How to calculate resonant frequencies in a room. View full version. Defining Reflection Points

Although acoustic reflections can cause problems in the clarity of the mix, the solutions that Mike Senior proposed are cost effective, and feasible to implement so that the problem of the “comb filter effect” does not arise in your mind. paths when creating a commercial grade recording. It is not surprising that the owners of ultra-modern studios followed the same direction. However, there is another aspect of acoustic design that is almost often and deliberately neglected due to the complexity of the problem and the high cost - room resonance.

Mike Senior:“To understand how the resonance of a room works, you need to understand how it resonates guitar string. At its lowest resonant frequency (the first level or, as they say, the “fundamental tone”), the string is stationary at the ends and vibrates mostly in the middle. However, the string has a second resonating tonality (second level or overtone) - it is twice the first frequency, as if the string were divided into two equal vibrating parts. The third resonating tonality (third level or second overtone) already has the string divided into three equal parts, the fourth into four, etc. top of the spectrum.

Why we needed an example with a string, but so that you would mentally understand that the air space of a room between its parallel boundaries (for example: between its opposite walls or floor and ceiling) has the same series of resonating frequencies. A simple, but not very accurate way to find the first resonating frequency of a room is to divide the number 172 by the distance between two parallel boundaries of the room itself (in meters). Subsequent overtone values will be multiples, as in the string example. For example, if the ceiling of your studio is 2.42 m from the floor, then the first resonance frequency of the room (in the “floor-ceiling” plane) will be within 71 Hz, the second at 142 Hz, the third at 213 Hz, etc.

Each level of the resonating frequencies of the room divides the distance between its boundaries in its own way, creating its own equal intervals. And if your listening point falls between these intervals, then in the sound spectrum of the room you will hear a decrease in the level at this resonating frequency, and if your listening point falls in the middle of the interval, this will lead to its increase. Since each pair of parallel surfaces will introduce its own series of resonating frequencies (and most rooms are “rectangular” in shape, meaning three pairs), the studio space is generously strewn with intervals of different frequencies in three planes.

Figure: The diagram shows the effect of room resonance on the frequency response of the monitor system. The figure shows the resonating frequency levels of a room 4.3 meters long from the front to the back wall. Resonance will occur at 40Hz, 80Hz, 120Hz and 160Hz. The letter N marks the boundaries of the intervals, and the letter A marks the middle of the interval. You must understand that they are shown separately in the figure for clarity of understanding, but in reality they are completely superimposed on each other. Two sections demonstrate how the frequency response changes when the listening position is moved to a distance of 75 cm.

So what does all this mean in practice? This means that even the first level of the resonating frequencies of the room will easily raise the spectrum in the resonance region by 20 dB. Only a flying pig is likely to be able to find a spot in the studio that gives the correct spectral balance if there are multiple simultaneous resonances. Plus, if you move around the studio, the frequency response of the monitor system will “writhe” like it’s “already in a frying pan.” I tried to illustrate the changes in frequency response in the figure. But to be precise, I will say that the levels of resonating frequencies first of all affect bottom part spectrum, since high-frequency resonances are more easily damped by the right room environment, but remaining distress zones below 1kHz will really spoil your proper mixing.

Since every room has a different structure, do this experiment to get a real picture of the impact of room resonance on your monitoring system: play the LFSineTones file while sitting at the listening position in front of the monitors and compare the relative volume of pure sine halftones. They will be played in ascending order over a range of three octaves. If your studio is like those small, unprofessionally prepared control rooms, you'll notice that some midtones are barely audible, while others are noticeably loud. Table 1 shows which semitones, as well as their frequencies, are played over time in the LFSineTones file. So grab a pencil and mark those wayward frequencies that stand out in the level. Now move from your listening point a few tens of centimeters in any direction, and you will notice that those frequencies that were overactive are now quiet, and those that were quiet before are overactive.

Now it's pretty reasonable to say that sine waves have little to do with real music, so you need to focus on how room resonance actually affects the bass line of professional commercial tracks (as you know, they have no problems with this topic). I offer as a standard the song “All Four Seasons”, it was invented and mixed by Hugh Padgham for the string album Mercury Falling. The bass range on this track is quite wide, but also extremely consistent, so the bass notes in this song will be fairly flat when played on any monitoring system. If during listening they turn out to be uneven, then you should seriously think about how to mix correctly in this situation.”

Optimizing speaker placement in a rectangular room

For achievement High Quality sound reproduction, acoustic characteristics Listening rooms need to be brought closer to certain optimal values. This is achieved by forming an “acoustically correct” room geometry, as well as using special acoustic finishing of the internal surfaces of the walls and ceiling.

