Impact of room on speaker sound?

[mizuno]

Hi,

Could anyone share the key principles on how a room configuration affects speaker sound?

More specifically how does for example room size, one glass wall, affect the frequency response of speakers?

fyi, The speakers I'm considering are energy rc-70s and sounded bass heavy in a poor small demo room at the dealer.

Thx!

jf

 

[bandphan]

Hi,

Could anyone share the key principles on how a room configuration affects speaker sound?

More specifically how does for example room size, one glass wall, affect the frequency response of speakers?

fyi, The speakers I'm considering are energy rc-70s and sounded bass heavy in a poor small demo room at the dealer.

Thx!

jf

Understanding sound waves, acoustics, and physcoacoustics imo cant be summerized to key pricinapals without understanding how each works. Addressing accoustic issues within a room can be done by measuring the rooms response and then applying a combination of PEQ, EQ, notch filters, and treatments.

If you have a glass wall in your listening room, well thats not ideal as are all highly reflective surfaces, and should be addressed. If your looking for a place to start with room measurements, REW is freeware and a good place to start with the measurments. Once the responses are measured, you can then deceide what measures need to be taken to correct each flag or problem.


here is a nice page of links that will certainly be good reading if not come in handy at some point. http://www.sengpielaudio.com/Calculations03.htm

Also take a look at audioholics article... http://www.audioholics.com/education/acoustics-principles/

 

[Joe Schmoe]

Here is a short summary: Ugh, glass wall bad!

 

[fredk]

A room will have a big influence on the quality of sound.

Small rooms are hard on bass. They tend to give you fewer but higher peaks that can really accentuate a narrow frequency band (can = boomy sound).

Glass will be more transparent to very low frequencies, but be very reflective of high frequencies.

This is why many people here recommend you do your final listening in your room. Make sure you can return the speakers you choose should they not sound good in your room.

 

[no. 5]

Could anyone share the key principles on how a room configuration affects speaker sound?

More specifically how does for example room size, one glass wall, affect the frequency response of speakers?

Low frequency will be audibly affected the most by typical home theater and listening room's because there is a transition frequency when wavelengths become large compared to a room's dimensions, and because sound waves are reflected off walls back on to themselves with different phase relationships, the frequency response below that transition frequency will exhibit large variations, because some waves will add and some will subtract. This happens above the transition frequency too, but the increasingly smaller wave lengths prevent it from being an issue.

It is important to remember that it is where speakers, subwoofers and listeners are in a room that control what the frequency response at the listening position will be.

If, for example, a room's dimensions suggest there will be a room mode at 70Hz, it will only be a problem if the speakers or a subwoofer is located at or near where that mode can be energized, and your chair must also be at a location where the mode is energized. If not, the calculated room mode at 70Hz is academic.

 

[mizuno]

thank you

Thank you all for the great insights!

 

[fmw]

Room acoustics have more to do with the sound you hear from your system than the system does. It is all a matter of reflections and directions. It is a complicated subject and I'm no expert at it. But I've tested its importance in bias controlled listening tests and it is VERY important. It can reverse people's preferences for speakers.

 

[fredk]

But I've tested its importance in bias controlled listening tests and it is VERY important

Now thats just not nice. You can't just leave us hanging without some details!

 

[highfigh]

Now thats just not nice. You can't just leave us hanging without some details!

You can test it yourself, at home. Hang some blankets up and listen to the difference. If you have drapes, open them, close them and go partly open. If you have a doorway next to one speaker and not the other, put a piece of plywood (or something) where the wall would be.

He's right- the room matters in ways that a system will never compensate for.

 

[fmw]

Now thats just not nice. You can't just leave us hanging without some details!

I've posted information about our tests before. It isn't something I can describe in a sentence or two. Perhaps I need to write up some of these things and stick them on a web site somewhere. The nutshell is that, in extremem circumstances, people will prefer inferior speakers in rooms with good acoustics over superior speakers in rooms with inferior acoustics. And I'm talking about speakers separated in price by a factor of 10. The room is everything.

