Post by: OTR-jkl on June 02, 2006, 03:30:12 PM
I'm sure its a little more complicated than that but is that about the sum of it? or will I get into a whole lot more tuning issues by adding a 2nd...?
Thanks.
Post by: seriousfun on June 02, 2006, 04:50:04 PM
If you put the second sub on top or near the first, you will get the most gain from coupling.
If you position the second sub somewhere else in the room, from your listening position you may or may not get 3 dB of gain, depending on the room modes each subwoofer excites. In some cases, this positioning can use one subwoofer to excite different modes than does the first one, resulting in flatter frequency response, but in practicality this happens in very few rooms.
6 dB is actually a lot of headroom. Bass needs a lot of headroom. Enjoy!
Post by: Andy Krehm on June 03, 2006, 01:14:39 AM
| OTR-jkl wrote on Fri, 02 June 2006 15:30 |
If I add a 2nd sub, theoretically I will only have to use somewhere near about 1/2 the power on both than what I'm using for 1 now. IOW, I should be able to turn the level of 2 subs down to about 1/2 of where my 1 is operating at now. Yes? No? Kinda...? I'm sure its a little more complicated than that but is that about the sum of it? or will I get into a whole lot more tuning issues by adding a 2nd...? Thanks. |
I used a single sub for years. Recently, based on positive comments posted by others, I tried stereo subs.
I would never, ever go back! Mind you, my room is on the small side and the mains are Lipinski 505's which roll off fairly high. So, because of that, my Velodyne DD-10 subs are calibrated higher than most set-ups. I was amazed at the amount of subtle stereo information comes from the upper range of the subs. They provide a perfect foundation for the Lipinski's, much better than a single sub did. With full range mastering towers, the stereo image would already be there right down to 20 or 30 Hz and in that case, using a single or stereo sub would make little to the the stereo field.
When our new room was tuned by the designer, we spent a lot of time trying the subs in different positions. The most useful ones were directly below the satellites, off the floor, and secondly, just to the outsides. Of course we tried the inside as well, just to be thorough. The clear winner and permanent position is now just outside and below the mains.
The other benefit is that there are very few "hot spots" as the stereo subs smoothed them out. I can't remember about the power difference but I'm pretty sure running two subs means that each one is working less than a single.
Andy,
Silverbirch Productions.
Post by: zetterstroem on June 03, 2006, 09:12:01 AM
two subs rocks
Post by: bblackwood on June 03, 2006, 09:38:24 AM
Post by: Andy Krehm on June 03, 2006, 10:04:14 AM
| bblackwood wrote on Sat, 03 June 2006 09:38 |
After adding my second DD12 a couple of years ago, I was surprised at the diff. There are lots of potential explanations (and it's likely a combination of all of them), but one not mentioned so far in this thread is the difference between electrically summing the signals and doing so acoustically... |
Huh? Please explain!
Andy,
Silverbirch Productions.
Post by: OTR-jkl on June 04, 2006, 11:23:36 PM
As for placement, in this room it will have to be stacked on top of the current sub. I'll turn the first one on its side and then put some rubber feet on the side of the 2nd and lay it on top. Hopefully it will work well that way since there are very few other options...
Post by: bblackwood on June 05, 2006, 08:10:42 AM
| Andy Krehm wrote on Sat, 03 June 2006 09:04 | ||
Huh? Please explain! |
A signal common equally to both channels will give you a 6dB increase in gain when summed electrically. The same thing done acoustically will rarely give you the same 'ideal' gain you get from the electrically summed signal.
Post by: Dave Davis on June 07, 2006, 04:22:37 PM
-d-
Post by: barefoot on June 09, 2006, 01:35:10 AM
| bblackwood wrote on Mon, 05 June 2006 05:10 |
A signal common equally to both channels will give you a 6dB increase in gain when summed electrically. The same thing done acoustically will rarely give you the same 'ideal' gain you get from the electrically summed signal. |
You're in the right ballpark Brad, but I think it can be expressed more specifically. First of all, putting the signal through two subs rather than one yields lower distortion. Bass mostly runs up the middle, so that's 1/2 the amplitude and 1/4 the power going into each sub. Secondly, subs act as antinodes with respect to room modes. Two subs placed in different locations make the modal structure in the room more complex than a single sub and can actually help break up stronger modes, especially if you place them near natural nodal points.
