The #1 Speaker Placement Tip That Speaker Manuals Get Completely Wrong

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As you may already know, the energy sent backwards by a speaker hits the wall behind it and gets reflected. If the wavelength is long enough, this will add in-phase to the energy that the speaker sends forwards.

You can imagine it as if half of the balloon that expands outward from the speaker folds back on top of the other half.

These two halves add together, doubling the amount of energy. What you end up with can look like a low shelf boost at up to +6dB SPL. And, just like with an EQ in your DAW, you can bring it back down with a similar low shelf cut!

Space Loading: As you move your speaker closer to a wall, it’s as if someone is boosting your bottom end with a low shelf EQ.

The same thing happens again when you place your speaker in a corner. Now there are two surfaces that reflect energy, and half the balloon is folded over again. All that energy is now concentrated in ¼ of the volume. Another potential +6dB SPL low shelf boost[1].

So what does that mean in practice when placing your speaker? In simple words:

As you move your speaker closer to a wall or corner, it’s going to sound like somebody is boosting your low end with a low shelf EQ.

If you don’t like it, simply bring it back down with the low shelf EQ on your speaker. Done.

But this doesn’t mean you HAVE to place your speaker at any particular distance from the wall. In fact, you might like a little bit of extra energy in the low end! And if you don’t, it’s easy enough to take care of.

Those Dreaded Reflections

But what about energy that gets reflected back from the front wall and ends up combining out of phase with the sound sent forward?

What you end up with here is a classic comb filter.

You know those mono-to-stereo mixing tricks that you’re not “supposed” to do because of mono compatibility, but you end up doing all the time anyway? You know, like the one where you double the track, pan the two versions out and delay one side? Yeah. Sounds great. Just don’t hit that “mono” button.

That’s what happens when the reflected energy off the front wall combines out of phase with the energy sent directly forward.

Except, the reflected energy is effectively low-passed because of the dispersion pattern of the speaker. It only sends bass backwards, remember?

As a result, that comb filtering only substantially affects the low frequencies.

And, like with any comb filter, the frequency of the first and lowest cancellation is determined by the time difference between the direct sound and the reflection.

The important thing to understand is that this first cancellation happens at the membrane of the speaker itself!

Speaker Boundary Interference: Low frequency sound sent backwards gets reflected and combines with the direct sound at the speaker membrane.

You see, two sound waves interact by the laws of superposition. That means they interfere at every point in space while continuously passing through each other. But for us listeners, the effect is only “cemented” into existence at the very moment and point in space where the energy is transferred to a membrane[2].

And depending on what that membrane is (the speaker membrane in this case), the interference effects can be quite different.

In this case, the cancellation literally affects the power output of the speaker[1]. It changes the actual frequency response played into the room. Basically, it colors the speaker! And so that coloration stays the same no matter where you are in the room, as long as the speaker stays in the same place.

You may have heard of it. It’s sometimes called Speaker Boundary Interference Response or SBIR.

Note that this is not the same as your classic “mirror point” reflection, who’s effect does vary throughout the room as you change position.

Boundary Effects in Combination

So what does it actually look like as you move your speaker closer to the wall? You’d expect the cancellation to start low, because of the long time difference, and move up in frequency as you move the speaker closer.

Speaker Boundary Interference. The out phase part causes a comb filter that moves up in frequency as you move the speaker closer to a wall. The in phase part causes a 6dB low shelf boost. Image via GIPHY

So as long as your speaker is more that 4m (12 feet) away from the front wall, the fundamental cancellation notch lies beneath the audible spectrum. It’s probably outside of your speaker’s frequency range and doesn’t get created in the first place. So that’s good.

Unfortunately, the first harmonic above it still sits smack bang inside the audible bass region, wreaking havoc.

In between 3 meters (10 feet) and 1 meter (3 feet) in distance, the first cancelled overtone is now above 100Hz. And, the main notch moves right through the subs and bass. Not cool.

Once the speaker is less than 1 meter from the wall though, the main notch has moved above 100Hz as well. At those frequencies, simple insulation material absorbers on the wall are very effective.

Finally imagine what happens when you move the speaker all the way into the wall. Now the reflection doesn’t even happen in the first place, and you can simply ignore the entire issue. That’s the whole idea behind soffit mounted speakers.

So, to keep your front wall reflections from messing up your bass, place your speakers at least 4 meters away from your wall, or less than 1 meter away. Anywhere in between 1 meter and 4 meters and you are asking for extra trouble.

You can reduce the effect by placing an absorber right behind the speaker, but it will have to work at least down to 100Hz, or lower.

Optimizing For The Front Wall = A Game of Futility

This advice is all nice and dandy. The problem of course is that there are usually five more surfaces in your room apart from the front wall. And all of them cause the same effect.

