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.
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| Good example of manufacturer advertised "specs" that one should not trust. |
[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.]
- 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:
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| 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:
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| 0.8" (2x0.4") PET panel with 3M Command Strips applied, ready to stick up on the ceiling. |
[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!]
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| 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! |
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:
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| 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:
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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):
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| "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. |
... In for a pound!
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| 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".
Thanks for the detailed write-up and measurements on the ceiling PET panels. It’s always useful to see real before/after data in a domestic room.
ReplyDeleteI noticed your room is almost twice the size of mine. My ceiling is slightly higher and I have 4’ × 4’ × 4” thick Rockwool panels, so I can relate to some of your measurements (8 ft ceiling, ~9 ft listening distance).
Ceiling reflections therefore play a bigger role in overall level/loudness in smaller rooms than they might in a larger space. In concert halls, they sometimes lower reflective ceilings which can be moved for small ensembles (quartets, etc.) because the extra early reflections give the performance more acoustic “gain” and presence without amplification. Adding absorption does the opposite — it reduces that reflected energy.
Your ETC measurements show this clearly: ~2.5 dB drop at the ~2.7 ms ceiling bounce peak and roughly 3 dB less broadband energy across the first 200 ms. The C80 improvement above 400 Hz is also exactly what I’d expect from taming that reflection.
My main question/curiosity is around loudness compensation. Absorption lowers the total acoustic energy reaching the listener. If someone then turns the volume up to restore the previous perceived loudness (which is what most of us do in practice), the direct sound becomes relatively stronger compared to the now-reduced reflections. This should make things sound clearer and more precise (matching the C80 gain and your subjective comments on focus and vocal intelligibility), but it can also make the presentation feel slightly more distant or less enveloping, because early reflections help our ears perceive sources as closer and more present.
Did you listen at matched loudness levels before and after, or notice any change in perceived distance/depth once the room was quieter? I’m wondering whether the clarity benefit comes partly at the expense of that “intimate loudness” you sometimes get from a more reflective ceiling in a small room.
Please don’t misunderstand my comment — there are certain things that still make me wonder how we should really approach room treatment. For example, I used to have a very thick rug in my music room but now I’ve completely removed it (except for some stuffed toys in front of the speakers) on a bare marble floor . I can’t fully explain the rationale, but I felt the bass sounded nicer afterward.
On a separate note, I’ve noticed quite a few forum comments lately about the use of AI and concerns over the authenticity of posts. I confess that I use AI almost for everything to redraft my thoughts. I usually write very short sentences and straight to the point, which often causes confusion. AI seems to understand a better way to convey the message clearly. I’m wondering if I should now include this kind of disclosure in every post. lol!
ST
Hey there ST,
DeleteGreetings and happy Father's Day weekend!
Some excellent points. Yes, indeed I have noticed a correlation with the relative change in loudness as more absorption panels were introduced into the room. When I made the recent changes like adding the Mittzon panels and then these ceiling PET panels, I made sure to listen to the same songs right before and after the change. Obviously with all the work of putting the ceiling panels up, I would not be able to easily A/B compared to the side panels by just taking them out.
On the amplifier settings, I have noticed a tendency to increase the volume by about +1-2dB now with the extra Mittzon and these ceiling PET panels in my daily listening.
While I didn't mention it in the write-up, the last songs just prior to and then the first to play after putting up these panels were some Chinese pop on my playlist - Tsai Chin's "The Forgotten Time / 被遗忘的时光", and Michael Wang's "Fairy Tale / 童話" - without changing any of the volume and DSP settings.
Despite the limits of auditory memory (~30 hours to allow adhesives to settle), my impressions were quite positive. If anything, I thought the vocals on those tracks sounded more forward and intimate while the accompanying instruments were better defined in the soundstage, maybe even subjectively a wider soundstage.
An interesting change I thought I noticed was on Tsai Chin's vocal reverbs after the ceiling panels were installed. The reverb sounds a bit more distinct and at times even like they're emanating not from the singer's position but a little disjointed in front of her. This song came out in 1979 so I assume the reverb might have been added in the studio; maybe an example of how improving fidelity might allow us to spot anomalies (if we're too picky!)?
