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Air gap: maximum size?
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technocolour v2
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#1
13th November 2010
Old 13th November 2010
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Air gap: maximum size?

I'm building some broadband absorbers to treat early reflections on my side walls. One of the walls I think must've been a fire place as a large section of it is embossed by about 13cm. I'm using 10cm thick tiles so figured a 10cm gap, but the embossed wall is about 30cm in from the area I want to treat.

I was going to build one absorber 30cm wide and the other the rest of the length (90cm) and deal with the 13cm wide face of the embossed wall by... I don't know yet

But then I was thinking, if I built the absorber the original width I intended (120cm), would raising it 10cm off the embossed wall cause problems from the 30cmx150cm area that isn't, as the air gap for this section of the absorber would be about 23cm?
#2
13th November 2010
Old 13th November 2010
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Gap

Not exactly following the description but it doesn't matter. The gap is not critical. Equal gap is a popular rule of thumb but I am not sure if there is much science behind it. Certainly in practice much greater gaps are commonly used.
Consider a suspended ceiling. One inch tiles, sixteen inch gap, a great broadband performer. For more/better, see the Q4Avare thread.
DD
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13th November 2010
Old 13th November 2010
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I found better results with a 15cm gap behind a 10cm panel in a couple parts of my room compared to a 15cm panel with equal gap. It all came down to put it up and test and then try something different and test again.
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13th November 2010
Old 13th November 2010
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Mind the gap

Air gap: maximum size?-50mm-wool-50mm-gap.gif Name: 50mm wool 50mm gap.gif Views: 703 Size: 35.4 KB ID: 203445" style="margin: 2px" />
Air gap: maximum size?-50mm-wool-100mm-gap.gif Name: 50mm wool 100mm gap.gif Views: 528 Size: 36.5 KB ID: 203446" style="margin: 2px" />
Air gap: maximum size?-50mm-wool-150mm-gap.gif Name: 50mm wool 150mm gap.gif Views: 465 Size: 37.4 KB ID: 203447" style="margin: 2px" />
Air gap: maximum size?-50mm-wool-200mm-gap.gif Name: 50mm wool 200mm gap.gif Views: 538 Size: 38.4 KB ID: 203448" style="margin: 2px" />

Air gap: maximum size?-125mm-wool-125mm-gap.gif Name: 125mm wool 125mm gap.gif Views: 694 Size: 35.7 KB ID: 203449" style="margin: 2px" />

Screens taken from a beta version of AFMG Soundflow. More info here:
New EASE Tools Go Beta - AFMG - Ahnert Feistel Media Group
technocolour v2
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13th November 2010
Old 13th November 2010
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Thanks guys! Jens, what s/w is that you're using?
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13th November 2010
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14th November 2010
Old 14th November 2010
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125 250 500 1K 2K 4K NRC


703, plain 2" 16" air 3.0 pcf 0.66 0.95 1.06 1.11 1.09 1.18 1.05

703, plain 2" no gap 3.0 pcf 0.17 0.86 1.14 1.07 1.02 0.98 1.00

www.bobgolds.com

DD
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14th November 2010
Old 14th November 2010
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Thanks thumbsup
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14th November 2010
Old 14th November 2010
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Deja vu
#10
14th November 2010
Old 14th November 2010
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Netbook

I was going to PM but when not ask here, others may be interested.
Jens, you have and use an array of software which makes this Mac user a little jealous. Also, I intend buying some portable device for gathering location acoustic measurements. Way back you showed a wonderfully successful small room treatment using almost exclusively perf treatment.
I noticed a little PC maybe a Netbook in the pictures. Do you find this powerful enough to run REW or whatever you use on location? If so, could you tell me (us) which one it is. A decent netbook and some of that software would cost less than a Macbook, certainly a Macbook Pro.

DD
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14th November 2010
Old 14th November 2010
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Thanks for posting the info.

I get that adding an air gap behind an absorber allows it to be more efficient, especially in lower frequencies.

But this does work without an airtight encloser, right? For example if i space an absorber-panel some inches from a wall..

Is there a rule of thumb, like double/equal spacing in relation to the depth of the absorber? Of course i know that everything depends on factors like the density of the material, but especially if you work with materials for which you don't have exact data, a rule of thumb would be helpful.
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14th November 2010
Old 14th November 2010
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Horse Sense

Elmolemon, intriguing name. See Q4Avare. Andre mentions a couple of rules of thumb from actual professional practice. 1:1 to 3:1 seems a common zone, but 5:1 happens.

I am sure this could all be calculated but IMHO common sense and even visuals will suffice. Let's say 2 inch 703, 16 inches from the wall. Clearly one square inch of this stuff is not going to do anything. A single trap 2 x 4 feet is also unlikely to get noticed. Conversely a full fill of the area is likely to at least equal the predicted or tested figures. It's all relative. Are of absorbent vs wavelength and room size.

DD
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14th November 2010
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Wow.. Thanks for the link to the thread.

This was quite advanced stuff and i couldn't follow everything. Nonetheless an interesting read!

