Ceiling Absorption Panels (AudioSilk branded PET material 2'x4'x0.8", doubled thickness).

With the recent discussions about room acoustics and treatments, I thought it would be good to continue on this theme and move forward with the next logical step for my listening space. Let's talk about ceiling sound absorption as you can see installed in the picture above.

For years, I've been thinking of doing this but really didn't want to put something up there that could damage the walls. I definitely would prefer not to drill holes unless absolutely needed. Recently, I had some positive experiences with 3M's Command Strips when I put up some picture frames and artwork around the home. These double-sided tape strips were designed to be removable without damaging painted walls. Looking around at options, it seemed that this could be a reasonable ceiling installation solution within weight limits.

On Amazon, there are various options for acoustic absorbers these days. I settled on a package of 4 sheets of 0.4" thick x 2' x 4' AudioSilk-branded polyethylene terephthalate (PET, non-toxic, non-irritant, made typically from recycled plastics like bottles) absorber panels at a good price (~US$110) along with some strong 2-sided tape for doubling up the panels for thickness and of course the 3M Command Strips to stick it up on the ceiling.

These AudioSilk absorption panels are marketed for DIY home studio use to help improve clarity and reduce echo. Notice that they're thin 0.4" porous sheets and although they're described as having Noise Reduction Coefficient (NRC) "up to 0.91", this is technically not true.

Good example of manufacturer advertised
"specs" that one should not trust.

What they're suggesting is that at certain frequencies, PET can have a relatively high absorption coefficient (α) up to 0.91 but this would only apply to high frequencies likely above 2kHz and also dependent on thickness which is unspecified. The NRC value is typically a calculated simple average of midrange absorption at 250, 500, 1k, and 2kHz. Even in the advertising material as shown above, clearly, that inset graph with the red curve would average to something like 0.7 at best. While I agree that denser PET material would be better than acoustic foam at a mere 0.4" thickness, I have doubts that actual measurements would yield an NRC of 0.7 unless the company shows more official test results than that little corner cartoon graph!

Here's I think a more realistic model of how a thin 0.4" (10mm thick) piece of PET would perform installed against a hard, reflective wall compared to doubling it to 0.8" (20mm) and options like adding a 5cm air gap such as by hanging the panel from the ceiling:

So, realistically, while these thin 0.4" (10mm) sheets might be OK for absorption of waves above 1kHz, if you really want to go below 1kHz, 0.8" (20mm) double-sheet thickness (dotted blue) should be considered. Even better would be to hang the sheet(s) with an air gap of say 5cm (orange and purple) between the ceiling and the PET to achieve something like a floating "cloud" layer. Since I'm just looking for a simple, visually unobtrusive solution without putting holes in my ceiling, I'll stick with the "direct" adhesive double-thickness (blue) curve and consider the cloud idea down the road as a future project perhaps.

[In a room with hard flooring, since we're doing ceiling treatment, it's worth thinking also about the quality of the rug we use to tame floor bounce. While there's wide variability, I've seen thick 15-20mm carpets with stiffer backing layer and density of ~2-3kg/m3 quoted with NRC values of 0.25-0.4. The 0.8" double-thickness PET, estimated at NRC 0.5, would likely be equivalent if not better than most carpets.]

Let's grab the materials:

- Package of 4 x 0.4"x2'x4' AudioSilk PET panels - grey like my ceiling (~US$110)
- Gorilla Tough & Clear Double Sided XL Mounting Tape (~US$9)
- Genuine 3M Command Strips XL - 20 pairs for extra security to construct 2 panels (~$20)

Not expensive; something like ~US$150 for effectively two 2' x 4' x 0.8" panels. As usual, I got this stuff from standard retail channels, this article is not sponsored by any of the companies mentioned.

The hardest part of putting something on the ceiling was to make sure the panels are aligned properly and centered to my sitting area. For that I used easily removable painters tape to trace out first on the floor the orientation of the panels and then suspended a 7.5' length of fishing line with weight from the ceiling so I could correlate that floor plan directly overhead, again, marking with painters tape.

Once I did that, I sandwiched two of the 0.4" panels together using double-sided Gorilla tape along the edges like this:

Extra strength permanent gel Tough & Clear XL double-sided Gorilla tape used on the edges to sandwich 2 panels together.

The tape could hinder transmission of the vibrations from one sheet to the next when we stack them, so it's good not to use too much tape. As you can see, the tape is a clear gel-like material that adheres well to the semi-rigid PET plastic. Carefully aligned, I slapped 2 of the absorption panels together for functionally a single 0.8" unit. Press the sheets together for about 5 minutes to make sure the double sided tape makes full contact. I let it sit overnight to ensure a strong bond.

I weighed each 0.8" panel at 5lbs. I then applied the 3M Command Strips (largest XL-sized ones) by "clicking" 10 pairs of strips together as in the picture below and sticking them to the upper panel that will in turn adhere to the ceiling:

0.8" (2x0.4") PET panel with 3M Command Strips applied, ready to stick up on the ceiling.

