lots of bass traps=dulling of the highs...partially reflective traps?

[Nrt]

Originally Posted by SAC

Bounty or Brawny? And is there a difference in performance depending upon which printed pattern it has? Sorry, ...couldn't resist...

1 or 2 mil plastic sheeting (or even aluminum foil) is easily sourced and handled, inexpensive, and much more resilient in assemblage without tearing and easily accepts spray surface adhesive that makes it easier to apply and remain in place as it is covered and hung.

...And ironically, for a given quantity, cheaper than paper towels!

And while I must admit to never having bothered to compare the two, my money would be on the plastic for being a marginally better reflector that the fibrous paper...

Debating which substitute material might work really isn't that worthwhile with such readily available proven methods so easily sourced. But if you are going to try something different, I would confirm the absorbers behavior with measurements.

But this really isn't that complicated folks...

I don't understand why you bash Bounty. I'm not against plastic sheet or aluminum foil in terms of the sound. I don't know the difference of absorption coefficient between paper and plastic sheet, but Bounty has very favorable acoustic absorption coefficient as far as I measured. I just said what I know from my experience. Bounty is proven (at least for me).

Do you have a chart for those materials? I expect plastic sheet or aluminum foil should have much more aggesive Q than Bounty. Consider Bounty as a vintage tube EQ with wide Q.

[SAC]

Bash Bounty, the better picker-upper? Me????

I have been too busy grinning at all of this!

Besides, the little printed border patterns add aesthetic variety and interest! And you never know when they might come in handy as an emergency absorber for spills...

Personally I would use the inexpensive plastic simply as it is so readily available in large contiguous non-porous sheets and it is so resilient and easily handled. And when bonded to a semi-rigid underlying substrate is sufficiently non-resonant.

But that being said, FSK surfaced materials are easily sourced as well!

And to repeat what has already been mentioned, I would not personally use loosely woven absorbent paper (as opposed to a coated paper like butcher's paper) as it is simply an absorber. There is literally little to distinguish a roll of paper towels from a porous absorber. And there is nothing to indicate that a thin film of such a fundamentally absorbent material would suddenly become appreciably reflective. In fact, I don't imagine that it would be appreciably more reflective than the cloth used to cover the panel.

I am not sure what you are referring to as a 'chart'...as reflective qualities of non standard household items are not generally in high demand.

...But I will keep an eye out for a table of the acoustical characteristics of various household thin films, vegetables, plants and socks - sorted by various colors, clean/worn and aromas.

Bottom line: if it worked for you, great.
But all things being equal, I would personally opt for other readily available materials that, as mass is increased, tend to act more as reflectors rather than absorbers.

[Nrt]

You are right. Ultimately, our ears are much more sensitive than the measuring instrument. Paper will sound paper and plastic will sound plastic. Probably my studio sounds papery and your one sounds plasticky.

[SAC]

Now you have me wondering about dried fruit 'leathers'...

...As they would also impart a nice aroma as well as a fruity character to the mix... Mango...cherry...passion-fruit...kiwi...pomegranate...

[Yiannis]

I had some time for experiment so ...

I put plastic on my two back wall SuperChunks and on the Front wall behind my speakers.

The rezults were almost the same at its best and worst on the other hand.

Except that there was that awfull plastic smell !!

I couldn't breath right and I had the feeling that something had stacked into my throat.

Bad experience!!

I took it off,opened the doors and let fresh air come into the studio...

Back to normal again.

No plastic for me anymore

[SAC]

What kind of plastic are you using????????

I am sorry for your problem, but does every commonly employed option presented on this forum serve as a debilitating source of drama?

First we have folks who can't breath because semi-rigid fiberglass coated with binder is supposedly polluting the air, and now we have plastic that is off-gassing VOCs sufficient to create breathing difficulties!

All I can say is that folks either do not know how to properly handle semi-rigid fiberglass and are sourcing strange plastic components - as I have NEVER had a problem with either semi-rigid fiberglass if best practice handling methods were observed nor with such COMMONLY available plastic sources as 1-4 mil polyethylene sheeting (available in rolls in just about every department & hardware store).

