if you mean which software for minidsp - I believe their own is the only way to go ?
https://www.minidsp.com/products/plugins
https://www.minidsp.com/products/plugins
Yes possibly
I would recommend that software as well
. I don't know of any freely available good alternatives. I was just curious whether he found an alternative, or otherwise what his experience with MSO wasSince Mr Geddes' name is mentioned in the thread title line, perhaps he has some specific recommendations on the subject? It's been a while since I visited Floyd Toole's pretty thorough text-book "Sound Reproduction: Loudspseakers and Rooms" - should be required reading for us all - but I recall he touched on the subject of placement of multiple subs as well.
Yes possibly
I would recommend that software as well
dziemian has been discussing the software here.
Some of the guys on this thread are talking about advanced stuff but here is my simple response, of my basic understanding...
I've read as many posts by, and interviews with Dr. Geddes as I can find. When he shares tidbits of knowledge, it's gold. Here is a paper where he discusses multiple subs.
http://gedlee.azurewebsites.net/Papers/multiple subs.pdf
I could be wrong but I think he advocates for using a couple sealed subs down to their practical limit, and then a 4th order band-pass below that. I'm assuming that one of the sealed subs should be in the corner near the mains. And the other two go wherever else.
He uses a proprietary algorithm to process measurement data of the mains and subs to shape their response. I'm not sure how much he charges but I'm glad he offers his service. Here's how to do it. http://gedlee.azurewebsites.net/Papers/Setting up subwoofers.pdf
I'm no pro on acoustics and audio. But from what I've compiled it seems to me that following the Geddes approach to building a great home stereo is the way to go. There's a saying up here in Canada by a guy named Mike Holmes..
Make it right
Shawn
The frequency response deviations of the mic are probably small compared to what you want to measure. Only i would recommend Arta rather than REW: gives you more control. For LF response measurement only the amplitude response is really important. In arta you can manually set a low sampling frequency and long sequence length = high resolution measurement.
jag728 is right: the scale of artefacts, errors, and weird measurement issues is a whole lot bigger than the shortcomings of the mic.
The corrections shown on the individual calibrations of the Dayton mics I use are not worth bothering with 20-20kHz. And every time I check my MacBook, DACs, amps, REW, and everything else in my bargain-priced chain of gear, again 20-20kHz is quite flat and distortion reliably well below 1% or .01% (40-60dB).
Unfortunately, with special respect to your undertaking, the big issue that can't be fixed without a lot of labour is mic location since there are big changes every few inches away. Working with waterfall displays of echo time kind of helps. For me, I just stick to being pretty precisely at one standard location (usually occupied by a hard-shelled meat-filled spherical object). Like Rorschach blots, you can get good at interpreting them with time.
Ben
Thanks guys. Unfortunately I can't afford ARTA right now so I'll stick with REW.
Off topic; I am building my bass traps without frames and have seen vids of them without frames but with cardboard on the back. By using cardboard on the back, will they still work as traps. They will be 10 inches out from the wall.
Off topic; I am building my bass traps without frames and have seen vids of them without frames but with cardboard on the back. By using cardboard on the back, will they still work as traps. They will be 10 inches out from the wall.
Earl should really chime in here, but basically no, but nothing to do with the cardboard. "Bass traps" built based on velocity absorption and mounted on the wall (even with relatively significant spacing) will have negligible LF damping properties. This is, as Earl has stated before, a physics fact. The only way around this is by creating bass absorbers that can convert the pressure waves to velocity waves and then dissipate that. These are things like tuned Helmholtz traps or panel traps (which I believe are still a kind of Helmholtz trap). The problem is that the amount of damping provided by any of this is not great, so you need a lot. Earl's approach is to build the walls so they act as these LF damping traps. Basically CLD walls floated on hat channel with sufficient air space behind and I believe with additional fluffy stuff in the walls. I'm not sure if Dr. Geddes agrees on that last point, but I know at least Peter D'Antonio feels that way, that panel traps or walls acting as panel traps are many times more efficient when their is insulation in the cavity.
In any case the major point is this, hanging 4", 6", even 24" thick panels of fiberglass insulation will do little for bass damping and have the very negative effect of absorbing a very large portion of the mid and high frequencies. Rooms don't sound good with no reflections, and as I said, you still did very little to the bass itself.
