In some threads i came across the Invisible Alpha, but i can't find information about this system. Who can tell me more about this system?

Thanks,

Peter

Invisible Alpha© is an adjective I coined to make the use of sound absorption of walls and other partitions as integral part of the room acoustics design sound more fancy, mysterious, high tech and a great marketing/sales tool.

In its basic form Invisible Alpha© refers to the low frequency absorption component of a an apparent wall or other hidden absorber. To a layman, a wall is a wall. The layman does not recognize the acoustic effects of the surface. As an example, 100 mm of 703 or equivalent material against a wall with a ~80 Hz mam resonance would have great absorption down to ~63 Hz. The low end absorption is invisible to the lay person.

Another example of partion absorption not being visible is the panel absorbers pioneered by Hidley and championed by Newell. A quote from Newell in Recordng Studio Design is in post #42 in this thread. Even with panel absorbers 1 m deep membrane (Invisible Alpha©) absorbers are used the behind the panels for lowest frequency absorption.

Post #127 in this thread, is the first time I used Invisible Alpha©.
The Alpha comes from Greek letter used to denote some forms absorption of materials.

Some time after the I first used Invisible Alpha©, some discussions came about regarding getting even lower (frequency) absorption. I brought up the concept of using a triple leaf partition tuned to cover a wider deeper range of frequencies. Because the partition would use 2 air gaps (and I was having lots of with Invisible Alpha©), I decided to call that design strategy Invisible Alpha²©. In addition to appearing even more techy, fancy (dare I write it) sexy (well at least to acoustic geeks), and market savvy, it also challenges people to use character map even more. The dollar/euro/pound value is obvious if a cost analysis is done.

Invisible, sexy and cheap,
Andre

Thanks Andre for the explanation!! I'm wondering why it isn't more discussed in the forum. It sounds like the perfect solution for small room in a room home studio's!

I hope I understand it good, when i build a mam wall inside my room cover the wall facing the room with 100 mm of 703 or equivalent material and my mam resonance is in this case 36 hz and 57, it will trap all the low ends in the room. Without losing a lot of space!


Do you need further basstraps in the room with the Invisible Alpha walls? I'm thinking loud, you can even treat the ceiling with this system.

I start to think that the Invisble Alpha = Zero Reflection from delta H....

Do you put some slats on the invisible alpha to keep some lively in the room?

Thanks again for the explanation!!

Best regards,

Peter

Peter,

Yes. You will need much more trapping in the room. The problem with using the wall resonance and the invisible trapping you get from them in a small room, is that the trapping of this type of system often falls within the pressure zone.

- The Invisible Alpha is the walls. Invisible Alpha does not 'deaden' the room. It is strictly LF. You will have to treat walls and trap corners still. And yes, slats (in the right places) will help to keep some life in the room.

Cheers,
John

Andre, I beg you to write a paper with more comprehensive information for morons like me. Some Excel calculators, and some indicators on how to use this in the real world would be great. If this were an AES paper, I'd be happy to spend the $20 they ask of non members. Likewise, if it were an independent paper by Andre Vare

I know that this information is available across various texts, but it would be great to have it simplified and made specifically contextual to audio studios. I believe that this, and the VPR traps G.E. is working on, can change the quality of DIY studio building.

For example - In the attached pic from an online calculator (I have kept the material thicknesses constant and chosen an arbitrary mass of 700 Kg/m3) - the resonance frequency differs significantly, based on the angle of incidence. How does this relate to the pressure zone (which is not directional?), and how would this work in a relatively small studio?

You are welcome. The lack of discussion is one of the reasons for coining Invisible Apha©. My guess is that making, or recognizing aborption built right into a room is not sexy. Also, it involves the foour letter word M-A-T-H. Teh latter is something that seems to avaoided at all costs by way too many people.

Lots in that. The low frequecny absorption will be dependent on the construction of the partition. A triple layer, or Invisible Alpha²© partition's
peaks are calculated using a quadratic equation. The 2 air springs interact with each other through the common middle mass. For smooth absorption, the low frequency absorption of the porous material has to be selected together with the mam resonance to overlap providing smooth absorption over the frequency range.

It all depends on the room. Yes, you can do ceilings. That is why my first description of Invisible Apha© used the wording "walls and other partitions". A relatively full definition is this:

Who knows. It is possible. It has been years the claim of patent pending was first used on their website.

