My main quest started with research on how to reduce the room resonant modes that cause muddy bass response. There is another subject thread here on the diyaudio forum that deals with solving that problem by careful positioning of the subwoofer in the room, and/or using multiple subwoofers in ideal positions to smooth the response. Reading that thread took me into a "rabbit hole" of dozens of other websites, tech articles, audio journals, etc on the subject. My conclusion is that none of them work really well. They typically only deal with specific frequency modes and their harmonics and work somewhat ok with either the even or odd harmonics but not both.
Since co-planar parallel room surfaces are responsible for the standing waves that cause irregular low frequency response I briefly considered re-modeling to move walls so that there are no parallel surfaces, and re-doing the ceiling to make a vaulted, sloped ceiling into the attic space above. The cost of doing that quickly killed that idea.
My next idea for eliminating standing waves was to completely eliminate the reflective surfaces, creating essentially an outdoor listening environment. Not too comfortable in inclement weather, nor courteous to the neighbors.
Bass traps/absorbers placed within the existing room were vetoed by the wife for aesthetic reasons.
Then, thinking the through the fundamental problem, which is sound waves reflecting off of surfaces, I concluded that signal level DSP (Digital Signal Processing) could be used on each loudspeaker channel to add in a delayed version that would null out the first, second, and perhaps third reflections from walls/floor/ceiling that reach my listening position, leaving the direct path to my ears as the dominant sound. Of course this would work only if my listening position and loudspeaker positions were constant. There would be a "sweet spot" at the listening position, but that spot would be bigger at lower frequencies where the wavelength is longer. An 11 ft wavelength at 100Hz should encompass a couple feet where the cancellation signals arrive without too much phase shift relative to the reflected signal. I'd certainly be willing to sit closely on the couch with my wife. I would offer the prime seat to a visiting buddy if he brought the beer.
Above 100Hz, the room itself is evenly reverberant and damped with furniture, carpet, and drapery. So DSP on the higher frequencies may not be needed. Perhaps the DSP on only a single subwoofer channel is needed. Stereo channels could be high pass filtered so their woofers do not add much to the low frequency room resonant modes.
I strongly suspect that this DSP method is not an original idea of mine. Surely it has been done before. So my questions to the forum group here are: Does this technology have a name? If I go into an audio equipment store and ask for _____ will the salesperson understand what I want?
Can you recommend products like this that are commercially available? I expect something should be out there for less than $500.
Thanks in advance.
Since co-planar parallel room surfaces are responsible for the standing waves that cause irregular low frequency response I briefly considered re-modeling to move walls so that there are no parallel surfaces, and re-doing the ceiling to make a vaulted, sloped ceiling into the attic space above. The cost of doing that quickly killed that idea.
My next idea for eliminating standing waves was to completely eliminate the reflective surfaces, creating essentially an outdoor listening environment. Not too comfortable in inclement weather, nor courteous to the neighbors.
Bass traps/absorbers placed within the existing room were vetoed by the wife for aesthetic reasons.
Then, thinking the through the fundamental problem, which is sound waves reflecting off of surfaces, I concluded that signal level DSP (Digital Signal Processing) could be used on each loudspeaker channel to add in a delayed version that would null out the first, second, and perhaps third reflections from walls/floor/ceiling that reach my listening position, leaving the direct path to my ears as the dominant sound. Of course this would work only if my listening position and loudspeaker positions were constant. There would be a "sweet spot" at the listening position, but that spot would be bigger at lower frequencies where the wavelength is longer. An 11 ft wavelength at 100Hz should encompass a couple feet where the cancellation signals arrive without too much phase shift relative to the reflected signal. I'd certainly be willing to sit closely on the couch with my wife. I would offer the prime seat to a visiting buddy if he brought the beer.
Above 100Hz, the room itself is evenly reverberant and damped with furniture, carpet, and drapery. So DSP on the higher frequencies may not be needed. Perhaps the DSP on only a single subwoofer channel is needed. Stereo channels could be high pass filtered so their woofers do not add much to the low frequency room resonant modes.
I strongly suspect that this DSP method is not an original idea of mine. Surely it has been done before. So my questions to the forum group here are: Does this technology have a name? If I go into an audio equipment store and ask for _____ will the salesperson understand what I want?
Can you recommend products like this that are commercially available? I expect something should be out there for less than $500.
Thanks in advance.
Grossly oversimplifying but here goes:
Acoustic solutions (absorption) of low frequency is very hard. The dimensions of your room are a huge factor. Once the room is built, you can't do a whole lot about it. At the frequencies a subwoofer operates at, even if you had foam, fiberglass or other absorbent material even a few feet thick, it would have very little effect!
