"Acoustic Fields" on YT does the math

[kemmler3D]

I wasn't clear enough in my initial post.

• AF foam absorbers have similar performance to many other porous absorbers on the market (i.e., they are standard).
• AF bass traps are ineffective compared to other true bass trap products on the market, especially for the price (i.e., they are mediocre).
• AF diffusers have the following problems (i.e., their design is wrong):
  • Incorrect number of wells (the AF target is a prime number -1, giving you an even number) and are symmetrical, which aggravates lobing if you put them side-by-side on a wall (in correctly designed diffusers, which have odd numbers of wells and are asymmetrical, you set them against the wall by to mirror each other if using identical units, or you alternate and create a sort fractal pattern between units with different well amounts and sizes).
  • Foley recommends diffusion down to LF, but following the 3x lowest operational wavelength rule set by Cox and D'Antonio, this means their gigantic 17" deep 185Hz-3.5kHz QRD23 diffuser requires a minimum of 5.5m or 18'3" of distance to the listening position; diffusion is not recommended in LF because you are getting into the transitional/modal region, where the effects are not well understood; diffusion is very hard to measure, and all diffusers have a radiation pattern (similar to speakers), and Foley gives no measurements.
  • All diffusers absorb, and the deeper the wells the more unpredictable this becomes, and again no measurements are provided.

For what it's worth, I think diffusers are the most interesting and most complex acoustical technology.

Thanks, that all makes sense. I know enough about diffusers to know they can easily be designed wrong, (there are a lot of "diffusers" out there) so I appreciate your breaking it down about this specific case.

 

[alex-z]

If you to learn about room acoustics, I would strongly recommend Anthony Grimani, who did a video series with Audioholics. He has an excellent reputation in the high-end home theatre space, and while he does sell his own products, all of his advice is applicable even at the DIY level.

When it comes to acoustics, most of the math is easy, understanding what problems are audible and how to manage them cost effectively is the hard part.

 

[keenly]

They range from standard (foam), mediocre (bass traps) and wrong (diffusers). Usually expensive.

He has no formal background in acoustics. His videos are filled with misunderstanding.

He is the acoustic product equivalent of a self-taught boutique speaker manufacturer.

How many products absorb 30% AT 30HZ AND 100% at 50hz?

 

[keenly]

not quite. once you conned people, you are subject to more rigorous skeptics.
you seem to be his defender though

I Defend the idea that 30-300hz needs treating and most companies do not offer any products that do that, yeah sell 'bass traps'. Some that do like RPG have no youtube presence unfortunately.

 

[keenly]

Never mind, it is an important question, which materials suit best for low frequency absorption.

People measure the absorptivity (1 means 100% absorption) of all kinds of material like porous rubber or coconuts.

Let's check performance of tyical absorbers first:
I built some using homatherm flexCL cellulose, which is denser than glasswool or foam. Acoustic Fields/Dennis Foley use activated coal, which I had never considered.

There is a very good simulator on the net for diffuse sound http://www.acousticmodelling.com/8layers/porous.php.

Corner absorbers are different from wall absorbers, the best material depends on the absorber thickness: flexCL has a high flow resistivity 60000 kPa*s/m², so it works well on walls absorbers with ~100mm thickness, whereas in a corner with 400mm depth, foam with 10000 kPa*s/m² is more effective because sound is less reflected.
View attachment 296628
View attachment 296629

Now let's look at AF's ACDA panel. It's 200mm to 300mm thick for aroumd $1000 per panel, filled with activated carbon (which is used normally in air or water filters).
The hypothesis is that it's effective at low frequency, bc the carbon adsorbs air/gases/water and therefore has high flow resistance.

Low frequency sound propagation in activated carbon - PubMed

Activated carbon can adsorb and desorb gas molecules onto and off its surface. Research has examined whether this sorption affects low frequency sound waves, with pressures typical of audible sound, interacting with granular activated carbon. Impedance tube measurements were undertaken examining...

pubmed.ncbi.nlm.nih.gov

BTW if this is the case, it would work best in dry air below 60% humidity.

