speaker positioning

[manoj.p]

Hydra,

I have been thinking of doing an infinite baffle for my theater for some time now and doing lots of reading on this topic. This is what I have gathered so far.

When you place the speaker in a room, all the walls are affecting its response. But the back wall is affecting most because its reflections are in the same directions as the speaker sound is. The sound from the speaker does not radiate only in the front, but goes around all the direction. There are two factors at play here.
First is the baffle step. For simplicity, let's assume that a speaker width is 12". Since the sound radiates in all directions, the frequencies which wavelength is less than 12" will obviously bounce off the front baffle of speaker and go towards listeners. The frequencies whose wavelength is above this will go towards the back of the speaker to the wall and cause cancellation at certain frequencies. Now, speed of sound is around 1130 ft /sec. So, the frequency for 12" wavelength will be 1130 Hz. All the frequencies above 1130 Hz will bounce off from the baffle. At one octave below 1130 (565) frequency, half of the sound energy will go towards the back and there will be loss of loudness. The speaker manufacturers compensate by adding a boost in the crossover below this frequency to match to the high frequencies and its called baffle step compensation. Although, there are some speaker manufacturer who reportedly said they don't do these corrections. That's why its important to see at the polar response of the speakers.

Now, the next variable to this phenomenon is the distance from the back wall. The energy goes towards the back and then reflected. At very low frequencies, this reflection is in phase with the main sound and causes boost. As frequency goes up, the phase changes and at some point, there will be cancellation. As you move the speaker away from the wall, the frequency at which this will cause cancellation/dip also moves lower.
The cancellation/dip frequency = speed of sound /(4*distance from wall)
So, if one wants to move the dip to 40 hz, you will need to keep the speaker at 1130/(40*4) = 7 ft. This may not be possible in the living rooms.

As you move the speaker closer to wall, this frequency goes higher. If you have baffle which is quite big and the dip frequency is above the baffle step frequency, then you have taken care of cancellation dip completely. This is what happens when you flush mount the speaker to the wall. It's called baffle wall or infinite baffle. You have nullified the rear wall interaction of the speaker completely.

Hope that clarifies things.

 

[hydra]

Thanks for that explanation, Manoj. That was very interesting, esp. the distance to wall/frequency cancellation calculation!

 

[arj]

H.
As you move the speaker closer to wall, this frequency goes higher. If you have baffle which is quite big and the dip frequency is above the baffle step frequency, then you have taken care of cancellation dip completely. This is what happens when you flush mount the speaker to the wall. It's called baffle wall or infinite baffle. You have nullified the rear wall interaction of the speaker completely.
.

Thanks for this. i remember reading about folks having tried this with the older Altec single drivers.
Does the material of the Wall ie Wood Vs concrete have an impact ?

 

[manoj.p]

Thanks for this. i remember reading about folks having tried this with the older Altec single drivers.
Does the material of the Wall ie Wood Vs concrete have an impact ?

arj,

The wood walls flex a little and absorb some of the sound energy. Concrete walls wont flex and will reflect all of it.

 

[Hari Iyer]

The best speaker position for a room is the one if you can follow the golden ratio between the side walls, back walls, floor -(ceiling can be ignored) as it will be anyway more than the listening position to have any major impact.

Golden Ratio is 0.61 : 1 : 1.61

So if your floor stander is 3.5 feet tall (around 42"), then the distance from the floor is 42", the distance from the side wall should be 2.13 feet (around 25.6") and the distance from the back wall should be 5.63 feet (around 67.62"). This placement will allow no boom bass as the low freq cannot add-up for its booming. If implemented you can pratically avoid requirement for any bass traps and absorbents behind the rear wall. The speakers themselves can be around 6 feet to 7 feet apart. Assuming a 9 feet ceiling the distance of the speaker from the ceiling will be around 5.5 feet. This could add-up with the rear wave to give some amount of booming for low frequencies. If you experiment with placements try to follow the golden ratio as far as possible.

If you actually analyze this is possible to implement in a room size of 18 feet long and 12 feet wide with the far field listening position being around 9 feet to 10 feet.

 

[mpw]

The best speaker position for a room is the one if you can follow the golden ratio between the side walls, back walls, floor -(ceiling can be ignored) as it will be anyway more than the listening position to have any major impact.