Uh, yes. Invisible Alpha© is a fun phrase to add emphasis, mystery, good dressing, and sexiness to standard practice amongst professional acousticians to using what is in a room when designing the room acoutics. Uh, thes absorption characteristics for partitions are reflective at low mid frequencuenciews and higher. I do not understand why your question.
You are welcome.

Invisibly, but still sexy,
Andre

I have been sitting on this for several hours. I am still not clear on what you are refering to. The following paragraphs are drawn out to explain to other readers what we are talking about.

The pressure zone is the frequency below which a space does not have reinforcement of of sound. A goos example of a space with a high frequency for termination of the pressure zone is a car. Low frequencies are heard, but require a lot of power.

Assume a normal room, as in height is the shortest dimension, with a usual height of 8 feet. The lowest mode in the vertical dimension, which is the highest mode in the room, is 80 Hz. All other modes will be lower than that, which means the pressure zone is below that freqency also. Looking at IR 761 and the first 30 pages of TL data (pdf pages 21-50), only 2 of the partitons do not have mam frequencies in the 100-160 Hz range. A hint to make this analysis easy is to setup Acrobat Reader to show in full page size and then page down and up to see the differences in the TL curves and mam frequency. Looking at partitions with one leaf concrete IR 586 fig 3 shows mam resonances from 80-125 Hz.

Working usual construction methods as the start, where is there problem that I think you are refering to in the quoted text?

Visible and confused,
Andre

Thank you for the compliment. Unfortunately I have a previous commitment to write an article about gas flow resistivity (It is not forgotten DanDan).

Total agreement in the sense of straightforward and obvious use of acoustical engineering.

[quote] For example - In the attached pic from an online calculator (I have kept the material thicknesses constant and chosen an arbitrary mass of 700 Kg/m3) - the resonance frequency differs significantly, based on the angle of incidence. How does this relate to the pressure zone (which is not directional?), and how would this work in a relatively small studio?[/quoteNice capture. What is the link to the calculator?

Yes, varies with angle of incidence. In small room acousitcs, which is what studios we discuss here are, the interest is normal incidence for modes. As I type this, John has not yet explained his pressure zone qualifier.

Honoured,
Andre

Sorry, the calculator is not online... just found somewhere online, don't know where... it was in my computer, please find attached.

Thanks. Wow! I just recognized the colour scheme and format. It is by Eric Desart. Fantastic!

I guess we are waiting for John's pressure zone point to be explained before we have any more discussion.

Ecstaticaly,
Andre

so possible formations like:

m-s-m-s-m
m-s-m-S-M
m-s-M-S-M
m-S-M-s-M
M-S-m-s-m
m-S-M-s-M
M-S-M-S-M
etc

could all have different characteristics and the inner (left hand) mass could be panel, slat, etc absorption characteristics where the right hand may tend to be either another room or the exterior portion of the isolation space.

(where m = mass, s = spring and the M is the heavier/denser mass layer, and S is the larger or softer spring (and spring potentially is not just air...))

hmmmm... truly hakko... 第 8 回光

MSMresonance03.xls - File Shared from Box.net - Free Online File Storage And yes indeed, it is made by eric desart. Btw, does anybody know if this spreadsheet is with or without isolation?

Gulfo, you are discribing the invisible alpha2.

The bases invisible alpha is M-S-M-S, Am I correct?

Best regards,

Peter

for the final S to be a spring you need one (1) more mass layer or the triple leaf which is what Andre is referring to. the absorption characteristic of the assembly having varying coincidence to provide continuous and even absorption while attenuating enough for the isolation goals. we see this a lot in terms of membrane and slat absorbers but Andre is taking this to the room level where the decoupled masses of the boundary function as part of the absorption as well as isolation. he has coined a nice name for which i think it requires any one mentioning/using it to pay him a quarter... heh

In post 2 Avere wrote this:

In its basic form Invisible Alpha© refers to the low frequency absorption component of a an apparent wall or other hidden absorber. To a layman, a wall is a wall. The layman does not recognize the acoustic effects of the surface. As an example, 100 mm of 703 or equivalent material against a wall with a ~80 Hz mam resonance would have great absorption down to ~63 Hz. The low end absorption is invisible to the lay person.