And yes, there is research that activated carbon indeed does absorb low frequencies:

https://www.researchgate.net/profile/Trevor-Cox/publication/5327159_Enhancing_bass_absorbers_using_activated_carbon/links/5a2192b54585155dd41aa5e2/Enhancing-bass-absorbers-using-activated-carbon.pdf

So how much does carbon actually improve? Marin/Arenas in 2019 compared fiberglass and carbon and it showed a 2.5x improvement at low frequencies inside a resonator:

View attachment 296632

And Travenas showed, that different porosity of the carbon pellets can change the result slightly.

So Acoustic Fields' claim could be scientifically legit and the images in the video could be real. Active Carbon pellets can absorb more at low frequencies in dry air. And with less impact on high frequencies in the room. If this is due to porousity or adsorption is not 100% clear, but doesn't really matter.

How much is it DIY?
If you want to build one, you can order a ton of activated carbon on Alibaba for $1000 and build 8 ACDA10". Or use the rest in your Britta water filter

Data on the acoustic performance:
Acoustic Fields provides a Riverbank lab measurement. It shows 33% of absorption for the 200mm panel at 33 to 50Hz, compared to my simulated 25% of cellulose of same thickness.
Above 65Hz absorption drops to 13%. So ACDA helps for deepest modes only.
Above 1kHz a normal porous absorber would be >90%, where ACDA would be still 13%.

Summary: this corresponds to a deep bass trap: you can filter out lowest modes without impacting high frequencies. You can add a foam in front of it to absorb high frequencies as well. Interesting stuff, but too expensive vs my cellulose DIY solution.
Realistically, you need at least one wall of absorbers, so about 8 panels for $8400 and a ton of weight to carry.

Good post, but the carbon used IS NOT the same as in filters for air purifiers and fish tanks.

 

[NTK]

How many products absorb 30% AT 30HZ AND 100% at 50hz?

Acoustics Fields only asks for a mere $750 for something like this. (And I'd trust BBC's measurements much more than Acoustic Fields'.)

The design of a modular sound absorber for very low frequencies

The design of a modular sound absorber for very low frequencies.

www.bbc.co.uk

 

[fpitas]

Business might be better if he didn't look like he was coming off a two-week bender. Just saying.

 

[AdamG]

I have a story about his company that I would like to share that way you can see how he really was.

About 2 years ago during the pandemic I picked up the hobby. I had a lot of free time on my hands, lol. I think we all did. I was interested in getting my home office treated for better sound.

I filled out the form and he called me about 3 days later. He was very arrogant. His requirements for a room are ridiculous. He complained I had windows. He complained I had hard wood floors. He complained I had sheetrock. He complained I had a closet. He even complained I had a door. I kid you not. Said I needed a sealed door like in the movies so it mounts flush with the room and you cant find your way out lol.

He told me my room is too small for even decent sound and that nothing will make it sound good.

Truthfully, I was devastated and insulted by his comments. He is beyond crass and his products were stupid overpriced.

I ended up contacting GIK Acoustics and I ended up having the exact opposite experience. The sales rep asked for layout of the room, asked for measurements (if I could). I must have sent him 30 measurements. Some single point, others RTA. Then finally he came up with 3 packages for me. Good, better and best. He was very clear with the expectations and I had told him I had an awful issue at 200-300 hz. He made it a priority based on speaker position, etc to target that. He spent a lot of time going over things with me. I was very, very impressed.

I could have built the traps myself and for half the cost, but honestly, after all the help he gave me I went with the middle of the road package. His time was more valuable and he put in a lot of effort for the customer with no expectations of a sale. In the end, the difference between the untreated and treated room is stark. And even though I could build these traps myself even more so today then back then, I would certainly give them another go if the level of service was still the same.

I had a similar experience with him. I had a phone conference with him about my room. Leaving out lots of details because of trying to be brief. After discussing the room dimensions and arrangement he said that he could fix 70% of the problems and it would only cost between $120 to $180 Thousand dollars. He was pleasant with me but definitely barking up the wrong tree. I almost fell out of my chair when he quoted the cost. I think his primary customer is high end customers and professional studios. The things he suggested for my room would come with a built in Coffin for my Wife to bury me in. This was about 10 years ago, with inflation I would say his quote would be at or above the $200k range. This is just for room treatments.

