Hi guys. Sorry it took a while to get back. For some reason the bbs isn't emailing me when there is a reply to a thread I'm watching.
Anyway....
I don't see how any of my remarks could be interpreted as mocking or scoffing!
Ok, but just for accuracy sake, this is what I really said John.
With all due respect John, I don't understand why the cynical tone from xspace and you. :
scoffing tone, rolling eye attitude, in-significant error checks......
I don't see the word "mocking", do you?...you put words in my mouth.
My point was, I tried to bring something of relevant interest to the forum. What I get back is like " a defence" of the common use of the term leaf"...but in a scoffing "tone". Like rolling your eyes at something that SHOULD be important to you, but you want to pretend that it isn't. I mean, people are asking questions now, no?
Ok, maybe I over reacted John, but it comes from MANY previous experiences here,. Anticipation of flaming is my only defence.
Well, lets drop it, ok?. I APOLOGIZE if I was incorrect.
However, there are still a few things to clear up though. This WHOLE leaf thing STILL is up in the air as far as I'm concerned. For instance, here's yet ANOTHER conflicting set of statements
Andre states...
Thanks for the excellent post just above this one. Acoustically speaking, your definition of leaf as a single mass is correct.
Which is odd, as xspace says this AFTER andre confirmed my interpretation....
A leaf is not mass.
This is why I get frustrated. Ether it IS or it ISN'T!!! Again, how many THOUSANDS oif references can be found on this forum alone, that defines a LEAF as a membrane of MASS, no?
But then he goes on...
If you consider the leaf the framing then you may get a better picture. When the author says, "double sided" this may well be the confusion. A double sided (READ: two distinct pieces of wall board on one side of one single frame) double leaf (two separate walls) this is what is very commonly called a double leaf wall assembly, ad hoc, two distinct walls with mass on opposite sides.
This is absurd...... DOUBLE LEAF(two seperate walls)
A DOUBLE LEAF WALL ASSEMBLY????? IS VERY COMMONLY CALLED....WHAT???? That statement is completely at odds with not only the content of this thread, but the common use of the term LEAF on this bbs......I've NEVER seen anything you or anyone else has ever said that aligns with this statement. In fact, if thats the case, then even this statement becomes somewhat of a misnomer....
the one we've grown accustomed to no doubt.
So John, exactly what is this definition "we've grown accustomed to...NO DOUBT!??? hmmmm? It sure isn't tthe the way the BBC uses it, and never has...at least from what I've read here, and ALL OVER THE NET!!
This is what I mean by contridiction. SHOW ME, ANYWHERE on this bbs, where the term DOUBLE LEAF is used or defined as xspace says ..a DOUBLE WALL is VERY COMMONLY CALLED a DOUBLE LEAF WALL ASSEMBLY, and I'll eat my goddamned hat!!! GEEEEEZUS, even Andre said I WAS CORRECT!!!
Unless Erics "double leaf" is something ENTIRELY DIFFERENT than the way its used on this bbs, even YOU used the term as andre said is CORRECT...
The 2 leaf system was proposed by Eric Desart when he built Galaxy studios in Brussels. The design was an Eastlake Audio (
http://www.eastlake-audio.co.uk/ea_news.html ) project but the client wanted one main recording room with 3 control rooms fronting onto it and they wanted 100db STC between all 4 rooms!!
Ok, enough of that for now. However, there are STILL some questions that come to mind. Let me start with the "100db
STC" as you mentioned above. Not only is the terminology of LEAF somewhat of a conundrum, so is STC. At least to ME. This is why.
Read this,
http://www.greengluecompany.com/understandingSTC.php
and THEN tell me how Erics use of 100db
"STC" RATED assemblys is in fact a !00db assembly if this article is indeed true.
Here is a quote from the author at GREEN GLUE
Why are the folks at The Green Glue Company the only people that talk about this?
We aren’t! In fact, the very recognized ASTM standard which explains how to calculate STC - ASTM E413 - directly warns us that STC is not suitable for most situations.
“These single-number ratings correlate in a general way with subjective impressions of sound transmission for speech, radio, television, and similar sources of noise in offices and buildings. This classification method is not appropriate for sound sources with spectra significantly different from those sources listed above. Such sources include machinery, industrial processes, bowling allies, power transformers, musical instruments, many music systems and transportation noises such as motor vehicles, aircraft and trains. For these sources, accurate assessment of sound transmission requires a detailed analysis in frequency bands.”
The standard itself openly recognizes exactly the limitations that we discussed above. Why these limitations have been so consistently overlooked by novice and expert alike is something we don’t understand.
Astounding. But what I really don't understand is this, from the GALAXY website.
The biggest problem was to insulate the lowest frequencies.
