Hey guys, I have a problem in my room with the frequencys 40-80-120 hz mainly. I wanted to build a or some helmholz resonators so I can get rid of these peaks! Does any one know which type and which size I need?
Perforated or slat absorber? Panel traps as Ethan Winner says on Acoustic Treatment and Design for Recording Studios and Listening Rooms "Better Bass Traps" Thanks to him I understand Acoustics a lot better!!!

Ive been doing some reaserching but, I am pretty confused now on what will work best for my room.
Would maybe building a helmholz at 60hz with a Widder Q and one at 120hz with also a widder Q be better?




My room, if it helps I will post pictures up
13,77 Feet Long
11,50 Feet wide
07,93 Feet high

Thanks guys
I live in Switzerland and I am a student so building my own things is the only things I can affort right now, otherwise I would have my room treated by Ethans amazing products.

I bet you have installed your monitors horizontal.... heh

I do not recommend you to go the Helmholz resonator way for a number of reasons:

- Hard to manufacture and tune

- Too easy to miss the target frequency (a fraction of a millimetre deviation in the slot width, depth or the slab width can move the resonance frequency off-target, or even an uneven slot -i.e. bent, curvy slab- can cause a distorted resonance performance, which is not unexpected during manufacturing, for 99% of the cornershop carpenters are not used to working to such tolerances, they are just too rough to give you what the acoustics wants in a Helmholz Resonator.)

- Wider the Q, the less effective it is, causing the requirement for the bin to be larger than what you thought you could manage initially.

- Even if you did manage to tune the bugger to the right frequency and right gain, soon you'll realize that you need a box quarter the size of your room in order to cure "that" dip. What you've done is just too small in size to absorb that energy circulating in your room.

- Except for the part that absorbs the energy, the rest of the box is another acoustic problem that you need to tackle in your room: A big reflector.

You've got to understand that every piece of furniture in the room is a cure for one acoustic problem, but at the same time, the source of another. The selection must be made very carefully, and it is not a skill a hobbyist can accummulate with a saved pocket money believe me. A lot of blood, sweat and tears. And cash.

Your room is simply too small to cure. It is a known issue that the rooms smaller than 1500 cubic ft (43cubic m) are literally impossible to deal with and fully cure from an acoustic point of view. This is a rule found out and revealed by the BBC engineers in the past, and I am telling you that when I decided to be a professional acoustic solutions provider I read about this and arrogantly said "pah! Not a problem for me, I'll find a way..." and I am passing you my first hand experience that there is NO way around that barrier. I've learned it the hard way, but you don't have to.

Just like we and our equipment all need a space, sound needs a space too. If the room is too small, it is never comfortable. No matter what you do, it will let you know of its restlessness. You'll try to fix one side, and you'll realize it popped from another hole.

I suggest you:

- go for broadband solutions until you understand the behaviour of the airwaves and their interaction with the furniture better (which is a topic on its own, I do not recommend you to dig too deep into it if you don't want to lose your interest in making music in that room.)

- do not try to fix frequencies you simply don't have enough room in your room to tackle. (Even if you managed to design a resonator tuned to 40Hz, it would require at least 1 metre off your room in order to be effective, may be even more, depending on the design you choose. It's like having a 1 metre or more deep double-door wardrobe in your room. Let alone the space you'll lose, how you are going to solve the reflections and comb filter effects its solid surfaces will cause in other -mainly higher- frequencies in the room will be your next question to this forum.)

- do not set your targets too high until you find yourself a larger room. (Forget about 40Hz for instance, you need 2 metres 15 depth only for that. Anything shallower will miss that frequency. Don't even bother. You'll thank me. Target for 80Hz, which is 110cm. If you use 60x120s longitudinally into the corners, you may grab that one a bit.)

Hope this helps. I'm off to have my tea.

B.

LOL, I bet there are no chairlegs.

Regarding Helmholtz all what Barish said about it. I made 2 rather big ones, it's a lot of 'meditative' labor and IMO they are not so effective and in a small room such great absorbers will create other standing waves etc. .
You better can threat the room with lots of absorption first. And better post in the acoustic forum here in GS, lots of know-how.

I think you measured the wrong way (the heighth is approx. 120 cm - so I agree you have placed your monitors horizontal - and there's almost no room for standing waves).
heh
Most acoustical products are available in Europe.

