The No.1 Website for Pro Audio
 Search This Thread  Search This Forum  Search Reviews  Search Gear Database  Search Gear for sale  Search Gearslutz Go Advanced
50Hz ring, 60Hz hole, best material to treat? Studio Monitors
Old 9th January 2012
  #91
Gear Guru
 
Glenn Kuras's Avatar
I am glad to see more people using the soffit design in there places. It really does work at those lower frequencies as you show/prove!!
Old 10th January 2012
  #92
Lives for gear
 
amishsixstringe's Avatar
 

Lights, don't forget that you have 2 speakers. Just because your right speaker is closer to the right wall doesn't mean that the right speaker can't shoot at the left wall and back to the listening position, which is a longer distance. I will try to post a few screen shots for you and others to look at this evening.

Neil
Old 10th January 2012
  #93
Lives for gear
 
Lights's Avatar
 

Thread Starter
I've been running the measuing tape all over the place to try to find any reflections that meet those milisecond figures... but also the dimensions of the room are in a pic on the first page of the thread :D

I'll keep looking and I'm excited to see your pics as well.
Old 11th January 2012
  #94
Gear Guru
 
DanDan's Avatar
ETC

If you suspect a particular source corresponding to a particular 'millisecond' spike on the ETC, move the mic towards or away on an axis pointing directly at that source. If the spike shifts you have the culprit.

DD
Old 11th January 2012
  #95
Lives for gear
 
amishsixstringe's Avatar
 

Here is just a before and after of the impulse response for the RIGHT speaker only. Let's just slow down and focus on one thing at a time.

BEFORE:


AFTER:


The reflection at almost exactly 1ms actually gets worse in the after plot by as much as 3dB.

Did you happen to move the microphone, desk, speaker, etc between measurements? That is my suspicion. Either way, that reflection is the worst offender. There is a similar corresponding reflection present in the left speaker. I assume desk in this situation.

When messing around with your tape measure, be sure to measure from the tweeter of your speaker, not the woofer.

Dan's advice to move the mic closer to the desk is a good one. I remember hearing that trick in a thread here awhile ago. Check out this thread that is currently going on: Measurements of Desk Reflections

If you decide that your desk is causing the spike, you have to do whatever you can to either get rid of or reduce it. It's only about -13dB, which is about 7dB more than what's normally acceptable. Speaker stands help with desk reflections. Maybe just toss a small chuck of fiberglass (compressed) or even some of that foam on the desk in front of the speaker and see if it goes away. Leaving stuff on your desk is usually unpractical. You may have to come up with a way by moving the speaker/desk around.

Good luck,

Neil
Old 11th January 2012
  #96
Lives for gear
 

Quote:
Originally Posted by Lights View Post
I've been running the measuing tape all over the place to try to find any reflections that meet those milisecond figures... but also the dimensions of the room are in a pic on the first page of the thread :D

I'll keep looking and I'm excited to see your pics as well.
see below for SAC's string test, which will easily assist in identifying ACTUAL reflection paths as measured via the ETC.

https://www.gearslutz.com/board/6133764-post8.html
and
https://www.gearslutz.com/board/6397239-post80.html
Old 11th January 2012
  #97
Lives for gear
 
Lights's Avatar
 

Thread Starter
Thanks guys. At 1ms, I can redo the math and see if the desk makes sense. I was calculating 2ms which didn't equate to anything. Also I can put some foam on the desk and re-run the test. Once I figure that out, I could potentially move the speakers to reduce the reflection. It is VERY likely the speakers moved in the last 6 months since the July measurement
Old 11th January 2012
  #98
Lives for gear
 
Lights's Avatar
 

Thread Starter
First off thanks so much Neil for both taking the time to analyze my REW file and post pictures that I could easily understand and duplicate at home. The difference between 1ms and 2ms made all the difference. The 1ms reflection perfectly lined up with my desk and by taking one of my spare 2" auralex foam panels and placing it on the desk between the speaker and the mic, the reflection was 100% completely GONE.

I wanted to see if I could minimize the desk reflection without going to the extreme of laying foam on my desk when I want to make critical mixing decisions, and was able to bring the level of that 1ms reflection down to -21dB for the left and -23dB on the right. Is that considered the acceptable range?
Old 11th January 2012
  #99
Lives for gear
 
Lights's Avatar
 

Thread Starter
Impulse Pictures

Here are the measurements I did today.