Isn't that what every studio designer tries to achieve? Afterall, a rock drummer produces 100dba SPL LOW FREQUENCY impacts, and MOST of the studios people on this bbs deal with ROCK drummers as a given, no?
Peter Newell even says
For example, one cannot turn down the volume of a drum kit. Playing
quietly is no solution, because it produces an entirely different tone quality to
playing loud. Realistic drum levels are more in the order of 110 dBA, so
75 dB of isolation (the 110 dBA SPL [Sound Pressure Level] of the drums
minus the 35 dBA acceptable to the neighbours) would be a basic requirement,
though this could be reduced at low frequencies, as will be discussed in Chapter 2
And...
The inside to outside isolation is usually dominant, as few studios are sited next to neighbours producing upwards of 110 dBA. As the 30-dBA region is reasonably close to the limit for
tolerance of background noise by either the neighbours or the studio, it is principally
the 110dBA or so produced in the studio that dictates the isolation needs.
Yet, it is commonly stated on this bbs that 2 layers of 5/8" drywall ...in a DOUBLE LEAF assembly, will provide the kind of isolation needed for drums.
Then the author at Galaxy states this..
To insulate frequencies as low as 20 or 30hz, Vermier and Desart calculated that the insulation capacity had to start four octaves below. This means it was necessary to find a way to insulating a 30HZ frequency or even lower."
Hmmm, all this makes me wonder after reading this....
So why is the STC system used at all?
As frequency falls, the ability of the different labs to get consistent results also falters. +/- 3 STC points from lab to lab is typical, but if the STC system were extended down to, say, 40 Hz, this might increase to +/- 10 STC points or more, making the results basically meaningless.
Meaningless? even at only 40 Hz? errrr........now I'm really getting curious. Especially after reading this from Green Glues article. Hmmm, didn't I read that most labs can't test below 85hz? Then how does one "guarantee 100db iso at 20Hz if you can't even test it in a lab?????????
Problem 1 - STC does not correlate at all to low frequency performance.
The graph(see website) to the right shows two walls, one of STC 47, one of STC 48. Note that in the low frequency range – important for music, theaters, traffic, aircraft, and most other real-world noise sources – the lower STC wall is literally 30 decibels better, yet lower STC
And then this
Problem 2 - Misleading results due to frequency cutoff.
The 125 Hz cutoff also leads to some very misleading results. Take the two hypothetical walls below. They are both poor walls, with very bad low frequency performance, but one is STC 32, the other is STC 42
Two very bad walls, one gets a bad STC score, the other gets a reasonably respectable STC score. Why??? Because with one wall, the big problem occurs at 125 Hz, inside the STC frequency range, but in the other wall the big problem occurs just below the STC frequency range.
This creates misleading situations where some construction change or product simply causes a huge problem to shift ever so slightly down in frequency and yields a huge gain in STC. Impressive marketing value, but in reality it doesn’t make the wall better at all. So, yes, problems really do occur.
and finally..
.
Summary:
The STC score has only very limited relevance for most sound isolation applications because it is calculated in an archaic fashion, it assumes noise sources that are unrealistic for most situations, and it is calculated over a very limited frequency range, ignoring perhaps the most important of the frequency band.
Therefore you should strive to avoid buying products because of high STC, and strive to find products and designs that yield actual real-world reductions in noise level.
sigh................(goes on reading Mr Newell)
It can be seen from Figure 2.1 that
60 dB SPL at 3 kHz will be very audible, in fact it will be over 60 dB above
the threshold of hearing at that frequency, yet a tone of 30 Hz would be
inaudible at 60 dB SPL; it would lie on the graph below the 0 phon curve of
‘just audible’.
Consequently, if a flat reading of 60 dB was taken on an SPL meter measuring
a broad-band noise signal in a room, then 25 dB of isolation would be
needed at 3 kHz if the neighbours were not to be subjected to more than
35 dBA. However, at 30 Hz, nothing would need to be done, because the
sound at that frequency would not even be audible in the room, let alone outside
of it. Hence, providing 25 dB of isolation at 30 Hz to reduce the outside
level to less than 35 dB SPL unweighted (i.e. a flat frequency response) would
simply be a waste of time, money, effort and space.
I guess I'm just a dummy. I don't get it. Why in the world would the people at Galaxy waste all that time and money to isolate 30hz, not to mention 20hz at 100db...if as Mr. Newel states..."yet a tone of 30 Hz would be
inaudible at 60 dB SPL,"..........".NOTHING WOULD NEED TO BE DONE"! )$^&^*^(_)_((_&^&$##^&&**))))_)_))()&(
What am I missing?
I think its time for a drink.....make that a double.
Just to be on the safe side John, IF you were mistaken by quoting STC as a rating used by Galaxy, something else comes to mind then. But I've had enough brainburn today.
alright, breaks over , back on your heads......