laminate floor over carpet ?

[neuro]

i keep reading that carpet is bad for "reverberation" in the control room.
my little (approximately 30cubic meters) home studio is carpeted.. with a very thin, quite ugly, and STRONGLY glued carpet, on top of a concrete floor.
taking the carpet out doesn't seem easy at all, but i'm considering adding some laminate floor over it, for esthetic, hygienic, and perhaps sonic reasons.
do you think that would be a good idea ?
would removing the carpet prior to flooring be a better solution ? (how much better and why ?)
here's a typical "RT60" graph of my room (measurement taken at my listening position) :



carpet doesn't really look like my main problem. but i'm trying to view things as a whole, before taking too many unconsidered decisions.

edit : some more info about the room :
the room is an attic, there are no parallel surfaces between the floor and the ceiling.
i don't record instruments in the room, but sometimes voice overs, late at night.
i'm not concerned about sound isolation.

[Ethan Winer]

You RT60 is fairly uniform over the entire range, except for the bass ringing that shows in the lowest frequencies. Carpet does absorb frequencies selectively, but you seem to have other stuff in the room balancing that out. So you probably don't need to remove the carpet, unless you want to for other reasons.

--Ethan

________________
The Acoustic Treatment Experts

[Rod Gervais]

Setting acoustics aside here for a moment...... if you want to change to a hard surface in your room - I would recommend removal of the carpet......

Carpet in not made to be used as a base for other products - it is meant to be (and requires) cleaning on a regular basis, and not just because we walk on it.

Carpet is actually a pretty good breeding ground for mites and mold, hiding it beneath a hardwood floor is not a real good idea.......

Rod Gervais
GIK Acoustics
Director of Education
GIK Acoustics. Acoustic Panels and Bass Traps. (USA)
GIK Europe, Bass Traps, Acoustic Panels (Europe)
Tel.(US)1.888.986.2789
Tel.(UK)+44(0)20.7558.8976

[Jens Eklund]

Based on your RT-values alone, there’s no need to remove the carpet but if you intend to add treatment (to address possible early reflections for example) you might reduce the decay time further and then you might (based on new measurements of course) want to add a wooden floor over the carpet. As you say, your biggest problem at the moment (as we know, an ETC and water fall graph might reveal more issues) is the long decay time in the lowest range. Some modal investigation and treatment would be useful but don’t forget to check the ETC as well.

Also check this post if you haven’t already:

http://www.gearslutz.com/board/6493935-post13.html

[neuro]

many thanks for your help.

other stuff in the room :
the room is wallpapered with some vinyl based material. the ceiling is covered with wood slats.
other than that, at the moment i have bags of fluffy stuff on the front wall (10kg/m3 fiberglass, 325x95x40cm), two broadband absorbers (50kg/m3 rockwool, 100x60x15cm) on the side walls, and a polyurethane couch (25kg/m3, 190x130x10cm) on the backwall.
i'm not sure what i'll replace the couch with. would the backwall be a right place for perforated panels, to reduce that decay in the lowest range ? wouldn't i still need absorbers there, for "early" reflections ?

i was thinking of removing the carpet mainly for hygienic reasons, so i will definitely try to follow your advice, Rod. i have no idea how i would unglue this though. perhaps with some deadly chemicals that will make me die ?

RT values are somewhat less constant than waterfalls and ETC. i mean, i can take several measurements at the exact same position and get almost exactly identical waterfalls and ETC, but quite different RT graphs. why is that ?

[SAC]

The reason? The RT60 calculation assumes something exists that does not - namely a reverberant soundfirld!

In a small acoustical space you are dealing with a space literally dominated by specular reflections which have a very real directional attribute.
In a statistically reverberant field (which the TE60 calculation presumes), this means that the reflective field is so diffuse that the arrival direction of the specular vector cannot be determined - that it is equally probable that the energy came from any and every direction simultaneously. Needless to say, such is not the case.

Reverberant soundfields and RT calculations make sense in spaces - large acoustical spaces - where such behavior exists.

[neuro]

does that mean these RT60 values are totally useless for measurements made in small rooms ?
i can see some correlation between (some of) these and waterfall or decay graphs. the rt60 graph "pattern" i posted is the one that i most often get in my measurements. and it looks sort of similar to my waterfall graphs.



btw, how would you name the soundfield found in a small space like a bedroom home studio, or a pro studio control room ?

[SAC]

The waterfall is NOT an 'RT' anything.

It displays persistence - and in this case, that persistence in the modal range of frequencies corresponding to the energy reinforced by modal resonance.

The soundfield is typical of that defined by a "small acoustical space"

It is a mix of modal behavior below the Schroeder (Davis) critical frequency and specular reflections above.

I might suggest that whatever you (and others) are reading that explains the behavior of the "reverberant" field and RT values in a small acoustical space - that you look for a more reliable source. Get a copy of the Davis and Patronis Sound System Engineering and READ chapters 6-9 - of which half are pictures. If you actually read it and have any questions you can PM me and I will clarify any point they raise that is not clear.

Oh, and Everest's MHOA is derivative from the material presented in this text - where you will also see where Everest literally sourced the vast majority of his illustrations and diagrams (he too attended and participated in the seminars!). So, if you understand this material, the rest is easy. Oh, and there is NO math of which you must be intimate - what is provided is simple algebra simply included to illustrate the sources of concepts that are completely described logically in words. So there is no excuse on anyone's part for not being intimate with this book. (And if you get the latest edition - you can ignore the chapter n Digital Signal Processing - which is (by definition) math because DSP IS mathematical processing.)

So no, no one can use the 'math excuse' as a legitimate excuse to avoid the book.

But you are forewarned - you do that and you will suddenly become aware that there are indeed some dumb questions.

But not to worry, as there are quite a few much more fascinating questions to be asked!

[neuro]

sorry for asking dumb questions, if that's what you implied.
if there was no ignorance, there wouldn't be any questions. wouldn't you miss a bit of fun ?
i didn't, and still don't, really understand the RT60 graphs in REW. i thought they displayed persistence of frequencies over time, just like watefall, decay, and spectrogram, but in a different, wronger, , and more cryptic way. i admit that doesn't make much sense so i must be missing something.
there is no such thing as reverberation in a small space. i get that.
i have a few books already, but i haven't managed to read them entirely, in an "organized" way, yet..
will try to get a copy of Sound System Engineering to add to my collection.. cheers

[DanDan]

The RT60 in REW is of course not RT60 for the reasons SAC stated.
There are other ways to refer to and calculate how sound sustains or decays in small rooms. None will be perfect because modes will interfere.
Despite the name used by REW, the decay calculation algorithm is remarkably sophisticated. A very useful measure IMHO, particularly the 1/3 octave variant.
Fuzzmeasure more appropriately calls their version EDT, T20, T30, and so on.
The recent versions include 1/3 octave also.
All good.
DD