I understand heh Continental Europeans should never get involved with imperial.

The standard room height in modern buildings is usually between 270 to 310 cm (9 to 10ft approx.)

B.

Barish has the right answer. A room that size needs broadband absorption, not tuned traps. Make enough of them, and thick enough, and you can tame pretty well even down to 40 Hz.

--Ethan

First off thank you all for the quick reply, and thank you for the detailed reply!!
Yes, I got the hight way wrong it is :

13,77 Feet Long
11,50 Feet wide
07,93 Feet high



Thank you all again for the response, I really appreciate the help

It's all right here:

Acoustics FAQ

The short answer is 4-inch thick rigid fiberglass wrapped in fabric, straddling as many corners as you can manage.

--Ethan

Anyone here heard of a so called "VPR absorber"?

It seems that it addresses the lower frequencies much more efficient (less thick porous material needed) compared to rigid fiberglass wrapped in fabric.

Might be a better option if room space is scarce....

Hello, so I am back. Had some Test and a lot of work these weeks but now i can get back to getting my studio ready again.

Thank you all for the replys!! Been doing a lot of researching lately.

So I planed and decided to do the following.

I am building 6 broadband absorbers this week, and will cover up as many sealing-to wall corners as possible

I am also taking a closet dest thing out of my room, so I can pull the mixing desk farther apart from the front wall, and center the mixing desk a bit more in the room. This is difficult, as I am allready almost in 40% deep in the room listening position, but the speakers are not far away enough from the wall.

Between the wall behind the mixing desk I am going to put a mattress that will also absorb the bass.

I will treat early reflection sites on the side walls.

"Armand"'s My Photos Photo Album - MySpace Photos

there are the pictures with more details in the link above


Srry if the room is a mess, at the moment they are building in our apartment and i had to stuff a bunch of things in there! Normally I have everything clean and tidy!!

im excited to tame that bass

Hey, here some pictures of the broadband absorbers, I didnt do a frame for them because it will be easier for me to hang them up the way I want on the cealing to wall.

Everything together costed about 100 Dollars, the Fabric was expensive but it was important to get the right one to keep the fibers in since they are going in my bedroom.

Is it better to put more broadband absobers up front by the mixing desk or in the back of the room?

In the link there is two pictures SETUP 1 and SETUP 2, which one do you guys recomend?
They say that speakers should be on speaker stands because of early reflections with the mixing desk, on both setups the tweeters are at ear level. But which one do you think would be better as of early reflections?

"Armand"'s My Photos Photo Album - MySpace Photos

Oh, sure, the good old Verbundplattenresonator!

It looks like it's this:

This thing
This thing

Yeah, they look good as well!

I actually never noticed in how many places they are to find!
Even in our school they have these!

Both. heh

--Ethan

Thank you

What about the Setup 1 and 2?

I'm flying out the door to the AES show until next week, so I don't have time to wade through all those photos. Hopefully someone else can advise you. There are lots of knowledgeable people here!

--Ethan

I know this is an old thread, and the topic has strayed from the title, but...

Here's a link to the basics on Helmholtz resonators, as well as an excel calculator to help design tuning.

What the Helmholtz is a Helmholtz resonator?

Admittedly, I know very little about these devices... mostly because topics here rarely touch on them. This isn't me suggesting their application... this is me trying to learn more about them.

From what I gather, there seem to be two types. The panel type, which is sealed and filled with insulation, and the panel's depth and amount of perforation determine the affected frequency? And the type posted in the link above... which appears to be a sealed vessel, partially filled with insulation, and tuned using a sliding port... to change the internal volume.

What the article or calculator doesn't seem to mention, is amount of internal volume needed to achieve appropriate results. For example, you can open the calculator and achieve the same resonant frequency by playing with the relationships between cubic volume, length of port, and diameter of port...

It only makes sense that getting a lower frequency by increasing the internal volume, and decreasing the port will allow more absorption, as you are able to fill the vessel with more absorptive material.

Has anyone used these types of devices in a modest sized room with some success, and do you have any pictures? I'm particularly interested in the vessel type, as they appear to be more forgiving in regards to their ability to be tuned.

I vote for set-up 2 by the way.

Here are some interesting links :

Acoustics Forum - Helmholtz formula, is this incorrect?

