The sound quality of the bluetooth speakers
The quality of the sound reproduced by a bluetooth speaker is certainly of vital importance. I personally don’t like those overly cheap audio sources or the speakers of some smartphones that reproduce sounds and consequently also music with distortions.
Music is music and should be listened to well and from my speaker I expect the best in this regard. Moreover in this case we are talking about a product that is specifically dedicated to listening and therefore how to think not to claim the top.
How do we know if the bluetooth speaker we have spotted is good in terms of sound quality? There are two parameters that we can check immediately on the product’s technical sheet, which make us understand how high the audio output of the case will be. I speak of two quantities that concern all the products of this type:
- Signal to Noise Ratio, or signal-to-noise ratio, indicated with the abbreviation SNR.
- Total Harmonic Distortion, or total harmonic distortion indicated by the initials THD
Let’s start with the first one. The signal-to-noise ratio (SNR) is a number that relates the useful signal, in this case the reproduction of a piece of music, and the noise, which is usually always present in any type of speaker and is due to the simple fact that it is an electronic device. It is measured in decibels (dB) and clearly the greater this number, the higher the sound quality of the case. Being a relationship between signal strength and noise power, it works like this: if you had a case with a 10 dB SNR in your hands, it means that the signal is 10 times more powerful than the background noise, and it’s not absolutely satisfactory, when you turn it on you will clearly perceive a disturbance in the reproduction. To make you understand even better, just think of a radio: if we don’t tune in to the correct frequency, you will definitely hear a song or the speaker speak, but in the background you will also hear a whole series of audio disturbances that act as a carpet for the broadcast. This is a very clear example of low SNR. Another example is analogue television, the one that had to be tuned « by hand » by moving the antenna, some will surely remember. When the antenna didn’t work as it should, the image on the screen was completely distorted and full of noise. This instead is an example of analog video SNR.
Returning to our bluetooth speakers, a more than satisfactory SNR value is 80 dB or greater. Clearly, if this is higher than 80 dB we will certainly have a clearer audio experience.
The total harmonic distortion (THD) tells us how much distortion the device introduces into the signal being played. Any electronic device not only produces noise, as seen above, but also a distortion that goes to alter the reproduction itself. It was established many years ago by the Deutsche Institut für Normung (DIN), a German organization that deals with standards and standards, that the maximum THD threshold was 1%. To better understand something, we can think that the speakers that are usually used for concerts and clubs have a THD 10 times lower than the standard level, or THD = 0.1%. The hi-fi systems instead come to have a THD of a hundred times lower if not more, in the cases of more valuable devices.
The maximum THD threshold is already sufficient to guarantee a device that optimally reproduces music.
Now let’s look at the features related to the frequencies and how they are treated by the device. First of all, let’s start by saying something fundamental that concerns us. Our ears can only perceive sounds that are in a certain range of frequencies, and this range is divided into different types.
- <20 Hz. Below this frequency the human ear does not hear any sound. Here fall what we commonly call infrasound, or sounds below the minimum threshold.
- 20 Hz – 40 Hz. Very low frequencies. These are typically emitted from a subwoofer.
- 40 Hz – 160 Hz. Low frequencies.
- 160 Hz – 315 Hz. Medium-low frequencies.
- 315 Hz – 2.5 KHz. Average frequencies.
- 2.5 KHz – 5 KHz. Medium-high frequencies.
- 5 KHz – 10 KHz. High frequencies.
- 10 KHz – 20 KHz. Very high frequencies, still perceptible but strongly dependent on the age of the person and other factors. However, they are fundamental and enrich the listening of a piece of music.
- > 20 KHz. Here we find the ultrasound, or sounds that are no longer perceptible to the human ear. Bats are an example of a living species that can « hear » these frequencies, and use them to avoid obstacles at night. Even our best friends, dogs, have such « powerful » ears.
When we buy a bluetooth speaker, one of the first things to check is the so-called frequency response, which tells us the range of reproduction of the musical pieces.
How does an electronic device like a bluetooth speaker deal with the different frequencies? First of all, a bluetooth speaker is nothing but, in technical terms, a transducer, or a device that transforms one form of energy into another. In this specific case, the input is an electrical signal, the output is a sound. And since we talk about music, an acoustic speaker manages frequencies differently depending on the model and the price. Depending on how the frequencies are subdivided and treated, we talk about channels or ways. Each of this route is dedicated exclusively to a specific range. Clearly, the more we have, the better the reproduction will be and the higher the price.
Economical bluetooth speakers will generally consist of a single loudspeaker and a single channel, ie a single channel that simultaneously manages all the frequencies. The most expensive and best ones will often be two-way or even three-way. In the case of the two ways, there will be dedicated channels for medium-low and medium-high, while for the three-way channels, we have dedicated channels for bass, middle and treble.
The size of a bluetooth speaker strongly depends on this. A single-way speaker will certainly be cheaper but also more compact. One multi-way will be more cumbersome but the audio response is better, clearer and fuller.