Any "real world" room is going to have room modes -- many of them. They will be peaks and nulls and will vary wildly, depending upon where in the room one is. Since there's no easy way to be rid of them (other than not playing low frequencies) the question is how best to manage them or minimize the effects. If money were no object, of course a listening room could be designed with acoustics in mind. There are reasons that fine auditoriums are shaped and finished in certain ways.
For exactly the same reason that the listening position will have dramatic peaks and nulls, so will the location of the sub(s). Yes, having two or more strategically placed will tend to even out peaks and dips.
I'm not sure that DSP will do much for you. Any delay scheme would likely add even more modes, needlessly complicating matters. What will help is EQ. It is a fool's errand to try to fill in a deep null, because (theoretically) it is a complete cancellation at a specific frequency. But taming a peak? Easy, just cut as needed with a narrow band EQ filter. But even that is not a perfect solution, because EQ is amplitude only, and there is a phase/time factor too, much harder to correct. The boomy notes will have the longest decay times and there is no simple way to fix that. It's not perfect, but typically the ear is less offended by the absence of a few notes rather than several of them booming.
I've tuned my room using the general principle I outline above. My tools were a cheap mic set-up, a PC with REW and my EQ is built into my player software, J River (JRMC). I've been very satisfied with the sound for many years and rarely change it.
Acoustic solutions (absorption) of low frequency is very hard. The dimensions of your room are a huge factor. Once the room is built, you can't do a whole lot about it. At the frequencies a subwoofer operates at, even if you had foam, fiberglass or other absorbent material even a few feet thick, it would have very little effect!
Any "real world" room is going to have room modes -- many of them. They will be peaks and nulls and will vary wildly, depending upon where in the room one is. Since there's no easy way to be rid of them (other than not playing low frequencies) the question is how best to manage them or minimize the effects. If money were no object, of course a listening room could be designed with acoustics in mind. There are reasons that fine auditoriums are shaped and finished in certain ways.
For exactly the same reason that the listening position will have dramatic peaks and nulls, so will the location of the sub(s). Yes, having two or more strategically placed will tend to even out peaks and dips.
I'm not sure that DSP will do much for you. Any delay scheme would likely add even more modes, needlessly complicating matters. What will help is EQ. It is a fool's errand to try to fill in a deep null, because (theoretically) it is a complete cancellation at a specific frequency. But taming a peak? Easy, just cut as needed with a narrow band EQ filter. But even that is not a perfect solution, because EQ is amplitude only, and there is a phase/time factor too, much harder to correct. The boomy notes will have the longest decay times and there is no simple way to fix that. It's not perfect, but typically the ear is less offended by the absence of a few notes rather than several of them booming.
I've tuned my room using the general principle I outline above. My tools were a cheap mic set-up, a PC with REW and my EQ is built into my player software, J River (JRMC). I've been very satisfied with the sound for many years and rarely change it.
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I use the MiniDSP SHD with Dirac3 to manage speaker response problems and some room modes, it works very well provided you understand what you are doing. I didn't initially and it took a lot longer to get good results than I expected, but I am pretty happy with the results now and don't feel the need to tinker unless I make a system change. (fairly frequent)
System is an tri-amped horn based system with line level analog 3 way LR crossovers.
The SHD provides good options for managing a pair of sub woofers in addition to the main speakers. (You can also do active 2 way if you want)
System is an tri-amped horn based system with line level analog 3 way LR crossovers.
The SHD provides good options for managing a pair of sub woofers in addition to the main speakers. (You can also do active 2 way if you want)
Place the sub where you normally listen, and play some music. Move around the room until you find a spot where
you like the bass. Put the sub there, and the bass sound will be the same at your listening position, by reciprocity.
you like the bass. Put the sub there, and the bass sound will be the same at your listening position, by reciprocity.
Yes, a good classic tip. The generalization of that is the tried and true "trial and error" method. Just try the sub in different locations, and measure (if you have the gear) and/or listen for happiest sound. Unless one's listening position is in the dead center of a cube or worse, perfectly spherical room 😀 there should be an optimal location.
I have tried the technique of moving the subwoofer around until it sounds "good". Unfortunately, I am a sucker for impressive bass that you can feel in your chest rather than hear in your ears. But that comes with the resonant amplification that room modes provide. I will need to get some measurement equipment.
My goal is to get a response that is "minimum phase" so that low frequency transients have an "impact" rather than a "boom".
