Stereo image / centering issue in a acoustically treated room

[john_k_antony]

Move your speakers closer, say, keep them 8 ft apart and sit within 8 - 10 ft from each speaker. If things improve, you can try to change the 8 ft a little bit but not beyond 9 ft. In home listening environments, speakers are never kept apart more than 9 ft and ideally 7 to 9 ft. The listening position is always 80 - 100% of that distance from each speaker.
I wonder what you are trying to achieve by dragging the speakers so much apart. With good speakers, the soundstage does not change beyond a certain distance and in fact, the more they are apart, the less will be the center focus. Toe-in is only for precise fine tuning and locking the center and never to get the center focus from dispersed pattern.

Trust this helps.
murali

Murali,

I totally get what you are talking about and I know very well that my positioning is not optimal.

The reason for speakers being 12' apart is that this is my HT + Stereo room. The projection screen is 11' long. So I have to keep speaker at 12' apart. I know this is not the optimal positioning.

Here the issue is due to the widening of sound stage on one side, on the left side. When I play test tones and also music, the sound is coming from the left wall on the left side and on the right side, sound is coming pretty much directly from the right speaker.

Thanks,
John.

 

[murali]

Even if your screen is 11 ft wide, why do you want to keep the speakers outside its boundaries? You can lift your screen higher and move the speakers closer so that they do not hamper your visibility of the screen.
I do not believe that a pair of home speakers more than 9 ft apart is going to give you any pleasure.
Why do you think our creator placed our eyes closer and ears wider? The eyes are supposed to focus on a single image while the ears are meant to locate sounds in a 3-dimensional space. So you can have your speakers like our ears but then do not expect them to focus. If, as you say, your problem is left-right imbalance, as others have said, it could be non-symmetry between left and right. Otherwise, the speakers are losing their cohesive effect by being too far apart and each one is subjugated by the room effects that need not be the same for both.
The only way of knowing is to get your speakers closer and see whether your balance issue is solved. If that is not the issue, you have to look for other reasons. In fact, in my case, I have extended window on one side and a solid wall on the other side, thus unsymmetrical, but do not hear any such imbalance. The speakers are just 7 ft apart as my room is only 10 ft wide. Believe me, I have heard several pieces of music, especially vocal, where the singer always sounds a little to one side. Remember, the singer's mouth is in front of a mic and even the subtle moments of head are captured in many recordings as no one can sing with the head and mouth still and clamped at a fixed position, unless of course the natural distortion is artificially straightened in the mixing.

As they say, you can't have the cake and eat it too. Within your constraints, you have to decide what is best for you.

Good luck.
murali

 

[sdurani]

Here the issue is due to the widening of sound stage on one side, on the left side. When I play test tones and also music, the sound is coming from the left wall on the left side and on the right side, sound is coming pretty much directly from the right speaker.

Seems like the first reflection from your left speaker isn't being sufficiently absorbed. So the wall acts like an acoustical mirror, asthough there is a copy of your left speaker the same distance away on the other side of the wall.

John, you already know what happens when you feed the same signal to two speakers: you don't hear the sound from the speakers themselves but instead it appears to phantom image in between the speakers. This is what you're describing on the left side of your room: the sound is coming from the left wall, which is in between your left speaker and virtual left speaker (on the other side of the wall).

By comparison, the first reflection from your right speaker seems to be sufficiently absorbed, since the sound is coming from the speaker itself and not exhibiting any image shift due to reflections.

A visual check of the room might make the speakers and treatments look symmetrical, but your hearing is detecting asymmetry. If you can have someone walk a hand mirror along each side wall and see where the first reflections of your L/C/R speakers are hitting the side walls, then you'll be able to see if there is a difference on the left and right sides of your room.

 

[john_k_antony]

This is what I am experiencing. The red marking shows the perceived sound source. For right channel, its from the speaker and for left channel its from the left wall and the sound is emanating from 2-3' in front of the left speaker.



Thanks,
John.

 

[sdurani]

This is what I am experiencing.

View attachment 11815

And this is what I was describing.

Re-read my previous post with the above diagram in mind.

 

[BLASTO]

Did you try to swap the speakers and see if the problem persists?

What was the result of swapping amp ports?

 

[john_k_antony]

And this is what I was describing.

Re-read my previous post with the above diagram in mind.

Got it Sanjay. I will try the mirror method again now and recheck all the absorber panels.

Thanks,
John.

 

[john_k_antony]

Did you try to swap the speakers and see if the problem persists?

What was the result of swapping amp ports?

Yet to do that as I didn't get time today as I had to attend to a personal emergency. I will be able to try it over the weekend now.

Thanks,
John.

 

[sdurani]

I will try the mirror method again now and recheck all the absorber panels.

Yup, keep in mind that the problem might be a reflection, but our human hearing will perceive it like a virtual speaker on the other side of the wall.

 

[venk61176]

I too have similar issue and my room is not treated yet. The only way, I have solved it is by increasing balance of right speaker to one r two points.

 

[venk61176]

Based on your viewing distance, here's your separation ratio
Home Theater Speaker Placement - Theater Experience At Home

You need to aim for 75db at reference volume using spl meter with c ratio.

Home Theater Speaker Placement - Theater Experience At Home - I have configured my theatre as per this reference. For spl I have used an ipad app.

Calculate reflection points using this formula and double confirm with mirror

Home Theater Speaker Placement - Theater Experience At Home

For my stereo I went with tweaking balance as there are constraints in room with window on one side and door on the corner on other side.

Thanks
Venkat

 

[venk61176]

RealTraps - How To Set Up a Room

Calibrating Your Audio With an SPL Meter - Blu-ray Forum correct links.

 

[Thad E Ginathom]

And this is what I was describing.

Something is giving you a wider soundstage. For free! hyeah:

In my crazy desk alcove, the sound stage stretches from the L speaker to the wall about 1m from the R speaker. I don't mind it at all.

But, sure, I would if, like you, I had spent a great deal of time and trouble arranging and treating a room to get the thing right.

One odd idea occurs to me, which is not to assume that it is all due to the left speaker. You may have to adjust the right speaker position.

 

[john_k_antony]

Something is giving you a wider soundstage. For free! hyeah:

In my crazy desk alcove, the sound stage stretches from the L speaker to the wall about 1m from the R speaker. I don't mind it at all.

But, sure, I would if, like you, I had spent a great deal of time and trouble arranging and treating a room to get the thing right.

One odd idea occurs to me, which is not to assume that it is all due to the left speaker. You may have to adjust the right speaker position.

Thanks Thad. I am trying all the different options. But not getting enough time as I am busy at work as well. I think I can spend some time this weekend. However its fun doing this all yourself .

-John.

 

[sdurani]

Something is giving you a wider soundstage. For free! hyeah:

In my crazy desk alcove, the sound stage stretches from the L speaker to the wall about 1m from the R speaker. I don't mind it at all.

Same reason I use almost no absorption on the side walls of my room: the soundstage stretches well past my side walls (like they're not even there).

 

[john_k_antony]

I too have similar issue and my room is not treated yet. The only way, I have solved it is by increasing balance of right speaker to one r two points.

I tried Audyssey EQ correction for my HT setup and it did the same correction. It increased the level of my right channel by 1.5db. The stereo speakers are fed from a power amp directly connected to the CDP. So I didnt do any room correction procedure. But from what Audyssey found, there is definitely a sound reflection problem.

I think it will be fun to investigate the issue and get a solution. As the room looks exactly symmetrical from the acoustic point of view and I still have a sound reflection issue. I love debugging technical problems. I guess this will keep me busy for a while. I will keep you guys posted with findings.

Thanks,
John.

 

[john_k_antony]

Friends,

I got some time today to play around with my setup. I used the mirror method to find out the first reflection point of my "problematic" left speaker. I found out that the first reflection point was coming at the point where two of my absorber panels are meeting. At the meeting point of two panels, there is close to 2" wide reflection point because of 19mm plywood from two panels are meeting at that point. So that point has become a small reflection point rather than an absorption. I just tried a quick fix by moving the speaker around so that the reflection point is coming inside one of the absorber panels and not at the meeting point of two panels. I also put couple of Aurica absorber cum diffuser panel I had spare at the meeting point of two panels that created a small reflective area. I think it did solve the problem to a greater extent. Now I don't need to increase the sound level for right channel to create a balanced phantom center image for stereo. But still I feel that for some frequencies, the image is shifting to the left a little bit. It may be the recording though, need to double check with a good headphone . But I still have that crazy feeling that the problem is not 100% fixed . BTW, the vocals seems to be 99% centered. Earlier it used to be shifted slightly towards left.

However, I would like to know your expert opinion on this. Will a 2" reflective surface can create an audible difference in sound if that 2" reflective surface is at the first reflection point of your main speakers? I think it does from my experience. But would like to know the comments from experts.

