Are GIK Acoustic's Sound Blocks really a revolutionary concept?

[sarumbear]

Dear members, I am acoustician and whenever I see a product that is designed to treat a room, I check its specs. The company GIK Acoustics is a well known supplier of acoustic treatment materials. I recently saw one of their ad for Sound Block series of absorbers. This is what they say on the website (emphasis mine).

Sound Blocks are a revolutionary concept in the GIK Acoustics product line, establishing a new benchmark in performance and flexibility for high-end audio rooms that need world-class performance.

Each Block is 60cm x 60cm x 25cm deep. They can be mounted on the wall like normal acoustic panels, or they can be interlocked together with rails to make large, freestanding arrays to precisely fit your space as a false wall. Because they are so thick, these are powerhouse broadband bass traps with great performance still active below 50Hz, in all configurations.

They advertise this panel as a "broadband bass trap" and declare that it is active even below 50Hz. How? Their own charts show that below 60Hz, there is sharp drop in efficiency. Besides, the wavelength of 50Hz is 6.8m how can a 25cm panel absorb that wave?

The sound absorption coefficient is the ratio of absorbed energy to incident energy. If the acoustic energy can be absorbed entirely, then α = 1. How can it be above 1 then? A higher value than 1 means the panel is generating sound! (I do know that often measurement create errors around the knee frequency but here the difference is up to 22% across ten octaves.) Also, why is there a discrepancy in the coefficient value between the charts. All measurements are stated as random incidence measurements. How do they then differ up to 22%?

Meanwhile, they link to a test of one of their panels. The panel is simply referred to “242” and doesn’t match any products on the website as far as I can see. It is however about a panel that is 600 x 1200 x 74mm deep. About three times deeper than the panel in subject. The chart from the test shows that the panel stops being effective below around 160Hz and its coefficient is 0.05 at 50Hz. In other words it absorbs just 5% of the energy. (Note the measurement error around 500Hz I mentioned earlier.) Why are the tests I linked above are not following the expected behaviour? And if they are tested why not show the actual tests?

All of this makes me not to trust anything GK ACOUSTICS are selling. I wanted to show you the data that formed my reasoning for you to make up your mind.

 

[Eetu]

They vaguely mention they have some tests done according to "Annex b of bs en iso 354:2003" which probably means at least some of the tests are with a large airgap behind.

The "242" refers to their 242 panel. They mention it's 67mm thick so not sure if the 74mm includes some sort of mounting mechanism.

 

[sarumbear]

They vaguely mention they have some tests done according to "Annex b of bs en iso 354:2003" which probably means at least some of the tests are with a large airgap behind.

The "242" refers to their 242 panel. They mention it's 67mm thick so not sure if the 74mm includes some sort of mounting mechanism.

The page for 242 is what you expect a panel with such dimensions will perform. They also linked to the test document which is good. If you understand how to present your products why not do the same for all of them? Especially when you are boasting physics defying values?

 

[Kal Rubinson]

The panel is simply referred to “242” and doesn’t match any products on the website as far as I can see. It is however about a panel that is 600 x 1200 x 74mm deep. About three times deeper than the panel in subject.

???? The quote above this statement says "Each Block is 60cm x 60cm x 25cm deep."

I see a difference in the units of measure indicating that the tested panel is less than 1/3 as deep as the one in the title.

 

[sarumbear]

???? The quote above this statement says "Each Block is 60cm x 60cm x 25cm deep."

I see a difference in the units of measure.

It is indeed careless of me. Thank you for pointing out my mistake. However, this doesn't alter the points I made.

• Why the coefficient values are wildly different between charts?
• Why the coefficient values are above 1 all the way through ten octave?
• How can an absorber as deep as at 1/30th of the wavelength have "great performance still active below 50Hz"?
• Not to mention that it is advertised as a "broadband bass trap."

 

[Bjorn]

It's based on random incidence absorption coefficient which is not valid in a small rooms. Besides, I don't know for sure if the room at Salford is large enough to achieve a true reverberation. Haven't seen how large the room is.

A coefficient above 1 is common primarily due to diffraction issues from the material.

The absorber seems like it's simply made out of loose porous material. If so, with 25 cm thickness, it will not be very efficient this low in small rooms and obviously one needs to use many to cover a large surface to achieve efficiency below 100 Hz.

But I'm sure they will sell well.

 

[sarumbear]

It's based on random incidence absorption coefficient which is not valid in a small rooms.

True but all three set of values are for the same type. Why the discrepancy?

Besides, I don't know for sure if the room at Salford is large enough to achieve a true reverberation. Haven't seen how large the room is.

We don’t know if the subject product’s measurements were done at Salford. The measurements I linked is not from the subject product.

A coefficient above 1 is common primarily due to diffraction issues from the material.

All through ten octaves?

The absorber seems like it's simply made out of loose porous material. If so, with 25 cm thickness, it will not be very efficient this low in small rooms and obviously one needs to use many to cover a large surface to achieve efficiency below 100 Hz.

