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Author Topic: Purchasing powered subs  (Read 5309 times)

Ian Appleby

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Purchasing powered subs
« on: July 05, 2011, 06:52:24 pm »

Looking to purchase the vrx918sp or kw181
Vrx 126 db full space
Kw 135 half space


How is it the Qsc subs is 4db louder?
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Ian Appleby
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Rob Truesdell

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Re: Purchasing powered subs
« Reply #1 on: July 07, 2011, 02:28:44 am »

Looking to purchase the vrx918sp or kw181
Vrx 126 db full space
Kw 135 half space


How is it the Qsc subs is 4db louder?


Put the VRX in a "half space" condition (on the floor) and those numbers start to equal out. Providing you are talking the same freq.
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Nathan DePaulo

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Re: Purchasing powered subs
« Reply #2 on: July 07, 2011, 10:53:23 pm »

Looking to purchase the vrx918sp or kw181
Vrx 126 db full space
Kw 135 half space


How is it the Qsc subs is 4db louder?

It's a "calculated" figure I suspect.  Which from what I understand that just means they add a certian number, 6 db, probably to the real figure.  The KW has a 1000W amp, which means if it produced 135db then it would require a sens of 105. That would be unusual for a small front loaded single 18".  This leads me to believe that 135 isn't exactly a real world number.

I've heard great things about the KW181, and the VRX918sp for that matter.  The PRX618XLF has the same driver, as the VRX I believe.  You should be able to A/B those two subs (the PRX & KW) at some music stores.  This should give you an idea what each one is best suited for.
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Ian Appleby

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Re: Purchasing powered subs
« Reply #3 on: July 08, 2011, 12:15:49 am »

It's a "calculated" figure I suspect.  Which from what I understand that just means they add a certian number, 6 db, probably to the real figure.  The KW has a 1000W amp, which means if it produced 135db then it would require a sens of 105. That would be unusual for a small front loaded single 18".  This leads me to believe that 135 isn't exactly a real world number.

I've heard great things about the KW181, and the VRX918sp for that matter.  The PRX618XLF has the same driver, as the VRX I believe.  You should be able to A/B those two subs (the PRX & KW) at some music stores.  This should give you an idea what each one is best suited for.

Thanks for the info.
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Ian Appleby
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Kurt Stephens

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Re: Purchasing powered subs
« Reply #4 on: August 03, 2011, 05:19:33 pm »

Thanks for the info.

I was in this conundrum as well not too long ago and ended up with the VRX.

While I did not compare the KW and VRX directly - I have used the HPR181i extensively and like my VRX better. I pair my VRX with K12's.

Again, though I cannot show any hard data - I suspect the VRX would outperform the KW in terms of max real-world SPL. Going by spec-sheets is pretty useless for the most part.
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Brad Weber

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Re: Purchasing powered subs
« Reply #5 on: August 06, 2011, 09:50:54 pm »

It's a "calculated" figure I suspect.  Which from what I understand that just means they add a certian number, 6 db, probably to the real figure.
What are you saying is calculated and what is "real"?  The difference between a source in true whole space conditions and that same source in true half space conditions would theoretically be 6dB, however whether specs for a speaker are whole or half space is often a function of the related testing process and environment.


The KW181 specs are pretty clear that the maximum output is calculated.  However, you often have to be wary of any sensitivity or maximum output specifications that aren't clear about what they actually represent.  One manufacturer could address the output possible at all frequencies within the stated operating range while another may reference the maximum level at any single frequency with a third referencing the total level rather than at any discrete frequency.
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Ivan Beaver

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Re: Purchasing powered subs
« Reply #6 on: August 06, 2011, 10:38:28 pm »

  However, you often have to be wary of any sensitivity or maximum output specifications that aren't clear about what they actually represent.  One manufacturer could address the output possible at all frequencies within the stated operating range while another may reference the maximum level at any single frequency with a third referencing the total level rather than at any discrete frequency.
Something else that is often overlooked is what exactly does the "MAX SPL" number really mean?  You can get different numbers from exactly the same test setup, that are all legit numbers-they just differ in how they are "measured" as you know.

Lets assume a loudspeaker or sub or whatever is running with pink noise (6dB crest factor), and the meter is reading 130dB.

So that means that the loudspeaker can produce 130dB.  Yeah, and it is ALSO producing 136dB at the same time.  Yes those are the peaks.  And yes they can be measured if you use a meter with a fast enough response time.

So is the spec of 130 or 136dB correct?  They both are.  Now the average person would argue that what would be measured would be the 130dB by a normal meter.  But what if the spec sheet says the loudspeaker can do 136dB?  Is that wrong?  Yes-no maybe-it depends on how you want to interpret the spec.

This is why it is important to not only understand whether the measurement was made in half or whole space-but also where the SPL specs come from.  Without knowing the details, it can be hard to compare-at least accuractely.

And then of course you run into the whole spec game vs actually doing a side by side and hearing/measuring under the same conditions.
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Ivan Beaver
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Chuck Simon

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Re: Purchasing powered subs
« Reply #7 on: August 07, 2011, 01:28:42 pm »

Quote
The PRX618XLF has the same driver, as the VRX I believe.  You should be able to A/B those two subs (the PRX & KW) at some music stores.  This should give you an idea what each one is best suited for.
That's a good idea, and if you do that comparison, please let us know the results.  As an owner of the XLF's I would be interested in hearing what you think.
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