"Acoustic Fields" on YT does the math

[Astoneroad]

I just stumbled upon this guy today, although he's been around for a long time. This is his most recent vid. I know that he's selling a product, but he appears to understand the math and physics of room acoustics and how his products work within the numbers. I watched several of his vids in succession and seems sound and rational. I'm sure a lot of you guys are familiar with him, any thoughts? From my non tech perspective this doesn't seem like snake oil... unless it's buried in the science that is proposed I guess.

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[Somafunk]

He’s a con artist with previous convictions

 

[Astoneroad]

Do tell.

 

[delta76]

Do tell.

Dennis Foley ... "measure, measure, measure "... !

I discovered Dennis Foley yesterday for the first time. I just love his way to kill all BS on the internet about acoustic treatment. He has the ASR mindset. One of his many videos : / Bo Thunér

www.audiosciencereview.com

 

[keenly]

He’s a con artist with previous convictions

His products are great, and his youtube vids are the best. Stop judging people on their pasts.

 

[delta76]

His products are great, and his youtube vids are the best. Stop judging people on their pasts.

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

 

[anotherhobby]

https://inmatedatasearch.azcorrections.gov/PrintInmate.aspx?ID=149184

 

[ozzy9832001]

He knows enough to sell a product. He often contradicts himself and most of his videos are repetitive.

If you listen to him, you can't have doors, windows, closets, furniture or anything else in the room. Multi subs are bad. Acoustic panels are bad. Mineral wool/any other insulation are bad. Everything except what he sells is bad. No science, no tests, no data. Just his uninformed opinion. He'll often quote how he's done hundreds of rooms.

There are so many variables for each room even having the same dimensions you'd have to do hundreds just to get all the variables down.

While I don't think he's a con...as I said, he knows enough to sell a product. Nothing more, nothing less.

 

[sarumbear]

I just stumbled upon this guy today, although he's been around for a long time. This is his most recent vid. I know that he's selling a product, but he appears to understand the math and physics of room acoustics and how his products work within the numbers. I watched several of his vids in succession and seems sound and rational. I'm sure a lot of you guys are familiar with him, any thoughts? From my non tech perspective this doesn't seem like snake oil... unless it's buried in the science that is proposed I guess.

I want to comment on your views about the person. Why do you think his videos are “sound and rational.” You say you are not technical, hence shouldn’t know anything about acoustics, which is a very niche discipline anyway. How can you than think that he “appears to understand the math and physics of room acoustics and how his products work within the numbers”? Is that because he is a good orator? Every con artist is believable. That’s why they can con. How can you know if this guy is not one?

 

[Astoneroad]

I want to comment on your views about the person. Why do you think his videos are “sound and rational.” You say you are not technical, hence shouldn’t know anything about acoustics, which is a very niche discipline anyway. How can you then think that he “appears to understand the math and physics of room acoustics and how his products work within the numbers”? Is that because he is a good orator? Every con artist is believable. That’s why they can con. How can you know if this guy is not one?

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.

 

[Curvature]

His products are great

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.

 

[Curvature]

your personalities

We are winning all the charisma contests.

 

[Astoneroad]

We are winning all the charisma contests.

Absolutely... just ask Danny in Texas.

 

[ozzy9832001]

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.

 

[kemmler3D]

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

Curious why you would call diffusers "wrong"? Aren't they helpful if you have echo or too much early reflection?

 

[sweetsounds]

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.

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.

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:

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.

 

[kemmler3D]

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 to coconuts.

Let's check performance of tyical absorbers first:
I built some using 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 thivkness: 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 does carbon actually work for absorption? Actually yes, 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 absirbers, so about 8 panels for $8400 and a ton of weight to carry.

This is really interesting, thanks. I guess it makes sense that carbon would work in a scenario when you need something porous to resist the flow of air. AFAIK it is the most porous material you can easily buy. The low absorption at high frequency is also an advantage. But I think if I were going to spend $8K on absorbers... you could probably get further with more membrane traps using cheaper filling.

 

[Curvature]

Curious why you would call diffusers "wrong"? Aren't they helpful if you have echo or too much early reflection?

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.

 

[Curvature]

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.

I would like to address your post in detail but I don't have the time now. My basic point will be that AF bass traps are junk.

 

[Chrispy]

Familiar enough with him to ignore him....