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Now more and more people are beginning to like heavy bass.
From the shock effects of DJs, metal and movies, fist-to-flesh heavy bass has become an integral part of young people.
Even, if you have read the author's previous article, you can understand that many of the instruments and vocals that make up HIFI music can only be controlled by a high-quality subwoofer.
So whether it's listening to HIFI or watching a movie, opening the body or hiing yourself.
If you can have the support of high-quality heavy bass, the down-to-earth experience will make you more "live".
But the facts are often a slap in the face.
Many friends bought a subwoofer home with great anticipation, but found that it was not what they imagined at all.
Low frequency, it's really fierce.
But what followed was a headache-blowing roar.
The whole room rumbled, as if the house was about to collapse.
Why is that?
Is a subwoofer really so fun?
No.
Because there may be something between you and the fist to the heavy bass of the meat.
It is standing wave.
This is the main culprit that subwoofers are difficult to tame, and it is one of the reasons why many HIFI players talk about subwoofers.
What is standing wave?
Standing waves are ubiquitous in nature, referring to two waves with the same frequency and opposite transmission directions (not necessarily radio waves, as large as gravitational waves of the earth's magnetic field, as small as the undulations of the water surface. ), a distribution state formed along the transmission line.
Mechanics, acoustics, electromagnetism and other fields have been applied, and the Mach ring of the supersonic fighter engine shown above is also due to the standing wave phenomenon.
But in acoustics, we are generally talking about the standing waves of sound waves.
This phenomenon is very common in low frequencies, and the reason is not for him, mainly because the wavelength of low frequencies is too long, so long that a single crest can span several of your audiovisual rooms.
Unbelief?
So let me list some data:
Length of 200Hz sound waves: 1.71 meters
Length of 100Hz sound waves: 3.43 meters
Length of 50Hz sound waves: 6.86 meters
20HZ Sound Wave Length: 17.15 meters!
Okay!
The length of a crest reaches a length of 3-17 meters, so what is the order of magnitude of the length of a complete crest trough compared to your audiovisual room?
Normally, it is very good to have an audio-visual room or home theater space of 30-50 square meters.
But even a 50-square-meter audio-visual room is only 6 meters and 8 meters in length and width, which is only enough for a 63Hz sound wave to run a crest.
What about lower frequency sound waves?
Before the energy in the room could even form a complete crest, it hit the wall and reflected back.
Energy generally does not disappear for no reason, but only superimposes with the next crest or trough that follows, and forms a standing wave.
It's a complicated process.
Because whether it is a Mach ring or a water wave, the release of general waves and energy is relatively uniform.
The tone of the sound is changing at any time, which means that the energy reflected back each time is different from the new sound wave, and the waveform of the standing wave is also changing at any time.
Thus, the disturbing rumble of chaos appeared.
It makes you have a headache and even want to smash this damn unlucky thing directly.
But having said that, we can't do anything about Zhubo?
Of course not.
Since the emergence of the first subwoofer to the present, various experts have tried to solve the problems, in addition to how to restore the timbre of low-frequency sound more accurately, how to eliminate low-frequency standing waves in a small space is also a key research direction.
How to solve the problem of standing waves
First of all, let's "see" what sound waves really look like?
Really see him clearly in order to better control it.
The author put a picture on it, which should be most people's understanding of sound waves.
There are peaks, and there are troughs.
But in fact, such a conceptual map is actually just a section of the sound wave.
If we want to "see" the sound waves more vividly, we need to extend these profiles and connect a circle with the sound source as the center.
Then, if we could find a place that could make the vacuum and the atmosphere have a clear boundary like the surface of water and air, it would look like this:
Yes, sound waves and water waves are really similar, with peaks and troughs.
It's just that the visual effect of this perception is still only a one-sided understanding of sound waves, after all, sound is a kind of energy, a vibration of the emitter, a way to change the density of the air.
Enough already.
Because it's a little hard to imagine deeply.
It's as if visually, we can't understand a space above four dimensions.
And through this actual picture of sound waves, we can also speculate a lot of things.
It's like when the length of a wave exceeds the size of the room, what does it become?
The answer is this:
A crest of about 100Hz occupies the entire space, and then when it is reflected back, it must have a superposition and cancellation between it and the trough.
Just ask such an environment, where is the standing wave?
If you think a little more, it should not be difficult to find its location, right?
Very good.
When we master this, we can understand the next content very vividly.
The low-frequency sound waves hit the smooth surface and reflected, then met themselves and formed several harmonics and standing waves, which is also the culprit we hear rumbling.
OK。
I don't know if everyone understands?
Anyway, I'll move on.
