Searching for matching(?) Subwoofer solution
hleeid they are both doing the exactly the same thing but DEBRA is using bass reflex enclosures and Audiokinesis uses sealed enclosures. I would go with Audiokinesis for two reasons. 1st is I prefer sealed enclosures for subwoofers. 2nd is I just came from the DEBRA web site and the marketing was beyond belief. Mike |
Come on clio you can be more honest than that! Cable risers are for people who want to show off their silly $10,000 speaker wires. Anything they do to the sound is purely psychological. Hleeid, just buy a role of the thickest gauge you need and use it on all four speakers. Like clio I make all my wires to fit. |
If you have wall to wall carpet there will be a space between the carpet tack strips and the wall. You can usually tuck the wire into this space just by pushing the wire down between the base trim and the carpet with something like a screw driver. If you are going longer than 20 feet I would consider going to 14 gauge wire. I like this stuff
https://www.parts-express.com/audtek-electronics-14a2c500-in-wall-cl2-14-2-speaker-wire-500-ft--100-1010
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I hear you Duke but the market for smallish subs might be higher than you suspect. Most people do not have large rooms and wife do not like tripping over big boxes. I would not charge much less for them, whatever the difference in materials is. Four 8" drivers equalized and running in a smaller room should do just fine for many of us. The other way perhaps to deal with the aesthetics are to make them look like something other than a box. What about a cylinder, driver in the bottom slot loaded into the room? |
Duke, I think what people are concerned with is the size of the subs in a small room. I'm sure you know all this already but using a smaller enclosure with the appropriate driver then digitally equalizing it may suit people with smaller rooms....as long as you have the power to do it. It is just like treating the room as a Honda Hatch Back:) Might be a good product for you. |
Tim, Once I read Gedde's explanation of how DBAs work it makes absolute sense. My problem was that Duke was using terms that I was not familiar with that were not self explanatory. He was talking in a language I did not understand. Now that I know what is going on it makes perfect sense and is indeed intuitive. However it has limitations the biggest one is that you have to keep the crossover under 60 Hz or it will start messing up your image. This may work well for people with regular point source speakers that get down to 40 Hz ok. I firmly believe that with any dipole speaker, Planar magnetic, ribbon or ESL you have to cross up higher at least at 100 Hz. This disqualifies a DBA. On the other hand my way of doing things may not work well with regular dynamic speakers. Pick your poison:) My media room is 16 X 25 feet. The back wall is 75% open to the kitchen and then 30% open to the dinning room the back wall of which is 75 feet away. So, the back wall reflection is broken up all over the place. I designed it that way. Between my speakers is a 113" diagonal Stewart screen the idea being that I can either listen to music or watch TV while cooking and having dinner. The projector hangs from the ceiling. Mike |
Tim, in this case I don't think psycho-acoustics is the reason. An example of psycho-acoustics is masking. MP3 compression strategies operate on this principle. The normal undistorted music masks the distortion because or brains can only pay attention to the loudest noise. If you don't want to hear your car rattle, turn on the radio. Nodes form in rooms below what is called the Schroeder Frequency which depending on the size of the room is somewhere around 130 Hz. Where the nodes are depend on the frequency, room size and the position of the woofer. By positioning the woofers at different places in the room you create nodes in different places which overlap at different phases creating what I think Duke is referring to as a minimum phase system. This is a bit of a tough one to explain but I will give it a shot. Draw a sine wave on paper now draw another one 10 degrees out of phase with the first. Keep drawing sine waves 10 degree off from the last one until you come around a full 360 degrees. Now lets say these sine waves represent volume. The very bottom is zero dB and the very top is 20 dB. If you average all of these sine waves what you get is a flat line at 10 db. Or as Duke implies a minimum phase system. Geddes seems to think that just three sine waves is enough to create reasonably flat response and you can do this at any frequency below 80 Hz because below 80 Hz you can not locate the source. I personally think that should be below 60 as I know for a fact me and my audiophile friends can locate a 60 Hz test tone. The problem with this approach is what about the frequency band up to the Schroeder Frequency? By absolute coincidence I cross over at 125 Hz just below the Schroeder point. So my subs have to deal with all the room nodes from 125 Hz down. Above the Schroeder Frequency nodes do not form. My way of dealing with the node problem is to limit the dispersion below 125 Hz by forming a line source that is right up against the front wall. Now there are only reflections off the ceiling and rear wall. In my case the rear wall is broken up or there really is not a rear wall. The nodes that do form are easily managed by room control. I am not sure this approach would work well with point source speakers. Such an array may overwhelm them. When a concept is counter intuitive it usually means it was not explained well. |
