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Author Topic: Turbosound Flashlight + Lab Sub ?  (Read 10500 times)

Merlijn van Veen

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Turbosound Flashlight + Lab Sub ?
« Reply #10 on: June 06, 2013, 06:51:52 am »

Don't guess, measure or make at least an educated guess. When using a sinus signal for x-over alignment, judging by the increase in volume, you might end up in phase for that specific frequency. However, you very well may be anything from half a cycle up to a couple of complete cycles apart. Resulting in different phase slopes. True, you'll have summation at XO but, to left and right of XO you'll have ripple throughout the XO region. In case of 24 dB/oct. slopes you'll have a crossover region of about 1 octave wide (where the individual bands differ less than 10 dB), assuming that levels and corner frequencies are identical, which leaves considerable room for error. Using filters at different corner frequencies, unless intentionally, is another cause for asymmetry in phase slopes.

Ivan Beaver

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Re: Turbosound Flashlight + Lab Sub ?
« Reply #11 on: June 06, 2013, 07:20:33 am »

Don't guess, measure or make at least an educated guess. When using a sinus signal for x-over alignment, judging by the increase in volume, you might end up in phase for that specific frequency. However, you very well may be anything from half a cycle up to a couple of complete cycles apart. Resulting in different phase slopes. True, you'll have summation at XO but, to left and right of XO you'll have ripple throughout the XO region. In case of 24 dB/oct. slopes you'll have a crossover region of about 1 octave wide (where the individual bands differ less than 10 dB), assuming that levels and corner frequencies are identical, which leaves considerable room for error. Using filters at different corner frequencies, unless intentionally, is another cause for asymmetry in phase slopes.
And remember that you HAVE to look at more than just the crossover freq.  The old way of "adjust the time till you get maximum addition at crossover freq can lead to cancellations above or below crossover.

Yes the delay was right to get that ONE freq (the problem with using a sine wave as the source), but not across the range where the 2 pass bands interact with each other.

Most people are interested in more than just one freq.

But if you only look at ONE thing (and choose ti ignore everything else)-then life becomes much more simple.
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Alan Star

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Re: Turbosound Flashlight + Lab Sub ?
« Reply #12 on: June 06, 2013, 07:27:32 am »

I kind of reached the conclusion that considering the tops are never stacked directly on top of the subs, as I run a central mono block of subs, that really the phase coherence will never be perfect because it will change depending on where you are on the dance floor in relationship to the two points A) the top boxes slightly off to the side and B) the subs in the center. So there is no point trying to get it perfect because in relation to what ? Can only get it close to where the majority of people will be most of the time, and yes I do make an educated guess of the time delay, and then check freq resp to polarity inversion, measured front and centre, once again where most the people will be.
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John Halliburton

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Re: Turbosound Flashlight + Lab Sub ?
« Reply #13 on: June 06, 2013, 09:34:29 am »

It is a VERY important difference.

The only way to adjust relative phase is with time.  Polarity has nothing to do with time.

"Time is an illusion.  Lunchtime doubly so."  Douglas Adams

I would add:  "Closing time is crucial"

Sort of puts loudspeaker time issues in perspective. ;>)
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Merlijn van Veen

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Re: Turbosound Flashlight + Lab Sub ?
« Reply #14 on: June 06, 2013, 09:43:43 am »

I kind of reached the conclusion that considering the tops are never stacked directly on top of the subs, as I run a central mono block of subs, that really the phase coherence will never be perfect because it will change depending on where you are on the dance floor in relationship to the two points A) the top boxes slightly off to the side and B) the subs in the center. So there is no point trying to get it perfect because in relation to what ? Can only get it close to where the majority of people will be most of the time, and yes I do make an educated guess of the time delay, and then check freq resp to polarity inversion, measured front and centre, once again where most the people will be.