Borrow a picture to speak:
This is a deduction of wave reflection, and we can see that when the sound wave hits a corner, its reflection and superposition effect is stronger.
Borrow another picture:
This deduction also shows us that when a wave encounters an irregular surface, it will be beaten into a more fragmented structure.
Scattered sound waves are not easy to form standing waves, and standing waves in corners will be more intense.
According to these two characteristics.
We have a solution: break up the low frequencies and absorb them
How do you absorb low-frequency sound waves so that they disappear before standing waves are generated?
This question is easy to answer, let's first reduce the number of "corners" in the room, and then appropriately increase the sound-absorbing material.
The fewer the angles, the less likely the room is to produce relatively strong pulsed standing waves.
But the problem is, we can't always design rooms to be round, can we?
After all, real estate is expensive.
Therefore, low-frequency traps are a much better solution than the value generated by wasting area.
This is a structural part made of a strongly attractive material, usually arc-shaped.
By installing it on the edges and corners of the room, the corners can be structurally disappeared, and the strong sound-absorbing material can better absorb the energy of low-frequency sound waves and reduce the number of its reflections.
The sound we hear is nothing more than a cross-section of sound waves, so without considering high fidelity, it really only needs to walk completely out of our eardrums once.
The problem of the corner is solved, what to do with the reflection of the wall?
With the previous simulation graphics, this question is actually not difficult to answer.
A better solution is to properly install diffuser panels to break up the low-frequency sound waves reflected by the wall.
Once the sound wave is scattered, the angle and time difference of reflection will be different, turning into scattered energy and then contacting other waves, and the production is no longer standing waves, but beautiful odd harmonics and even harmonics.
As for what is a diffuser plate?
This question is better explained.
A diffuser plate is an acoustic sheet made of an irregular structure.
When the sound wave passes through the diffusion plate, due to the special structure of the uneven surface, the time and direction of contact between the sound wave and the surface will be wrong.
As errors occur, the angle and time of sound wave reflection become different.
Without a uniform structure, the fine energy is less likely to form a clear "echo".
Originally, this is the point of proliferation.
But for ELF sound, it can also indirectly solve the problem of standing waves, which can be described as a multiplicity.
It's just that when choosing a diffusion plate, you must pay attention to the fact that with the change of material and structure, the effect of diffusion will become different.
Choose the most suitable one according to your home environment, which is the best.
The preparations have been completed, so are there any details to pay attention to?
Yes, that is, even with the above equipment, the positioning of the subwoofer is also very important.
In fact, positioning those things is not only for the subwoofer, you need the same as your noble HIFI audio.
Unlike low frequency, medium and high frequency sound waves have strong directivity, wrong positioning, inaccurate positioning, your sister Cai Qin always sings with her neck crooked, how uncomfortable?
However, the article on the HIFI positioning problem is what the author should write later, and I will not do too much to describe today.
That there is no directional subwoofer, is positioning also important?
Yes.
Significant.
Although not as important as high frequencies, better positioning reduces the influence of standing waves at the root.
As for the method?
The low-frequency crawl, which is a bit dirty, but all talked about, is indeed a good way to locate the subwoofer: low-frequency crawling.
The method is to place the subwoofer in the listening position, that is, the emperor's seat, and play some low-frequency heavy music.
Then we ourselves need to crawl on the ground and crawl back and forth in the room like a large lizard, listening to low-frequency sounds from various locations with our ears.
This pose is really difficult to hold, and it is also quite indecent.
But only if you have tried it can you know that even with diffuser plates and low-frequency traps installed, the low-frequency effects you hear in different locations will still be very different.
At this time, you need to find the location where you can hear the low-frequency sound quality most clearly, and at the same time have the least standing wave phenomenon.
And this position is where you can hear the best low-frequency effect in the emperor's position when the subwoofer is placed in reverse.
One step away from perfect bass
Just follow the steps above and get ready.
It stands to reason that as long as the quality of the subwoofer is not bad, the bass in your home is already clean.
But in order to improve, we better also put on the equipment and make some appropriate fine-tuning of the parameters.
Next, we set up the microphone, turn on the device and the computer, and when the subwoofer gives a sine wave, we measure the frequency response curve in the current room.
Then see if there are particularly prominent peaks at certain low frequencies.
Where high, where it falls.
It's simple, right?
But I still have to say more, how to tune the low-frequency crest is also a matter of opinion.
The differences on this point are indeed very large, and the approaches of the old school and the new school are very different.
The old school will prefer to make the curve infinitely close to the straight line, let alone ± 3dB, even if it is a 0.5dB gap, it will be uncomfortable to watch.