One can only wonder what type of plastic sheeting is being employed...

I am sorry that so many find using such common materials so debilitating and a source of SO much drama , but I would also maintain that they provide little concern for the vast majority of folks!

And as a result, I suspect that many will be terrified to see what materials the plastic sheathed versions of common insulation products are skinned! (Poly!) Rather amazing as they are widely used in SO many places without anyone having any problems...but then, I suppose that this is partly due to no one being informed that they are even being used.......

Thank goodness no one tried aluminum foil or Mylar! One can only imagine what egregious malady they would precipitate. I tremble at the thought of so many falling ill as Buddy Ebsen did while filming the Wizard of Oz, or whatever imagined horrible fate befalls some who come within 100 feet of Mylar! Its simply too painful to imagine!

And just give it more time, the bleaching of the paper to make it white will, I'm sure, precipitate some reaction, real or imagined, be it birth defects or debilitating lung disorders or, heaven forbid, whiter paper towels!

Fresh air...indeed!!!!

...Just one more reason to spare no effort or expense in the crusade to save the Neoprenes and Naughas! ...such gentle creatures - and just think, they don't even start wars and they are friends with the dolphins...

[DanDan]

Hi Yiannis, take no notice of the taunts and insults from SAC. That's what he and his friend foxfyr do. Try a search and you will quickly see.
However, I am very interested in your tests, even if you regard it as a failed adventure.
I have wondered for some time if plastic on the front of corner chunks would be effective or not. It certainly is effective on the front of corner absorber panels, so one wonders why not on SSC's.
Can you post some waterfalls of before and after. I would actually like to have the files so maybe you would PM me with those?
Best, DD

[SAC]

Poor dd, his pet Naugha made him object to the OBVIOUS tongue in cheek post.

But then my previous post was interpreted as "bashing Bounty"!!!!

After all, I am sure the plastic is responsible for at least some of the reputed global warming that is not a result of his hot air.

[Yiannis]

SAC,

I didn't wrote my experience to terrify people.

Its just that plastic didn't work for me acoustically first of all.

If I had good results I could have gone to some other store and by a better one.

The plastic I bought was from a hardware store.

What plastic was that?I don't know....I didn't care to know because it was just plastic.

I didn't expect to be that bad for my lungs.

BUT as I said if it was working I should have find another solution.

No drama at all...just bad experience.

[DanDan]

Yiannis, do you have those test results still? I would love to see them.

Here's an indicator of the other reality-

11th July 2009, 07:03 PM
foxfyr
This message has been deleted by jayfrigo. Reason: repeated insults, bickering, and unnecessary escalation.

foxfyr stopped or was banned from posting shortly after that. He then returned as SAC. You will find constant sneering, snide remarks, and LOL about other's lack of knowledge. Ironic, since the creature doesn't seem equipped with basic human comms. skills.




Best, DD

[Yiannis]

Yes I do,
just give me some time to post the results


Here are the results (watefall in a minute) 1/24 smoothing

LEFT

RIGHT


RED no plastic cover
GREEN plastic on Sc (both back wall) only
BLUE plastic on Sc (both back wall) and front wall


LEFT NO COVER


LEFT COVER ON SC BACK WALL


LEFT COVER ON SC BACK WALL AND FRONT WALL

[SAC]

Just a note - your measurements are not an effective indication regarding the the later arriving reflections nor the frequency content of the later arriving reflections. Instead you are merely measuring the frequency response that is dominated by the higher gain direct arriving energy.

...And a log display of frequency does not help in any event as much detail is lost.

But it is interesting to note the 'change' in response of the rt blue curve with both covered - although that could also easily be a result of mic placement.

In order to examine the frequency content of the later arriving reflections, you would need to carefully/properly window the impulse response and then perform an IFFT back to the frequency domain.