Golden Ratio is 0.61 : 1 : 1.61

So if your floor stander is 3.5 feet tall (around 42"), then the distance from the floor is 42", the distance from the side wall should be 2.13 feet (around 25.6") and the distance from the back wall should be 5.63 feet (around 67.62"). This placement will allow no boom bass as the low freq cannot add-up for its booming. If implemented you can pratically avoid requirement for any bass traps and absorbents behind the rear wall. The speakers themselves can be around 6 feet to 7 feet apart. Assuming a 9 feet ceiling the distance of the speaker from the ceiling will be around 5.5 feet. This could add-up with the rear wave to give some amount of booming for low frequencies. If you experiment with placements try to follow the golden ratio as far as possible.

If you actually analyze this is possible to implement in a room size of 18 feet long and 12 feet wide with the far field listening position being around 9 feet to 10 feet.

================================================

thanks hari. The above is already discussed much earlier in this thread.

This is not practical in most indian living rooms as the speakers end up too far into the room.

mpw
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[Hari Iyer]

================================================

thanks hari. The above is already discussed much earlier in this thread.

This is not practical in most indian living rooms as the speakers end up too far into the room.

mpw
===================================================

I have implemented this in my small room of just 18 feet X 10 feet. It helps a lot in the imaging and depth of the sound stage. Will post image later.

 

[jls001]

The best speaker position for a room is the one if you can follow the golden ratio between the side walls, back walls, floor -(ceiling can be ignored) as it will be anyway more than the listening position to have any major impact.

Golden Ratio is 0.61 : 1 : 1.61

So if your floor stander is 3.5 feet tall (around 42"), then the distance from the floor is 42", the distance from the side wall should be 2.13 feet (around 25.6") and the distance from the back wall should be 5.63 feet (around 67.62"). This placement will allow no boom bass as the low freq cannot add-up for its booming. If implemented you can pratically avoid requirement for any bass traps and absorbents behind the rear wall. The speakers themselves can be around 6 feet to 7 feet apart. Assuming a 9 feet ceiling the distance of the speaker from the ceiling will be around 5.5 feet. This could add-up with the rear wave to give some amount of booming for low frequencies. If you experiment with placements try to follow the golden ratio as far as possible.

If you actually analyze this is possible to implement in a room size of 18 feet long and 12 feet wide with the far field listening position being around 9 feet to 10 feet.

Thanks for the formula, Hari.

For speaker height, do we consider the height from ground to the top baffle of the speaker? or should we consider the center of the tweeter? Or is it the mid point between the tweeter and woofer?

Assuming my BS is 36" tall, sparing (36 x 1.61 = 4.83 feet) seems a bit tough in my small room

Just to share my experience:
I tried something almost similar to what Hari recommends - I don't remember exact distance to side wall but it would have been about 1'6" but the distance to the front wall was one third of the room length (about 18'). So the speakers were placed 6 feet away from the front wall. I don't even remember whose formula this is, but it was something I read from somewhere. As you predicted, there was no boom, but there was no liveliness either, perhaps because the front wall (by which I mean the wall behind the speakers) wasn't giving any reinforcement. As my BS uses small 5 and 1/2 inch woofers, it does need room gain to produce respectable quantum of bass.

Besides, when placed 6 feet into the room it was intruding too much into the small room (think the Arab's camel). So the formula was revised to 1/5. This worked much better with better balance of the frequencies.

I have been constantly revising the positions, and the current distance to the front wall (as measured from the point on the rear baffle nearest to the front wall) is about 24 inch. This is much lesser than 1/5 (one-fifth is 3'6"). Side wall distance (again the distance from the edge on the side baffle nearest to the side wall) is about 12". I get the most optimal sound at these distances. Bass boost is to my taste. After toe-in, lateral imaging and depth are also sharp and deep, respectively.

I have also tried the extreme version of pushing them to within a feet of the front wall. After proper toe-in, lateral imaging is quite nice but the image depth flew away like a deflated balloon. My speakers are rear ported. Everything sounded like it was emanating from the same plane, whereas earlier it was decently deep and layered. So that was discarded as a no go.

Further, at least in my room, variations in the distance to the sidewall is much less important than the variations in the distance to the front wall. Variations in sidewall distance had lesser effect than variations in front wall distance.

I also found out that using a tape to measure distances is not being anal retentive. It is a necessary tool.

 

[arj]

I also found out that using a tape to measure distances is not being anal retentive. It is a necessary tool.

true..that and masking tape for "X marks the spot". Also a laser pointer

 

[Hari Iyer]

If you need to reinforce bass then keep the distance between any two ends same to add up the low frequency after reflections. If your BS height is 36" (3 feet) then keeping them 3 feet away from the side walls will re-inforce bass from the flloor + side walls. Keeping them again 3 feet apart from rear wall will further add-up to the boom (floor + left + rear). The wave-length is important here again.

For a 3 feet distance the wave-length is 0.9144 meter which becomes 375Hz. Hence freq below 375Hz will be more enhanced with this placement.

 

[jls001]

If you need to reinforce bass then keep the distance between any two ends same to add up the low frequency after reflections. If your BS height is 36" (3 feet) then keeping them 3 feet away from the side walls will re-inforce bass from the flloor + side walls. Keeping them again 3 feet apart from rear wall will further add-up to the boom (floor + left + rear). The wave-length is important here again.

For a 3 feet distance the wave-length is 0.9144 meter which becomes 375Hz. Hence freq below 375Hz will be more enhanced with this placement.

Room width is 11'. If I place 3' from side walls, then speakers will be only (11'-6'=5') apart. I think I will lose too much by way of lateral imaging. Also, from purely cosmetic point of view, everything will bunch up near the equipment rack. The speakers will be too close to my turntables, and I may end up with acoustic feedback. If my room was two feet wider, I think it would have been practical. The listening distance will also become more like a near-field, monitoring distance.

 

[mpw]

Thanks for the formula, Hari.

For speaker height, do we consider the height from ground to the top baffle of the speaker? or should we consider the center of the tweeter? Or is it the mid point between the tweeter and woofer?

Assuming my BS is 36" tall, sparing (36 x 1.61 = 4.83 feet) seems a bit tough in my small room

Just to share my experience:
I tried something almost similar to what Hari recommends - I don't remember exact distance to side wall but it would have been about 1'6" but the distance to the front wall was one third of the room length (about 18'). So the speakers were placed 6 feet away from the front wall. I don't even remember whose formula this is, but it was something I read from somewhere. As you predicted, there was no boom, but there was no liveliness either, perhaps because the front wall (by which I mean the wall behind the speakers) wasn't giving any reinforcement. As my BS uses small 5 and 1/2 inch woofers, it does need room gain to produce respectable quantum of bass.

Besides, when placed 6 feet into the room it was intruding too much into the small room (think the Arab's camel). So the formula was revised to 1/5. This worked much better with better balance of the frequencies.

I have been constantly revising the positions, and the current distance to the front wall (as measured from the point on the rear baffle nearest to the front wall) is about 24 inch. This is much lesser than 1/5 (one-fifth is 3'6"). Side wall distance (again the distance from the edge on the side baffle nearest to the side wall) is about 12". I get the most optimal sound at these distances. Bass boost is to my taste. After toe-in, lateral imaging and depth are also sharp and deep, respectively.

I have also tried the extreme version of pushing them to within a feet of the front wall. After proper toe-in, lateral imaging is quite nice but the image depth flew away like a deflated balloon. My speakers are rear ported. Everything sounded like it was emanating from the same plane, whereas earlier it was decently deep and layered. So that was discarded as a no go.

Further, at least in my room, variations in the distance to the sidewall is much less important than the variations in the distance to the front wall. Variations in sidewall distance had lesser effect than variations in front wall distance.

I also found out that using a tape to measure distances is not being anal retentive. It is a necessary tool.

==========================================================

similar observations here..

the arabs camel is something to be seen to be believed and that means too much real estate.

:lol:

i started with the camel fully inside the tent as per the "golden formula " and slowly pushed it out of the tent to a position where the sound is satisfactory and the room intrusion is bearable by folks at home.

Currently i have about 18 inches from the rear wall. I think what helps me is that my wall is not a wall but a 2 inch think solid wood. If it were a real wall.. maybe 18 inches would not be sufficient.

The idea is to start with the theory and arrive at a practical room position for the speakers suitable to all inhabitants at home and also to avoid pushing / pulling of the standmounts each time you want to listen at a good position.

I find slightly more then 6 feet to be a good distance between speakers.

distance from the side walls is about 35 inches approx.

The guys / gals with their own room are the luckiest in this regard i suppose.

mpw
==================================================

 

[Hari Iyer]

Room width is 11'. If I place 3' from side walls, then speakers will be only (11'-6'=5') apart. I think I will lose too much by way of lateral imaging. Also, from purely cosmetic point of view, everything will bunch up near the equipment rack. The speakers will be too close to my turntables, and I may end up with acoustic feedback. If my room was two feet wider, I think it would have been practical. The listening distance will also become more like a near-field, monitoring distance.

