Question for those with external subs

cjf

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Nov 19, 2012
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#41
Thanks for your thoughts and additional detail Kal

I guess it could be argued that having a properly integrated sub/subs via whatever method that it takes may very well result in a better sounding system beyond what any minor SQ benefits a slightly better DAC/PRE could bring to the table assuming the use of a decent DAC/PRE to begin with.

In my case I'm fortunate to have a room with very minor issues in terms of "modes/nulls" due to its size/shape. I'm using ROON's PEQ to fix the two areas that require PEQ touch-ups (39hz -4db cut & 168hz -2.5db cut) but beyond that I'm in the clear everywhere else.

I'll probably pick up a single JL-F113 to poke around and see what I can do with it as a test to see what I'm missing.
 

Kal Rubinson

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#42
I'm using ROON's PEQ to fix the two areas that require PEQ touch-ups (39hz -4db cut & 168hz -2.5db cut) but beyond that I'm in the clear everywhere else.
You can use Roon for crossover and delays as well.
 

Folsom

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#43
Impulse response is a measure of abrupt switches in phase. All dynamic drivers vary in phase naturally at different frequencies. It doesn't matter if you're closer, for improve impulse. In fact the closer you are the easier you may hear problems with it. The best way to keep down "smear" of multiple frequencies that naturally have differences in phase, is to use equipment that controls the subwoofers better. Servo subwoofers do just that. While it isn't the imperative to integration per se, for quality you want this to be good.

*Impulse is a function of recovery, not distance.

What makes the subwoofer sound natural with the speaker? It's not "delay" distances. It's about a smooth blend, which means trying to get a power response that is compatible-ish with the room, particularly while finding a similarity in phase around the "hand off" frequencies.. The phase area is almost "rough" but it needs to be as smooth as the phase shift that naturally occurs within a midwoofer at least.

Most cues in music for bass transients are found wholly outside of the bass region, which is why it's all possible. Frankly pure bass doesn't sound like much, most of the time (we can't even "hear" a lot of it), without accompanying information. For that same reason small speakers can produce surprisingly defined sounding music that has bass, while the SPL isn't that high in the bass region.
 

Kal Rubinson

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#44
*Impulse is a function of recovery, not distance.

What makes the subwoofer sound natural with the speaker? It's not "delay" distances. It's about a smooth blend, which means trying to get a power response that is compatible-ish with the room, particularly while finding a similarity in phase around the "hand off" frequencies.. The phase area is almost "rough" but it needs to be as smooth as the phase shift that naturally occurs within a midwoofer at least.
Well put. Impulse response is also a way to measure delay/distance and the electronics and mechanics of subs make that apparent. Unfortunately, the market has adopted a standard subwoofer configuration that imposes a delay difference between subs and main speakers.

Most cues in music for bass transients are found wholly outside of the bass region, which is why it's all possible. Frankly pure bass doesn't sound like much, most of the time (we can't even "hear" a lot of it), without accompanying information. For that same reason small speakers can produce surprisingly defined sounding music that has bass, while the SPL isn't that high in the bass region.
True.
 

PeterA

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Dec 7, 2011
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#45
Most cues in music for bass transients are found wholly outside of the bass region, which is why it's all possible. Frankly pure bass doesn't sound like much, most of the time (we can't even "hear" a lot of it), without accompanying information. For that same reason small speakers can produce surprisingly defined sounding music that has bass, while the SPL isn't that high in the bass region.
Perhaps this is the reason why I find that a good sounding pair of small speakers often sounds better than a system in which a subwoofer is added. If the subwoofer is not extremely well integrated, then it actually detracts from these very bass transients which so often define the musical message. If overall system clarity is diminished with the addition of a subwoofer, I prefer it without the subwoofer. I prefer a system that has more clarity to one that has more "extension".
 

Folsom

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#46
Well put. Impulse response is also a way to measure delay/distance and the electronics and mechanics of subs make that apparent. Unfortunately, the market has adopted a standard subwoofer configuration that imposes a delay difference between subs and main speakers.

True.
So let me see if I can make an interesting example of why you don't outright "win" with the concept of moving a subwoofer closer to you because of impulse response.