 

[keenly]

Acoustics Fields only asks for a mere $750 for something like this. (And I'd trust BBC's measurements much more than Acoustic Fields'.)
View attachment 296770

The design of a modular sound absorber for very low frequencies

The design of a modular sound absorber for very low frequencies.

www.bbc.co.uk

Where can I buy these then?

 

[NTK]

Where can I buy these then?

Your money, your decision. I also sense there is a lack of creative thinking skill.

 

[krabapple]

I Defend the idea that 30-300hz needs treating and most companies do not offer any products that do that, yeah sell 'bass traps'. Some that do like RPG have no youtube presence unfortunately.

The modal frequencies need careful subwoofer placement , and DSP EQ, more than they need 'bass traps'.

 

[Andysu]

I had a similar experience with him. I had a phone conference with him about my room. Leaving out lots of details because of trying to be brief. After discussing the room dimensions and arrangement he said that he could fix 70% of the problems and it would only cost between $120 to $180 Thousand dollars. He was pleasant with me but definitely barking up the wrong tree. I almost fell out of my chair when he quoted the cost. I think his primary customer is high end customers and professional studios. The things he suggested for my room would come with a built in Coffin for my Wife to bury me in. This was about 10 years ago, with inflation I would say his quote would be at or above the $200k range. This is just for room treatments.

you should have told him , 200k

 

[Andysu]

his thumbnails i have to say , load of clickbait , sick of seeing that blackboard

 

[keenly]

I had a similar experience with him. I had a phone conference with him about my room. Leaving out lots of details because of trying to be brief. After discussing the room dimensions and arrangement he said that he could fix 70% of the problems and it would only cost between $120 to $180 Thousand dollars. He was pleasant with me but definitely barking up the wrong tree. I almost fell out of my chair when he quoted the cost. I think his primary customer is high end customers and professional studios. The things he suggested for my room would come with a built in Coffin for my Wife to bury me in. This was about 10 years ago, with inflation I would say his quote would be at or above the $200k range. This is just for room treatments.

My assessment was only 22K LOL.

Too be honest RPG or Artnovion are better, but the later is far more expensive than Acoustic fields.

 

[keenly]

The modal frequencies need careful subwoofer placement , and DSP EQ, more than they need 'bass traps'.

For one spot to sound great? How about the WHOLE ROOM. That takes a lot of treatment.

 

[dasdoing]

I think his primary customer is high end customers and professional studios.

I mean, Capital Records? https://www.acousticfields.com/capitol-records/
personally I wouldn't even ask someone like that for a personal project lol

 

[AdamG]

I mean, Capital Records? https://www.acousticfields.com/capitol-records/
personally I wouldn't even ask someone like that for a personal project lol

I don’t know that at the time.

 

[René - Acculution.com]

After reading the comments, I realized that I took the bait. I mentioned that I just stumbled upon his stuff today... so I posted here to see it in an objective light. Now I do. That's why I hang out with you guys. You didn't think it was for your personalities... lol.

Edit: I took the bait by spending 20 minutes watching his vid, not a cent on his "stuff"... I spit out the bait after reading what you guys had to say.

Do not watch for learning anything technical. It is one of the worst channels for that with inconsistencies and made up theory every few seconds. Absolute garbage. However, the products might be fine.

 

[krabapple]

For one spot to sound great? How about the WHOLE ROOM. That takes a lot of treatment.

You don't need 'great sound' in the WHOLE ROOM. You need it where the seats are.

For that, might I suggest exploring the literature on multi-sub use in listening rooms?

 

[ozzy9832001]

I had a similar experience with him. I had a phone conference with him about my room. Leaving out lots of details because of trying to be brief. After discussing the room dimensions and arrangement he said that he could fix 70% of the problems and it would only cost between $120 to $180 Thousand dollars. He was pleasant with me but definitely barking up the wrong tree. I almost fell out of my chair when he quoted the cost. I think his primary customer is high end customers and professional studios. The things he suggested for my room would come with a built in Coffin for my Wife to bury me in. This was about 10 years ago, with inflation I would say his quote would be at or above the $200k range. This is just for room treatments.

You could build an extension to your house for that, lol.