Here is Earl Geddes explaining subwoofers https://mehlau.net/audio/multisub_geddes/ Smoothing the bass frequency response in a room with multiple subs is a simple matter of overlapping nodes. He thinks that three subs is optimal the 4th adding little to the solution. He also wants the subs as far apart as possible. He would cross over somewhere below 80 Hz where he thinks bass becomes non directional. So his approach is radically different than mine. I cross over higher but still below the Schroeder frequency and create a line source. Funny thing is that he greatly favors directional speakers over omni directional speakers because they reduce room interactions in a way superior to room treatments. He does not say that in this paper but relates this strongly in other papers. My array does exactly this. Again, I have a sophisticated room correction system which is to some extent cheating. If I bypass it my speakers sound like crap because of the rising response of the transformers I am using. I can not separate the subs from the satellites in this regard. It is either all on or all off. This paper was written for lay people so he does not use terms like minimal phase system. He may well use terms such as this in more scientific papers aimed at people who understand what he is talking about. I got as far as the Fourier wave equations and gave up. So Tim, According to Earl Geddes I am wrong. You want to keep your subs as far apart as possible and throw the fourth one away. It is just taking up space. Or, you could try making a line array using all 4 subs and see what happens. Couldn’t hurt to try:) Mike |
Ok Tim, first of all this is not my method. It a rule of acoustics and speaker design. I started applying it to subwoofers because I was having difficulty matching subwoofers to my Line source ESLs. So I created a horizontal line source subwoofer array which has the added benefits of being very efficient and greatly reducing reflected sound in the room because of the way a Line Source radiates. Now I have no experience doing Swarm systems around point source satellites. But I find it an interesting concept as I too have great performance using four subwoofers. Your numbers are about right. So, if you are crossing at 40 Hz you would want 14 or less feet from one sub to the next. Theoretically the drivers are now acting as one acoustically and are phase coherent. But, then you have to add the room into the equation which I think is Duke's message and I would like to understand what he is trying to describe better. With subs at various distances from walls and each other you have a very random pattern of reflections at different times (phase) and with dimensions in and around the wavelengths of the frequencies you are producing certain frequencies are going to resonate longer. Simplifying the situation, what Duke is saying is that placing subs randomly throughout the room creates a situation that smooths out the frequency response throughout the room. I am trying to understand how that happens. I would not say that the line array is better bass in all situations. It is better in my situation because I cross over much higher and I have line source satellites. If I put my subs around the room it would really screw up the image. In your case crossing over at 40 Hz you can not tell where the bass is coming from. The question I have Tim is if you arrange your subs so that any gap is not longer than 14 feet can you detect any difference in the bass. 40 Hz is way down there. What you might try is playing a 30 Hz test tone. Many test records have test tones. You can even download them digitally. Play the tone and some music with deep bass before and after you rearrange things. It may not make any difference at all. |
Thanks Tim, Subs oriented in a line array are going to project more power because the volume drops off slower as you move away from the speaker than a point source. I can up with this approach because it is the best way to integrate subs with line source loudspeakers. I also cross over to my subs at 125 Hz which may be why Duke and I have somewhat opposing views. Duke I need you to define what you mean by a minimum phase system. Yes, I understand if the decay is slower at a certain frequency that frequency will be emphasized. Your ears register everything immediately just like any good microphone. It is your brain that takes time to register just about anything. I think you missed my point about impact. It is the visceral component that adds excitement to the music and why live performances can be so exciting. You not only hear sound but at lower frequencies you feel it. When you confuse phase like that the impact goes missing. When said individual reconfigured his system he described it as having more impact without my prompting him. The result I would have expected. I have to admit I also cheat because I am using very elaborate room control. Anyway there is more but my wife is pressing me to go out for a bike ride. Time to go out and assault the motoring public. Back later:) Mike |
Hi Duke, You will have to give me some time to think about it. Humans are extremely sensitive to phase. It is why we have two ears 8 inches apart. In nature it is how we locate danger and why a listener can put himself perfectly in phase with two speakers just by moving his head side to side a little. So the statement that the ear (which should be ears) have very poor time domain response is 180 degrees wrong. Now most of us can accurately locate a test tone at 60 Hz. Anyone can prove this to themselves by unplugging all the subs but one. Blindfold the listener and in the middle of the room spin them around a few times, play the tone and ask them to point to it. Below 60 Hz and it gets progressively more difficult. Now this is a test tone, not music which is more complicated. If you put two subs in front of you and reverse the wires on one putting it 180 degrees out of phase the bass output decreases dramatically everywhere in the room. With more subs out of phase at various angles things get more complicated. Next in regards to very low bass, sensory input is not just coming from your ears it is also coming from visceral sensation. If I set off an M80 50 yards away from you you will hear