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 Post subject: Re: My room measurements
PostPosted: Tue Aug 08, 2017 5:34 pm 
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Joined: Wed Jun 18, 2014 11:04 am
Posts: 202
Location: Chicoutimi, QC, CA
RT60 will give the decay time. If you clap your handicap you'll get the sound of the clap, and then the "rebounds" of that sound a couple of millliseconds later. It refer as reverb if you want. I saw on web site and mxing forum that a response between 0.3 and 0.5 ms would be ideal, but hard to acheive un small room. I have and average of 2.3 - 2.5ms

-- 08 Aug 2017 21:39 --

Impulse also refer to time. In the graph you have time and db of the impulse and the "rebounds". You should aim below -20, from 0 to 40 or 50ms.

Bad RT and impulse response affects the image and the clarity, details. Let say a bass note last 1sec it will "blend" with the other notes.

I may not ne the best person to explain since my first language is french. But you can have a look at REW help documentation and informations on various web site

-- 08 Aug 2017 21:44 --

I still not fully understand Group delay, and it will be hard for me to explain. But I've read that if you want to EQ you'll look at flat response spot. An EQ won't have alot of effects on peaks.

I think group delay refer at phase. Phase is something a don't understand. I found that rePhase program may help to EQ the phase, but I think it's more usefull for speaker designing.

I hope it helps and I also hope someone will correct me if I'm wrong.


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 Post subject: Re: My room measurements
PostPosted: Tue Aug 08, 2017 5:52 pm 
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Location: Chicoutimi, QC, CA
The waterfall graph is practical because you can see your frequency response with his decay time. On the last graph I posted you can see that frequencies below 25 last more than 5ms. Since those frequencies are more felt than heard it won't affect too much the listening experience. But it shows us that the vibrations stays active longer in the room


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 Post subject: Re: My room measurements
PostPosted: Tue Aug 08, 2017 5:53 pm 
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Joined: Fri Jun 13, 2008 9:14 am
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Location: St.Catharines, ON, CA
Thankyou very much.I have a fully treated room but have never really measured it.Not that I'm disappointed in it but its about time that I did some measurements...Basically I DIY'd GIK room layouts..

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 Post subject: Re: My room measurements
PostPosted: Tue Aug 08, 2017 6:05 pm 
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Location: Chicoutimi, QC, CA
If you have a chance measure it you'll be surprise. No rooms are the same and there's different fournitures.

I first do the basic room setup : equilateral speaker placement, covered all the first reflexions, etc. By measuring I found that some acoustic panels were doing nothing (again on my room). It gives me the opportunity to try different layout.

There's 2 cement walls and 1 gyspe only wall in the room. They both affect the bass differently. Today I regroup 4 panels on the cement wall and kept the ceiling panels to acheive my bass response. If I remove one I loose some bass.
Attachment:
IMG_20170808_203158130.jpg
IMG_20170808_203158130.jpg [ 261.56 KiB | Viewed 309 times ]


Next time I would like to see what the ceiling panels are really doing. There's 2 doors in the room, I have to keep one open to get mid bass right. The other gives better results closed for bass and open for low mid. There's thousands configurations. I spent a lot of hours to tweaking everything. Acoustic panels, couch cushions, bean bags are your friends for quick tests.

Btw I just rediscover what bass is. This ~70hz bass dip was sucking a lot good music!!!


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 Post subject: Re: My room measurements
PostPosted: Tue Aug 08, 2017 6:09 pm 
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Location: Markham, ON, CA
Nice work and the graphs look pretty good.

The final question is : does it sound good, or the best when it's the smoothest?

I did the same and unfortunately it's not ....


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 Post subject: Re: My room measurements
PostPosted: Tue Aug 08, 2017 6:16 pm 
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Location: Chicoutimi, QC, CA
chuttt wrote:
Nice work and the graphs look pretty good.

The final question is : does it sound good, or the best when it's the smoothest?

I did the same and unfortunately it's not ....


