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In Reply to: RE: EQ and subs - preliminary results posted by bartc on January 02, 2009 at 07:30:57
I'm sure you must be aware of REW if you visited the Home Theater Shack's forum's.
On thing you may not be aware of is that the Behringer unit introduces a 1ms delay to the output.
This type of set up was originally meant for HT receivers and processors that have distance/time settings for the mains, center, and rears. This allows you to compensate for the time delay of the dsp unit.
I'm not saying that you can't get acceptable results without compensating for this delay, only that it would be better if you could.
I had planed to use a DEQ (strictly in the digital domain) for the amp driving main input of my Gallo Ref 3s which has a time delay feature.
Then use the BFD 11/24 for the amp driving the Gallo's woofers second voice coil. I never got around to it, as the aes/ebu input of the used DEQ 24/94 didn't work.
Please keep us posted on your results.
Julien
"There's someone in my head, but it's not me"
Follow Ups:
No one can hear a 1 millisecond delay from a subwoofer.There have been studies showing a 5 millisecond delay (subwoofer five feet further from ears than main speakers) is the minimum audible delay. Some experts suggest no more than three foot differences (3 ms) to be safe.
No one has ever presented any evidence that a one millisecond bass delay is audible by even one listener.
But ... most people CAN hear a room bass resonance that stays audible for roughly 200 milliseconds AFTER the sound from the subwoofer (or full-range speaker0 stops (-30dB attenuation assumed to be "inaudibility").
So if a one second delay bothers you, just move the subwoofer one foot closer to your ears to eliminate it!
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.Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"
Edits: 01/04/09
There are other places where you can introduce delays with a sub including the existing sub placement which is often (probably usually) further away than the speakers, and the filters and circuits already present in active subs.
A 1 ms delay may not be audible on its own but, added to existing delays which are also inaudible both individually and together, that additional 1 ms may be the difference between an inaudible and an audible total delay so it is possible that someone may notice a delay on introducing the BFD.
If you've got an existing delay which is very close to audibility, it needn't require much to push it all the way to audibility. There will be a point at which a mere 1 ms addition is enough to do just that and if you're unlucky enough to be at that point you will notice it.
David Aiken
With a subwoofer, typically located 8 to 12 feet away from your ears, the majority of bass energy that reaches your ears will bounce off one or more room surfaces first.
Most of the bass energy that reaches your ears IS ALREADY DELAYED by many milliseconds because of the time needed for reflections off walls, floor, and ceiling ... before reaching your ears.
Also, there is no test evidence that any human can hear a 3 millisecond delay, much less a 1 millisecond delay, in the subwoofer frequencies under 100Hz.
I'd say the use of a digital subwoofer parametric equalizer to eliminate 2 to 4 bass peaks of +3 to +6dB .... is FAR more important to the bassline than the added 1 millisecond delay (that could be immediately eliminated by moving the subwoofer 1 foot closer to one's ears).
The probability that a subwoofer is currently located in a position where a mere 1ms of additional delay makes the "time gap" between the subwoofer and main speakers audible ... seems like a low probability event.
Let's say a specific listener with really good hearing can hear a 5ms subwoofer-satellite speaker time delay.
For an additional 1ms delay to make an audible difference, his subwoofer would have to be located where it had at least a 4ms delay (which would need an additional 1ms delay to become audible) ... but had no more than a 5ms delay (which would already be audible).
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Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"
I could swear he said the human ear/brain combo was capable of discrimination on the order of a few femtoseconds. Is that wrong???
The direct sound always arrives first and is always higher in level than the first reflections.
What you say about most bass being reflections and delayed is true of all frequencies, not just bass frequencies. That doesn't make the direct sound unimportant. Some parts of our perception are drawn from the direct sound and some from the reflected. The direct sound usually gives us our timing for a sound since it arrives first. Exceptions can occur when a later arrival is louder, which doesn't occur with individual reflections, or arrives after an exceptionally long delay which won't occur in a room. The fact that, in some cases, the reflected sound field can, in total, be louder than the direct sound is usually irrelevant in small room situations like ours because it simply isn't sufficiently louder than the direct sound for the direct sound to lose precedence and, in any case, the brain is taking information from individual reflections, especially the first ones which arrive as separate events with clear intervals between them.
And you said: "Also, there is no test evidence that any human can hear a 3 millisecond delay, much less a 1 millisecond delay, in the subwoofer frequencies under 100Hz."
That still misses my point. There can be other factors delaying the direct sound and they may not delay it enough to make the delay audible so we have an inaudible delay. Add another delay and you can end up with a total delay that is audible. An additional delay of 1 ms will, in the right circumstances, be enough to make the total delay audible so it is possible to notice the addition of a 1 ms delay. I never said it will happen every time but it can happen in some cases.
David Aiken
Such a large percentage of the bass energy under 80Hz. is reflected energy that it's almost irrelevant to discuss direct versus reflected sound at those frequencies.
If subwoofers are set up properly, placed near other speakeres and located approximately the same distance from one's ears, then adding a 1ms subwoofer timing delay by using a digital parametric EQ is very unlikely to be audible.
But if the subwoofers were located far behind the main speakers, perhaps in the room corners where they produce the most uneven frequency response possible in a rectangular room, then it's possible adding just 1ms additional delay could create an audible deterioration of the bass note quality. (Moving the subwoofers 1 foot closer to one's ears would regain 1ms.)
One could also buy an analog parametric equalizer, which is more expensive, and much harder to set precisely, compared with a digital parametric equalizer ... but an analog EQ would avoid the 1ms time delay caused by A to D to A processing.
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Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"
It's always relevant to consider direct vs reflected sound because they contribute different things to our perceptions.
And you keep missing the point that it's not the delay added by a particular device but the total delay introduced at all stages that can be the critical factor.
End of discussion.
David Aiken
The point seems to be whether an added 1ms delay for subwoofer frequencies would be audible, and not sound right.
I say that's very unlikely to be audible.
You had no point, other than pontificating that 1ms of additional delay might be the 'straw that broke the audio system's back'.
The benefit to the bassline frequency response from parametric EQ is so much more audible than a 1ms time delay, that I can't understand your theoretical problem with a +1ms delay.
An analog EQ would avoid the 1ms delay.
Or use a digital EQ, and move the subwoofer 1 foot closer.
Ho hum
Case closed.
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Richard BassNut Greene
"The Floyd R. Turbo of Bingham Farms Michigan"
I didn't know about that 1 ms delay injection. Now how to cure that other than more DSP or different positioning?
David Aiken had originally suggested time factors to me when I started this exploration. His solutions: change position to have sub significantly closer or use the full time domain processing of an HT receiver.
I was able to play a bit with positioning before the BFD experiments and did indeed realize some timing improvement, but may be out of luck on any close positiong -- WAF issues.
As to the HT processor, that's not somewhere I can either afford to go or want to go at this time. I don't want to introduce more complex circuitry for 2 channel music. This BFD may be quite enough DSP for my taste; I have it limited to the real LF regions, where it's less critical to the musical signal, rather than all across the spectrum, where its side effects might be more noticeable.
Thanks for the info, Julien. I will keep you guys posted. Don't expect quick changes, though, as I have to get my wife out of the house to do any serious experimentation, and that waits unitl next week when she goes back to teaching school.
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