what could reduce the amount of echos in this room?

Answer 1

1. why is this in Chemistry????????
2. turn down the volumn.
3. put soft things throughout the room to absorb the sound
4. put things around that will break up the large flat surfaces of the walls and ceilings (e.g., wall hangings, exposed beams, etc.)
5. put carpets or throw rugs on the floor

Answer 2

Insulation

Answer 3

Wall to Wall Shaggy Carpet! :-)

Answer 4

Strategic placement of sound attenuating materials (stuff that absorbs noise).

Aloha

Answer 5

tack up a blanket to the wall

Answer 6

Room Acoustics

Rooms resonate just like organ pipes. The room is an unwanted extra instrument playing along with the musicians. The design goal for a good music room is to minimize this coloration, which is strongest at bass frequencies between 20 and 200 Hz. At higher frequencies the room still has an influence, but resonances are much less of a problem since it is much easier to obtain high absorption at higher frequencies. This section deals with acoustic design within the subwoofer band of roughly 20-100 Hz. A wall treatment aimed at higher frequencies is discussed in the section on my music room.
The advent of high speed digital signal processing has raised the possibility of correcting room acoustics with a digital filter. Some of the available systems are noted in the section on signal processing.

Both measured and calculated results are presented in this section. Calculations are based on image analysis. For all calculations the "subwoofer" itself is idealized; it is assumed to generate sound at an absolutely flat level from 0 Hz to 200 Hz, so we can focus attention on the room itself. The measured data unavoidably includes the effects of a loudspeaker. Measurements were made using the CLIO system.

A lot of the literature on this subject is mainly directed towards the design of professional sound studios, where the acoustics should be fairly uniform over the entire room. As far as I am concerned, a "sweet spot" where my ears will be located is (literally) the focal point of my design - although it is generally desirable to make this spot as large as possible. The ideal frequency response is flat with no peaks and valleys. This could only be obtained inside a perfect anechoic chamber - a room where the walls absorb sound without any reflections. This is not a feasible solution for most of us (actually it would probably sound pretty weird), and for almost any sound system the room will pretty much determine the frequency response at low frequencies. Room effects virtually always swamp out imperfections in drivers, enclosures, crossovers, and yes, even cables (joke).

Room Resonances

The physics of room resonances is derived and discussed in detail in the physics section. Any room (including rooms with odd shapes) will resonate at many frequencies. The bass response is sharply boosted for a narrow frequency band near resonance, and then is depressed between resonances. A figure derived in the physics section [5.44 kb] shows the response for one series of room modes. The sharpness and height of the resonant peak depends on the sound absorbing properties of the room. A room with a lot of soft furniture, heavy carpeting and drapes will be relatively "dead," and the peaks and valleys of the frequency response typically vary by 5-10 dB. A room with bare walls and floor will be very "live," and the peaks and valleys vary 10-20 dB or more. The absorption coefficient of 0.2 used to produce the figure referred to above is about average, corresponding to a reverberation time of about 1/2 sec. A web site with a handy calculator for resonances for a rectangular room, and for reverb time, can be found at the here.
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"Optimum" Room Dimensions

The standard modal approach for designing a room with good acoustics is to create as many different resonances as possible, and to spread them as evenly as possible across the frequency spectrum, as discussed in the Handbook for Sound Engineers, Chapter 3. There is even a complicated "Bonello Criterion" to evaluate the spread. The lowest resonance is determined by the largest dimension of the room. (Technically there is also a resonance at zero Hz for all rooms, but this is generally not considered a true resonance). In general, the lower the better for the first resonant frequency, because this region is where the frequency response is most variable. Bigger rooms also reduce the spacing between resonances. The limiting factor here is usually cost. For a 19-foot long room the first resonance is about 30 Hz. Every harmonic of this frequency (60, 90, 120, etc.) is also a resonance. The width and height of the room each give rise to another series of resonances. These are the primary "axial" resonances, involving reflections from two opposing surfaces. Additional resonances are created by reflections that ricochet off four different surfaces. These "tangential" resonances are generally weaker, because energy is lost at each reflection. Finally there are "oblique" resonances which ricochet off all six surfaces. Each resonance gives rise to a "mode" with a characteristic spatial pressure variation. The mathematical description of a mode is given in the physics section, and some graphical examples are illustrated below. To spread these resonances as uniformly as possible, various ratios between the room height, width, and length have been proposed. Three such sets from the Handbook for Sound Engineers are shown in the table below.
"Optimum" Room Dimensions