I’m glad that you agree.

But I'm sure they will sell well.

That is the problem. Show them some numbers, mention a university and sell them bucketloads of it…

 

[Inner Space]

The sound absorption coefficient is the ratio of absorbed energy to incident energy. If the acoustic energy can be absorbed entirely, then α = 1. How can it be above 1 then?

This is a common anomaly with reported absorption. It's because the test is actually conducted as a reflection test. Sound of known intensity is directed at a defined surface area of material, say 1 sq meter, measured in two dimensions. The reflection back is measured and subtracted from the original and the difference is assumed to have been absorbed. This ratio becomes the coefficient.

But the material will inevitably have 3 dimensions, not 2, and the absorption via the third dimension (the edges of whatever depth) are expressed as part of the 2-D surface's absorption, hence often giving values greater than one.

 

[sarumbear]

This is a common anomaly with reported absorption. It's because the test is actually conducted as a reflection test. Sound of known intensity is directed at a defined surface area of material, say 1 sq meter, measured in two dimensions. The reflection back is measured and subtracted from the original and the difference is assumed to have been absorbed. This ratio becomes the coefficient.

But the material will inevitably have 3 dimensions, not 2, and the absorption via the third dimension (the edges of whatever depth) are expressed as part of the 2-D surface's absorption, hence often giving values greater than one.

As I said in my post I realise that. However, the measurement error is frequency dependant. You don’t get an error through a ten octave range.

Besides, why the measurement set don’t agree?

 

[Bjorn]

Bottom line is that these type of measurements and today's measuring standards are simply inadequate. This is also why RPG acoustics uses an impredance tube to meausure low frequencies.

Read about diffraction effects by Ron Sauro here:

https://nwaalabs.ipower.com/Files/NWAA%20Labs/Measuring%20Absorption,%20Bad%20Methods%20and%20Worse%20Assumptions.pdf

Ron's conclusion is the following:

The author now thinks that “Absorption Coefficients” that are calculated using the methods recommended in ASTM-C423 and ISO-354 and ISO17497-1 may be inaccurate at best.

 

[sarumbear]

Bottom line is that these type of measurements and today's measuring standards are simply inadequate. This is also why RPG acoustics uses an impredance tube to meausure low frequencies.

Read about diffraction effects by Ron Sauro here:

https://nwaalabs.ipower.com/Files/NWAA%20Labs/Measuring%20Absorption,%20Bad%20Methods%20and%20Worse%20Assumptions.pdf

Ron's conclusion is the following:

Agree 100%. That’s why I said:

All of this makes me not to trust anything GK ACOUSTICS are selling.

 

[Bjorn]

Simple marketing works better than honest information unfortunately.

Take for instance the typical scattering units that many sell today. Do we want to scatter the sound in an uneven fashion with polar lobing if we don't want to absorb the sound? Absolutely not. Even distribution of sound (=quality diffusion) should be the goal then. Something most so called diffusers don't achieve at all.

 

[abdo123]

There could be a tuned membrane in there around 80Hz. that's what the data suggest anyway. I have seen this with other companies.

 

[abdo123]

Something most so called diffusers don't achieve at all.

Outside dedicated audio palaces (calling them rooms or cinemas would be an understatement at this point) this is really not feasible at all though.

it's not a lack of engineering, but rather lack of demand for something that needs to be handmade (expensive) and extends 50 to 100 cm from the wall.

 

[sarumbear]

There could be a tuned membrane in there around 80Hz. that's what the data suggest anyway. I have seen this with other companies.

View attachment 246515

and that satisfies "broadband bass traps with great performance still active below 50Hz" how?

 

[sarumbear]

it's not a lack of engineering, but rather lack of demand for something that needs to be handmade (expensive) and extends 50 to 100 cm from the wall.

You are exaggerating. You do not need diffusion below frequencies whose wavelength are longer than the room dimensions.

 

[sarumbear]

Outside dedicated audio palaces (calling them rooms or cinemas would be an understatement at this point) this is really not feasible at all though.

All acoustic treatment for low frequencies are bulky and not at all suitable for a domestic living room. What is your point? We are discussing the situations where people use them.

 

[abdo123]

and that satisfies "broadband bass traps with great performance still active below 50Hz" how?

Yeah that's probably poppycock.

You are exaggerating. You do not need diffusion below frequencies whose wavelength are longer than the room dimensions.

broadband diffusion requires space and time to build, there is no argument about that. @Bjorn was specifically talking about broadband even diffusion.

 

[sarumbear]

@Bjorn was specifically talking about broadband even diffusion.

Well, the top eight octave range is pretty broadband and that is where the ear is sensitive to the direction of the sound waves. and when walls becomes reflective. The bottom two octave range is perceived non directionally, hence no there is not much benefit from dispersion.

 

[Bjorn]

I haven't said anything about diffusion in the lows. That's not needed. You have misunderstood abdo123.