Diffusion vs absorption? My set up

0 Members and 1 Guest are viewing this topic. Read 15036 times.

BobRex

Re: Diffusion vs absorption? My set up
« Reply #40 on: 22 May 2012, 06:27 pm »
So what does the response graph look like above 100Hz?  Below that, I wouldn't touch a thing - +-3dB is essentially perfect.  Although, given what I do see above 100, it would appear that you are running the subs a little hot.  Assuming the graph shows all speakers being driven of course.

Nuance

Re: Diffusion vs absorption? My set up
« Reply #41 on: 22 May 2012, 07:30 pm »
So what does the response graph look like above 100Hz?  Below that, I wouldn't touch a thing - +-3dB is essentially perfect.  Although, given what I do see above 100, it would appear that you are running the subs a little hot.  Assuming the graph shows all speakers being driven of course.

Yes, I am running a little hot; I just like it better that way. :) 

« Last Edit: 23 May 2012, 12:14 pm by Nuance »

BobRex

Re: Diffusion vs absorption? My set up
« Reply #42 on: 22 May 2012, 08:55 pm »
That might be tough to get rid of.  540Hz has a wavelength of 2 feet.  Typically you'd move the listening chair or shift the speakers, but that may screw up your <100Hz performance.  Have you tried a blanket over the tv?

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #43 on: 22 May 2012, 09:59 pm »
ETC of each speaker and waterfall for each speaker below 500 Hz is much more useful looking at.

Nuance

Re: Diffusion vs absorption? My set up
« Reply #44 on: 22 May 2012, 10:23 pm »
That might be tough to get rid of.  540Hz has a wavelength of 2 feet.  Typically you'd move the listening chair or shift the speakers, but that may screw up your <100Hz performance.  Have you tried a blanket over the tv?

I have not - will try that now, then take more measurements.  How do you do ETC with REW?

Edit: adding the blanket didn't change anything measurements wise, but I will perform listening tests later.

I have added the impulse and waterfall plots; there's some obvious ringing in the nether regions. :)  I also added a current L & R in-room averaged response.

Will update later with the proper plots.
« Last Edit: 23 May 2012, 12:14 pm by Nuance »

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #45 on: 23 May 2012, 07:59 am »
How do you do ETC with REW?
Under Impulse, choose Envelope (ETC) at the right bottom and remove all the others. Zoom in on the first 50-70ms. What comes after that is of no interest, since the reflections will been attenuated a great deal.

Your waterfall shows that you have some troublesome resonances and a bit of a long decay.You might want to change the settings to 500 ms for both window and time.

Nuance

Re: Diffusion vs absorption? My set up
« Reply #46 on: 23 May 2012, 12:15 pm »
Under Impulse, choose Envelope (ETC) at the right bottom and remove all the others. Zoom in on the first 50-70ms. What comes after that is of no interest, since the reflections will been attenuated a great deal.

Your waterfall shows that you have some troublesome resonances and a bit of a long decay.You might want to change the settings to 500 ms for both window and time.

I'll post those this evening.  Thanks.

Nuance

Re: Diffusion vs absorption? My set up
« Reply #47 on: 23 May 2012, 11:43 pm »
Here's the ETC measurements; any help is most appreciated.  Other than widening the room and adding a false wall behind the LP, should I treat anything else (diffusion, more bass traps, absorption)?







That might be tough to get rid of.  540Hz has a wavelength of 2 feet.  Typically you'd move the listening chair or shift the speakers, but that may screw up your <100Hz performance.  Have you tried a blanket over the tv?

That peak at 540 Hz and 3.5KHz definitely shrinks if I move the mic to the left or right seat, as opposed to the center seat.  It's prominent in both the L and R speaker measurements, though, so it must be room interaction, eh?
« Last Edit: 24 May 2012, 10:18 pm by Nuance »

kiwi_1282001

Re: Diffusion vs absorption? My set up
« Reply #48 on: 24 May 2012, 02:12 am »
I just read all four pages of your thread in AudioEnz. A fascinating and very informative/helpful read. It was fascinating to study your journey and the huge improvements you gained.

Very few people document and explain their changes any where near as well as you have. I found it way more helpful than reading piles of documents on the theory of room setup.

