Author Topic: Sub strategy  (Read 18067 times)

Offline _Scotty_

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Re: Sub strategy
« Reply #30 on: August 25, 2015, 06:23:58 PM »
Here are links to QSC DSP30 processors for sale on ebay.
http://www.ebay.com/itm/QSC-Audio-DSP-30-Computer-Configurable-Digital-Signal-Processor-/171904588902?hash=item28064fdc66

http://www.ebay.com/itm/QSC-DSP-30-Audio-Signal-Processor-Compressor-Limiter-Crossover-Parametric-EQ-/262009621088?hash=item3d00fd8a60

http://www.ebay.com/itm/QSC-DSP-30-Computer-Configurable-Digital-Signal-Processor-/321838983041?hash=item4aef192781

This model has been discontinued by QSC and alternative processors are more expensive.

There are also any number of inexpensive prosound digital amps that have configurable digital delay built into them as part of their feature set.
What you are looking for is delay capability between 1millisec and 30millisecs. This gives you the ability to put the sub-woofer immediately behind the listening position or up to around 28ft. behind you. The DSP 30 has sub millisec delay capability and up almost 1000ft. of delay for use in large venues.
 
Shameless plug for HAL's MS-3 Music Server and dspMusik DSP DAC. The dspMusik DSP DAC has the necessary programmable delay capability.
I use a HAL MS-2 Music Server in my system to good effect.
Scotty

Offline Werd

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Re: Sub strategy
« Reply #31 on: August 26, 2015, 01:10:42 PM »
Here is from the Cabs paper.

"The advantages of CABS are:
• More even sound level distribution below 100 Hz is achieved throughout the room. • The effect of the room resonances in the reproduced sound is decreased considerably. • Only simple signal processing is needed"

End quote

The problem with Cabs appears to be in the first advantage. The advantage of more even sound distribution below 100hz is not a desirable effect at the source when using subwoofers. Only because that statement exists in a pure theoretical environment and not practically. It never ends up like that. If it did cabs would function in a room with any dimension. The system that works in every environment and room dimension is sub placements - raised- for resolution (basically over 100hz) and as the waves move out subs for ambience. Subs on the floor to radiate the room boundaries. Phase or out of phase what ever floats your boat.

Think of sitting in front of a bass drum. The kick gives you a sensation above the 100hz range.  Raised subs will form the sound of the kick (resolution)  and will also give you a threshold of low frequency slam. Since raising subs doesnt eliminate ambience but only reduces it. As the wave radiates out, the room becomes the major factor for ambience.  
What becomes apparent in the sweetspot is the resolution of the raised sub and  the loading of the sub at room boundaries or the ambience adjustable by sub volume. Cabs is taking a problem easier solved and making it more difficult and it only works in certain environments. Though Its got good info about how low frequencies move around the room.  
« Last Edit: August 26, 2015, 01:12:43 PM by Werd »
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Offline _Scotty_

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Re: Sub strategy
« Reply #32 on: August 26, 2015, 05:29:25 PM »
If you are using a standing wave zone that is located on top of your listening position to compensate for program material that may be lacking in bass impact then you wouldn't necessarily want an effective solution to standing wave problems.
 CABS actually does work with any room having six walls regardless of their dimensions, it even works to a lesser degree in the an L shaped which is covered in Chapter E starting on page 97. This is the shape of room that I have to contend with.
Scotty

Offline richidoo

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Re: Sub strategy
« Reply #33 on: August 27, 2015, 02:05:10 PM »
Hey Scotty, what do you think about these driver placements on my front/rear walls?

They all follow the CABS placement rules pretty closely... except for the 3 driver version, where the top driver is centered between where the two top drivers would be if the room was cuboid, but the distance between the 3 drivers is not constant like it should.

I'm not sure if distance to the wall is more important than driver spacing, and with my wall shape one of them has to give. However, the one with 2 drivers per wall seems to fit all the rules despite the slant ceiling.  

