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Author Topic: Help me understand about SPL please?  (Read 2117 times)

Mike Henderson

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Help me understand about SPL please?
« on: September 15, 2020, 10:48:46 AM »

Hey guys, how are you all doing, hope you all are being safe and all is well!

So this is troublesome Mike again [sorry] this time with a related issue as a spin-off from my previous questions.

If you guys might remember I was wondering why the SB1000 power-wise would be more pounding and give more distance than my Dual 18" Sonic:

https://www.sixstardj.com/sonicr218sub.html

I just got the EAW SB1000e sub [FINALLY!!] and it has the RCF LP300 Woofers and looking at it's specs I was very surprised to see that it is only 1000 Watts "continuous" power:

https://usspeaker.com/rcf%20-%20L18P300-1.htm

The Eminence Kilomax Pros I had on the Sonic is higher rated than that RCF 300:

https://www.eminence.com/speakers/speaker-detail/?model=Kilomax_Pro_18A

So I was told by a speaker tech friend of mine that it's the SPL which makes the difference.

The Sensitivity in the Kilomax is 95.8 and in the RCF is 97 so not much difference. The SPL in the Sonic cab is 102 and in the SB1000 132 Long Term and 138 Peak so that's a whopping difference so that I can understand, regarding the cabinets themselves that is.

So my question is it seems to me when comparing those 2 mentioned above that it is the cabinet's specs and design which mainly determines the power and distance of the bass, is this correct please? you guys know I am not all that technically sound so I am just trying to understand this as best as I can, thanks.

« Last Edit: September 15, 2020, 10:51:09 AM by Mike Henderson »
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David A. Williams

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Re: Help me understand about SPL please?
« Reply #1 on: September 15, 2020, 01:06:27 PM »

I'd like to put off talking about driver specifications for a minute and hone in on the following:
Quote
... I was wondering why the SB1000 power-wise would be more pounding and give more distance than my Dual 18" Sonic:

People are often misguided about the relationship between SPL and distance. To set the record straight: each time you double your distance from a speaker, that speaker becomes 6 dB quieter. There's no way to design a single cabinet or a horn to skirt this issue (we'll ignore line array theory for now...). Manufacturers who advertise "long throw" speakers really mean "loud, with a narrow coverage angle" and it seems to confuse people. Without diving into spec sheets I'd fully expect an expensive product like the SB1000 to play louder than your other option, but "more distance" is a shaky claim.

Now, let's get into some of those specs:

A thermal limit is implied by a "continuous" power rating. Exceed this for long enough and the voice coil will overheat, causing irreversible damage. A 250W difference in this specification isn't by any means remarkable, and isn't enough to overcome the difference in sensitivity in this case.

Now, you've given some cabinet specs as well, but keep in mind these are only valid for the OEM drivers, which you don't have. Disregard them; besides, the number you've given for the Sonic is likely a halfspace sensitivity number, and for EAW a halfspace max spl number. Completely different information.

Finally, let's deal with the fact that you aren't using OEM drivers. Without knowing the volume and tuning of the enclosure, you can't be sure that your drivers are even safe at their max rated power. The TS parameters could be such that your drivers over-excurt at far below their rated power.
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Caleb Dueck

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Re: Help me understand about SPL please?
« Reply #2 on: September 15, 2020, 01:21:28 PM »

I just got the EAW SB1000e sub [FINALLY!!] and it has the RCF LP300 Woofers and looking at it's specs I was very surprised to see that it is only 1000 Watts "continuous" power:

There isn't any one single spec that determines the difference between a Pro subwoofer and a DJ subwoofer.  Roughly - Pro grade is the best, MI (Musical Instrument, IE music store brands) is a step down, and DJ is yet another step down.  There are a whole list of variables that get their corners cut each time you take a step down.  Power handling is one of the more minor variables. 

Without rehashing the whole list (a week with Google, the DIY subwoofer threads on soundforums.net, etc will really open your eyes) - the very short summary is that if you need real bass, ignore DJ brands, step over the MI brands, and look at Pro brands.  Used Pro, like you bought, is a good way to ease into things.  The more modern Pro offerings are even better than the older pro offerings like the SB1000.

A subwoofer is the sum of all parts - the quality of the drivers themselves, the design of the enclosure, the type of enclosure (horn loaded, rear horn, vented, band pass, T-line, infinite baffle, sealed, etc), the quality/stiffness/density of the enclosure, the type of amplifier powering it, the processing in the amplifier. 

As David said - subs don't 'throw' bass.  Part of why horn loaded subs 'throw' better is that the mouth of the sub isn't right against the face of the driver, so the most drastic drop has already happened.  When you eliminate the artificial 'super loud up close', at distance it's more even.  It's easier to visualize than explain. 

The first step to learning how subs really work - is to ignore the number of watts in the advertising, especially with lower end products.  All they are is for marketing, where larger numbers sell more boxes.   

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Chris Grimshaw

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Re: Help me understand about SPL please?
« Reply #3 on: September 15, 2020, 01:22:24 PM »


The Sensitivity in the Kilomax is 95.8

Bet it isn't.
As I said in another thread, those things barely had enough motor for a 15", let alone an 18". They'll probably have fairly low sensitivity below 100Hz.

Chris
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Caleb Dueck

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Re: Help me understand about SPL please?
« Reply #4 on: September 15, 2020, 01:36:49 PM »

Bet it isn't.
As I said in another thread, those things barely had enough motor for a 15", let alone an 18". They'll probably have fairly low sensitivity below 100Hz.

