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Let's say I had a few thousand dollars to spend.... What's the closest I could get to a room with an impulse response that's like white noise with a decaying exponential envelope (see above)??
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Since every room is different and each type of speaker has a different acoustic radiation pattern, an engineering analysis must be performed using a test tone generator, with at least one test tone, 315 Hz works very well but you can use others too, say 100 Hz or 1000 Hz. Those test tones can be found on most if not all Test CDs and Test LPs. You also need a SPL meter.The objective is to locate sound pressure peaks in the room occur, in the 3-D space of the room since some standing waves occur out into the room. So, map out the room's sound pressure peaks that are 6 dB or higher than the average sound pressure in the room, obtained using SPL meter. Those locations are where you need to focus, using a variety of room treatments, absorbers, diffusers, echo absorbers, bass frequency traps, Helmholtz low frequency resonators, high frequency resonators, etc.
This methodology is guaranteed to produce sound with more dynamics, greater clarity and greater focus.
Edits: 11/05/22 11/05/22
Hi
Without a time scale it's hard to say, but if that is say 50ms of time or more, to me that doesn't look much like a speaker in a room but more like an ambience processor.
Normal room impulses, especially viewing as an ETC curve clearly show the loudspeakers impulse followed by a short time where there is no reflected sound, followed by the first second and third arrivals etc.
Not the fuzz per se, but the decay envelope. I took it as a desire to make a smaller room sound like a big one. It's not an easy desire to satisfy.
Ah, that wasn't clear from his post and why i thought it looked much more like a processor than a measurement of loudspeaker in a room..
What he may want is something an acquaintance at work, Steve Barbor developed called LARES which creates that impression on command impression.
My introduction with it was my partner at work Mike playing a trumpet on stage in a large church while the LARES operator took the room sound from a very dry semi-anechoic space slowly to a giant cave in a very believable manner.
The trick is having multiple microphones in the room and DSP that de-correlates the sound, the opposite what what i have to do with speakers themselves.
If one is concerned with "the stereo image", the impulse he showed would be TERRIBLE if that was 1 speaker at the listening position. The space between the first/ direct arrival and the trail of reflected signals that follow is critical for stereo imaging, with LARES, all the late energy is well behind that critical range (and why close sidewall reflections screw up the recording's image too).
https://www.wikiaudio.org/haas-effect/
Tom Danley
Danley Sound Labs
A Canadian acoustics consultancy put up a great, simple, common-sense method to map early reflections in 3D. I wrote it up in Stereophile 20 years or so ago. At the link.
If you want to nerd out, go here: http://www.mcsquared.com/
If you have a couple of grand to spend, I'd recommend RPG Binary Amplitude Diffusor Panels, BAD Panels for short.
https://www.rpgacoustic.com/bad-panel/
I believe that you can get art images printed on them now.
There are panels out there that cost less. However, they are mostly all absorption and zero diffusion. The RPG BAD Panel does both.
good luck,
john
JM,You might be interested in Ron Sauro's measurement results of the RPG BAD panels. He says they work (in a specific frequency range [14kHz-16kHz]), but not the way RPG says they do.
He says it has absolutely no diffusion what so ever.
RPG BAD/binary amplitude discussion starts @ timecode 10:42:xx.
https://www.youtube.com/watch?v=ZuhzgTbuY-A&list=PLY9FC0yl_myIGGAX-mqiuD3edDTNLQ6Zf&index=1
Ron Sauro runs the NWAA Labs measurement facility.
https://www.stereophile.com/content/nwaa-labs-measurement-beyond-atomic-level
Another similar discussion starting at timecode 1:55:xxhttps://www.youtube.com/watch?v=5JgeF05kr2o
.
2022/03/30 Historical Records CENSORED
Edits: 07/01/23 07/01/23 07/01/23
I'm pretty sure I had RPG panels many years ago, along with Skyline diffusers for rear wall, Tube Traps, which don't necessarily go in the corner, Corner Tunes, Golden Sound Acoustic Discs for room corners, Large Brilliant Pebbles xtals for room corners on floor, Constrained layer dampers for glass doors and walls from Ron, DIY 10 foot folded Helmholtz resonator, Mini Brilliant Pebbles xtals for windows, tops of Tube Traps, top of Skyline diffuser, top of Speakers and room walls,. Also, tiny little bowl resonators at high sound pressure points. The one thing I didn't have is that horrid charcoal foam you see a lot of in recording studios. Last but not least Blue Meanies for each wall and a Green Meanie for the ceiling.
Thanks, all good answers.
A real room will not have a cleanly decaying impulse response due to reflections and room modes.
Typically, the problems to treat are:
- Flutter echoes between parallel walls
- Early reflections from the walls and ceiling
- Bass peaks due to room modes
Flutter echoes and early reflections are broad band, and they can be dealt with using absorption, diffusion, or a mix of both. Room modes require absorption, a lot of it, and it should be narrow band.
The benefit of using absorption for flutter echoes reflections is that a relatively thin (2 inches) absorbing panel will be effective over the whole midrange and not just the treble. A diffusor that covers the midrange will be too deep for most people's rooms. The disadvantage of using absorption is that the more you add, the more you reduce the room's reverberation time.
A key metric for assessing the sound of the room is the RT60 vs. frequency curve. RT60 is the rate of decay of the envelope of the impulse response: high RT60 = long decay, low RT60 = short decay. I found it important to measure this as I was adding treatments to my room. Because my initial experiment of putting absorbing panels at every reflection point produced a very clean impulse response tail, but resulted in a dead sounding room.
After a lot more experimentation, I reached the conclusion that the frequency dependence of RT60 matters more than the absolute level. The room sounded worst with a lot of high frequency absorption and minimal low frequency absorption. But it sounded good even with a very low RT60, as long as RT60 was relatively flat vs. frequency. I guess I shouldn't have been surprised, since recording studio control rooms are made like that.
So I think you'll have to experiment and decide for yourself how low you are willing to go in pursuit of the perfect impulse response. If you want to get the best benefit from the least amount of absorption, you really should get yourself a measurement microphone so you can see the effect of a placing treatment on the impulse response.
Room acoustics is a complex subject, it has evolved over many years to include such tools as Helmholtz resonators, ebony wood, tiny little bowl acoustic resonators, room echo absorbers, corner treatments, diffusers, Tube Traps, crystals, constrained layer dampers, and a boatload of other audiophile devices. There are many different acoustic issues, some of which may be counter-intuitive, that should be addressed separately.Trying to treat the room without knowing what and where the problems are beforehand is like trying to solve x number of simultaneous equations in x + n unknowns.
One should map out the existing room acoustics using test tones and SPL meter to determine problem areas: standing waves, first reflection points, second reflection points, echo, sound pressure level peaks much greater than average level. There is the related issue of speaker placement, which itself evolves along with the application of room treatments. Looking at room acoustics as a long-term project, be prepared to relocate speakers along with your program of room treatment.
"No matter how much you have in the end you would have had even more if you had started out with more." - audiophile axiom
Edits: 09/29/22 09/29/22 09/29/22 09/29/22
That graph doesn't indicate the time of the decay. But if that is what you want, (as it appears, a pretty slow decay with some lingering reverb) it shouldn't be too hard. A little diffusion and minimal absorbtion should do the trick. But it really depends on the actual time of decay you are looking for. Impulse response is an indicator of clarity/time domain smearing of the signal. The ideal if one is interested in removing the room from the sound of the playback is just the initial impulse (impossible in any kind of home listening environment) All that follows is room sound.
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