Please don't advise the one with 14 drivers per wall. ;)  I only did that because I like playing with CAD, although it would be fun to hear it. :D

I think the CABS concept of wall reflections is key to making compromises like this work, but I'm still trying to wrap my head around that. The reflection idea suggests that there will be sound bouncing back and forth across the side walls and floor/ceiling while traveling toward the rear, but I'm not sure why that is significant. It seems to me that the only thing that matters is having the radius of individual wavefronts large enough to they are flat enough to merge into one relatively flat wave. So that the bumpiness of the wave front due to multiple drivers is of small enough deviation to be small error during the cancellation. Due to wall reflections and arbitrary room length the phase bumps in the wavefront will not stay in the same location relative to the pitching and catching walls throughout the trip. So the wave has to be flat enough to allow the dips to migrate randomly across the planar wave and still be flat enough to be cancelled with decent efficiency. Make sense to you?

So then what happens if there is only one driver in the center of each wall? How do you calculate Fc?  Would CABS even work? The wavefront will be hemispherical coming from one driver, so to flatten it sufficiently to be cancellable at the rear the 1/2 wavelength should be largest wall dimension? In my case Fc = 49Hz. But my fundamental room modes are 36, 49, 70. So CABS with Fc = 49Hz can't prevent the floor ceiling mode at 70Hz. So I need at least 2 drivers per wall.

Considering the small window in the center of the front wall and the need for a entry door on the rear wall, (and my driver and amp budget) I think my best option is 2 drivers per wall.
« Last Edit: August 27, 2015, 02:17:37 PM by richidoo »

Offline Werd

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Re: Sub strategy
« Reply #34 on: August 27, 2015, 03:50:26 PM »
If you are using a standing wave zone that is located on top of your listening position to compensate for program material that may be lacking in bass impact then you wouldn't necessarily want an effective solution to standing wave problems.
 CABS actually does work with any room having six walls regardless of their dimensions, it even works to a lesser degree in the an L shaped which is covered in Chapter E starting on page 97. This is the shape of room that I have to contend with.
Scotty

What you are saying is buy the right speaker for the room. That will solve the bass problems.

The entire cab model including examples and math are all based in the time domain. Multiple woofers vertical mounted (raised) on your mains operate in the time domain. They operate like this because of floor bounce. If you have a main speaker with at least 2 woofers and a sub that operates at a different height than the mains. There will be no standing waves in the sweetspot. Unless you are right up against a wall.
Then who knows. You can correct any malfunction by using  subs out of phase in the back. But the entire paper is based on 4 subs all operating at the same height in a rectangular room. Its all there to read. The reason that the time domain problem exists is because all the drivers are at the same height on the floor! To eliminate this problem put the drivers at different heights especially the subs. The more i read that paper the more it becomes clear they reversed the engineered the problem. They look at a rectangular room with 4 subs and what it looks like with no time sucks or humps. Then they reversed engineered the math back to the problem. That helps nobody because it isn't realistic. They even claim a major drawback is furniture. It diminishes the effect.

Anyways i like the delay on subs but you won't need it if you have a raised forward sub.
Nola Viper Reference iii, Nola Blue Thunder Subs, Chapter Couplet 400s, Chapter Précis 250 integrated set to pre, Bryston BDA2/BDP1.
Torus RM-20 240v

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Offline _Scotty_

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Re: Sub strategy
« Reply #35 on: August 27, 2015, 06:52:30 PM »
I don't know if you've had any experiences with wave tanks in high school or college physics classes but a planer wavefront can simulated in a wave tank. Any frequency propagated in the wave tank that has the a wavelength with a close harmonic relationship to the length of the tank will nicely demonstrate the concept of standing waves. It will be seen that there are no reflections from the sidewalls of the tank at all. A planar wave can also be simulated in your common garden variety bathtub by moving your palm to and fro until your find the frequency that causes all of the water in the tube to move as single mass.
 If you propagate a mostly planer wavefront in the bass frequencies from the front of the room the sidewall reflections are sufficiently suppressed to the point that you can deal the standing waves that are function of the rooms' longitudinal dimension by generating anti-phase counter planer wave from the back of the room.
 I think your 2 drivers per wall solution is the most economical approach that will work in your room. If the subs are not mounted in the wall you could play with their height off the floor to achieve the best results.
 The operational wavelengths are so long relative to the box mounted woofers location away from the plane of the wall that I think that any negative from this is out weighed by the placement flexibility gained.
 From Figure 45 on page 91 its obvious the having the ability to relocate the sub-woofers vertically and horizontally to fine tune the cumulative spectral decay results is a useful option to have. REW RT 60 measurements would allow one to zero in on the optimum vertical locations for the subs on both front and rear walls.
Even with a considerably compromised room shape and lacking the ability to put the subs in the best location in either
the horizontal or vertical planes on the walls I am still very happy with limited results I have in this situation. The bass is much less audible at the end of the hallway where the master bedroom is situated and is a godsend for late night listening sessions.
The slick thing is that one can boost the bass via EQ in the playback software when more impact is desired and the corresponding boost will show up in the rear channels to cancel it out with less likelihood unplanned boominess.
Scotty