From what i understood, i can use 1:1 as a rule of thumb with the option to add further space up to 2:1, without screwing the absorption-curves up, while gaining additional low frequency absorption, right?
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14th November 2010
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Jens:

When posting graphs for room absorption, please use diffuse field settings, or show both. Normal is only appropriate for the special case of axial mode absorption. Of this is important if that is what is desired, but most of the time broad band absorption is what is desired from the people on this forum.

Thanks.

Andre
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14th November 2010
Old 14th November 2010
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Yes

elmolemon, yes.
DD
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15th November 2010
Old 15th November 2010
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Quote:
Originally Posted by DanDan View Post
I was going to PM but when not ask here, others may be interested.
Jens, you have and use an array of software which makes this Mac user a little jealous. Also, I intend buying some portable device for gathering location acoustic measurements. Way back you showed a wonderfully successful small room treatment using almost exclusively perf treatment.
I noticed a little PC maybe a Netbook in the pictures. Do you find this powerful enough to run REW or whatever you use on location? If so, could you tell me (us) which one it is. A decent netbook and some of that software would cost less than a Macbook, certainly a Macbook Pro.

DD
I can imagine the frustration of not having access to a proper computer.

The netbook I’m using for measurements a very cheep Asus EEE 901. The nice thing with this model is that you can turn off the fan completely and it still only reaches 70 deg (C) core temp even if stress tested with Prime 95, and since the HD is SSD the computer is completely silent, perfect for critical measurements in other words. The built in 3G-modem and real world battery time of >5h is a nice bonus.

I only use it with ARTA to capture impulses but I don’t think REW or Soundflow would be a problem. I wouldn’t want to run Reflex or SoundEasy on it since these apps are quite slow even on a normal machine.

Air gap: maximum size?-img_9036.jpg Name: IMG_9036.jpg Views: 328 Size: 154.4 KB ID: 203682" style="margin: 2px" />
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15th November 2010
Old 15th November 2010
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Sorry to digress, but Netbook type computers are brilliant for things like this. Lets hope the market in them isn't killed off by the iBad..... sorry iPad
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15th November 2010
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Quote:
Originally Posted by Dange View Post
Lets hope the market in them isn't killed off by the iBad..... sorry iPad


/Jens
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15th November 2010
Old 15th November 2010
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Proper Computer

My new MacPro has awesom god-like characteristics. Every morning it demands a sacrifice of 5 Wintel PC's. Then it starts up. I can't quite follow it's ambitions and don't dare to question them. At the moment it appears to be crashing the Irish economy as a punishment for greed.
However, I don't dare interfere.......


Thanks Jens, that is really useful information. There are many little PC apps which I have to borrow for. e.g. updating firmware in a SLM, a Fostex D2424, even the TV! I am now seriously considering this act of heresy.....

DD
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15th November 2010
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Quote:
Originally Posted by DanDan View Post
Jens, you have and use an array of software which makes this Mac user a little jealous.
Have you used Boot Camp to load Windows when needed? Or Parallels or VMware to run Windows simultaneously under OSX ?

Both options are cheaper than an entire new computer for some apps.

Andre
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15th November 2010
Old 15th November 2010
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Old Fashioned

Thanks Andre. I have thought about that, haven't tried it.
I have been in transition for a long time now. This is due to a failed sale agreed on a large ProTools rig. My habit is to keep computers apart. e.g. MacPro running PT9 in the studio does not run anything else. Only occasional Internet for software updates.

In the new year I intend replacing the office computer ( a very environmentally friendly iMac lampshade, about 10 years old). I will very likely get another iMac and I will very likely run Windoze on it. From Jens information it is now very likely that I will also buy that Asus.

It's a long and winding road, changing three computers. It is made more so, when the old ones are still working perfectly as I type.

DD
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15th November 2010
Old 15th November 2010
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Quote:
Originally Posted by DanDan View Post
My new MacPro has awesom god-like characteristics. Every morning it demands a sacrifice of 5 Wintel PC's. Then it starts up. I can't quite follow it's ambitions and don't dare to question them. At the moment it appears to be crashing the Irish economy as a punishment for greed.
However, I don't dare interfere.......
Sounds like you need to knock the Paganism on the head and get yourself a proper computer *basks in heavenly light of overclocked PC running Win7*
#23
9th December 2012
Old 9th December 2012
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Quote:
Originally Posted by Jens Eklund View Post
I can imagine the frustration of not having access to a proper computer.

The netbook I’m using for measurements a very cheep Asus EEE 901. The nice thing with this model is that you can turn off the fan completely and it still only reaches 70 deg (C) core temp even if stress tested with Prime 95, and since the HD is SSD the computer is completely silent, perfect for critical measurements in other words. The built in 3G-modem and real world battery time of >5h is a nice bonus.

I only use it with ARTA to capture impulses but I don’t think REW or Soundflow would be a problem. I wouldn’t want to run Reflex or SoundEasy on it since these apps are quite slow even on a normal machine.

Attachment 203682
That's a schwing-a-rific setup. I have no authority to do so, but if I did, I'd give it something like a Gear Slutty Award.
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