Audio
glossary.

Three numbers describing a surround system: horizontal channels, subwoofers, overhead channels. 5.1 is 5 horizontal speakers + 1 sub. 7.1 adds rear surrounds. The third number is the Atmos overhead count: 5.1.2 has two overheads, 7.1.4 has four. So a 7.1.4 build is 7 horizontal + 1 sub + 4 overhead = 12 speakers. Higher numbers aren’t always better — a properly placed 5.1.4 in a small room beats a poorly-placed 7.1.4.

Object-based surround format that adds height channels above the listener. Where traditional 5.1 and 7.1 mix sound to fixed channels, Atmos mixes to “objects” the AVR places dynamically using whichever speakers it can find. The .x in 7.1.x notation is the overhead count: 5.1.2, 5.1.4, 7.1.2, 7.1.4. Most cinema mixes since 2014 are mastered in Atmos. The point is verticality — rain falling, helicopters overhead, sound that doesn’t sit in the horizontal plane.

Auto-cal system on every Denon and Marantz AVR in the catalogue. Measures the room with the supplied mic, applies a frequency-response correction, sets per-channel distances and levels. The mobile Audyssey MultEQ Editor app (£15) unlocks target-curve control and frequency-limit settings the AVR menus hide. Not as transparent as Dirac Live, but available on entry-level AVRs where Dirac isn’t an option. The default correction is good; the manual-pass tweaks afterwards make it great.

The brain of any home cinema system. An AVR combines audio decoding (Dolby Atmos, DTS:X), multi-channel amplification, HDMI switching, and room-correction processing in one box. Decodes the incoming signal, applies room EQ, and drives 5–11 channels of speakers plus the sub LFE output. Modern models — Marantz Cinema 50, Denon AVC-X3800H — handle 9.4 channels of amplification with 11.4 of processing, meaning a true 7.1.4 build needs an external 2-channel power amp on top.

Standard for cable thickness. Lower number, thicker conductor — counterintuitive, but it’s how it works. 12 AWG is the recommended default for any home cinema speaker run; 14 AWG is fine for short surrounds and overheads under 10m; 16 AWG is the bare minimum. Thicker cable carries more current with less voltage drop, which matters more on high-power systems and long runs than the cable industry pretends. Spec 12 AWG once and stop second-guessing.

Acoustic absorber for low-frequency energy, installed in room corners. Bass collects in corners — that’s where every room mode reaches maximum amplitude — so a corner trap with thick rockwool or fibreglass can take the edge off the worst peaks before EQ has to work. Room treatment is the broader category: corner traps for bass, first-reflection panels for upper-mid clarity, diffusers for soundstage. GIK, Vicoustic, or DIY rockwool wrapped in fabric. The single most overlooked upgrade in serious cinema rooms.

Three speaker form factors. Bookshelf is the small two-way stand-mount (KEF LS50 Meta, Q Acoustics 3030i) — sits on a stand or shelf, typically 5–6.5″ mid-bass driver, doesn’t reach the bottom octave alone. Floorstander is the tall full-range cabinet (Klipsch RP-8000F II, Dali Oberon 9) — multiple drivers, deeper bass, more sensitive to placement. “Standmount” is the UK term for what the US calls bookshelf — same thing, named for the stand it needs.

Fire-safety ratings for in-wall speaker cable. CL2 and CL3 are the US categories — CL3 is the higher standard, rated for higher voltages and more demanding applications. The UK and EU equivalent is the CPR Euroclass rating: Eca minimum, Cca preferred for residential. Either marking will be printed on the cable jacket. The principle is the same on both sides of the Atlantic: bare PVC speaker cable inside a wall cavity is a fire-spread risk and a building-regulations violation.

The point at which audio signal is split between the subwoofer (below) and main speakers (above). Set in the AVR. The default 80Hz works for typical 6.5-inch bookshelves, but is wrong for many systems. Small bookshelves want 90–120Hz, floorstanders want 60–80Hz. Set it to where the speaker naturally rolls off — too low and the speaker distorts trying to play frequencies it can't, too high and vocal energy moves to the sub's location, breaking the image.

Room correction software that measures your speakers in your actual room, then digitally adjusts the signal before it reaches the speakers to flatten the response and fix timing errors. Generally considered the most transparent and accurate auto-cal system available — better impulse-response correction than Audyssey, less aggressive sculpting than YPAO. Ships on Marantz Cinema 50 and the higher Denon flagships, with a £350 full-bandwidth licence on top of the AVR price. Worth the upgrade if your AVR supports it.

Digital signal processing applied to audio before it reaches the speakers. In an AVR or sub, DSP is the room-correction layer — Audyssey, Dirac, YPAO — adjusting frequency response and timing to compensate for the room. DSP can reduce peaks but cannot fill nulls. Sometimes called Room EQ when it’s specifically tuning bass. The audio press tends to oversell it: DSP fixes small problems with a properly placed system, not big problems with a badly placed one.

Three subwoofer configurations. Front-firing: driver points forward, simplest design, easy placement (most SVS subs). Down-firing: driver fires into the floor, couples bass into the room boundary, slightly less placement-sensitive. Passive radiator: a tuned mass that moves in sympathy with the active driver, replacing the port and giving extension without port noise (REL S/812’s twin 12″ passive radiators). All three reach low; the choice is mostly cabinet shape, room aesthetics, and how aggressively the sub couples to the floor.

The time it takes different frequencies to travel through a system. Ideally constant — every frequency arrives at the ear at the same moment. Ported subs ring at the port-tuning frequency, meaning low frequencies arrive a few milliseconds late. Audible signature: bass that sounds “boomy” or “loose” rather than tight. Sealed cabinets have lower group delay across the bass range, which is why dialogue and bass-kick edges stay time-aligned. The technical reason sealed subs sound “tighter.”