it and feel it at the same time. All frequencies travel at the same speed. Regardless of what your ears are hearing if your woofers are out of phase with each other you may hear bass but you will not feel it. Speakers + Room do not equal a minimum phase system. They equal a confused phase system as you have the primary signal from all the drivers and their reflections bouncing all over the place. With the drivers acting as one the bass drum impact will strike the listener in phase with the greatest force resulting in the largest smile. The decay afterwards is of no great significance. So I suggest to those interested in this thread who have SWARM systems to play around with positioning and see what happens. This is a group experiment. I only know what happens in my room with my system which is different acoustically than most of yours. I know of one person who set up his four subs as I suggested and he thought it made an improvement. But, others indifferent situations may not feel this way. Or maybe not:) Mike |
Wow this topic has legs. I like to simplify things. First of all it is not a sweet spot. It is a sweet line 90 degrees from the center of the speaker axis. On this line the speakers are in perfect phase with each other and will cast an image of the recording to the degree that the system is capable. Now because of standing waves and interference patterns the frequency response below about 100 Hz on this line can vary up to 10 db. It depends on room dimensions and the way the subwoofers are used. You can hear this easily in your system. Just play a test tone at say 60 Hz and walk back and forth across the room and you will be flabbergasted at how the volume changes within just a few feet. When I was using two woofers I dealt with this by moving my listening position along the "sweet line" until I felt the bass sounded right. Doing this even with room control is a benefit because it will cost you much less amplifier power to correct the response at your listening position. With a point source system and one favored listening position 2 subs can do the job fine and as Raul suggests I think two good woofers is better than 4 bad ones. But, when it comes to other situations like having multiple listening positions along that line or having line source or linear array speakers you run into trouble. It is difficult to compensate for two positions and two point source subs will not project as well as line array speakers so the sound gets thinner as you move away from the system. This is where multiple subwoofers come into play. It seems that the SWARM group wants to place their subs anywhere in the room. This will smooth out the frequency response throughout the room but depending on the distance between to subs may cause phase issues. Here is a rule of thumb. For the drivers to act as one they can be no farther apart than 1/2 the wavelength of the crossover point. So say you are crossing over at 100 Hz. That is about 10 feet at sea level. If your subs are less than 5 feet apart they are acting as one and no matter where you are in the room they will always be in phase and as long as additional subs are closer than 5 feet to the last one in line they will always be in phase no matter where you are in the room. If you make the array longer than the lowest frequency you want to reproduce you have created a line source subwoofer. At lower cross over frequencies say 80 Hz the distance would increase to 7 feet between subs. Now in my case I need a subwoofer linear array to match the output of my ESL linear arrays and the woofers are arranged across the front wall with the outside subs in the corners. I am doing this to make the array function to below 20 Hz but a point source system does not have to worry about this. So, what I am suggesting to the SWARM people is to place their woofers in configurations so that one is no farther than 7 feet from the next assuming you cross at 80 Hz, 5 feet if you cross at 100 Hz. This will make all of them in phase no matter where you are in the room and should increase the dynamic response of the bass. Try it and let us know what happens. This rule is used by designers that use multi driver arrays. If you study various designs you will always notice that tweeters are always closer together than midranges which are always closer together than woofers. We are just extending the same principle to subwoofers and the much longer wavelengths involve. Pheyew that was tiring. Mike |
Using sine wave test tones at five Hz intervals audiophiles can reliably locate 60 Hz and a few even down as low as 50 Hz. Nobody can locate 45 Hz. Below that the whole house is shaking. At 20 Hz your vision blurs. My wife can not locate 80 Hz. Having said that it is my understanding that mastering engineers mono bass below 100 Hz because they can get another 3 db before every ones systems start distorting. Hans, you still alive or has everyone burn out all your fuses? |
Hey Hans, I live 15 miles north of you in Atkinson NH, just across the border. Your speakers are only 6 feet apart so although I would prefer two subs one better sub with an eye towards getting a second in the future would be better than two cheaper subs. The Ologe model 10 price is a bit steep for two 10 inch drivers. For that price you could have two JL labs Fathoms complete with amps and room control. Buy one now and get the second later. With one sub you would put it in the middle up against the wall. With two you would put them in the corners. It is a squarish room so you are going to have some standing wave issues best handled by moving the listening position to an area where the bass is hot then using room control to flatten it out. You could use 4 subwoofers but in a room that small that approach might be problematic. Again, 2 good subs is better than 4 not so hot ones. At any rate crossing over at 100 Hz 24 db/oct will be fine. I am sure there are several JL Labs dealers in the area. Mike |
