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:eek: as are all highly reflective surfaces, and should be addressed. If your looking for a place to start with room measurements, REW (http://www.hometheatershack.com/roomeq/) 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!:D

[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 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! :D

[highfigh]

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

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! :D

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? :D

[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. :D

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? :D

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.

[haraldo]

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


I don't quite agree on this

If you look at measured characteristics of some professional bass traps they have very very good effect way down into the bass, but as a result of physics, if you want bass traps that are efficient in the lower bass, they must be BIG... like VERY BIG

Check for instance thee products, very powerful even at low bass, but not cheap :eek:
http://www.rpginc.com/products/modexcorner/index.htm
http://www.rpginc.com/products/modexcorner/modc_imp.htm

http://www.rpginc.com/products/modexbroadband/Modex-Broadband.pdf


Many of the products like bass busters and the likes from echobusters have very little effect in the lower bass, simply because they're not large enough

I have made a room mode calculator that shows frequencies of standing waves in a room, but this only really works for rectangular rooms, enter room dimensions in feet and it will show distribution of the different standing waves. This is from a model presented in the master handbook of acoustics.

Where you have X's in the columns besides room modes, the modes are very close to each other and may need particular attention. I have added dimensions for a sample room.

[fmw]

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. :D



I'll go as quickly as I can. We did a bias controlled listening test in my home in 1998. Room A was a 12' X 12' bedroom with terrible acoustics Room B was a 26' X16' bedroom with very good acoustics. In the larger room we could place the speakers about midway leaving lots of room behind them and between them and the listening position. The small room had the speakers placed near a wall. In the small room we used a pair of B&W Matrix 802 speakers which had a list price of around $8000 at the time. In the larger room we put a Sub Sat 6 system from Boston Acoustics which has a pair of very small boxes with an 8" subwoofer. Its list price was about $700 at the time.

The group was 10 audiophiles. Normally, we don't actually blindfold people to do blind listening tests but we did for this test. Each tester was taken to each room blindfolded and we played 2 minutes worth of well recorded music in each room. The audiophiles were told there was an expensive pair of speakers in one room and a modestly priced pair in the other. After hearing the music in each room, the testers were asked to id the expensive pair - room A or room B. We ran the test twice for each listener. We changed the music on each pass and changed which room they heard first on each pass. So we had 20 iterations of the test. 7 of the listeners (14 of 20 id's in all) were incorrect. They thought the Boston Acoustics speakers were the more expensive pair.

Our conclusion was that they were actually voting for the room with the better acoustics. Better speakers in an acoustically poor room couldn't make up the difference. That's the basics of the test we ran.

[DD66000]

I'll go as quickly as I can. We did a bias controlled listening test in my home in 1998. Room A was a 12' X 12' bedroom with terrible acoustics Room B was a 26' X16' bedroom with very good acoustics. In the larger room we could place the speakers about midway leaving lots of room behind them and between them and the listening position. The small room had the speakers placed near a wall. In the small room we used a pair of B&W Matrix 802 speakers which had a list price of around $8000 at the time. In the larger room we put a Sub Sat 6 system from Boston Acoustics which has a pair of very small boxes with an 8" subwoofer. Its list price was about $700 at the time.


Our conclusion was that they were actually voting for the room with the better acoustics. Better speakers in an acoustically poor room couldn't make up the difference. That's the basics of the test we ran.

Its a given a square room, at probably any size, will always be less than good, no matter what speakers you use. So why is that a surprise?

And any quality system, setup wrong, will not sound as good as it should and that means being too close to walls, unless the speakers were designed as onwall/inwall.

But put the two systems in the same room and do a blind test, as they do at Harman's Northridge testing rooms and then it a whole different thing.

[haraldo]

Its a given a square room, at probably any size, will always be less than good, no matter what speakers you use. So why is that a surprise?

And any quality system, setup wrong, will not sound as good as it should and that means being too close to walls, unless the speakers were designed as onwall/inwall.

But put the two systems in the same room and do a blind test, as they do at Harman's Northridge testing rooms and then it a whole different thing.

fmw shows a point that room acoustics is more important than probably anything else that you may put into your system, that's not a surprise if you know a few things about acoustics, but still important to write about.

[DD66000]

fmw shows a point that room acoustics is more important than probably anything else that you may put into your system, that's not a surprise if you know a few things about acoustics, but still important to write about.

Some rooms will be better than others, but even many bad rooms, can be made to sound fairly good, if you can give the speakers some space, and if needed, laid out diagonally across the room. And if needed add some wall treatments at the first reflection points for really narrow rooms.

The big problem is even with the popularity of HT, many houses don't have even one room that could be considered good from a stand point of sound reproduction: too many windows, large rock fireplaces, too many openings to the room, L shaped. Add to that in-wall/ceiling speaker installs that are poorly thought out, using ceiling speakers for the LCRs.

The constractors just stick their HT option in a L shaped great room, wide open to the majority of the house, with the area for the TV laid out off center from the built-in speaker system. Over the last four years I've seen about every kind of crap room setup you can think of. And it doesn't have to be that way, just a bit of thought by the Architect.