[Yiannis]

Even I don't understand a thing I must say that the mic was always at the SAME position

[DanDan]

yiannis, Thank you for posting those. Rest assured they will be useful to many of us, and there is nothing 'mere' about them. Similarly a log frequency response is one chosen by many of us when we want to see the lower frequencies in more detail. Not a random, nor ignorant nor inappropriate choice. The 160mS duration seems extremely short for a lowest axial mode. There may well be information we are not seeing on your files. Let me take a look at them so that I can apply some zooming etc. PM'd you back regarding this.
Best Regards, DD

[SAC]

As usual, dd misses the point of the thread which was the higher frequency reflected response of the bass traps for which a standard FR/waterfall is not the appropriate measurement. But for a derived FR convolved from a properly windowed IR of the later arriving reflected signals, a linear scale FR is optimal - and anything but "arbitrary". As for that we don't care about the modal analysis.

But then, for dd, there is nothing else.

You see, dd's focus is not on the issue at hand, but merely an attempt to counter anything I say as he feigns an oh-so-caring patronage while worrying about non sequitur modal analysis... and "zooming"...

The Russian-Czech hockey game is much more interesting....

[DanDan]

Countering SAC nonsense is unfortunately far too easy. I do so in the hope that he will go where foxfyr went. A search of SAC/foxfyr posts will show a litany of abuse, sneering, insults and so on.

So to the topic at hand.
yiannis joined this thread, kindly contributing the results of his tests. He also sent the files to me, in case I could tease out any better or more information.
Foil on the front of these chunks hopefully should have led to an increase in level and evenness of the bass response. Intuition would also suggest an increase in HF at the listening position. The waterfalls suggest a very dead and/or very small room. I reckon there will be little or nothing of anything arriving 'later'.
There is certainly no beneficial effect visible. I have been informed elsewhere, that FRK or plastic film needs to be bonded, spraytacked to panels for best LF effect. It is a pity yiannis did not know this at the time.
I am told that the layer of plastic was 1-2 mil, quite thick. It was mounted on the wooden frame front, not really touching the rockwool.
If this wooden frame were sealed to the wall this would appear to be a membrane trap. If it is not sealed to the wall, then a leaky membrane trap. The lack of positive or perhaps any results from the tests should give us pause to think about membrane traps.
Looking at the octave band decay times, the HF decay is considerably longer with the plastic, albeit still short.
So it does appear that plastic will brighten things up a bit.

So, thanks again to yiannis, for doing the tests and sharing the results with us.
No experiment is a failure. There is at least a strong suggestion here that foil in front of a SSC does increase HF decay times in the room.

DD

[Yiannis]

Yes the room is small.

3,90 L 3,20 W 3,15 H.

The back wall superchunks are 3m H x 1m W.

I have a lot of bass trapping in here.....no room for more

[PaulP]

I don't understand the waterfalls. All frequencies are constant for the first
20ms and then most of them just drop like a cliff. What could cause this ?

Paul P

[Glenn Kuras]

Originally Posted by DanDan

Countering SAC nonsense is unfortunately far too easy. I do so in the hope that he will go where foxfyr went. A search of SAC/foxfyr posts will show a litany of abuse, sneering, insults and so on.

So to the topic at hand.
yiannis joined this thread, kindly contributing the results of his tests. He also sent the files to me, in case I could tease out any better or more information.
Foil on the front of these chunks hopefully should have led to an increase in level and evenness of the bass response. Intuition would also suggest an increase in HF at the listening position. The waterfalls suggest a very dead and/or very small room. I reckon there will be little or nothing of anything arriving 'later'.
There is certainly no beneficial effect visible. I have been informed elsewhere, that FRK or plastic film needs to be bonded, spraytacked to panels for best LF effect. It is a pity yiannis did not know this at the time.
I am told that the layer of plastic was 1-2 mil, quite thick. It was mounted on the wooden frame front, not really touching the rockwool.
If this wooden frame were sealed to the wall this would appear to be a membrane trap. If it is not sealed to the wall, then a leaky membrane trap. The lack of positive or perhaps any results from the tests should give us pause to think about membrane traps.
Looking at the octave band decay times, the HF decay is considerably longer with the plastic, albeit still short.
So it does appear that plastic will brighten things up a bit.

