I know everyone has been waiting eagerly for a technical report on 3rd gen cabin air filters (lol), but the wait is now over!

A year or so ago I was lucky enough to snag one of the canister-style cabin air filters from the Russia manufacturer. It's 3D printed over a cylindrical filter and pops into the air box above the fan. The canister fits down into the squirrel fan blades. It's a really nifty design and I've been happy to have it BUT... I have always been annoyed by the sound quality of the fan with the filter installed. There's a distinct high-pitched whine at all fan speeds, getting worse with higher speeds. The air flow is also reduced (which is to be expected). Also, the media is not washable or replaceable.

A fella on BookFace named Tommy recently made a run of flat-style 3D printed filters that feature being able to replace the media. I figured I'd grab one and compare it. He's a super nice guy and I've had fun chatting with him. He also shipped my filter promptly!

Taking cues from Leon @Spiker engineering I thought this would be a great opportunity to gather some real DATA to help inform the community's decision about cabin air filters.

Experimental setup:
- El cheapo aneometer from Amazon ($15)
- DecibelX iPhone app (free, with in-app purchases but I didn't use any)



Here's the Tommy filter







The two halves screw together (props to Tommy for printing some really clean threads). He ships it with a thick but porous foam filter.

I opted to also experiment with some Merv4 charcoal air filter media. This is the stuff you'd wrap around a big paper air filter element on a room air filter; it's basically a pre-filter that you can change more often and get the charcoal odor-absorbing functionality. It's pretty thin which should be good for flow which was important to me. I cut out a circle from the material.





Tommy filter with the Merv4 stuff installed. The two halves clamp it on the perimeter so it stays put even though it's thinner than the cavity in the filter holder.





And now, on to some data!

Quick refresher on the design of the Russia filter





Here's where the air filter plugs in.

Russia filter:



Tommy filter:



I took measurements while sitting in the driver's seat. Vents were set to the top vents only (all open), and I'm focusing the recirculation setting only. Phone was placed on the Spiker Engineering phone mount for audio data consistency. The anemometer was placed on one of the center vents slightly to the side to avoid the little handle in the middle.

I tested four configurations:
1) No filter installed (factory) as control
2) Russia filter
3) Tommy filter with supplied foam media
4) Tommy filter with Merv4 media

I took data for fresh and recirc at all fan speeds but to spare you the gory details here's the punchline with respect to flowrate:



All the filters are very close. In general they knock the flowrate down by about 1/2 of the fan setting. So with the fan at 2 it's like having the fan at 1 without a filter. The Russia filter flows the best but only marginally, and the Merv4 stuff is a teensy bit better than the foam.

Looking at simply total dB(A), which is the overall sound volume to your ear there is a clear correlation between flow rate and sound. This is not looking at any frequency analysis yet. What this means is that for the same flowrate having a filter doesn't make the fan any louder, it's simply a function of how fast the air is moving out of the vents. This is the data for all the configurations I tested.



Here's where it gets more interesting. The DecibelX app lets you see the real-time spectral analysis showing dB(A) vs. frequency. You want to look at the blue line which is the rolling average data. The orange line is the instantaneous and it is slightly higher because it's picking up the sound of me clicking the screenshot buttons LOL. All data is recirc at fan speed 4 (highest).

No filter installed



Tommy filter with foam



Tommy filter with Merv4



Russia filter



So what do we see here? First notice that without a filter the sound spectra is pretty much what you'd call brown or pink noise, since it is a very flat curve that tilts downward from low to high frequency. Pure white noise would be a flat, horizontal curve from low to high. Brown/pink noise prefers the lower frequency content in the spectra.

Both Tommy filter configs are also pretty similar. But the Russia filter has two pronounced peaks at just above 2kHz and around 6kHz. This is definitely the whine that I noticed which bugged the crap out of me. Both peaks are about 10 dB above the overall curve meaning they are distinct tones that you can hear against the background.

I noticed immediately that the Tommy filter has a much nicer sound. After driving around for a few hours my observation was the same. It's a big improvement over the Russia filter.

Summary (or TLR) --
- The Russia filter has a pronounced tonal noise which impacts the sound quality. The Tommy filter, especially with Merv4 filter element, is a much easier sound to take and more like the original sound without any filter
- The Tommy filter flows a tiny bit worse than the Russia filter but it is only marginal and not noticeable. Adding any filter element will reduce airflow by approximately 1/2 the fan setting.

Thanks for reading!

Further, after removing the Russia filter now only the second time two of the retaining tabs broke off



The Tommy filter is a tension fit instead of tabs, and comes out easily while fitting snugly. It will be easy to remove and replace the filter element to keep it clean and renew the charcoal odor absorption.

Reserved

Had no idea this design was a thing. I have the russia one and yea the high pitch noise can be annoying. Going to hit this guy up on facebook and get this one. Thanks for all the info!

Do you have a link to buy the "Tommy Filter"?

awesome experiment, very thorough (to the level needed for this kind of thing) and i reckon tommy will be getting a fair few orders in now - got a link or contact? i'm not on the book of faces but would love to get a filter in my setup

Tommy on Facebook said the best way to get in touch with him is to text him at 681-404-7344

Feels sketch to post someone's phone number here but he told me it was OK!

Thanks for taking the time to post all this. Can I ask what you paid shipped for the Tommy filter? My wife suffers from bad seasonal allergies in the spring and a good filter could help. One of those creature comforts Toyotas didn't have in 1998.

Truly excellent work here! Glad Tommy provided a number because I don't use social media at all. Thanks for sharing all this!

Here's a link to Tommy's recent Facebook post about his cabin air filters.

I'm glad to be able to find new products and ideas on FB, but everything else about it is so awful. Navigation, finding information you glanced at before, pretty much anything you actually want to do you can't. And most people act like complete fools. Please let's not let this forum die... Rant over!

The Facebook book is private, so everyone can not see the information.

I'm glad to see you found some information you were after. To me, I want nothing to do with cabin filters. They are a pita in the newer vehicles, but they do keep the rig interior cleaner.


I used to post on fb groups and put links to this forum in those groups. Nobody wants to use other sources other than fb. Along with the information being spoon feed. Lots of folks won't even use the advanced search to see if their issue has a solution in here. I just how it is sadly.

Facebook really needs redone and quit being life log. However, I don't see that happening any time in the near future...



Sent from my SM-A536V using Tapatalk

I like the Tommy design filter, filter medium is dense, less could be more.
You've found the extremes no filtration-50% CFM lose, attack it from the middle.

Split hairs and find a medium that looks 50% less dense, gain cfm filtration acceptable?
Comes to mind looking at what's next to make it suit me, I don't need alergy level filtration.

Agreed, I'd be interested in trying an even free-er flowing media. Even the ability to filter out gross particles like bits of leaves and stuff would be a benefit. Let me know if you have ideas!

I too, don't want to see this forum go by the wayside but, judging by forum traffic it's seems to be going that way.


Agreed


I'm just spit wading here...how bout like a KN type of filter media? I don't know about the oiling thing though, hate to be breathing that in. And Im sure the oil will seep all around making a mess.
I do have a friend who did have a gauze type of air filter without oil, he says its the oil less type?
I also liked how the bmw's has their cabin filters on outside top of the cowl itself that uses rectangle filters. Maybe someone could 3d print a jig to copy that somehow?