Sub crawl and when to perform it? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 14 Old 05-23-2020, 07:03 AM - Thread Starter
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Sub crawl and when to perform it?

Jumping right to the point... when building a listening space, how soon in the build process can or should you do the sub crawl or break out the microphones and start taking measurements? I want my subs behind an AT screen, but I've read so much about people encountering a lack of bass due to nulls and such that I'm worried if I plan for that location, I'll become one of those statistics. Also, I'm guessing that you have to have a certain amount of finishing materials installed before you take measurements or sub crawl to avoid echoes or reflections that won't be there when the room is complete?
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post #2 of 14 Old 05-23-2020, 07:11 AM
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Sub crawl and when to perform it?

Maybe try some room sim with REW and see which place is best when you are planning the room, it won’t be 100% accurate but it will give you a good start.

The best way to deal with nulls and such is with multiple subs.

Also can you say the dimensions of the room and is it closed off or open to other area?

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post #3 of 14 Old 05-23-2020, 07:39 AM
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Sub crawl and when to perform it?

Sub crawl is not the way to find the nulls in the room, as said before multiple subs is the way to get rid of those bulls in the room. I am no expert but @cdy2179 is the expert and he has many videos to help us non experts to get amazing bass.

Here is a couple of his YouTube videos on sub alignment and calibration.

Hope this helps, Steve has many videos on his channel that will help your through this process.





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post #4 of 14 Old 05-23-2020, 10:11 AM
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Leave mounting the AT screen until last.

Get the room buttoned up, and then take measurements.
(Assuming the subwoofers aren't IB or going in the columns...)

There are two ways:
1) Place a sub at ear level at the golden seat and walk the mic around the room until you've found the best spot(s).
2) Place the mic at ear level at the golden seat and move the sub(s) around the room until you've found all the best spot(s).

Generally the second option is more accurate.
Echoes don't really impact bass, but drywall does and so the drywall must be in place before taking measurements.

Room treatments mainly treat high frequencies above 1khz,
bass cannot be trapped even with 12inches thick panels.
Will they cure bass? Not really.
Will they help a bit? Maybe...

Unless you are willing to move walls around (highly unlikely), then multiple subs and EQ is the only solution that is effective.

You can only make 1 seat measure perfectly, or you can make multiple seats measure less-ugly.
Multiple subs helps lots in this regard.

Only 1 seat can be perfectly on-axis with the LCR and subwoofer time-alignments. All the other seats will have off-axis sound with horribly unbalanced timing, this is due to physical distance/layout... it's unavoidable.

At least with multiple subs, the further from one sub you get, the closer to another subwoofer you get.
Also the interaction between the subs smooths out the bass. Good results can be obtained with 2-4 subs, but it still won't be flawless even with 32 subwoofers.

You can EQ down peaks, but you can't EQ up nulls. So the best spots will either be flat or with mostly-peaks (i.e. the least nulls).

When adding multiple subwoofers, they should net you about 6db per doubling (assuming they are summing in-phase correctly.) Give or take a few db...

Last edited by BassThatHz; 05-23-2020 at 10:14 AM.
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post #5 of 14 Old 05-23-2020, 10:15 AM
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As mentioned by Mahuzz13, I would use rew to aid in sub placement. Using the subcrawl while generating one frequency will only give results for that one frequency.

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post #6 of 14 Old 05-23-2020, 01:25 PM - Thread Starter
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@bogaboga & @Mahuzz13 , thanks for the replies, I appreciate them!


For information purposes, my room is 21'L x 15'W x 9.5'H (finished level) and it is located underneath the main garage. It is completely enclosed and the ceiling, floor and walls are all concrete, basic stud walls are up as are the ceiling joists, but no drywall. It will be mostly used for movies and while my goal is impressive bass performance, I don't want to get caught up in locating subs all over the room... I'd prefer two behind an AT screen and perhaps a third if absolutely necessary in a nook at the back of the room.


I have watched a number of the Home Theater Gurus videos, but still have a bunch to go. So, if I have the subs I'm planning to use, could I use REW get a general idea of the rooms bass performance even though the walls are essentially bare? I would think the massive echos I currently have would skew the results, but I don't really know.
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post #7 of 14 Old 05-23-2020, 01:51 PM
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My experiment with a very simple double bass array was pretty eye opening. Not my thread but I posted some results there, just one sub in front and one in back. Bass array sound is like deleting a lot of the boomy sound, at first it sounds flat but that’s because you’re used to the tubby sounding bass. Then you notice the bass waves go by but don’t come back nearly as much, nulls are reduced and there is more clean bass. Ultimately I plan to do a real one but does require a lot of cabinets.

http://Double Bass Array (DBA) - The...ink_source=app
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post #8 of 14 Old 05-23-2020, 02:21 PM
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You could implement a DBA behind your AT screen.

That's about all you can do, placement-wise.

https://en.wikipedia.org/wiki/Double_bass_array

edit: Looks like Vince_B beat me to it.

As for echoes, if you look at the design of most anechoic chambers you'll see they have like 4ft fiber glass wedges on all 6 sides of concrete, and when they measure acoustical panels they still can't measure them with statistical-significance much below 125hz. Either that or... the absorption coefficient at low frequencies is so close to zero that it's not worth measuring.

