My office was near Schroeder's at Bell Labs, Murray Hill, NJ., when I worked there 1967-69*. His departure was surprisingly sudden. Don't ask.
I understand that he did return for periods years later.
B.
* "office was near" does not mean being anything comparable in professional stature at the Labs.
Here's something different as far as interacting with a room: a 17-foot labyrinth in the corner of the room with the driver near the floor and the exit port near the ceiling. Hint: it has an odd-number of ducts and an even-number of bends conducting the rear sound*. Footprint is just a mere 17 x 18 inches.
17 foot pipe sub 12-230 Hz ±5dB
B.
* 3 ducts and not strictly speaking from the "rear" of the driver
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Is this because the weight of the cone mostly change the drivers' ability to play lower in frequency in a smaller box at the cost of efficiency?
Since there is plenty of power available, that idea is a little bit more stretchable these days with enough active EQ'ing.
Given that the driver can handle the power as well as having enough cone excursion.
A larger enclosure will enhance the LF response, but not the passband dB level. It is independent of the enclosure size.
The only thing a bigger enclosure does, is give more "acoustic" power.
But you can EQ a 3 liter box to 20Hz no problem as well tune it that low with a BR solution or something.
When there is enough xmax and power available, would also easily go to 105dB.
Idealized of course, but that "iron law" is also idealized
Meaning not taking any other non-linear effects of other constraints into account.
When you pure and only talking about the acoustic part of the equation, yes it's true.
That's why I said it can be stretched these days, not the same as being totally untrue.
Indeed, I know this very well - no free lunch here either.
But I was referring to the "Full system" part
Now I have 2 x 12" and 2 x 15". I might need to build them even stronger, since cabinets have to be super stiff not to vibrate.... but for the moment I think I nailed it pretty good. Added an extra stereo power amplifier and a 4 way DSP to handle the subwoofer alone.
Question is. How far can I expect to go, when it comes to linear response? I mean. Right now I have +/-5 dB at around 1 m radius of my listening position, and no severe dips around the area where my subwoofers cross to my mains. I followed the advice to let my mains smoothly fall off at lower frequencies and then individually adjust each of my subwoofers to find their own best slope and crossover point to blend smoothly with the mains.
I remember Earl saying that ones you make the bass good in the listening position - when done right - it should be good almost everywhere in the room. I do hear the bass being much more smooth when moving around the room. But is there a limit to searching for perfection?
Question is. How far can I expect to go, when it comes to linear response? I mean. Right now I have +/-5 dB at around 1 m radius of my listening position, and no severe dips around the area where my subwoofers cross to my mains. I followed the advice to let my mains smoothly fall off at lower frequencies and then individually adjust each of my subwoofers to find their own best slope and crossover point to blend smoothly with the mains.
I remember Earl saying that ones you make the bass good in the listening position - when done right - it should be good almost everywhere in the room. I do hear the bass being much more smooth when moving around the room. But is there a limit to searching for perfection?
Ok... I do not quite follow. How would that be possible with these long wavelengths? What distance? 2 subs have been fine in many cases, also mine for some years... but I do find it a little more fun with 4 - and also more smooth to integrate. Again - reason to pursue better than +/-5 dB in bass below around 3-400 Hz? Above Schroder I do find +/-1 dB to be a much better goal - love it here for neutrality
DigitalThor, the point is this. Room modes are where your room functions as a resonator. In other words, standing waves form between hard surfaces.
Where a standing wave meets a hard surface, the air does not move, but the pressure varies. In the middle of the wave, the velocity varies, but the pressure not that much. In Dutch, we call these points the knots and bellies of a wave.
A standing wave is most efficiently driven from a pressure point or knot. The floor is such a point. Driven from a high velocity point, like some distance from the wall and floor, standing waves are much less efficiently induced.
So, float your subs and induce less standing waves.
Where a standing wave meets a hard surface, the air does not move, but the pressure varies. In the middle of the wave, the velocity varies, but the pressure not that much. In Dutch, we call these points the knots and bellies of a wave.
A standing wave is most efficiently driven from a pressure point or knot. The floor is such a point. Driven from a high velocity point, like some distance from the wall and floor, standing waves are much less efficiently induced.
So, float your subs and induce less standing waves.
Given enough subs the location doesn't matter. With one it matters a lot. Two less so and by three or four it doesn't matter much at all. It's most efficient to not have them placed symmetrically, like all four corners. Moving one off the floor may help some.
But the idea of "minimizing" the modes is false. At LFs it is the lack of modes that is a problem - they don't interact with one another. Damping the modes helps to make them overlap and interact, that's about the only improvement that you can make beyond more subs. But LF damping (without undue HF damping) is really hard to do.