The newcomers don't think so, preferring to keep the curve curvaceous.
The low and high frequency parts should have appropriate bulges so that they can be more natural from the hearing.
Why is the gap between the two so large?
The reason is not for him, it is all the trouble caused by this curve, and his name is called: equal sound curve.
ISO226-2003 standard isophony curve
Although our human ears can hear 20-20kHz sound, this limit is actually this value.
As the lower the low frequency dives and the higher the high frequency rises, the less sensitive the human ear is to sound in that band.
According to the standards shown above, if we want our ears to feel that the sound loudness of 63Hz is the same as that of 40dB at 1kHz, then we must adjust the sound pressure level in the 63Hz band up to 50dB separately.
If you take into account the logic that 3dB is doubled, the current 63Hz sound has reached 1kHz three times!
Is it really that high?
Judging from the author's several audiometric auditions, there is indeed such a need.
Moreover, the equal response curve has a certain gap according to different factors such as race, age, physical condition and other factors.
As shown in the figure above, Chinese people are much more sensitive to sounds with frequencies above 10K than other races, but there are obviously small defects before and after the 200-400Hz band.
So at this point, the author is on the side of the new school.
The adjustment on the curve cannot be according to a certain law, and the curve that is more in line with the user's own hearing is the most suitable curve.
Because there is another factor that no one can avoid here, that is, as we age, our hearing ability will also be damaged to varying degrees.
If it is really a bit "behind the ear", then it is also necessary to properly turn up the sound of the insensitive zone.
This is the greatest value of EQ itself, and it is also the detail adjustment of personalized settings.
These, diffuser plates and low-frequency traps can't give, bass crawling can't do.
But the devil is in the details.
How can I restore the most realistic sound?
How can you get the best out of your home?
EQ。
It's a good solution.
One more mouth
After listening to the above steps, many people may be even more deterred by the subwoofer.
Why?
Because it's expensive!
Originally thought that if you want low frequencies and texture, you can buy a good subwoofer.
As a result, in order to solve the standing wave, it was necessary to engage in so many things.
Then go to see the diffusion of good quality, look at the trap board, one set, there are tens of thousands of pieces can not be taken at all!
So think again, forget it.
Why don't you have this money to do something?
Well, yes, too.
However, the above content is actually aimed at most ordinary subwoofers.
If you start with a budget of forty or fifty thousand, there are several high-end subwoofers that come with a magical feature.
Without further ado, let's start with the previous picture:
When you are choosing a cannon everywhere, have you ever seen a product with this kind of microphone?
The price of such subwoofers is generally tens of thousands, and they will basically take the initiative to insert this thing on the gun and take an artistic photo.
Why?
Does it mean that this type of subwoofer can sing karaoke?
Not ha, and no one will howl with a subwoofer, right?
This microphone is learned, it is an acoustic test microphone, the main role is to collect acoustic data.
What is the data collected for?
Of course, for debugging!
But there is no EQ on the subwoofer, how to adjust it?
The answer is: autotune.
The high-end, subwoofer with the room adaptive system no longer needs to be equipped with so many weird things.
Just connect the microphone, fix the position, and then start the tuning system with one button, and the system that comes with the subwoofer can adjust your subwoofer to ten or nine.
As for the point that is not enough, what is the short?
It's mainly personalization.
After all, the program is dead, and the person is alive.
What kind of sound is best for you, of course, the device does not know.
But personalization does not affect its work.
Even if no diffuser plate or low-frequency trap is installed in the home, the subwoofer will release the hedge wave through reverse wave and similar noise reduction to eliminate the standing wave in the room.
So it's still the same question just now: where is this money spent?
Instead of buying extra diffuser plates and low-frequency traps, isn't it fragrant to go directly to a more professional subwoofer?
And when your home is also equipped with some diffuser plates (even if there is no subwoofer, the diffuser plate cancels echo very well. ), and when the most suitable subwoofer placement is found according to the principle, the effect of the adaptive system can be better.
Ay......
How to say it?
Automatic, artificial intelligence, AI, did steal a lot of people's jobs, including me.
If adaptive systems continue to develop, my long article today will really be a blank slate.
However, there is still a lot of room for subwoofer choices, and there are many guns that need to be carefully tuned to produce good results.
The main system is divided into three parts of equipment and seven points of adjustment.
Isn't playing fever playing on the last seven points?
epilogue
Let's talk about it today.
I wanted to say something more, but the number of words is already so much, and it is inevitable to say too much.
So the rest is left for the next issue, pay attention to me, and then tell you how many subwoofers at home are enough, and what the phase and delay of the subwoofer are for.