But very often you have to deal with a room whose shape cannot be changed. At the same time, the room’s own resonances can have an extremely negative impact on the sound quality of the equipment. An important tool for reducing the influence of room resonances is optimization relative position acoustic systems relative to each other, enclosing structures and listening area.

The offered calculators are designed for calculations in rectangular symmetrical rooms with low sound absorption capacity.

The practical application of the results of these calculations will reduce the influence of room modes, improve the tonal balance and equalize the frequency response of the "AC-room" system at low frequencies.
It should be noted that the calculation results do not necessarily lead to the creation of an “ideal” sound stage; they only concern the correction of acoustic defects caused, first of all, by the influence of unwanted room resonances.
But the calculation results can be a good starting point for further search for the optimal location of the speaker from the point of view individual preferences listener.

Determining the sites of the first reflections

A listener in a room listening to music perceives not only the direct sound emitted acoustic systems, but also reflections from walls, floors and ceilings. Intense reflections from some areas of the internal surfaces of the room (areas of the first reflections) interact with the direct sound of the speakers, which leads to a change in the frequency response of the sound perceived by the listener. At the same time, at some frequencies the sound is amplified, and at others it is significantly weakened. This acoustic defect, called "comb filtering", results in unwanted "coloration" of the sound.

Controlling the intensity of early reflections allows you to improve the quality of the sound stage, making the speakers sound clearer and more detailed. The most important early reflections are from areas located on the side walls and ceiling between the listening area and the speakers. Besides, big influence Reflections from the rear wall may affect the sound quality if the listening area is located too close to it.

In areas where early reflection sites are located, it is recommended to place sound-absorbing materials or sound-diffusing structures (acoustic diffusers). The acoustic finishing of early reflection sites must be adequate to the frequency range in which acoustic distortion is most observed (comb filtering effect).

The linear dimensions of the acoustic coatings used should be 500-600 mm more sizes sites of first reflections. Parameters of the required acoustic finishing in each specific case It is recommended to consult with an acoustic engineer.

Calculation
Helmholtz resonator

The Helmholtz resonator is an oscillating system with one degree of freedom, so it has the ability to respond to one specific frequency corresponding to its natural frequency.

A characteristic feature of the Helmholtz resonator is its ability to perform low-frequency natural oscillations, the wavelength of which is significantly greater than the dimensions of the resonator itself.

This property of the Helmholtz resonator is used in architectural acoustics to create so-called slot resonant sound absorbers (Slot Resonator). Depending on their design, Helmholtz resonators absorb sound well at medium and low frequencies.

In general, the absorber design is wooden frame, mounted on the surface of a wall or ceiling. A set of wooden planks is fixed to the frame, with gaps left between them. The internal space of the frame is filled sound-absorbing material. The resonant frequency of absorption depends on the cross-section of the wooden planks, the depth of the frame and the sound absorption efficiency of the insulating material.

fo = (c/(2*PI))*sqrt(r/((d*1.2*D)*(r+w))), Where

w- width wooden plank,

r- gap width,

d- thickness of the wooden plank,

D- frame depth,

With- speed of sound in air.

If in one design you use strips of different widths and fix them with unequal gaps, and also make a frame with variable depth, you can build an absorber that operates effectively over a wide frequency band.

The design of the Helmholtz resonator is quite simple and can be assembled from inexpensive and available materials directly in the music room or studio space during construction work.

Calculation of a panel LF absorber conversion type (NCHKP)

The conversion type panel absorber is a fairly popular means of acoustic treatment for music rooms due to its simple design and fairly high efficiency absorption in the low frequency region. A panel absorber is a rigid frame-resonator with a closed volume of air, hermetically sealed with a flexible and massive panel (membrane). The membrane material used is usually plywood or MDF sheets. An effective sound-absorbing material is placed in the internal space of the frame.

Sound vibrations set the membrane (panel) and the attached air volume in motion. Wherein kinetic energy membrane is converted into thermal energy due to internal losses in the membrane material, and the kinetic energy of air molecules is converted into thermal energy due to viscous friction in the sound absorber layer. Therefore, we call this type of absorber conversion.

The absorber is a mass-spring system, so it has a resonant frequency at which it operates most effectively. The absorber can be tuned to the desired frequency range by changing its shape, volume and membrane parameters. Accurately calculating the resonant frequency of a panel absorber is a complex mathematical problem, and the result depends on large quantity initial parameters: method of fastening the membrane, its geometric dimensions, housing design, sound absorber characteristics, etc.

