I thought I would post this to encourage anyone who only has a small room (perhaps a second bedroom) for a hifi system. It is possible to get really good sound in a small room. This past weekend I set up a system for a person in a room that was 11'X10'X9'. Not exactly a cube but pretty close. The system consisted of a pair of 2 way' vivids, a pair of 10" subwoofers, a Luxman integrated and both a digital and analog source. In the end the sound was open and warm with very nice imaging and soundstage.
There is a pic of the axial room modes. As the room is almost a cube they come in groupings of 3. The first length, width, height modes are at 51Hz, 57 Hz and 62 Hz, The second group is at 102 Hz, 112, Hz and 125 Hz. The third group is at 153 Hz, 169Hz, and 187Hz. The fact that the three lowest modes are close but have a little spread means that although there is a large bump in the bass it is also more spread out. When I integrated the two subwoofers we ended up with a very broad bump rising from 90Hz peaking at 60Hz and then dropping down to 20Hz. The sound of this was not objectionable at all. But I am cutting to the end.
I took an initial measurement of the room at the listening position (MLP) and where the speakers were initially located. You can see this in the pic called baseline. This is really not so good. The large peak in the 60Hz region, a peaks in the 110Hz region and the peak at 190Hz. With a big gulf between 120 and 180Hz. Note all of the modal ringing from 90hz to 150hz and again at 180Hz. The ringing causes voices, piano or really anything to sound really thick and not very natural.
We added corner traps to the back corners. The impact of this is seen in the pic labeled "CornerTraps". All of the ringing has been reduced quite a bit. although still not good enough. Note the "ringing" at 120 Hz seen in the waterfall that is not decaying. This is the ceiling fan. This was barely noticeable in the previous baseline. For measurements after this the ceiling fan was turned off. Still have some pretty severe frequency response issues to address.
The next step was to expore how to improve the frequency response issues. I moved the listening position forward. Initially, the ear was about 10" from the rear wall. Once I found the smoothest bass response from 80-300 Hz this is where we planted the chair. This improvement can be seen in the pic labeled "MoveLP". Still not super great but the best within the constraints of the room. The Gulf moved a little higher up in frequency.
I added a 3'X5' 10" thick bass trap mounted on the wall with a 2" gap directly behind the listening chair. This does two things. First, it helps more with modal ringing and second it helps with hf bounce from the rear wall causing listening fatigue. The improvement can be seen in the pic "absorber Behind LP". This really cleared up the ringing at 127Hz and helped a bunch with the 52Hz Mode. Only one mode left to clear up. The one at 112Hz.
I added two absorber panels (2'X5"X 7" thick) to the side walls at the point of first reflection. This does two things. First it absorbs that nasty reflection from the side wall and second, it help s with the modal ringing of the width modes. You can see this in the pic labeled "Absorb Sidewalls". This cleared up the ringing at 112Hz. The waterfall now looks very respectable up to 200Hz (and above) with the exception of the 52Hz fundamental length mode. I know some like to debate the merits of absorbing the sidewall reflection. In this case the speakers are so close to the wall that without them the sound is very hard and edgy. I don't believe anyone would choose to listen without the side panels in place.
The next step is to really dial in the speaker placement. I had moved them a little prior to this but now we are getting down to business with fine tuning precise position, toe-in, level & rake angle. The speakers ended up about 3' from the front wall and about 22" from the side wall. The toe-in was pointed almost directly at the listeners ears. And the speakers were raked up about half a degree. The speakers are farther apart than the listener to the speaker meaning he is sitting a little near field. This coupled with the high toe-in really helps minimize the room effects even further. The final result can be seen in the pic "Speaker Placement Tweaks".
The subs were integrated and unfortunately I don't have a graph of this as I didn't hit save. But as I mentioned the bass gradually rises from baseline and peaks 5dB over at 60Hz and then gradually drops back to baseline by 20Hz. Not optimal but not offensive. Definitely not one-note bass. One interesting thing is that the Luxman has tone controls. These were useful to help flatten the response even further. We could bump up the bass knob which gave a more visceral bass. This is a great feature to have for anyone in an acoustically challenged space.
There are a couple further things that could be done but the customer was finished for now. Bass trapping could be added to the front corners which I feel would greatly smooth the 52Hz mode and enable an overall flatter bass response. Also there is a rather high reflection occurring 7.2ms after the direct sound. This needs to be investigated. The equipment was spread across the front wall between the speakers. Although the speakers were about 1' in front of it, moving the equipment to the side wall toward the rear of the room would be beneficial. It would not interfere acoustically between the speakers and would allow greater flexibility in speaker placement. Using the JL Audio CR-1 would destress the 30W amp and woofer. If this were used then flat bass could be achieved using the subs at least up to 80Hz.
