoid
Copying someone else's crossover points instead of reading your own car's measurements.
Crossing a tweeter higher than the mid can play, as with the Boxster's 4.5 kHz tweeters and a 5.25-inch mid.
Trying to EQ out a cancellation, or boosting hard to cover poor aiming.
Skipping the polarity check, or timing left against right but not each pair against the next.
Rolling off the top above 2 kHz to tame harshness, when the cause is usually an untreated peak.
Turning up the sub knob for more bass instead of fixing the integration.
Watch Peter explain it
This is an independent, plain-English summary of Peter Steinbacher's public YouTube videos, written by VA3 Car Studio. It is not affiliated with or endorsed by Pssound. The links jump to the moment in each video where he makes the point. Part of our series: Car audio lessons from Pssound, start here
Comments