Optimizing Your Listening Position Using the 38 Percent Rule

Positioning your speakers and finding the ideal listening position is the first step toward achieving great sound, especially at low frequencies. While optimal placement alone won’t eliminate the need for bass traps and other acoustic treatments, it’s an easy and free way to help reduce low-frequency response errors and improve imaging.

It's the easiest step you can take to ensure you start on the right foot and make your room sound great. In just a few minutes and with no fancy equipment required, you can find your ideal listening position.

By finding your ideal listening position, you can be confident that you are sitting in the low-end sweet spot of your room. This means you are sitting in the one spot in your room where low frequencies are the most balanced.

In a critical listening environment, you want accuracy, balance, impact, and clarity in the low end.

Understanding the 38 Percent Rule

The method used here is based on the 38 Percent Rule, a theory popularized by acoustician Wes Lachot. Lachot has shown that the theoretical best listening position is 38 percent into the length of the room, when measured from the front wall. This offers the best compromise of bass peaks versus nulls for any given room size.

Understand that 38 percent is only the theoretical best location. It’s a good starting point, but in practice, it may not be best due to other factors - wall properties, speaker type and location, or perhaps a mixing console that’s too large to fit that way.

The 38% rule states that the most balanced listening position will be 38% of your room's length from the front or back wall. The 38% rule is more of a guideline - it’s a great starting point but not a hard and fast rule.

Here’s how to apply the 38% rule:

1. Measure the length of your room.
2. Multiply that measurement by 0.38 (38%).
3. Position your listening chair so that your head is at the calculated distance from the front wall.

For example, if your room is 7 meters long, the ideal listening position would be 2.66 meters from the front wall (7 * 0.38 = 2.66). You may find that 42% into the room actually sounds better.

If you’re stuck with a square room, try treating it like a diamond and put your speakers diagonally in a corner. To do this, measure the distance from one corner to another. Then multiply that distance by 38%.

Why it matters:

• It sets you up for success with a solid foundation: If you put your listening position in an unbalanced spot in your room, you’ll never be able to accurately hear your music/sound source and the true capabilities of your speakers and equipment
• It doesn’t change as you move your speakers or acoustically treat your room: You can find your listening position regardless of whether or not you have any acoustic treatment, you’re changing speakers soon, or you’re adding a sub, etc.

When it comes to acoustics, optimizing the listening position in your room is by far the easiest, fastest, and cheapest way to make massive improvements to the balance, accuracy, and tonality of your speakers!

Room Modes

Let’s take a quick second to discuss room modes. Room modes are resonances at specific frequencies in a room, excited by an acoustic source such as a loudspeaker. These resonant frequencies are usually in the 20 Hz to 200 Hz region. Room modes can cause certain frequencies to be amplified or attenuated in specific areas of the room. This can result in "boominess" at some frequencies and a lack of bass in others.

Identifying room modes is key to avoiding mix overcorrections or low-mid buildup during tracking. (You can also use a room mode calculator like Amroc)

Keep reading to find out how you can use room modes to help you find the best listening position in your room!

Speaker Placement

Once you’ve decided where to put your seat, the next step is placing the loudspeakers. The speakers and listening position should define an equilateral triangle, with the distance between the left and right speakers the same as the distance from your head to each speaker.

Tweeters should also be at ear level and pointed toward you for the flattest response, because most speakers have a skewed response with less high-frequency output off-axis.

Generally, a larger triangle creates a more accurate stereo image. However, this isn’t a hard-and-fast rule. Keep in mind that the larger your triangle size is, the closer your speakers are to the wall. You don’t want your speakers up against a wall if you can avoid it.