I agree that like in medicine, "First do no harm!" should be our mantra with room treatments as well. I figure for small to medium room sizes, if we can generally achieve:
-- Low ambient noise level <30dB(A) (no loud HVAC, fans, outdoor noises)
-- Reasonably flat frequency response 40Hz-15kHz (ideally 20Hz-20kHz)
-- Low RT60 between 200-500ms, reasonably smooth and flat
-- C80 "Music Clarity" between +10 to +20dB
-- Predictably straight ETC downward slope within first 50ms without many gross spikes in that early reflection time period
we probably would have achieved a pretty good-sounding and not excessively "dry" room.
Wondering ST did you run any measurements with and without the thick rug on your marble floor? Curious what happened to things like the reverb time and magnitude of the floor bounce.
As for AI, I think these days so long as we're communicating what's in our minds honestly and as intended without AI hijacking thoughts and intruding with its own content, that's what matters on public forums and comments.
Mindless AI spam including AI-written articles which often contain errors are unfortunately very annoying these days, eating up mental and Internet bandwidth! 😒
Belated Father’s Day to you too! Though I sometimes wonder if turning one day into such a big celebration is he reason the other 364 days feel a little less like everyday father. You know what I am trying to tell here. 😏
DeleteRegarding the rug on marble floor:
This was back during my Harbeth Super5 period. While waiting for the UMIK-1 to arrive, I was using a standard condenser mic, a Marantz calibration mic, and Roland CM-10 binaural mics. When I noticed an inexplicable dip in the REW measurements, I blamed the mics and hoped the calibrated UMIK would reveal the “truth.”
That was a period of wild experimentation — I was throwing everything at the room: the thick rug, kitchen crockery, pots, frying pans, and my favourite bottles as makeshift treatments. It was truly my “blind era.” I didn’t yet understand the gap between what the measurements were showing (especially reverb) versus what I actually heard and preferred.
When the UMIK-1 finally arrived, I was surprised by how little the results changed compared to the binaural mics in my particular setup. At the time it felt like it wasn’t adding much value for my needs. That experience made me wonder how critical a calibrated mic is for casual domestic room work, even though I fully accept that the UMIK (and proper calibration) is the proper tool for accurate, repeatable measurements — especially when sharing data or doing serious optimization like you do. The measurements maybe in the local forum. Will try to get them.
I’ve thought about doing another round with my DPA binaural mics, and with the stuffed toys. though I’m not sure it would serve much practical purpose.
ST
Hey ST,
DeleteYeah that's an important question about the value of a calibrated microphone. I've done recordings with vocal mics and binaural work but when it comes to measuring room acoustics, have only even used measurement electret condenser mics like the UMIK series, Behringer, etc.
Personally, I've found that calibration is important for extra accuracy but even without customized calibration, most decent full-range mics would do the job assuming we have a sense from the manufacturer the kind of frequency response curve to expect. Even the cheap room measurement microphones that come with AV receivers I think can be quite capable. Obviously when given the option, go with the calibrated one!
Interesting phase of "wild experimentation". When you get a chance to measure again, would certainly would love to see your results as an example of how in real-life we audiophiles manage our rooms and what works to achieve good sound.
Hey, Arch, you’re going in the right direction, but, if you don’t mind let me give you some advice since I’ve been there and have gone through it a few times:
ReplyDelete• What you’ve done is mitigated first reflections and some low bass build-up that occurs behind the speakers. This is all actually very good, but you haven’t done enough to effectively alter the RT60 of the room.
• What you have done is actually the first things you need to treat in any room and those changes will pay dividends. They don’t have almost any effect on the RT60 of the room.
• Your ceiling treatment is well intentioned and truly moving in the right direction, but, from more than one experience, I’ve found that the way you’re going about it is less efficacious than the latest methods I’ve struck upon
• It’s actually well documented: applying acoustic foam (or any sound absorbing material) to a surface is less effective than suspending it a few inches from the surface
• Flat acoustic foam is actually less desirable than ridged foam because the ridges offer more surface area to absorb sound as well as diffuse it because…
• Acoustic foam is not 100% absorptive at all frequencies. It is somewhat reflective at certain frequencies which is also why it has ridges to diffuse those reflections
• Sound absorbing blankets hung or suspended an inch or more from the surface will be way more effective than foam. This is especially true below 500Hz. A 7ft x 8ft sound absorbing blanket hung an inch from the wall absorbs a tremendous amount of the low frequency energy. The bass wave is like a fist and blanket is a huge bag of water.
