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Author Topic: Suitability of 2 LABs for a smallish venue  (Read 5815 times)

Ivan Beaver

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Re: Suitability of 2 LABs for a smallish venue
« Reply #10 on: October 06, 2017, 08:13:27 pm »



The room dimensions are not great, I agree. The punters are up close to the PA and then back to 4-5m, so "best" would be them experiencing as quality a sound in this middle zone as possible.

The heat was a concern with some of the music we get. I think you're saying even at 400w we might still have issues?
It all depends on how loud you actually want/need it to be.

Different people have very different expectations on what is "good".

Remember that music is very dynamic, so how much your material (or you) compress the signal.

Typically music has a 10-20dB crest factor.

With a 10dB crest factor, and a 400 watt amp, the "average" wattage would be around 40 watts.  But if you "squish" it up, the average level could be much higher.

Typically I recommend an amp size of around 1 to 1.5 x the continuous wattage.  With some styles of music, you could use an amp rated to 4x the continuous rating of the driver.  But ONLY if that headroom is used for headroom, and NOT to have a higher average level.

Remember that a speakers power rating is and "either/or", NOT AND.

So for a 400 watt continuous driver, the ratings would be 400 watts continuous OR 1600 watts peak.  NOT both.

With a 10 db crest factor, and 1600 watt peaks, the average would be around 160 watts.  With a 20dB crest factor signal (which is the only time you should be running an amp that size) the average would be around 16 watts.

As usual, it depends.
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Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

davidsavill

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Re: Suitability of 2 LABs for a smallish venue
« Reply #11 on: October 07, 2017, 05:32:16 am »

It all depends on how loud you actually want/need it to be.

Different people have very different expectations on what is "good".

Remember that music is very dynamic, so how much your material (or you) compress the signal.

Typically music has a 10-20dB crest factor.

With a 10dB crest factor, and a 400 watt amp, the "average" wattage would be around 40 watts.  But if you "squish" it up, the average level could be much higher.

Typically I recommend an amp size of around 1 to 1.5 x the continuous wattage.  With some styles of music, you could use an amp rated to 4x the continuous rating of the driver.  But ONLY if that headroom is used for headroom, and NOT to have a higher average level.

Remember that a speakers power rating is and "either/or", NOT AND.

So for a 400 watt continuous driver, the ratings would be 400 watts continuous OR 1600 watts peak.  NOT both.

With a 10 db crest factor, and 1600 watt peaks, the average would be around 160 watts.  With a 20dB crest factor signal (which is the only time you should be running an amp that size) the average would be around 16 watts.

As usual, it depends.

Cool.

Well, we are supposed to be limited to 110db (but we are up around 120db sometimes). So say 4-5m from PA we would want to be around here.




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davidsavill

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Re: Suitability of 2 LABs for a smallish venue
« Reply #12 on: October 07, 2017, 06:22:27 am »

If you decide on the Keystone, use the suggested 18" B&C drivers- although they are a tad less sensitive, they get rid of heat far better, so end up being louder than the LAB 12" due to less power compression.

Maybe outside my budget and amp. Although you recommend running at 1/2 RMS right?
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Ivan Beaver

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Re: Suitability of 2 LABs for a smallish venue
« Reply #13 on: October 07, 2017, 08:43:02 am »

Cool.

Well, we are supposed to be limited to 110db (but we are up around 120db sometimes). So say 4-5m from PA we would want to be around here.
A dB "statement is pretty much worthless, unless you also state the weighting and speed of the response.

There can be as much as a 30 dB difference (a factor of 1,000) between A slow and unweighted peak.

So saying "110dB", means that the peaks could be 140dB, or the average could be 80dB.  Or something else.

Sure, you may "know" what the meter says, but the rest of us have no idea what is also tied to the number

It is kind of like saying "I got paid 2000 "money" for a gig.  Unless we know what units, we have no idea if you are cheap or expensive.
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Mark Wilkinson

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Re: Suitability of 2 LABs for a smallish venue
« Reply #14 on: October 07, 2017, 01:35:46 pm »

Hi David, I've used a pair of labsubs in small rooms, although maybe not quite as small as you've given.
If you have the space, they should work great.  Maximum impact will come from corner stacking them together in one corner.
Either side-by-side, or one on top of another, point them in to the corner (acts like a mouth extension I'm told) and play with distance from corner.  I seem to remember about a foot and a half working well.  Then make sure you don't have stuff that can walk off shelves or counters  ;D

As far as driving them, one amp channel per box, with drivers in parallel.
Makes a pretty nice 5.6 ohm nominal box by my measurements.
Do watch out for 40Hz droning, like Art mentions.  I get 3 ohms or less from about 37 to 45 Hz. There's also a drop in impedance below 3 ohms at around 115Hz if you're crossing over higher than the norm. 
That's for one box, two together will have lessor dips.

Art gives wise voltage recommendations IMO. 
But that said, I've never run them with less than 1250w @4ohms, and prefer 2500w if the input is very dynamic.
They're tough buggers.....I've measured 130v peaks  that sound fine (with very dynamic music only).
As far as heat dissipation, I can't speak to EDM use, but I've never had a noticeable problem.

It looks like I used the same build plans you found. FWIW, Rob's comment about the Keystone being an easier build makes alot of sense to me.
I consider myself a pretty decent woodworker, grew up making specialty millwork etc, and the compound flare / miters needed by the labsub were still tricky.  Made a pretty good scrap pile.  And it's essential all the fits are air tight and solid...I think maybe alot of issues, maybe even overheating, might be due to leaks??  Art, would lack of sealing, rear chamber, or other, lower impedance ??? Just spitballing.....