 

[DD66000]

All rooms have an impact on what you hear. But the more space you can provide around your speakers, the less of an effect the room will have.

Lets say you sit 10 ft from the speakers and the speakers are 1 ft from the side walls and the distance from that first wall reflection to your seat is 11 ft. That's a total of 12 ft distance of the reflected signal, or only a difference of 2 ft longer than the direct signal. That screws up the entire signal you're listening to,

If the distance to the side wall is 5 ft and from that first reflective point to the seat is 12 ft, then you have a total reflective distance of 17 ft - the 10 ft direct = 7 ft. The result is the reflective signal will have no influence on your spatial perception, as sound travels 5.6ft/5milliseconds.

That's because the spatial information relating to a sound source is mainly detected by the brain in the first five milliseconds, everything which follows will at first be ignored.

http://www.audiophysic.com/aufstellung/index_e.html

 

[haraldo]

Two of the most important things to address in a room
- Standing waves
- First reflections

Standing waves depends on room size and are absolutely worst if width and height is in direct correlation to room length, i.e. you get standing waves in multiple directions at same frequencies. All rooms have issues in this sense and there will always be an effect of adding some sort of bass traps in the corners.

Many many ways to tame standing waves and reflections, I would suggest something better than drapes, like rockwool acoustic glassfibre board or something else that's specifically made for the purpose (cover them with fabric of your choice). Drapes have absolutely no effect on room acoustics, perhaps slightly at high frequencies but in bass and midrange not at all whatsoever.

These are products made for acosutic treatment that will work!
http://www.illbruck-sonex.com/products.php

http://www.roxul.com/sw34142.asp

http://www.audiophysic.com/aufstellung/index_e.html

He he, remember where that link came from?

 

[DD66000]

Two of the most important things to address in a room
- Standing waves
- First reflections

Standing waves depends on room size and are absolutely worst if width and height is in direct correlation to room length, i.e. you get standing waves in multiple directions at same frequencies. All rooms have issues in this sense and there will always be an effect of adding some sort of bass traps in the corners.

Bass traps only work on frequencies above 100htz. No affect at all in low bass.

Drapes have absolutely no effect on room acoustics, perhaps slightly at high frequencies but in bass and midrange not at all whatsoever.

Drapes do work if they're of the thick, full velour type.

Move into a new house, and setup the audio system first, before you do anything else. And have it playing while you bring in the rest of your stuff.
And then notice the difference in sound as you add drapes and other things to break up the flat walls.

 

[fredk]

I've posted information about our tests before. It isn't something I can describe in a sentence or two. Perhaps I need to write up some of these things and stick them on a web site somewhere.

fmw, Did you post here or on another site? Are there any key words I can use in a search that will be more likely to pull up those posts?

Maybe you could do an article for audioholics.

Bass traps only work on frequencies above 100htz. No affect at all in low bass.

I think it would be more accurate to say that they become less and less effective under 100Hz. From what I have read and measurements in my room, I think you could see audible effects as low as 70-80Hz, but probably/possibly not much below that.

Given that what we hear as bass goes well above 100 Hz (can't remember the range right now), bass traps will still have a significant effect on the quality of the bass you hear.

 

[highfigh]

Drapes have absolutely no effect on room acoustics, perhaps slightly at high frequencies but in bass and midrange not at all whatsoever.He he, remember where that link came from?

Anything that has different absorption characteristics will make a difference if there's enough, so saying that draped make absolutely no difference doesn't work when it's so easy to hear the difference just by opening or closing them. I have a cellular shade on the window between my speakers and there's a big difference between open and closed. Heavier material does more but if the room doesn't have lower mid-range issued, lightweight does help tame some reflections. Rigid insulation works well for mids, too and using more than one layer helps them absorb more in the middle. Move that away from the surface and it absorbs at the front and back. As in all materials, more affect will be noticed by treating more surface area. Also, having the correct amount of absorptive, diffusive and reflective materials on each surface, as well as the correct placement can make a bad room sound much better.