• Put some heavy, ruffled curtains in front of the blankets to dress them up (the blankets aren’t pretty) and you’ve made that design twice as effective (or more) than foam at all frequencies. The curtains diffuse (some what) and absorb bass, mids and treble while the sound absorbing blankets suck up everything getting through.
• Hang 2 sound absorbing blankets an inch apart with heavy curtains in front and, for all normal purposes, you eliminated the wall behind it as a reflective surface at any frequency.
So, how much does this cost?
• Blankets: $60 for two 8ft x 7ft
https://www.vevor.com/moving-blankets-c_11895/vevor-2-pcs-sound-dampening-blankets-soundproof-curtains-with-96-x-80-in-soundproof-blanket-with-grommets-studio-grommeted-blanket-for-window-door-light-blocker-music-recording-black-p_010721525430?requestId=6a3a7ffe7a599002f51fa0a
• Curtains: a pair of heavy curtains will run you $50-60 on sale… hey, pick whatever aesthetic pleases you, but make sure they are thick
• Hanging hardware: $20-40 depending upon the installation requirements
Less than $200 eliminates an 8x7ft section of your room from having any reflections. You can get creative and do this for your ceiling as well.
Hey, folks, in my life, I’ve spent well over $5K on all manners of Auralex foam products and they are good, but not this good
Arch, let me offer you 2 things to do moving forward:
ReplyDelete• Auralex makes foam corner fills. They absorb the energy coming into the corner, but are intentioned for any intersection. These work especially well on wall/ceiling intersection. People don’t think about that boundary, but sucking up that energy starts making your room sound less like your room and more like a space… less definable. The cost? $120 for nine, 4”x4”x2ft pieces. Two boxes of them run all along the ceiling/wall boundary from your listening position to behind the speakers will make an audible and positive difference in your room’s sound.
You’re into experimenting… Buy one set of the aforementioned sound absorbing blanket sets for $60. Buy 6, maybe 7, 1”x1”x8’ pine shafts from a lumber yard or hardware store and some wood screws.
• Take the 1x1’s, put wood screws in them perpendicularly at their ends and use them like tent poles to temporarily suspend the sound absorbing blankets in your room. You want the poles to be between the blankets and the walls.
• You also want them to be away from the walls and, since you have some traps behind the speakers, taking them from the traps to as for back as they can go in the room will most likely work best.
• If the 1x1’s aren’t tall enough to reach that ledge in your ceiling, extend them with pieces from that 7th 1x1
• Set up your 1st tent pole (obviously, angled) into the corner and hang the middle section of blanket and then do the same for the ends
• Once you have this cheap, flimsy arrangement jiggered up, you will then have a glimpse of the true beauty that awaits you when you make a LEDE room (live end, dead end).
Of course, your listening room is not really a listening room yet. It’s still a living room with a stereo. How you want to proceed is up to you, though I would absolutely recommend those foam corner fills. They come in 3 colors.
All the best, MoFo!
Link to the Auralex Corner Fills:
ReplyDeletehttps://auralex.com/cornerfills/?searchid=0&search_query=corner
Hey there Jeff,
DeleteThanks for sharing your experience. Yeah an interesting way of doing it! At some point would be great to see some pictures and if possible some measurements around what is doable with room treatments like this!
Interesting Auralex Cornerfills. Esthetically and practically, I can see those working in my room.
Arch, to go into the whole LEDE thing and try to explain it myself, I hit up my favorite AI, Claude, and asked him for greater explanation into the scientific principles of what I empirically struck upon.
ReplyDeleteHere’s a link to that conversation:
https://claude.ai/share/6ac4d6df-fb12-4086-8611-023b61bf4ebc
As to why I went this route, well, when you got four 300W subwoofers In your room, you want them to sound good.
http://jeffrey-henning.byethost5.com/LS50-&-Rythmik-subs.jpeg
Hey, Arch, something just struck me: After reading the analysis by Claude a second time, this is the first time in my entire life that I can recall something being a “limp mass” is actually great. Who’da thunk?
ReplyDeleteNice conversation Jeffrey. Will have to go through that in a bit more detail.
DeleteJust wanted to make a note also that these PET "plastic felt" panels are significantly denser than acoustic foam so that 0.8" panel should have midrange/treble NRC similar to foam 3-5x thickness.