The bass dip was taking a lot of good bass out!! I really like what I heard so far. I still have to do a critical listening with my favorite cds

Today I moved my sweet spot at ~ 6 feet from speakers (currently 8 feet, the max the room can give me if I want to stay in the center), the soundstage was huge, no comparison possible. But bass response was more flat, and I have to say that I prefer the boost that I have at 8 feet. I don't feel I'm loosing something in the highs, and those are difficult to measure correctly. But let see what the 1200 - 2300hz is hiding. If it gets too bright I'll know what to do.


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 Post subject: Re: My room measurements
PostPosted: Fri Aug 11, 2017 4:01 pm 
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Location: Chicoutimi, QC, CA
Today I removed the ceiling panels and I need to keep them there. While having the panels in hands I tried a couple of configuration but I didn't manage to remove the 1000 to 2000hz dip. Closer to speaker there's no dip, so the issue comes from the room or with a the speaker's interaction.

I'll play with the speaker's angle for the next tests.

Here's my room layout
Attachment:
IMG_20170811_192143943.jpg
IMG_20170811_192143943.jpg [ 134.72 KiB | Viewed 269 times ]


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 Post subject: Re: My room measurements
PostPosted: Fri Aug 11, 2017 6:39 pm 
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Location: St.Catharines, ON, CA
Why so many panels on lefthand wall and none on the right hand?You can use a mirror from your listening position to pick up the first reflection on your right hand wall..Move mirror on right hand wall until you see your lefthand speaker from your listening position..There is also a mathematical equation to pick up first and second reflections..

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 Post subject: Re: My room measurements
PostPosted: Fri Aug 11, 2017 6:53 pm 
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Joined: Wed Jun 18, 2014 11:04 am
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Location: Chicoutimi, QC, CA
When I first setup my panels I placed a panel on left and right wall at first reflexion point using a mirror and behind each speakers. I was always having the bass dip at 70hz. So I tried various configuration, including corner placement to act as a bass trap but nothing worked.

I knew the biggest problem was coming from the corner beside the couch. I ended aligning my panels on this wall and I finally ended up with an improvement. Like I said in a previous post, If I remove a panel here, the bass response is screwed.

Today I used the ceiling panels on the right wall in combination of those on the left, but I did not have any gain. (I guess since the begining I did at least 40 to 50 panels, furniture configurations)

The reason I think this wall needs to be treated that much it's because it's a solid cement wall. The right wall is gypse only I guess it doesn't affect bass as much as a solid wall.


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 Post subject: Re: My room measurements
PostPosted: Sat Aug 12, 2017 2:02 am 
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Location: St.Catharines, ON, CA
I have a similar scenario with a corner and an opening in my rear room as well.With out measuring I could here a distinct bass rise as I walked towards the "closed" corner..Bass pools up in every corner of a room..All panels are not created equal...For the rear I used a 4 inch stack of Owen Corning versus the 2 inch (with air gap) that i used for the first reflection points.This should actually be thicker for a corner bass placement but if you place diaganally this of course increases bass absorption.I also covered the rear bass panel with a membrane to increase the bass absorption while still reflecting HF..Once again no measurements to prove any thing just just results by ear...

I also built super chunk bass traps for the front wall..Most room tuning kits and acoustiticians will recommend to bass treat your "front corners" as well as all reflection points first..

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 Post subject: Re: My room measurements
PostPosted: Sat Aug 12, 2017 5:02 am 
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Joined: Wed Jun 18, 2014 11:04 am
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Location: Chicoutimi, QC, CA
Thanks for the advice. I'm sure corner bass trap would help. And it is part if my plan for the future. I just want to make sure that I will do something positive.

What's the membrane material? If have it I'll do some experiment.

With the currently setup if I keep the rear door open I have a peak at 40hz, one or two db, but it gives me a less flatter bass response after, nothing extreme though. I'm amazed each time I do tests. To be able to "see" and hear the changes is fantastic. Some changes give instant results but I have to admit that some don't change the listening experience. But I prefer to know that everything is good, maybe it's a "downside" of room measuring.