Thomas
Post by: matucha on June 09, 2006, 04:32:18 AM
Post by: OTR-jkl on June 09, 2006, 11:31:46 AM
Also, do subs like to be run hot or do they do better at a lower setting?
Post by: barefoot on June 10, 2006, 12:22:21 AM
| OTR-jkl wrote on Fri, 09 June 2006 08:31 |
So if I have any low-end problems (likely) and add a 2nd sub placing it on top of the existing one, will I then accentuate those problems making them worse?? |
Yeah, it will probably make things worse
| OTR-jkl wrote |
Also, do subs like to be run hot or do they do better at a lower setting? |
Pretty much every speaker works better at lower levels. Lower level means lower distortion - one of the advantages of dual subs I mentioned above.
Post by: OTR-jkl on August 13, 2008, 12:01:23 AM
I've moved into a new room which is much larger than my previous little box and, so far, things are much easier to dial in. I'm trying to tighten up the bottome end a bit. I've put my 2 subs about 3-4' apart from each other close to the front wall and have (somewhat) decoupled them from the floor. I'm wanting to experiment with their placement and have a question or 2:
How far apart should the subs be from each other (the room is about 12' wide)? How close to the wall should they be? How far from the corners? Is there some formula for figuring a starting point for this? Do they need to be time-aligned with the mains (by physically aligning the drivers)?
I'm sure I'll have more questions as I play with this....
Thanks.
Post by: Bob Olhsson on August 13, 2008, 12:15:55 PM
Post by: seriousfun on August 13, 2008, 05:23:56 PM
| OTR-jkl wrote on Tue, 12 August 2008 21:01 |
... How far apart should the subs be from each other (the room is about 12' wide)? How close to the wall should they be? How far from the corners? Is there some formula for figuring a starting point for this? Do they need to be time-aligned with the mains (by physically aligning the drivers)? ... |
You can't predict the distance between the two subs. You have to experiment with placement, measuring and listening carefully. There is no real formula.
Sounds eminate from the subwoofer cabinet essentially omnidirectionally, and reflect from adjacent surfaces. It can have one adjacent surface (the floor), two (the floor and one wall), or three (the floor and two walls - a corner). Each additional reflecting surface will increase gain from the subwoofer, and each will probably engage more ringing at different frequencies. In some rooms, the placement with the fewest adjacent surfaces gives you the least-colored sound, and in other rooms the corner gives you the most gain with relatively uncolored sound.
Every sound travels at the speed of sound
(well, the front of the compression, or rarefaction, moves at that speed), and a subwoofer needs to be in polarity with the main speakers as much as any speaker. Moving the subwoofer so it is perfectly time-aligned with the main speakers - the same distance from the subwoofer voicecoil to the listener as from a tweeter voicecoil - is an admirable goal, but that repositioning in many rooms will result in the excitment of different room modes, with more ringing at different frequencies - compromises often must be made, and flat frequency response should be the first goal.Post by: OTR-jkl on August 13, 2008, 10:09:39 PM
For fun, I re-mastered a few songs from a recent project and was able to quickly make some adjustments that made big improvements. The translation is bigger, more open and the bottom is cleaner, tighter and yet more full.
I shouldn't be so surprised, but acoustics is voodoo. Sure makes a world of difference when you can hear stuff (as Bob O says over and over and over again....). I may still need some traps in the corners but its sounding really good so far. Its like, I don't want to touch anything cause its the best I've heard yet....
Post by: Sam Lord on August 14, 2008, 12:35:46 AM
Unless you can adjust drivers singly or in pairs for time alignment, there will be *only one* sweet spot or, sadly, none at all. You can do it yourself most quickly by using single-miked percussion samples, listening to one speaker channel only. Adjust woofer-to-midrange first, then mid-to-tweeter. Do separate subs vs. woofers last. Pray that the design *has* a coherent point.