Quick Guide

For those who are looking for quick and simple steps to set up their room, we’ve included some general practices that can be helpful for your room sound. While every room will have its own challenges, here are some good places to start:

• Place your speakers along the shortest wall
• Form an equilateral triangle between either speaker and a point ~0.5 meters behind your head
• Maintain a minimum distance of 1 meter between you and either speaker
• Avoid placing objects between you and either speaker
• Position tweeters at ear level and angled slightly towards your ears

Symmetry

Left-right symmetry in a room is critical for good stereo imaging. If your setup is placed more to one side of the room, instruments and voices coming equally from both speakers will not sound centered as they should. When perfect symmetry is not possible throughout a room, at least aim for symmetry in the front. The most important area is along the side walls between your head and the speakers.

The speakers and listening position should define an equilateral triangle, with the distance between the left and right speakers the same as the distance from your head to each speaker.

The spacing of your speakers is different from person to person. If space allows, you should shoot for anywhere between 1.5 and 2.2 meters of distance. A good way to determine speaker spacing is by playing a reference track you’re familiar with and periodically moving the speakers inwards towards each other.

As you inch the speakers inward, take note of the stereo field. Does the track sound too wide or too narrow?

At about 1.5 meters, start gently toeing in the speakers until you feel the track is properly centered. Be careful not to toe-in the speakers too much!

Boundary Effect Compensation

There are a number of ways to compensate for the boundary effect:

• Place your speaker close to the wall, and use acoustic treatment to absorb any frequencies before they can be reflected.
• Place your speakers sufficiently far away from the wall such that reflected frequencies are out of the audible region of your speakers.
• Embed your speakers directly into the wall.
• Use EQ to compensate for the boundary effect!

Horizontal vs Vertical Placement

The type of speaker you choose will determine if you should place your speakers vertically or horizontally. Most speakers are traditional 2-way bookshelf monitors. Horizontal placement of these units may result in some unwanted interference, resonance, and can negatively impact your stereo image.

Some speakers are designed to function in any position as a point source. These speakers can be placed on their side. Because high frequencies tend to be more directional and low frequencies tend to be more omni-directional, orienting your tweeters on the outside will widen the stereo image and keep the low end more centered.

Optimal speaker placement can significantly improve sound quality in your listening space.

Identifying and Treating First Reflection Points

Now let's look at treating the first reflection points. The first reflection points are exactly halfway between you and the loudspeakers. This is valid for only a single listening position.

The most important area is along the side walls between your head and the speakers. The first step is to identify the ideal listening position within the room, and from there you can determine the best speaker placement.

In rectangular rooms, the low bass response is most lacking at the halfway points:

• Halfway between the front and rear walls
• Halfway between the left and right side walls
• Halfway between the floor and ceiling

Therefore, the bass response is worst if you sit in the exact center of the room, at a height that puts your ears halfway between the floor and ceiling. You shouldn’t put speakers along any of those centerlines for the same reason; when a loudspeaker is in a room’s null spot, its output is reduced considerably at low frequencies whose wavelengths are related to that dimension.

The best way to know if small positional changes help or hurt is with room measuring software, such as the freeware Room EQ Wizard program. This lets you experiment with different speaker distances by sliding both speakers along their axes as shown, while measuring the response at different proposed listening spots. Otherwise, simply put the speakers at a distance that’s convenient and sensible for the size of your room while keeping an equilateral triangle.

Bass Traps

Bass frequencies are the most difficult to tame in a small room because the wavelengths are long, which requires thick absorbers called bass traps.

Most rooms have many such nulls in the range below 300Hz or 400Hz, but some people fear that adding bass traps will reduce the amount of bass even further. In truth, bass traps reduce peaks and also raise nulls, so they make the response flatter, rather than add or remove bass. In many rooms, the main problem is deep nulls caused by reflections from the wall behind you combining out of phase with the direct sound from the loudspeakers. Therefore, adding bass traps increases the perceived level of bass. But in some rooms, especially those that are square- or cube-shaped, peaks can dominate the response. In that case, adding bass traps reduces the peaks, again making the response closer to flat. Whether peaks or nulls are the larger problem also depends on where in the room you listen.

Because deep nulls cause you to hear less bass than is really present, you’ll tend to add too much bass to compensate. As you can see, the finest loudspeakers in the world are of little value if your room skews everything you hear this badly.