First is the original speaker position, all the way back against the wall with no changes from the last waterfall.
50Hz ring, 60Hz hole, best material to treat?-right-old-impulse.jpg

Second is the original speaker location with a simple 2" thick piece of foam placed on the desk. Note that the foam is of the type pictured on my back wall, which varies between 2" thick and almost 0" thick in triangular wedges which might explain the two little bumps to the left and right of 1ms that sit at about -27 and 28 dB. I also did an experiment with a LENRD bass trap on the desk which further attenuated any early reflections below 30dB, but that's not pictured here as the 2" foam proves that it's the desk.
50Hz ring, 60Hz hole, best material to treat?-right-old-foam-impulse.jpg

Then I repositioned the speaker further forward on the desk by about 2". This has no foam... just the bare desk with the keyboard, mouse, and Steinberg CMC controllers on it, positioned as I'd normally use them. Note that the later reflections are now just as strong as the desk reflection.
50Hz ring, 60Hz hole, best material to treat?-right-impulse.jpg

Given that seemed like a success, I moved the left speaker to match. For some reason even though the situation should be exactly symmetrical, the reflection is a tad stronger but still more than 20dB less than the original sound.
50Hz ring, 60Hz hole, best material to treat?-left-impulse.jpg

Now if the experts tell me that this -21dB reflection will make it hard to mix clearly, we know that 2" of foam placed on the desk surface during the critical final mixing and "self-mastering" can solve the problem.
Old 11th January 2012
  #100
Lives for gear
 
Lights's Avatar
 

Thread Starter
Uh oh...

But repositioning the speaker on the left created a new bass null...

Here is the NEW left:


Compare that to the left I captured just a few days ago:

Attached Thumbnails
50Hz ring, 60Hz hole, best material to treat?-new-bass-null.jpg  
Old 11th January 2012
  #101
Lives for gear
 

Quote:
Originally Posted by amishsixstringe View Post
Here is just a before and after of the impulse response for the RIGHT speaker only. Let's just slow down and focus on one thing at a time.
ETC - set peak T=0 should be DESELECTED.

Quote:
Originally Posted by amishsixstringe View Post
When messing around with your tape measure, be sure to measure from the tweeter of your speaker, not the woofer.
measure from the acoustic center of the speaker, not the tweeter - there is little energy emitting from the tweeter.
Old 11th January 2012
  #102
Lives for gear
 
Lights's Avatar
 

Thread Starter
Localhost--nevertheless we did identify the desk S the source of the reflection and (I believe) we mitigated it to an acceptable level-at the cost of making a null on the left worse than it was before. I'm looking for confirmation that I did that right since I'm a 'learner'
Old 11th January 2012
  #103
Lives for gear
 
Lights's Avatar
 

Thread Starter
So obviously with a 41Hz hole, I am going to need a serious bass trap. The strange thing is that the hole only appears when sound eminates from the left speaker. A 41Hz wavelength is approximately 26ft long, and I need to figure out where to treat. I walked around the room and didn't find any crazy bass concentrations (aside from right behind the speaker).

In their old position, the speakers were directly against the back wall pretty much. Is moving them forward to avoid the ER on the desk a big mistake? Am I getting into some sort of boundary effect?

Of course there was already a pretty serious null there... but it went to zero after the move.

The picture with dimensions of the room is on the first page and if anybody has any idea where I should be looking to place a trap, LMK!
Old 12th January 2012
  #104
Lives for gear
 
amishsixstringe's Avatar
 

Lights, you are welcome. This is learning for me too. I am by no means an expert. I encourage you to listen to others, and don't just take what I say as gospel.

With that said--where I would go next is just take note of what you have done. Just determining that your desk is reflecting as well as the 41Hz null that increases when you move your left speaker off the wall is HUGE. You are still gathering data. Keep doing that.

Reflections are easier (still not EASY) to deal with than a 41Hz mode, so at this point I would just note the data you have collected. Complete the rest of the traps in your room. Realize that when you put the second wave of traps in there that you may end up moving them around a bit to make them work best. More Data.

Best case scenario is that you can take care of that 41Hz problem with trapping, and your early reflection with moving the speaker (or similar). You are always going to have to find a middle ground--a happy medium, if you will.

With the data you have collected, you now know that in the worst case scenario, you'll have to put a couple foam pads on your desk when you mix/master/critical listening. I think we may be able to improve on that. I would say that the 41Hz problem is more important than the desk reflection, so I would start with that speaker back to its original spot.

Can you hear the difference with the foam pads on the desk? My guess is that it's very subtle-if at all, but it's the sum of many small victories that will ultimately produce great results.