The electrical resistance a speaker presents to the amplifier, measured in ohms (Ω). Most speakers are rated nominal 8Ω or 6Ω, but the actual impedance dips far lower at certain frequencies — KEF R3 Meta is rated 8Ω but drops to 3.2Ω in the bass. Lower impedance means the amp has to deliver more current to produce the same voltage. Cheap AVRs struggle at 4Ω and below; check the AVR’s minimum-rated impedance before pairing.

The dedicated subwoofer channel in a surround mix — the .1 in 5.1, 7.1, 7.1.4. A discrete low-frequency track authored separately by the mix engineer, typically for explosions, low rumble, and effects with sub-50Hz content the mains can’t reproduce. The AVR routes LFE plus the bass content from any “small” speakers to the sub output. Different from the bass already in the main channels — LFE is film-specific cinematic punctuation.

KEF’s damping technology behind the tweeter. A maze of tuned channels absorbs the rear wave before it reflects back through the dome. Conventional designs leave that energy to bounce inside the cabinet, which causes upper-midrange smear and treble ringing. MAT removes about 99% of it. Audible result: cleaner decays, less sibilance, treble that resolves without the hard edge typical of cheaper aluminium-dome designs. Found across the KEF Q-series Meta and LS50 Meta, paired with the Uni-Q driver.

A frequency at the listening position where two waves arrive 180° out of phase and cancel each other. The signal isn’t there. Nulls cannot be fixed with EQ — boost the cancelled frequency by 12dB and you’ve added 12dB of amplifier work for zero output, while clipping on transients. The fix for a null is geometry: move the speaker, move the sub, move the seat, treat the room. The most misunderstood problem in audio, and the reason placement matters more than EQ.

The relative timing of waves arriving at the listening position. When two speakers play the same frequency in phase, the waves add; out of phase, they cancel. Subwoofer phase controls (0°/90°/180°) shift the sub’s output so it adds rather than fights at the crossover frequency. Set by software measurement (REW), not by ear — phase-by-ear works in obvious cases but masks subtler offsets. The single most common cause of disappointing sub integration in otherwise well-placed systems.

The professional standard listening level for film calibration. THX defines it as the volume at which the AVR’s internal pink-noise calibration tone produces 75dB SPL at the listening position. Cinema mixes are mastered against this level, meaning a Saturday-night listen at reference level hears the film exactly as the mix engineer intended. Most home listening sits at -10 to -15dB from reference for normal use. Calibrate at reference, listen at whatever; never the reverse.

Free room measurement and analysis software for Windows, macOS, and Linux. Runs sweep tones through your speakers, captures the response via a measurement mic (UMIK-1), and produces frequency-response, waterfall, group-delay, and impulse-response plots. The standard tool for verifying what auto-cal does and doesn’t fix. Free — properly free, not freemium. The on-ramp is steeper than auto-cal, but a couple of evenings with it transforms how you hear your own system.

A frequency where your room's dimensions cause sound waves to reinforce or cancel each other. In every rectangular room there are predictable peaks (where waves stack) and nulls (where they cancel) — typically in the 30–300Hz range. Modes are why bass sounds different in different parts of the same room. Speaker placement affects which modes get excited; EQ can reduce peaks but cannot fill nulls. The single biggest reason why 'the sub sounded fine in the shop but boomy at home.'

The two main subwoofer cabinet designs. Ported uses a tuned port to extend low-end output by 3–4dB at the bottom octave (SVS PB-1000 Pro, PB-Ultra series). Sealed is acoustically simpler — the driver fires into a sealed box (SVS SB-2000 Pro, REL T/7x) — which gives lower group delay and a “tighter” character at the cost of some output. For mixed-use systems doing both film and music, sealed integrates better with mains. For pure film duty in big rooms, ported earns its place.

A speaker's efficiency rating: how loud it gets per watt of input. Measured in dB at 1 metre, with 1W (or 2.83V) input. A speaker rated at 88dB needs twice the power to match a 91dB speaker at the same volume. High-sensitivity designs (Klipsch RP-8000F II at 98dB) are easy to drive — small AVRs reach reference volume without strain. Low-sensitivity designs (KEF LS50 Meta at 85dB) want serious power. Read it like miles-per-gallon for amplifiers.

A measure of loudness in decibels — the number on a meter when it’s pointed at a sound source. 0dB SPL is the threshold of hearing; a quiet room is 30dB; conversation 60dB; a cinema mix peaks at 105dB. THX reference is 75dB with the AVR’s internal calibration tone. SPL is logarithmic: every 10dB is roughly doubling perceived loudness. Useful as an objective check that “loud enough” means what you think.

Calibrated USB measurement microphone made by miniDSP. Around £90. Plugs straight into a laptop, ships with a unique calibration file that REW reads automatically — meaning the measurements you take on this exact mic are accurate to within a fraction of a dB across the audible range. The standard tool for hobbyist room measurement: significantly more accurate than the supplied auto-cal mic, much cheaper than professional alternatives. If you do nothing else from the calibration guide, do this.

KEF's signature driver design where the tweeter sits inside the cone of the mid-bass driver, creating a single point-source per channel. The result: imaging that's locked tightly between the speakers and stays consistent off-axis — meaning the soundstage doesn't collapse if you stand up or sit at the side of the room. Found across KEF's range, from the Q-series upwards. Pair the Uni-Q with KEF's MAT damping and you get the brand's defining sound.