By simply moving the subwoofer around, the "best" location I found is directly behind my listening couch. The direct path from the subwoofer is about 18" thru some loose polyfill of the couch back. I think the reason this may be "best" result is because what I hear and feel most is the direct wave from the subwoofer cone rather than reflections from room surfaces which are somewhat attenuated.
This concept may be better suited for continued discussion in the Room Acoustics thread. I posted here in the Digital Line Level thread because I wanted to explore options for DSP control of room reflections.
My goal is to get a response that is "minimum phase" so that low frequency transients have an "impact" rather than a "boom".
By simply moving the subwoofer around, the "best" location I found is directly behind my listening couch. The direct path from the subwoofer is about 18" thru some loose polyfill of the couch back. I think the reason this may be "best" result is because what I hear and feel most is the direct wave from the subwoofer cone rather than reflections from room surfaces which are somewhat attenuated.
This concept may be better suited for continued discussion in the Room Acoustics thread. I posted here in the Digital Line Level thread because I wanted to explore options for DSP control of room reflections.
I would read a bit more into multi-sub solutions.
(Geddes and Toole)
They are perfect to get rid of most room modes, and with a bit of creativity, one could make such a system extremely discrete.
Two or three subs can already make a situation a lot better.
Just only EQ will not get rid of everything.
That being said, and attenuated standing wave is still better than no-attenuated standing wave. It is not perfect, but at least it's less harmful.
Boosting dips is unfortunately never really gonna work.
(Geddes and Toole)
They are perfect to get rid of most room modes, and with a bit of creativity, one could make such a system extremely discrete.
Two or three subs can already make a situation a lot better.
Just only EQ will not get rid of everything.
That being said, and attenuated standing wave is still better than no-attenuated standing wave. It is not perfect, but at least it's less harmful.
Boosting dips is unfortunately never really gonna work.
I have read quite a few articles regarding the Toole and Geddes and Wilke methods. Adding subwoofers gets to be expensive. I am on a budget, hence the Do It Yourself forum rather than buying a lot of equipment and hiring a professional installer to set it up.
I do believe there are ways to use DSP to fix room resonance influence at the listening position.
I am NOT contemplating fractional octave EQ to equalize. Only cancellation of time delayed reflections.
I do believe there are ways to use DSP to fix room resonance influence at the listening position.
I am NOT contemplating fractional octave EQ to equalize. Only cancellation of time delayed reflections.
Yes, this has been done before and really good "state of the art" DSP software is available for under $500 plus a freeware version. And absolutely DSP can kill room modes and low frequency time delayed reflections as I have many examples in the links below. With or without subs.
Audiolense and Acourate and Focus Fidelity can all take care of room modes with a high degree of accuracy and precision and at more than one listening position.
Denis's DRC is a freeware DRC software program. You can find folks using it here on diyAudio: A convolution based alternative to electrical loudspeaker correction networks
All of these software DSP/DRC use psychoacoustic filtering, frequency dependent windowing and excess phase correction at low frequencies to ensure properly designed filters that sound good. It is a complicated subject to go over these terms and why they need to be considered in a good DSP/DRC program. I wrote a book on the subject, "Accurate Sound Reproduction using DSP" and have written a number of articles/reviews of the aforementioned products.
A soon to be released video presentation covering these topics along with examples is what I am working on now. Will come back with a link when it is done.
Hope that helps and good luck on your DSP journey!
Audiolense and Acourate and Focus Fidelity can all take care of room modes with a high degree of accuracy and precision and at more than one listening position.
Denis's DRC is a freeware DRC software program. You can find folks using it here on diyAudio: A convolution based alternative to electrical loudspeaker correction networks
All of these software DSP/DRC use psychoacoustic filtering, frequency dependent windowing and excess phase correction at low frequencies to ensure properly designed filters that sound good. It is a complicated subject to go over these terms and why they need to be considered in a good DSP/DRC program. I wrote a book on the subject, "Accurate Sound Reproduction using DSP" and have written a number of articles/reviews of the aforementioned products.
A soon to be released video presentation covering these topics along with examples is what I am working on now. Will come back with a link when it is done.
Hope that helps and good luck on your DSP journey!
You absolutely don't need ANY expensive equipment for this at all.
Just a simple microphone with an audio interface and some optimization software that is available for FREE.
Subwoofers also don't have to expensive at all.
What is your budget?
Just a simple microphone with an audio interface and some optimization software that is available for FREE.
Subwoofers also don't have to expensive at all.
What is your budget?
This question is about using subs to prevent sound getting to the walls and so removing the walls from the equation. Another word for this is active absorption. It's also the same thing as the multi-sub approach except multi-subs do active absorption and boosting at the same time, and it's all about position.