I urge that the coherence be gotten first, then the nodes be tackled within the time coherence constraint. You can still move the speakers around, just keep the driver-ear distances correct wrt one another. For example, tweeter-mid ear-distance offset = +x inches, mid-bass ear-distance offset = +y inches, and bass-sub ear-distance offset = +z inches. All rooms ring, and you may have to compromise a little time accuracy. But unless your room is just too small or square, you *can* maintain timing with acceptable nodes.
** If you push them they might spill the beans.
Post by: bslobodian on August 16, 2008, 11:17:26 AM
| Bob Olhsson wrote on Wed, 13 August 2008 12:15 |
I screwed around with subs for twenty years. What finally worked for me translation-wise was placing the subs right next to the speakers, treating it as a full range speaker and dealing with the low frequency room issues. |
Ditto here (except for the 20 years, I would modestly put on a good 10 years or so). I have Klein & Hummel 0300D with 0800 subs and the alignment procedure makes it quite clear that the integration of the subs with the satellites have a lot to do with phase at the crossover point.
There's also a very good paper about multiple subs that you will find here: http://www.harman.com/wp/pdf/multsubs.pdf
Bernard Slobodian
Post by: Samc on August 21, 2008, 03:52:37 AM
| Sam Lord wrote on Thu, 14 August 2008 05:35 |
That usually requires setting higher-freq drivers farther from the ears, depending on the crossover and the rise times of the drivers. That's a big reason many tweeters now are recessed a half-inch or so into flared mounting plates. Manufacturers should provide correct ear-to-driver distance for any 3-or-more-driver rigid loudspeaker, because *one and only one* distance is correct. What, yours don't?** Big surprise... |
Care to explain this?
| Quote: |
Unless you can adjust drivers singly or in pairs for time alignment, there will be *only one* sweet spot or, sadly, none at all. You can do it yourself most quickly by using single-miked percussion samples, listening to one speaker channel only. Adjust woofer-to-midrange first, then mid-to-tweeter. Do separate subs vs. woofers last. Pray that the design *has* a coherent point. |
And this?.....I understand the principle of coherence etc, but I'm not sure I understand what you're trying to say here.
Post by: Samc on August 21, 2008, 04:06:19 AM
| Bob Olhsson wrote on Wed, 13 August 2008 17:15 |
What finally worked for me translation-wise was placing the subs right next to the speakers, treating it as a full range speaker and dealing with the low frequency room issues. |
Yeah, keeping the sound source as a single point/system works and makes the most sense to me, I never understood the principle of treating them as two different systems and separating the sound source.
Post by: Adam Dempsey on August 21, 2008, 07:29:03 AM
| seriousfun wrote on Thu, 14 August 2008 07:23 |
Every sound travels at the speed of sound |
But only if it has no direction, otherwise we're talking velocity. At sea level. In a vacuum. Unless the speaker/source is travelling at the speed of light...
Post by: seriousfun on August 21, 2008, 05:22:08 PM
| Samc wrote on Thu, 21 August 2008 00:52 | ||||
Care to explain this?
And this?.....I understand the principle of coherence etc, but I'm not sure I understand what you're trying to say here. |
| Quote: |
...keeping the sound source as a single point/system works and makes the most sense to me, I never understood the principle of treating them as two different systems and separating the sound source. |
The front of the air compression leaves the speaker, compressing and rarefacting the air between the speaker/transducer and your ear/transducer. Whether it is a low-frequency or high-frequency sound, all should leave the speaker at the same exact time. These take the same amount of time to reach your ears. The frequency is determined by the number of times the air is compressed and rarefacted, and loudness is determined by the amplitude of this action.
(This is not one continuous wave - it is like electricity where an electron does not travel from one end of a wire to the next but one electron transfers energy to the next electron and so-on)
Let's say that the tweeter is exciting the air from the back of its cone or dome, and a mid driver is sending lower-frequency sounds from the back of its cone. Unless these two drivers are physically aligned, common sounds will be smeared.
This would seem to say that multiple-concentric drivers or full-range planar speakers would be the perfect solution, but each of those designs has its own strengths and weaknesses.
If the woofer is two feet below the mid driver, sounds common to both of them will be smeared. If the woofer is in a separate box five feet away, common sounds will be smeared worse.