In any case the major point is this, hanging 4", 6", even 24" thick panels of fiberglass insulation will do little for bass damping and have the very negative effect of absorbing a very large portion of the mid and high frequencies. Rooms don't sound good with no reflections, and as I said, you still did very little to the bass itself.
I don't mean to speak on Earl's behalf, but having known him for a while and knowing something of the history I thought I would correct this. Earl's approach has long discussed the notion of 3 subwoofers, two of which are most capable in the 150hz to ~40hz range (what has popularly been characterized as a midbass module) and one ULF sub that is really more capable down to 20hz and below. It doesn't matter if they are bandpass or sealed, but Earl doesn't seem to be a big fan of ported.
Earl used to make bandpass subwoofers for the MBM's and the ULF. They are all LF sources and the purpose of the bandpass was due to increased efficiency, natural LP filters, and potentially lower distortion. They are imperfect though and I think Earl must have found that the benefits were not outweighed by the problems, and had switched to sealed subs. The advantage of sealed subs over ported subs is that their natural HP filter is a 3rd order roll-off and that allows them to maintain cone control to a much lower frequency and not need a HP filter of any kind. Ported designs, while offering an efficiency advantage down low, to have higher group delay and a sharper 4th order roll-off. They are popular because you often see a big bump in the low end without needing special EQ or more speakers. However, you could achieve the same results with simply having more woofers, more power, and EQ. I own some of Earl's bandpass subwoofers and can say that while I've had some problems with their maximum output (port noise by 100db's or so), they do in fact show evidence of lower distortion. Namely, I took measurements at 20hz and 30hz and found the harmonic distortion was much lower, suggesting the HP filter action of a bandpass design does in fact reduce this issue. I think the problem with the bandpass designs, besides how critical their overall design and tuning is, is that getting the ports or passive radiators to be sized right and designed right such that port or mechanical noises are lower than these other problems is hard, and realistically, the distortion issues with sealed subwoofers in real world use is just not an issue. If your subwoofer in a sealed cabinet is distorting, get a bigger or more subwoofers.
You don't have to use 3 small subwoofers in Geddes approach. The key is the distribution of LF sources, but what those LF sources are is unimportant. You could have 3 subwoofers that contain dual 18" subwoofer drivers in say an 8 cubic foot sealed box each and get very significant output.
Look at this as an example:
Data-Bass
That's 102db's with low distortion at 16hz and more than 130db's at higher frequencies. If you doubled that box volume to say 8-10 cubic feet, those dual 21" drivers would produce significantly more output at 20hz. I can't imagine anyone finding that to be not enough.
Oh I meant to say, in terms of LF smoothness, having 3 different subs or 3 identical subs isn't all that important. At low frequencies in these small rooms, the subwoofers response is somewhat unimportant. I believe the reason Earl had suggested two subwoofers that are good in that midbass region and one ULF sub is just that at ULF frequencies, say below 35hz, the smoothness isn't impacted by multiple LF sources anymore, so just having a really high ouput ULF sub in a corner and eq will get what you need, but you need full overlap from all subwoofers and the mains (so we are really talking about 5 LF sources here) above that point, fully up to the transition frequency of the room
Hi Joe, thanks for the post (and poke.)
First let me apologize for the necessary brevity of my response. Recent right shoulder surgery has left me with a very stiff and sore right arm. This makes typing difficult and the fatigue factor on my arm is enormous.
When I talk about LF in small rooms, it is based on a statistical analysis. Specific rooms may have specific differences, but, short of a complete analysis of each room with a viable ray tracing program (extremely expensive), one can only look at what the "normal", "average" or "typical" room does and see if there is something "common" that we can see. In my experience the "average" room is by far the best place to start in any LF room design.
Example: my heavily damped room has only one or two LF modes apparent in the modal range, so while it is not "normal", using a "normal" approach has still been ideal. The biggest deviation from the "normal" assumption is likely when a room is highly coupled to other comparable or larger volumes - this will be surely different than just considering the source room.
The typical small room has discrete modes from about 30 Hz to about 120 - 150 Hz. It can be shown (my PhD thesis) that the more LF sources (LFs) one has in the modal region, the smoother the net response will be throughout a fairly large space - even the entire room. I consider all sources to be relevant - mains, subs, Ultra low subs. They all contribute and must be blended and analyzed as a group.
