Experts teach you how to solve the low frequency standing wave method

The first thing to declare is: I am not an acoustic expert, so this article does not talk about theory. The second thing I want to make is: I haven't tried some methods myself, but I have experienced some magical use in some of my predecessors' homes. The third point is to start with the needs of the living room and sound room in the general family. If you specialize in acoustics, this article does not have to be read, I should know everything I said. If the hostess in the house does not allow you to make a big effort, you can't stick to the West, or don't agree to spend money, but when you listen to the sound, you will suffer from the rumble of the low-frequency standing waves. Welcome to try it out, maybe you can Find a solution.


Is the mid-low frequency standing wave so terrible? In fact, each room has a standing wave, but the frequency distribution is different. The smaller the frequency, the lower the frequency of standing waves, and the smaller the impact. How do you know the standing wave frequency of the room? The distance of the longest side of the room is removed to remove the sound wave by 340 meters per second. For example, the room has a length of 5 meters: 340/5 = 68. In half wave, there will be a larger protrusion at 32 Hz. Moreover, the standing wave is not only a single frequency, and the multiple of 32Hz like 60Hz, 128Hz??? also has a weak standing wave. Not only that, there are three sets of opposing walls in a confined space, so there are three different sets of standing waves. Even if a pair of super speakers with a frequency response of ±0 dB in a non-sounding room is placed in a normal space, the spectrum analyzer looks like the low frequency band is still high and low, the main reason is here.

As long as they cleverly handle or use low frequency standing waves, they are not as terrible as they think. I have heard a pair of American Legacy ultra-small speakers, in the magazine's dozens of ping space, you can understand that it has a low-frequency extension of excess volume, but it also pays the price of a high-power amplifier. Later, the agent was located at the opening of Tianmu's store. The same pair of small speakers in the first floor of the exhibition room, actually "grow up", the drums are low and strong, the double bass is pulled up to make people crisp, but the power amplifier is used instead. smaller. People who have heard don't believe that the small speaker can have such a sound, and even suspect that it is secretly picking up the subwoofer, but my speculation is that space has helped a lot, and the moderate amount of low-frequency standing waves makes the music more intense and heavy.

Unfortunately, not everyone is so lucky, the standing wave frequency generated in the space is not necessarily what you need. When the standing wave energy is concentrated at about 100 Hz, the drum point and the subsequent drum body will resonate too much, even if there is only a bang. At the same time, when bass and drum sounds appear, the two are easy to mix together and there is no clear melody line. At this time, the vocals usually carry some nasal sounds, as if the cold did not take medicine, and there is no transparency or detail at all. In case the energy of this standing wave is too strong, the sound can't be heard loudly, otherwise the window and the cabinet will be shaken together. In Taiwan's home space, the most common anomalous standing wave is about 50Hz. You can find a test piece to try it out. Usually, the sine wave signal will be full of sounds in the vicinity. The best way to avoid it is of course to plan a dedicated audio space, such as the golden ratio of 1:1.25:1.6 and 1:1.6:2.5. The IEC International Electrotechnical Commission also recommends this, but the apartment family can’t dream, so Don't mention it. You can also start by choosing the right size horn to avoid greed, and squeeze into the subwoofer in the three-flat space. The other is to use some props to overcome.


In the personal experience, to deal with the low-frequency standing wave, the diffusion is more effective than the absorption. In the professional studios and small concert halls, they deal with another method of standing wave, which is a low-frequency empty box. The manufacture of this empty box has a set of formulas that can be calculated. The material is mainly MDF board, which is then stuffed into fiberglass cotton. Its main function is to absorb a certain range of frequencies, and when the sound waves enter the empty box, they will be attenuated and absorbed by the energy conversion. The reason for the calculation is that the conditions of each space are different, and the frequency of attenuation needs to be different from the amount of energy, so this kind of thing cannot be mass produced. The studio's control room is at most six pings, but it can hear 20Hz extremely low frequency completely and straightly. The main secret is here.

Then the home can also be absorbed in the same way? No. Commercially available sound absorbing materials such as fireproof Sonex, the thickest absorption frequency is only about 500Hz, abuse of this sound absorbing material, maybe the low frequency standing wave is not solved, but even the precious intermediate frequency pass is sacrificed. Adding a wood partition to the cement wall is a method, but one project is quite large, and secondly, you can't know exactly what frequency will be absorbed (there is rarely a single frequency of absorbent material). It is also one of the ways to make a large curved arc, but to change the 100 Hz acoustic path, the required surface is 1.7 meters (340/100/2). How many rooms can you make? A more practical way is to put some empty boxes, wooden cabinets, or some high-quality objects in the corners of the room, such as boxes filled with books, chairs made of solid wood, and so on. These props have the effect of absorbing, or dispersing, the standing wave, but the frequency at which the frequency is affected, the degree of influence, must be tried by yourself. The wooden cabinet made of solid material nails is quite easy to use. It can be said that it is a replica of the low-frequency empty box in the studio, which is ideal for turning off the air or placing the record. It should be noted that the wooden cabinets need to be moved in and tried one by one, and there are side effects if they are large and not. In addition, posing a few large sofas also has some effects. Welcome to the home theater network shopping guide network!
You probably found out that the methods mentioned above have uncertainties. Some people find that the improvement is obvious, and some people may be indifferent. Uncertain factors include room size, equipment, environmental structure, etc. I can't provide you with any answers. Rather, it is easier to handle medium and high frequencies. Commercially available "Poli diffusion plates" made by styrofoam or various PRGs are useful. Those who wish to take care of the beauty can put artificial bonsai near the first reflection area of ​​the side wall behind the horn. It is best to use a fake tree with a relatively wide leaf. The height can be equal to the person. Are there any more scientific and available items for reference? The commercially available styrofoam diffusers are only effective for medium and high frequencies, and the imported or Taiwan-made wood-panel RPGs are also designed on the basis of 1000 Hz, and they pass Mofa at low frequencies. A year ago, I shrugged my shoulders on the low-frequency standing wave. Please ask others to experiment with the above methods. Can you cure them all by luck? I recently saw the advertisement of Taipei Luohua Company. They designed a large wooden diffuser plate for 100Hz~3100Hz. I am very interested to try it out.


