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[InflatableMouse]

I'd like to experiment with some panels to absorb mid-to-high frequencies in my room. I realize the best thing to do is to get a professional/calibrated mic and take measurements with REW or some other software but to be honest, I think the learning curve for that stuff is pretty high and I don't want to invest a lot of time into that when I will probably never use it more than once.

The problem is when playing at louder volumes loud shouts (vocals) they echo in the room, its annoying and sometimes even hurt. Muddy Waters Folk Singer is a good example, when he does these shouts on that album it echos in the room. Another example is Alison Krauss' voice, when she sings louder it does the same thing. Higher frequencies are less of a problem.

I'm not really interested in getting it perfect, I really only want to try and dampen that echo effect. I read rockwool is a good material, or certain kinds of foam. I understand the denser the material is, the lower frequencies it dampens and the more higher frequencies it will reflect.

From the examples I gave, can anyone help me with what density foam or rockwool I could try? I would create the panels myself and wrap them in linnen cloth. I am also interested in experimenting with corner panels (triangular shaped) as opposed to flat panels, although I have no idea whether my problem has anything to do with corners or not. If not, please let me know so I don't waste my time on that .

This will be a little project I'll be working on during the winter months. Since its basically just hobbying, cost should be kept to minimum.

Thanks for any suggestions!

[dean70]

Don't know if you can get hold of this http://www.attaudiocontrols.com/acoustic-treatment/tontine-acoustisorb-3 - I built timber frame panels 1200hx600wx100mm deep and filled with this 50mm thick and covered in black material.

I placed these at the first reflection points on the sides and suspended from the ceiling.

To measure:
-  Use REW and a Radio Shack SPL meter with a timing reference hooked up to one channel to get the total time of flight for the reflections by measuring the Impulse Response. - The time in ms can be converted to a distance in meters within REW.
 - Take a length of string attached at one end to the acoustic center of the speaker (or approx) and measure out the string to see what surface it reaches.
 - Mark the point on the wall with masking tape.
 - Repeat for each speaker and each surface (and each reflection in the first 50ms)
 - Place the panel over the marked spots and remeasure the Impulse Response.

* The first 50ms is crucial to keep the reflections >15db down from the primary signal.

* Acoustic Panels work better with equal air gap behind the acoustic material. Ideally they should be 8" thick, but that may not look too good atheistically.

You can get lots of good info here: http://www.hometheatershack.com/forums/home-audio-acoustics/ They are quite helpful with sharing knowledge.


 

[mwillems]

Here are two very good resources with lists of materials with their absorption coefficients at different frequencies:

http://www.sae.edu/reference_material/pages/Coefficient%20Chart.htm
http://www.atsacoustics.com/page--Selecting-the-Right-Acoustic-Material--ac.html

The second link has prices and links to buy.  

The key to reading absorption coefficients is that a coefficient of "0" means the material is perfectly reflective at that frequency, whereas a coefficient of "1" means the material only absorbs at that frequency.  It's important to recognize that a rating of "1" or higher does not mean that all possible sound will be absorbed (i.e. it's not a black hole), just that no sound will be reflected by the material at that frequency; some will be absorbed and some will pass through the material to the other side (where it may be reflected or absorbed depending on what's behind the material).  

You'll note that very few materials are perfectly absorbent at all frequencies; that's why the pros tend to layer multiple different materials when trying to create broadband absorbers (which also improves bass absorption).  The Owens-Corning 703 4-inch thickness Rockwool is probably the best all around absorbing material I know of.  

Corners and first reflection points are the best candidates for treatment.  It's super easy to make home corner bass traps out of stacked rock-wool triangles.  Google around, there are a few really awesome youtube tutorials on how to make corner absorbers at home. Dean's advice on panels for first reflection points is very good.  I would try building a panel or two and trying them in different locations (including across corners) before building corner traps though.  Corner treatment was very important for sound at all frequencies in my room (because my speakers are near the corners), but may be less so in your room.

And, I know you said you don't want to bother with it, but I'd strongly recommend borrowing or buying a cheap calibrated microphone to take some measurements.  It's hard to even know what frequencies you want to treat (or whether treatments are working) without some measurements.

I'm not really interested in getting it perfect, I really only want to try and dampen that echo effect. I read rockwool is a good material, or certain kinds of foam. I understand the denser the material is, the lower frequencies it dampens and the more higher frequencies it will reflect.

It's not just a matter of density, it's also a matter of the actual composition of the material itself.  Different sizes and shapes of fibers have different acoustical properties (which is why two rockwools of the same weight and size can have different properties).  Always try to find some testing info on the absorption coefficients of any material you are considering (especially foam, which can be either great or more or less useless).

[InflatableMouse]

Thanks guys! Good tips and info.

I'll be reading up on those links.

I've skimmed your topic again mwillems, about how to take measurements. It makes my head spin but I'll think about it. If I can find a cheap enough microphone I might give it a shot. Thing is, all those cheap ones are in the US and shipping and customs don't make it easy (let alone cheap) to get it here.

[mwillems]

Thanks guys! Good tips and info.

I'll be reading up on those links.

I've skimmed your topic again mwillems, about how to take measurements. It makes my head spin but I'll think about it. If I can find a cheap enough microphone I might give it a shot. Thing is, all those cheap ones are in the US and shipping and customs don't make it easy (let alone cheap) to get it here.

I know how it goes; you might be able to find a Behringer mic semi-locally that's a bit cheaper (their ecm-8000 is not a bad mic, but needs phantom power).

