Why can't Bluetooth speakers talk about sound quality

In the past few years, the biggest change in the speaker equipment market has been the crazy growth in sales of portable Bluetooth speakers. With the advantages of no cables, small size, and no need to toss the front end, in the statistics of many home appliances, the overall sales of Bluetooth speakers have begun to catch up with or even surpass the traditional active 2.0 or 2.1 speakers.
 
However, in contrast to the huge sales volume, many users find after purchasing that the sound quality of the Bluetooth speakers they buy is often not as good as they thought, so there is a saying that "Bluetooth speakers can only hear a sound."
 Bluetooth Speaker
The sound quality of Bluetooth speakers is generally not good. Whose "pot" is it? Let's talk about this issue.
 
How much does Bluetooth audio transmission affect the sound quality?
 
When it comes to factors that affect the sound quality of Bluetooth speakers, the first thing many people think of is the loss caused by Bluetooth audio transmission.
 
In fact, as early as the Bluetooth 2.0 / 2.1 era, the Bluetooth transmission rate has reached 2.1 Mbps, which is sufficient for high-quality audio transmission. However, when performing Bluetooth audio transmission, whether it is the early Bluetooth 2.0 / 2.1 or the now very popular Bluetooth 4.0, the same A2DP protocol is used (some manufacturers equate Bluetooth 4.0 with "good voice" during publicity. Even "lossless" is nonsense).
 
Since the A2DP protocol greatly limits the transmission bandwidth, the audio signal needs to be effectively compressed to ensure real-time playback at the receiving end. This provides a variety of different encoding and decoding schemes in Bluetooth audio devices.
 
There are three main existing Bluetooth audio codec schemes: SBC, AAC and apt-X. Among them, SBC is the ancient but still the most common Bluetooth audio codec scheme, while AAC and apt-X are relatively new. Certain improvements have been made in the SBC scheme. Theoretically, the sound quality is better than the SBC scheme. The AAC scheme is mainly Used in Apple devices such as the iPhone, the apt-X solution is more common in mobile phones of brands such as vivo and Samsung.
 
It should be noted that although apt-X claims to be a "CD-level" audio codec solution, in actual use, apt-X is much better than the old SBC, but it is still far from "CD-level" transmission. distance. In addition, apt-X needs to support both the transmitting device and the playback device. If you want to use apt-X, in addition to a mobile phone that supports apt-X, you must check whether the speaker itself supports it before buying a Bluetooth speaker.
 
If you want to name these three codec schemes, apt-X is better than AAC and SBC under normal performance, and there is still a significant gap compared with traditional wired audio transmission. However, if this gap is placed in a small-volume Bluetooth speaker, the impact on sound quality is actually far less than theoretical.
 

In addition to "conventional protocols" such as SBC, AAC, and apt-X, Sony has also introduced a Bluetooth transmission standard called LDAC, which can provide a bandwidth of up to 990kbps, which is higher than apt-X, and theoretically can further improve Bluetooth audio transmission. Sound quality, but currently LDAC only supports part of Sony’s own devices. If you want to experience LDAC, you need a ZX2, ZX100 and other players or Xperia Z5 and other smart phones, and buy a MDR-100ADN Bluetooth headset or X99 wireless speakers and other equipment. The application range is narrow.

 
sony-srs-x5-bluetooth-speaker-product-photos04.jpg AUX port on the back of Sony SRS-X5
 
We can prove through a simple test that most Bluetooth speakers have an AUX linear input interface (3.5 mm headphone jack). We can use a dual-head 3.5 mm audio cable to directly connect the analog audio output from a mobile phone or Hi-Fi player Input to the Bluetooth speaker, and then compare the difference in sound quality using Bluetooth transmission.
 
In most cases, with these two modes, the difference in sound quality is often small or even inaudible. Take the Bose Soundlink Mini (first generation) as an example. After switching to the linear output, the sound will retain more high-frequency details, the low-frequency will become less "heavy", and the sound will become more "clear", but this The improvement of this kind of sound is still relatively limited, and there will be no feeling of "Alto changed to Audi". In addition, the sound quality of most Bluetooth speakers on the market is not as good as that of Bose Soundlink Mini. Bose is still so. The sound quality improvement of other products using linear input is often smaller than that of Bluetooth.
 
