Limp mass membrane material

Posted: Wed Jul 30, 2008 4:19 am

Something is very odd with those measurements for the frequency response graph. Can you use Room Eq and make the measurements ? ETF is not the easiest software to work it.

Posted: Wed Jul 30, 2008 7:05 pm

I agree, it looks odd to me too! Wink

I know most people smooth their results to 1/3 octave...

I would like to try roomeq but I don't have IE (java) on my work machine so that would mean doing a temporary install to a different hard drive (from scratch)

I'm seriously thinking about doing it though as I don't trust etf. It's not like I've missed an omni switch on the ecm8000 (I hope!)

@camsr everything's changed! lol
Speaker position (L/R), height, distance, wanted more flexibilty to find the 'perfect spot' (as perfect as I'm gonna get in my room anyway)
Something of interest I found on the Genelec site was a pdf that stated in small rooms you actually want to go closer to the front wall as it moves the first cancellation up the frequency range (hence the 300hz canyon?). The further from the wall the lower the canellation, at around 2m it starts getting into the >100hz area killing the percieved response.

Posted: Sat Aug 02, 2008 12:32 am

As requested, the roomeq version. I ended up taking my net machine down there and used that for the measurements (taking the mixer and the other soundcard out of the equation)

3rd octave version

12th

raw

How can I lose the 380hz dip?

Posted: Sat Aug 02, 2008 9:47 am

Guys, I really need your help here, have I done something wrong or are people bored with the topic?

I'm trying to do this but it's difficult on my own. I'm guessing the cancellations are to do with wavelength. One measurement that coincides with both nulls is 0.85m which is a full wavelength for 400hz and a quarter of 100hz. Should be looking to move the speakers a
way from this length?

I don't know where I picked up this 370 hole, it wasn't there before.

I used 45kg/m3 rockwool for the ceiling cloud, which I think is 3lb/ft3

Posted: Sun Aug 03, 2008 5:35 am

scoobz,

Again, I'm no expert on these charts, but the hole at 388 is (by simple math) a 4th order harmonic of the hole @ 97.

Actually, I'm suspicious that you're in a null.

I'd look for something that is just under 3, 6, 9 and 12 feet away to see if some movable physical object is introducing some sort of unwanted phase relationship?

However, my guess is that it's your mix position still needing to be at 38% with your speakers needing to be forming the 30 degree angle. e.g. you might need to push back your mix position a few more inches to get out of that null.

Posted: Sun Aug 03, 2008 8:53 am

Hi Max,

Thanks for the input. I had my tape measure out yesterday and not only was the distance from front wall to centre of driver 0.85m but the distance from the ceiling was 0.85 too!
I think what you advised is the way to go but I'm already at 38% (from the front wall). I've tried moving the speaker forward and listening position back but then I'm sitting in the dead centre of the room and the response is horrible.
So the speaker has gone right back and up a inch or two, that has helped with the 100hz dip.
Like I said the only thing that's changed is the ceiling cloud so this 400hz thing is killing me.
I'll look for those distances you quoted next time I go in there.

I'm also concerned about the high end comb filtering, if anyone could have seen me yesterday the would have worried for my mental health! I was walking around singing into the traps, tutting, clapping etc
I have different fabrics covering my traps, the potato sacking (hessian?) traps return no top end, the ceiling trap is the same but there was something coming back off the brown cotton fabric (which is now only in the side RFZ points).

I'll get some photos tonight of the new setup

Posted: Sun Aug 03, 2008 10:01 am

scoobz wrote:

if anyone could have seen me yesterday the would have worried for my mental health! I was walking around singing into the traps, tutting, clapping etc

Sometimes the neurosis doesn't work for you.

Posted: Sun Aug 03, 2008 10:34 am

Sometimes you feel like a nut, sometimes you don't...

Posted: Sun Aug 03, 2008 11:53 am

I wish I could be of more help. This room mode calculator might help you. It seems a change of a few centimeters can drastically change the way room modes align. The node for 98Hz is 0.868 meters. (1/4 the wave length) So you don't want your listening position that far from a wall.

