Sweepin' out the room a.k.a Show Us Your Pink Noise Room Plots!

mulletchuck

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So, i borrowed my roommate's monitor stands to try them out in place of mine.    they're 30" vs. my 36".    And let me tell you, it's amazing what you can do with 6".  THANK YOU AND GOODNIGHT

lol

Anyway.  Here are some before and after results:

First up is me playing a full-spectrum mix direct into SpectraFoo (1 channel) and then capturing it in the room with my old monitor stands.  Notice the massive holes throughout the bass region. 

di-D09T.png


Now, here's what my room sounds like with the speakers lowered 6" and pushed a bit further away from my listening position.  Also included is the noise floor of my room after the chinese restaurant shuts off their kitchen ventilation fan on the roof of the building. 

di-PJXA.png
 

So, check out the nice "flat" (lol) response from 50-110-ish now!  I'm stoked!  i can hear bass now! 

Sr1200 was askin' me to try moving the speakers away from the wall because of that bump at 125hz (I have 8-9' ceilings).  Check out how that affected the signal:

di-0X74.png


here's the info behind that plot:
Blue line at the top is the internal sine sweep signal (40hz-1000hz)
Rust line is Sine sweep position1:  Front of Speakers flush with rear side of IKEA Jerker support poles.  Aimed straight out.  Roughly 7" from rear walls with bass traps behind them.
Blue line is sine sweep position 2a:  Rear of Speaker flush with front side of IKEA Jerker support poles.  Aimed straight out.  Roughly 22" from rear wall.  check out that dead spot at 80hz
Green line is sine sweep position 2b:  same as 2a, just angled towards the mic. 
Yellow line is Sine Sweep position3:  Front of speaker aligned with front of desk, angled towards sitting position.  like 5" forward from position 1, and angled towards the user.

So, that's pretty eye opening.  I'm not sure how to get rid of the bump at 125hz that occurs in EVERY plot or fix the hole between 125hz and 250hz.   

While i was at it, I did some sweeps of my headphones!  This is interesting, to say the least. 
Sennheiser HD280 vs HD650. 
di-KPYN.png


here's the test rig: 
di-FRX0.jpg


Regarding the noise floor for all the testing, I used my Symphony I/O with mic Pre card, and set the gain to 60db for the mic, which was a Behringer omni measurement mic for like $50 or so.  I did these tests pretty late at night, so the output level was around -45db on my interface (not very loud) cuz I didn't want to wake the neighbors.  Still, the results were very eye opening, and while i was doing the 40-1Khz sweeps, it was really easy to hear where the signal would duck in and out due to room modes. 

What do your room sweeps look like when you pink-noise sweep your room?
 

Kingston

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Great measurement data!

I noticed a similar change when I made big fat speaker stands filled with rocks. But didn't measure it. I really oughta get one of those behringer measurement mics. In my case it was the opposite "boomy" additive standing wave that disappeared in a similar region, instead of that subtractive hole like yours.

mulletchuck said:
While i was at it, I did some sweeps of my headphones!  This is interesting, to say the least. 
Sennheiser HD280 vs HD650.

Nice one! I didn't realise you can measure headphones like that (but knew that the HD650 are awesome). How much do the high frequency plots change when you move the mic around just an inch or two?
 

fazer

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nice work chuck.  The bottom line is you hear the improvement with the changes you made.  30" height is kind of low for standing while you work (which was a post from awhile ago) but if it all works.  Also you have those HD650's.  I've got to hear a pair.  $500.00 phones.  They better sound good. 
 

mulletchuck

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lol i gave up working standing a long time ago.  I'll record sax standing, but that's it lol.    Let's see your plots, gents!    i found a bunch of those mics on ebay.  http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313&_nkw=behringer+measurement+mic&_sacat=0&_from=R40
 

JohnRoberts

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Yup, this is one of the ugly little secrets about audio while we wrestle over .01dB frequency response errors in hardware.

Speakers matter, and the room matters. Even where you stand/sit in the room matters.

Many night and day claims from unscientific listening tests, are influenced by the rooms, and perhaps listener position.

JR
 

mulletchuck

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oh lol  I thought that mic was discontinued.    I haven't seen how much the plots change when i move the mic on the headphones.  I tried to set the diaphragm as close to the foam covering the driver as possible, without actually touching the foam itself.  it's funny, when i did the headphone test, as soon as they swept up past 16K i couldn't hear them anymore.  it was literally like someone pushed mute on the interface.  beeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-op.      Guess i gotta clean out the ears lol
 

zayance

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Nice.

I actually liked DT880 pro better when testing them, for build quality, confort and sound, but that's just taste as always...
 

PRR

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Those headphones semi-seal to your head.

Without seal, bass escapes.

You need an ear's-worth of head.

Bash a hole in a plank, put the mike tight in the hole, clamp that to the headphone.

(A wig-holder may be more convenient.)

Ideally you could model the bulk of your external ear, swath the plank in flannel to simulate skin absorption.... you can get crazy.

But not emulating the blockage due to your head is fairly wrong.
 

PRR

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> how to get rid of the bump at 125hz

Half-inch drywall?
 

mulletchuck

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PRR said:
> how to get rid of the bump at 125hz

Half-inch drywall?
Could you provide a bit more detail on this suggestion?    I'm renting the spot, so i can't really do much construction other than hanging stuff from the walls.
 

PRR

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Drywall resonates. Thump the wall, it has a pitch like a drum.

Books say that 250Hz(?) is typical, but there is a lot of variation.

If your 125Hz bump is the drywall, the fix is a better wall. Perhaps a second layer of drywall with rubbery goop between. Perhaps a different amount of added mass on each wall so they don't all boom the same pitch.

All of which is unlikely in rental space.

You can try a lot of corner-foam "bass absorber". Stuck it with FunTak and take it with you when you leave.
 

gemini86

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Some bass traps may help, If you've got the corner space to spare. Cut up a bunch of rockwool into triangle shapes and stack them high. Make sure they're sitting up against two walls, so they can absorb as much of the vibration as possible.

John Sayers' forum has a goldmine of info on acoustics for different situations, from mild treatments to full purpose built studio construction techniques.
 

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