However, the use of some assumptions and simplifications allows us to achieve an acceptable practical result.

In this case, the resonant frequency fo can be described by the following evaluation formula:

fo=600/sqrt(m*d), Where

m- surface density of the membrane, kg/sq.m

d- frame depth, cm

This formula is valid for the case when the internal space of the absorber is filled with air. If a porous sound-absorbing material is placed inside, then at frequencies below 500 Hz the processes in the system cease to be adiabatic and the formula is transformed into another ratio, which is used in the online calculator "Calculation of a panel absorber":

fo=500/sqrt(m*d)

Filling the internal volume of the structure with porous sound-absorbing material reduces the quality factor (Q) of the absorber, which leads to an expansion of its operating range and an increase in the absorption efficiency at low frequencies. The sound absorber layer must not touch inner surface membranes, it is also advisable to leave an air gap between the sound absorber and back wall devices.
The theoretical operating frequency range of a panel absorber is within +/- one octave relative to the calculated resonant frequency.

It should be noted that in most cases the simplified approach described is quite sufficient. But sometimes solving a critical acoustic problem requires more precise definition resonant characteristics of a panel absorber taking into account the complex mechanism of flexural deformations of the membrane. This requires more accurate and rather cumbersome acoustic calculations.

Calculation of studio space dimensions in accordance with EBU/ITU recommendations, 1998

It is based on a technique developed in 1993 by Robert Walker after a series of studies conducted by the Research Department Engineering Division of the Air Force. As a result, a formula was proposed that regulates the ratio of the linear dimensions of a room within a fairly wide range.

In 1998, this formula was adopted as a standard by the European Broadcasting Union, Technical Recommendation R22-1998 and the International Telecommunication Union Recommendation ITU-R BS.1116-1, 1998 and recommended for use in construction of studio premises and music listening rooms.
The ratio looks like this:

1.1w/h<= l/h <= 4.5w/h - 4,

l/h< 3, w/h < 3

where l is the length, w is the width, and h is the height of the room.

In addition, integer ratios of the length and width of the room to its height should be excluded within +/- 5%.

All dimensions must correspond to the distances between the main enclosing structures of the room.

Schröder diffuser calculation

Carrying out calculations in the proposed calculator involves entering data online and then displaying the results on the screen in the form of a diagram. The reverberation time is calculated according to the methodology set out in SNiP 23-03-2003 “Protection from Noise” in octave frequency bands according to the Eyring formula (Carl F. Eyring):

T (sec) = 0.163*V / (−ln(1−α)*S + 4*µ*V)

V - hall volume, m3
S - total area of all enclosing surfaces of the hall, m2
α - average sound absorption coefficient in the room
µ - coefficient taking into account sound absorption in air

The resulting estimated reverberation time is graphically compared with the recommended (optimal) value. The optimal reverberation time is the one at which the sound of the musical material in a given room will be the best or at which speech intelligibility will be the highest.

Optimal reverberation time values are standardized by relevant international standards:

DIN 18041 Acoustical quality in small to medium-sized rooms, 2004
EBU Tech. 3276 - Listening conditions for sound programme, 2004
IEC 60268-13 (2nd edition) Sound system equipment - Part 13, 1998

Apartments for the system

I often think that we are lucky to be born with two ears - otherwise how could we enjoy stereo sound? Of course, every benefit has a downside - this gift poisons the lives of some, forcing them to spend a lot of time fiddling with all sorts of parts and cables in a constant search for even greater audio pleasures.

The ability to hear the difference in the sound of components, change the topology of circuits, apply new stands, and finally, all this keeps the passion of hi-fi fans burning. Some pundits believe that we should be attentive to the technical characteristics of components, others urge us to replace parts in serial equipment, and still others advocate a systems approach...

With so much attention on the hardware, it's easy to forget about the rooms in which we listen to it. Meanwhile, sound quality depends on the acoustics of the room no less than on the quality of the equipment. To make sure of this, go out with a friend and talk to him, standing two to three meters apart. Then go back to your room, do the same - you'll see what I mean.

Believe your ears

Although many can imagine how a flow of water generates electricity, this is not at all enough to understand the energy of acoustic waves. Even for specialists, acoustics is a complex science that involves complex calculations along with some intuitive guesswork.

In this article I will try to simplify the subject by talking about it in terms that an educated layman can understand. First of all, you must trust your own ears and remember that in this area everything is relative. Just listen carefully to your system. What does it sound like? Volumetric? Flat? Dry? Where does the sound come from?

