Home Theater Forum and Systems banner

1 - 8 of 8 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter #1
Hi,

Can someone link me to the most relevant article about how to use REW to position a sub?

I found a number of articles like http://www.hometheatershack.com/forums/rew-forum/28894-case-study-sub-alignment-using-rew-v5-3.html but they seemed to require an Audyssey and other special hardware and seemed experimental.

I am using a pair of Focal Solo's with a JBL LSR 2300 sub set at 80hz x-over. I also have 16 2'x4' 2"703 + 2" rockwool absorbers that I have to figure out where to place. I initially bought the whole RPlusD package but I found it two finicky, so far REW has been much easier but Im stuck at the sub.

Last night I did the whole gamut of measurements for the nearfields, using REW for the first time. Todays task is the sub and traps but most of the articles I'm finding seem speculative. Is there not an agreed on straightforward approach for positioning the sub (especially for beginners)?

Any help would be greatly appreciated.
 

·
Banned
Joined
·
516 Posts
A few comments...

Take care of the subs before doing anything with the satellites.

As far as the sub, you can try in in a number of places, from the corner where it will couple and you will get an additional bass boost, to the center of the wall to placement at a 1/3 position on the wall.

In any case you WILL have bass modes determined by the dimensions of the room.

And while you can try each of the locations and then map the region including and around the listening position (create a grid) using sweeps and also playing REW tones to note position of peaks and nulls over the listening 'region', an easier way that effectively does the same thing is to SECURELY position the sub at the listening position on a small table, and to then crawl with your head at about the same level as would be the sub about the room, visiting possible sub positions and discover which has the best response between modal peaks and nulls. Place the sub there.

Otherwise, you can variously place the sub at each possible location and run sweeps at the listening position and at points forward and behind the listening position in order to note the presence of nulls and peaks. You can then select the position providing the best most even response and adjust the listening position forward or backward (maintaining left-right symmetry) to a position that is best located 'between' peaks and nulls.

The methods are functionally equivalent, but the crawl benefits from your only having to do the process once and not having to repeat the process for every possible point.

Its not fancy and you don't want anyone whose opinion you value to see you doing this, but it works just fine.

I would then make a full range frequency response and generate the waterfall from the unsmoothed FR This will allow you to observe any remaining anomalies that you May be able to mitigate further by fine tuning the position of the sub. But do not be surprised if artifacts remain, as sub position will not eliminate modal behavior.

After you have established the sub position, you can then apply the bass traps (which I would seriously suggest modifying into superchunk style corner traps filled with fluffed 'cheap pink fluffy stuff' and faced with at least 6mil plastic membrane mounted behind the fabric face frame. Use plastic orchard bird netting to create several vertical compartments to keep the fluffy stuff from compressing under its own weight and cover the front with netting to contain the fill and cover with a 6 mill plastic and fabric covered face frame.

Repeat said measurements and observe what remains. At this point you may wish to use a small amount (3-6dB) of EQ to reduce modal peaks (you cannot EQ modal nulls).

After you are satisfied with these adjustments you will then want to establish an optimal placement for the satellites and then make ETC measurements for each speaker driven individually.

It will be from the ETCs that you will then identify the Actual high gain early and late reflections and corresponding energy paths and points of boundary incidence. Then, depending upon the acoustical response desired, THIS will determine the places to surgically use absorption. Additionally, you may want to double the panels and use a 4 in thick panel spaced 4 inches from the boundary to maximally address the broadband specular issues over their full spectral bandpass down to ~200-250 Hz.
 

·
Registered
Joined
·
2 Posts
Discussion Starter #3 (Edited)
This is extremely helpful, thank you . I had a few points that I was unclear on, below

A few comments...

Take care of the subs before doing anything with the satellites.

As far as the sub, you can try in in a number of places, from the corner where it will couple and you will get an additional bass boost, to the center of the wall to placement at a 1/3 position on the wall.

In any case you WILL have bass modes determined by the dimensions of the room.

