Multi-sub: adding DIY-SG flatpack 18"+15" sub to 4x15" IB line array - AVS Forum
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post #1 of 89 Old 12-21-2012, 12:10 PM - Thread Starter
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I'm joining the multi-sub approach, my IB sub does a great job but I can't get decent seat-seat flat respone in 1st row, the 2nd row is pretty decent seat-seat..
[edit] adding some good multi-sub related threads in post#1
Option 1:
Build a "helper" sub using Dayton Audio TIT400C-4 15" Titanic Mk III Subwoofer in 3.5 cu ft sealed box
(this has tight fit into the corner due to my screen and LH Main location......)
[edit]
Option 1 has evolved into 2nd and 3rd sub approach, using an 18" driver for 2nd sub and 12" driver for 3rd sub
Here is graphic of that:
HT%2520Plan%25202x4%2520Seats-Riser-acoustics%2520multi-sub.jpg

Option 2: (this thread discussion point)
Build a specific room designed Triangle sub w/ Dayton Audio RSS460HO-4 18" , amp, the sub triangle box will have 24" sides x 34" face x 32" tall; give or take 5.5 cu ft internal space after braces/etc.

Question:
If a triangle sub is possible and does not "break" the laws of boxed subs, then I'm doing option 2 and this thread can become a build thread, if not then I'll continue with option 1 and I'll get flat pack from Eric H (I posted in that thread a few days ago)

Basic triangle sub image is this:
CornerSubwoofer3.JPG

Located just as shown here ................. This will give symmetric balance to the IB 4 x 15" line array on the RH side:
CornerSubwoofer.JPG . HT%2520Scope%2520screen%2520wall.jpg
You can see my corner bass trap triangle support, this triangle corner sub would be located just under that.

My main goal is the first row has modal issues that can't be solved via all the corner bass traps I've installed, so I'd like to smooth them more by installing a just as (almost?) capable sub on the LH side as my IB sub on RH side.
(I can't do a stereo IB sub on LH side or I would have)
It will be sticking out into the room, while the IB baffle plate on the RH side is about 4" into the room, not purely symmetric.....
1st row seats 1-4, you can see/hear the seat-seat variations..............................2nd row seats 5-8, very consistent across the seats::
jul-01-2011%252020-200hz%2520bass%2520seats%25201-4.jpg . jul-01-2011%252020-200hz%2520bass%2520seats%25205-8.jpg

I'm looking forward to planning and "fixing" my 1st row seats modal issues.
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post #2 of 89 Old 12-21-2012, 12:11 PM - Thread Starter
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I was thinking that by symmetry, looking at seat 1 vs 4 and seat 2 vs 3, and combining their individual charts, the summed charts showed a flatter graph.....which dove me to consider 2nd sub in LH corner.
HT%2520Plan%25202x4%2520Seats-Riser-acoustics.JPG

Here is seats 1 & 4 plots from 1+ year ago, those seats are "nearly" symmetrical .. Here are seats 2 & 3 plots, those seats are "nearly" symmetrical
jul-01-2011%252020-200hz%2520bass%2520seats%25201and%25204.jpg . jul-01-2011%252020-200hz%2520bass%2520seats%25202%2520and%25203.jpg

The 2nd sub then should "fill in" the nulls from the 1st sub
So by visual overlay looks like it should work.
I'm sure not 100% symmetrical but quite close.
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post #3 of 89 Old 12-21-2012, 01:55 PM
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I vote for option 2 (triangle idea) I would test that placement out to see if it will in fact impact your 2nd row seating. If it were me I'd buy a decent commercial offering from a big box store, test the location, and return it before I built a sub that may not fix my modal issues. I would also try the store bought option nearfield to see what impact that has on your results. It's not impossible a small sub located near the 2nd row of seating could fix some variances (think Geddes sub theory).
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post #4 of 89 Old 12-22-2012, 07:17 AM - Thread Starter
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I got up early this morning with intention of deep dive into REW and 2nd helper sub locations:
-moved my existing 12" Atlantic Technology 350 PBM sub from family room to HT
IMG_3865.jpg
-moved the 24" iMac from craft room to the HT
-fired up REW v5 on my iMac, which I've used many-many times

Yep - this is why you don't upgrade OS on a older computer just for the sake of having the latest.... frown.gif
On some Mac's there was an issue with JAVA and Output, using Mandolane M3DMixer was a known work around that JohnM was aware of, but now there is a conflict with OSX 10.7.x it seems....just when I want to get down and dirty with REW!