Chris

Your're right, at 30Hz, it's 78dB. 
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David A. Williams

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Re: Help me understand about SPL please?
« Reply #5 on: September 15, 2020, 02:09:08 PM »

Part of why horn loaded subs 'throw' better is that the mouth of the sub isn't right against the face of the driver, so the most drastic drop has already happened.  When you eliminate the artificial 'super loud up close', at distance it's more even.

Is there data on this somewhere? I have no hands-on experience with bass horns, and as driver/amp power handling improves it seems like there's less of them around every year.
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Ivan Beaver

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Re: Help me understand about SPL please?
« Reply #6 on: September 15, 2020, 03:05:02 PM »

You can't just take the "rated sensitivity" as fact.

If you look at any actual freq response (especially of a raw driver) you will see that the sensitivity varies with freq.

Often a driver with a lower sensitivity than another will be LOUDER at some freq than the one with the higher sensitivity.

The sensitivity is a simple number to a very complex answer, that often gives a wrong answer.

If the drivers are going into identical cabinets, you can start (but that won't give a totally accurate answer) by comparing freq by freq and seeing what you have.

But in the cases of horn cabinets, often a "wimpier" driver can produce greater output, depending upon many factors.  It all depends on the particular parameters (SPL, and power capacity are not in the list-or down the list a bit) of the particular driver and the "needs" of the particular cabinet it is going in.

You need to start to think in terms of dB differences, NOT actual power numbers, to begin to understand that often the sensitivity has a greater influence on the final outcome.  But it also depends GREATLY where that sensitivity number actually comes from.

Some manufacturers may choose it in the intended range of operation (which will often result in a lower sensitivity number), and other may choose it in a freq range where it is simply higher.

Take a "typical" woofer.  Do you want the number to tell you what the sensitivity is below 100Hz? or maybe up into the 500Hz range, where it could also be used?  You will have different number for those different ranges, but yet you have to choose a SINGLE number to describe the behavior over different freq ranges.

It is not an easy task, and don't get caught up on the simple number answers.  You could very easily be wrong.

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Mike Caldwell

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Re: Help me understand about SPL please?
« Reply #7 on: September 15, 2020, 07:30:42 PM »

Bet it isn't.
As I said in another thread, those things barely had enough motor for a 15", let alone an 18". They'll probably have fairly low sensitivity below 100Hz.

Chris

And in that same thread I ran some numbers on the Kilomax loaded into the Sonic cabinets and the Sonic cabinets had no where near the internal volume needed for a pair of Kilomax 18's

Mike Henderson

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Re: Help me understand about SPL please?
« Reply #8 on: September 15, 2020, 08:17:36 PM »

And in that same thread I ran some numbers on the Kilomax loaded into the Sonic cabinets and the Sonic cabinets had no where near the internal volume needed for a pair of Kilomax 18's

Thanks all of you guys, I will need to re-read and soak in all post's info given here.
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Tim McCulloch

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Re: Help me understand about SPL please?
« Reply #9 on: September 16, 2020, 12:45:05 AM »

Thanks all of you guys, I will need to re-read and soak in all post's info given here.

In addition to all the good stuff above...

SPL is SPL is SPL.  Perception is another matter and I think that's at the heart of your quest.  You're trying to find numbers that reflect the perception or "audition" of a particular subwoofer.  You are not the first and you won't be last, because it's based on things that aren't being measured.

{Measure what you can; if you can't measure it does it matter?}
Physics and a bunch of Not So Famous Dead Guys identified electrical and physical phenomena that allows us to use mathematics to represent how things work, and demonstrate what happens when various Dead Guy parameters are changed.  But even with that, subwoofers with identical 'numbers' can sound very, very different.  All fine and lovely, but what about things we aren't measuring for?  Maybe because we haven't found a way to define what we're perceiving in ways that fit our understanding of the physics?  OTOH, if we can hear it we should be able to measure it, eh?

The difference in basic designs - bass reflex, rear loaded horn, band pass, tapped horn - represent a different way of interfacing the piston of the woofer to the surrounding air and each will sound different and exhibit various trade-offs in compensation for the thing(s) they do well.  Caleb gave you the condensed version and if we get Ivan started, you'll have lots of reading to do... ;)

Probably the biggest differences are with bass reflex (vented, ported) design and various pass band designs.  Bass reflex lets us put a lot of bass in a relatively small box, and the trade off is typically high levels of 2nd and 3rd order harmonic distortion.  Pass band designs have tended to be "one note wonders" but improvements in design and muti-tuned designs have mitigated some of that (smiling at you, Nexo).

Here's my advice on subs - go out and listen to as many as you can.  Any gig, work your way up front if you can and spend some 'quality time'.  Then move back, walk around.  You'll find big variations in coverage that are created by the distance between sub stacks (if left/right) and solid, boundary surface like walls, floors, ceilings that create reflections (and therefore cancellations).  The subs that sounded great at last weeks gig not sounding great at this week's gig, in a different room with different dimensions?  The subs didn't change...

Finally, in the Product Review forum there is a thread about playing subs for non-sound people and getting their impressions.  Find it, some of those pesky perceptions were surprising.

It's a great time to be in audio. :)
« Last Edit: September 16, 2020, 12:47:51 AM by Tim McCulloch »
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Re: Help me understand about SPL please?
« Reply #9 on: September 16, 2020, 12:45:05 AM »


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