Offline _Scotty_

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Re: Sub strategy
« Reply #36 on: August 27, 2015, 07:13:51 PM »
werd, if you were to download the free REW program and take RT60 measurements you will find ample evidence that the standing wave problem exists in any untreated average listening room regardless of where the woofers are located in the vertical plane. It looks like the CABS approach can generate RT60 measurement results similar to that of a well treated room.
 This is the reason I am enthusiastic about it, as complete acoustic treatment of my living room to solve the bass settling time problems it has are both physically and financially out of the question.
 While the Swarm approach can yield similar results, I already have the equivalent of 4 subs in the front of the room and no way to afford or room to place the multiple small subs in my room that a using Swarm would require.
Scotty

Offline richidoo

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Re: Sub strategy
« Reply #37 on: August 27, 2015, 07:26:55 PM »
Cool, thanks Scotty. 

What does he mean by CABS .2.2 vs CABS .2.0?

Offline _Scotty_

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Re: Sub strategy
« Reply #38 on: August 27, 2015, 07:52:36 PM »
It looks like these labels apply to two different vertical locations on the subs, the second one looks like it give a little better cumulative spectral decay results, ie faster settling time/RT 60 numbers.
Scotty

Offline rollo

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Re: Sub strategy
« Reply #39 on: September 01, 2015, 07:11:27 AM »
   IMO most of the issues of sub placement is most subs are in a box. Open baffle is a huge advantage over seled or ported subs IMO.
   Add servo drivers with a plate amp designed for such will change your sub opinions.
    We recently showed at Capitol Audiofest using three per side servo open baffle subs with great success.
     Using servo controlled drivers eliminates any box coloration from the back wave. All drivers are designed to act as one with a computer controlled coil on the drivers.
    Tight articulated bass wit zero boom or or overhang. tone with harmonics. One is easily able to discern foot pedal action on organ as never heard before.
    After hearing open baffle design done right it would be impossible for me to listen to a sub in a box.


charles
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Offline Werd

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Re: Sub strategy
« Reply #40 on: September 03, 2015, 09:46:35 AM »
OB subs will be my next venture if i ever get to it.  :thumb:
Nola Viper Reference iii, Nola Blue Thunder Subs, Chapter Couplet 400s, Chapter Précis 250 integrated set to pre, Bryston BDA2/BDP1.
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Offline rollo

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Re: Sub strategy
« Reply #41 on: September 10, 2015, 11:40:27 AM »
  You should get to it , you will NOT be disappointed.


charles
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Offline shadowlight

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Re: Sub strategy
« Reply #42 on: September 11, 2015, 07:02:09 AM »
  You should get to it , you will NOT be disappointed.


charles

Charles,
Which subs did you use?

Offline rollo

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Re: Sub strategy
« Reply #43 on: September 11, 2015, 08:11:24 AM »
Inner Sound SI 300 servo subs, powered by Rythmic plate amps made to our spec.
    The servo controlled GR Research drivers are a dipole OB design. Down to 16HZ at 3db.
    Fast, accurate with tone , no bloat or boom. just clean articulated bass.


charles
contact me  at rollo14@verizon.net or visit us on Facebook
Lamm Industries - Aqua Acoustic, Formula & La Scala DAC- INNUOS  - Rethm - Kuzma - QLN - Audio Hungary Qualiton - Fritz speakers -Gigawatt -Vinnie Rossi,TWL, Swiss Cables, Merason DAC.

Offline shadowlight

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Re: Sub strategy
« Reply #44 on: September 11, 2015, 10:10:31 AM »
Inner Sound SI 300 servo subs, powered by Rythmic plate amps made to our spec.
    The servo controlled GR Research drivers are a dipole OB design. Down to 16HZ at 3db.
    Fast, accurate with tone , no bloat or boom. just clean articulated bass.


charles

~8K - Ouch