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PostPosted: Thu Aug 17, 2017 8:21 am 
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Joined: Wed Jun 18, 2014 11:04 am
Posts: 202
Location: Chicoutimi, QC, CA
I did a lot of room measurements in the last weeks and I wanted to share how small changes can affect your room response. Every room are different, what's happening for me will certainly differ in a different room. We can find a lot of good advices and calculation tools on internet, but that's almost for square or rectangular rooms. For the other rooms I guess measurements and experimentations will give you the better results. I'm open to suggestions and advices,correct me If I said something wrong.

I did my measurement with a usb minidsp Umik-1 with REW. I'm no expert but I improved my measurements method over the weeks as well as my understanding of acoustic.

viewtopic.php?f=36&t=47241

Here's how my room looks like (note that I changed the four panels configuration at the left)
Attachment:
Room setup.jpg
Room setup.jpg [ 32.17 KiB | Viewed 1735 times ]


Now let see what happen if the door at the back of the room is open or not.

Frequency response (REW's ''All SPL'' tab)
Blue = door open
Light green = door close
No smoothing
Attachment:
Comp freq.jpg
Comp freq.jpg [ 48.2 KiB | Viewed 1735 times ]


There's a peak at 43,7hz of 3 db, and other dips go lower. It still looks good but let see what happen with time.

RT60

Attachment:
Comp RT60.jpg
Comp RT60.jpg [ 55.45 KiB | Viewed 1735 times ]


Again Blue = door open, Light green = door close. It still in the range of 0.3ms to 0.5ms but clearly bass reflects or reverb longer.

Since RT60 won't give data below 60hz and since waterfall gives a better global portrait let's give a look at it

Waterfall blue = door open

Attachment:
Comp water open.jpg
Comp water open.jpg [ 101.6 KiB | Viewed 1735 times ]


We clearly see that the bass peak reverb pass 0.5ms, almost 800ms, which will result in a less clear bass note.

Waterfall Light green = door close

Attachment:
Comp water closed.jpg
Comp water closed.jpg [ 92.57 KiB | Viewed 1735 times ]


Looks better and sound better.

Same thing happen with the door to the right

Light green = Back door close, right door open
Gold = back door close, right door close
No smoothing

Attachment:
Comp freq right door.jpg
Comp freq right door.jpg [ 58.71 KiB | Viewed 1735 times ]


It's not the kind of measurment I want.

Note that high frequencies are hard to measure precisely, you move your microphone for 1 or 2 cm and you'll get a different reading. For highs I suggest to point the microphone forward, not ceiling. You will have to find a way to mark your microphone spot, I used electrical tape on the couch.

For speaker placement I use a laser level. It can be setup to draw the line verticaly and it makes it easier to point speakers at the sweet spot.

This is just an example, and there's hundred of changes that can be done in a room to helps getting better sound : speakers placement, corners, reflections points (not necessarily first but seconds and up), etc. it's fun and rewarding.

Lastly trust your ears! After measurements, sit in your listening spot and listen. I got better graphs results but when listening the image was not clear or soundstage was poor, etc.


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PostPosted: Thu Aug 17, 2017 10:32 am 
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Joined: Sun Aug 21, 2005 12:29 pm
Posts: 666
Location: SW, ON, CA
Congrats on doing the work to improve your sound...it makes a big difference.

A couple of questions;

- why don't you have acoustic panels mirroring the right side to the left? I appreciate you can't put any over the door, but putting them along the side would help I think
- would the ceiling panels work better rotated and in one strip across the two speakers at the reflection point?
- is there carpet on the floor?
- any plans to add bass traps in the corner behind the speakers?
- any plans to put a panel or two above the equipment rack at the reflection point?
- have you tried the speakers out further away from the wall?

Good luck with your room improvements.

Paul

_________________
Ride hard, shoot straight and tell the truth.


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PostPosted: Thu Aug 17, 2017 11:01 am 
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Joined: Wed Jun 18, 2014 11:04 am
Posts: 202
Location: Chicoutimi, QC, CA
A couple of questions;

- why don't you have acoustic panels mirroring the right side to the left? I appreciate you can't put any over the door, but putting them along the side would help I think.

Before I got a microphone I placed my 6 panels like this : 2 panels mirroring left to right at first reflection points, 2 ceilling and 2 behind sepakers. My panels are made with 2 comfortboards and with this configuration the mid bass bass was messed up,
too much absortion. I replaced a panels on right and side wall and really never got good reading. Same thing for door placement, bad mid bass response. I recently add foam matress (having it on hand) and covered the door with it. Even if the door is open it really helps with reflections, expecially above 1khz. Today I took some curtains (don't say this to my wife) and placed them to cover only half the door opening : bass not affected and highs get slightly better. But still wondering if it worth it. A rectangular couch cushion almost at reflection point on the right, angled on the floor/wall has enough effect on bass. In fact I placed panels almost on every walls and never got good results.


- would the ceiling panels work better rotated and in one strip across the two speakers at the reflection point?

The ceiling panels are at first reflection points. The ceiling light won't let me a perpendicular placement. I tried without them and things get ugly

- is there carpet on the floor?

Big shag rug between couch and speakers/rack as well as foam puzzle pieces (kids stuff). I need a carpet between couch and right door.

- any plans to add bass traps in the corner behind the speakers?