There is a thread at the Shack I'm in trying to get it to work with OSX 10.7.5.
REW%2520issue.jpg
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post #5 of 89 Old 12-22-2012, 07:54 AM
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Can you have enough room to sneak the new HO 18 in the corner? Or maybe an SI 18? Just tacking on some more displacement to help it keep up with the IB.

 

Originally Posted by Bill Fitzmaurice:
It's also the very sort of Voodoo Engineering that should never be done.

 

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post #6 of 89 Old 12-22-2012, 08:13 AM - Thread Starter
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Quote:
Originally Posted by WiSounds View Post

Can you have enough room to sneak the new HO 18 in the corner? Or maybe an SI 18? Just tacking on some more displacement to help it keep up with the IB.

I can fit an 18" driver as shown in a triangle approach subwoofer, LH side as shown in 1st post.
The LH main speaker has to go outboard of my 130" screen, and that limits the width/depth of a box sub to just 18" wide max.
I'm all for keeping up with the IB, the IB actually has the ULF below 20hz covered pretty well in all seat positions as the graphs show.
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post #7 of 89 Old 12-22-2012, 08:34 AM
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There is no guarantee you will get good results with symmetrical position for the second sub. You are likely to have better chances with the second sub away from the front wall, perhaps along the left wall closer to the lseating area.
It does not need to be a powerful or very extended subwoofer. Multisub is useless below 30Hz or so anyway. But it would greatly help if the sub has variable LPF, phase/delay and volume controls .

Good read on the subject
http://mehlau.net/audio/multisub_geddes/
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post #8 of 89 Old 12-22-2012, 09:43 AM
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Can you borrow a sub to move around the room and measure a few different positions before settling on a final location?

 

Originally Posted by Bill Fitzmaurice:
It's also the very sort of Voodoo Engineering that should never be done.

 

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post #9 of 89 Old 12-22-2012, 11:45 AM
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Quote:
Originally Posted by WiSounds View Post

Can you borrow a sub to move around the room and measure a few different positions before settling on a final location?

That's what he was trying to do before REW failed to start
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post #10 of 89 Old 12-22-2012, 12:24 PM
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I need to read better. That's what I get for multitasking.

 

Originally Posted by Bill Fitzmaurice:
It's also the very sort of Voodoo Engineering that should never be done.

 

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post #11 of 89 Old 12-22-2012, 01:45 PM - Thread Starter
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I appreciate the help and time from everyone, we are all busy.
I've got REW working again, new cal file/etc.
I've also had to learn my new Denon 4520CI and mapping HDMI to front panel while audio is Ext in so no EQ applied.
Family time now, so looks like another 5am measurement session Sunday morning
As sanity, seat 2 and seat 6 are pretty close to long ago measurements.....
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post #12 of 89 Old 12-23-2012, 04:35 AM - Thread Starter
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Lets say getting up 4:30am to measure subs on a Sunday morning....

Started out with facing the 12" box sub along same triangle plane

Measured in all 8 seat positions box sub alone, IB sub alone, then both combined. Put good notes for each measurement.

Then, moved the box sub along LH wall 5ft, 6ft, 7ft from front wall and took measurements seat 6 and seat 1.

Later will post results .
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post #13 of 89 Old 12-23-2012, 05:01 AM
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Quote:
Originally Posted by mtbdudex View Post

Lets say getting up 4:30am to measure subs on a Sunday morning...Later will post results .
Woke up at 04:15 and am currently at work. Let's see those results!

OT. Those wood trimmed sound absorbers, did you use OC703 or cotton? I ask because I am days away from purchasing the cotton batts at Home Depot along with the wood trim and wanted to know what you thought of yours.

YID DIY
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post #14 of 89 Old 12-23-2012, 06:57 AM - Thread Starter
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Quote:
Originally Posted by Looneybomber View Post

Quote:
Originally Posted by mtbdudex View Post

Lets say getting up 4:30am to measure subs on a Sunday morning...Later will post results .
Woke up at 04:15 and am currently at work. Let's see those results!

OT. Those wood trimmed sound absorbers, did you use OC703 or cotton? I ask because I am days away from purchasing the cotton batts at Home Depot along with the wood trim and wanted to know what you thought of yours.