It is highly likely that the number of LFs needed to yield a smooth result (minimum frequency and spatial variations,) will drop as the frequency goes up. This means that we can expect the sub LFs to fade away as the frequency goes non-modal (LP filter, but all at different frequencies, slopes, etc.) This is exactly what the optimized rooms that I have dealt with have done. At the very lowest frequency, there is one mode and any source anywhere will drive this. So only one LFs is required to go down to the lowest mode. As the mode number(s) goes up, more and more spaced subs are required, but each will have diminishing returns. One will never do the job, two gets probably twice as good depending on where the subs are, three gets better by about 25%, four, at best a 15% improvement. To me, three seems to be a good choice, that's what I have. But then as the frequency gets to the mid modal, if the mains are still in the picture (I have five LFs) a very smooth response will result. Then the sub-LFs fall away and only the mains are playing. The transition is virtually impossible to measure or detect audibly.
This technique creates an extended bass (mine goes down to about 20-25 Hz at very high SPL's) that is incomparably smooth.
Hearing bass in a room like this and you come to realize- when listening to other installations - what "boomy bass" is. My system can play as high a bass level as you want - you want to "feel" it, that's doable, but remember, the rest of the system is going to get very loud as well to get to those levels. Most bass that I hear is way out of proportion to this, with the builder thinking that over accentuated bass is "good bass" - it just ain't so.
First let me apologize for the necessary brevity of my response. Recent right shoulder surgery has left me with a very stiff and sore right arm. This makes typing difficult and the fatigue factor on my arm is enormous.
When I talk about LF in small rooms, it is based on a statistical analysis. Specific rooms may have specific differences, but, short of a complete analysis of each room with a viable ray tracing program (extremely expensive), one can only look at what the "normal", "average" or "typical" room does and see if there is something "common" that we can see. In my experience the "average" room is by far the best place to start in any LF room design.
Example: my heavily damped room has only one or two LF modes apparent in the modal range, so while it is not "normal", using a "normal" approach has still been ideal. The biggest deviation from the "normal" assumption is likely when a room is highly coupled to other comparable or larger volumes - this will be surely different than just considering the source room.
The typical small room has discrete modes from about 30 Hz to about 120 - 150 Hz. It can be shown (my PhD thesis) that the more LF sources (LFs) one has in the modal region, the smoother the net response will be throughout a fairly large space - even the entire room. I consider all sources to be relevant - mains, subs, Ultra low subs. They all contribute and must be blended and analyzed as a group.
It is highly likely that the number of LFs needed to yield a smooth result (minimum frequency and spatial variations,) will drop as the frequency goes up. This means that we can expect the sub LFs to fade away as the frequency goes non-modal (LP filter, but all at different frequencies, slopes, etc.) This is exactly what the optimized rooms that I have dealt with have done. At the very lowest frequency, there is one mode and any source anywhere will drive this. So only one LFs is required to go down to the lowest mode. As the mode number(s) goes up, more and more spaced subs are required, but each will have diminishing returns. One will never do the job, two gets probably twice as good depending on where the subs are, three gets better by about 25%, four, at best a 15% improvement. To me, three seems to be a good choice, that's what I have. But then as the frequency gets to the mid modal, if the mains are still in the picture (I have five LFs) a very smooth response will result. Then the sub-LFs fall away and only the mains are playing. The transition is virtually impossible to measure or detect audibly.
This technique creates an extended bass (mine goes down to about 20-25 Hz at very high SPL's) that is incomparably smooth.
Hearing bass in a room like this and you come to realize- when listening to other installations - what "boomy bass" is. My system can play as high a bass level as you want - you want to "feel" it, that's doable, but remember, the rest of the system is going to get very loud as well to get to those levels. Most bass that I hear is way out of proportion to this, with the builder thinking that over accentuated bass is "good bass" - it just ain't so.
Thanks for the explanation Dr. Geddes and for the clarification Joe.
I'm curious, people have talked about failed attempts at multiple subs, issues of localization. At first I assumed the subs were not blended properly. But now I wonder this. Is it possible that although the subs are exiting modes equally that because of their placement in room that they are exciting resonances of structure, furniture, etc unevenly?
I think of when you mention a sub is only necessary in one of the two front corners, modally you've proved this, but what if the sub is localizable because of some resonance in the corner, and if placing a sub in each corner alleviates this?
I don't know much and I'm pulling this out of my imagination, but let me know if I'm on to something please.