Dimension Design #1 Design #2 Design #3
Width 1.14 x Height 1.28 x Height 1.60 x Height
Length 1.39 x Height 1.54 x Height 2.33 x Height

According to the modal design theory, the worst possible room shape is a cube. The next worst is a room where all dimensions are multiples of the height. A pretty horrible example is a room 8-ft high, 16-ft wide, and 16 ft long. The resonances for an optimum room (design #3) and for the latter horrible example illustrate the difference in the resonances [10.7 kb]. The two rooms have the same total volume. The horizontal frequency scale varies from 0 to 200 Hz. Each vertical line represents a resonance. There are three tiers of lines; the highest tier represents axial modes, the middle tier tangential, and the lower tier oblique. The resonances for the horrible room are less dense, because many occur at exactly the same frequency, and there is a fairly large gap between the second and third resonances, at about 60 Hz. The blue, green, and red lines represent resonances related to the room length, width, and height, respectively.

Measured and Calculated Frequency Response of My Music Room

Calculations in this section are obtained using a computer program based on image analysis. To indicate how closely the results correspond to the real world, here we compare computed and measured data. My music room is not totally rectangular (see the floor plan [4.2 kb]), it contains furniture, and the absorption coefficient of the floor and walls is different. The image calculations assume an empty rectangular room, and the same absorption coefficient at all surfaces. The measured data involves a real loudspeaker; the image calculation assumes a perfect speaker. So one does not anticipate terrific agreement between measured and calculated response curves. The frequency response was calculated at the listening location shown in the floor plan, at the elevation of my calibrated mike. The room has a measured reverberation time of 1/2 sec at 125 Hz, and using the table in the image analysis section, this corresponds to an absorption coefficient between .20 and .25. The agreement between the results [42.8 kb] is not too bad; the red curve is computed, and the black measured. Some features are shifted around, but I would say that the flavor of the real response is well captured by the computation. The agreement is actually quite a bit better than I expected. The lines across the top show the modal resonances of the room. The calculated results show a peak at the 1st and 4th resonances. The measured results have lower peaks at somewhat shifted frequencies. Why aren't there peaks at the 2nd and 3rd resonances? Mainly because these modes have a dip in their response at the sweet spot location where the response is calculated. Examples of modal spatial variation are shown below. A comparison of the measured and computed time-domain response [8.4 kb] indicates a similar degree of agreement. The blue curve is the measured response, and the red "+" marks are the computed response. (I removed my sound absorbing panels for this measurement. A similar measurement with the panels [5.8 kb] in place shows the reduction in the first wall reflection produced by the absorbing panels - the black curve compared to the red. This latter measurement used a different microphone placement, and has a different time scale). The reflection surfaces for the first six echoes are identified in the measured/computed figure. Most measured echoes arrive pretty close to the computed time. The timing discrepancies are less than 0.2 milliseconds, which corresponds to a path length difference of about 3-inches. I don't think my measurements were off by this much, but it is still quite reasonable agreement. There are a few stray reflections in the measured data that probably come from furniture in the room. One significant difference is that the levels of the computed echoes, relative to the direct path, are much higher than the measured values. This is apparently due to two factors: (1) the directionality of the microphone, which was pointing directly at the real speaker, lowers the echo responses, and (2) all of the calculated echoes are perfect impulses; the real-world reflected pulses are smeared out in time compared to the direct path pulse, reducing the relative peak value. This smearing is too small to effect the computed frequency response at low frequencies.

Answer 7

a duck quacking because a duck's quack doesn't echo.

Answer 8

use porous wall papers... they're effective...

Answer 9

carpeting...curtains