[highfigh]

I don't quite agree on this

If you look at measured characteristics of some professional bass traps they have very very good effect way down into the bass, but as a result of physics, if you want bass traps that are efficient in the lower bass, they must be BIG... like VERY BIG

Check for instance thee products, very powerful even at low bass, but not cheap :eek:
http://www.rpginc.com/products/modexcorner/index.htm
http://www.rpginc.com/products/modexcorner/modc_imp.htm

http://www.rpginc.com/products/modexbroadband/Modex-Broadband.pdf


Many of the products like bass busters and the likes from echobusters have very little effect in the lower bass, simply because they're not large enough

I have made a room mode calculator that shows frequencies of standing waves in a room, but this only really works for rectangular rooms, enter room dimensions in feet and it will show distribution of the different standing waves. This is from a model presented in the master handbook of acoustics.

Where you have X's in the columns besides room modes, the modes are very close to each other and may need particular attention. I have added dimensions for a sample room.

Harald- did you see the link I posted? That one does two wall modes, tangential and all six walls. I have an Excel sheet that does the first set but hadn't seen the link until last night.

[fredk]

Thanks for the reply fmw. Thats a lot of effort for a few audio enthusiast to go through to satisfy curiosity.

[highfigh]

I'll go as quickly as I can. We did a bias controlled listening test in my home in 1998. Room A was a 12' X 12' bedroom with terrible acoustics Room B was a 26' X16' bedroom with very good acoustics. In the larger room we could place the speakers about midway leaving lots of room behind them and between them and the listening position. The small room had the speakers placed near a wall. In the small room we used a pair of B&W Matrix 802 speakers which had a list price of around $8000 at the time. In the larger room we put a Sub Sat 6 system from Boston Acoustics which has a pair of very small boxes with an 8" subwoofer. Its list price was about $700 at the time.

The group was 10 audiophiles. Normally, we don't actually blindfold people to do blind listening tests but we did for this test. Each tester was taken to each room blindfolded and we played 2 minutes worth of well recorded music in each room. The audiophiles were told there was an expensive pair of speakers in one room and a modestly priced pair in the other. After hearing the music in each room, the testers were asked to id the expensive pair - room A or room B. We ran the test twice for each listener. We changed the music on each pass and changed which room they heard first on each pass. So we had 20 iterations of the test. 7 of the listeners (14 of 20 id's in all) were incorrect. They thought the Boston Acoustics speakers were the more expensive pair.

Our conclusion was that they were actually voting for the room with the better acoustics. Better speakers in an acoustically poor room couldn't make up the difference. That's the basics of the test we ran.

By any chance, did that larger room have a 10' ceiling? If it did, the proportions almost exactly match the Golden Ratio.

Too bad you couldn't have used the same speakers in both rooms. That would have been interesting, especially if the listeners had no idea what kind were being used.

[haraldo]

Harald- did you see the link I posted? That one does two wall modes, tangential and all six walls. I have an Excel sheet that does the first set but hadn't seen the link until last night.

Yes, nice I saw the link after I did my post, thanks :cool:

I believe that probably even the most unlistenable rooms can be made quite good, with simple means, if you're able to tame the worst modes and to some extent control first reflections, you could possibly be making significant progress,

Can you post (or send me) the excel sheet?

[fmw]

By any chance, did that larger room have a 10' ceiling? If it did, the proportions almost exactly match the Golden Ratio.

Too bad you couldn't have used the same speakers in both rooms. That would have been interesting, especially if the listeners had no idea what kind were being used.

No my house has 8' ceilings. What makes the long bedroom so good acoustically is the ability to place the speakers well. Speakers do poorly when backed up against a wall. They need breathing room.

We could have done a test with both pairs of speakers in the same room but we didn't think it would tell us anything. We were testing the rooms, really and the concept of room acoustics trumping equipment. We simply assumed that, in the same room, people would have picked the B&W as the more expensive speaker pair. While we didn't test it, I still think it is a safe assumption. The 802's are fairly short on flaws while the Sub-Sat 6 has plenty of them. Incidentally, I still use the Sub Sat 6 system with my bedroom TV. Same bedroom, too. It is our master bedroom.

http://www.foodieforums.com/otherimages/brtv.jpg

[highfigh]

No my house has 8' ceilings. What makes the long bedroom so good acoustically is the ability to place the speakers well. Speakers do poorly when backed up against a wall. They need breathing room.

We could have done a test with both pairs of speakers in the same room but we didn't think it would tell us anything. We were testing the rooms, really and the concept of room acoustics trumping equipment. We simply assumed that, in the same room, people would have picked the B&W as the more expensive speaker pair. While we didn't test it, I still think it is a safe assumption. The 802's are fairly short on flaws while the Sub-Sat 6 has plenty of them. Incidentally, I still use the Sub Sat 6 system with my bedroom TV. Same bedroom, too. It is our master bedroom.

http://www.foodieforums.com/otherimages/brtv.jpg

Having the proportions for the length of two walls close to the Golden Ratio makes a big difference. I have installed many systems in different sized rooms and can't remember a square one sounding good, but with a little time spent in speaker placement, I also can't remember the rectangular ones sounding bad unless the acoustical properties of the materials just weren't conducive to good sound. Those ratios not only look better, they sound better.

[DD66000]

Any rectangular room can sound very good, unless the dimensions are multiples (8'x 16'x 24')
And you don't stick the speakers in the corners, because of having a screen too wide for the room's width.
The closer you can get the main L/R speaker locations set to 27.6 % of the room width from the side walls the better. And that will result in your hearing to reject the first reflective signal, as it will get to the seat well after the direct signal.

But if you have to use a square room, it would be much better to setup the speakers diagonally across the corners, so they're 45* to the walls.