Those are oc703, rapped in speaker grille cloth, 2" thick with 2" air gap positioned at first reflection points , forget using cotton will not absorb freq correctly, more here http://www.avsforum.com/t/1312693/diy-construction-methods-of-hang-able-acoustic-panels-not-fixed-frames#post_19947600
_MG_4097.jpg

What do I think of acoustic treatments?
Best low cost upgrade by far, immediately noticeable. too many people chase speaker upgrades w/o addressing the room/speaker interactions.
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post #15 of 89 Old 12-23-2012, 09:42 AM
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Quote:
Originally Posted by Looneybomber View Post

Woke up at 04:15 and am currently at work. Let's see those results!
OT. Those wood trimmed sound absorbers, did you use OC703 or cotton? I ask because I am days away from purchasing the cotton batts at Home Depot along with the wood trim and wanted to know what you thought of yours.

I used a combination of both.

1" thick linacoustic 48" up sides, and cotton batting from 48" to ceiling. Only exception was back 1/3 of theater behind surrounds, and back wall, I didn't put cotton on upper walls to keep from reducing surround effect.

Don't forget the front wall either. That made a huge difference for me when I covered entire front wall with linacoustic and cut out triangles from OC703 for corner bass traps.

Achievement Unlocked

Psychotic Episode Averted

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post #16 of 89 Old 12-23-2012, 11:10 AM - Thread Starter
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Quote:
Originally Posted by bass addict View Post

Quote:
Originally Posted by Looneybomber View Post

Woke up at 04:15 and am currently at work. Let's see those results!
OT. Those wood trimmed sound absorbers, did you use OC703 or cotton? I ask because I am days away from purchasing the cotton batts at Home Depot along with the wood trim and wanted to know what you thought of yours.

I used a combination of both.

1" thick linacoustic 48" up sides, and cotton batting from 48" to ceiling. Only exception was back 1/3 of theater behind surrounds, and back wall, I didn't put cotton on upper walls to keep from reducing surround effect.

Don't forget the front wall either. That made a huge difference for me when I covered entire front wall with linacoustic and cut out triangles from OC703 for corner bass traps.
Ok - let's not get too OT in this thread.....
1" is not thick enough to absorb the lower bass above 300hz, that is applying EQ by not truly absorbing down to 300hz, and wrapping it all around the whole HT can be debated in the Master Acoustics thread.
There is no need to absorb that much sonic energy, just at specific first reflection points, live sounding rooms are a good thing!

Use the mirror method to help guide you placement of your panels.
The ETC will guide you the real need if in doubt, and confirm if they properly located and thick enough.
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post #17 of 89 Old 12-23-2012, 12:28 PM - Thread Starter
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Back to this thread....

Some charts to share:

I always start with 4" nearfield measurements, in this case the IB sub show how flat it is from the get go to ULF, the 12" box sub.....well it shows what looks like a HPF at 27hz?
I had both of these gain calibrated @ 75db seat #2 - about 11 ft away, the box sub it was put away from the corner to lessen the effect of corner on it.
I was kinda surprised how much "hotter" the box sub was at nearfield than the IB sub, which of course means the IB sub just carries itself so much better thru the room.
nearfield%2520box%2520and%2520ib%2520sub.jpg

Here is overlay of the IB sub seats 1-4 with overlay of the IB sub seats 5-8, both these are pretty close to what I measured 1 year ago so I feel my hardware set-up and cal file is correct
dec-23-2012%2520sub%2520seat%2520%25231-4%2520ib%2520only%2520analysis.jpg .. dec-23-2012%2520sub%2520seat%2520%25235-8%2520ib%2520only%2520analysis.jpg


Now, after I took all these measurements, and extracted charts, I realized that I did the 75db calibration yesterday, box sub via its front gain knob, while the IB sub the MV gain, and then it was home movie time for the family so I shutdown the set-up.
However, upon waking up this morning and firing up everything, I think I forgot to re-set the AVR to -27.5db, it goes to -40db at shut-down...duh on me tongue.gif
(the box sub of course gain is via the front knob)
I changed it during initial set-up back....or partly in....it was 5am.....
So I'll have to re-do a few to see if all my work this morning is good or needs re-doing.

anyway some observations:
I had the 12" box sub set-up like this; low pass 140hz, phase normal, pretty basic settings
12%2522%2520AT%2520sub.jpg

It was actually facing the corner, along the 34" triangle face, to simulate same driver plane as outward corner box would, hopefully this was ok?
12%2522%2520sub%2520corner.jpg

