I don't think I can push my OB widebands any lower. At 80Hz Toole says bass is non directional and multiple subs should be mono in order for them to be advantageous regarding room modes. I have two next to my main speakers in stereo at the moment. Should I be feeding them mono instead of stereo crossed at 100Hz?
The subs are two U-frame OB with two 12" woofers in each
The subs are two U-frame OB with two 12" woofers in each
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Run them stereo. If the signal is different in each channel, you'll want it different (bass and druns on separate channels as mentioned). If the signal is the same, it will act as mono anyway. I think you'd be hard pressed to find a recording where it would make a difference one way or the other though.
Dan
Dan
Isn't directional information contained in the upper harmonics of the 'strike' ? That will come from the main speakers helping us locate the sound. The sub just provides the weight provided there is no gross timing delay between the transient and the LF frequencies.
Open baffles are only exiting a few of the modes in a room, while a normal subwoofer tend to exite many room-modes, especially if the sub is located in a corner.
Its almost impossible to solve this with EQ, as the room-modes develop over time.
A solution is to use several, smaller cubs placed so the tend to cancel the dominant room-modes. As an example 4 Subs placed in the corners of the room, on the floor, will cancel the fundamental modes along the length and the width of the room, but NOT the mode between floor and ceiling, but this mode is typically at 70Hz.
You'll get much tighter bass this way, and even 4 small cubs are able to play loud, since they get a lot of gain from being in the corners.
Its almost impossible to solve this with EQ, as the room-modes develop over time.
A solution is to use several, smaller cubs placed so the tend to cancel the dominant room-modes. As an example 4 Subs placed in the corners of the room, on the floor, will cancel the fundamental modes along the length and the width of the room, but NOT the mode between floor and ceiling, but this mode is typically at 70Hz.
You'll get much tighter bass this way, and even 4 small cubs are able to play loud, since they get a lot of gain from being in the corners.
I was just wondering If you have done any measurements of the room, if you do not have any equipment, any modern smart phone should at the very least be able to install a frequency generator and has a microphone that is reasonably dependable for stuff happening under 8khz.
Should you want something better, there are cheap measurement microphones available with calibration files, also for smartphones.
If you have identified your room modes, it should be possible to re-evaluate speaker placement to reduce them.
It is near impossible to completely eliminate all room modes.
I also vote for stereo bass.
Edit:
Ashok: I think GP was referring to the use of one channel to both subwoofers, I am not certain if "mono" signal referred to in this thread is a summed-mono or just the left channel, it is not specified. At any rate, there is no directional information in ANY signal, it is the interpretation of our brain that is the issue. If my memory serves me correct, the signal coming from our ears are summed in mono before it is interpreted by the brain. So there is a gradual reduction in localization in relation to lower frequencies, there is no hard limit. But we also have a whole body to perceive sound with, especially bass.
Should you want something better, there are cheap measurement microphones available with calibration files, also for smartphones.
If you have identified your room modes, it should be possible to re-evaluate speaker placement to reduce them.
It is near impossible to completely eliminate all room modes.
I also vote for stereo bass.
Edit:
Ashok: I think GP was referring to the use of one channel to both subwoofers, I am not certain if "mono" signal referred to in this thread is a summed-mono or just the left channel, it is not specified. At any rate, there is no directional information in ANY signal, it is the interpretation of our brain that is the issue. If my memory serves me correct, the signal coming from our ears are summed in mono before it is interpreted by the brain. So there is a gradual reduction in localization in relation to lower frequencies, there is no hard limit. But we also have a whole body to perceive sound with, especially bass.
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The only measuring I've done is with an on-line tone generator, Panasonic WM61A, oscilloscope and ears. Before I went mono (summed L & R), DonVK did a sim for me on another thread which correlated well with my findings, that is, placement against the side walls and about 5 feet from the front wall.
id some tests this year in my room (The room is 5/5meters, 1 sofa, 1 couch, rockwool panels behind speakers, thick carpet).
I have 2 sealed subs with 12", one tapped horn sub, 2 open baffle with 18" on them.
The measurements show that the OB is the best option. When I listen to more subs in system (OB + sealed or OB+ TH) the measurements are bad. I adjusted delay and measure with REW. FIR filters.
Also there is a pressure in room I don't like when sealed or TH is used.
I place the OB 1m from wall behind them and 50cm from lateral wall. The baffles are 80cm wide, 60cm height. Also I noticed that power amp that feeds the subs is very important.