Thanks
Shawn
I'm curious, people have talked about failed attempts at multiple subs, issues of localization. At first I assumed the subs were not blended properly. But now I wonder this. Is it possible that although the subs are exiting modes equally that because of their placement in room that they are exciting resonances of structure, furniture, etc unevenly?
I think of when you mention a sub is only necessary in one of the two front corners, modally you've proved this, but what if the sub is localizable because of some resonance in the corner, and if placing a sub in each corner alleviates this?
I don't know much and I'm pulling this out of my imagination, but let me know if I'm on to something please.
Thanks
Shawn
Earls approach typically deals with purpose built rooms. What happens in make shift rooms adds variables that a single approach can't really account for. If the room has a specific resonance that causes a rattle, that's a bad room, no? Let's say a closet door resonated at 75hz and caused a flapping rattle sound when excited, but happened to sit in a null, maybe multiple subs, which would even the response out, would then excite that area, I guess. Just my guess though, I have no real idea if this would be true.
I think there are two reasons for multiple subs failing for many people. First is that they aren't set up right, the crossovers are set wrong, the levels are set wrong, the alignment is wrong, etc. Most people align the subwoofers to the frequency response, not the alignment of the impulse response.
Another problem is not having the subwoofers placed correctly, while it may be true that symmetric or pseudo random could each get good results, I've seen people do some kind of half and half approach, and I don't know if that's great.
The majority of rooms have very little LF damping and most people have a poor understanding of this concept. There is a ton of misinformation on LF damping out there. Earl mentioned that the LF damping was critical to his phd work, so it would seem to me that his approach depends on it as well. Now, I've seen good results both with and without, so there might be good benefit to multiple subs or rooms might have more damping than I realize, but I still think that's an issue.
Another possible problem is the subwoofer producing audible harmonics which would be up higher, possibly at a directional level.
Finally it could be that it's a an effect in their head, they want to believe it's a worse approach and their skepticism is creating made up ideas. The research on LF directional cues is clear, nobody can hear the direction of bass below a certain point, and certain transition zone our ability is severely limited. If someone is localizing subwoofers operating below 120hz they either have a huge head, loud harmonics, a bad room, or are making it up.
That's just my opinion and certainly I'd love to know what Earl thinks on the topic. He probably has more data and inside knowledge on why this has failed for so many.
Dr. Geddes, if you are feeling up to responding, how do you align the subwoofer phase? So I've been using the impulse response alignment method where I take an impulse response of both mains, average the distance, then use that as my zero point for the subs. Then I take measurements to align all subwoofers to that zero point. Then I take measurements of the overall system and if things ar a little off, I make some minor adjustments. Is that right?
I think there are two reasons for multiple subs failing for many people. First is that they aren't set up right, the crossovers are set wrong, the levels are set wrong, the alignment is wrong, etc. Most people align the subwoofers to the frequency response, not the alignment of the impulse response.
Another problem is not having the subwoofers placed correctly, while it may be true that symmetric or pseudo random could each get good results, I've seen people do some kind of half and half approach, and I don't know if that's great.
The majority of rooms have very little LF damping and most people have a poor understanding of this concept. There is a ton of misinformation on LF damping out there. Earl mentioned that the LF damping was critical to his phd work, so it would seem to me that his approach depends on it as well. Now, I've seen good results both with and without, so there might be good benefit to multiple subs or rooms might have more damping than I realize, but I still think that's an issue.
Another possible problem is the subwoofer producing audible harmonics which would be up higher, possibly at a directional level.
Finally it could be that it's a an effect in their head, they want to believe it's a worse approach and their skepticism is creating made up ideas. The research on LF directional cues is clear, nobody can hear the direction of bass below a certain point, and certain transition zone our ability is severely limited. If someone is localizing subwoofers operating below 120hz they either have a huge head, loud harmonics, a bad room, or are making it up.
That's just my opinion and certainly I'd love to know what Earl thinks on the topic. He probably has more data and inside knowledge on why this has failed for so many.
Dr. Geddes, if you are feeling up to responding, how do you align the subwoofer phase? So I've been using the impulse response alignment method where I take an impulse response of both mains, average the distance, then use that as my zero point for the subs. Then I take measurements to align all subwoofers to that zero point. Then I take measurements of the overall system and if things ar a little off, I make some minor adjustments. Is that right?