I read this as M-A-M+100mm 703, I hope i'm right

Maybe some drawings/pictures will make things clear.

Best regards,

Peter

Yes, you are correct in your analysis of that particular example of the use of Invisible Alpha©.

Correctly,
Andre

Pffff, i'm happy , to read that I understand it good. It will be a great for my small studio.

Can you put different kinds of glasswool/rockwool together on the same wall? Vary with airflow recistance of the types of wool, say a softer kind(rw2) on the first reflectionpoints?

BTW I found this picture on the site from Delta H Design: Delta H Design ~ Acoustics + Studio Design: Pagewood Studios, Music and Film Production, Sydney Australia, ZR Acoustics, Trasnparent Acoustics, DHDI.

Best regards,

Peter

Sorry for the delay.. I've been so busy.
That is exactly what I was referring to for a small room. (above)
For example: H=8.2', W=11.4', D=9.4 will have a modal region from 50Hz to 240Hz if the treatment brings the decay down to 0.4 Sec. This means that below 50Hz there is no modal support and like the car, need a lot of power to be heard at the same level as the supported frequencies. - And that calculation is for concrete walls...

There is NO problem.. just a 'figure of speech' as it seemed like Peter did not understand and was not going to trap his room.

Cheers,
John

There is no advanatge to mixing densities in studios.

ZR Acousitcs has been an unknown. For all the years that there has purportedly a patent pending, the patent would have been granted, or refused by this time. Who knows what is going them?

Andre

Here are the walls of my studio:

From inside the control room to outside (right to left).

1-Slats
2-Fabric
3- 3" roxul
4-Chicken wire (to keep the roxul off the membrane)
5-3/4 blocking (to fasten the chicken wire)
6-1lbs/sqf MLV stapled and sealed to the 2X4 framing
7-2X4 framing with fluffy in the cavity (fluffy not touching the mlv also)
8-5/8 Drywall
9-Green Glue
10-5/8 Drywall

The MLV makes a membrane absorber with a center frequency around 90 hertz. Above is dealt with by means of the porous/velocity layer placed in front and the double drywall (back) takes care of the lowest frequencies.

Somewhat time consuming but pretty cheap to build ...

The whole thing is a variation on a Newell concept expressed in chapter 5.8 (small and neutral).

This system also serves as the isolation envelope ... as after the drywall you have a foot of airpsace and then the concrete foundation walls.

Thanks for the picture, I just ordered the Newell's book:-)

But what is 1lbs/sqf MLV?


Best regards,

Peter

This.

or this.

Is there a sealed airspace between the drywall-green glue sandwich and the outer shell wall, or is the room sitting in there like a portable telephone booth? If the latter is the case, is the membrane absorption by the drywall sandwich still effective? My understanding is that there has to be a sealed airspace.

Thanks,

The room is sitting in there like a telephone booth.

The room IS sealed at the drywall layer all around. Each layer is sealed with a backer rod and caulk (2 seals total for the walls).

When assembling the membrane portion I went like this:

I'm standing in front of the 2X4 framing which has drywall to its back:

1-Run a bead of caulk all around the 24" cavity (or 16 depends how you frame) It connects the 2X4 to the drywall.

2-Run a bead of caulk on the face of the 2X4 framing

3-Fill the cavity with light fluffy that is shallower than the depht of the 2X4 assembly (aim for 3" as a 2X4 is 3 1/2")

4-Hang a piece of MLV over the frame and staple tightly all around.

5-Test your seal, form your hand in a fist an press against the MLV if the seal is not happening you'll hear air coming out. Run your free hand around the perimeter ... you'll feel air coming out where it leaks. Add caulk ...

Once it works you'll push the MLV and feel the resistance ... no air coming out. That means your spring (air) is in place.

6- Add 1 1/2" wide rips of 3/4 ply to the top and bottom plate and fasten chicken wire to that.

7-Start building the frame that holds the roxul and serves to staple the fabric in front of that.

Avare wrote in the link in 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!

With the porius absorber calculator and 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)

At which frequency starts the invisble alpha to work in this case? Will there be a dip between the 703 and and the invisible alpha?

And if the mam frequency is for example 70 hz can I use 40/56*70 to get an indication?

Best regards,

Peter