Here is a site regarding diffusors :
Google can be your friend....
Google can be your friend....
There is no simple answer to your question, there are books written on this subject. The 'dead feeling of absorbsion' occurs in an overly damped room. Diffusion per se is not your solution, for example, if your 'deadness' is caused by excessive furnishings, drapes, furniture, etc.
FWIW, it depends on the sonics of your room, why they are what they are, where your problems areas are, and what you are trying to accomplish by putting up room treatments.
Diffusors are good for reducing the effect of direct reflections without deadening them - I would use them on walls behind the speaker or behind the listener. For example, the back wave from a panel speaker usually sound best when it hits the wall behind the speakers and it is diffused, not deadened by absorbers. Diffusors are likewise best behind the listener because it will diffuse, but not reduce second reflections from walls which will continue to bounce around randomly (a good thing, it can make your room sound more spacious, with out excessive brightness.
Absorbion panels are best used for killing first reflections from the wall near speakers (and ceilings - rugs work well enuf on the floor. This is a good thing because you will get a much cleaner initial signal from your speakers - the sound will have a purer tone, less distortion. It will help to enhance and expand the sense of soundstage.
FWIW, there is no cheap/easy fix. I'd suggest that you don't buy anything for your walls until you know exactly what you are doing and why...Of course if you've got spare money and don't like to study acoustic's, hire a pro service like Rives provides. :-)
Typically diffusors and their brethren are applied to treat an empty four wall space to make it suitable for use as a recording space, monitoring environment, home theater or listening room
If you already have a room full of furniture and furnishings it may very well negate the effect of a specialized piece
Before you start spending - and fighting the WAF battles - you might try rearranging furniture or the speakers to see what difference it makes
To the OP
1. What are diffusors?
**** Proper diffusion scatters sound not only in the physical domain but also in the time domain. There are a variety of uses from minimization of comb filtering behind bipole/dipole speakers to minimization of slap echo high in a room to providing the illusion of a larger sound field in the rear of the room.
2. What's the minimum I'd pay for these in a room my size
**** I'd need to know a lot more about it in terms of usage, construction, seating locations, furnishings, etc. before we could even make a rough guesstimate as to what would be appropriate.
3. How do they make a room sound bigger than it is?
**** When you scatter sound physically and in time, it can give the same aural cues as being in a larger space by giving you lower amplitudes from more directions and generally later in time.
It is an excellent idea to look at acoustics...but where do you sit? So many sit with a wall right behind their head - if that is the case then start by finding a better listening position.
FWIW - Broadband is the most effective treatment in any space. The "dead room" issue comes from applying too much mid and HF absorption from thin "cosmetic" panels. Diffusers are necessary in small spaces - if you have a speaker within two feet of a wall or you sit within 3 or 4 feet of a wall then diffusers will be essential. Diffusers can also help in asymmetrical situations. The best place for diffusers will be close to the listener - in a very small room they are essential.
Sorry - I'll have to disagree. Diffusion is best when you're farther away as the waves need proper time and distance to spread out. When you sit very close to a boundary, the biggest issue is actually bass buildup which requires absorption.
I agree that many people put up too much thin absorption and ignore the bottom end. A balanced approach is much better.
Smaller rooms require proportionately more broadband bass control. On the positive side, their modal activity is higher in frequency due to the smaller room dimensions.
Lead Acoustical Designer - GIK Acoustics
I agree with Bpape. My experience with diffusors is when too close they tend to act as absorption, deaden the sound, definitely need space to spread out the sound. I also agree that in a smaller room bass control is the first place to start, this pays off more than any other treatment.
In the end, balance and synergy is critical. Absorption, diffusion and reflections (untreated surfaces) all need to be in balance. I suspect over-treatment is too often done, I've ended up taking out some of my treatments over time. Once you get your basic system optimized, less treatment is needed.
Diffusion is best when you're farther away as the waves need proper time and distance to spread out. When you sit very close to a boundary, the biggest issue is actually bass buildup which requires absorption.
And I fully agree with that.
What I meant was that diffusion is more essential for close reflections at either end (Close to speaker or close to the listener - if you are unlucky enough to have a terrible setup). Of course, diffusion is much more effective as you get further away from it.
I also agree that bass is the biggest issue when you sit close to a boundary but that does not mean that higher freqency reflection are not a problem too even if they are smaller).
Sorry if I wasn't clear.