You've never tested it but it doesn't hold true?
hm....
A quarter wavelength at my tuning freq is nearly 20ft. In any case, I found that the sofa was acting as a lowpass, so I raised the subs up and the passives are now very close to the ears too. Measures that way as well, though I can't measure below 20
We're talking about listening very close to the source at about 30cm. Get out your measuring gear and measure in 10cm steps from 10cm to 1m distance with the diaphragm of the sub facing the mic and then with the port facing the mic.
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I measured at a few different locations across the sofa, and got smooth response down to 20 (where the passive is contributing a decent bit) at all spots- in fact, the higher up was the bigger challenge. There are 2 subs and there's no indication that there's an issue with integration between the passive and the active.
Start with a single source. Measure at different locations. Then add a port, a second sub, etc.
I don't think that measuring "a few different locations across the sofa" will result in meaningful data.
Here's more data how different sources behave in the direct field:
Comparison of different near field and far field subwoofer configurations
What Markus76 is saying, I believe, is that at the frequency where the driver and port are contributing about the same SPL in the farfield, when you are in the nearfield and very close to one (e.g. the driver) but the port is then relatively farther away there may be some imbalance in the level.
Strictly speaking this is true, but I think in practice any imbalance will not be sufficient to be audible unless you are 10cm from the driver and the port/PR is 6 feet away, e.g. the distances are very different. In fact you could make use of the imbalance in a positive way, putting the driver farther away and the passive radiator as close as possible. In that way the lowest frequencies (produced only by the radiator) will be loudest where the ear's sensitivity is starting to decrease.
Strictly speaking this is true, but I think in practice any imbalance will not be sufficient to be audible unless you are 10cm from the driver and the port/PR is 6 feet away, e.g. the distances are very different. In fact you could make use of the imbalance in a positive way, putting the driver farther away and the passive radiator as close as possible. In that way the lowest frequencies (produced only by the radiator) will be loudest where the ear's sensitivity is starting to decrease.
Moving a woofer to different locations in a typical listening room will change where the nulls in the room occur. It's about reflections causing comb filter effects. Where the reflected sound is delayed a half wavelength, relative to the direct sound, at a given listening position, you'll get your first null, and you will also get nulls at all the integral multiples of that frequency. If you first null is at 100HZ, you'll also get nulls at 200HZ, 300HZ, 400HZ and so on. In the real world, there may be several reflection paths that create nulls at different frequencies. If you're lucky, the nulls of one comb filter mechanism will be largely filled in by other reflection mechanisms that have their nulls at different frequencies.
Moving a woofer real close to the listing position substantially reduces the room reflection contribution, but unless the woofer is very close to you, there is still some room contribution, which would be worst case if you were in the middle of a sphere or cube shaped room. When I tried the close woofer, I didn't like how it integrated with the rest. So I looked at alternatives.
Linkwitz deals with room acoustics by having dipole woofers, the energy of which cancels out at the sides due to diffraction and phase differential. The idea being that if you confine your stimulation of the room acoustics, you'll be better off. That makes sense theoretically, but when I listened to the Orions in a pretty good listening room with top notch program material, although the mids and treble were stellar, the bass was weak. There didn't seem to be much if any low bass, below 40 or 50HZ. Low bass isn't just for the rare low bass note, it makes virtually all drums sound much better; more real, and warms up everything that has any percussive element to it. It gives a sense of size and emotion to the overall sound.
