Hello everyone.

Having done a stack of reading online I decided to treat myself to a treated room. My room has a very uneven bass response and ringing echoes after hand claps.

I set about building some broadband absorbers... 110 cm by 70 cm - 4 inches of padding, 1 inch wooden frame and then installed them around the room - especially in the corners (although not on the roof). There are six of this size and a further 3 wich are not as wide.

The design of the asbsorbers was found here..
http://au.youtube.com/watch?v=iyYUpkpL0gw

The absorbers removed the echoes in the room but made the uneven bass response even more obvious. (I'm sure its not my speakers/amp btw).

Ive tried putting the absorbers in a few different positions but nothing seems to stop a huge bass boost at around 100 - 110 hz and then a dip and another boost as the pitch gets higher.

Here are some images and a sound file (recorded with a cheap mic) which tell the story.







And Here is the mp3 of the sine wavs as seen in the purple part of the picture.. Blue waves were played. Purple is these same waves having being recorded in the room.

http://gdsamples.com/images/roomstuff/Bass_Sine_01.mp3


and a modecalc plot...



This mode calc image is for an even room - without the corner angled off like my room so it may not be that relevant... still the height and length stuff may apply.

If anyone can help me understand what is happening in this room and how to go about treating it to even out the sine waves recorded above then please let me know... I can rearrange everything and do another recording to see the results.

Thanks,

Chris.

The absorbers removed the echoes in the room but made the uneven bass response even more obvious. (I'm sure its not my speakers/amp btw).

So you have obviously tried moving the speakers to differnt locations within the room then - even movements of 1cm in / out / further apart / closer together / toe in etc. can have amazing results from the listening position?

Yes that phrase "Im sure its not my speakers/amp" is a little ambiguous. I was refering to the hardware and its output but not to the position of the speakers.

I have moved the position of the speakers forward, backward and to the left and right. Different positions give minor changes to the bass boost - especially on either side of the 104 hz note. Still, these changes are minor and often difficult to perceive, especially when compared to the increases in volume of these pitches relative to their neighbours.

I might try building yet more traps and fill up even more of the corner space...

Cheers,

Chris.

Ha, wow, that's pretty cool (sucky too, of course) but if you compare the modecalc graph to the measured peaks, there are several correlations... especially the predicted peaks around 100-110Hz and 150-160Hz.

It seems bizarre that you're getting almost no response below 100Hz... what's the mic and it's specs? You realise, of couse, that the mic will "colour" and measurements you make? If the mic performs poorly at low freq's then your measurements will look dodgy no matter how good your room is.

It might help if you provide a diagram showing the current placement of the traps.

I've just finished planning and ordering the materials to do a similar thing. I'm wondering, have you got enough panels? From what I can gather, you're using 9 altogether, but with the room dimensions, those six large ones would cover maybe three of the corners and still leave large gaps. For a similar sized room to yours I'm planning on using about 20 traps (combo of bass traps for corner and rear-wall, as well as thinner ones for the sides and ceiling to do reflection points) and it was only $$$ that stopped me ordering another pack of fibreglass panels to get the total up to 30.

What sort of materials are the traps made of?

I've learnt that the rear wall is also important for bass... equally important to the corners. If you can get at least a couple of 10cm thick panels mounted 10cm away from the rear wall you might find some improvement too.

The loud speakers roll off at 80 hz and I don't have a sub woofer so that explains some of the lack of response below 100hz,

The mic is truly a cheap and nasty stick mic - no doubt its coloring the recording. but how much? With the foreknowledge that it will not be perfect, what I hear in the room still corresponds quite nicely with what I see/hear in the recording.

Material is rockwool for 4 panels and tontine acoustizorb for the other 5.

PLacement in reference to pictures posted above is:

2 straddling bottom right corner(from floor to about 60 cm below roof).

2 straddling top left corner - 1 placed 30cm above floor - 1 mounted 30 cm below roof.

1 straddling bottom left corner - again mounted 30 cm below roof.
(note my futon bed is in this corner so its a big absorber parallel to the floor. not sure how effective it is but its there)

1 on angled wall top right where corner has been walled in.