Posted: Sun Aug 03, 2008 1:46 pm

GeckoMusic wrote:

I wish I could be of more help. This room mode calculator might help you. It seems a change of a few centimeters can drastically change the way room modes align. The node for 98Hz is 0.868 meters. (1/4 the wave length) So you don't want your listening position that far from a wall.

Actually you want it further......

38% back into the room from the wall you are facing is a good starting point.

This puts you in between nulls...... then your moves shouldn't be in feet - but in inches........ you have to move very little and test a lot to locate the sweet spot. Inches can make HUGE differences in what you are hearing.

And the move is inches forward and back......

Also remember that you can create a null off the front wall that is not room rellated but is related to reflections off that wall mixing with the direct sound from the speakers.... this is known as SBIR and (if that is even a part of you problem) you can handle that with 2 " of 3pcf rigid fiberglass mounted directly behind the speakers (I like to use stands in this case so the placement is directly adjacent to the speaker itself.......

try that at your 38% location and see if it makes a difference.

let us know what happens.......

Rod

Posted: Sun Aug 03, 2008 2:11 pm

Right I'm home, lmao Greener you're like a sniper, ready to pick people off. Btw the neurosis is all good thanks, the voices in my head agree too Wink

Hey Gecko, nice to hear from ya, this graph is what the BGRMC came up with

...so er......yeah lol (doesn't mean alot to me) You're right about the distances, the speakers were 0.85 from the front wall AND the ceiling, moving them back and up helped. I'll post a new response when I get chance.

And funnily enough Rod i was reading up on SBIR yesterday, I always knew the rough theory but not the name for it.
would filling the 4" air space behind the rockwool panels around the speaker help? More density is better than an airgap right? Just to help a little bit more with the absorption, reducing the power of the reflecting wave causing the cancellation
So I'll be placing additional panels above and behind the speakers, behind the panels that are already there.
I think Max was also onto something with the distances. So I have alot to do and check tonight, I'm off in there now so will report back later, hopefully with pics too

Thanks all, (even Greener Wink

)

Posted: Sun Aug 03, 2008 4:31 pm

if you have 4" only - then 2" of air with 2" of glass is better than 4" of glass and no air........

Rod

Posted: Mon Aug 04, 2008 9:10 am

Hi,

My camera was playing up last night so I'll have another go later.

In the meantime this was my old 'comby' repsonse....

And the new reponse, same scale.....

So I'm reading this as an improvement

Both are unsmoothed

It's been mentioned a few times and maybe my responses haven't made it clear, the room is 4.63m and the listening postition is 1.8m so that's 38% ish isn't it? Or am I missing something?

The cloud is 4" thick and about 5" from the ceiling behind it, I tried putting another sheet of 4" above the speakers but it didn't make any meaningful difference to the response the the plot, it's just wierd that the valley wasn't there before.
I did realize the importance of the microphone placement last night though and you're right a few inches in any direction does affect the response alot.

So as far as diagnosing this 400hz problem goes I've identified the wavelengths that might be causing an issue, done some measuring, moved what I can, added panels. Dunno whart else to do. I'll stick some photos up later so hopefully you can look at it and go 'I can't believe you missed that! Just move the X to the left" etc

I can dream! Wink

Posted: Mon Aug 04, 2008 10:45 am

38.87%

5mm off 39%.

It really seems like you're chasing dragons.

If you removed all treatments from the room and started again, measuring with something you trust every step. Could you arrive somewhere better than by doing what you are doing?

Can you "over do" acoustic treatment?

Posted: Mon Aug 04, 2008 10:50 am

Greener wrote:

Can you "over do" acoustic treatment?

Like anything in life, it can be done wrong, if that is your question. There are clear guidelines/recommendations/specifications on what to achieve with acoustic treatment of a room's sound for monitoring.

Andre

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