Quote:
Originally Posted by localhost127 View Post
ETC - set peak T=0 should be DESELECTED.



measure from the acoustic center of the speaker, not the tweeter - there is little energy emitting from the tweeter.
Local, thanks for that comment. I unchecked t=0, but the result ended up exactly the same for time and amplitude after subtracting the peaks. I have heard this before from SAC, but never understood why this should be set this way. Can you please explain it for me and others?

As for measuring from the center of the speaker and not the tweeter, I agree. I never thought of it that way before, but I will at least take it into consideration when doing SAC style 'string theory' measures in the future.

Thanks for your input in this thread.

Neil
Old 13th January 2012
  #105
Gear Guru
 
DanDan's Avatar
PM

Lights asked me to check back in here. I just did a quick scan so please ignore if I am repeating or out of context.

I am also interested as to the reasoning behind the Desect t=0.

A desk reflection can be redirected if absorption is impractical.

Desktop Reflection Revealed

The 41 Hz hole looks nasty. Try moving that speaker towards/away from the front wall, then the side wall.
See if the frequency changes. If it does, then you have identified SBIR and the culprit wall.

DD
Old 13th January 2012
  #106
Lives for gear
 
Lights's Avatar
 

Thread Starter
Thanks DanDan. Here's what I know at this point:

1. The wall to the left of the left speaker contains 2 feet of owens corning ecotouch fiberglass

2. When the speaker was all the way against the back wall, the graph looked like this:

So there was a notch at 41Hz but it wasn't completely nulled.

3. Moving the speaker forward a bit (I can't recall how much but it was about 3-5 inches) resulted in the big null you saw:


4. The SUPER-weird thing is that I did NOT have a null before I treated the room. Here is the original un-treated left speaker:

Maybe I should remove the big giant box of fiberglass and see what happens??

5. I tried an experiment of moving one of my 4" bass traps (Knauf 3PCF ecotouch) between the speaker and the back wall and it didn't seem to change the measuremengt on my cheap SPL meter. There wasn't really space to give it any air gap for the trap, BTW.

6. The identical change in distance from the back wall and the identical distance from the side wall on the RIGHT speaker produce a near-perfect waterfall, even better than the one posted on page 3 of this thread.

I'm not at home now so I can't run more tests, but given those 6 pieces of information, can we draw any conclusions? What would your suggested next steps be?

For the reflection, I did have the desk built with adjustable height feet. I will experiment with the height difference before that really cool slide-out keyboard drawer won't stay in
Old 14th January 2012
  #107
Lives for gear
 
amishsixstringe's Avatar
 

Lights,

How would adjusting the height of your desk change the reflection without speaker stands? It may do something to SBIR, but doubtful to ETC.

The 41Hz gouge appearing doesn't surprise me. I've seen that happen a many times. There are theories as to why this happens, but it's not really that important right now. Just know that it does happen when you start clearing out some of the muck.

Dan gave you good advice on trying to find what boundaries are causing the dip. Moving the speaker left and right, up and down, back and forth a couple inches at a time and measuring--taking accurate notes of each will help you to find which room dimension(s) is(are) causing the cancellation. This is your next step. It will tell you what your options are. (Moving the speaker locations, placing more traps (where to place them), etc...)

I think the redirection of the desk reflection would be difficult with the current desk you have. That's why many work surfaces are angled. It helps that first reflection bounce either low or high (depending on the angle) under/over the listening height (position). An angled desk with your speakers on stands would help give you more variables and fine tune-ability.

Your room is like 85% of the way there... The last umph is really the most challenging and tedious. Be patient, please. You will reap the rewards in the end.

Neil
Old 14th January 2012
  #108
Lives for gear
 
Lights's Avatar
 

Thread Starter
Quote:
Originally Posted by amishsixstringe View Post
How would adjusting the height of your desk change the reflection without speaker stands? It may do something to SBIR, but doubtful to ETC.
Well, here was my thinking, let me know if I'm onto something:

1. I assume that the sound leaves the desk at the same angle that it hits the desk.
2. I can control the angle of the speakers independently of the desk. They sit on Auralex Mopads which can angle the speakers up a lot, up a little, down a lot, down a little, and flat.
3. If I raise the rear of the desk or lower the front, making it angle slightly downward, and adjust the angle of the speakers to still be at my ears, the reflection may be redirected lower.

Does that make sense? If not I won't bother, because it's not easy to crank those feet up and down.

