1d or 2d Diffusors In My Control Room?

[morebutter]

I will be putting diffusors in a medium-size control room (25 x 13 x 10ft) on the side walls and behind the speakers, at ear level. I am wondering if it makes more sense to do 1d QRD or 2d Skyline diffusors in these places?

[SAC]

bnmbn

[morebutter]

Thanks for your reply. My main goal is to make the room less dead, as there is no ambiance right now and it is unpleasant to listen to music in there. I'm hoping that a collateral effect will be a smoothing of the midrange frequencies.

I should add that there a large number of full range absorbers (most surfaces). I plan to add some more on the back wall of the room, to help the null around 40-50hz caused by a lengthwise axial mode.

I know you said that a graph is not of primary importance, but since I have it, here's a recent measurement at the listening position:

[SAC]

bh their use.

[PaulP]

I'm not highjacking your thread morebutter, just feeding SAC an example so he'll keep talking

Originally Posted by SAC

Since many are using RoomEQWizard, I am curious to have a look at the ETCs generated. Additionally I am curious to know if there exists the ability to move the cursor along the curve - or x-axis - and to have a precise direct readout of the time value defined by the x-axis to at least msec precision. With a bit of luck, they will have sufficient resolution to identify individual specular reflections along with the correlative data.

(I am very new to RoomEQWizard so have no idea if my measument is valid.)

Here is the ETC plot I got when I measured my almost empty, untreated
room [12'6" x 25'9" x 9' (3.8m x 7.8m x 2.7m) though the room has large
openings into adjacent spaces.]



Zoomed in to show only the first 30ms :



The program does let you move the cursor with ms accuracy.

Paul P

[SAC]

vbvv

[PaulP]

Originally Posted by SAC

My first reaction: What are the limits of its precision and its ability to rescale the display?

It looks like you can zoom in as much as you want. I don't know how
accurate the plot is, though.

Can you redefine the y-axis gain intervals to show greater detail? In other words, to 'zoom in' to see the actual curve with greater detail?

Here's an expanded version of the previous plot :

And is the x-axis limited to millisecond resolution (1.18feet), or can this be changed to reflect "microsecond" precision?

It'll go as fine as you want but the 'window' gets awfully small.

Can you select the "Energy Time" (Curve) from the header for that impulse response?

The above plots were in the "Impulse" window with the "ETC" box checked.

The "Energy Time" window appears to be identical in function :

Paul P

[SAC]

vbnvbn

[terry j]

Originally Posted by PaulP

I'm not highjacking your thread morebutter, just feeding SAC an example so he'll keep talking

keep feeding paul!

[Nordenstam]

Hi SAC, great posts!


While the experts are gathered..

A thing that have been in the back of my mind for a while.. Seems this may be the right place to ask this question. How much reflection does it take to intrude in the Haas zone?

The reason for asking is the use of diffusers anywhere else than the rear wall. In rooms small enough to make the rear wall the only place to have more than 20ms path length. Lets assume a 2D diffuser to be perfect in that it spread energy in all directions. This means that any such diffuser with a speaker->diffuser->sweetspot path length of less than 20-50 milliseconds will send some energy back to the sweetspot, within the Haas time window. The placement will not matter, if it is an omni radiator, it will be a first reflection point no matter where it's placed in the room! Any qualified guesses on how much such a reflection have to be attenuated to be nonintrusive? My hunch says 10-20dB should do it, but.. I don't really know!

A single diffuser will probably not do much of a difference. But if we take something like Massenburgs room at Blackbird, or Ethans diffuser room. How much energy is sent to sweetspot within the Haas window?

Is this possibly consequential at any level or can the issue be disregarded as theoretical musings?

The reason for asking in this thread is that it may be on topic of the 1D vs 2D question. 1D's can be oriented so that it does not spread energy directly back at the sweet spot. 2D's however, being omni devices, may potentially be less benifitial in such a situation. On the other hand, 2D's spread energy more, perhaps making the reflection weak enough to be nonintrusive in the Haas window.


Would love to hear some musings on this question.


Cheers,

Andreas Nordenstam

[morebutter]

Unfortunately (or fortunately) I am on vacation and not able to do a time domain measurement however when I get back I will post one. For the time being I will follow this thread with interest, and thank you SAC for taking the time to share your knowledge here.

[SAC]

bnbvn

[SAC]

vbcvb

[Nordenstam]

Massive!

Thanks for taking your time to do this great writeup!


If I take your hints correctly.. For treating small listening room; rear wall diffusion is safe (due >20ms to time delay), while other surfaces can benefit of diffusion, checking the effect of the diffusers in the room using ETC measurements to make sure the reflections stay at -30dB or below with respect to excitation signal.

Does that seem right?

[PaulP]

Originally Posted by Lupo

If I take your hints correctly.. For treating small listening room; rear wall diffusion is safe (due >20ms to time delay), while other surfaces can benefit of diffusion, checking the effect of the diffusers in the room using ETC measurements to make sure the reflections stay at -30dB or below with respect to excitation signal.

How are we going to get a 30db drop in our reflections without using a lot
of absorption ? Are diffusors that will fit in a small room capable of this ?

Paul P

[SAC]

vbcvb

[PaulP]

Originally Posted by SAC

We are not damping the entire room! We are surgically damping ONLY the early arriving reflections sufficient to create the ISD at a given spot.

I understand that. I was remarking on lupo's summary that diffusion could be
used in places other than the rear wall if the diffusion caused a 30db drop in
the reflection. I imagine this rules out diffusion for at least the first order
side and ceiling reflections (or can you get a 30db drop out of a diffusor).

Paul P

[SAC]

vbvbnot?