This would seem to say that digital delays could fix the smearing, but that has its own strengths and weaknesses.
To sum it up - no speaker design is perfect, and placing a subwoofer directly below a main speaker might not be better than placing it elsewhere.
Now - the other big problem with reproducing the bottom two octaves in a typical small room is: the room. Whether the woofer is concentric with the tweeter or five feet away, the room will happily screw up the bass frequency response - ringing due to reflections causing dips and peaks.
If you can find a place in the room to place a subwoofer where it returns flat frequency response sound to the listener, you've won most of the war already. Nine times out of ten, if you predetermine a subwoofer location, even if based on time coherence, the subwoofer will end up where it can't play flat.
IMO play the bottom two octaves from a speaker that's designed to do that job. And embrace the room, don't fight it - put that speaker where it plays flat frequency response.
Post by: Samc on August 21, 2008, 10:54:55 PM
| seriousfun wrote on Thu, 21 August 2008 22:22 |
If the woofer is two feet below the mid driver, sounds common to both of them will be smeared. If the woofer is in a separate box five feet away, common sounds will be smeared worse. |
If this is true......
| Quote: |
To sum it up - no speaker design is perfect, and placing a subwoofer directly below a main speaker might not be better than placing it elsewhere. |
How can this also be true?...... this situation (you describe) has nothing to do with the inherent problems of loudspeaker design, it is about correcting low frequency issues in the room. This would also seem to be setting up perfect conditions for group-delay issues.
I'll quote Bob O again...Please note what he wrote about the low frequency issues:
| Bob Olhsson wrote on Wed, 13 August 2008 17:15 |
I screwed around with subs for twenty years. What finally worked for me translation-wise was placing the subs right next to the speakers, treating it as a full range speaker and dealing with the low frequency room issues. |
Post by: Sam Lord on August 22, 2008, 12:00:41 AM
| Samc wrote on Thu, 21 August 2008 03:52 | ||
Care to explain this? |
| Samc wrote on Thu, 21 August 2008 03:52 | ||
And this?.....I understand the principle of coherence etc, but I'm not sure I understand what you're trying to say here. |
Let's look at the single-channel, 2-dimensional model (a side view) for a rigid 3-way speaker with a fixed crossover and vertically-spaced drivers. The geometry of three sources, fixed in space wrt one another a which radiate sound to a specific source, in this case your ear, yields a certain result. Assume that the midrange distance will be a little shorter than the tweeter distance, and the bass distance still shorter. The critical point is that those differences are are *fixed* for a given speaker type. I call those differences "absolute offsets," e.g. Otm and Otb. Let's say you're a speaker designer and you've chosen your drivers and crossovers and recorded those absolute offsets. You then draw a box with some slope of front baffle with three points on it to represent the infinite-distance acoustic center of those drivers. Now draw the ear-to-tweeter line and the other two. Is there any ear-to-tweeter distance and speaker angle at which the lines converge at the ear? If yes, you have found your *only* time-coherent listening position for that speaker. Now, if just one driver on the speaker can be adjusted to move forward or back, *and* the other two drivers can be tilted, you will have a large area in which your speakers can be placed wrt your ear yet still achieve time coherence. The model for stereo simply adds the vertical dimension and uses the equation for a sphere, x^2+y^2+z^2=R^2. My spreadsheet models for our adjusting speakers treated each speaker independently, having inputs for the distance between a given listener's ears. Any deviation in floor flatness has to be accounted for.
Now you know a big reason why designers use active crossovers. You can use them to adjust the signals for phase (always adding delay--no going backwards in time!) and get time coherence with a flat, vertical baffle. Or you can set them to default to converge *downwards* to your ears, as ATC does. They expect most folks now to soffit-mount. Thomas Barefoot has his MM27's sub drivers mounted on the sides, so he has to slow the tweeter some and the mids a bit more, I expect. My ATC20 passives (fixed, 2-way example) converge on a line normal to a point about at the top of the woofer. There are more details, such as the fact that a driver's acoustic center varies some with distance. A woofer converges to roughly the surround inner edge with distance at infinity, for example. Does that help? Sorry, it's much easier with drawings which I no longer have...