Acoustic problems in a listening room are most likely caused by a combination of factors, such as reflections, resonance and, most importantly, room proportions. Let's look at all this in order.

Singing walls

Everyone knows that sound reflects off the wall. But how does this happen? When a sound wave hits an obstacle, part of it is reflected, and part is either absorbed or passes through the obstacle. The harder and denser the wall, the more of the acoustic energy it will reflect - those of you who like to perform opera arias in a tiled bathroom know what I mean.

Sound waves are reflected in a highly directional manner, and as a result, additional “images” appear on the wall, that is, away from the loudspeaker itself. They may impair the clarity of the sound picture. Now imagine what happens when the sound from two speakers bounces off six surfaces in a room (don't forget the ceiling and floor), and you'll realize it's not that simple.

Output in dispersion

The best way to deal with reflections is by scattering, where sound waves are randomly dispersed by uneven surfaces. When the result is good, listeners feel as if the sound is coming with equal force from all directions.

Probably the easiest way to create such surfaces at home is with the help of bookshelves and other hanging interior parts. Or you can simply use “lattice” for eggs, securing them to the walls.

The correct placement of scattering surfaces is very important. Ideally they should be symmetrical. Be sure to place them behind the listening position to reduce major reflections from the back wall. The diffusive surfaces on the side walls should be located where the image of the speaker is “visible” from the listening position. A mirror and a friend will help you in your search, although I usually do it alone, knowing that the angle of reflection of a sound wave is equal to the angle of its incidence.

Homes and gardens

Don't forget about reflections when furnishing your room. The average loudspeaker is capable of producing sound waves ranging from less than 2.5 cm in length to more than 10 m in length. Longer waves (low frequencies or bass) will easily pass through pieces of furniture. But the same cannot be said about high frequencies; they are reflected by such obstacles. Clearly, putting a wardrobe in front of a speaker is not a good idea.

Remember also that it is important not to confuse sound dispersion with absorption, which is inherent in curtains. Although banners or drapes are often used by acousticians to adjust reverberation times in concert halls, your living room is unlikely to be such a large room, so the problems there will be different. Large area curtains simply “suck” all the mid- and high-frequency energy out of the sound, leaving you with lifeless music. Try using blinds instead, which will provide some sound diffusion but not sound absorption.

The same applies to carpets. If the floor of the room is entirely covered with a thick carpet, and the windows are covered with thick curtains, the sound will be even more boring and gray. As with blinds, experiment with thin, small rugs or mats if possible to diffuse sound rather than absorb it.

I would like to point out that reflections can be helpful and some listeners (like me) prefer the room to be a little "live". Of course, this is a matter of personal taste, so as always, you will have to experiment to achieve the desired result.

Room dimensions in resonance

The proportions of the average living room are commensurate with sound wavelengths at the lower end of the audible spectrum (between 70 and 140 Hz). These frequencies are in the most problematic range. If music is played that contains sounds that have a wavelength that is twice the size of the room or a multiple of this, then room resonances (modes) are formed - the most annoying of all acoustic problems associated with ordinary rooms.

Sound waves in air travel at about 330 m per second, so a pure tone (one frequency) of say 31.5 Hz has a wavelength of 330/31.5 - about 10 m. If this tone is generated in a room, the length which is half as large, i.e. 5 m, then such a sound wave will be reflected from the back wall (except that it will be absorbed) and reach the other side of the room at the exact moment when the second tone is generated, thus amplifying it and creating resonance.

Resonances (wavelength/room size) also occur at frequencies that are multiples of this first resonant frequency. The same effect simultaneously occurs in two other “directions” of the room - width and height. When resonances coincide in two or more dimensions of a room, an unpleasant boominess appears.

Check your room

Probably the most significant factor affecting resonances is the relative proportions of the room. You can calculate them using a simple calculator and tape measure. Needless to say, a real audiophile looking for a new home will definitely do this!

If the room has rectangular shape, measure all its main dimensions - height, width and depth. Then build your own table by dividing 330 by twice the dimensions of your room - you will get the first resonance (mode) values. You will get the values of the second resonance by multiplying these values by two, the third by three, and so on. There is no point in calculating resonances above the fourth, since after it you are already out of the “danger zone”.

As an example, I took a typical living room with a length of 4.5 m, a width of 3.5 and a height of 2.3 m. Table 1 shows the results. Obviously, if the resonances coincide in different directions in any order, you will get an uneven frequency response in the bass and an unpleasant “boom.” In our case, around 71 Hz and then -141 Hz. Do not forget that the room, not the system, is to blame for the “muttering”. Don't try to adjust your equipment!