If your impulse response "delay" is 10msec, and you have another 10msec due to distance: Well if you move the subwoofer closer to close that 10msec gap, because your main towers only have the 10msec gap without the + 10msec "delay"... Based on this theory what's amusing is that if you have an 50hz signal, only the first 10msec is group delayed, and if the 50hz signal lasts for even 1 second, you've essentially made a 50hz signal be early for 980msec when it's not coming in or out (the group delay) of the frequency.

Based on the principles the guy suggests, you've created a bigger issue. Reality? He has never noticed it, and no one else will, at least not anymore than having a subwoofer by the mains or even behind. All the other factors in the room still dominate this, including the impulse response itself if it's coming from a non-servo subwoofer.

I'm not even sure why the dude goes on about being behind or ahead in phase. The phase knobs on subwoofers have nothing to do with delay (common misconception). Furthermore if you're blending 40hz from your mains and subwoofers, that's a 28ft sinewave. If you were to lead it by 180* that requires 14ft (assuming you can actually introduce delay, and you probably can't without a HT receiver or specialized DSP). To make them sound like separate sources you need a distance exceeding 1 wavelength (assuming all else is setup well). Basically it isn't going to happen.
 

cjf

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#47
The one thing that I thought about when seeing mention of moving the sub closer while reading the article was that by moving the sub 9-10ft closer to the listening chair would essentially result in needing to place a seat cushion on top of the sub cabinet and sitting on it instead of your normal chair. The only way this would not be the case is if your room was massive (figure 25-30ft from front wall to seat). This would put the sub dead center of the room in line of site between you and the front plane of the main speakers. Not very practical or realistic.

The more likely scenario would be moving the sub the same 9-10ft forward but instead of it being in the middle of the room it would be along one of the sidewalls. But, doing this isnt really moving it closer either since you still have the distance from the sidewall to seated position to contend with which in my case is still the same 9-10ft anyway. Uggh!

So it looks like moving the sub forward is out of the running if we want to be realistic
 

Folsom

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#48
The one thing that I thought about when seeing mention of moving the sub closer while reading the article was that by moving the sub 9-10ft closer to the listening chair would essentially result in needing to place a seat cushion on top of the sub cabinet and sitting on it instead of your normal chair. The only way this would not be the case is if your room was massive (figure 25-30ft from front wall to seat). This would put the sub dead center of the room in line of site between you and the front plane of the main speakers. Not very practical or realistic.

The more likely scenario would be moving the sub the same 9-10ft forward but instead of it being in the middle of the room it would be along one of the sidewalls. But, doing this isnt really moving it closer either since you still have the distance from the sidewall to seated position to contend with which in my case is still the same 9-10ft anyway. Uggh!

So it looks like moving the sub forward is out of the running if we want to be realistic
That is a funny math problem as well, isn't it?
 
Nov 3, 2014
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#49
That is a funny math problem as well, isn't it?
It sure is. But, not really in a Mch setup where DSP distance calibration in the processor can delay other channels to match the sub's delay. Freedom of distance placement is thereby assured.

I checked JLs CR-1 $3,000 external stereo xover/controller. I don't see the ability to delay the main channels in the specs, but perhaps it can do that or perhaps not.
 

cjf

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Nov 19, 2012
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#50
OK, I'm going to admit my slowness up to this point in totally missing another option that would also address the Sub delay problem. Some may have already been hinting at this and I missed it.

So am I right in assuming this issue could be addressed by choosing to simply not use the internal DSP/Crossover included within the Sub and do "All That Jazz" within software before the DAC? This may even the playing field in terms of the Delay seen by the Main Towers and the Sub/Subs since all of them would be affected by the same default delay of the DSP function upstream. I suspect that any positioning differences between Main Tower and Sub could also be "Tweaked" if necessary.