So, thanks again to yiannis, for doing the tests and sharing the results with us.
No experiment is a failure. There is at least a strong suggestion here that foil in front of a SSC does increase HF decay times in the room.

DD

thumbsupthumbsup

[DanDan]

I don't understand the waterfalls. All frequencies are constant for the first
20ms and then most of them just drop like a cliff. What could cause this ?

Paul P

Interesting observation Paul. The room is very small and very very dead. Perhaps near the limits of what this software can do. No smoothing fills in that area with a lot of black lines. 1/48 sort of fills the gap a little. Other graphs in my FM2 version show anomalies.
e.g. the log squared response shows a very discrete repeating pattern. A strong flutter I would suggest. This may also have something to do with the odd step in the graphs.

DD

[Nordenstam]

Originally Posted by PaulP

I don't understand the waterfalls. All frequencies are constant for the first
20ms and then most of them just drop like a cliff. What could cause this ?

The ~20dB range from top to bottom explains the cliff like drop.


Yiannis: any chance of posting new pics with something like 400ms duration and -100dB minimum magnitude? You'll probably see what the most useful ranges are when you play around a bit with the parameters. At some minimum magnitude all the lower stuff will be included, at some time range everything will drown into the noisefloor.

[DanDan]

Lupo, I tweaked the parameters in a forensic search for evidence of change.
600mS and 75dB worked quite well. I note the low mode appears to be much longer. 340 mS or so. However no visible difference with plastic. Yiannis sent me files exported as FM2. I note the overall measurement hovers around -20dB. This does seem low, thus Lupo's suggestion of lowering the threshold is a good one. However for future measurements, unless this is an export anomaly, I recommend getting close to 0dB. I would certainly like to see high points in the curve hit -6 to -3 dB
yiannis, perhaps your version of FM does ETC. Don't worry about what that actually is for the moment. Lupo will be good at reading it. Worth a look, it might illustrate that flutter which I suspect.
DD

[Nordenstam]

Hi Dan!

Originally Posted by DanDan

I note the overall measurement hovers around -20dB. ... However for future measurements, unless this is an export anomaly, I recommend getting close to 0dB. I would certainly like to see high points in the curve hit -6 to -3 dB

This also explains the post in another thread about ignoring the clip light and push the peaks of the graph towards zero. In short: don't ignore the clip light!

The time domain signal (what the sampler/input is reading) may very well clip even if the frequency domain signal (frequency/waterfall) plot have peaks way below zero. The time domain signal is the sum of all frequencies. The only time this corresponds directly to frequency domain signals is when sampling a sine wave that's exactly centered in one of the frequency bands and compare that RMS value of that signal to the frequency domain value (which is the RMS value of all frequencies in each band/bin of the fourier transform). Sorry if this is too technical. There's a lot to be said about measurements!

The basic idea is the same that there is a difference between average and peak level in music. Music typically have peaks 10-20 dB above the average value. In frequency domain, the difference is much more pronounced. A white noise peaking at 0dBFS measures about -35dB in a frequency graph. Depending on how you set up the graph.. There's a lot of options that can alter the levels as seen in the frequency domain. If you where to push that white noise so it peaked at 0dB in the frequency graphs, the time domain signal would be 30dB clipped!

[Yiannis]

I couls do some more measurements so I can get near zero but without plastic..


should I do it Dan?

I could sent the files again to you.

That flutter echo is a PITA.

It is hiding well

[DanDan]

