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Author Topic: How much power for subs outdoors?  (Read 16437 times)

Jeff Bankston

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Re: How much power for subs outdoors?
« Reply #30 on: January 18, 2014, 01:57:51 AM »

concerning frequency response. i built some 3 way speaker stacks recently. the woofer is a top of the line 15" Ciare model 15NDH-4S. Ciare says the sensitivity at 1 watt 1 meter is 96 db. i used Emminence speaker design software and modeled the cabinet for the flatest frequency response. as i'v done in the past i measured the response with an spl meter and sound generator. i actually wrote the numbers down on the woofer box and there still there. it would have ben better if i had measured it outside with no wind and no other sounds or noise present. these measurements were taken inside with the stack next to the refridge. the spl meter was mounted on a stand 3 feet back and centered at the cone. the amp power setting stayed the same and no eq was used, flat settings only. i use an Ashly xr1001 24db/oct crossover and triamp the system. no crossover was connected during the measurements. the only thing between the amp and speaker is the speaker wire. no cap, resistor, or coil is used in the system. heres what i got.

HZ      DB
30      89
35      94
40      98
45     100
50     102
55     104
60      99
65     101
70     101
75      99
80      99
85      99
90      99
95      92
100    93
105    94
110    95
115    95
120    94
125    96
130    94

crossover point is 130hz so no more measurements were taken. the box internal volume is 5 cubit feet for the speaker. the total box volume is 6.27 cubic feet because of all the internal bracing. i could have made the box smaller BUT the low end frequency response would have rolled off up higher. Ciare speakers are used by companies like Clair , Meyer sound and others. i have seen 15" woofers advertised to go to 25hz. it can be done with caps,coils,and resistors in the box but what they are doing is rolling off the upper end and you end up with a woofer with a sensitivity of something like 88 db 1 watt 1 meter. i'v also showed a couple of friends how a manufacterer will spec something like 30-200 hz -+15 db or something that the general public musician doesnt understand.

the Ciare 8 ohm woofer i have has a rated power handling of 1000 watts rms/aes. its driven by a bridged qsc amp rated at 900 watts rms/aes at 8ohms bridged. i didnt measure the max spl because i would want to eq it to get a flat response first.
« Last Edit: January 18, 2014, 07:29:21 AM by Jeff Harrell »
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Ivan Beaver

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Re: How much power for subs outdoors?
« Reply #31 on: January 18, 2014, 11:42:04 AM »

The lack of accuracy (or even existence) of real specifications has been around for 30-40 years. 20 years ago I decided to measure the performance of a box I was building to compare to the "big boys" (JBL, EAW, etc). After numerous phone calls to various departments I had very little luck in discovering how they came up with their numbers. I attempted (with a very crude set-up) to accurately measure the box in a whole-space environment using first noise and then a sine wave in increments from 30-120hz. Realized later that none of the published specs were done in a whole-space environment, and were averaged very broadly, including using the -10db trick in one case. I gave up after talking with another engineer who said they used formulas from some tests to extrapolate the published spec. Hope to actually test one again (or pay someone to do it) before I'm too old to build them.
Ivan has always voiced (in a much more educated manner) my frustrations with the blatant lack of true test data on most cabinets out there.

In my opinion whole space measurements of subs is pretty worthless.  Because if either the sub or the mic (person) is on the ground you will get half space loading. 

So you can fly the subs-but in most cases the audience will always be on the ground.

Well I will describe how Danley measures subs.

We measure outside with both the speaker and the mic on the ground.  No you do not get additional "gain" by putting the mic on the ground.  You only get the "boundary gain" once.

The reason the mic is on the ground is to eliminate ground bounce and the associated cancellation notch.

If you measure a relatively large box (like a sub) up close (at 1M) you will get a measurement that is HIGHER than what you would see if you used the numbers in trying to get an idea of the SPL out of a sub in a room (id designing the system).

So for that reason we measure subs at 10M (a 20dB loss of level over distance).

We apply a 28.3V signal (20dB rise in voltage over 2.83V)-so the increased drive level and distance cancel each other out.

This provides a number that can then be used in calculations for SPL over distance-even though the number is actually smaller than what would be actually measured at 1M.

The whole idea is to come up with numbers that make sense and that people can actually use/expect-not just what looks good on a spec sheet.

We calibrate an Earthworks M30 mic and use TEF as the measurement platform.  The setup is the output of TEF into an amplifier and the voltage is measured via a HP400 analog meter.

No high or low pass filters or eq is used. 

I use a sweep time that allows for the resolution to be 1/10th of the low corner of the cabinet.

