If you listen carefully to musical instruments attempting to play in unison with each other, you might be surprised by what you hear. You might think if one player plays a note at a particular dynamic and then another player joins in perfectly in unison at approximately the same dynamic, the volume you hear should double. But it doesn’t. I’ll talk about why this is in this post.
The human ear hears on a logarithmic scale – doubling the sound level on the same frequency does not double the sound perceived by a listener. Doubling the sound level on a different frequency, however, does. This is due to different receptors in our ears being excited by different frequencies and when a new receptor is excited, the perceived sound is louder.
If you’re listening to a band playing, the balance of the sound is very important. You don’t want to hear one instrument loudly above all the others (unless it’s playing a solo). A big part of getting this balance right is getting the instruments in tune. You may not be consciously aware of it, but if a section of an orchestra is not in tune within itself, it will appear louder than the others.
This ability of the ear to pick out when a section is out of tune is very inconvenient for players. If you have a flautist, for example, who is out of tune with the others flautists, the last thing you want is for them to actually be louder than the others. But this is the unfortunate truth when it comes to the perception of the human ear. Let’s talk in more detail about why this is.
How does the human ear hear sound?
To fully understand this topic, we need some basic understanding of how the human ear works. We can think of this in a series of steps:
- A sound wave enters the ear canal
- The sound wave reaches the ear drum, causing it to vibrate
- The vibrations pass through the ossicles (middle ear bones) into the cochlea (inner ear)
- There are hair cells in the cochlea – different frequencies of sound are caught by different hair cells and turned into electrical signals
- The electrical signals are sent to the brain through the hearing nerve
The part we need to consider in detail here is step 4. When the vibrations from the sound wave get to the hair cells, receptors in some of the cells will be excited. Different hair cells are designed to detect different frequencies. The (high frequency hair cells are more delicate and easily damaged)The part we need to consider in detail here is step 4. When the vibrations from the sound wave get to the hair cells, receptors in some of the cells will be excited. Different hair cells are designed to detect different frequencies.
High frequency hair cells are more delicate and easily damaged, so people that experience hearing loss are more likely to lose their hearing of high-pitched sounds. This is because the wavelength of high-pitched sounds is shorter, so the receptors are smaller and more likely to be bent or broken. Keep this in mind for the next section.
Why aren’t two instruments twice as loud as one?
As I said above, if you hear one player play a note at a specific dynamic, then another player joins in perfectly in tune and at the same dynamic, you should hear double the amount of noise. But that isn’t how we perceive it. Yes, the noise you hear gets louder, but it definitely isn’t doubled. But how can this be the case, when the actual volume is twice as much?
The answer is that humans hear on a logarithmic scale. Volume is measured in Decibels. If 1 decibel of sound is produced, you hear a certain amount of sound, through the excitation of the set of hair cells designed for that frequency of sound. If you double the amount of sound you allow the ear to perceive, you are sending two Decibels to the hair cells instead of one. You are exciting the same receptors, just with more sound.
Because the receptors you are sending the sound to are already excited, the introduction of twice as much sound does not double the amount of perceived sound. The human ear, like many other senses in the human body, hears on a logarithmic scale. This means that 10dB is double the volume of 1dB and 100dB is double the volume of 10dB, assuming the sounds are the same frequency. That means you’d need 10 flutes playing perfectly in tune at the same dynamic to sound twice as loud as one!
Why do we hear instruments louder when they’re out of tune?
The fact that different frequencies excite different receptors in the ear is the main reason why the reason why we hear out of tune instruments more loudly within a group. You often find that if the flute section is playing a passage with high notes in unison, they will be very easy to hear if they’re not in unison with each other. This is a pretty unfortunate consequence of the way the human ear works.
If you think of one flautist playing one note and then another flautist joins in at the same dynamic but a different pitch, this will sound louder than two flautists playing in unison. This is because you’re exciting different receptors. There isn’t more noise coming from the instruments, but the sound perceived will be greater, assuming they are out of tune far enough to excite different receptors.
The main point is that a particular frequency excites a particular receptor in the ear. Once excited, to hear twice the volume at the same frequency requires 10 times the amount of volume from the players. However, playing at a different frequency excites different receptors and therefore two different notes, or two notes that are out of tune will actually sound twice as loud.
This is why getting the tuning right in a band is so important. Bad tuning can’t be hidden easily because it’s fundamentally going to be heard more clearly by listeners. The in tune parts will be drowned out and you’ll get a rubbish overall sound. Make sure everyone is listening out for their tuning – if you think you’re playing too loud, it’s possible that you might just need to get your tuning right.