And while you can try each of the locations and then map the region including and around the listening position (create a grid) using sweeps and also playing REW tones to note position of peaks and nulls over the listening 'region', an easier way that effectively does the same thing is to SECURELY position the sub at the listening position on a small table, and to then crawl with your head at about the same level as would be the sub about the room, visiting possible sub positions and discover which has the best response between modal peaks and nulls. Place the sub there.

Otherwise, you can variously place the sub at each possible location and run sweeps at the listening position and at points forward and behind the listening position in order to note the presence of nulls and peaks. You can then select the position providing the best most even response and adjust the listening position forward or backward (maintaining left-right symmetry) to a position that is best located 'between' peaks and nulls.

The methods are functionally equivalent, but the crawl benefits from your only having to do the process once and not having to repeat the process for every possible point.

Its not fancy and you don't want anyone whose opinion you value to see you doing this, but it works just fine.

I compose cartoon music... if only the rest of it involved crawling around on the floor.

Do I use pink noise? sweeps? REW Generator?

I would then make a full range frequency response and generate the waterfall from the unsmoothed FR This will allow you to observe any remaining anomalies that you May be able to mitigate further by fine tuning the position of the sub. But do not be surprised if artifacts remain, as sub position will not eliminate modal behavior.

After you have established the sub position, you can then apply the bass traps (which I would seriously suggest modifying into superchunk style corner traps filled with fluffed 'cheap pink fluffy stuff' and faced with at least 6mil plastic membrane mounted behind the fabric face frame. Use plastic orchard bird netting to create several vertical compartments to keep the fluffy stuff from compressing under its own weight and cover the front with netting to contain the fill and cover with a 6 mill plastic and fabric covered face frame.
Here is a link to a panorama of the space:

pan0_dot_net_slash_w_slash_up-2879 <-- sorry for that url, its a mess but the forum wont let me post urls yet.

There may be a panorama of a tavern, just click the skip button and it will take you to the right one.

Currently, not shown in the picture, my workstation is facing the french doors in the middle of the room, between the kitchen and the far empty wall.

I would be interested in building super chunks but given the space do you think its worth it? I'd be a little sketchy about having fiber glass in the corner that the bed is in, though the plastic may help. Its a big space but its a little uneven.

I was more or less planing on facing the french doors because I could use the kitchen and far wall to bounce the early reflections. If it's necessary to place the sub first how does the nearfields position change in relation to it. What am I looking for to combine the two?

Repeat said measurements and observe what remains. At this point you may wish to use a small amount (3-6dB) of EQ to reduce modal peaks (you cannot EQ modal nulls).

After you are satisfied with these adjustments you will then want to establish an optimal placement for the satellites and then make ETC measurements for each speaker driven individually.

It will be from the ETCs that you will then identify the Actual high gain early and late reflections and corresponding energy paths and points of boundary incidence. Then, depending upon the acoustical response desired, THIS will determine the places to surgically use absorption. Additionally, you may want to double the panels and use a 4 in thick panel spaced 4 inches from the boundary to maximally address the broadband specular issues over their full spectral bandpass down to ~200-250 Hz.
The 16 panels are all currently 4" (2 of 703 + 2 of rockwool). I can't hang much because I can't drill into the ceiling so I'm very into repurposing them. I did build 8' x 2' pvc frames to hold the bass traps stacked two tall in the corners. I will probably adapt them to handle the super chunks if you think that will work in my space.

For the ETC's, in using REW this process is nothing more than hitting the measure button and looking at the SPL and Waterfalls right?
 

·
Banned
Joined
·
516 Posts
This is extremely helpful, thank you . I had a few points that I was unclear on, below




I compose cartoon music... if only the rest of it involved crawling around on the floor.

Do I use pink noise? sweeps? REW Generator?

Perusing the waterfall, you should easily get a good estimation of the frequencies where resonances exist and where nulls exist.
You can use the tone generator in REW to generate the tones, Step through them starting from ~10 or so Hz below each and continue it to about 10 Hz above the displayed resonances. When you locate a resonance or null it will be obvious.
By mapping the listening area in front and back of the existing listening location, you can fine tune the listening position forward or backward to a position in between peaks and nulls why maintaining L/R symmetry.


Here is a link to a panorama of the space:

pan0_dot_net_slash_w_slash_up-2879 <-- sorry for that url, its a mess but the forum wont let me post urls yet.

There may be a panorama of a tavern, just click the skip button and it will take you to the right one.

Currently, not shown in the picture, my workstation is facing the french doors in the middle of the room, between the kitchen and the far empty wall.

I was unable to see the picture - I saw the example and I was taken to the heme page, but I saw nothing reminiscent of this post....:((

I would be interested in building super chunks but given the space do you think its worth it? I'd be a little sketchy about having fiber glass in the corner that the bed is in, though the plastic may help. Its a big space but its a little uneven.

You can enclose the Fiberglass in 6mil plastic. Also, if you use Knauf Ecose product, the binder has minimal VOCs to off-gas and uses no formaldehyde - issues that are quite frankly more significant than the actual Fiberglass. Also, be prudent and lay the unwrapped product out in the sun for a couple of days, Give it ample time to stabilize and to off-gas any latent manufacturing residue. Fiberglass particles will not be moving to any significant degree in the trap. Their suddenly deciding to become mobile is not a significant function of the music. We only wish we could stimulate the material in such a manner, as that would make the traps much more effective!

Also, it is rather simple to make a superchuck using 2 triangular base and top plates with 3 trim sticks - 1 in the back corner and two in the from corners. Adjusting the base and top or any moldings, plastic orchard bird netting can be used to contain the fill, along with at least a front facing 6mil plastic film and then a face frame can then be attached to the front trim sticks after the space is filled with 'pink fluffy stuff' - the optimal fill for LFs. I have skipped quite a few steps, but if you need more details, PM me and provide a YM or Skype username and I can describe it in more detail...

I was more or less planing on facing the french doors because I could use the kitchen and far wall to bounce the early reflections. If it's necessary to place the sub first how does the nearfields position change in relation to it. What am I looking for to combine the two?

Actually, if you can, have these doors open at the rear of the room, and leave them open. If this is possible you will want to take waterfall measurements with these open as well. You will create a coupled space, making the modal distribution more complex and a function of both combined spaces, but it will also act as a trap and effectively remove some of the LF energy from the primary space.



The 16 panels are all currently 4" (2 of 703 + 2 of rockwool). I can't hang much because I can't drill into the ceiling so I'm very into repurposing them. I did build 8' x 2' pvc frames to hold the bass traps stacked two tall in the corners. I will probably adapt them to handle the super chunks if you think that will work in my space.

Ideally you would have the panels comprised of only one material - Fiberglass with Fiberglass and Rockwool with Rockwool. But don't worry to much.

For the ETC's, in using REW this process is nothing more than hitting the measure button and looking at the SPL and Waterfalls right?
With REW properly configured and calibrated and with the hardware loopback configured and only the "Use loopback as reference" in Preferences-> Preferences->Analysis. You will run a full range sweep for each speaker individually generating an unsmoothed frequency response - with the mic remaining in precisely the same position for all 'listening position' measurements. Select "Impulse Response" in the menu and "ETC" in the field below the IR.
 

·
Registered
Joined
·
13 Posts
All rooms are different and playing with sub placement can be challenging. It's kind of a combination of both sub placement and seat location. I've used 2 subs which does help with smoothing the bass throughout the room. Corner placement definitely gives you more room boost and better loading. Parametric bass EQ or using an auto EQ system can help tame/smooth some of those room peaks/dips even more.
 

·
Premium Member
Joined
·
257 Posts
In my room I've always found corner placement over powering, it always ends up sounding farther less controlled, more boomy. I will be trying front and rear sub placement soon. I am hoping this will solve my 50hz dip issue?
 
1 - 8 of 8 Posts
Top