Thank you very much.

Rod

Thanks for the kind words Rod.   Journey is indeed the right word and that journey continues.  The improvements have indeed been huge, far bigger in fact than any equipment upgrade has ever delivered.   Somewhat foolishly the room was the last thing I worked on and it should have been the first.

 I am presently experimenting with different options for rear wall treatments; listening and measuring results with different treatments including absorption, polyfusors, 1D & 2D diffusers.

Some audiophiles justify their choice of treatments by reading piles of theory and following others.   While I understand this I also think that experimenting in your own room, with your own measurements and own ears is the way forward if the goal is maximum enjoyment of the music rather than +/- 3dB 20Hz-20KHz.

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #49 on: 24 May 2012, 07:25 am »
Here's the ETC measurements; any help is most appreciated.  Other than widening the room and adding a false wall behind the LP, should I treat anything else (diffusion, more bass traps, absorption)?
You need to let the window only show the first 50-70 ms. You zoomed in, but you also moved the window to the right. We need see more details to say anything. Let 0 start at the far left.

Pictures of the rear of the room would also be nice.

BobRex

Re: Diffusion vs absorption? My set up
« Reply #50 on: 24 May 2012, 12:40 pm »
That peak at 540 Hz and 3.5KHz definitely shrinks if I move the mic to the left or right seat, as opposed to the center seat.  It's prominent in both the L and R speaker measurements, though, so it must be room interaction, eh?

More than likely it is a room interaction, you've got a summing going on at that spot.  What happens if you move the mic front or back?

Nuance

Re: Diffusion vs absorption? My set up
« Reply #51 on: 24 May 2012, 03:45 pm »
More than likely it is a room interaction, you've got a summing going on at that spot.  What happens if you move the mic front or back?

That's what I figured.  If I move the mic forward it's still present, though the width of the peak changes a little.  I haven't tried moving the mic back, as there's no way I'll be moving the couch further away.  Although, maybe I could convince the wife we need a 60-65" plasma then instead. :D

You need to let the window only show the first 50-70 ms. You zoomed in, but you also moved the window to the right. We need see more details to say anything. Let 0 start at the far left.

Pictures of the rear of the room would also be nice.

Jeez...I cannot get it together this week; sorry about using the wrong graph limits.  I will re-post them tonight, as the .mdat file is at home on my laptop.  I could also just post the entire file if that would be easier. 

I appreciate the help fellas!

Something you could consider is setting up angled wall dividers that will redirect the energy to rear sidewalls where you have diffusors but will still pass the bass through.

I forgot to ask about this: do you have any recommendations from a manufacturer that already offers something such as this?  I mean, I can research wall dividers all day long, but does one specific brand or model stick out among the others for this type of use?

youngho

Re: Diffusion vs absorption? My set up
« Reply #52 on: 24 May 2012, 03:46 pm »
Something I would consider in a room that's somewhat narrow is getting speaker with controlled dispersion. For example a good waveguide speaker. These will give less reflections from sidewalls and you don't need to dampen them as much and one can therefore avoid the headphone feeling which easily comes with much absorption on sidewalls. Here's some examples of that type of speaker:
http://gedlee.com/Loudspeakers.htm
http://www.jblpro.com/products/recording&broadcast/lsr6300/JBL.LSR6332.pdf

The JBL LSR6332 are actually wide dispersion but great linear on- and off-axis response. A better example of controlled dispersion would be the JBL Project Array series, which have a higher directivity index for most of the frequency spectrum.

Nuance

Re: Diffusion vs absorption? My set up
« Reply #53 on: 24 May 2012, 03:51 pm »
The JBL LSR6332 are actually wide dispersion but great linear on- and off-axis response. A better example of controlled dispersion would be the JBL Project Array series, which have a higher directivity index for most of the frequency spectrum.

