Subwoofer calibration in a private cinema runs in a fixed order: physical placement first, then level matching, then time alignment and crossover, and only then electronic room correction. Multiple subwoofers exist to even out bass from seat to seat, not to play louder. In a reference room the last step is always done by ear, because the measurement tells you what the room is doing and only listening tells you whether the result is right.
That order matters more than any single setting. Almost every disappointing home theater we are asked to look at in Beverly Hills, Bel Air or Pacific Palisades has the same history. Excellent equipment, a room correction pass run on day one, and nobody ever moved a subwoofer.
Why does the bass sound different in every seat?
Because low frequencies are longer than the room. A 40 Hz tone has a wavelength of roughly 28 feet, which is wider than most screening rooms. At that scale sound stops behaving like a beam and starts behaving like pressure filling a container. The wave reflects off the back wall, meets itself coming forward, and in some places the two add together while in others they cancel.
Those places are fixed. They do not move with the movie. One seat gets a bass hump you can feel in your chest, the seat beside it gets a hole where the same note nearly disappears. The difference between two adjacent seats can exceed 15 dB at a single frequency, which is the difference between a rumble and nothing at all.
This is a room problem, not a speaker problem. No subwoofer, at any price, fixes it on its own.
Where do subwoofers actually go in a private cinema?
Position is the only tool that changes the physics rather than masking it. Everything else is compensation.
A single subwoofer in a corner produces the most output, because the corner loads it against three surfaces. It also produces the most uneven bass, because it excites every room mode at once. In a room where one person sits in the exact center this can work. In a room with three rows it rarely does.
Two subwoofers placed at the midpoints of opposing walls cancel the strongest lengthwise mode almost completely. Four subwoofers, one at the midpoint of each wall or one in each corner, flatten the response further and make the seat to seat difference small enough that the back row and the front row hear the same film. This is why high end rooms use four modest subwoofers rather than one enormous one. The goal is uniformity across seats.
The practical method is unglamorous. Put the subwoofer at the main listening position, play a sweep, and walk the room with a measurement microphone to find the places where the bass measures smoothest. Those places are candidate positions. Then measure again with the subwoofer actually there. It takes an afternoon and it changes more than any setting in the processor.
Architecture usually limits the options, which is exactly why the pre wire stage is where subwoofer positions should be decided. Once the millwork is in, the good positions may no longer be available.
What do level matching and time alignment do?
Level matching sets how loud each subwoofer plays relative to the main speakers. The convention in cinema is that each main channel is set to the same reference level and the low frequency effects channel sits 10 dB above it, because the LFE track is authored with that offset built in. Get this wrong and every film in the library is either thin or bloated, and the owner spends years adjusting the volume knob per movie instead of once.
Time alignment matters because the subwoofer is usually at a different distance from the seats than the front speakers, and because bass drivers and their processing introduce their own delay. If the subwoofer arrives a few milliseconds late, the region where it hands over to the main speakers partially cancels. On a measurement this looks like a dip around the crossover point. In the room it sounds like a kick drum that has lost its front edge and a gunshot that has lost its punch. Correcting it costs nothing and is one of the largest audible improvements available.
With multiple subwoofers, each one is aligned individually. Aligning them as a group defeats the purpose of having more than one.
Where should the crossover be set?
Eighty hertz is the standard handover point, and it is standard for good reasons. Below roughly 80 Hz human hearing cannot localize a source, so the bass detaches from the subwoofer and appears to come from the screen. Above it, the ear starts pointing at the box in the corner. Eighty hertz also relieves the main speakers of the work that distorts them fastest.
Rooms with large full range front speakers sometimes justify a lower point. Rooms with in wall speakers sometimes need a higher one. But moving the crossover to solve a bass problem is almost always treating a symptom. If 80 Hz sounds wrong, the answer is usually in position, level or alignment.
Does electronic room correction fix bass problems?
It fixes some of them, and only some.
Room correction is very effective at reducing peaks. A peak means there is too much energy at that frequency, and turning it down works. Correction is much weaker at fixing nulls, because a null is cancellation. Adding energy at a frequency the room is actively cancelling mostly heats the amplifier and pushes the driver toward distortion without raising the level at the seat.
This is the reason correction runs last. Its job is to refine a room that is already physically sound, not to rescue one that is not. Correction applied to badly placed subwoofers produces a graph that looks acceptable and a room that still sounds wrong, and that gap between the graph and the experience is what most owners are actually describing when they say the theater cost a fortune and does not satisfy.
Physical treatment and electronics solve different halves of the problem. Bass traps and thick absorption address the decay time of low frequencies, which no equalizer can shorten. Correction addresses the frequency balance that remains.
What does a mastering engineer hear that the microphone does not?
A microphone reports level over frequency at one point in space. It does not report whether dialogue stays intelligible when the score swells, whether the bass supports the image or sits behind it as a separate event, or whether the room holds together at reference level for two hours without fatigue.
Those judgments are what final voicing is. At Ermine the voicing pass on a private cinema is done by Anton Chilibi, a mixing and mastering engineer credited on the Eurovision winning song Stefania (Kalush Orchestra), whose work includes MONATIK, Jamala, alyona alyona, Jerry Heil, The Rasmus and LOBODA. Mastering is the last quality check on how a record will sound to a listener, and that is the same question a finished cinema asks. Measurement makes a room correct. A trained ear makes it sound right.
How do you know the calibration held?
Write it down and check it. Subwoofer positions, distances, levels, crossover, correction filters and the date, stored with the project file. Firmware updates reset settings. Housekeeping moves a subwoofer three feet to vacuum. A new sofa changes the absorption in the room.
A yearly verification pass catches drift before it becomes the complaint that the theater is not what it was. This is part of our ongoing care programme rather than a separate call out.
Frequently asked questions
Do I need four subwoofers?
You need enough to make the bass consistent across your seats. In a single row room, two well placed subwoofers usually achieve that. In a room with three rows, four modest units almost always beat one large one.
Can you calibrate a system another company installed?
Yes. Calibration and voicing are offered as a standalone visit, including on systems Ermine did not install.
Will room correction alone fix my bass?
It will reduce peaks and improve balance. It cannot fill a cancellation null or shorten decay time. Position first, correction last.
How much does subwoofer calibration cost?
It depends on the room, the number of subwoofers and whether acoustic work is needed. We quote after seeing the space. Call (888) 818 9996.
How often should it be redone?
Once a year as verification, and any time equipment, firmware or the furniture layout changes.
Ermine Smart Home designs and calibrates private cinemas across the Los Angeles Westside, including Beverly Hills, Bel Air, Malibu, Pacific Palisades, Santa Monica and Brentwood. To discuss your room, call (888) 818 9996 or get in touch.