How To Fix Low Frequency Problems - Panel Diaphragmatic Absorbers
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- čas přidán 2. 08. 2024
- FREE Acoustic Treatment Guide: www.soundproofyourstudio.com/...
Low frequency issues are the biggest problem for soundproofing and acoustically treating a room. In this article I will discuss how to treat low frequency issues below 125Hz in your room using panel bass traps.
1) What Is A Diaphragmatic Panel Bass Trap?
Low frequencies below 125Hz are hard to treat with acoustic panels made from fiberglass batts. To treat these lower frequencies we need a different tool. The best tool for the job are pressure traps that use a closed air space to attenuate low frequencies. These traps are efficient at reducing low frequencies, but they have a narrow Q, meaning they only work in a narrow frequency band. For this reason I only recommend building these traps after you have extensively treated your room with velocity traps aka insulation with fabric over it.
The bass trap I will be discussing has many names ranging from diaphragmatic absorber, low-bass panel trap, resonant absorber and so on, but the theory remains the same. These traps use an enclosed box with a calculated airspace depth to create a resonant chamber that attenuates bass at a specific frequency.
To calculate our panel mass and depth we need to use the following formula to ensure our bass panel trap will attenuate the correct bass frequency. The formula is as follows:
f (frequency) = 170 / square root of (mass x depth)
*For metric change 170 to 60 -
m = mass is in pounds per square foot of resonate panel
d = depth in inches
Now the easiest way to calculate potential panel depth and materials is to create a spreadsheet for plywood thicknesses and depths and see what materials you need and depth you need to attenuate the correct frequency.
Adding loose glass fiber to the back of your panel will increase absorption, but it also will move the peak absorption lower down the frequency spectrum.
These panels are only effective when placed at a pressure maximum in your room for the desired frequency you are trying to treat. This means that you need to find out where a room mode is ringing out in your room and place the panels on that wall or ceiling. To do this you can use a calculator like, AMROC online to see where room modes in your room are, or you can play a sine wave through your speakers and walk around the room noting where the bass note sounds louder or completely gone. The places where the bass notes are louder is a pressure maximum and is where you should place a trap.
Lastly, it is important to make each panel absorber at least 5 sq/ft to have an affect on the room. You will need to place one or two in your room to and re-measure your rooms response to see how many absorbers you will need.
2) So What Frequencies Do You Need To Treat?
This is a good question. We know we have bass problems in our room, but now what? First, you need to measure your room. You must use REW or equivalent room software and a measurement mic that is properly calibrated to measure your room. This will show you what frequency problems you have in the low end. Let's use my studio as an example.
Below is a picture of my REW results for the spectogram. I like to look at the spectogram because it shows which room modes are "ringing" out in my room at my listening position.
Notice how most of my room is flat in the upper frequencies, but down low we get those flame like peaks. Those are my room modes ringing out where I mix. This will make my bass a bit muddy to hear since those frequencies don't decay at the same rate as ones nearby.
The solution is to build traps that target those frequencies. It is analogous to a sniper rifle vs a shotgun approach. The panel trap can isolate those problem frequencies.
So, the first ring out is at 106 Hz. Let's now look at where to place that panel.
3) Where To Place Your Panels
As I mentioned before, you can use AMROC or sine waves to find your pressure maxima at 106Hz in my example. For this example I will use AMROC to show you where that frequency modal issue is at a maximum.
That 106Hz frequency is a tangential and oblique mode that is maximul at the blue and red areas on the Room 3D visualizer on AMROC. AMROC plays the tone when you hover over it...
read full blog article - www.soundproofyourstudio.com/...
0:00 - Intro
1:31 - What is a diaphragmatic panel?
5:24 - Which Frequencies do we treat
7:13 - Where do you place the traps
9:06 - Calculating the box depth
11:48 - How to build your panel trap
14:38 - Conclusion
FREE Acoustic Treatment Guide: www.soundproofyourstudio.com/acoustic
As a hobbyist, I've found using carpet padding to be sufficient. I "sandwiched" the padding at the very top between two cheap boards, then used a screw hook and "eye" screw to dangle the absorber about an inch off of the wall. It is better than "good enough."
Immensely useful and much awaited video 😊😊😊❤
So glad!
Thanks for this video! Great content 👌
Glad you liked it!
Wow. Nothing but great information, sir. Damn fine work.
Glad it was helpful
Congratulations!!!🎉 clear explanation a guides me towards a more informed decision! tsk
Awesome! Thank you!
Excellent video, please post a follow-up showing the spectrogram before and after!
Well I would have to build all the panels. The truth is that I’m actually really happy with my room and I can mix perfectly fine and record great sounding songs in it. This is another great example of why you don’t necessarily need to go over the top with acoustic treatment. Maybe one day I’ll take the time and money to build these out for right now. My personal Studio is fine just the way it is.
Thanks for the in-depth explanation and math. I've built really large and heavy 40hz diaphragmatic absorbers using math from this video. It's really made a measurable difference. However, I see almost everyone recommend 12-24 inches of rockwool in the corner and calling it a day. I've used and compared both methods in my room and the diaphragmatic absorbers make a noticeable difference while the rockwool in the corner did almost nothing. Why does everyone recommend rockwool in the corners? Are they uninformed and just repeating everything they've heard from other CZcams channels (who probably got their information from other CZcams channels)? Your channel is only 1 of 3-4 others that state rockwool won't absorb lower frequencies and that you need pressure-based absorbers. Your channel is also one of only a handful that provides the math and tools to back up the information. Just a question because I keep seeing almost everyone recommending rockwool all over the room to absorb lower frequencies and that anyone that disagrees with that doesn't know what they are talking about. I very much appreciate the information you've provided as it has really pushed my ability to mix accurately forward.
That is so great to hear! Well, there are a lot of philosophies out there on the Internet. The main problem is that diaphragmatic absorbers have a very narrow Q so you really can only treat a few frequencies and the absorber take up a lot of space. This being said you might get a more even response in your room by just using insulation. Also, the air gap behind the insulation can help treat lower frequencies because of the wavelength rule. The funny thing is no one is absolutely wrong or absolutely right the more I learn about acoustics the more I learn about physics and are on human psychology.
Interesting video. Do you have another video showing the panels as-built and the impact of them on the measured room response after installation?
I haven’t built them myself. A lot of people also say not to use them since they are highly focused and take up a ton of space.
If these panels are so inefficient, wouldn't it be easier to just make all your velocity traps thicker? Like 4 inch vs 8 inch? They're probably about the same efficiency at lower frequencies right?
This seems extremely counterintuitive to use a thick piece of very rigid plywood for this type of absorber? In my mind, I'm thinking about something that has a lot of flexibility in order to vibrate with the room mode. It seems like rigid plywood would just reflect, doesn't it?
So, yes, I was right. This is the formula for limp mass membranes, not rigid plywood.
This formula was for a membrane rigid membranes. The limp mass formula is different.
Hi, please help me to understand amroc calculator, at the room 3d image, does the red and blue represent the pressure zone? If they does, so i have to put the absorber on that area? Thank you
Yes, that is the idea.
When calculating my room with amroc, the result has so many modes, even the axial mode has so many frequency results.
How you sort the frequencies2 in order to make & place the diaphragmatic absorber below schroeder frequency?
What metric units would be used for the M and D figures?
Sorry I didn’t do metric. I am trying to include those more now