Table 1

Room 4.8 m x 3.6 m x 2.4 m.

Room dimensions

1st reason. frequency

2nd reason. frequency

106.5 HZ

3rd reason. frequency

4th reason. frequency

From this table we can correctly conclude that a square room will simultaneously resonate in two directions and, accordingly, worsen the sound even more. Only a cube-shaped room will surpass it in terms of poor acoustics. Fortunately, there aren't that many cubic rooms.

Likewise, mechanical resonances produced by a speaker stand resting on spikes on a wood floor can cause problems. The latter is to some extent a resonating panel, enhancing the cabinet resonances of the speaker. Owners of these floors and speakers may perceive an audible increase in bass output as an improvement, but in reality the sound is worse. Much less problems with a concrete floor - I hope that's what you have.

How to improve room acoustics.

Based on the conclusions made in the previous chapter, the easiest way to improve room acoustics is to choose the right location for installing your speakers. This is very important because resonances (modes) are excited more when speakers are close to walls, and even more when they are located in a corner. In this case, the corners of the room become uncontrollable horns. Since typical speakers with narrow front panels sound better when placed as far away from corners as possible, placing them against the long wall of the room can help alleviate this problem.

Although the room may look symmetrical, it is hardly so from an acoustic point of view. Therefore, a change in sound can be achieved by moving the speakers to the opposite wall. An even more drastic solution is to move the audio system to another room. Naturally, do not forget to check it for resonances before doing this!

Through experimentation, I've found that it works best to mount the speakers from the back wall about a quarter the length of the room, with the distance between each speaker and the side walls being about a quarter the width of the room. Then the listener needs to position himself from the front wall at a distance equal to a quarter of the length of the room.

Floors and ceilings.

If your speakers are spiked on a wood floor and you suffer from unwanted resonances, you can improve the sound by placing a thin, flexible felt mat, such as a marble slab, on top of the speaker before installing the spiked speaker.

Listening room height is often the biggest culprit in sound deterioration, as a typical ceiling height of approximately 2.4m corresponds to half the 71.5Hz wavelength, which can cause annoying "booming". Of course, you are unlikely to be able to install bookshelves on the ceiling, but you can attach narrow wooden slats of different thicknesses there, which will act as diffusers. By the way, this is quite an original interior decoration.

Hollow beauties.

In the USA, it has become fashionable among audiophiles to install so-called trap pipes in listening rooms to combat resonances and reverberation. Trap pipes are cylindrical devices made of fiberglass pipes about 28 cm in diameter, half of the circumference of which is covered with a perforated metal plate, and the curved metal surface is directed outward into the room. Theoretically, such a trap works partly as a tubular and partly as a chamber resonator.

According to the manufacturers, these devices are transparent to low-frequency sound, so acoustic energy below 440 Hz is absorbed, but the trap moderately reflects higher frequencies and then acts as a dissipative surface. One of the manufacturers of trap pipes in the States is ASC. For anyone who wants to find out more about these devices, we provide its Internet address -

Frequency loves purity.

Recording studios use special resonators that work on a similar principle to trap pipes, selectively absorbing unwanted frequencies or adjusting their level. They are usually flat panels, perforated or solid, mounted with an air gap on the wall and sometimes partially filled with a man-made material such as fiberglass.

The way these devices work is that the air acts as a spring, absorbing sound energy, much like when you blow over the neck of a bottle and produce a note. In this case, the neck of the bottle is the body, and the air acts as a spring. Making such a resonating device is relatively simple and cheap. You need to fix the wooden slats to the wall, and hang the panels on them, then there will be an air gap between them and the wall. But correctly placing these panels is much more difficult, so if you decide to choose this path, it is better to contact an acoustics specialist who will analyze the proportions of your room and advise you on how best to place the panels. It may only cost you a fraction of the money you would otherwise spend on upgrading your system.

By the way, do you want an idea? I haven't personally tried leaving a bunch of empty beer bottles in the corner of my room, but a true audiophile should try everything to achieve the best sound!

Stick to the Golden Ratio.

The mention of beer brought to mind the very best version of the room. However, I must warn that this method is not for the faint of heart as you will likely have to remodel or extend your home! One evening, while making calculations over a large mug based on the proportions of my room, I thought what would happen if its dimensions corresponded to the well-known Golden Ratio.

