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tonefight
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Joined: 14 May 2003
Posts: 1409
Location: Ebensburg
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 Posted: Monday May 28, 2012 |
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Adding pole mount sockets to a sub, directions say to find the center of balance for the sub and mount them there. If I do that my top driver will be 1.5" back from my sub driver ( measurements are to the cone ).
From my understanding of driver alignment ( very limited understanding ) low frequencies travel slower anyway and this shouldn't be a real issue. Is this something I should even bother concerning myself with ? If so what what suggestions do ya got. The tops are lightweight and should cause no balance issues goin off center of balance to the sub however if I or anyone else uses a heavier speaker it would be off balance and of course its driver alignment would be different anyway.
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floodcitybrass
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Joined: 31 Jan 2003
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| Posted: Monday May 28, 2012 |
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One and a half inches will not make a difference. That's about 0.1 milliseconds of delay difference.
The speed of sound is independent of the frequency. So low frequencies do not travel slower than high frequencies.
Balance issues would be more concerned with coverage pattern. High frequencies are typically more directional than lows. Depending on the speaker design, polar plots will typically reveal that subwoofers spray sound in a wider/shorter pattern compared to the high frequency speakers. But this is beside the issue of 1.5 inches of misalignment.
Bottom line is that 1.5" will not be an issue. |
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tonefight
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Location: Ebensburg
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| Posted: Monday May 28, 2012 |
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| floodcitybrass wrote: |
Bottom line is that 1.5" will not be an issue. |
Thanks
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lonewolf
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Joined: 25 Sep 2003
Posts: 6249
Location: Anywhere, Earth
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| Posted: Tuesday May 29, 2012 |
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If you are doing those EV subs, keep in mind that the center of balance is not going to be the physical center of the top. The speaker makes it front heavy, so the center of balance will be back from center:
Looking at the spec sheets, the speaker is 22 lbs and the cabinet is approximately 44lbs and 18" deep. The front of the cabinet has a 44lb force and the rear has a 22lb force. The center of balance is found by setting their moments equal to each other:
44x=(18-x)*22=396-22x.
66x=396
x=6" from the rear.
As far as time alignment goes, you want to keep the rear of the diaphragms (cones) as closely aligned as possible. As FCB said, this is a secondary concern, especially since you are probably setting this up to accept any top cabinet.
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LHSL
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Joined: 31 May 2006
Posts: 181
Location: Johnstown
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| Posted: Friday Jun 01, 2012 |
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| lonewolf wrote: | | As far as time alignment goes, you want to keep the rear of the diaphragms (cones) as closely aligned as possible. As FCB said, this is a secondary concern, especially since you are probably setting this up to accept any top cabinet. |
Unless you are measuring the speakers impulse response, phase, and amplitude with an FFT and correcting for delay, the physical alignments of cabinets (top over a sub) is of very little concern if less than a foot or three.
Why? Crossovers. The phase shift through the crossover region will delay one or the other cabinet from the other by a few milliseconds.
That said, if you are using an electronic delay unit to time align the speakers the placement does become more critical. But even then, assumptions about how to align them in the < 1 ft range is probably an effort in futility. No speaker manufacturer is going to give you instructions on how to exactly align two speakers with that level of accuracy even if they give you time delays for each pass band and expect you to use an DSP for crossover/delay. Delay matters the most for bi-amped or tri-amped cabinets whose drivers are offset in distance or phase after the crossover and more generally for getting the tops mostly aligned with the subs or other speaker systems separated by some distance like delay towers.
Actually, if you don't have an electronic delay but could measure the delay, you could move the top cabinet forward or backward to properly align the top to the bottom. However, this is often impracticable as the tops would need to be several feet forward or behind the tops (1 ft = 1 ms approximately) and there would be no way to stack them. It would also look silly which may or may not bother some folks concerned with aesthetics.
Some people with golden ears may be able to align them by ear, but I doubt they could get more accurate than a millisecond or two.
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LHSL
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Joined: 31 May 2006
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Location: Johnstown
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| Posted: Friday Jun 01, 2012 |
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| tonefight wrote: | | From my understanding of driver alignment ( very limited understanding ) low frequencies travel slower anyway and this shouldn't be a real issue. Is this something I should even bother concerning myself with ? If so what what suggestions do ya got. The tops are lightweight and should cause no balance issues goin off center of balance to the sub however if I or anyone else uses a heavier speaker it would be off balance and of course its driver alignment would be different anyway. |
First as others have said, don't worry about it.
Second, the speed of sound does not vary with frequency (much). It does vary with the density of the medium it travels through. Water vs. dry air vs. humid air, etc.
What you might be thinking of is attenuation. Sound attenuates over distance. The rule is 6 dB down per doubling of distance. However, HF do attenuate faster than LF frequencies in air because air is a "less-good" impedance match for HF. For instance, on a hot and humid day here in PA in the summer, at 100 feet 5 kHz will be about 3dB down (compared to LF) 10 kHz would be about 8 dB down, and 20 kHz would be about 15 dB down. Mind you, this is in addition to the 6 dB per doubling of distance.
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lonewolf
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Joined: 25 Sep 2003
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| Posted: Friday Jun 01, 2012 |
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| LHSL wrote: | | lonewolf wrote: | | As far as time alignment goes, you want to keep the rear of the diaphragms (cones) as closely aligned as possible. As FCB said, this is a secondary concern, especially since you are probably setting this up to accept any top cabinet. |
That said, if you are using an electronic delay unit to time align the speakers the placement does become more critical. But even then, assumptions about how to align them in the < 1 ft range is probably an effort in futility. No speaker manufacturer is going to give you instructions on how to exactly align two speakers with that level of accuracy even if they give you time delays for each pass band and expect you to use an DSP for crossover/delay. Delay matters the most for bi-amped or tri-amped cabinets whose drivers are offset in distance or phase after the crossover and more generally for getting the tops mostly aligned with the subs or other speaker systems separated by some distance like delay towers.
Actually, if you don't have an electronic delay but could measure the delay, you could move the top cabinet forward or backward to properly align the top to the bottom. However, this is often impracticable as the tops would need to be several feet forward or behind the tops (1 ft = 1 ms approximately) and there would be no way to stack them. It would also look silly which may or may not bother some folks concerned with aesthetics.
Some people with golden ears may be able to align them by ear, but I doubt they could get more accurate than a millisecond or two. |
If you are standing there with a screwdriver and a drill, the easiest way (rule of thumb, if you will) is to just line up the acoustic center of each audio source...this is best approximated by the primary source of the sound in each speaker...aka the rear of the cone or horn. Not much you can do about crossover delay...at least not with a screwdriver and a drill.
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LHSL
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Location: Johnstown
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| Posted: Friday Jun 01, 2012 |
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| lonewolf wrote: | | If you are standing there with a screwdriver and a drill, the easiest way (rule of thumb, if you will) is to just line up the acoustic center of each audio source...this is best approximated by the primary source of the sound in each speaker...aka the rear of the cone or horn. Not much you can do about crossover delay...at least not with a screwdriver and a drill. |
The point is if you don't measure it, there is no point.
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