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 10th February 2012
  #151
Lives for gear
 
Lights's Avatar
 

Thread Starter
I did that. It seems as if there is a floor-to-ceiling null band widthwise across the middle of the room only when played from the left speaker. I will post a plot of SPL readings this weekend
Old 10th February 2012
  #152
Gear Guru
 
DanDan's Avatar
Plot

No need for a map.
A null in the middle of the room suggests a mode. Which will be confirmed if there are hot spots at the boundaries creating that mode.
That is where to trap. The VPRs here seem likely candidates
My Experiment with a Metal Panel Absorber

Obviously you are sitting within or nearly within that null. Can you shift listener position?

The interrogation is not over until we know the cause of that null.
Given you odd room and the difficulty so far it may have several causes working together.
That again leaves only positional changes as a solution.

I would sacrifice so called symmetry for better LF response any day, so don't rule out being off 'centre'

However let's keep asking. What is the distance from L speaker to the wall behind YOU?

DD
Old 14th February 2012
  #153
Lives for gear
 

this might be a really stupid suggestion, but can you categorically rule out physical/electrical differences in speaker units, (and your amp/desk electrical L/R for that matter?)... I'm thinking if some baffle/fluff or WHATEVER internal to the speaker was, say, altering how the reflex port was behaving, i dunno... just another random suggestion anyway.
Old 15th February 2012
  #154
Lives for gear
 
Lights's Avatar
 

Thread Starter
Thanks guys. I will continue to do experiments this weekend to try and pinpoint where I need treatment. The problem is that I can't find the location of the problem!! I will try steps like moving around several of the bass traps and speakers and if I see any change in the 43-44Hz null I will then worry about what kind of trap I need to fix this last problem.

As DanDan suggests, I will concentrate on the back wall areas.

And first, just for grins, I will swap the left and right speakers and see if the null remains or shifts to the other speaker.
Old 16th February 2012
  #155
Lives for gear
 
Lights's Avatar
 

Thread Starter
Well guys, a session I was going to do tonight got cancelled and I had a bit of time to try this:

0. Baseline = Yup, null still there
1. Swap speakers = same null on left side
2. Move speaker all the way back to the wall = null did not change in a meaningful way
3. Move speaker almost to the front of the desk = null did not change in a meaningful way

I'm willing to try treatment options, but at this point I'm not sure where to treat because I'm not sure what is causing the null. I have 10 4" bass traps. At least 5 of them are hung in a manner that they can be relatively easily moved around. But I'm just not sure where to put them.
Old 16th February 2012
  #156
Lives for gear
 
Lights's Avatar
 

Thread Starter
Mic Position Experiments

Ok, maybe this is interesting. Instead of moving the speaker, I moved the mic approximately 1ft backwards (away from the speakers and the front wall), forwards (all the way up to the edge of the desk), left (same distance from front wall but directly left, so it's closer to the speaker), and right (same distance from front wall but right, farther from the speaker) from the mix position. As you will recall, the room gets narrow as you go left because the back wall is diagonal.

Here are the waterfalls.

As you can see, aside from the single null, the mix position looks really good. Moving the mic forward simply amplifies everything, not really fixing the null. Moving the mic back just 1 foot makes everything fall apart with 2 new nulls appearing higher up. The 43Hz null is still prominent, but not as much as before.

Left looks pretty good across the board and the null is better than any other measurement. The null returns when I move the mic right of the mix position.

Thoughts??
Attached Thumbnails
50Hz ring, 60Hz hole, best material to treat?-mix-position.jpg   50Hz ring, 60Hz hole, best material to treat?-forward.jpg   50Hz ring, 60Hz hole, best material to treat?-back.jpg   50Hz ring, 60Hz hole, best material to treat?-left.jpg   50Hz ring, 60Hz hole, best material to treat?-right.jpg  

Old 16th February 2012
  #157
Gear Guru
 
DanDan's Avatar
That's a Mode

So, speaker movement does not change the null in any appreciable way.
Listener Position (Mic) movement changes the level but not the frequency.
That's a mode or several modes working together.
Tune a Sine Wave carefully to that mode. Be very exact there may be two or even more modes within Hz of each other. SignalSuite is good.
When you hit strong resonance, walk about and find a hot spot which is treatable. Put an enormous trap there. Or a VPR
My Experiment with a Metal Panel Absorber

DD
Old 16th February 2012
  #158
Lives for gear
 
Lights's Avatar
 

Thread Starter
Sounds good DanDan. I'll search around some more this weekend for the hotspots. I've done this a few times and found that the only really hot spot is directly behind the speaker, but I have this giant 32 cubic foot pink fluffy absorber in that corner already
Old 16th February 2012
  #159
Gear Guru
 
DanDan's Avatar
Done

It is odd to find only one really hot spot. Including the next hottest and so on, can you find a modal pattern. e.g. Peak Null Peak between boundaries?

Well, perhaps you are getting better at testing and refining the information as you work through this. Something is causing the null and if you follow a logical path you will find it.

Do you have a test with and without this huge corner trap?
It may be doing a good job but not enough of it.
It is really very difficult to make an impression on 41 Hz.
Only enhanced LF devices or absolutely vast fibre traps will do this.
Do consider the VPR.
But you still need to get fully clear about the cause and it's trappable location.

DD
Old 16th February 2012
  #160
Lives for gear
 
Lights's Avatar
 

Thread Starter
The very first waterfalls I posted prior to any treating did not show such a big null. Here it is again from the first batch of waterfalls from page 1:



I suspect trapping some things exposed others more clearly.
Old 16th February 2012
  #161
Gear Guru
 
DanDan's Avatar
Iterative

Treatment and Noise control as well are iterative processes.
As you say things become revealed.
Sometimes the only way to figure this is to make an intervention.
e.g. Place a 2mm VPR in that corner. If it softens the null that confirms the source.

DD
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