In most typical home studios, like converted spare bedrooms, attics, garages or basements, you will neither have the space nor the ergonomic luxury to place your speakers to optimize for all 6 reflecting surfaces. (And often, not even for one.)

Even if you could do this, which surfaces and reflections would you prioritize? Which are the worst offenders?

As you optimize for the front wall, you may be missing the mark on the back wall reflection. And to actually get the oft-recommended “equilateral triangle” going, you end up completely ignore getting the right distance to the side walls. Finally, there’s the floor, and whatever you do, I’m sure you won’t be successful in setting up your speaker within 1m of the floor.

I think you can see what I’m getting at.

Ever wanted to have a great way to chase your tail for weeks in the studio? This is it. It’s a lesson in futility.

Sure, you might be able to squeeze a little bit of an improvement out of your setup with lots of patience and trial and error. But looking at the bigger picture, all of your efforts are going to be swamped by the effect of room modes anyway.

Rather than optimizing for wall distance, optimizing for room modes is a method of fixing your low end that actually works.

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  • Carl T

    Many small rooms don’t have the luxury of being able to move the monitors away from the front wall so a boundary compensation switch on most active monitors can be helpful. However, the larger issue is not only space restraints, but also the need to avoid placing the listening position in an axial mode null which can very effectively suck out the low end in a nasty unfixable selective way.
    All of our TEC Award-winning PhantomFocus MixRooms™ with https://uploads.disquscdn.com/images/4ad600d7b10e3934eeb5a55d69f1a1c18b394278cc243f99aa00bab12d3a705d.jpg PhantomFocus™ Monitor Systems rely on our Null Positioning Ensemble http://carltatzdesign.com/acoustic-tools.html. No simple procedure in your studio will render greater results than spending a little time to follow this easy to understand diagram to a T. This is not something we invented per se but rather utilizes the laws of physics as the fathers of stereo intended.

  • Mr Bones

    Yeah, but a lot of us want accurate bass – not boomy, bloated Deadmau5 concert type bass that sounds like a16 yr old’s car.

  • Dwayne Hunt

    I’ve always thought that to solve this positioning dilemma, simply put the speakers very close to your ears…..as in a pair of good studio grade headphones. Seriously, why are we beating this deadhorse? I suspect that the new guys coming up that don’t have a room to accommodate the proper positioning simply put them just anywhere. I just hope they are careful to place them so that they don’t fall and hit them on the head. If their room will accommodate the proper specifications, they probably have read a hundred times where to place the speakers.
    By the way, Mr Bones, sometimes I enjoy my pickup truck that can sound like a 16 year old’s. I’m in my seventies.

  • Rumi

    in my experience, even the “equilateral triangle” advice is a myth. I almost always end up widening the speaker angle. My ATC SCM100A are almost parallel to the back wall, for example.

  • Justin C.

    If you follow the full guidelines here you should be able to get that too!

    With that said, if you did want mixes that have tons of bass, it’s probably not best to be monitoring on a system that puts out exaggerated bass anyway.

    Unless you learn to really fight what you’re hearing, your mixes will tend to sound like the inverse of your speakers:

    Bright monitoring tends to lead to dark mixes, boomy monitoring tends to lead to bass-light mixes, and so on.

  • Scott

    Your comment made me fall asleep.

  • Jason Kohnke

    Unlike the comment from the cro-magnon, this is great information. The spreadsheet was interesting. Thanks Carl for taking the time to comment.

  • Carl T

    Thank you Jason. Please let me know your results if you decide to follow the NPE. The secret is to follow it exactly as prescribed.

  • Jason Kohnke

    I have looked at the sample version and am curious how you came up with the suggestions. Based on the graph, I do not see how the suggestion of “ear height” equates? Is it the intersection of certain axials or? https://uploads.disquscdn.com/images/66d3a60c2dc661b6e62013bf916ec9847057dbe7b139e16377fc66ccbeb6a428.png

  • Carl T

    Call me on my cell (615) 400-5479 and I’ll walk you through it.

  • Jesco Lohan

    Hi Carl,

    thanks for chiming in and the amazing work you do! I wouldn’t be here without it.

    I’ve studied your approach in great detail, and after much experimentation came up with these adaptions to them, to apply the same theory in small and asymmetrical home studio rooms and only using music and your ears.

    On boundary compensation: you’ll find that I covered that under “The Magic of “Room Control” (aka “Space Loading”)”.

    To place your sweet spot in the best position in terms of room modes (including avoiding the axial null), I’ve developed the Bass Hunter technique, which you can find here:

    http://www.acousticsinsider.com/fixing-low-end-without-knowing-acoustics/

    All the best,

    Jesco

  • Jacob W-Petersen

    A useful tips for small spaces is to start with a listening height at about 87 dB and then adjust down into small step. Here it is possible to hear most details without bass frequencies blurs the mix. Another tips is to listen to the whole mixed in mono and make adjustments, and then switching back to stereo.