[mattkhan]

If I can find a cheap enough microphone I might give it a shot. Thing is, all those cheap ones are in the US and shipping and customs don't make it easy (let alone cheap) to get it here.

there is this place in Germany - http://www.acoustics.isemcon.com/shop.htm

[InflatableMouse]

I know how it goes; you might be able to find a Behringer mic semi-locally that's a bit cheaper (their ecm-8000 is not a bad mic, but needs phantom power).

But it needs to be calibrated right? It needs to come with some info that I need to input into REW, otherwise how does it know what sound pressure the mic registers is really what level?

Phantom power might not be an issue soon (hopefully), as I'm trying to sell my Teac DAC and buy a Tascam UH-7000 instead. I really want it for the A/D conversion but it has mic inputs and supports phantom power. I never thought I would use that so now its become a nice bonus . If I can sell the Teac  .

there is this place in Germany - http://www.acoustics.isemcon.com/shop.htm

Thanks, the cheapest I see is nearly 100 euros ex shipping. At minidsp they offer a calibrated usb mic for 75 dollars, which is considerably less (dollars to euros). If I could find one used with low shipping costs, I might take the plunge. But for something I will only use once and for which I don't expect too much due to my extremely limited knowledge on the matter ... I don't know. I'm kinda hesitant to spend more than a few dozen to be honest.

[mwillems]

But it needs to be calibrated right? It needs to come with some info that I need to input into REW, otherwise how does it know what sound pressure the mic registers is really what level?

Calibrated mics are best, but for basic measurements around the room even an uncalibrated mic would be usable.  Typically the mics have a "default" calibration curve printed on the box.  They're not super accurate, but probably accurate enough for you to tell what frequencies are causing your room to echo, but probably not accurate enough to go through the whole speaker correction process.

But, here's a calibrated mic for $50 from parts express:  http://www.parts-express.com/dayton-audio-emm-6-electret-measurement-microphone--390-801

No clue about the shipping, but the base price is getting closer to your "few dozen" euros.

[InflatableMouse]

Thanks, appreciate the effort.

Products  (1) $48.26
Shipping $44.98
Order Total $93.24

That's what I mean, some of the stuff over there is really cheap but the shipping just kills it.

Don't worry about it too much mate, I'm in no hurry. I'll watch out for one 2nd hand. Someone must have ordered one, used it once or twice and decides to sell it again. I'll get one eventually.

[mattkhan]

The only thing I can think of in the <€40 camp is going to be using an SPL meter that has a decent reputation, this pretty much means the RS SPL meter which you can still get on ebay in the UK at least. The major downside is the response is useless above may 2kHz but if you're only using it to measure decay times & look at ETCs and so on then it should be good enough (assuming you limit the frequency range you sweep accordingly). The next cheapest is going to be an ECM-8000 from Thomann but that's still €50 or so and, if the fact that the CSL guy no longer sells them is anything to go by, they don't have such a good rep these days. You also then need a pre amp which will add at least another £30 say (second hand from ebay) unless you have one already.

[dean70]

a RS SPL would be good enough to take Impulse Response measurements to check room reflections. The freqs you would capture are not that high anyway & well within the range of a simple SPL meter.

Corner traps would mainly tame any low freq room nodes (to a certain extent). I built panels 2400x900x150mm thick lined with 150mm of Acoustisorb for the front corners and placed them diagonally to get a decent air gap.

The air gap allows any sound that goes through the absorbing material to maintain some velocity to reflect off the wall behind and be filtered a second time by the panel on the reflection.

This tool will help you visualize how sound reflections behave.

[AndyU]

GIK Acoustics sell a wide range of acoustic treatment products, including the raw materials for DIY constructors. You might be able to get some good information from their site, and buy suitable material locally.

But you can also experiment for free - use spare bedding, cushions from sofas, pillows, coats and clothes and prop them up or hang them on walls at the first reflection points. The room will look a mess, but if you get an improvement along the lines of what you're looking for, you know it'll be worth spending money doing it right. Don't forget diffusion can be as important as absorption.

[Ninouchka]

I just read your post, you are from Holland, I thought.
I just bought a cheap and good calibration microphone at bax shop.
http://www.bax-shop.nl/landingpages/muziek-en-visie
You can order online or go to the shops. Bax shop now also has a shop in Antwerp.

[InflatableMouse]

Well which one did you buy because the cheapest there is 91 euros. I'm looking under Geluid & Recording / Rand apparatuur / Meet Microfoon.

[Ninouchka]

Sorry for the late reply..

http://www.bax-shop.nl/pencil-overhead-microfoon/devine-sm-200-condensator-meetmicrofoon

For the moment at 39 EURO. I bought this low budget to try out and learn the soft, but it is actually very good for measuring.

I also bought this db meter http://www.bax-shop.nl/audio-tester-meter/dap-digitale-db-meter/product-details.html
a bit more expensive but really good.

[InflatableMouse]

It looks like a gaslighter .

Thanks, I've added it to my wishlist.

[LeoB]

Owens Corning Fiberglass panels are very effective at dampening the echo effect.
I used Type 703 2” ASJ panels (http://owenscorning.eu/docs/products/700series_DataSheet.pdf) to make my sound absorbers and they worked very well. The price here in the US is about $65 for six panels, and I bought them locally.
I put a thin layer (about ¼”) of synthetic batting on top of each board, reinforced the corners with cardboard, draped the boards with fabric from a local crafts store and fixed them on the wall with the Rotofast Snap-On Anchors.
I don’t remember the exact cost of materials, but each finished board was less than $30 or so.

There is a picture of the room with the boards in the attachment.