I have 2 sealed subs with 12", one tapped horn sub, 2 open baffle with 18" on them.
The measurements show that the OB is the best option. When I listen to more subs in system (OB + sealed or OB+ TH) the measurements are bad. I adjusted delay and measure with REW. FIR filters.
Also there is a pressure in room I don't like when sealed or TH is used.
I place the OB 1m from wall behind them and 50cm from lateral wall. The baffles are 80cm wide, 60cm height. Also I noticed that power amp that feeds the subs is very important.
You mean that it has to be far more powerful than the mid/tweeter amp ?
Or some other parameter ?
I forgot to mention the subs are two U-frame OB with two 12" woofers in each. I'll edit my first post. At the time I was focusing on mono vs stereo but this now seems more relevant to the discussion.
@arcgotic, I too find the sensation of pressure in the room of sealed (and ported) enclosures uncomfortable
@arcgotic, I too find the sensation of pressure in the room of sealed (and ported) enclosures uncomfortable
Regarding "sensation of pressure": I also had the same feeling before, but not on the most recent build, which might strike some as odd, one should think 6 x 15" in boxes would cause more of this feeling than fewer and smaller speakers, but it is not so.
My 2 x single Alpair 10.2 setup can cause this sensation in some spots, but I made those boxes to take advantage of room modes.
Have had very few problems with room modes in OB.
One of the setups I had that made a lot of this sensation was with a >300 liter TH with 2 x 12" firing into a corner. I am leaning towards induced coupling of room modes as the explanation. The sensation or pressure is not omnipresent, it is enhanced where you get bombarded with multiple sounds of the same wavelength only shifted in phase because of reflections.
If you focus and listen/sense for it carefully you can hear the original and the shifted-in-phase reflection where it occurs, perceiving it as two different sounds can be difficult, to avoid overload we sense it as "pressure". Measuring can also be difficult, sometimes gating may give a less than optimal result because of delay in measurement/reflections. Slow sweep to get the main problem frequencies, then pure sine of each problem frequency, moving around to measure where the modes are worst.
May it be that there is mixed strength of signals/compensation? Different strengths of amplification? Have you tried using resistors on output of power amp to your widebanders, to get more accurate matching of the in-signal to the subs? I have sometimes experienced that 1db in one place can be very different to 1db in another place.
Edit:
Sometimes, placing a sub in a problem spot can be good, then find the spot with the worst room modes, then move the sub to the "bad spot" and see what happens.
Edit:
I'm probably just way off with my understanding of room modes though. But at least I do not struggle with them at the moment.
My 2 x single Alpair 10.2 setup can cause this sensation in some spots, but I made those boxes to take advantage of room modes.
Have had very few problems with room modes in OB.
One of the setups I had that made a lot of this sensation was with a >300 liter TH with 2 x 12" firing into a corner. I am leaning towards induced coupling of room modes as the explanation. The sensation or pressure is not omnipresent, it is enhanced where you get bombarded with multiple sounds of the same wavelength only shifted in phase because of reflections.
If you focus and listen/sense for it carefully you can hear the original and the shifted-in-phase reflection where it occurs, perceiving it as two different sounds can be difficult, to avoid overload we sense it as "pressure". Measuring can also be difficult, sometimes gating may give a less than optimal result because of delay in measurement/reflections. Slow sweep to get the main problem frequencies, then pure sine of each problem frequency, moving around to measure where the modes are worst.
May it be that there is mixed strength of signals/compensation? Different strengths of amplification? Have you tried using resistors on output of power amp to your widebanders, to get more accurate matching of the in-signal to the subs? I have sometimes experienced that 1db in one place can be very different to 1db in another place.
Edit:
Sometimes, placing a sub in a problem spot can be good, then find the spot with the worst room modes, then move the sub to the "bad spot" and see what happens.
Edit:
I'm probably just way off with my understanding of room modes though. But at least I do not struggle with them at the moment.
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Because it is coupled more directly with the room, induced room loading.
There is no pressure, it is just what you perceive. Move it to the middle of the room and most likely there is very little to no pressure, because the room is not reflecting on the same wavelengths anymore. You may still get some of the sensation very close to the walls, but on different frequencies.
Edit:
Scott, is your listening position close to a wall?
There is no pressure, it is just what you perceive. Move it to the middle of the room and most likely there is very little to no pressure, because the room is not reflecting on the same wavelengths anymore. You may still get some of the sensation very close to the walls, but on different frequencies.
Edit:
Scott, is your listening position close to a wall?
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