are room reflections good or bad for audio?

Question

I understand that loudspeaker power required is a function of distance from the speaker and the decibels required. However, when someone asks for advice on subwoofers, one question being asked is "how big is the room". I think this means that the smaller the room, the more bass is reflected, and the less power needed versus in open space. This would seem that reflections are good for bass volume.

Also, people often sound better in the shower due to reverb, but sounding better is not the same as sounding natural.

Some people pad their home theater with dampening material, like in an anechoic chamber, which would mean reflections are not wanted, even though reflections help with the bass. Is this usually done mainly to prevent reverb, or simply for soundproofing purposes, ie. prevent outside sound from entering and home theater audio from leaving?

Based on these, my interpretation is that room reflections are good for volume, but they add reverb to the original audio which may or may not be desirable. Is this right?

Answer 1

You should order a book by the author of the Master Acoustics Handbook:



http://www.amazon.com/Sound-Studio-Construction-Budget-Everest/dp/0070213828/ref=sr_1_1?s=books&ie=UTF8&qid=1390152179&sr=1-1&keywords=sound+studio+construction+on+a+budget



It is a ... Readers Digest description of the effect of walls and reflections in rooms and gives about 10 examples of recording studios and home theater rooms.



The big problem is early reflections for the higher frequencies and the "doubling" of reflections from the subwoofer at the lower frequencies that you need to tame.



People have surrounded their front speakers with cargo-blankets to stop reflections but found the sounds to be 'dead' and somewhat lifeless. So you do want some reflections to mimic a theater or concert venue.



The enhanced bump by some wall reflections for the sub are good for action/adventure movies. But music lovers hate anything that changes the volume at different frequencies away from the original recording.



So it's a room-by-room issue. Search for "Subwoofer Wall reflection calculations" on google and you will find lots of articles on room responses.

Answer 2

This is a excellent question, and you'll get many different answers in these forums on the subject.



The short answer to your question is that reflections are good in a music room, but not typically desireable in a dedicated home theater room.



Both parts of your question have one central aspect to them and is important to understand. First thing to understand is typically the acoustical treatment and approach of acoustics for home music systems is much different than that for"dedicated" home theater systems.



Home music systems you dont want a room that is overdamped, but rather one that is more live but has controled reflections. Typically a room with 1 to 1.5 second delay times is ideal for music room. But how it is treated, the materials that are used to control these relections, and where they are placed is critical. You want the front wall to be live, and the rear wall to have careful choice in materials to carefully delay the reflextions without absorbing to much. The issue with absorbion is that it is not linear, it will absorb at certain frequencys and reflect at others, causing large variations in the frequency responce known as comb filtering.

Defusion is much better to use in a music room to help eliminate early reflections and not create comb filtering effects and a overdamped room.



In a home theater system your trying to achieve completely different results. Most home theater systems you want a heavily damped room to give more direct sound. With absorbtion it allows more pinpoint placement of sounds in a multchannel speaker system.



That is one of the main reasons dedicated home theater systems do a poor job of playing back music. It doesnt allow for a natural presentation of the music, and colors the sound in a negative way.



So there are completely different desireable results and approaches for acoustics of rooms used for music and room used for playing back movies.



The rooms size and dimensions affect both the bass responce, soundstaging, as well as how big or full the system will sound. So when people are asking what size the room is, to get the best bass responce, the size of the room matters, as well as how much air movement you need to provide to get a big sound. Larger room ideally needs more surface area (larger or more bass drivers) to fill the room to get a full big sound.



There is allot to acoustics to much to go into allot of detail here, but this gives you some idea what your trying to achieve.



Kevin

40 years high end audio video specialist

Answer 3

Bass frequencies produce standing waves and nulls inside rooms with parallel walls ......if you have a room that is only 9 ft by 9 ft by 9ft there is no way to produce a 20hz tone that will be useful to you...in order to produce a 20 hz tone without a standing wave you would need a room 56 ft long by 56 feet wide and 56 ft high....if your room is 28 ft by 28 ft you can produce a 20hz tone with one standing wave this wave will create one null in the room if the room is 14 feet then it will produce the 20 hz tone with two nulls in the room... a seven foot room will produce more null than tone as the four nulls it produces will cover more space than the tone covers....this is only one frequency and one bounce , you also get standing waves from ceiling to floor and also there is a double bounce wave created that goes from floor to wall etc...the size of the room needed varies to create effects and the effects vary according to the size of the room for all frequencies 20 hz 19.5 hz 19 hz 18.5 hz 18 hz etc until you get to about 300 hz where the modes become insignificant to our hearing ability...check out "standing waves in a room" ..."room; modes" etc....for a better understanding of this and why you cannot get full bass output in a small room....

Answer 4

When you want to hear only the original recorded sound which comes from the loudspeakers, you need no reflections from your listening room. Total acoustical damping of a room sounds terrible. Sound diffusion is much better. Your room neads acoustical treatment.

"Acoustic Treatment and Design for Recording Studios and Listening Rooms":

http://ethanwiner.com/acoustics.html

"Acoustic Treatment Exposed":

http://exposed.ethanwiner.com/1280x720.htm



Good and bad early reflections - MusicPlayer.com":

http://forums.musicplayer.com/ubbthreads.php/topics/2378707/Good_and_bad_early_reflections



Cheers ebs

Answer 5

What do you mean, natural ? Recordings are put though all sorts of changes with overdubs, echo, compression etc so they don't sound natural at all, they sound how the producer wants.

What you should ask yourself is: what do I want to hear ? Until you know that, you can't expect to know how you will get it.