A "few" measurements later....and extracting charts....(for people who have not done this, this is the part that needs attention, putting good notes into each measurement group so later don't get confused)
I did each seat position like this, mic same position of course:
-12" box sub separately
-IB sub separately
-both subs running

Seat#1; you can never use the avg to join 2 subs measurements, , my early guess said should be able to but it never matched the combo sub measurement.
dec-23-2012%2520sub%2520seat%2520%25231%2520analysis.jpg

Seat#2 & Seat#3
dec-23-2012%2520sub%2520seat%2520%25232%2520analysis.jpg . dec-23-2012%2520sub%2520seat%2520%25233%2520analysis.jpg

Seat#4
dec-23-2012%2520sub%2520seat%2520%25234%2520analysis.jpg


From those 4 charts, hard to see;
-I find it hard to grasp why the box sub pulls down the IB sub consistently in it's roll-of below 27hz area......I'd love to have a real capable sub to test this out, one that goes at least 15hz before roll off.
-Next round of charts I'll not show the "avg plot", that confuses

Next post: seats 5-8
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post #18 of 89 Old 12-23-2012, 12:41 PM - Thread Starter
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...continuing with seats 5-8

seat 5
dec-23-2012%2520sub%2520seat%2520%25235%2520analysis.jpg

seat 6 & seat 7
dec-23-2012%2520sub%2520seat%2520%25236%2520analysis.jpg . dec-23-2012%2520sub%2520seat%2520%25237%2520analysis.jpg


seat 8
dec-23-2012%2520sub%2520seat%2520%25238%2520analysis.jpg


Extracting just the combined charts for each seat 5-8:
I went from a consistent seat-seat response like this:
dec-23-2012%2520sub%2520seat%2520%25235-8%2520ib%2520only%2520analysis.jpg

To this "mess":
dec-23-2012%2520sub%2520seat%2520%25235-8%2520combo%2520overlay.jpg


My conclusion:
The box sub is "messing up" with the 2nd row.

Next up:
I put the 12" box sub in various positions along the LH wall 5ft, 6ft and 7ft from front wall, and took measurements......kinda revealed some stuff.
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post #19 of 89 Old 12-23-2012, 12:59 PM
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Quote:
Originally Posted by mtbdudex View Post

Seat#1; you can never use the avg to join 2 subs measurements, , my early guess said should be able to but it never matched the combo sub measurement.
Averaging won't work because it doesn't consider phase, but REW has a math feature that does. On the All SPL tab you can do A+B.

Not to belittle your efforts, but you could be drawing completely all sorts of short sighted conclusions if you don't consider relative phase and the effect that applying a delay to one of the subs vs. the other can have in the resulting frequency response.
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post #20 of 89 Old 12-23-2012, 02:38 PM
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^^^
+1

I'd add that you should not rule out any position until you tried all phase/LPF/volume variations there. RTA feature in REW is very helpful for this task.
I normally roll sub(s) around the room on a dolly cart, tweaking controls and watching the effect at the LP real time in REW RTA window.
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post #21 of 89 Old 12-23-2012, 06:24 PM - Thread Starter
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Quote:
Originally Posted by Stereodude View Post

Quote:
Originally Posted by mtbdudex View Post

Seat#1; you can never use the avg to join 2 subs measurements, , my early guess said should be able to but it never matched the combo sub measurement.
Averaging won't work because it doesn't consider phase, but REW has a math feature that does. On the All SPL tab you can do A+B.

Not to belittle your efforts, but you could be drawing completely all sorts of short sighted conclusions if you don't consider relative phase and the effect that applying a delay to one of the subs vs. the other can have in the resulting frequency response.

Quote:
Originally Posted by zheka View Post

^^^
+1

I'd add that you should not rule out any position until you tried all phase/LPF/volume variations there. RTA feature in REW is very helpful for this task.
I normally roll sub(s) around the room on a dolly cart, tweaking controls and watching the effect at the LP real time in REW RTA window.

Guys, I'm a hobbyist so appreciate all help/insight.

Basic Q's:
1) Is this 12" box sub doing a decent job guiding me for 2nd sub placement, since it's got a HPF at 27hz or so?
2) I really would have liked the LH corner to give better results....that would be ideal, stereo subs behind the mains, hidden in the room, etc....what more can I do there to simulate better?