All-in-all, it sounded really good. I hope anyone with a small room can read this and find direction and hope in achieving audio bliss.
~Todd
There is a pic of the axial room modes. As the room is almost a cube they come in groupings of 3. The first length, width, height modes are at 51Hz, 57 Hz and 62 Hz, The second group is at 102 Hz, 112, Hz and 125 Hz. The third group is at 153 Hz, 169Hz, and 187Hz. The fact that the three lowest modes are close but have a little spread means that although there is a large bump in the bass it is also more spread out. When I integrated the two subwoofers we ended up with a very broad bump rising from 90Hz peaking at 60Hz and then dropping down to 20Hz. The sound of this was not objectionable at all. But I am cutting to the end.
I took an initial measurement of the room at the listening position (MLP) and where the speakers were initially located. You can see this in the pic called baseline. This is really not so good. The large peak in the 60Hz region, a peaks in the 110Hz region and the peak at 190Hz. With a big gulf between 120 and 180Hz. Note all of the modal ringing from 90hz to 150hz and again at 180Hz. The ringing causes voices, piano or really anything to sound really thick and not very natural.
We added corner traps to the back corners. The impact of this is seen in the pic labeled "CornerTraps". All of the ringing has been reduced quite a bit. although still not good enough. Note the "ringing" at 120 Hz seen in the waterfall that is not decaying. This is the ceiling fan. This was barely noticeable in the previous baseline. For measurements after this the ceiling fan was turned off. Still have some pretty severe frequency response issues to address.
The next step was to expore how to improve the frequency response issues. I moved the listening position forward. Initially, the ear was about 10" from the rear wall. Once I found the smoothest bass response from 80-300 Hz this is where we planted the chair. This improvement can be seen in the pic labeled "MoveLP". Still not super great but the best within the constraints of the room. The Gulf moved a little higher up in frequency.
I added a 3'X5' 10" thick bass trap mounted on the wall with a 2" gap directly behind the listening chair. This does two things. First, it helps more with modal ringing and second it helps with hf bounce from the rear wall causing listening fatigue. The improvement can be seen in the pic "absorber Behind LP". This really cleared up the ringing at 127Hz and helped a bunch with the 52Hz Mode. Only one mode left to clear up. The one at 112Hz.
I added two absorber panels (2'X5"X 7" thick) to the side walls at the point of first reflection. This does two things. First it absorbs that nasty reflection from the side wall and second, it help s with the modal ringing of the width modes. You can see this in the pic labeled "Absorb Sidewalls". This cleared up the ringing at 112Hz. The waterfall now looks very respectable up to 200Hz (and above) with the exception of the 52Hz fundamental length mode. I know some like to debate the merits of absorbing the sidewall reflection. In this case the speakers are so close to the wall that without them the sound is very hard and edgy. I don't believe anyone would choose to listen without the side panels in place.
The next step is to really dial in the speaker placement. I had moved them a little prior to this but now we are getting down to business with fine tuning precise position, toe-in, level & rake angle. The speakers ended up about 3' from the front wall and about 22" from the side wall. The toe-in was pointed almost directly at the listeners ears. And the speakers were raked up about half a degree. The speakers are farther apart than the listener to the speaker meaning he is sitting a little near field. This coupled with the high toe-in really helps minimize the room effects even further. The final result can be seen in the pic "Speaker Placement Tweaks".
The subs were integrated and unfortunately I don't have a graph of this as I didn't hit save. But as I mentioned the bass gradually rises from baseline and peaks 5dB over at 60Hz and then gradually drops back to baseline by 20Hz. Not optimal but not offensive. Definitely not one-note bass. One interesting thing is that the Luxman has tone controls. These were useful to help flatten the response even further. We could bump up the bass knob which gave a more visceral bass. This is a great feature to have for anyone in an acoustically challenged space.
There are a couple further things that could be done but the customer was finished for now. Bass trapping could be added to the front corners which I feel would greatly smooth the 52Hz mode and enable an overall flatter bass response. Also there is a rather high reflection occurring 7.2ms after the direct sound. This needs to be investigated. The equipment was spread across the front wall between the speakers. Although the speakers were about 1' in front of it, moving the equipment to the side wall toward the rear of the room would be beneficial. It would not interfere acoustically between the speakers and would allow greater flexibility in speaker placement. Using the JL Audio CR-1 would destress the 30W amp and woofer. If this were used then flat bass could be achieved using the subs at least up to 80Hz.
All-in-all, it sounded really good. I hope anyone with a small room can read this and find direction and hope in achieving audio bliss.
~Todd