I will play around with the speaker position... but I don't really feel that I know enough to make an educated decision about what to do with the data I have yet.

If I move the speaker back against the wall and the notch gets smaller or bigger, what does that tell me and what do I do?

If I move the speaker left or right and the notch gets bigger or smaller, what does that tell me and what do I do?

Is there any benefit in moving the speakers up or down?

Is there any benefit in moving a bass trap into certain positions (which ones?) to test the response?
Old 14th January 2012
  #109
Lives for gear
 
amishsixstringe's Avatar
 

Ok. I like your idea with messing with the desk. I was not understanding what you meant. You could totally do what you are thinking. I would make the desk as low to the ground and angled toward you as much as possible. This should redirect that reflection below your ears. I would do this AFTER trying out some stuff with your modal problem.

If you move your speaker left to right and it doesn't change the 41hz problem at all, that tells you at least one thing: The mode doesn't correspond to the side walls. It sounds like the depth of the room is what is likely causing the mode. 41hz is 27.5 feet (8.4 meters) in length. I don't remember the dimensions of your room and I am in the middle of charting a song arrangement at the moment, but does that seem to fit into anything in your space? Maybe even half of that distance could be causing the problem. i.e. 1/2 wave = 13.75 feet (4.2 meters).

Moving the speaker along the axis that the mode is occurring in will give you confirmation that these two walls are causing the mode. THEN you can figure out which way to move the speakers and,or place traps.

Neil
Old 14th January 2012
  #110
Lives for gear
 
Lights's Avatar
 

Thread Starter
Question: when looking for modes, should I be only be measuring modes that could be running through the mixing position?

Here's why I ask: the only obvious multiple of the 41Hz wave is the 13ft distance at the back part of the room between the wall at the head of the bed and the short wall across from it by the door.

However, I did the old A^2 + B^2 = C^2 calculation and found that from the floor-wall corner to the left of the mix position to the ceiling-wall corner of the wall to the right is almost exactly 14 feet. (Close enough--half of 41Hz is 13.7?)

It's also about 14 feet from the far back wall (by the door) to the front wall. But I'm befuddled why that distance, which is across from the right speaker, doesn't affect the right speaker more than the left.

If we go to a quarter wavelength, you get 6.8 feet and you could find a lot of 6.8ft distances given that there's a diagonal wall behind me that starts 6.4 feet from the front wall and goes back to about 10ft behind me.
Old 14th January 2012
  #111
Lives for gear
 
amishsixstringe's Avatar
 

When looking for modes you can look everywhere. Obviously, the idea is to make things right at the listening spot, but standing waves will effect many areas. Have you tried moving the speaker and measuring at all? Use the data to find the problems rather than making a theory and then trying to fudge the data to align with your idea-not that you are doing this-just a reminder.

Also, I seem to recall you saying you did this already, but get your spl meter out and play 40, 41, 42, etc and get some measurements around the room. If there is that big of a null at 41 in your listening spot, either there is a spot in the room where it is super hot ooorrrr your speaker is broken.

Keep truckin!

Neil
Old 14th January 2012
  #112
Lives for gear
 
Lights's Avatar
 

Thread Starter
I emailed Neil and DanDan offline with the REW file of all of my experiments. As it turns out, the null at around 40-44Hz doesn't change much when I move the speaker. It does move a tad, and get slightly bigger or smaller... but only slightly. I think the most interesting thing is when I did the SPL meter test... I started with a 44Hz sine wave on the left speaker (the volume calibrated to 80dB by pink noise) and my SPL meter at the mix position. I got low 60dB levels. I ran the SPL meter horizontally from wall to wall. Pretty much no change. I then started in the mix position and ran it front-to-back and saw the levels go to mid 80dB at the front and back of the room. So there's a horizontal trough at the mix position.

I *assume* this means I need a bunch of back wall trapping on that diagonal wall.
Old 14th January 2012
  #113
Lives for gear
 
amishsixstringe's Avatar
 

Awesome! You found what is causing the problem. Does it seem consistent with both speakers? I assume it is. Try the biggest, thickest son-of-a-gun you can muster up on that back wall. It should be good to do this anyhow, because of the asymmetrical angle of that wall. It could be causing some of those later reflections in your ETC, too.

You're on track man. Most people would have stopped messing with that room a week ago and left well enough alone. Congrats on being a nerd and making it better!

Neil
Old 14th January 2012
  #114
Lives for gear
 
Lights's Avatar
 

Thread Starter
I'm a total nerd.