I might do some more investigation and experiments later. I think enough is enough now. Now I need to sit back and enjoy some music and movies and don't worry too much about the "perfection". I might take it up some time later when I have nothing else to do .

I really appreciate all your help in identifying the problem.

Thanks,
John.

 

[sdurani]

Excellent detective work John. Glad you were able to find the cause of the imbalance. All it took was a simple mirror.

I just tried a quick fix by moving the speaker around so that the reflection point is coming inside one of the absorber panels and not at the meeting point of two panels. I also put couple of Aurica absorber cum diffuser panel I had spare at the meeting point of two panels that created a small reflective area...

...But still I feel that for some frequencies, the image is shifting to the left a little bit...I still have that crazy feeling that the problem is not 100% fixed .

Did you move the right front speaker to a symmetrical location to re-establish left-vs-right balance? Is there a "small reflective area" on the right side wall to keep the soundstage symmetrical? Did you re-run Audyssey to calibrate correct delays and levels for the speaker you moved?

If 'no' to any of the above, than that could explain the lingering asymmetry you're hearing.

Keep in mind that when you put up treatments, you cut down on many reflections that were masking small problems. With those reflections minimized, small left-to-right imbalances are no longer drowned out by a sea of reflections and can therefore be heard more easily now.

 

[john_k_antony]

Sanjay,

You have been a GREAT help. Really appreciate your effort in explaining things technically and simple enough for people to understand.

Did you move the right front speaker to a symmetrical location to re-establish left-vs-right balance? Is there a "small reflective area" on the right side wall to keep the soundstage symmetrical? Did you re-run Audyssey to calibrate correct delays and levels for the speaker you moved?

After covering the reflective junction with absorbers on both sides of the room, now my L and R speakers are symmetrically placed. Equi-distance from front wall and side wall. And they are also set at the same volume levels.

I didn't run Audyssey again. I used my SPL meter and adjusted the levels in my AVR and Stereo Pre Amp (Oppo 105). Because I always play in Pure Direct so Audyssey EQ is anyway not used. I used Audyssey initially to measure the speaker distance and setting the channel levels. Now, I did the distance measurements using a tape and changed the values in AVR and Stereo Pre Amp manually.

Keep in mind that when you put up treatments, you cut down on many reflections that were masking small problems. With those reflections minimized, small left-to-right imbalances are no longer drowned out by a sea of reflections and can therefore be heard more easily now.

EXACTLY Sanjay. Spot on. I was thinking in similar lines. I also feel that with most of the reflections controlled, I feel that the "sweet spot" really narrows and with a slight tilt of my head, I can feel that the sound stage actually moving . Only if you pay attention though.

You know what, after getting immersed into music, closing my eyes, I really stopped caring about any imbalance and started enjoying the music. At the end of the day, what you want is a setup that immerse you into your favorite music

The KEF speakers I have claim to have a wide sweet spot. I think it does create an artificial sweet spot on a non treated room exactly for the same reasons you mentioned. I think an untreated room is masking lots of problems . But when you play these speakers in a treated room with controlled reflections and bass, these speakers turn out to be completely different. So I got a winner and loser at the end with my acoustics.

1. My KEF iQ7, I thought was bass shy, started to fill my room with good musical bass :thumbsup:

2. Again the same speakers I thought would present a very wider sweet spot because of their proprietary UNI-Q driver technology, turned out to be creating a pretty narrow sound stage in a treated room.

But overall I am happy because my KEF iQ7 seems to have got a second birth and is now pumping out good musical bass and are sounding pretty "big". I would say around 60% closer to the "hefty sound stage" delivered by Zu Omen Defs. I can now hold off my speaker upgrade for a while now. Feels like, I got myself a new pair of floor standers. I think the sound might improve if I get myself a good pair of mono blocks. Right now my I am using a stereo power amp rated at 70W/ch directly connected to my Oppo 105. This is not bad at all, but who doesn't want more head room from a more powerful amp hyeah:

Off Topic : I don't know how a 35W SET, Pure Class A will drive my KEF iQ7 rated at 90db sensitivity

Thanks,
John.

 

[sdurani]

Again the same speakers I thought would present a very wider sweet spot because of their proprietary UNI-Q driver technology, turned out to be creating a pretty narrow sound stage in a treated room.

If you want a wider soundstage, you know what to do since you already did it (by accident) on the left side of your room. Just repeat that accident for the right side and your front speakers will image past the side walls for a spectaculary wide soundstage.