Room Impact for Your Stereo Sound

Most audiophile people probably is more focusing on their sound system or the equipment components rather than their room acoustics. This might be fun to do but it could be quite costly especially when you are starting to fight for some imperfections of your sound quality. Actually your room and speakers placement have the most impact on your sound. Some of the components changes actually is due to their interaction with your room especially for your current speakers placement. 

Your speakers and their room placement are the most critical factors for your stereo sound system performance. You shall get the best speakers you can afford first, then have the speakers placement optimized before chasing the other components issue. Sound phase shifting impacts might be different from different components and different speakers. In this sequence you can avoid the unnecessary upgrades and save money along with your audiophile journey.

Our listening room, or for most of us the family room or living room, will affect stereo sound significantly. Here I will explain some major impact that is very common issue for most of our situations.

First, let’s see how the world famous music hall looks like. Here is the top 10 best sounding music halls from two different surveys. You can see 7 out of 10 of them have the shoebox shape along with 2 more having the parallel sidewalls for these music halls. This means a rectangular room or parallel sidewall is the best shape for music listening. 

Ranking	Concert Hall Names	Design	Built
1	Vienna, Musikvereinssaal, Austria	Shoe Box	1870
2	Boston, Symphony Hall, USA	Shoe Box	1900
3	Buenos Aires, Teatro Colón, Argentina	Horseshoe	1908
4	Berlin, Konzerthaus, Germany	Shoe Box	1821
5	Amsterdam, Concertgebouw, Netherlands	Shoe Box	1888
6	Tokyo, Opera City Concert Hall, Japan	Shoe Box	1997
7	Zurich, Tonhallesaal, Switzerland	Shoe Box	1895
8	New York, Carnegie Hall, USA	Parallel	1891
9	Basel, Stadt Casino, Switzerland	Shoe Box	1876
10	Cardiff, St. David's Hall, UK	Surround	1982

Now in recent decades the so called vineyard shape or surround shape has been dominating the world new music halls and some of them are getting very good reputation on their acoustics performance. But looking on these graphs for the sound reflection paths, you can see how complicated to design the vineyard shape to achieve the good acoustics results. You need to manage the perfect sound reflecting points to balance the sound reflection amount to the listeners.

For our audiophile, the simplest way to get the best sound out of our listening room is to find a rectangular room, or at least two parallel walls for the room. Luckily it is quite common for the residential environment for this kind of room. Square shape room tends to have more standing wave issue so it could be difficult for better sound. We probably cannot change the dimension of the room easily but most of the time we have reasonable shape of the room. Your furnitures and everyday living stuff actually can serve for sound diffusion or as acoustic treatments, so if you arrange them properly they can help for your listening room. But here is what you want to avoid to have better chance to achieve the best sound from your stereo sound system.

1. Avoid too many open wall area for nooks and crannies on your listening room especially close to your speakers placing locations, as we need the walls to leverage the reflection effect. Without some good reflection the sound will become thin and dry. Good reflection will make music warmer and lively.
2. The floor shall be covered with thick carpet as reflective floor will mess up your sound quality. Floor is actually the closest reflecting surface comparing to all other surfaces in your room, so you need to take care of this first to minimize its reflection. 
3. The ceiling shall not be too low as this will cause more sonic issues. Otherwise you will have to add more acoustic treatments on it.

Each room has its default sound room modes that completely and solely depends on its three dimensions, its height, width, and length. These room modes affects the bass response only. The larger the room is the lower the frequency for these sound room modes will be. Here is one example for the room sound response that you can see below 300Hz the response is showing more up and down on the sound pressure. These major variation below 300Hz is due to the sound modes on this room. Higher than 300Hz you can see the variation is much less as the impact here is not due to room modes but other room acoustics and speakers factors.

Let’s say the room size might be 10 feet wide, 12 feet long, and 8 feet high as a small listening room, or 16 feet wide, 28 feet long, and 9 feet high as a large listening room. For the smaller room here, its sound room modes will be below 300Hz as the example showed on this plot. For the larger room, its sound room modes impact will be below 150Hz. 