Aligning to where the majority of people are might seem like a democratic and sensible approach but physics won’t always agree. As displacement between subwoofers and mains increases, the area where you can maintain minimum variation in phase slopes throughout the crossover region decreases. From a physics POV, meaning predominantly level and time, it makes most sense to align in the back of the venue. Here the variation in level and delta path, assuming you’ve your subs stacked on the ground and your mains flown/hung somewhere above, over area is minimal. Meaning the marriage between subs and mains will last the longest over area. You might end up however with an unhappy BE. As a result, most of the time alignment is done at or near FOH. In case of EDM, if everybody is crowding in front of the DJ booth, supposingly the front of the venue. It might be tempting to align there. This is however the most volatile area in terms of level and delta path, to the point where time becomes irrelevant because the subwoofers drown the mains by more than 10 dB. Basically reducing the system to two unrelated channels. Also, excuse me for splitting hairs, the term “phase coherence” is confusing to me. I’d like to think that I understand, what it’s that you’re trying to say. Though related, AFAIK they’re two different aspects of audio measurement. Phase is time over frequency and coherence is a ratio between signal and noise. I don’t doubt that you make educated guesses. You clearly demonstrated your understanding that, as soon as you work with more than one speaker, it’s all about compromise. There are however some tried and proven methods to address these issues. I strongly recommend that you read a book like “Sound systems: design and optimization” if you haven’t done so already. Don’t get me wrong, I’m not trying to be condescending. Personally, subwoofer alignment is one of the things that took me the longest to get a fix grasp on. Sometimes it helps to make a reference measurement up close, relatively free from reflections, in order to see what you have to look for at a greater distance.

Alan Star

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Re: Turbosound Flashlight + Lab Sub ?
« Reply #15 on: June 06, 2013, 10:31:34 am »

Hey guys thanks all for your responses but I wasn't really questioning all this so much as if the lab subs upper freq is usable, 100 to 150 hz ? I don't really have any problem with where the labs meet the lo mids, as I've mentioned, I've run it with dedicated lo mid horns before and was more than happy with the sound. I was wanting to know if anyone had any experience crossing them over higher around 150hz with edm ?
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Art Welter

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Re: Turbosound Flashlight + Lab Sub ?
« Reply #16 on: June 06, 2013, 12:49:11 pm »

Hey guys thanks all for your responses but I wasn't really questioning all this so much as if the lab subs upper freq is usable, 100 to 150 hz ? I don't really have any problem with where the labs meet the lo mids, as I've mentioned, I've run it with dedicated lo mid horns before and was more than happy with the sound. I was wanting to know if anyone had any experience crossing them over higher around 150hz with edm ?
The sound quality of the LabSub at 150 won't be as much an issue as how much it will change when people are in front of the cabinets.
If you are elevating the subs above head height, the "mud factor" in the 100-150 range when blocked by bodies is not a big issue, otherwise it will be.

That said, phase  alignment gets more critical the higher you cross over, at 100 Hz the wavelength is 11.3 feet, reversing polarity may put the output within 1/4 wavelength at the crossover point, but lagging by one cycle.
At 150 Hz, the crossover won't be right unless time aligned to within 1.9 feet.
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Merlijn van Veen

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Turbosound Flashlight + Lab Sub ?
« Reply #17 on: June 06, 2013, 06:36:12 pm »

Regarding muddiness, harmonic distortion from the subwoofers came into mind? Especially because the OP mentioned that the LPF @ 60 Hz, effectively creating a gap or underlap, sounded "cleaner". EDM is notorious for its LF content. Maybe at demanding levels, this distortion, if any, may become noticeable.

Alan Star

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Re: Turbosound Flashlight + Lab Sub ?
« Reply #18 on: June 09, 2013, 02:59:21 pm »

The sound quality of the LabSub at 150 won't be as much an issue as how much it will change when people are in front of the cabinets.
If you are elevating the subs above head height, the "mud factor" in the 100-150 range when blocked by bodies is not a big issue, otherwise it will be.

That said, phase  alignment gets more critical the higher you cross over, at 100 Hz the wavelength is 11.3 feet, reversing polarity may put the output within 1/4 wavelength at the crossover point, but lagging by one cycle.
At 150 Hz, the crossover won't be right unless time aligned to within 1.9 feet.

Thanks Art, that's a good point about phase alignment being more critical in the higher freq, I think the lower it's possible to cross them over the better in all respects. Also, considering the weight of these boxes, and even though they are going fairly cheaply and I'm sure still sound good, I think I'm better off to look for another solution that goes lower. Thanks everyone.
« Last Edit: June 09, 2013, 03:02:46 pm by Alan Star »
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