The Golden Ratio is based on the Fibonacci series -1, 2, 3, 5, 8,13, 21, 34, 55, etc. In it, each subsequent term is equal to the sum of the previous two. If you go higher up this series, the quotient of any number divided by the previous one will be very close to the Golden Ratio, the value of which is 1.6180339887.

I have found that for a room with proportions based on the Golden Ratio, the resonant frequencies for height, length and width will not be multiples and thus cancel each other out. Table 2 shows the result.

table 2

Room 6.3m x 3.9m x 2.4m

Room dimensions

1st reason. frequency

2nd reason. frequency

3rd reason. frequency

4th reason. frequency

Moreover, since I was planning to build an extension to my house, I decided to take the opportunity to build a room with these proportions. And what do you think? It worked! So here's my advice. Before spending money on “upgrading” equipment, pick up a tape measure and check your room. Maybe it will be a waste of time, or maybe it will save you a lot of money and nerves.

By the way, I finally replaced the capacitors!

David Lewis He worked as an architect for 27 years and has experience in the construction of art salons, radio studios and recording studios. Currently involved in the design of a rehearsal space for one of London's leading orchestras.

15.03.2007, 16:02

There are acoustics (small floor-standing speakers), and there is an awesome resonance at 55 hertz (the width of the room is 3.25 m, the length is 5.62 m, the speakers are located along a long wall, about 60 cm from the wall, the listening position is almost against the wall - there are no options here). Furniture includes a sofa, an armchair, a TV and a small shelving unit. Carpet on the floor.

Moving - moving the acoustics away from the wall, muffling the bass reflex - it is not possible to achieve much improvement.

Maybe a bass cleaner will help? How to calculate it - maybe there are some programs? Or try some other methods?

Thanks in advance to everyone who responded to my request. I think this problem often occurs in our small rooms :-)

15.03.2007, 16:52

Please tell me relatively simple and low-cost ways to minimize room resonances (if they exist)..No!
However, you can stack empty cardboard boxes up to the ceiling in the corners of the room :)

Maybe a bass cleaner will help? How to calculate it - maybe there are some programs? Or try some other methods? Its size of a quarter of a room will upset you.

Thanks in advance to everyone who responded to my request. I think this problem often occurs in our small rooms :-) It’s okay - it’s 18m - small, people in 12-14m are trying to install floorstanders - it works.
Hang out: http://www.acoustic.ua/Article_225.html (http://www.acoustic.ua/Article_225.html)

15.03.2007, 17:23

There are acoustics (small floor-standing speakers), and there is an awesome resonance at 55 hertz... Tell me - what floor-standing speakers?
How are they placed on the floor (spikes, plate, etc.)?
What kind of floor is in the room (structurally)?
How did you determine that it is 55 Hz?
And what does awesome mean?

16.03.2007, 17:06

Schweik, thanks for the link. I'll definitely take a look. As for placement along a short wall - because... The room is used not only for audio; such placement is not yet possible. I would be glad to try, but I am limited in possibilities... To Viktor - Monitor Audio Silver RS 5 floor speakers. Placed on 9 kg slabs (30x30 sidewalk) + original spikes, I tried installing them without slabs. The floor is concrete (an ordinary 5-story panel building) + thick linoleum. I determined that 55 hertz from the test disk from "Salon AV" (there is a track with a cut from 20 to 150 hertz). Awesome is when 40 Hz and 60 Hz - significantly quieter, but at 55 it puts pressure on the ears.

16.03.2007, 17:44

Awesome - this is when 40 Hz and 60 Hz are much quieter, and at 55 it puts pressure on the ears. It’s strange... .
It is believed that Monitor Audio Silver RS 5 starts working normally from ~70-80 Hz.
But... if it's a fact -
As a cheap method, you can also add cellular egg cartons to empty Schweik boxes, but... not aesthetically pleasing :-).
Branded ones are not cheap.
I don’t know any simple programs for calculating room acoustics.
If necessary, we use CARA programs (http://www.cara.de/). The same company, by the way, also produces audio absorbers for different frequencies (but at a higher price...).
Installing some other furniture may help you - soft chairs, shelves with books.

26.03.2007, 05:39

And a parametric equalizer can also help you. Only a good one is expensive, but if you are not a special esthete... suddenly.

You can also “cut the lows” graphically. Perhaps, by decreasing a couple of decibels, the problem will be solved, but perhaps all 12 will not help. It happens in different ways, just experiment here.