Hope this helps, best, Sam
Post by: Samc on August 22, 2008, 10:56:18 AM
| Sam Lord wrote on Fri, 22 August 2008 05:00 |
The critical point is that those differences are are *fixed* for a given speaker type. I call those differences "absolute offsets," e.g. Otm and Otb. Let's say you're a speaker designer and you've chosen your drivers and crossovers and recorded those absolute offsets. You then draw a box with some slope of front baffle with three points on it to represent the infinite-distance acoustic center of those drivers. Now draw the ear-to-tweeter line and the other two. Is there any ear-to-tweeter distance and speaker angle at which the lines converge at the ear? If yes, you have found your *only* time-coherent listening position for that speaker. Now, if just one driver on the speaker can be adjusted to move forward or back, *and* the other two drivers can be tilted, you will have a large area in which your speakers can be placed wrt your ear yet still achieve time coherence. The model for stereo simply adds the vertical dimension and uses the equation for a sphere, x^2+y^2+z^2=R^2. My spreadsheet models for our adjusting speakers treated each speaker independently, having inputs for the distance between a given listener's ears. Any deviation in floor flatness has to be accounted for. |
I understand the principle you are trying to explain, although I'm not sure I agree with some of the details.
After all there are many good sounding systems that do not have the voice coils of all the components perfectly 'lined-up', and there are some loudspeaker designers that do not consider this an absolute requirement. I also know that there is a margin of 'misalignment' that is beyond human hearing, the misalignment must result in group delay that is beyond the threshold of hearing and my google search turned up this little tidbit:
"Given that the minimum audible group delay is claimed to be 1ms at 2kHz, that amounts to a physical driver displacement of 345mm - assuming the velocity of sound to be 345m/s (22
Post by: Sam Lord on August 22, 2008, 11:51:59 PM
| Samc wrote on Fri, 22 August 2008 10:56 | ||||||||||||||||||||||||
I understand the principle you are trying to explain, although I'm not sure I agree with some of the details. After all there are many good sounding systems that do not have the voice coils of all the components perfectly 'lined-up', and there are some loudspeaker designers that do not consider this an absolute requirement. I also know that there is a margin of 'misalignment' that is beyond human hearing, the misalignment must result in group delay that is beyond the threshold of hearing and my google search turned up this little tidbit: "Given that the minimum audible group delay is claimed to be 1ms at 2kHz, that amounts to a physical driver displacement of 345mm - assuming the velocity of sound to be 345m/s (22 Post by: seriousfun on August 23, 2008, 08:53:25 PM
Not contradictory. Moving a woofer far away from a tweeter might always smear common sounds, but the effects of arbitrarily placing a subwoofer below the speakers because the idea seems right to you, resulting in horrid frequency response, *might* be worse. I've placed essentially full-range speakers in rooms where they had to sit in order to present a proper image, but the room made their bass response horrid; adding a properly integrated subwoofer, and placing it where it delivered flat response, would have been a good solution (yes, with potential, predictable compromises everywhere). No speaker design is perfect. A car might have wonderfully precise steering, but if it's not fast enough to drive on a highway, it's still not a very good car (stupid analogy alert). Post by: Samc on August 24, 2008, 06:19:09 AM
Doug, I would like to suggest that there is nothing "arbitrary" about placing the subwoofer close to the rest of the system to preserve coherency; science dictates it.
It would seem that the acoustics of the room was out of whack and the ROOM needed to be treated.
Are you suggesting that splitting up the loudspeaker system, and placing the components around the room as a viable means to treating acoustic anomalies in a room? Why not just treat the room, wouldn't that result in a more predictable situation? Post by: Samc on August 24, 2008, 07:18:17 AM
Thank you for the education.....
Lets assume that this is correct... I don't dispute your argument by the way, I'm trying to figure which way is up on this issue, anyway, how do you explain the many good sounding systems that do not abide by this theory? Has anyone ever actually done any scientific tests on this topic?
I could hardly find two people who agreed on this subject too and hence my question about scientific tests.
My "tailoring" statement refers only to choosing appropriate amplification type and power for each frequency band.
What loudspeakers are these pray tell. |