If there is a thread/info that shows me how to go about this please point me there and I'll read/learn/absorb and do it.

fwiw, I just went into REW and here is the A+B, which still does NOT come close to the real time combo measurement.
Gold = 12" box sub
Green = IB sub
Red = combo - both ran together
Purple = A+B
dec-23-2012%2520sub%2520seat%2520%25235%2520a%252Bb%2520vs%2520combo%2520overlay.jpg

I did measurements along LH wall at 5', 6', and 7' locations from front wall.
dec-23-2012%2520sub%2520seat%2520%25231%2520combo%2520corner%2520vs%25205%2527%25206%2527%25207%2527%2520analysis.jpg

Honestly, due to room layout I can put added subwoofer(s):
-on LH side corner thru 7' back, more then it would intrude too much into 1st row seat area
-anywhere along front wall
-Behind 2nd row seat either corner and anywhere along the back wall
Room layout:
HT%2520Plan%25202x4%2520Seats-Riser-acoustics.JPG

I need some "quick" way to get a go/no go for each spot as I put the sub in perhaps many locations considering 0.5 ft increments ...
Or a gut feel guide on some best chance for success places (1/3 location, LH rear corner as it's opposite the IB sub...etc)
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post #22 of 89 Old 12-23-2012, 07:42 PM
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Quote:
Originally Posted by mtbdudex View Post


I need some "quick" way to get a go/no go for each spot as I put the sub in perhaps many locations considering 0.5 ft increments ...
Or a gut feel guide on some best chance for success places (1/3 location, LH rear corner as it's opposite the IB sub...etc)

Here is what I would do.

Get REW running in RTA mode and set the mike at the MLP.

Set the sub in the position you want to evaluate and start adjusting controls while watching the RTA screen for effect it makes at the MLP . I found volume and LPF settings most useful. My second sub runs quieter than the main and goes only upto 60Hz or so. Continues variable phase/time delay maybe very useful, but all I could do with my sub is switch between 0 and 180.

Find settings that produce the smoothest FR at the MLP then measure other seats.

Move to the next spot and repeat the steps.

At the end you should hopefully have one position that is markedly better than the others and the IB solo. You may tweak controls further in favor of better seat to seat FR which would probably mean losing some at the MLP. I am personally too selfish to do this.

If you have not worked with RTA before, here is something that may not be clear from the manual:
1. Use RTA mode, not "spectrum"
2. Proper signal to use is called "pink PN"

Good luck!

If you have not already, read that article on Geddes multisub I linked before
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post #23 of 89 Old 12-23-2012, 08:29 PM
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I like the corner build, but it might do a lot of "dancing" around if it is not bolted to the wall or restrained in some manner. A friend of mine tried this aproach and it was not useful until he fastened them to the floor and wall to eliminate the rocking of the enclosures. Just a thought.

Keep cranking,

Robert
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post #24 of 89 Old 12-23-2012, 10:38 PM
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Quote:
Originally Posted by mtbdudex View Post

fwiw, I just went into REW and here is the A+B, which still does NOT come close to the real time combo measurement.
I've found A+B predictions to give very accurate results to the actual measurement. So close the prediction and actual sit on top of each other and you basically can't tell there are two traces.

Does your receiver / pre-pro have 2 subwoofer outputs? Or how do you have these connected? Are you using a sub EQ with multiple outputs and delay capability (MiniDSP, QSC DSP-30, DCX2496)?

My first suggestion is to find a place where the sub has an opposing response to your IB. IE: peaks and valleys in the opposite places. That way when you blend them you'll get a flatter net response before equalization.
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post #25 of 89 Old 12-24-2012, 05:24 AM
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I'd imagine the fact that the subs are not identical and one of them is a four driver IB may complicate the A+B calculations.

I have to try the feature one day. I am surprised it can give accurate predictions for in-room source summing at all given how much the response is affected by the room itself.
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post #26 of 89 Old 12-24-2012, 06:57 AM - Thread Starter
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Due to Christmas preparations and travel, this multi-sub analysis will take a break and resume Thursday Dec-27th @ full speed.
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Originally Posted by zheka View Post

There is no guarantee you will get good results with symmetrical position for the second sub. You are likely to have better chances with the second sub away from the front wall, perhaps along the left wall closer to the lseating area.
It does not need to be a powerful or very extended subwoofer. Multisub is useless below 30Hz or so anyway. But it would greatly help if the sub has variable LPF, phase/delay and volume controls .