They are a fantastic speaker (objectively, as I've never heard them).  I believe they are Harman's best measuring speaker, period.  The fact that they use those instead of the Revel Salon2's is telling IMO.  Or maybe it's because they play the nicest in a variety of rooms due to their superior polar and sound power response.  My speakers have a very good polar response, but not that good; I don't think many speakers measure that well, actually.

youngho

Re: Diffusion vs absorption? My set up
« Reply #54 on: 24 May 2012, 05:36 pm »
They are a fantastic speaker (objectively, as I've never heard them).  I believe they are Harman's best measuring speaker, period.  The fact that they use those instead of the Revel Salon2's is telling IMO.  Or maybe it's because they play the nicest in a variety of rooms due to their superior polar and sound power response.  My speakers have a very good polar response, but not that good; I don't think many speakers measure that well, actually.

I had wondered about whether part of the reason for the JBL Pro speakers was easy duplication of the reference rooms in various countries, sort of the way some studio monitors seem to be chosen for easy availability anywhere?

I never directly compared the LSR6332 graphs with the Salon2 and Array 1400 graphs on page 399 of Toole's book (they're not named but pretty clear). Not at home, so don't have book handy, but the accompanying text was part of why I was happy to get the 1400s...

Nuance

Re: Diffusion vs absorption? My set up
« Reply #55 on: 24 May 2012, 10:19 pm »
Post 47 has been updated with ETC measurements within the specified window.

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #56 on: 25 May 2012, 07:41 am »
Post 47 has been updated with ETC measurements within the specified window.
Good. 0 represents the direct sound. Of course, it doesn't arrive at 0 ms but that's how REW shows it. What comes after 0 are reflections of surfaces in the room. What we want is an ISD-gap. An ISD-gap is a gap in time where the reflections are attenuated enough so we can hear the recorded signal undisturbed. For this to happen the reflections need to be down -20 dB at minimum. -30 dB would be better, but can be difficult to attain with many speakers in small rooms. After the ISD-gap there should be a strong termination where the energy is arriving from diffusors. The length of the ISD-gap is determined by the space of the room, but ideally we want it to be a bit longer then the time the sound travels in a recording room. 20-25 ms is something you could aim for in your room.

So what you need to do is to find those spots that create specular reflections and treat them and measure again. Always start with the earliest arriving ones. You can either use an mirror or the string method. Then you place an absorbent at that spot, measure and see if it attunuates. You continue with this till you have all reflections up to a certain time below -20/-30 dB.

Here's an example of what you want. Tha first picture is before treatment. The second shows and ISD-gap, or a RFZ as they call it here, and it follows with diffuse energy.


Big Red Machine

Re: Diffusion vs absorption? My set up
« Reply #57 on: 25 May 2012, 10:46 am »
Are the absorbers at the first reflection point?  They appear to be forward of where I would expect them to be.  They are also high and not in line with your ears and the speaker cones.  The left side is going to hit the couch which is fine.  Lay that left one horizontally along the top of the couch and lower that right one down 2 feet and see what you get.

Based on that ETC plot you have zero delay and lots of mush gong on at once. 

I attached a (crappy) picture.  The DVD rack has since been moved, but other than that the layout is the same.  Obviously I am limited in what I can do, but the speakers fire down the long dimension and are about 7.5 feet apart (flanked by dual subs) and just over 2 feet from the side walls; they are 4 feet from the wall behind them.  The listening position is 10.5 feet from the speakers.  As you can see I have a first reflection absorption panel at the lateral walls, and a pair of bass traps in the corners.  The room isn't dedicated and extends well beyond the couch (passed where I was standing when I took the picture), which then becomes the children's play area (lots of toy boxes, toys and various kiddy stuff everywhere).  The room then L's around and open to another 12x15 section (complete opposite end of the TV and speaker system).  Obviously it's not an ideal setup, and my plan is to expand the right wall another 5 feet (the laundry room is way too big), and perhaps use wall dividers like you mentioned behind the listening position.




Anyway, do you have an suggestions?  And yes, I want an accurate listening environment (as much as I can get with this crappy room).  My apologies to the OP - don't mean to hijack the thread.  I didn't want to start another one, though, since I am pondering adding diffusion myself.  Thanks for letting me post in your thread.

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #58 on: 25 May 2012, 10:57 am »
The couch will quite certaintly reflect some. A thick woolen blanket can be placed upon it and then look at what the measurement shows afterwards. The most troublesome area right now, however, would be the untreated ceiling.

Bjorn

Re: Diffusion vs absorption? My set up
« Reply #59 on: 25 May 2012, 10:57 am »
double post