Anyway, what I'm getting at is another vote for the Keystone. 
I've been thinking about building one for a long time if I can use the 18" drivers i have ,
which begs one last question Art, how would the bms 18n862 work?   thx,  mark
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Art Welter

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Re: Suitability of 2 LABs for a smallish venue
« Reply #15 on: October 07, 2017, 02:50:17 pm »

Maybe outside my budget and amp. Although you recommend running at 1/2 RMS right?
The AES rating of speakers is done open air at a voltage equivalent to the power rating into the nominal impedance. Because a speaker's impedance is actually much higher open air than loaded in a cabinet, as a "rule of thumb" 1/2 the RMS figure is about right for RMS limiting.
I know from experience that a sine wave at the RMS rating will burn a voice coil pretty fast when loaded in a TH, especially when the magnet structure has been baking in the desert sun  >:(...
« Last Edit: October 07, 2017, 06:14:28 pm by Art Welter »
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Art Welter

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Re: Suitability of 2 LABs for a smallish venue
« Reply #16 on: October 07, 2017, 03:45:31 pm »

It looks like I used the same build plans you found. FWIW, Rob's comment about the Keystone being an easier build makes alot of sense to me.
I consider myself a pretty decent woodworker, grew up making specialty millwork etc, and the compound flare / miters needed by the labsub were still tricky.  Made a pretty good scrap pile.  And it's essential all the fits are air tight and solid...
1)I think maybe alot of issues, maybe even overheating, might be due to leaks??  Art, would lack of sealing, rear chamber, or other, lower impedance ??? Just spitballing.....

Anyway, what I'm getting at is another vote for the Keystone. 
2)I've been thinking about building one for a long time if I can use the 18" drivers i have ,
which begs one last question Art, how would the bms 18n862 work?   thx,  mark
Mark,
1) The LAB 12 has a fairly loose suspension, leaks in the compression chamber of the LAB Sub usually result in torn suspension rather than burnt voice coils. That said, as Ivan and I have noted, burnt coils are all about average power, you could do a hundred live gigs with the clip light hitting on kick drum peaks, then a DJ feeds you the equivalent of LF sine waves, and the coils burn in one song, no clip light..
2) The BMS 18n862 TS parameters look like they would "work" in the Keystone. The cone is a little light for horn loading, Mms of 267 grams with 19mm Xmax compared to 304 grams & 16mm Xvar for the B&C18SW115. With the lighter cone and more potential excursion, distortion would likely be higher than the B&C at Xmax/Xvar.
That said, with six dB more average sensitivity than a BR, it only takes 1/4 the power to achieve the same SPL, 9.5mm travel rather than 19mm, distortion will be higher than the BR when pushed to Xmax, but level six dB higher is a big deal, and harmonic distortion is "rock & roll" ;^).

Time to get off the computer and back to the shop and finish and test the new Keystone B-Low. I bought the plywood for them 9/15/16, two hurricanes, one brain injury, another move, and shop build ago..
Finally have the sub-assemblies for six units done, hopefully will finish the testing sometime soon, then will post results in the Keystone thread.

Cheers,
Art
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Ivan Beaver

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Re: Suitability of 2 LABs for a smallish venue
« Reply #17 on: October 07, 2017, 05:20:40 pm »

The AES rating of speakers is done open air at a voltage equivalent to the power rating into the nominal impedance.
I know some manufacturers that rate the power as the voltage into the minimum impedance.

This can give a higher rating than if rated into the nominal impedance.

It is all "part of the game", and it helps to understand how the ratings are achieved.

As you know, there are lots of variables that can skew the results.

They are not wrong, just often not what the user "thinks" they should be.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Mark Wilkinson

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Re: Suitability of 2 LABs for a smallish venue
« Reply #18 on: October 07, 2017, 05:50:23 pm »

Mark,

2) The BMS 18n862 TS parameters look like they would "work" in the Keystone. The cone is a little light for horn loading, Mms of 267 grams with 19mm Xmax compared to 304 grams & 16mm Xvar for the B&C18SW115. With the lighter cone and more potential excursion, distortion would likely be higher than the B&C at Xmax/Xvar.


Time to get off the computer and back to the shop and finish and test the new Keystone B-Low. I bought the plywood for them 9/15/16, two hurricanes, one brain injury, another move, and shop build ago..
Finally have the sub-assemblies for six units done, hopefully will finish the testing sometime soon, then will post results in the Keystone thread.

Cheers,
Art

Thx Art, the ability of the bms to handle the loading has been my concern, but it sounds like you're saying, while maybe not optimal, it would work aok...

Good luck with the B-Low !

Cheers indeed, 
mark
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davidsavill

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Re: Suitability of 2 LABs for a smallish venue
« Reply #19 on: October 07, 2017, 07:03:19 pm »

The AES rating of speakers is done open air at a voltage equivalent to the power rating into the nominal impedance. Because a speaker's impedance is actually much higher open air than loaded in a cabinet, as a "rule of thumb" 1/2 the RMS figure is about right for RMS limiting.
I know from experience that a sine wave at the RMS rating will burn a voice coil pretty fast when loaded in a TH, especially when the magnet structure has been baking in the desert sun  >:(...

Thanks heaps for all your input Art. I should be able to avoid the sun! So I have these subs running of an XTI 4002, so 1200W a channel @ 4h ohms. Should be plenty?

Also... if the B&C18SW115 is out of reach... would you recommend the 2xLab12 as the next best thing?

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