 

[GZA]

is there anyway to fix this problem?

i have a small room 9x10 and i have my system in there. when i turn my music up i notice lots of bass when i sit up against the wall but then in the center of the room it sounds hollow like all you can hear is the mids and high with no bass to be heard. when i take my stereo out into the big room upstairs it sounds amazing anywhere in the room but its not the case in my bedroom. can i fix this because it sucks not being able to hear my full music unless against a wall

 

[DD66000]

is there anyway to fix this problem?

i have a small room 9x10 and i have my system in there. when i turn my music up i notice lots of bass when i sit up against the wall but then in the center of the room it sounds hollow like all you can hear is the mids and high with no bass to be heard. when i take my stereo out into the big room upstairs it sounds amazing anywhere in the room but its not the case in my bedroom. can i fix this because it sucks not being able to hear my full music unless against a wall

The lower the frequency the longer the wave length, that's one reason for hearing more bass against the wall.
Obviously where you're sitting (middle) is in a null. If you are using a sub try putting it in a different location.
The easy thing to do is put the sub where you sit and run pink noise through it, while walking around the room. Wherever the bass sounds the loudest is where the sub needs to go.

 

[highfigh]

is there anyway to fix this problem?

i have a small room 9x10 and i have my system in there. when i turn my music up i notice lots of bass when i sit up against the wall but then in the center of the room it sounds hollow like all you can hear is the mids and high with no bass to be heard. when i take my stereo out into the big room upstairs it sounds amazing anywhere in the room but its not the case in my bedroom. can i fix this because it sucks not being able to hear my full music unless against a wall

The air molecules are at their highest velocity at the room's boundaries and this is the principal behind the Crown PZM microphone. If you were to run an RTA in a room and move the mic across the room, you'll see peaks and dips in the low frequency response and these are called "modes". The standing waves are a product of the speed of sound and the room's dimensions. The first mode is 1/2(Speed of Sound)/Distance, the second is 2/2(Speed of Sound)/Distance, and so on. When the frequencies coincide because of dimensions or modal frequencies being similar, a peak or null will occur, depending on which mode it is.

By reversing the polarity of the speaker wires or moving them away from the walls, you will alter the points in the room where the sound is good or bad. Don't place the speakers so they're aimed at a wall at a right angle. Angle them in toward your listening position. If you aim them so their paths meet in front of you, the sweet spot will be larger.

 

[highfigh]

If you have Excel, I can send a room mode calculator to you. It's not very elaborate but it does show which frequencies are close together. I did a frequency sweep with the software that was linked in one of the threads and the cancellations coincided with the calculations.

Your room's dimensions are very similar and you'll have a narrow band of notes that are strongest, with deep valleys between. Unfortunately, it's not practical to recommend changing the room dimensions. If you find a way to build a dedicated room, using the Golden Ratio (see http://www.answers.com/main/ntquery?s=Golden+Ratio&gwp=13) gives a pretty even distribution of modes. To ballpark this, take the desired middle dimension of the room and multiply it by .618 to find the
smallest dimension, then divide by .618 to find the largest. Usually, the smallest will be the height.

Here's a link to another, more detailed calculatorthat I hadn't seen before:
http://www.marktaw.com/recording/Acoustics/RoomModeStandingWaveCalcu.html

Assuming an 8' ceiling, your modes are:

Length 9
Mode 1 62.77777778
Mode 2 125.5555556
Mode 3 188.3333333
Mode 4 251.1111111
Mode 5 313.8888889

Width 10
Mode 1 56.5
Mode 2 113
Mode 3 169.5
Mode 4 226
Mode 5 282.5

Height 8
Mode 1 70.625
Mode 2 141.25
Mode 3 211.875
Mode 4 282.5
Mode 5 353.125

 

[highfigh]

The lower the frequency the longer the wave length, that's one reason for hearing more bass against the wall.
Obviously where you're sitting (middle) is in a null. If you are using a sub try putting it in a different location.
The easy thing to do is put the sub where you sit and run pink noise through it, while walking around the room. Wherever the bass sounds the loudest is where the sub needs to go.

One thing to add to this is that if the sub has a variable phase control, have someone adjust it so the sub/main speaker response is as seamless as possible.