26.03.2007, 11:28

You are looking for a solution to your problem in the wrong place, my dears!
Everything is very simple.
You should not try to understand the phenomenon of resonance, much less regulate the frequency response.
More important in your case is the phenomenon of ECHO (sometimes called reverberation). It is minimized by simply draping the walls with fabric gathered into an accordion. Remember pleated skirts? Then draw the Greek alphabet symbol "omega" on the paper and flatten it from top to bottom until it is almost flat. This is the shape you need to attach the fabric to the entire height of the room. Using a stationery stapler on a wooden sheathing made of slats 30-50 mm thick. There must be a gap between the fabric and the wall - the air in a confined space is also a damper. Any fabric, not synthetic.
Multiple reflections of sound (the wall is soft and not flat) will be eliminated, the bass will not be booming, and higher harmonics will be suppressed. The sound will be clear.
In terms of suppression efficiency, fabric drapery is slightly inferior to egg cells. But more beautiful.

But is it necessary to be so sophisticated in your own apartment?
This is done in rehearsal rooms for orchestras so that poor intonation and poor arrangement can be heard more clearly.

Maybe it's easier to listen at a lower volume level?

26.03.2007, 16:31

Please tell me relatively simple and low-cost ways to minimize room resonances (if any).
:-)

I cut out resonances with a parametric equalizer.

18.04.2007, 02:09

There is only one solution - move your floor stands further from the wall. At least 1.5 m. And try to close the bass reflexes, if any.
I believe that in a REGULAR living room there is NO NEED to take special acoustic measures. It is prudent, of course, if possible, to allocate a separate room for this, as I did. But this is a separate topic.

18.04.2007, 02:14

By the way, about floor-standing units.
As much as I don’t like budget floor standing speakers, I was recently pleasantly surprised by the sound of the new French highland acoustics. Classical, jazz - GORGEOUS! Rock is terrible.
I recommend listening. ;)

18.04.2007, 17:13

and there is an awesome resonance at 55 hertz. Excuse the simple-minded amateur, but couldn’t those 55 hertz just be the influence of the power supply network?

25.04.2007, 22:45

Effectively changing the acoustic environment in a room at 50 hertz is unrealistic. Try plugging the bass reflex hole, first with loose padding polyester, gradually increasing the density of the plug.

Musatov Konstantin

28.04.2007, 21:01

Resonance 55 Hz is the main resonance and cannot be treated with any cells or draperies. Although general damping of the room is necessary, this is a different question. The best way to combat fundamental resonance is speaker placement. Most likely, you should try to place the speaker as close to the wall as possible. If there is a phasic port at the back, then insert a light parallel into it. Next, you need to select the distance between the speakers so that the 55Hz peak is minimal. It is difficult to judge the tuning using discrete frequencies from the test disk, since other frequencies may be excited. It's better to find a sweep tone.

15.09.2007, 14:08

I have a similar problem, only the frequency is lower - 41Hz.
What I didn’t do was a “floating floor”, an acoustic ceiling, a false wall made of 2 layers of 12mm plasterboard and mineral wool and bars, in two corners of the room I made shelves for CDs from plasterboard, mineral wool and bars.
I changed the equipment, dragged “Jamo C809” speakers around the room in search of the lowest low-frequency resonance.
Tired......
I’ll gain strength and do something else, maybe I’ll buy a big sofa.
I heard about low-frequency scatterers, but I don’t know how to calculate them and what to make them from.
If anyone knows please tell me.

It is well known that room has a significant influence on the sound of hi-fi systems. Enough has been written about this phenomenon in both special and popular publications. Perhaps many of our readers have independently studied this problem, if not theoretically, then in practice - choosing the optimal location of the acoustic system in the room, trying to change the absorption properties with the help of carpets, heavy curtains and upholstered furniture. Having some additional capabilities, namely our measuring complex, we also decided to participate in the study of the resonant properties of rooms. Of course, our results are largely illustrative in nature, but it seems that this is the very case when it is useful to see once than to hear a hundred times...