yiannis, I don't think there is any need to do the measurements again. For the future though I would get close to 0dB. FM seems to be doing things its own way here, so Lupo's headroom warning probably does not apply.
Lupo.
I think we are talking about several different items as if they were the same. I think both FM and REW take Impulse Responses and extract various graphs from them. The two have very different approaches to level, but I am sure both know what they are doing and there is certainly no need for -20dB graphs in FM. I note my FM2 vertical scale goes from - infinity to plus as far as I can see! I do the obvious, try to get close to 0dB (whatever that is) with curve peaks. REW goes about this is a very different way, i.e. gives you all the meters and tools to tinker and get it exactly right. Funnily this is a very common scenario with Mac vs PC software. The Mac has done the job without opening the bonnet, the PC bonnet is open all the time.
White or even Pink noise does indeed have a high peak to average ratio. However sine sweeps?
I noticed a post ( I reckon by Chris FM) some time ago, where levels were examined using other graphs, perhaps ETC, to check if the S/N ratio was good enough for decay readings.
In the other post mentioned an REW user seemed to be having issues finding a balance between low level and clipping. My suggestion to 'perhaps ignore the clip' was based on a comment that the guy could actually not achieve a working level and gave up. I have let REW clip occasionally with no apparent ill effect. Perhaps unwise. Incidentally I just fired up REW and had no problem setting a level.
DD

[Nordenstam]

Originally Posted by DanDan

Lupo, I think is valid to set levels based on the resulting graphs. After all the vertical scale is a meter is it not? White or Pink noise does indeed have a high peak to average ratio. However the sine sweeps of FM have no such ratio, so the recorded level on the graph should be correct surely?

Peak to RMS value of a sine wave is 3dB. The sine is however, in this case, not a single frequency. When doing the FFT, the program will analyze a chunk of time containing different frequencies. The length of this chunk will vary depending on the FFT routine. Hence, how many frequencies is contained per given chunk will vary as well. Longer chunks gives bigger difference between time domain peak and frequency domain peak. There's no way to predict the peak to observed value difference without having the total info about input signal and all FFT parameters.

Originally Posted by DanDan

I am quite sure the designer has taken precautions so that the limited metering provided keeps us safe. I have certainly not encountered problems in practice with FM2.

The program should halt if the process if the signal is clipped. It's hopefully what it's doing!

[DanDan]

Point taken re peak to rms in a sinewave, although not exactly the same thing as white noise or a sweep eh?
I think we should avoid causing confusion here. I am reasonably sure both programs work just fine. I have never had trouble with levels in FM2. I use the outboard metering to avoid clipping. I am sure there is some significance to Chris's odd vertical scale. I am sure he is quite aware of the need for calculation headroom as you allude to.
The manual says little on levels. But as I said, typical Mac. The job is done perfectly well, no need to open the bonnet. REW level does indeed seem a bit tweaky but the level setting procedure seems to work absolutely fine also.
DD

[Nrt]

Originally Posted by Yiannis

I had some time for experiment so ...

I put plastic on my two back wall SuperChunks and on the Front wall behind my speakers.

The rezults were almost the same at its best and worst on the other hand.

Except that there was that awfull plastic smell !!

I couldn't breath right and I had the feeling that something had stacked into my throat.

Bad experience!!

I took it off,opened the doors and let fresh air come into the studio...

Back to normal again.

No plastic for me anymore

Plasitic kills the vibe of your studio.
But seriously, why don't you try the Bounty method? I understand your left brain refuses it, but it actually works. Staple them directly on the OC. It's will take only 20 minutes.

[Yiannis]

Originally Posted by Nrt

Plasitic kills the vibe of your studio.
But seriously, why don't you try the Bounty method? I understand your left brain refuses it, but it actually works. Staple them directly on the OC. It's will take only 20 minutes.

I will, and post the results

[DanDan]

FRK is bonded to panels. SprayTac or some such is used. Ethan has assured me, from experiements with films and FRK, that this bonding is necessary to achieve the desired result. Thus there would surely be no point whatsoever in repeating these tests without bonding. This is irrespective of whatever material is chosen.
yiannis if you are up for more tests, which would be great, I am very willing to help out.
If your frames are removeable perhaps you could staple film to the inside of the frame? Maybe pressure would be enough to simulate the bonding? I have seen a figure of 0.6mil for the plastic film somewhere. If you wish to proceed, let me know and I will track down that info. 0.6 seems a bit closer to FRK (which works) than 1 or 2 mil.
You may have an industrial insulation fabricator near you. They have FRK and SprayTac. I found such a source here, in a city of 150K.
DD