Some more questions about Invisible Alpha

[petertjed]

A view months back I started this thread: Invisible Alpha

After reading Recording Studio Design in which P. Newell describes in chapter 5.3.4 and in figure 5.1 Acoustic control wall a version of Invisble Alpha which will be effective from 30hz to about 250hz. It uses a pkb2 which is about 5 kg/m2.

In the linked thread Avare describes an invisble alpha:

" post 2, the link 127 that: Build the booundary to have a MAM frequency coinciding with 56 Hz and cover with 100 mm of porous absorber. Good absorption down to 40 Hz! "

I calculated with the porius absorber calculator that incase of 23000 pa sm2 (703) the absorption is 0.4 at 100hz,almost 0.8 at 200 hz and at 300hz and higher about 0.9. (random incidence, komatsu 2008)

Does the Invisble Alpha described by Avare has the same range of absorption( 40 hz- 250hz) or does it go up because of the absorbtion of the 10 cm OC703 which is about 0.9 at 300hz and higher?

Which of these forms of invisble is the best in a small room, in which the walls have a mam frequency of about 50hz?

I'm looking forward for your answers,

Best regards,

Peter

[petertjed]

Please, does anybody experience with both forms of Invisible Alpha?

Best regards,

Peter

[DanDan]

Timezones, I'm still up! I'm sure Andre won't mind.
Invisible Alpha is said with a tongue firmly in cheek. However it is a very genuine reference to a free lunch. i.e. Using what is going to be there anyway, e.g. plasterboard or other panel boundaries, creatively. Look further at Newells reference to the thin skin of a mobile truck as a 'limp bag' in terms of LF.
Look also at Jeff Hedbacks award winning design which uses incorporates simple stud wall partitions. Play some bass in a stud partitoned room, place your hand on the plasterboard, hey, we can use this....
This can go much further with the use of semi rigid layers which semi act as panels. Homatherm. Actis.
DD

[avare]

My apologies for my delay. Dan's summary of Invisible Alpha© is spot on.

Originally Posted by petertjed

I calculated with the porius absorber calculator that incase of 23000 pa sm2 (703) the absorption is 0.4 at 100hz,almost 0.8 at 200 hz and at 300hz and higher about 0.9. (random incidence, komatsu 2008)

Does the Invisble Alpha described by Avare has the same range of absorption( 40 hz- 250hz) or does it go up because of the absorbtion of the 10 cm OC703 which is about 0.9 at 300hz and higher?

The absorbent material increases the absorption. AT higher frequencies it is the exclusive source of absorption.

Which of these forms of invisble is the best in a small room, in which the walls have a mam frequency of about 50hz?

It is not a question of which si best, but determining what is needed in the room and then designing the absorption for that.

I hope this helps.

Not invisibly, but delayed,
Andre

[petertjed]

Thanks for the answers and my impatience;-)

Maby I asked the question wrong, English is not my first language ( I'm Dutch). I'm trying to learn, i read the books Recording Studio Design and build it like the pro's. Can you recomend books which discribes more about the invisible alpha?

What I meant with what is the best, which of both forms does the broadest range of absorbtion in the low regions(30hz, 50hz, 60 hz and up till?), will the backwall covered with invisble alpha(10cm oc703) work as adequate as say 50/60cm glasswol. Is this a full range basstrap? This will save a lot of space.

I'm building a small bedroom studio: 2.42h, 3.42 w, 5.10l, i used hunecke.de | Room Eigenmodes Calculator to calculate the modes and the pressure on the walls.

I found this thread over Jeff Hedback: Jeff Hedback designed acoustical panels Am I correct that in picture 2 the mlv is covering a "hole in the wall"

I will read the Newells reference to the thin skin of a mobile truck again!

Thanks and best regards,

Peter