Acoustics Forum - Looking for input on my bass trap design...

Helmholtz Resonant Absorber - Reviews and News from Audioholics

Apparently the formula for Helmholtz resonators given in Master Handbook of Acoustics is incorrect
(see the first link).

Paul P

Interesting indeed.

In the first link, there was a gentleman who claimed having success with resonators... but not as a trapping device to cure modes, rather being a device that introduced sympathetic resonation in areas where there were nulls.

The third link explains that, even with an empty cavity, the vessel works as an absorber, due to the constant air pressure battle at the vent. Physical absorption, as it would seem, is added only to match the vibration duration to the reverb time of the room, but at an expense of less effectiveness?

It gives me little hope, that someone as intelligent as DanDan couldn't have success with these.

Nice links, Paul.

I'm not sure if Alton Everest had it wrong or not in his Master Handbook, but the ones I've built so far seem to work well. Is it possible that the formula is for a different object?

The resonators out on the site you showed was for a pure hemholtz device, which is a cylinder. The formula in his book is for building a rectangular box, based on an "array" of hemholtz resonators. By drilling holes in the front surface of the sealed box at predetermined distances, diameters, and depths, you can create the effect of many such resonators.

These bass trap types are much easier to get right than the slat type resonators. And according to what I've seen in experimentation, any resonator type trap is more powerful at absorbing sound than other trap designs I've seen. Of course, I haven't tested this observation myself.

Do you have a link or spreadsheet containing front panel treatments for different tunings?

There are two formulas stated on the thread "Need 31 Hz bass trap info". The first one is aimed at deciphering the actual perforation percentage of your front surface, based upon the thickness of the face and the depth of the airspace within, front to back.

The second formula is based on how to convert that perforation percentage to hole diameter (bit size) and how closely to drill those holes.

There are really a number of patterns you can use, but the formula I stated is actually for the holes stacked in perfect columns and rows. Take care that each "resonator" is behind each hole, so the distance between holes is, in your mind's eye, separated down the middle. If the distance between your holes is 4 inches, then 2 inches from the hole marks the resonator boundary for that hole. This is how you know how far from the edge to start drilling. In the end, your holes will be closer to the outside (interior) edge than to each other. Otherwise, it may not work right.

Note that the holes drilled must be fairly precise, so you must be careful to drill directly downward, and using drywall for the face is out of the question. Use high quality plywood (with smooth surfaces) for the face.

We actually put this design to work in our last small, commercial production studio, in the piano room. Audio testing before and after proved it to be a stellar success. That was a very small room-just enough room to get around the piano (I don't know why people put pianos in small rooms, but it wasn't my idea!), but no longer sounded like a small room in the recordings. The traps were used in 2 corners and 2 of the 4 walls contained wide frequency absorption panels, like those described by this forum. So although people may argue that a small room simply cannot be "fixed", it most certainly can be improved.

Here are the relevant pages from Master Handbook of Acoustics 5th ed.
(which I have, by the way) :

Helmholtz (Volume) Resonators

Click the blue arrows to open the box and scroll down a bit.

I think the formula that might be in error is the first one at the beginning
of the section, the array type resonators referred to by ejbragg are dealt
with a few pages down.

There have been many editions of this book and everyone has a different
one so what might have been an error in a previous edition may no longer
be.

Paul P

Thanks, Paul. That's precisely where I got my information. I do have a slightly different edition (4th). Page 213, example A is the model I just described. 12-9 is the first formula I referred to. A more useful arrangement of this formula deserved to be posted:

12-9b: p = t * (f / 200)^2

Using this arrangement, you can insert the frequency you wish to blast, enter the thickness of plywood (or whatever) you wish to use, and get your perforation percentage.

The second formula I used is given in example A; only used the variable "m" instead of "S", since I tend to confuse "S" with Sabins!

Just to add you can also use thicker then 4" which will work better or fill the whole corner which is even better then that!!!!!!!!

Here's some more audio porn that I came across while following a link in
another thread : Listening Rooms. Several helmholtz resonators are
apparent in the pictures (there's a second page). I like the way they're
layed on their sides and become furniture.

Goes to show that treament doesn't have to be ugly.

Paul P

Sure, but that looks very expensive! As I always say, with acoustic treatment you can have effective, attractive, or affordable. Pick any two. heh

--Ethan