When a big card comes in four diffusers, it really scares people! How to put such a big thing? How big is the diffuser for low frequency? How big is the diffuser for low frequency? It is about 120 cm high and 60 cm long and wide. All of them are nailed with MDF boards. Two strong men must be lifted. However, since borrowed, I had to go to the house with a hard scalp. Luohua's diffuser plate is also made according to the theory of quadratic residue sound diffusion proposed by Manfred Richard Schroeder, a professor of mathematics in Germany. However, the calculation method is changed to 1/4 wavelength, otherwise a 100Hz diffuser will have more than one length and width. There are no more people in the meter. In terms of production quality, the appearance of the black flat paint on the MDF board has been much improved compared to the first appearance of the veneer. I privately hope that Luohua can also produce some lacquer-transparent lacquer products. The color of wood in the home environment is not so great, and it is easy to match with furniture.

My large listening room has about 13 pings. The ceiling and the back wall of the horn and the two sides of the wall are treated with some PRG diffusing plates. Behind the listening position is a piano and a large tapestry, plus a sofa and wooden cabinet. , carpets and other furnishings. It turns out that there is a depression around 125Hz, and after adding two M&K subwoofers, it is adjusted by the spectrum analyzer. It can maintain the ideal state within ±2dB under 200Hz. These four giants, of course, only have such a large space to put up without a compelling sense of oppression. I placed them in the four corners of the room, hoping to further improve the resolution of the low frequency. In the past, we used arc or slanting plates at the corners, which usually have the effect on medium and high frequencies. The RoomTrap or RoonTune are also absorbed for medium and high frequencies so that they do not have excessive tightening energy. They are helpless at low frequencies. Nevertheless, the use of these methods has significantly helped the expansion and clarity of the back of the sound field. If Luohua’s diffuser can be evenly matched with low frequency, wouldn’t it be awkward?
For more than a month, I moved and swayed, and carried out unprecedented physical labor. Because the Luohua diffuser is too big, it is often necessary to change the position and even the equipment to move, and these latter stages expand the mobile to move more than five or sixty kilograms, but fortunately the weather is still cool, or it must be heat stroke. In my big listening room, the Luohua diffuser did not bring earth-shaking changes. It should be said that there was no serious low-frequency standing wave in this space, so it could not be allowed to exert its strength. However, if you compare them carefully, you will still find that the sound below the mid-range is all relaxed. Dorian's sacred "harmony" symphony still has air fluctuations caused by extremely low frequencies, but the energy spreads evenly; RR's "Beachcomber" drum beats down. The floor will also be shaken, but the disgusting stimuli are reduced; the special effects of Telarc's "Starship Adventures" are scary, but the turbulent shock waves will not let the dirty ones roll.


Mr. Luo Hua Yao suggested that the effect of these diffusers in the small room would be more significant, so they moved to the small listening room of about six and a half. The two side walls are filled with records, and the uneven surface is deliberately created. The back of the listening position is a wall book. As for the back of the horn, there are floor-to-ceiling windows with curtains. The window is the rare green mountains and green waters in Taipei. In the summer, there are often cool breeze blowing, I can't bear to modify. After a large amount of diffusion treatment, the mid-high frequency is quite smooth and flexible, but there are still some low-frequency standing waves with a large fluctuation below 50Hz. It’s hard to “plug” the four low-frequency diffusers to the four corners, and the visual pressure has increased a lot. This is something that buyers interested in must consider. Welcome to the home theater network shopping guide network!

Sure enough, the low-frequency diffuser played a role here, and the low-frequency of the Magnepan MG-35 flat-horn speaker extruded through Aragon's front and rear stages is strong and powerful, and the control is tight and transparent. However, in this space, the lowest part of the electric bass is prone to a low frequency peak. Listening to some Mandarin songs is also prone to uncomfortable sounds. After the diffusion treatment, the low-frequency peak disappeared, and the feeling of the bombing was gone. This pair of flat speakers can finally sing loudly here, giving a very natural and transparent sound. It should be noted that the low-frequency sense is not reduced, but spreads evenly. When the volume is turned on, there is no special energy, and the sense of hearing is much more comfortable. According to Luo Hua Yao, his audition room is only three pings. After using the low-frequency diffusion board, the large-scale horns are still brave and powerful, and there is no trouble with low-frequency standing waves. Mr. Yao often participates in discussions on the BBS computer network. Those who want to know more about it may wish to ask him directly.

Although the low-frequency diffuser is quite effective, due to the huge size, it is still necessary for readers to first look at their own space, and don't buy it home to be scared. However, I would particularly recommend Luohua's other diffuser for medium and high frequency. Its volume is 61×121×21cm, and its weight is also more than 30 kilograms. It is designed according to the theory of quadratic residue diffusion, but the data is changed to 1/1. The 4 wavelength is calculated, so the step is twice as long as the common soap PRG, and the diffused waveform is more uniform. I put the Rova diffuser on the sides of the large listening room to replace the original RPG, and also placed behind the small listening room speakers (that is, in front of the floor-to-ceiling windows), and found that they are more effective than RPG. The smaller the room, the more you can appreciate the ad: the room seems to be missing!