In short, in portable Bluetooth speakers, Bluetooth audio transmission does have an impact on sound quality, but it is not enough to become a bottleneck for sound quality.
 
The speaker size determines the upper limit of the Bluetooth speaker
 
Compared with Bluetooth audio transmission, the larger limitation of Bluetooth speakers in terms of sound quality performance is the size of the speakers.
 
In audio equipment, the volume and sound have a great relationship. The sound quality of a large volume is not necessarily good, and the sound quality of a small volume is almost impossible. The Bluetooth speaker belongs to the latter.
 
In portable Bluetooth speakers, due to volume limitations, the most common solution is to place a full-range unit of about 1 inch on each side, and use a passive diaphragm to increase the low-frequency sense of volume. The number and quality of the sound units are the same as those of traditional 2.0 speakers. A relatively large gap. At the same time, limited by the volume, the interval between the two full-frequency units in the Bluetooth speaker is often very small, which will also affect the degree of sound separation.
 
Due to this "compact" design, the sound quality of Bluetooth speakers will be relatively limited. In order to get a better sense of hearing, there are often trade-offs in sound style. The most common solution is to increase the low frequency, and use the "moving and hitting" bass to "catch" the user's ears for the first time.
 
The Bose Soundlink Mini we mentioned above is an excellent representative of this aspect. Although its internal structure is not very special (two full-frequency active units + passive diaphragm), but with many years of technical accumulation, Bose The low frequency of Soundlink Mini has a very good sense of volume and texture, which is even a little incredible under this volume (if you have heard it, you should have a similar feeling).
 
It should be reminded that Soundlink Mini does not represent the average level of such "heavy taste" Bluetooth speakers. Many Bluetooth speakers on the market are tuned in this style, but with the exception of a few products such as the innovative Sound Blaster gong (a volume larger than Bose), the sound quality of most products is much worse than that of Soundlink Mini.
 
This low-frequency sound style will also bring some side effects. If you just want to listen to podcasts on Bluetooth speakers, or like me, because I am too old and don’t "cold" low frequencies, the sound style of Soundlink Mini is very likely. It's "the wrong way."
 

There is another type of Bluetooth speaker products on the market, which tend to retain the original sound style, such as Sony SRS-X5, Sugr Cube (Bluetooth version). The sound of this type of product sounds a lot "normal", but the result is that it doesn't sound as "powerful" as Bose's style. Those who like this style will like it very much, and those who don't like it will think that this type of product is completely compatible. Not on the price.

 
In addition to the above two types of products, there are some products that try to use "stacking" to fundamentally improve the sound quality. For example, the Edifier M7 "squeezed" into 4 speaker units (a pair of tweeter and woofer), 3 passive diaphragms, and adopted a two-way design that is common in 2.0 speakers. The result is that although the sound is good However, the volume of the product is greatly increased, and the most important portability of Bluetooth speakers is gone.
 
Bluetooth speakers are not born for "good sound"
 
The small size and "compact" design determines that the upper limit of the sound quality of Bluetooth speakers will not be too high, and Bluetooth transmission will also bring certain side effects to the sound quality of Bluetooth speakers.
 
In order to get a better sense of hearing under limited conditions, Bluetooth speakers need to make a trade-off in the sound style.
 
The value of Bluetooth speakers lies in the richer application scenarios compared to traditional speakers: when we go out, we can pack the Bluetooth speakers in our backpacks like a bottle of water; for square dance enthusiasts, we have a "big voice" Bluetooth speakers can help them engage in "battle" anytime, anywhere; by adding lanyards to the speakers, adding waterproof functions, etc., Bluetooth speakers can also cover places that traditional speakers simply cannot imagine.
 
And this is also the original intention of the design of products such as Bluetooth speakers. It is not to provide the best sound, but to adapt to more occasions, and then try to make the sound better.
Passive Speaker:Bluetooth Speaker