Try this placement if your w-t centre point is around 39".

2 feet from the left and right wall.
5.3 feet from the rear wall.
You still get 7 feet between two speakers for proper imaging and depth.
You can sit some where 8 to 9 feet in the far-field.
You still preserve the golden ratio with the above.

 

[manoj.p]

Further, at least in my room, variations in the distance to the sidewall is much less important than the variations in the distance to the front wall. Variations in sidewall distance had lesser effect than variations in front wall distance.

Yes, this is very much true, because the direction of the reflection and sound is not same as the back wall.

Sometimes, side wall reflections can be used to an advantage. If you tweak the placement, then at some point the reflections will act like a mirror of your speaker beyond the wall. This helps creating a wider sound stage which extends way beyond your side walls. You would have converted room's disadvantage to your strength.

 

[jls001]

Yes, this is very much true, because the direction of the reflection and sound is not same as the back wall.

Sometimes, side wall reflections can be used to an advantage. If you tweak the placement, then at some point the reflections will act like a mirror of your speaker beyond the wall. This helps creating a wider sound stage which extends way beyond your side walls. You would have converted room's disadvantage to your strength.

Thanks for this advice. Is there some guideline on how to place it to achieve this "out-of-speaker" width?

I won't mind achieving this upgrade in my setup

 

[manoj.p]

Thanks for this advice. Is there some guideline on how to place it to achieve this "out-of-speaker" width?

I won't mind achieving this upgrade in my setup

It's a bit of trial and error process, because there are few factors here. One being the speaker's dispersion pattern.

• Best way is to start with the equilateral triangle position. Distance between each speaker and listening position being equal, you will get 60 deg wide angle. This also ensures that your stereo speakers have good separation.
• At this point, check the distance between side wall and speaker. It should be within 1 to 3 ft. Don't worry about the direct reflection. We can deal with little later.
• The next is tow-in. More the tow in, it reduces the first reflection from the wall. This depends upon the dispersion pattern. If the pattern is small, there is not much reflection. If its big, the energy is directed at listeners yet there are still some reflections. Play with tow-in till you get a solid center image yet wider sounds with good separation. A good track to try is "Radhaa kaise na Jale" from Lagaan. That CD has some nice wide soundstage.
• Now, You may hear some reflections that may be unwanted. To tame these, we have to put diffusers at the first reflection point of the speaker. You can do this by using mirror trick to find reflection points. With you in listening position, have a friend walk along the left side wall with mirror facing opposite wall. You will see the reflection of right speaker in the mirror. Mark that location. As he walks towards the front of the room, you will see the left speaker. That's the first reflection point of the left speaker. Repeat this on the right side wall.
• Now, at the first reflection point of each speaker, place a diffuser. Some people put absorber there, but it will dampen the sound. Diffusers will rather scatter the reflection and it will have a positive effect.
• Next is the space between your two speakers. As you tow-in, your speakers will also reflect off the back wall. You can either put a absorber or small diffuser at the center between these two speakers. Or if you want accurate, do the mirror trick on the front wall as well, find the reflection point and put absorbers there. Absorbers are preferred here because reflections from here will bring the sound stage in the room.
• Now, the next step is optional. The place where you have marked the reflection of opposite speaker, put a big absorber. Aim is to absorb most of the reflection of opposite speaker, so you won't hear any of right speakers reflection from left wall. This will clear up your sound stage a lot.

You can try these step by step. Tweak it as you go along and gradually see the benefits. Hope this helps.

 

[robertpaul0221]

thank for your report.

 

[Hari Iyer]

My current speaker placement,

Distance from Left wall= 2.5 feet
Distance from Right wall= 1.25 feet
Distance at Back of speaker = 5.5 feet
Listening distance from speaker = 10 feet
Distance between the two speakers = 5 feet.

Toe-in is approxmiate 30 deg in-phase at center.

 

[tiger0691]

Hungry Apply.....

My room arragement is some how so so.....

After reading this thread, I tried .....................
Speakers are on the speakers since I have no speaker stand.

The results of repositioning are
It was easy to control bass part. (less booming)
And sound stage became much wider.
Vocal sound is better and goes little back.



Before and after

 

[mpw]

Wow.. Nice to see folks experimenting with speaker positioning.

Way to go... To realize the full potential of your setup.

Njoi !

Mpw