The Command Strip XL is their largest/strongest size which is supposed to be able to handle a maximum of 20lbs with 4 pairs. Normally, these are used in a vertical orientation for picture frames against a side wall so they're suppose to handle shear forces rather than the direct downward pull from the ceiling; hence I used extras and 10 pairs should be more than enough.

[Since I'm installing these panels in my basement here in Vancouver where the temperatures are not extreme and humidity is rarely very high, the 3M Command Strips will not be exposed to very harsh environmental conditions. Consider where you live whether these Command Strips would still work!]

As you can see, I've used the painters tape to mark the position of the panels on the ceiling. I also stuck up some Lego bricks to use as physical guides for the 90° edges.😉
Given the adhesive nature of those ten 3M Command Strips XL, take your time and be careful with the positioning as it's going to be hard to reposition if the angle is off with the first try!

Because it takes some time for the Command Strips to start "curing", I made sure to put pressure on the panel continuously over the next hour (yes, it gets tiring)! And then left it for about 24 hours before playing music with bass that could shake the walls.

As you can see in the picture above, both 2' x 4' x 0.8" panels are up and ready for clean-up of the tape. Notice that I unfortunatley have a plastic HVAC vent there which I have to work around. I'll consider it a bit of "forced" diffusion. 😉

Here's another angle of the relative position of the ceiling panels in relation to my main seating position on the sofa. The first reflection points are located at each side of the front panel, and the rear panel is basically right overhead of the main listening position.

I figure just in case over time gravity tugs at the 3M Command Strips to reduce the grip, maybe once a year during spring-cleaning time, I'll push the panels up to counter any shift. I'll let you know if I run into any issues over time.

So, how well do these simple 0.8" thick (2x0.4") PET ceiling panels work?

As you may recall from our discussions of the IKEA Mittzon absorption panels recently, what we need to focus on is in the time domain. For the specific effect of these PET ceiling panels, let's have a close look at before and after measurements of the Energy Time Curve (ETC), in particular the first 20ms, looking for changes in those early reflections:

For this comparison I've turned Dirac Live Bass Control on since I almost always listen with DSP active. All measurements done with miniDSP UMIK-2 microphone at 48kHz.

In my room with the microphone positioned about 9' from the loud speakers, speaker height ~4.5', ear height ~3.5' and ceilings 8' high, we can calculate the indirect diagonal ceiling bounce to arrive around 2.7ms after the direct sound. Indeed, we can see in the ETC a peak at 2.7-2.8ms. Since I moved the seating a little bit when I put up the ceiling panels, and height of the microphone changed a little bit, the ~0.1ms change indicates just ~1.4" difference.

Overall, we're seeing a drop of ~2.5dB with the ceiling absorbers in place at that ~2.7-2.8ms early reflection peak. Not a huge amount and I assume that this alone would be subtle.

[Eagle-eyed readers might notice that the 2.7ms spike without ceiling panels is actually not just higher in level but also wider! I suspect what we're seeing is that the measurement mic wasn't exactly centered and when I ran the L+R sweep, we're seeing a slight displacement between the left and right speaker ceiling bounces. Since I don't like to be dramatic, I'll just stick with the 2.5dB difference between peaks. In reality, the difference is greater that just this peak level change.]

However, the effect is not just with that single early reflection but in general the blue tracing has fewer prominent peaks across those first 20ms and there is a reasonably predictable downward slope to the ETC with reduction in broadband energy across time which is what we want to see. We can expand the X-axis to cover 200ms and add 0.2ms smoothing to have a better appreciation of this difference:

While I wouldn't call the effect dramatic, it's good to see that with the ceiling absorption in place, these panels are taming the initial reflection more and reducing the total energy circulating in the room with a separation of ~3dB across time. This difference should be reliably audible if we were to have direct A/B listening comparisons with potentially better perceived clarity, low-level nuance retrieval, vocal intelligibility, stereo focus and dynamic contrast.

[For more discussion on the ETC graph among other metrics of a good sound room, check out this Mellor, Hedback, and Acoustic Frontiers article from 2011: "Acoustical Measurement Standards for Stereo Listening Rooms". Important stuff!]

Let's see if these anticipated changes could be correlated with the "Music Clarity" C80 metric:

Yup, we can indeed see the improvement above 400Hz which is what we would expect given the 0.8" PET thickness; it's a mid-range and treble absorber as per the Absorption vs. Frequency graph shown above.

Since these are strategically placed, relatively small 2' x 4' panels compared to the size of my large thick rug, all the furniture in my room, and the floor-standing side absorption panels 2-3" thick, we would not expect much change in the overall RT60 (measured as Topt for small room):

Indeed, very marginal change. Just a drop in peak Topt from 360ms to around 350ms.