Hrrrrm?
 

awsmone

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Apr 7, 2014
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#51
As someone who has spent too much of his life integrating multiple subs my points would be

1. Multiple subs integrate better than single, this is because you smooth out the room bumps of single sub position
2. In order to coordinate main to sub I prefer to not use the subs controls but external crossover
3. To be able to control delay is very helpful to integrate subs well and I use it
Even a cheap digital pa speaker management crossover has this feature, along with phase changes and variable frequency cut off and crossover rates
4. You don’t need to locate the sub near the speaker plane Remember if you using a sub as a fill against a main it’s omnipresent ambience you adding not midbass , this is general information that is very complicated phase sound, with different delays , I would recommend at least delaying by 10 msec in first instance to use the Hass effect to your advantage
5. If your optimising for music and not theatre then shift cuts to actual musical pitches, to decrease boom when these pitches are struck

Typical bass pitches are 41; 55: 73 98; sometimes 31 in five string double bass, if you listen to bass player and have a guitar tuner when you hit a booming note you write down the pitch played and decrease in this area with High q cut out

These are general ideas I have formulated

I use seven smaller subwoofers 10 to 12 inch, I locate near boundaries as then you maximise room gain, and decrease compression issues of the amplifier and driver, I then correct the frequency anomalies,

6. In general your biggest anomalies are actually related to the room dimensions and not the position of the subwoofer, so not amount of moving them around can rid you of room resonances, other than by using multiple subwoofers at different positions to fill in the holes between the peaks

You must then correct these room anomalies, this can require big corrections , hence my idea of concerntrating on the corrections at musically significant pitches rather than room specific to concerntrate the correction where it’s needed most

7. I note in penning this, that I fact I am talking about two things , integrating a subwoofer with main speakers , and
Integrating a subwoofer with a room , they are different, but once you add a subwoofer into a room, then lower room modes come into play, and as JA famously noted, that’s a big problem to get away with

8. All subwoofers will effect the sound in midbass, midrange and treble, blending the effect to get a musical whole that is pleasing and believable is the art, not science of it.

My integration and bass pitch definition is excellent, I Note Al M comments and agree that there is big variability in bass output mainly in jazz and popular music, less in classical, I choose not to correct in general as it’s too time consuming for me, and it’s whats on the recording, but agree some of these corrections seemed designed for radio or iPhone playback, not audiophile playback
 
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audioguy

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#52
3. To be able to control delay is very helpful to integrate subs well and I use it a cheap pa speaker management strip has this feature, along with phase changes and variable frequency cut off and crossover rates
Can you elaborate on what you mean by this process? What is a "speaker management strip"
 

Folsom

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#55
OK, I'm going to admit my slowness up to this point in totally missing another option that would also address the Sub delay problem. Some may have already been hinting at this and I missed it.

So am I right in assuming this issue could be addressed by choosing to simply not use the internal DSP/Crossover included within the Sub and do "All That Jazz" within software before the DAC? This may even the playing field in terms of the Delay seen by the Main Towers and the Sub/Subs since all of them would be affected by the same default delay of the DSP function upstream. I suspect that any positioning differences between Main Tower and Sub could also be "Tweaked" if necessary.

Hrrrrm?
You're assuming the "delay" is a problem. If anything has been shown with math so far, it's that servo based subwoofers combat group delay, and location doesn't work to help it or delay.

Group delay is not delay. Two very different things.
 

awsmone

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Apr 7, 2014
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#56
You're assuming the "delay" is a problem. If anything has been shown with math so far, it's that servo based subwoofers combat group delay, and location doesn't work to help it or delay.

Group delay is not delay. Two very different things.
To expand on Folsom s excellent response

Some definitions from Wikipedia:-

In signal processing, group delay is the time delay of the amplitude envelopes of the various sinusoidal components of a signal through a device under test, and is a function of frequency for each component. Phase delay, in contrast, is the time delay of the phase as opposed to the time delay of the amplitude envelope.

Subwoofer group delay

Group delay has been found to be a major predictor of the "tightness" or transient accuracy of a subwoofer system. Group delay, in it's mathematical form, is the negative derivative of acoustic phase with respect to♪ requency. That is, group delay is a measure of how fast the acoustic phase of the system changes.
 

audioguy

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#57
Got it. In my case, since I use a multi-channel processor (Datasat RS20i) as a "pre-amp", I have most of that functionality built in but also have a miniDSP (THIS ONE) that I only apply to the multiple subs if necessary. It has PEQ, high and low shelf fillters, delay, etc and it uses XLR connectors which is compatible with my equipment.

