SFM
Hi, I am just coming into this thread, and catching up, so excuse the late post. The SFM approach has several patents pending, with one about to issue. However, if anyone is interested in using the approach for their own space, and can make the required measurements, I can probably run the optimization for them.
Another point is that with SFM you can evaluate any number of potential sub locations and chose the best. So it is not limited to any particular sub locations. In fact, that is how SFM got started. We only added the level/signal delay and single parametric eq later!
There is another product from JBL called BassQ which is somewhat similar, at least in the end result. It uses FIR filters for each sub, and does not evaluate potential sub locatiosn as SFM does, just four locations. But it does include a measurement system (i.e. just push the button). As I recal, latency could be an issue with that product.
As to differences to the Gedlee approach, one obvious one is that SFM requires measurements. This may not be for everyone. If we can get it into a commercial product where the measurements are automated, then it would be much more accessible.
Cheers,
Todd Welti
Research Acoustician
Harman International
breez said:
Hi, I am just coming into this thread, and catching up, so excuse the late post. The SFM approach has several patents pending, with one about to issue. However, if anyone is interested in using the approach for their own space, and can make the required measurements, I can probably run the optimization for them.
Another point is that with SFM you can evaluate any number of potential sub locations and chose the best. So it is not limited to any particular sub locations. In fact, that is how SFM got started. We only added the level/signal delay and single parametric eq later!
There is another product from JBL called BassQ which is somewhat similar, at least in the end result. It uses FIR filters for each sub, and does not evaluate potential sub locatiosn as SFM does, just four locations. But it does include a measurement system (i.e. just push the button). As I recal, latency could be an issue with that product.
As to differences to the Gedlee approach, one obvious one is that SFM requires measurements. This may not be for everyone. If we can get it into a commercial product where the measurements are automated, then it would be much more accessible.
Cheers,
Todd Welti
Research Acoustician
Harman International
Re: SFM
Hi Todd,
great to have you here!
My current setup uses Earl's approach (see http://www.mehlau.net/audio/multisub_geddes/).
I'm very interested in evaluating SFM. What kind of measurements do you need?
How long is the delay the FIR filters produce and is it fixed? I guess it can be easily compensated within the AVR.
Best, Markus
Hi Todd,
great to have you here!
cap'n todd said:
My current setup uses Earl's approach (see http://www.mehlau.net/audio/multisub_geddes/).
I'm very interested in evaluating SFM. What kind of measurements do you need?
cap'n todd said:
How long is the delay the FIR filters produce and is it fixed? I guess it can be easily compensated within the AVR.
Best, Markus
Re: Re: SFM
Measurements would be impulse responses, in a form that can be imported into Matlab. If it is in ascii format i could probably import it. MLSSA .tim files would work. i would need transfer functions from each sub to each receiver location. So if yo have two subs and two seats, thats four measurements. If there are any alternate sub locations, you would include them too, so you might have more than 4 measurements.
I'm not sure hwat the delay is, but I just remembered that it might be a bit long.
markus76 said:
Measurements would be impulse responses, in a form that can be imported into Matlab. If it is in ascii format i could probably import it. MLSSA .tim files would work. i would need transfer functions from each sub to each receiver location. So if yo have two subs and two seats, thats four measurements. If there are any alternate sub locations, you would include them too, so you might have more than 4 measurements.
I'm not sure hwat the delay is, but I just remembered that it might be a bit long.
Re: Re: SFM
Sorry, i just reviewed your technique again to refresh. I should have done that before posting. In that case the differences are less than I thought. SFM doesn't really care where you put hte subs, it just selects the best combination from the availble ones. It also precalculates (using linear theory) many possible outcomes for different setups and chooses the best. We routinely calculate in the millions of combinations/permutations, and the code had to be optimized to be able to do that.
There is a patent app for the BassQ technique. I did a bit of work on it. It is basically a matrix inversion with some bells and whistles (you can ask Ulrich Horbach about that). I dont think that app has issued yet.
The other patent app(s) are for SFM.
gedlee said:
Sorry, i just reviewed your technique again to refresh. I should have done that before posting. In that case the differences are less than I thought. SFM doesn't really care where you put hte subs, it just selects the best combination from the availble ones. It also precalculates (using linear theory) many possible outcomes for different setups and chooses the best. We routinely calculate in the millions of combinations/permutations, and the code had to be optimized to be able to do that.
There is a patent app for the BassQ technique. I did a bit of work on it. It is basically a matrix inversion with some bells and whistles (you can ask Ulrich Horbach about that). I dont think that app has issued yet.
The other patent app(s) are for SFM.
Re: Re: Re: SFM
I don't really care where you put the subs either, I just assume that you know where you want them and how many you will use. In my experience location of any individual sub is not very critical and once you have enough its totally irrelavent. If my basic suggestion is followed (corner for one, side wall away from the first, etc.) then I have never found a case which does not come out well. Sure you can obsess over numerous posible locations to find the ones that are "just right", I just have not found that this makes much difference. Hence, put them where you want then and then optimize the setup. This has always worked for me.