Finally, let's have a look at the frequency response as we always do since tonal difference are typically more noticeable. Since DSP will be the main contributor based on the target curve used, let me show you the pre- and post-ceiling panel curves without DSP, overlaid with DSP active:

"Sides + Rear" refers to acoustic panels laterally and behind speakers, no ceiling panels. "Ceiling + Sides + Rear" is with the added ceiling panels. And of course "Ceiling + Sides + Rear + Dirac" is with the DSP activated for better-controlled bass and sub-bass.

Again, no surprise that frequency response is mainly a function of the Dirac Live DSP which I can fine-tune to preference.

Finally, let's have a peek at the Spectrogram with and without the ceiling panels (DSP on):

As in my previous article, I've put a marker at 300ms. A subtle improvement above 400Hz.

... In for a pound!

With the encouraging results shown above, I took the "final" step of ordering another 4 sheets of 0.4" PET panels to create another 2 more 0.8" panels to expand the side coverage. Since this is a multichannel and home theater room, I wouldn't mind an even lower RT60 and coverage for those who sit on either side of the main listening position:

I'm pretty happy with this being the "final" room treatment addition for the next while. ☺️

I did not see much change in the ETC, and as usual, frequency response will be optimized with DSP so no need to show that. However, with more of the ceiling surface area covered, we do have better RT60 (Topt):

Peak reverb time is now below 350ms and the curve is basically flat from 300Hz up. I always strive for balance in the sound including the avoidance of an overly "dry" room. While I'd be okay with a reasonably smooth RT60 with <500ms peak, I find the current 300-350ms reverb time combined with low ambient noise (below 30dB(A) SPL) very comfortable and conducive to hi-fi appreciation.

Furthermore, there's some improvement in the C80 "Music Clarity" index:

Again, notice that the effect of the 0.8" (2x0.4" sheets) PET is in the mid and higher frequencies above 400Hz or so.

Spectrogram for completeness:

Toned down the sub-bass a little hence the range of 85-35dB compared to 87-37dB in the spectrograms above. Average midrange and treble levels remained the same. 

So, what about subjective listening impressions?

In a word, it's about improving sonic FOCUS. While it's impossible unless I have identical rooms side-by-side to do a direct A/B listening comparison, the best I can say is that there was what sounded like a palpable "tightness" to the details and impression of space from where the sounds "emanate".

As expected, with PET panels of this thickness, it's about midrange and treble focus/clarity, not bass or sub-bass enhancement. As such, female vocals like Jennifer Warnes' "Ballad of the Runaway Horse" (Famous Blue Raincoat, 1986, DR12) with its dynamic central voice, subtle occasional sounds of crickets, and sparse instrumentation really stood out with clearer contrasts, and subtle details. On the initial vocal solo portion of Camille's "Festin" (Ratatouille soundtrack, 2007, DR9), her voice just hung there, firmly anchored to a space slightly in front of my speakers about 8' away. Likewise, the birds singing throughout Yosi Horikawa's "Dawn" (from recent album Impulse, 2025, DR7) sounded clearer, easier to pin-point across the soundstage with some sounding like they're perhaps sitting on a tree above and behind me (with multichannel remixing turned off, of course!).

For more classical instrumental listening, I had a great time with the Atmos/multichannel version of Joe Hisaishi: A Symphonic Celebration - Music of the Studio Ghibli Films of Hayao Miyazaki (2023) - the track "Symphonic Variation (from Howl's Moving Castle)" is great. Since the surround channels already carry room reverb, it's good to keep room RT60 lower and low ambient noise when listening in multichannel.

I'm pleased by this simple project that didn't cost much money, didn't divert too much "hobby time" away from music listening, with measurable and subjectively pleasant results. If you have bare ceilings in the sound room like me, consider getting some treatments up there to tame the early ceiling reflections, and more panel surface area will help with reverb time. Even a little bit of room treatment can go a long way!

I remain convinced that a few hundred bucks in room treatments, with some intelligent placement of these products will take you to a much better hi-fi experience than thousands of dollars in stuff like hi-res DACs or even "high end" amplifiers. As discussed before, room acoustics belong to a separate domain/dimension from the hardware products often discussed by audiophiles and will have far-reaching effects beyond just a component change here and there.

For now, I think I'm "done" with my room treatments needs. 🤔

Some ending music from Olivia Rodrigo - "The Cure" from her new album you seem pretty sad for a girl so in love (2026):

My kids tell me it's a good album and already I have family coming into town for her concert in Vancouver in December, crashing at my place. I haven't listened to the whole album yet, all I know is that the multichannel version has better dynamic range, as usual (DR6 stereo, DR12 multichannel). 😉

Wishing you fond memories and musical enjoyment as we enter the summer months here in the Northern Hemisphere, dear audiophiles! Lots of FIFA2026 excitement here in Vancouver.