Last edited by BassThatHz; 05-23-2020 at 02:26 PM.
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post #9 of 14 Old 05-23-2020, 11:06 PM
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Quote:
Originally Posted by mumbles60 View Post
Sub crawl and when to perform it?
Well, not after a pub crawl!
You'd want walls in place, but final finishing is not going to affect really low frequencies. Also for your situation maybe nearfield subs built into the seating would be better?
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post #10 of 14 Old 05-25-2020, 02:10 PM - Thread Starter
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Quote:
Originally Posted by Vince_B View Post
My experiment with a very simple double bass array was pretty eye opening. Not my thread but I posted some results there, just one sub in front and one in back. Bass array sound is like deleting a lot of the boomy sound, at first it sounds flat but that’s because you’re used to the tubby sounding bass. Then you notice the bass waves go by but don’t come back nearly as much, nulls are reduced and there is more clean bass. Ultimately I plan to do a real one but does require a lot of cabinets.

Double Bass Array (DBA) - The modern bass concept!
https://r.tapatalk.com/shareLink/topic?share_fid=47413&share_tid=837744&share_pid=5 7828314&url=https%3A%2F%2Fwww%2Eavsforum%2Ecom%2Ff orum%2Fshowthread%2Ephp%3Fp%3D57828314&share_type= t&link_source=app
Quote:
Originally Posted by BassThatHz View Post
You could implement a DBA behind your AT screen.

That's about all you can do, placement-wise.

https://en.wikipedia.org/wiki/Double_bass_array

edit: Looks like Vince_B beat me to it.
I watched episodes 7 & 8 from Home Theater Gurus and he seems to discuss the DBA you both mentioned.



I've attached a diagram of my room layout with dimensions. The green wall does not exist, but is meant to show the AT baffle wall. If I were to locate a sub in positions A & B, would that accomplish DBA principle? Also, as mentioned, I don't really care for speakers in view, but what about stacking two subs in position C at the back of the room? Would they help at all?
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post #11 of 14 Old 05-26-2020, 03:11 PM
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No that wouldn’t be a dba, you probably should read a little about the principle but basically it’s two opposing walls with probably at least four subs front and four back, spaced at quarter distances from floor and ceiling and mirrored. Think a wall of bass so that it creates a pulse that goes front to back. The back array is set using dsp to fire out of phase at the right moment to absorb the wave coming from the front. My little experiment was one 24 front and one rear, so not really in the ballpark but it had measurable and audible advantages enough to convince me to eventually do it right.

In your room you could try two subs at a and b and two stacked at c and see how it sounds. If you look at the post I linked, the spectrogram shows a lot more bass energy with the dba test. And cleaner waterfall. The effect in room is like pulses of bass through your body and a lot less boominess.
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post #12 of 14 Old 05-26-2020, 03:47 PM
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A few issues and some personal experiences. First, if you have REW and a microphone then forget the sub crawl. It’s better than nothing, but I’ve found it just finds the location with the loudest peaks not the most complete bass. As to the when, you can get a general idea when the walls are up but I wouldn’t make final decisions until you can see how things interact with whatever’s going to be in the room. As to how, I’ll second BTH’s suggestion about putting the mic at your mlp and moving a sub around. My process was sketching my room and every conceivable sub location, doing a sweep at all those locations, then matching up peaks and nulls. Mine started like this:




My room is terrible but these two back corners complimented each other nicely:



How many subs you need will depend on what your room gives you but the more positions you have to work with the more likely you are to find one that fills whatever null some other location has. Best of luck!

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post #13 of 14 Old Yesterday, 08:49 AM - Thread Starter
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Thanks to all for the replies, and I apologize for my incorrect terminology, particularly the use of "sub crawl"

@head_unit ... my pub crawling days are long behind me, LOL!

@BassThatHz & @Vince_B ... thank you for the links on DBA, I think I get it now, opposing locations for the subs, correct? So because of the odd nook at the back of the room, would stacking two subs centered relative to room width as @Vince_B suggested be useful? Maybe toeing in the front subs to point at the centered rear subs?

@lawdogx ... That is obviously a lot of work you went to and I will follow the step you @Vince_B & @BassThatHz recommend.



Moving forward, since all four walls and the ceiling are in place, can I install some subs and take room response measurements now, or do I need to wait until sheet rock is up?
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post #14 of 14 Old Yesterday, 05:05 PM
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Even half of a DBA is going to have some benefits, it requires 4 subs stacked up front.

Often where the subs will sound-best is where they will look-ugliest, or you'd be walking on/around it. Rarely does subwoofer-placement measure nice and look nice at the same time.

People often place their subs next to their front speakers, and rarely does that turn out to be optimal, but it looks the cool!
You'd think having subwoofers placed far away from the fronts would be bad, and some times it is... but more often it isn't. Trust the measurement charts.

There is no such thing as the perfect room.
All rooms / placements have nulls, it's just a matter of where, at what frequencies, and how-bad.
Usually it's about minimization, not cure.
Peaks can be tamed with EQ, nulls can't.

That said: an anechoic chamber measures perfectly-flat, and sounds perfectly-horrible. Ears/Brains aren't measurement mics/charts.

HiFi comes at a price, and I don't mean money.
and once you hear better, there is no going backwards either.
The rabbit hole is deep and steep and slippery. Careful what you wish for.

Last edited by BassThatHz; Yesterday at 05:17 PM.
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