I, on the other hand am a fan of the woofer tower on each side approach (Four 8 inch drivers on each side in a vertical array, closed box, active EQ to make them acoustically relatively flat to 30HZ at the couch). This creates different reflections on the Y axis (floor and ceiling bounce) which increases the probability of nulls getting at least somewhat filled in by the alternate comb filter mechanisms. Each driver will have slightly different null frequencies, so they average out a bit. With the really long wavelengths (20 - 70HZ) this makes little difference, but most of the problems with nulls that I've seen are usually up around 70HZ to 300HZ, where this can make a significant difference. Having the towers be separate from the "satalite" baffles that give you the higher frequencies gives you the ability to optimize further. The higher frequency satalites create the sense of soundstage position, and the woofer towers fill out the bottom with wavelengths that are hard to localize due to their size. I've noticed that several of the high end speaker companies are doing this. McIntosh, Infinity, etc. Here's the IRC Beta speaker for example:
Moving a woofer real close to the listing position substantially reduces the room reflection contribution, but unless the woofer is very close to you, there is still some room contribution, which would be worst case if you were in the middle of a sphere or cube shaped room. When I tried the close woofer, I didn't like how it integrated with the rest. So I looked at alternatives.
Linkwitz deals with room acoustics by having dipole woofers, the energy of which cancels out at the sides due to diffraction and phase differential. The idea being that if you confine your stimulation of the room acoustics, you'll be better off. That makes sense theoretically, but when I listened to the Orions in a pretty good listening room with top notch program material, although the mids and treble were stellar, the bass was weak. There didn't seem to be much if any low bass, below 40 or 50HZ. Low bass isn't just for the rare low bass note, it makes virtually all drums sound much better; more real, and warms up everything that has any percussive element to it. It gives a sense of size and emotion to the overall sound.
I, on the other hand am a fan of the woofer tower on each side approach (Four 8 inch drivers on each side in a vertical array, closed box, active EQ to make them acoustically relatively flat to 30HZ at the couch). This creates different reflections on the Y axis (floor and ceiling bounce) which increases the probability of nulls getting at least somewhat filled in by the alternate comb filter mechanisms. Each driver will have slightly different null frequencies, so they average out a bit. With the really long wavelengths (20 - 70HZ) this makes little difference, but most of the problems with nulls that I've seen are usually up around 70HZ to 300HZ, where this can make a significant difference. Having the towers be separate from the "satalite" baffles that give you the higher frequencies gives you the ability to optimize further. The higher frequency satalites create the sense of soundstage position, and the woofer towers fill out the bottom with wavelengths that are hard to localize due to their size. I've noticed that several of the high end speaker companies are doing this. McIntosh, Infinity, etc. Here's the IRC Beta speaker for example:
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They're behind the sofa with the actives at head height and the passives immediately below.
The response is smooth anywhere across the sofa, so I'm not sure why the hubbub. Having the sub at either end keeps the bass balance from changing as much across the sofa. There's definitely a little higher amplitude on either side of the sofa than the middle, but the response is smooth across the seating area.
I just noticed this thread!
Anyway, I've been experimenting with a sub behind the couch for some time and yes, "Moving a woofer real close to the listening position substantially reduces the room reflection contribution, but unless the woofer is very close to you, there is still some room contribution"
It is very apparent though, that for a sub behind the couch, which means roughly 3ft away from the ears, this contribution is spectacularly reduced, compared to a sub sitting beside the main speakers. Furthermore, the sub's output is set to a much lower level. The room is excited much less, objects stop rattling at very low frequencies, neighbors don't complain, but most important, resonances and reflections after the bass note ends, become far less audible.
BUT !!!
you have to pay attention to the subs interaction with the main speakers, especially when dealing with a plain stereo system and not a HT set, that is when there is no aid via electronic equalization and delay.
For example, in an ~8ft equilateral listening triangle, with a sub right behind your back (~3ft from your ears), the sound of the main speakers arrives with a ~5msec delay and frequencies of ~110Hz will be completely out of phase with the sub. Unless you cross extremely low, they will be cancelled at some degree. So now you have to reverse the sub's phase and 110Hz will be boosted. So you will reduce the sub's output, play a little with the phase setting if it is continuously variable, in order to achieve a good sounding compromise. OK if the main speakers are really small, but what if they are 55Hz capable? Now 55Hz is out of phase and will be cancelled! And now you have to work really hard for that golden compromise.
What I'm saying, is that the whole balance is very system dependent, and the two links in post#1 with contradicting results, don't provide much info on the specific setups. We can not generalize. Of course the Audyssey eq curve is a strong hint.
