All about acoustics,acoustic treatment etc..A DEDICATED THREAD

Subscibe to HiFiMART Newsletter

mandeep

Active Member
Joined
Dec 8, 2007
Messages
733
Points
43
Location
Mohali (Near Chandigarh)
Hi

Just like we have dedicated threads for equipment pricelist's, movies, music .. just thought ,we need to have our own dedicated thread for the basic ACOUSTIC/ACOUSTIC TREATMENT etc also, so without wasting any time here and there, one can have quick help for all basic info/links/personal experiences etc for an in depth knowledge.


For a start, please find below some very interesting articles on acoustics,which i have collected online , over a period of time.

----The book "THE HANDBOOK OF ACOUSTICS" by F. Alton Everest provides all the theory one needs to for basic and advanced acoustic theory.

----For a very good article on acoustic treatment/bass control/room dimensions please click here

----Gypsum DRY WALL on wooden framing ,pdf ( Couldn't upload the file,due to 100kb limit, Private message me your email address to send it via email)

----About Riser's and seating arrangement (Find pic attached below)

----Twiga India Glasswool Insulation, which is widely used for thermal and acoustic insulation applications. Article on Twiga fibre wool acoustics,pdf,( Couldn't upload the file,due to 100kb limit, Private message me your email address to send it via email).

----Anutone India one-stop, single-source company for all acoustic needs.

----A very nice step by step HT room construction

----Our own HT construction threads as below

http://www.hifivision.com/av-enhanc...rs-room-acoustics/av-enhance...tml#post104747

and

http://www.hifivision.com/av-enhanc...rs-room-acoustics/av-enhance...ht-room-4.html

----As suggested by my respected fellow member Santhol2(thanks to u), a fantastic thread called "Acoustical Treatments Masterthread" is very very informative for anyone going the DIY Home Theater Construction route.

(Will try to keep this starting post updated, for easy referral)

thanks

regards:)

RiserDiagram2.jpg
 
Last edited:

santhosh

Well-Known Member
Joined
Jul 8, 2009
Messages
2,591
Points
113
Location
Bangalore
Thanks Mandeep. Nice intiative. Avsforums has a fantastic thread called "Acoustical Treatments Masterthread" and has very very informative for anyone going the DIY Home Theater Construction route. I learnt a lot from there and our very own HFV threads.

Kindly email me the stuff that you are unable to upoad here. I will pm you my email address after this post.
 

mandeep

Active Member
Joined
Dec 8, 2007
Messages
733
Points
43
Location
Mohali (Near Chandigarh)
All rooms (a cavity volume enclosed by boundaries) has resonant frequencies at which the acoustic response to a source can be extremely large.As the result of room size and geometry/dimensions, a room excessively amplifies sound at certain frequencies. This is the result of standing waves (acoustic resonances/modes) of the room.Widely there are three acoustical problems due to standing waves:

1. A level boost at some frequencies.

2. An extent of the duration of sound at those same frequencies
(resonance) and

3. Some profound dips at other frequencies.

Standing waves problems can extend to about 300 Hz in HT Room.

STANDING WAVES

Standing waves may be created from two waves (with equal frequency, amplitude and wavelength) travelling in opposite directions. Using superposition, the resultant wave is the sum of the two waves. The animation below shows that the net result(blue) alternates between zero and some maximum amplitude. Unlike the travelling waves, the standing waves do not cause a net transport of sound signal (because the two waves which make them up are carrying equal sound signal in opposite directions).

super3.gif



WHY ROOM MODES EXIST MAINLY AT LOW SIGNAL FREQUENCIES

There are two distinct forces at work when sound signal is introduced into an enclosure such as a listening room.

(1)Mid and high frequencies, their wavelengths being far shorter than any room dimension,do not excite room modes. These frequencies travel in a ray-like manner, "beaming" about the room like shafts of light, or like a billiard ball striking and rebounding from the cushion of a pool table. The classic clapping of hands while walking about the listening room will excite these frequencies, manifested by an audible ringing accompanying the sound of the clap.

(2) Low frequencies, on the other hand, whose wavelengths are far greater than any room dimension, behave quite differently. The propagation of these frequencies results in room modes, or massive peaks and dips in sound signal caused by reinforcement and cancellation. These peaks manifest themselves as high-level hot spots in the listening room, resulting in very audible frequency response anomalies.

WHY ITS MORE DIFFICULT TO CONTROL/TREAT LOW FREQUENCIES

Sound can bend around objects but the bigger an object is the harder it will be for sound to do this.

First,wavelength =343m/s divided by frequency(For sound waves in air)

So, At 2o Hz ,wavelength = 343/20=17.15 m or say 17 metres
similarly,At 2o Khz ,wavelength = 343/20000=0.017m or say 1.7 cm

A basic rule states that to completely absorb (stop) a soundwave, an obstacle must be greater in size, or thicker, than the sounds wavelength.
The picture below shows what happens when wall thickness is reduced for same sound signal.

absorption_transmission.gif


When an object is large in relation to a sound waves wavelength, the sound will be partially reflected and/or partially absorbed. For example, high frequency soundwaves at 20kHz (with a wavelength of 1.7cm) will be easily reflected or absorbed by walls and ceilings because they will be thicker than the sounds wavelength.

In short, high frequency sound is more easily absorbed than mid and low frequency sound. Walls are not able to absorb soundwaves at 20Hz (with a wavelength of 17 metres) so they will be partially reflected and partially transmitted through. This explains why low frequency sound is more obtrusive and carries further.

So, its worth noting that to fully stop a soundwave the obstacle (wall, floor etc) must be wider than the wavelength of the sound
 
Last edited:

asliarun

Well-Known Member
Joined
Dec 22, 2008
Messages
1,225
Points
113
Location
Chicago
All rooms (a cavity volume enclosed by boundaries) has resonant frequencies at which the acoustic response to a source can be extremely large.As the result of room size and geometry/dimensions, a room excessively amplifies sound at certain frequencies. This is the result of standing waves (acoustic resonances/modes) of the room.Widely there are three acoustical problems due to standing waves:

1. A level boost at some frequencies.

2. An extent of the duration of sound at those same frequencies
(resonance) and

3. Some profound dips at other frequencies.

Thanks for the detailed explanation, Mandeep!

I have a very basic question. Can we control the sound characteristics by using a spectrum equalizer, and wouldn't this be a more versatile and effective solution than treating the room?

Actually, I have one more question. Is there a handheld device or product that will tell us the db at different frequencies in a specific listening spot? Would assume as a lay person that such a device combined with a spectrum or graphic equalizer would be a standard audio offering but I don't seem to find it.
 
Top