Good read on the subject
http://mehlau.net/audio/multisub_geddes/

zheka - I have to apologize, the article you posted earlier is spot on what I needed for multi-sub analysis! I have read it, and will re-read it and apply it.
I've read the multi-sub concept approach of course before, but never saw a good tutorial how to implement, that should be added to sticky here for others..
Thx for the Christmas gift smile.gif
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Quote:
Originally Posted by mtbdudex View Post


I need some "quick" way to get a go/no go for each spot as I put the sub in perhaps many locations considering 0.5 ft increments ...
Or a gut feel guide on some best chance for success places (1/3 location, LH rear corner as it's opposite the IB sub...etc)

Here is what I would do.

Get REW running in RTA mode and set the mike at the MLP.

Set the sub in the position you want to evaluate and start adjusting controls while watching the RTA screen for effect it makes at the MLP . I found volume and LPF settings most useful. My second sub runs quieter than the main and goes only upto 60Hz or so. Continues variable phase/time delay maybe very useful, but all I could do with my sub is switch between 0 and 180.

Find settings that produce the smoothest FR at the MLP then measure other seats.

Move to the next spot and repeat the steps.

At the end you should hopefully have one position that is markedly better than the others and the IB solo. You may tweak controls further in favor of better seat to seat FR which would probably mean losing some at the MLP. I am personally too selfish to do this.

If you have not worked with RTA before, here is something that may not be clear from the manual:
1. Use RTA mode, not "spectrum"
2. Proper signal to use is called "pink PN"

Good luck!

If you have not already, read that article on Geddes multisub I linked before

Good advice, I'll have this post on my 130" screen as I'm doing this Thur Dec-27.
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Originally Posted by robertcharles View Post

I like the corner build, but it might do a lot of "dancing" around if it is not bolted to the wall or restrained in some manner. A friend of mine tried this aproach and it was not useful until he fastened them to the floor and wall to eliminate the rocking of the enclosures. Just a thought.

Keep cranking,
Robert
I also desire the 2nd front LH corner for the hidden approach......possible if I go down that road then I'd be forced into the 4 corner sub approach for flat freq response, instead of the 3 sub approach as laid out in the article zheka linked?
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Quote:
Originally Posted by mtbdudex View Post

fwiw, I just went into REW and here is the A+B, which still does NOT come close to the real time combo measurement.
I've found A+B predictions to give very accurate results to the actual measurement. So close the prediction and actual sit on top of each other and you basically can't tell there are two traces.

Does your receiver / pre-pro have 2 subwoofer outputs? I have the new Denon 4520CI with true independent subwoofer pre-outs
Or how do you have these connected? For daily use the IB sub goes thru a FBQ2496 Feedback Destroyer in bypass mode (long story), then into the AVR, then into the EP2500.
For these REW measurements I bypass the AVR EQ by going thru the Ext In sub input, the 12" box sub is also bypassed via direct cable to it's plate amp, both come from the Mobile Pre directly split by Y cable.

Are you using a sub EQ with multiple outputs and delay capability (MiniDSP, QSC DSP-30, DCX2496)? For these measurements, no. I have a FBQ2496 Feedback Destroyer but not using it.

My first suggestion is to find a place where the sub has an opposing response to your IB. IE: peaks and valleys in the opposite places. That way when you blend them you'll get a flatter net response before equalization.

Stereodude - Response to your Q's above in RED bold, I have the new Denon 4520CI with true independent subwoofer pre-outs.
I also have for EQ the FBQ2496 Feedback Destroyer, prior with my 4308CI I ran some filters on that, but then I just let Audyssey handle the bass eek.gif and as "ok"
Your suggestion - find peaks/valleys in opposite location....YES, but the $ question is where is that?
My room really is non-symmetric from LF/ULF viewpoint:
LH/back walls true outside are concrete foundations walls, RH/Back walls are 2 x 6 sill plate with double offset stud construction, plus there is no "door", I have a 6' opening back RH side as semi-multi purpose room for game night.
I'm thinking the LH rear corner may be a good place to "try" as opposite...but I also thought the LH front corner would excite modes the RH side did not....
IMG_1981.jpg .. IB%2520Cut%2520ConcretePlan.jpg
Quote:
Originally Posted by zheka View Post

I'd imagine the fact that the subs are not identical and one of them is a four driver IB may complicate the A+B calculations.

I have to try the feature one day. I am surprised it can give accurate predictions for in-room source summing at all given how much the response is affected by the room itself.
Possible the harmonics of the fundamental of each sub in room response may cause the A + B REW summation not to work?
From basic wave theory it should work......

As clean-up to this thread, I'll re-size some of the charts I posted prior as they kinda clutter the thread....
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post #27 of 89 Old 12-24-2012, 07:16 AM
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Quote:
Originally Posted by mtbdudex View Post

Possible the harmonics of the fundamental of each sub in room response may cause the A + B REW summation not to work?
From basic wave theory it should work......
It seems to work fine in my experience. I just ran a few measurements this morning just to show you guys I'm not crazy or talking out my rear.

Here are my two subs individual responses:




Here's the predicted combined response & the actual:




They are all sealed subs, but with some familial connection on the drivers, but they're not identical. Further, it worked just as well when I was combining a DIY passive radiator sub with the UFW BBK subs.
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Quote:
Originally Posted by Stereodude View Post

It seems to work fine in my experience. I just ran a few measurements this morning just to show you guys I'm not crazy or talking out my rear.
Here are my two subs individual responses:

Here's the predicted combined response & the actual:

that's pretty cool. i should definitely give it a try
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post #29 of 89 Old 12-24-2012, 07:26 AM - Thread Starter
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Stereodude - good to know A + B does work, come Thursday I'll re-do my individual measurements to see if some anomaly in my set-up caused it not to work.
btw, I just checked the "Use Thick Trace" so the charts are more readable at smaller image size, seeing that in yours reminded me.
[edit]
I've added "Multi-sub help" to this thread title as I go thru the process....
I see that multi-sub article is by "Markus Mehlau", is he same as Markus767 here??

Some other multi-sub threads I had subscribed to, I know there are a few more:
http://www.avsforum.com/t/1388156/a-new-approach-to-multiple-subwoofers
http://www.avsforum.com/t/1386208/more-than-4-subs-is-completly-pointless
http://www.avsforum.com/t/1380013/my-multi-location-subwoofer-thread-inspired-by-welti-devantier-geddes
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post #30 of 89 Old 12-24-2012, 08:51 AM
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Quote:
Originally Posted by mtbdudex View Post

I have the new Denon 4520CI with true independent subwoofer pre-outs.
So you can set different distances for each subwoofer?
Quote:
Your suggestion - find peaks/valleys in opposite location....YES, but the $ question is where is that?
Well, IMHO, it's not likely to be in the adjacent front corner. When I was setting my system up I had a finite area where I could place the "fill" subs so I moved them around within that envelope, got things the best I could, and fixed the rest with EQ and delay.
Quote:
My room really is non-symmetric from LF/ULF viewpoint:
My great room ends up being very non-symmetric also. It's sort of a rectangular room by the footprint. However, the long interior wall on the side is missing opening the great room to the whole house. When I wanted to integrate my DIY subs with my previous UFW BBK subs I started with them in the back corner pointed forward for complementary fill. That didn't give me very good results. I tried messing with the direction they were pointed but that only made it worse. I started sliding them along the wall pulling them toward the front of the room and found things got better. I pushed them as far forward as I could until I started to encroach on the side surround (tower speaker). By comparing the raw frequency and phase responses I manipulated the net response as flat as possible with a delay on the UFW BBK subs. Finally, I EQ'd all the subs together.

Here's roughly what I ended up with:




One step I omitted above was determining an appropriate output level. It's just an important as placement since if you change the output level of the two subs relative to each other the overall frequency response changes. You don't want one sub to run out of steam before the others or go into distortion while the other(s) are still playing nice and clean. Since the two UFW BBK subs each have a 15" driver and a 1000W amp and each of the two DIY AV15-H sonosubs has 2 15" drivers and each enclosure gets 1200W I decided to set the combined two UFW BBK subs equal to one of the sonotubes. This way each set of 2 15" drivers was being called on for roughly the same SPL. Before any EQ'ing or messing with phase I used pink noise and found the two sonotubes were almost 6db apart in output (due to location) even though they were getting the same signal and power. So, I set the combined two UFW BBKs subs equal to the average of the two sonotubes and went from there. I should also point out that the two AV15-H sonotubes are treated as a single sub electronically. I plan to reevaluate that over the holidays and see if any improvement can be gained (specifically a reduction in the amount of EQ needed to flatten things out) by treating it as a 3 sub system instead of a 2 sub system.
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