When bass traps are added to a room, the low-frequency response also changes less around the room. The most effective place for bass traps is in corners where bass waves tend to gather, though other locations are also viable. Note that rectangle rooms have 12 corners: four where each wall meets another wall, four where each wall meets the ceiling and four more where each wall meets the floor.

After treating as many corners as is practical, the front and rear walls are good candidates for even more bass traps. When bass traps are added, the response not only becomes flatter, but also tighter and clearer because the decay times are reduced.

It’s impossible to make any small room perfectly flat, so the more bass traps you add, the closer you’ll get. It’s that simple. The only trade-off is how good you want versus how much effort and expense you’ll endure. The response and ringing in these graphs is about as good as can be expected in a small room, short of lining every single inch of room surface with extremely thick absorption.

Bass traps improve low-frequency response by reducing peaks and raising nulls.

Step-by-Step Guide to Finding Your Listening Position

Here is a step-by-step guide to help you find your ideal listening position:

1. Step 1: Post-it Notes or tapePlace a Post-It Note or strip of painter’s tape on the floor along the line of your string every 6 inches (15cm). Yes, it is a lot of Post-It Notes, but moving 6” forward or backward can make a massive difference, especially if your room is not acoustically treated.
2. Step 2: Place a speaker or sub in the front corner of your roomBy placing the speaker directly in the corner on the floor, we can amplify the distortions caused by the room modes and ensure we are not hearing dips or peaks caused by speaker boundary interference (SBIR) from the floor, side or front wall.
3. Step 3: Cue up your three favorite reference tracks or pink noise
4. Step 4: Take a seat - you’re ready to start listening!Be sure to keep your ears at the same height they’ll be when you are mixing, producing, or listening to music!
5. Step 5: Hit play and listen criticallyWhile playing either songs you’re familiar with or pink noise, sit in a chair (ideally with wheels) and slowly move from the front of the room to the back of the room along the center line you created earlier. As you are moving across your room, pay close attention to how balanced the low end is. Make mental notes of how things change and where you are in the room.
6. Step 6: Make your marksMark the most balanced-sounding locations with a piece of tape or by writing an ‘X’ on the Post-It note. The Post-It note method is so powerful because it allows you to quickly compare two or three spots in a very controlled manner.
7. Step 7: Narrow it downWith your options narrowed, go back and listen again, quickly comparing each location - speed is important here as we have terrible auditory memories. As you move through the room on your second, third, and fourth passes, start pulling up the Post-It Notes at the most imbalanced spots in your room. After a few passes, you’ll only have a couple of Post-It Notes left on the floor. Listen again to your last few spots taking your time to really pay attention to the subtleties between them.
8. Step 8: Finish up and enjoy your listening spot!Using all the marks you made, identify the sweet spot where your low end is the most balanced. Once you’ve identified the location with consistent and balanced bass, not too much or too little sub-energy, and no massive holes, you have found your listening position! Tear up all of the other Post-It Notes and make a note of your listening position unless you want to leave a Post-It Note on your floor forever.

Using Room EQ Wizard for Testing

Since every room is different, we still need to run actual tests to find the ideal setup. Sketch out 3 or 4 different speaker setups for your room. As you compare these setups, you’re looking for the position that gives you the flattest frequency response possible.

Room EQ Wizard is a free software that will help you measure the frequency response of different places in your room. Room EQ Wizard is kind of daunting when you first look at it.

1. First, you’ll want to set your room up in the position you’d like to test. Use a protractor to make sure the speakers are 30 degrees to the left and right of the mic.
2. First you’ll use Room EQ Wizard to calibrate your soundcard.
3. After that you can start measuring your different room setups. Make sure your measurement mic is set as the audio input.
4. Hit “Start Measuring.” A sine sweep will play through your speakers and Room EQ Wizard will create a graph of your room’s frequency content.
5. Once you’ve tested every position, click the “Overlays” button in Room EQ Wizard. Find the measurement that looks the flattest.

Acoustic Room Treatment Guide