Still, let's start with theory. As a result of multiple reflections from the walls in the room, a three-dimensional sound field is created. If the frequency of the sound coincides with one of the natural frequencies of the room, then a stable distribution of the amplitude of pressure fluctuations occurs in the space of the room, and it is perceived as sound. Imagine that we made the room sing with our voice (we can do this by turning off the sound source that excited the vibrations in the room at one of its own frequencies, and imagining that there is no attenuation). How will the resonance of the room be perceived? We will hear a tonal sound, the frequency of which, naturally, is equal to the frequency of the source that we have already mentally turned off, and the volume will change as the listener moves in space. Beautiful multi-colored figures in the figures show how the pressure amplitude (sound volume) changes in space for various natural frequencies of the room (numbers under the figures) with dimensions lx = 5.6 m, ly = 3.8 m, lz = 3.5 m. The lightest areas are areas of higher pressure amplitudes. The higher the natural frequency, the more the distribution actually tends to be homogeneous. Numerous sharp spikes are not realized, as if they had been driven over with a roller. The reason is sound absorption, which increases in proportion to the square of the frequency.
Let's now return to reality. Such stable pictures exist in the room as long as the sound source is operating. As soon as it is turned off, the amplitude of the oscillations begins to rapidly fall (remember the exponential law?), and the rate of decline depends on the attenuation in the room (i.e., on the exponent). The lower the attenuation, the longer the reverberation time - the echo of the room. But that's a completely different story...
The sound field of the loudspeaker is thus inseparable from the resonances in the room, and their interaction occurs according to the laws of diffraction and interference. This means that not only a local increase, but also a decrease in the amplitude of sound pressure is possible. And the fields are added not at one frequency, but over the entire range of those emitted by the source and the natural resonant frequencies of the room. The most pronounced distributions exist at low frequencies, which, of course, was well understood by those who tried to enhance the bass by moving the speakers to the corner of the room.
So, having refreshed our understanding of resonances in a room using computer modeling, we decided to see what happens in it with the sound of a Hi-Fi loudspeaker. By installing speakers in a room, we specify the resonant distributions. The place where we place the microphone will be in the zone of increased pressure amplitude for some frequencies, and vice versa for others. At the same time, let’s not forget that in a room with a normal level of reverberation, the direct radiation of the loudspeaker will still dominate the ear.

Usually, when we measure the amplitude-frequency characteristics of loudspeakers, we exclude the influence of the room, that is, we carry out measurements as if in a free field. This is achieved by moving as far as possible from all walls, floors and ceilings (in the center of the volume); a short pulse signal is used for radiation, and during registration, a time window is used that cuts off all reflected signals. In an effort to evaluate the actual contribution of the room, we used a continuous white noise source. In Fig. Figure 1 shows the frequency response of the loudspeaker (blue line) and the frequency response of the loudspeaker-room system (red line), obtained in our laboratory - a fairly large room with dimensions of 7.0, 7.5, and 3.6 m and well-damped walls. It is clearly seen that the room in this case plays an insignificant role - the difference is no more than 4 dB at low frequencies, and after 1 kHz it is practically non-existent. In another room (3.6-3.8-5.5 m), where the walls are not covered with absorbent panels, their influence in a similar situation is more significant (Fig. 2). However, it cannot be said that it radically destroys the frequency response of the loudspeaker. But even if the bookshelf speaker system is placed on the floor at a distance of 2 m from the sofa on which the listener is sitting (we have a microphone), then we will get the characteristic shown in Fig. 3. The sound becomes noticeably more bassy. Maybe this is not bad for a dance party... In fig. 4 you can clearly see what will happen to the sound if the speaker is placed in the very corner and listened to at a distance of 2 m from the wall. Alas, in the range up to 1 kHz the original frequency response is almost completely destroyed. The situation will not change if the loudspeaker and microphone are swapped (Fig. 5). Graph in Fig. 6 corresponds to the situation when the listener (microphone) is at a distance of ~20 cm from the wall, and the speaker is at a distance of 2 m from him.
Let's try to sum up some results and maybe give some advice. First of all, we note that the presented frequency response of the loudspeaker-room system is a little exaggerated. Let us remember that they were measured on continuous white noise, and in this case literally all possible resonant oscillations are established and maintained. When listening to music, the situation is somewhat different. Absorption plays a big role here, and since musical signals are often more impulsive in nature, in a well-attenuated room the process, figuratively speaking, does not reach “saturation.” Of course, when choosing acoustics, you need to take into account the nature and size of your listening room. Maybe you shouldn't always focus on deep bass. At the same time, please note that even in our “non-musical” experiments the frequency response of the loudspeaker itself plays an important role, and as a “source material” it is better to have acoustics with a smooth (without imbalances) frequency response. When installing and listening to speakers, it is best to stay away from walls and corners. Based on experience, we can recommend using not very musical, but informative white noise when setting up your room-acoustics system. The change in its sound as the loudspeaker moves around the listening room is very noticeable to the ear. You can, for example, become familiar with the reference “voice” of white noise by listening to it on good headphones or by placing high-quality acoustics in the center of a well-attenuated and fairly large room. However, we will not particularly insist on this “concert”...