I'm curious about patents simply because I was doing mutliple subs long before you wrote your paper. I even used matrix techniques to find solutions. Since in the US its first to invent, not first to file, my prior art may be significant.
cap'n todd said:
I don't really care where you put the subs either, I just assume that you know where you want them and how many you will use. In my experience location of any individual sub is not very critical and once you have enough its totally irrelavent. If my basic suggestion is followed (corner for one, side wall away from the first, etc.) then I have never found a case which does not come out well. Sure you can obsess over numerous posible locations to find the ones that are "just right", I just have not found that this makes much difference. Hence, put them where you want then and then optimize the setup. This has always worked for me.
I'm curious about patents simply because I was doing mutliple subs long before you wrote your paper. I even used matrix techniques to find solutions. Since in the US its first to invent, not first to file, my prior art may be significant.
For new houses in California at least ( a pretty mild climate) about 6" of insulation is required between the floor joists. If an audiophile has a house without floor insulation, then it would be a win win situation to install insulation as per the constantly mentioned data that insulation pays for itself in "x" years. In fact your local power company might subsidized it!
Todd,
I have only one seat that needs to be optimized. Is one measurement enough or would it be better to have several measurements around the mid point?
One of the advantages of Earl's approach is to treat the mains as additional low frequency sound sources. Would that be possible with SFM too?
Please enable email in your profile so I can send you an impulse for testing.
Best, Markus
I have only one seat that needs to be optimized. Is one measurement enough or would it be better to have several measurements around the mid point?
One of the advantages of Earl's approach is to treat the mains as additional low frequency sound sources. Would that be possible with SFM too?
Please enable email in your profile so I can send you an impulse for testing.
Best, Markus
The DBA approach is very complex to impliment and requires a rectangular room with sources in the walls at opposite ends. I don't see it as at all practical (I couldn't do it in my room) and there is nothing to say that it works any better than what Todd and I recommend.
In fact, I see the premise behind the whole concept to be flawed. They seek to achieve a "free-field" bass response and thats not generally what I would consider "good bass". Large room bass would be, IMO, the better goal and thats what I seek to achieve.
In fact, I see the premise behind the whole concept to be flawed. They seek to achieve a "free-field" bass response and thats not generally what I would consider "good bass". Large room bass would be, IMO, the better goal and thats what I seek to achieve.
Multi-sub configuration posts on AudioRoundTable.com
Now that Todd Welti has joined in, it might be helpful to list a group of posts related to his papers in additon to Earl's. At the link below, you'll find a collection of threads on the subject.
A brief outline of what's contained in the archives:
There were numerous discussions about multi-sub configurations on AudioRoundTable.com a few years back. I had read the document about Welti's process on the Harmon website and had begun adopting it. Earl Geddes posted his idea about random placement. Duke LeJeune describes his adoption of it. The CARA room acoustics program is discussed, with its author chiming in to describe the algorithms used. There was lots of talk about which placement method was best, or if there even was a clear "winner". I think a lot of what's being discussed here evolved from those earlier discussions.
Now that Todd Welti has joined in, it might be helpful to list a group of posts related to his papers in additon to Earl's. At the link below, you'll find a collection of threads on the subject.
A brief outline of what's contained in the archives:
There were numerous discussions about multi-sub configurations on AudioRoundTable.com a few years back. I had read the document about Welti's process on the Harmon website and had begun adopting it. Earl Geddes posted his idea about random placement. Duke LeJeune describes his adoption of it. The CARA room acoustics program is discussed, with its author chiming in to describe the algorithms used. There was lots of talk about which placement method was best, or if there even was a clear "winner". I think a lot of what's being discussed here evolved from those earlier discussions.
Well you just can't get large room bass in a small room. The modal density is just too sparce. Over the past few months I've played around with a number of different configurations for woofers and have come to the conclusion based on what I hear that the fewer mods excited at low frequency the better.
But I'm not trying to convince anyone except myself.
But I'm not trying to convince anyone except myself.
john k... said:
Thats good.
There is a lot of discussion of just this topic over at AVForum and the consensus there is that large room bass can be done in a small room. I believe that it can be done too. The reviews of the bass in my room are almost always "the best bass that I have heard" and I excite as many modes as possible. Its all in how its done.
markus76 said:
Well, if you only have one seat then the techniques under discussion are not really needed. SFM anyway is really oriented towards getting uniform bass at multiple seats. That is the real problem. You could still optimize the setup to require to minimum EQ to get the desired target at the single seat I suppose...
markus76 said:
There has also been some work by A. O. Santillan, and more recently by Adrian Celestinos and Sofus Nielsen (my old professor at Aalborg as it happens). I think this method can work in certain circumstances. Markus has summarized the disadvantages. I would add that the subs must be in certain locations to work, and what is the likelyhood that those locations are available for subwoofers? The advantages are that the optimization is over a wide area (ideally all of) the room, and it does not require measurements (though it could prabably be optimized with measurements).