Bass sound is omnidirectional with very long wave length. So placing the speakers in the right location of your room is very critical to manage the smooth music sound for the position that you are sitting on. It’s usually better for the listening position to face the short wall as this will give you more flexibility to move the speakers away from the front wall to work around the room modes. This tends to give a flatter bass response for your listening position when you find the best speaker location for your room. But try it out if you have the options to put the speakers on the short wall side or wide wall sited to confirm which is better for your room as the room dimension matters a lot for bass response. Sound wave cancellation always occurs at ¼ the wavelength from your wall as the reflected and direct sound are 180 degrees out of phase, regardless of the phase of the wave hitting the wall. 

For the smaller room, my suggestion is to put your stereo speakers on the long side which will allow you to put each speaker about 3 feet away from the sidewalls. This will give you much better sound stage effect as your speakers can be placed at least 6 feet apart while you are sitting about 6~8 feet away from the speakers. This way you can still get some room behind you to get better sound reverberation.

Speakers shall be placed 2~3 feet away from the front wall to get better bass response. Further away from the front wall normally will help more. But this is a room size and speaker design related issue so you have to adjust the distance based on the actual listening to optimize it. You just need to get the speakers to the locations for what you like how the bass is sounding. Most people have good sense on this so it is not that hard to optimize it, but you do have to move the speakers and listening some heavy bass music to find your best sound.

Putting the speakers on the short side of the smaller room will give you more flexibility to optimize the bass sound. But the challenge is this could reduce your sound stage as putting speakers too close to your sidewall might cause sound phase shifting issue and skew your sound image, especially if your room has asymmetrical furnitures arrangements.

For the larger room, I would suggest you to put the speakers to the short side as it is wide enough. This way you can move the speakers further away from the front wall which will help to form much better sound depth, sound image, and better layer of your music. Better layer means you can distinguish the music players or instruments better due to the reflection from the front wall has more space to form the proper delay. This is pretty much very similar to the shoebox shape if your room length is long enough. If your rear wall is reflective, it should be at least 10 feet from your ears to manage the reverberation. Otherwise, make sure you have more irregular stuff on the back wall surface to diffuse the reflection.

Treble or higher frequency sound is more directional so you need to adjust your speakers angle to be toed in to face your listening position to optimize your sound stage and sound image. Different speakers design has different off axis sound performance so you will have to play around this for your speakers to get the best result. 

Besides, there is no perfect room in our normal living home situation, so using the 9 test tones for your speakers placement is the most efficient way to find your optimized speakers placement.

Here is what you shall get for the 9 distinguished knocking sound by using the test tone. Both #1 and #9 tones shall be outside of the two speakers for better sound stage. The #5 tone shall be right on the center to give you good sound image. You also need to get all the 9 tones evenly distributed across your sound stage to get the perfect sound image and good sound layers.

Now here you can see if you have the speakers moved to one side of your room, some of these test tones will be skewed to one side and not evenly distributed.

Even worse, if you have some open area next to your speakers, the reflection wave will be badly affected so your sound stage will be completely messed up like this example.

Without these test tones, you will have to use some special music elements to do this which will require much better listening skill to achieve the best result.

You need to control how much reflection from each walls. Too much reflection will mess up your sound quality. Normally in living room or family room you will have some furnitures and decors on the walls which will help to diffuse the sound for the reflection. These are the good things. Bookcase or media shelf along with the sidewalls between speakers and listener locations are always good to help for this purpose. Blinds or thick curtains to cover the windows will serve this purpose too. Obviously the more symmetrical for these features the better for your sound stage and  sound image as we need to have the balance of the sound effect from stereo speakers. Since every room is different and sound acoustics is very complex topic so the best way to find your solution is to use the test tone to help you to achieve the best sound.

Hopefully this is helpful for you. Enjoy listening.