I was setting sub/mains delays by running frequency sweeps and adjusting delays (real time) until I got the smoothest transition at the crossover. Now, I do what someone else already noted, and what I used to do prior to having access to measuring equipment. I run a frequency sweep at the selected crossover point until I get the maximum output using an SPL measurement device. In my case, I still use OmniMic since in addition to frequency, phase, etc, it also can be an SPL meter.

Actually, I do it a tad different. Sometimes it is easier to measure minimum rather than maximum as the differences measuring maximum may sometimes more difficult to detect on a meter. So, I temporarily reverse the leads on, for example, my left speaker, do the same test and adjust the delays until I get the "minimum" output at the crossover. I then put the leads back to normal and, by definition, now have the maximum output at the crossover. Works like a champ and not only do the frequency sweeps look better at the crossover, it is really easy to hear the difference using real world material.

As an FYI, I have two subs in each of the front two corners (all driven by the same amp) and 4 subs across the center of the rear wall. "The more the merrier" ... and you most certainly can not localize the subs.
 
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Folsom

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#58
To expand on Folsom s excellent response

Some definitions from Wikipedia:-

In signal processing, group delay is the time delay of the amplitude envelopes of the various sinusoidal components of a signal through a device under test, and is a function of frequency for each component. Phase delay, in contrast, is the time delay of the phase as opposed to the time delay of the amplitude envelope.

Subwoofer group delay

Group delay has been found to be a major predictor of the "tightness" or transient accuracy of a subwoofer system. Group delay, in it's mathematical form, is the negative derivative of acoustic phase with respect to♪ requency. That is, group delay is a measure of how fast the acoustic phase of the system changes.
I think I'll try to provide a very simple explanation of your more technical one.

Group delay: The amount of time it takes for the subwoofer to "get up to speed" with the frequency it is trying to make, in particular from another frequency. If you want 31hz, and you're at 45hz, the amount of time to switch is the group delay. Analyzing it is more complicated, ala the above post. But if you think of it as a big, heavy, clumsy device trying to change speeds, that'll clue you in.

Servo subwoofers exert a lot more control to force subwoofer compliance to the source signal, so the time to switch frequencies is less. And hence, tightness, as awsmore pointed out.
 

awsmone

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Apr 7, 2014
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#59
Got it.

Actually, I do it a tad different. Sometimes it is easier to measure minimum rather than maximum as the differences measuring maximum may sometimes more difficult to detect on a meter. So, I temporarily reverse the leads on, for example, my left speaker, do the same test and adjust the delays until I get the "minimum" output at the crossover. I then put the leads back to normal and, by definition, now have the maximum output at the crossover. Works like a champ and not only do the frequency sweeps look better at the crossover, it is really easy to hear the difference using real world material.

As an FYI, I have two subs in each of the front two corners (all driven by the same amp) and 4 subs across the center of the rear wall. "The more the merrier" ... and you most certainly can not localize the subs.
I use the minimum methods for exactly the reasons, Kal also uses this method....
 

cjf

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Nov 19, 2012
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#60
You're assuming the "delay" is a problem. If anything has been shown with math so far, it's that servo based subwoofers combat group delay, and location doesn't work to help it or delay.

Group delay is not delay. Two very different things.
If servo subs are the answer then I'm curious why the more popular Sub brands like JL,Magico, Wilson, SVS, B&W..etc are choosing to not use that technology? I found a handful of Servo based brands (Rythmik, Velodyne, Paradigm) and I'm sure there a others but for whatever reason its seems very few of the higher end music centric systems (just looking on this forum as an example) seem to not be using them. Why do you suppose that is and what are the negatives against Servo based Subs?

If delay, of any kind, isn't a serious problem then why does it seem like such a popular topic with lots dedicated text on how to address/combat it when blending Subs with Main towers? Why are these people not just buying Servo Subs and calling it a day?

I obviously don't know which is why I am asking the questions.
 

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