So for 40hz this would be 4 Hz resolution.

This makes for some VERY long sweeps on some cabinets. But does give the accuracy needed.

When coming up with the numbers for the spec sheet I look for the AVERAGE SPL across the intended bandwidth.  NOT a maximum number at some freq that would give an  unusually high number-but is worthless at the freq of intended operation.

I know of one product that has a really high SPL number-it is a double 18 and that number comes from a peak around 1800 Hz.  Not exactly a sub freq.

So yes the sub WILL produce that SPL-but NOT at the freq you will be using it.

So now that I have a sensitivity number I look for the freq on the curve that is 3dB down FROM THAT SENSITIVITY!

That is REALLY IMPORTANT.  The SPL AND -3/-10 numbers MUST be tied together.

If they are not-then both are pretty much meaningless-just look at some measured specs and see for yourself.

If we were to rate the sensitivity higher (like 100Hz for example) then the SPL numbers would be higher-but if the low cutoff was linked to that number we would end up with low cutoff numbers that are much higher than what they actually are.

So you have to choose REALISTIC numbers that actually MEAN SOMETHING in terms of what the customer can expect when using it.

Or  you can just "make up some numbers" and go with that because they "look good".

Who measures or understands anyway?  is what I think many manufacturers think when doing spec sheets.  "TRUST US" seems to be the name of the game in many cases.

I hope that helps some.



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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!

duane massey

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Re: How much power for subs outdoors?
« Reply #32 on: January 18, 2014, 11:57:34 AM »

Very informative, Ivan (as always). One question, that may just be ignorance on my part. Is it necessary to adjust the gain settings at each measured frequency to assure that the actual power remains the same, because of changes is the resistance? I was told (years ago on my first attempt) that this was the only way to accurately measure the response of the box at each chosen frequency. My crude set-up was just not up to this task, so I just went with what was there.

I agree completely with the whole-space/half-space thing, and the next time (IF there is a next time) I try this I will take your approach. Rather meaningless exercise as I have no plans to mass-produce or market these things, and my clients buy what I build strictly on word of mouth (or would it be sound in ear?). I'm already too old for this, and there is still so much to learn.

Thanks again, Ivan.
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Duane Massey
Technician, musician, stubborn old guy
Houston, Texas

Ivan Beaver

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Re: How much power for subs outdoors?
« Reply #33 on: January 18, 2014, 06:43:15 PM »

Very informative, Ivan (as always). One question, that may just be ignorance on my part. Is it necessary to adjust the gain settings at each measured frequency to assure that the actual power remains the same, because of changes is the resistance? I was told (years ago on my first attempt) that this was the only way to accurately measure the response of the box at each chosen frequency.
DO NOT adjust the gain for a specific freq.  You will end up with something other than the actual freq response.

And how would you know that the power is the same going to the speaker?  Without an impedance CURVE, there is no way of knowing. Yes an engineer could draw a general curve of the impedance for a vented box-they all look pretty much the same-but with a fair deal of varience-depending on the design.

The whole concept of 1Watt is completely WRONG-and anybody stating it REALLY does not have an understanding of what is going on.

I do not know of a single manufacturer who is actually delivering 1 watt of power.

This is an old WRONG hold over from many years ago.

What they are actually doing is supplying 2.83V and with an 8 ohm rated (not actual impedance as it will vary with freq) load, the power would be 1 watt.  For a 4 ohm cabinet it would be  2 watts etc.

While it may be "standard talk" it is like saying you are flipping the phase when what you are ACTUALLY doing is flipping the POLARITY on the console.

Yes they are "kinda" related (phase must have a freq component-polarity does not), the ARE NOT the same.

NO amplifier delivers wattage to a loudspeaker.  It delivers VOLTAGE.  The actual wattage is determined by the drive VOLTAGE and the impedance (at a particular freq!!!!!!!!!!!) of the speaker.

If an amp COULD deliver constant wattage-we WOULD NOT like the sound!!!  There would be all sorts of peaks in the response that would sound really nasty.

Does that make sense?

YES these little things DO matter-but I think many manufacturers would rather go along with the WRONG public knowledge-than do it right.  So sad--------------

It makes you wonder what else they are doing in the spec sheets to make them look good for people who don't understand.

And the same goes for watts RMS.   There is no such thing. The RMS value is 70.7% of the peak of the VOLTAGE waveform, but that is another thread.

Let's get it RIGHT.

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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!

ProSoundWeb Community

Re: How much power for subs outdoors?
« Reply #33 on: January 18, 2014, 06:43:15 PM »


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