1 on bottom wall to right of door. directly beside speakers and listening position.

1 on back wall behind listener and one on front wall behind speakers.

A good question at this point is - Will I need more absorbers? and if so how many?

Any advice is of course much appreciated.

Cheers,

Chris.

What brand and model? Also, see this:

Comparison of Ten Measuring Microphones


Yes, and as many as you can manage. It's impossible to make any small room perfectly flat, but with a lot of bass traps you can at least get to where you can mix reliably.

--Ethan

Unfortunately the mic has no brand nor model number. It is a mic on a stick that is designed for voice over ip stuff.

I'll get a behringer ECM8000 and do another recording. (Ill do this before I change the room so a comparison with the other mics output is possible)

I will also build more traps - about 15 should do it.

It would also be convenient for me to build triangular chunks that fit in the corners and go from floor to ceiling. I have seem these referred to as "Super chunks."

Before I go and buy more materials though, I am wondering how 'super' these chunks really are, and about the dimensions of the chunks. Equilateral or not? and how deep/wide to make them.

As before any advice is appreciated.


Cheers,

Chris.

If the cost of material is not a problem, filling the corner totally is better than a four-inch thick panel. But it's only a little better. Like 20 percent better for using twice as much material.

"Like 20 percent better for using twice as much material."

...which would mean, I imagine, that you'd be better off taking the same amount of material, making 2'x4's and placing them over every corner possible (including where wall-ceiling & wall-floor meet) rather than chunking a couple of corners.

"Unfortunately the mic has no brand nor model number. It is a mic on a stick that is designed for voice over ip stuff. "

I would think that's part of the reason why you've got poor response below 100Hz, along with what you said about your speakers. It will be interesting to see how the ECM behaves in comparison.

One other thing I've noticed... it looks like you've got a stereo sine track playing as your measurement tone. Were both speakers going at once?

I don't know much about measuring room performance yet, but I have a feeling that you're only meant to test one speaker at a time. Can't be sure though.

I prefer to check LF response with both speakers playing because that's how music is usually mixed, with the bass and kick generally centered. But it's a good idea to check each speaker separately too.

--Ethan

Here are the images of the new recording with the ECM8000.
It would appear that the cheap mic did not do too badly down in the lower basses.

In picture one:
Purple is a cheap mic. (10$)
Orange is ECM8000 (perhaps also cheap but its all relative.)



In picture 2(which is an overlay):
Darkblue is cheap mic.
White is ECM8000.



Also, I'm not sure about the relative scale of the two audio files/recordings on the y axis(db). I scaled the ecm800's image so that the G# at 104 hz was roughly the same as that of the cheap mic. This is the reference point I chose.

And there you have it.

It will be about a month before I have had the cash and the time to make ten more bass traps for a total of 19 placed in the room. At which point, I will make yet another recording..

Cheers,

Chris.

Thanks for posting the comparison. I've always said cheap microphones are fine for testing bass frequencies, and you proved that correct.

Hello again,

Before I start building, I have a couple more questions regarding the size and position of the absorbers.

Is 60 cm * 120 cm too small for the absorbers?

The alternative is 80 cm * 120 cm which will mean less absorbers in total and thus less corner coverage.

I'm hoping that 60 cm wide will be fine so I can block off almost all the corner space in the room.

Also, there are some frills - ceramic decorations which protrude downwards from the ceiling. These will prevent the absorbers from being flush with the ceiling. Do absorbers placed in corners need to be flush with the walls/ceiling or can they be hovering 1 or two inches out?

Not sure when the room treatment will be finished but I'm hoping to have it done by Christmas. That way I can show the relatives after lunch and play them some music.

As before any advice is appreciated.

Cheers,

Chris.

60 by 120 is good, but larger is even better. With bass trapping, you can never have too many and they can never be too big. But 60 by 120 is typical, and works well.

A space of a few inches is okay. The main goal is to get them at least near to corners.

--Ethan

Fantastic - 60 by 120 it shall be.

Thanks for the advice. Ill get to work on the room soon and post up a recording when its done.

Cheers,

Chris.