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Re: Box alignment/tuning - different perspectives
A couple comments on rooms and bass. Because rooms are acoustically small spaces at low frequencies all of them have a "Schroeder Frequency". This is the frequency at which the room begins to take over and control the preceived response of the speaker. The Schroeder Frequency is based on the rooms volume and wall / ceiling/ floor surface area, the average absorption coefficient of the surfaces, and the T60 reverberation time of the room.
Based on this formula my family room has a Schroeder Frequency of 197 Hz. Most rooms will typcially fall in the range of 180 - 250 Hz. What happens below this frequency is that the acoustically small dimensions (with respect to the long wavelengths at low frequencies) and parallel walls of the room begin to control the behavior of low frequency propagation. This is where room gain gradually begins to roll-in along with any near-boundary effect, as Allison demonstrated. And, because of the parallel surfaces between walsl and ceiling and floor, standing waves develop with nulls and peaks at different locations in the room.
This is why Pallas (and many others, includeing Toole) recommend multiple subwoofers. When placed properly within the room their combination of peaks and nulls can be made to fill-in and significantly smooth the response in the room. While everything Pallas said is correct, there are a couple of things that change the weighting of these effects.
First, if you are like me you tend to sit in the same place when you listen to music or the home theater. If this is the case, you are likely much less concerned about how evenly distributed your bass response is veruse how it sounds where you are sitting. For me it was not hard to find subwoofer placement that gave me very nice bass where I sit, and I don't worry so much about other places in the room.
Second, when I turn the subwoofers off and listen to speakers with differing bass characteristics from my Continuums that are -3dB around 70hz to my Kairos that reach near 40hz there is most definitely a difference in how the bass sounds in my room. In addition, I can listen to the Kairos both vented and sealed. The differences here are all below 50Hz and it is quite obviously apparent. Even changing the tuning frequency changes the perception of the bass. So, it really isn't correct to say that the F3, slope, and Q of the bass are irrelevant. These are easily seen to make a difference, even when the room still controls much of our perception of the bass.
Now, I don't want to poo-poo efforts made to reduce the room's influence. The method Pallas gave is certainly valid and useful, so are bass traps, Room EQ, and use of dipole speakers to change the pressurization of the room . I'm just saying two things - If you listen in one location it doesn't have to be that complicated, and the differences between different bass alignments can certainly be audible.
Jeff B.
A couple comments on rooms and bass. Because rooms are acoustically small spaces at low frequencies all of them have a "Schroeder Frequency". This is the frequency at which the room begins to take over and control the preceived response of the speaker. The Schroeder Frequency is based on the rooms volume and wall / ceiling/ floor surface area, the average absorption coefficient of the surfaces, and the T60 reverberation time of the room.
Based on this formula my family room has a Schroeder Frequency of 197 Hz. Most rooms will typcially fall in the range of 180 - 250 Hz. What happens below this frequency is that the acoustically small dimensions (with respect to the long wavelengths at low frequencies) and parallel walls of the room begin to control the behavior of low frequency propagation. This is where room gain gradually begins to roll-in along with any near-boundary effect, as Allison demonstrated. And, because of the parallel surfaces between walsl and ceiling and floor, standing waves develop with nulls and peaks at different locations in the room.
This is why Pallas (and many others, includeing Toole) recommend multiple subwoofers. When placed properly within the room their combination of peaks and nulls can be made to fill-in and significantly smooth the response in the room. While everything Pallas said is correct, there are a couple of things that change the weighting of these effects.
First, if you are like me you tend to sit in the same place when you listen to music or the home theater. If this is the case, you are likely much less concerned about how evenly distributed your bass response is veruse how it sounds where you are sitting. For me it was not hard to find subwoofer placement that gave me very nice bass where I sit, and I don't worry so much about other places in the room.
Second, when I turn the subwoofers off and listen to speakers with differing bass characteristics from my Continuums that are -3dB around 70hz to my Kairos that reach near 40hz there is most definitely a difference in how the bass sounds in my room. In addition, I can listen to the Kairos both vented and sealed. The differences here are all below 50Hz and it is quite obviously apparent. Even changing the tuning frequency changes the perception of the bass. So, it really isn't correct to say that the F3, slope, and Q of the bass are irrelevant. These are easily seen to make a difference, even when the room still controls much of our perception of the bass.
Now, I don't want to poo-poo efforts made to reduce the room's influence. The method Pallas gave is certainly valid and useful, so are bass traps, Room EQ, and use of dipole speakers to change the pressurization of the room . I'm just saying two things - If you listen in one location it doesn't have to be that complicated, and the differences between different bass alignments can certainly be audible.
Jeff B.
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