+-5 dB is not great but may be the best that you can do in your situation. You might try writing down the details of what you have now and try again from the beginning doing things slightly differently. You might find a better result, maybe not. But where to end this quest is, and always will be, a personal choice relating to time and effort. It's up to you when to stop. (The classic engineers dilemma.)
But the idea of "minimizing" the modes is false. At LFs it is the lack of modes that is a problem - they don't interact with one another. Damping the modes helps to make them overlap and interact, that's about the only improvement that you can make beyond more subs. But LF damping (without undue HF damping) is really hard to do.
+-5 dB is not great but may be the best that you can do in your situation. You might try writing down the details of what you have now and try again from the beginning doing things slightly differently. You might find a better result, maybe not. But where to end this quest is, and always will be, a personal choice relating to time and effort. It's up to you when to stop. (The classic engineers dilemma.)
Thank you very much
I appreciate that you keep on answering all the question we come up with in our search and trials I will do better
I'm just slowly figuring out how to compare the use of my DSP's, measuring equipment and all the technical reading material that I have to digest - in my none native language But it sounds better and better with each advancement. And I start to get that experience, where it does not really matter that much what I listen to, it simply sounds the way it seems like it is supposed to.Do you think +/-5dB was not great, for one location, or if optimized for a wider seating area - maybe both?
As I say, it's right on the line of what I would hope to achieve, but there are situations where this is as-good-as-it-gets.
I found this one:
The Geddes Multi-Subwoofer Bass Optimization Approach
Will try and run it all through again. I can simply save my current setup - which is the awesome thing about using DSP software.
Ok... tried one more time, now with some more fiddling with time delay and gain.
1. Let the mains run smoothly off with a first order filter at 60Hz after EQ'ing them to fit with the midrange/tweeter combo.
2. Add one sub at the time until I had measurement for each of them for comparison in the same measurement screen.
3. Finding out, that if there is a dip in the combined response, then all other subs then the one not causing the dip, needs to be EQ'ed at that frequency, also changing the crossover for each sub individually, to find out where they each add most "value" to the combined response. Seems like each sub needs to have a different crossover point then the others, to gain best possible combined response. So overlap seems to work well, but not to much, and not little - tricky But that must be where Earl's software kicks in, mentioned in his presentations
4. A bit of trial and error to find the right delay for each sub... but quickly I honed in on the amount that either created a huge dip or smoothed things out.
5. Added global EQ - on the input - so that I could lower everything that peaked - on all measurement - the things they all had in common.
I measured in the listening position and 30cm to each side, to compare and better understand what happens when you move the mic... which I interestingly enough did not feel as a big compromise when moving my head during music, which might lead to a whole new dive down deep conversation about measured and perceived sound
I measure with a calibrated (both level and phase)microphone, Roland quad capture sound card with reference loop-back in ASIO mode with 96kHz resolution and a 100ms time window.
Looks better than the +/-5dB I got yesterday I think the difference in level, as I move the mic from side to side in and around the listening position, is due to the mismatch in phase between the mains and the subwoofers.
Sound pretty good now. But my best test is to listen to different kinds of music, movies and speech/dialog. If I over time forget the speakers and do not reach fatique.... then I believe I'm on to something better and can start believing that my measurements confirms my biased thinking
1. Let the mains run smoothly off with a first order filter at 60Hz after EQ'ing them to fit with the midrange/tweeter combo.
2. Add one sub at the time until I had measurement for each of them for comparison in the same measurement screen.
3. Finding out, that if there is a dip in the combined response, then all other subs then the one not causing the dip, needs to be EQ'ed at that frequency, also changing the crossover for each sub individually, to find out where they each add most "value" to the combined response. Seems like each sub needs to have a different crossover point then the others, to gain best possible combined response. So overlap seems to work well, but not to much, and not little - tricky
But that must be where Earl's software kicks in, mentioned in his presentations 4. A bit of trial and error to find the right delay for each sub... but quickly I honed in on the amount that either created a huge dip or smoothed things out.
5. Added global EQ - on the input - so that I could lower everything that peaked - on all measurement - the things they all had in common.
I measured in the listening position and 30cm to each side, to compare and better understand what happens when you move the mic... which I interestingly enough did not feel as a big compromise when moving my head during music, which might lead to a whole new dive down deep conversation about measured and perceived sound
I measure with a calibrated (both level and phase)microphone, Roland quad capture sound card with reference loop-back in ASIO mode with 96kHz resolution and a 100ms time window.
Looks better than the +/-5dB I got yesterday
I think the difference in level, as I move the mic from side to side in and around the listening position, is due to the mismatch in phase between the mains and the subwoofers.Sound pretty good now. But my best test is to listen to different kinds of music, movies and speech/dialog. If I over time forget the speakers and do not reach fatique.... then I believe I'm on to something better and can start believing that my measurements confirms my biased thinking