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 Post subject: Re: My room measurements
PostPosted: Mon Aug 14, 2017 3:46 pm 
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Location: Chicoutimi, QC, CA
Did some tests today and it's still improving.

I found a couple issues.

Regarding the highs : first while moving my panels I turned down the crossover L-Pad on compression driver. Get it back to be symetrical with the left speaker. The door to the right needs to be open but it was reflecting the highs a lot. Same thing goes for the wall. I tacked matress foam on it and on wall. There's still a dip but some frequencies don't go as deep as it was. The concrete floor between the couch and the door needs a carpet or a rug.

For the lows I placed my 4 acoustic panel differently : 2 stack in the corner and two stack lying on their side. I have the same result and it takes less space.

I was using a cheaper laser pointer for a dollar store to align my speakers and I found that when I turned the pointer on itself it was changing the pointing direction.... So today I used a construction laser level. Way more accarute and didn't need to tweak after.

I now have a big soundstage, center image and more details in the highs. There's still a dip at 1056 to 1530hz below 3 db.

1-6 smoothing that show the evolution
Red = oldest
Green = old
Purple = new
Attachment:
Aout 14 1-6 tous.jpg
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1-6 smoothing
Attachment:
Aout 14 1-6.jpg
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1-3 smoothing
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Aout 4 1-3.jpg
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Impulse response - looks pretty damn good to me
Attachment:
Aout 14 Impulse.jpg
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RT60
Attachment:
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And finally waterfall
Attachment:
Aout 14 Waterfall.jpg
Aout 14 Waterfall.jpg [ 103.02 KiB | Viewed 226 times ]


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 Post subject: Re: My room measurements
PostPosted: Fri Aug 18, 2017 10:27 am 
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Joined: Wed Jun 18, 2014 11:04 am
Posts: 202
Location: Chicoutimi, QC, CA
Today's test really surprised me!!!

Reverse polarity

1-6 smoothing
Green = normal polarity
Purple = left speaker, reverse polarity
Blue = right speaker, reverse polarity

Attachment:
Reverse polarity.jpg
Reverse polarity.jpg [ 57.74 KiB | Viewed 191 times ]


I wish I got the blue result 6 db higher.............

Currently there's a L-PAD wired between crossover and tweeter. I'm wondering if it may cause a change in the response????


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 Post subject: Re: My room measurements
PostPosted: Fri Aug 18, 2017 10:44 am 
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Joined: Wed Jun 18, 2014 11:04 am
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Location: Chicoutimi, QC, CA
I just had this thought :

If I reversed the polarité does it also reversed what the rotary switch (l-pad) was doing?

Now l-pad was at max, does he is now at low? If it's the case I'll ne able to get 3 to 6 db more and it would be perfect.

I'm no longer at home I'll have to wait to find out.


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 Post subject: Re: My room measurements
PostPosted: Fri Sep 01, 2017 11:54 am 
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Joined: Wed Jun 18, 2014 11:04 am
Posts: 202
Location: Chicoutimi, QC, CA
Still in my journey for acoustic goodness

I managed to correct the 1000 to 2000 hz dip but it created a huge dip at 70 hz. I put the bass back. By listening the difference between a dip at 70 hz is far more noticable than a 1000 hz dip. Note also that 1000 hz and above are more impacted by sitting position than 70 hz and bass in general.

1-6 smoothing

Purlpe =Old
Grey = New

Attachment:
Sept 1-6.jpg
Sept 1-6.jpg [ 53.78 KiB | Viewed 99 times ]


RT60

Attachment:
Sept RT60.jpg
Sept RT60.jpg [ 53.01 KiB | Viewed 99 times ]


I found a wall that needs treaments to remove a reflexion.

I also experiment a lot with room mode and speakers placement.

Everyone can do this at home : with rew generate sin wave and walk in your room, some frequencies can completly disapear in some areas.


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