That said, my experience in my system (ac. suspension boxes with f3 at 70 Hz), shows that the benefits from reducing the room's role are far greater then the drawbacks. But it really is a difficult compromise game.
When some time I will apply digital delay to the bass signal in order to synchronize all frequencies, I will post again
Anyway, I've been experimenting with a sub behind the couch for some time and yes, "Moving a woofer real close to the listening position substantially reduces the room reflection contribution, but unless the woofer is very close to you, there is still some room contribution"
It is very apparent though, that for a sub behind the couch, which means roughly 3ft away from the ears, this contribution is spectacularly reduced, compared to a sub sitting beside the main speakers. Furthermore, the sub's output is set to a much lower level. The room is excited much less, objects stop rattling at very low frequencies, neighbors don't complain, but most important, resonances and reflections after the bass note ends, become far less audible.
BUT !!!
you have to pay attention to the subs interaction with the main speakers, especially when dealing with a plain stereo system and not a HT set, that is when there is no aid via electronic equalization and delay.
For example, in an ~8ft equilateral listening triangle, with a sub right behind your back (~3ft from your ears), the sound of the main speakers arrives with a ~5msec delay and frequencies of ~110Hz will be completely out of phase with the sub. Unless you cross extremely low, they will be cancelled at some degree. So now you have to reverse the sub's phase and 110Hz will be boosted. So you will reduce the sub's output, play a little with the phase setting if it is continuously variable, in order to achieve a good sounding compromise. OK if the main speakers are really small, but what if they are 55Hz capable? Now 55Hz is out of phase and will be cancelled! And now you have to work really hard for that golden compromise.
What I'm saying, is that the whole balance is very system dependent, and the two links in post#1 with contradicting results, don't provide much info on the specific setups. We can not generalize. Of course the Audyssey eq curve is a strong hint.
That said, my experience in my system (ac. suspension boxes with f3 at 70 Hz), shows that the benefits from reducing the room's role are far greater then the drawbacks. But it really is a difficult compromise game.
When some time I will apply digital delay to the bass signal in order to synchronize all frequencies, I will post again
One needs to take into account all group delay, and latency on the sub processing. If the mains aren't highpassed, one doesn't need as much delay, and there is some inherent delay imposed by the processing of a typical subamp.
Sometimes you might need added delay, sometimes not.
Different strokes- some may wish to retain more bass extension from the mains to keep a little more bass as they move away from the nearfield subs. I listen all around the room, so I don't want to have nothing below 60 unless I'm on the sofa. Almost all mains will have a natural rolloff anyway, so there is a "crossover" just not an electronic one.
markus76,
How close do you think is close enough? I'm thinking about the practical ideas of having a subwoofer very close to the couch and it is either a box that also serves as a coffee table in front (with the distance to the ears being ~1,3 m), or a cardioid box directly behind the couch at ear level.
How close do you think is close enough? I'm thinking about the practical ideas of having a subwoofer very close to the couch and it is either a box that also serves as a coffee table in front (with the distance to the ears being ~1,3 m), or a cardioid box directly behind the couch at ear level.
Ha.. One night after imbibing a little too much I placed a sub on either side of my chair placing a lab 12 speaker less than a meter away from each ear.
The next morning my hangover was especially "tinny"
I'll never do that again, or, well maybe if I kept the volume down, and Hmmm
Dave
Thus far, the experiment looks to be a failure- The smooth response and intelligibility is wonderful, but I listen from lots of places, floor, sofa, other seats, walking around, etc.
Plus, turning the head makes too much of a difference, can't bob to the groove.
I'll tweak it a bit and see if a little more distance helps at all.
Plus, turning the head makes too much of a difference, can't bob to the groove.
I'll tweak it a bit and see if a little more distance helps at all.
I knew that it might be an issue going in. DBA is a very cool concept but I've had solid results with multilocation subs, too. DBA's not an option in my space.
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