It was my first plan : bass was lacking. But since I corrected the bass dip, bass is back (you can see it in the link I provided). Every time I placed and stacked panels in the corner behind speakers I get worst bass response. My speakers seems to like the rear wall. I did some tests where I tried to cover the corners from top to bottom and again no significant gain to justify buying materials for bass traps

- any plans to put a panel or two above the equipment rack at the reflection point?

For now no treatments have an effect when placed at the rack position. I did not try at ceiling. There's a TV above the rack. The TV Rack is bolted on the wall and the TV almost touches the ceiling. I covered it serveral time with different materials,
and again no change here. I tried a panels above the couch, nothing here too, and ceiling test are more complex. I'll try to add panels on each side to see what happen.


- have you tried the speakers out further away from the wall?

Yes but I'm limited here : Listening spot is 9 feet from speakers, and speakers are 2 feets large (26inches) and 21inches deep. But like I said earlier my speaker likes the rear wall, giving me a boost from 20hz to 60hz, and I'm really enjoying this :) They don't like side walls though (corners)


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PostPosted: Thu Aug 17, 2017 12:40 pm 
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Joined: Mon May 13, 2013 7:30 pm
Posts: 324
Location: Mississauga, ON, CA
I had a somewhat similar problems in my last place. As you say your speakers like the wall, not corner, reinforcement. I put my homemade large corner traps in the far wall in the room.extended area to soak up the longer reflected bass energy. I found it really tightened the low end up!

I.used Roxul stacked triangles behind.a nice pair of framed screens which were Velcro'd on to wall runners so that I could add and remove from either stack to adjust their effect.

prism


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PostPosted: Thu Aug 17, 2017 1:31 pm 
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Location: Chicoutimi, QC, CA
I also wanted to do something on the back corner but since there's a door it becomes hard, I'm sure would have benefits.

I like the idea of a "tunable" bass trap, thanks.


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PostPosted: Fri Sep 01, 2017 11:44 am 
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Joined: Wed Jun 18, 2014 11:04 am
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Location: Chicoutimi, QC, CA
Sitting position impact

I know ears are working differently than a micropohone but here's what happen if the microphone is about 3 - 4 inches higher, meaning that I sit perfectly square.

Blue = lower placement
Grey = Higher placement

1/6 Smoothing

Attachment:
Sept comp high.jpg
Sept comp high.jpg [ 52.36 KiB | Viewed 1304 times ]


No smoothing

Attachment:
Sept comp high no smooth.jpg
Sept comp high no smooth.jpg [ 74.72 KiB | Viewed 1304 times ]


I shows me that it's pretty hard to get accurate measurement, above 1 khz. Same thing for music listening sessions : I move and my sitting position change.

It also leads me, and confirm me, that people that are hearing differences between cable and like are tricked by their brain and acoustic. There's too much variable to perceives micro changes. I guess only a proper ABX test with good quality headphone could acheive this but I really doubt....


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PostPosted: Fri Sep 01, 2017 1:08 pm 
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Location: Vernon, BC, CA
I agree, anything above 1kHz is hard to accurately measure.
Even the microphone body causes issues.


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PostPosted: Fri Sep 01, 2017 3:12 pm 
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Joined: Wed Jun 18, 2014 11:04 am
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Location: Chicoutimi, QC, CA
Jared Rachwalski wrote:
I agree, anything above 1kHz is hard to accurately measure.
Even the microphone body causes issues.


Ho really, I wasn't aware of that.

I'm trying to correct a dip above 1khz but I have to say, that I don't really hear that dip, or let say it doesn't seems to be as pronounced as the graph shows, with a sine wave tone.


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PostPosted: Fri Sep 01, 2017 7:44 pm 
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Location: Leduc, AB, CA
It looks as if you have chosen your speaker placement for convenience or aesthetic reasons. If you have a "problem" room, you would be well advised to go to the Cardas website and carefully read the section on Room/System Setup. Right now you could easily be shooting yourself in the foot, no matter what moves you make. Try the Cardas method and see how it much it helps. If it is not very suitable aesthetically, you could place a single piece of dark tape on the floor marking the front of each speaker and move the speakers to these for times of critical listening. Otherwise, hopefully you will soon find a suitable placement position for less critical listening. Make sure your better half participates; have her check the math. In the end, after some involvement, she may be more flexible about placement and aesthetics. Good luck!


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PostPosted: Fri Sep 01, 2017 8:17 pm 
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Location: Chicoutimi, QC, CA
TwentyKHzPlus wrote:
It looks as if you have chosen your speaker placement for convenience or aesthetic reasons. If you have a "problem" room, you would be well advised to go to the Cardas website and carefully read the section on Room/System Setup. Right now you could easily be shooting yourself in the foot, no matter what moves you make. Try the Cardas method and see how it much it helps. If it is not very suitable aesthetically, you could place a single piece of dark tape on the floor marking the front of each speaker and move the speakers to these for times of critical listening. Otherwise, hopefully you will soon find a suitable placement position for less critical listening. Make sure your better half participates; have her check the math. In the end, after some involvement, she may be more flexible about placement and aesthetics. Good luck!


Thanks for the advice but I already went and read cardas. :D

Most calculators are for square or rectangular rooms, and it's not my case. Same thing goes for fournitures, they impact the sound and they are all different. And aesthetic is my last concern for now. When I'll have money to invest into that I'll get the look.

Theory is always fun but practices and experimenting is part of the learning procress and usually more fun.

Here's my measurements thread

viewtopic.php?f=36&t=47241


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