No, that's the crazy thing. The response for the right speaker is beautiful. Check it out--it's the first graph in the REW file I sent you today. That said, if you look at the diagram of my room, the room drops away behind the right speaker.

I'm assuming that it's the diagonal wall and flat wall directly behind the mix position that needs the treatment and not the far wall at the top of the picture with the door.
Attached Thumbnails
50Hz ring, 60Hz hole, best material to treat?-studio-room.jpg  

Last edited by Lights; 14th January 2012 at 11:34 PM.. Reason: Picture was way too big to insert inline.
Old 16th January 2012
  #115
Lives for gear
 
Lights's Avatar
 

Thread Starter
Good news! The 5 additional 4" bass panels are ready for pickup. Despite the fact that I went off a couple cliffs in the backcountry today in some over-zealous snowboarding I'm going to take some pain killers and try to get them hung and do some measurements tonight.

Even though they aren't likely thick enough to have the same level of impact on the 41-44Hz range, placing a few and testing the response will help me understand what areas are the trouble spots.
Old 16th January 2012
  #116
Lives for gear
 
Lights's Avatar
 

Thread Starter
Well guys I think I've just about run out of 2ft x 4ft spaces to hang bass traps. I even have one in what I'd judge to be a completely useless place (not pictured).

Here are the results of a first measurement. "Half space" measurements are with the Mackie-recommended half space switch since my speakers are basically against the back wall (or within a foot). This is a built-in highpass filter. The "Whole space" waterfalls have the speakers switched into the mode where they have no highpass filtering. There is still a notch on the left speaker between 40-45Hz but it's slightly mitigated.

Also included are pictures of the back wall, now with 4 bass traps straddling all corners and mounted on the wall itself (all have 4" spacers behind them). The left wall is quite short and hasn't changed much, but benefits from that corner trap on the back wall. The right wall has 2 new bass traps (one at the ceiling-to-wall gap and on the wall.

Remember that the traps on the left and right walls that look like auralex foam are 4" of fiberglass 4" off the wall, with an additional 2" of auralex foam on the front, so that's not *just* foam there.

And of course you can see the giant 2x2x8ft boxes of Owens Corning Ecotouch R-30 wrapped in the same muslin fabric as the bass traps.
Attached Thumbnails
50Hz ring, 60Hz hole, best material to treat?-jan-15-left-half.jpg   50Hz ring, 60Hz hole, best material to treat?-jan-15-left-whole.jpg   50Hz ring, 60Hz hole, best material to treat?-jan-15-right-half.jpg   50Hz ring, 60Hz hole, best material to treat?-jan-15-right-whole.jpg   50Hz ring, 60Hz hole, best material to treat?-back-wall.jpg  

50Hz ring, 60Hz hole, best material to treat?-left-wall.jpg   50Hz ring, 60Hz hole, best material to treat?-right-wall.jpg  
Old 16th January 2012
  #117
Lives for gear
 
Lights's Avatar
 

Thread Starter
So I think that left side is suffering from small room syndome, since the back diagonal wall starts less than 7ft from the front wall. Perhaps my only real option is to replace taht couch with a fiberglass-filled bench.

Now... should I just be cutting open and jamming the old couch frame full off owens corning R-30 Ecotouch?? The couch is pretty ugly and old... a reject from the "real" living spaces in our house.
Old 16th January 2012
  #118
Lives for gear
 
amishsixstringe's Avatar
 

The ones with more bass look better to me. Can you email me a new file? I'd like to see how the decay and even-ness looks now. Seems like that place probably sounds kinda 'dead' in there now huh?

Looks pretty gnarly though dude. How's it sound listening to stuff?

Neil
Old 17th January 2012
  #119
Lives for gear
 
amishsixstringe's Avatar
 

Oh, I see you DID email me. I check GS way more than my mail. Lemme checkadisout.

neil
Old 17th January 2012
  #120
Lives for gear
 
Lights's Avatar
 

Thread Starter
So I may have just re-emailed you then

I haven't listened to the room with reference tracks yet. I got them installed pretty late last night and only had time to run some quick sine sweeps and then head to bed.

I'm in the midst of tracking and mixing a new song so my plan is to get back to the actual music making until I have some new things to measure! So I'll let you know.
New Reply Submit Thread to Facebook Facebook  Submit Thread to Twitter Twitter  Submit Thread to LinkedIn LinkedIn  Submit Thread to Google+ Google+  Submit Thread to Reddit Reddit 
 
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump