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Author Topic: What does an simple SPL number tell you anyway?  (Read 4694 times)

Ivan Beaver

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What does an simple SPL number tell you anyway?
« on: May 31, 2017, 01:32:32 pm »

There is a current thread in the Subwoofer forum that is talking about this a little bit, but I thought I would put it as a more "general" topic.

I recently did a couple of "simple SPL" measurements on full range loudspeaker-the model is not important.

The SPL used was the NTI XL2.

I took a number of measurements, using different freq ranges, different types of pink noise etc.

The purpose of the test was to examine how different bandwidths affect the overall "simple SPL" that a meter reads.

I hope my notes to myself are self explanatory.  The "tilted" response was basically a HF rolloff that some people like the sound of.  I don't remember what the exact rate of decay is.

I turned on and off the different freq ranges (it is a triamped cabinet) so the SPL numbers reflect the partial and full freq response.

There is a little bit of a bump below 100Hz.

The SPL numbers are not relative to anything-I have no idea what the input voltage was-I just ran it at a comfortable level-so don't look at the absolute levels, just the relative differences.

The A and C numbers after the SPL are the A and C weighting curves.  The numbers are averaged between slow and fast response.

Maybe some people will find some of it useful.


SPL VS Bandwidth
H=High, M=mid,  L=Low
SPLs are approximately averaged between fast and slow response. +/0.5dB rounding error

 w/tilted response
IEC noise                              Pink noise
H           92C        93A              95C      95.5A
M         97.5C       95.5A           96.5C    95A
L            105.5C    89A           106C      89A
H+M      98.5C      97.5A         99C       98.5A
H+M+L  107C       98A           107C      99A


 flat response
IEC noise                               Pink noise
H               96C        97A           98C     99.5A
M               97C        95A          96.5C    94.5A
L                 105C     89A          105C     89A
H+M           100C     99.5A         101C   101A
H+M+L      107C     100.4A       107C     101A
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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!

Scott Bolt

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Re: What does an simple SPL number tell you anyway?
« Reply #1 on: May 31, 2017, 08:03:20 pm »

Hi Ivan,

From here:  https://upload.wikimedia.org/wikipedia/commons/thumb/3/39/Acoustic_weighting_curves_%281%29.svg/600px-Acoustic_weighting_curves_%281%29.svg.png

A single value calculated across a weighted average using a weighting curve seems like it is of very little use.  I suspect that many OEM's make use of the A weighting which de-emphasizes lower frequencies which are essential to a decent sounding speaker.  Since it is quite easy to make a speaker horn that puts out tons of 2-7K, such a screach monster of a speaker could easily show very high SPL numbers using the A weighting.

The real reason I feel that SPL is a bad indicator of how much usable volume you can get from a speaker is that the sound the speaker produces can be pure crap.  Louder crap is still crap ;)

Having said all this, there is no standard which accurately captures "usable volume" from a speaker..... and SPL is a better measure than "Watts"!!
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Ivan Beaver

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Re: What does an simple SPL number tell you anyway?
« Reply #2 on: May 31, 2017, 08:49:56 pm »

  Since it is quite easy to make a speaker horn that puts out tons of 2-7K, such a screach monster of a speaker could easily show very high SPL numbers using the A weighting.


And the A weighting actually has a BOOST around the area that the loudspeaker can get really loud.

I have seen specs of "peak SPL" that include the large peak between 1-2K that is capable with a large format driver.

But you have to get rid of (throw away) that peak in order to get the response to match above and below it.

So the "usable peak/max SPL" is not as loud as the unprocessed response would indicate.

BTW, my measurements were of the processed cabinet-so natural peaks were eliminated.
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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!

Tim McCulloch

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Re: What does an simple SPL number tell you anyway?
« Reply #3 on: May 31, 2017, 08:57:34 pm »

Hi Ivan,

From here:  https://upload.wikimedia.org/wikipedia/commons/thumb/3/39/Acoustic_weighting_curves_%281%29.svg/600px-Acoustic_weighting_curves_%281%29.svg.png

A single value calculated across a weighted average using a weighting curve seems like it is of very little use.  I suspect that many OEM's make use of the A weighting which de-emphasizes lower frequencies which are essential to a decent sounding speaker.  Since it is quite easy to make a speaker horn that puts out tons of 2-7K, such a screach monster of a speaker could easily show very high SPL numbers using the A weighting.

The real reason I feel that SPL is a bad indicator of how much usable volume you can get from a speaker is that the sound the speaker produces can be pure crap.  Louder crap is still crap ;)

Having said all this, there is no standard which accurately captures "usable volume" from a speaker..... and SPL is a better measure than "Watts"!!

In some genres that "screach" might be considered a benefit and not a defect, so determining what is usable SPL and what is simply a gratuitous (but measurable) number is also a matter of other considerations.

The jaundiced eye that I cast on spec sheet numbers falls on "calculated max SPL".  For long enough to make an o'scope trace hit a particular magnitude?  Long enough to make my pro-sumer SPL meter needle register at the listed spec?  Long enough to get my neighbors to call the cops?

I remember when all the reputable manufacturers had useful graphs, tables and measured polar data on their spec sheets... and I agree with JR's assessment that the marketing dept found those made it harder to sell loudspeaker systems to people who were not engineers - the masses with $$ to spend wanted simple comparisons (think: rating vacuum sweepers by the motor current draw) so we end up with vastly "massaged" SPL numbers, coverage angles instead of polar plots, no mention of distortion, use of "Watts" as some kind of nebulous specification...

Use of weighting curves go undisclosed, use of input signal processing to achieve a particular spectral output... don't get disclosed or no comparison info (words or graphs) is provided.

Perhaps more than ever it's important to get out and audition loudspeaker systems before making major purchases.  The results might be surprising in how similar different brands can be within the same price bracket, and sometimes in how small or large the incremental differences are as you move up an individual manufacturer's brand ladder.  Almost universally as you spend more things get better - the basic sound, development of feature set items like processing, lower weight, more output, better ergonomics, etc.  Then there is the "out of box experience" where you listen to your own audition audio for the first time and smile (or not).  Does the system need to sound 'right to me' or does it need to respond to EQ in a linear fashion?  System voicing that is diametrically opposed to what you *need* is often difficult to fully un-do...  These are considerations that don't show up on a spec sheet and the best you can hope for without an audition is an honest review from another user who is familiar with your intended use.

Attributed to Mark Twain-  "There are three kinds of lies.  Lies, damn lies, and spec sheets statistics."
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Ivan Beaver

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Re: What does an simple SPL number tell you anyway?
« Reply #4 on: May 31, 2017, 09:37:46 pm »


Perhaps more than ever it's important to get out and audition loudspeaker systems before making major purchases.  The results might be surprising in how similar different brands can be within the same price bracket, and sometimes in how small or large the incremental differences are as you move up an individual manufacturer's brand ladder.  Almost universally as you spend more things get better - the basic sound, development of feature set items like processing, lower weight, more output, better ergonomics, etc.  Then there is the "out of box experience" where you listen to your own audition audio for the first time and smile (or not).  Does the system need to sound 'right to me' or does it need to respond to EQ in a linear fashion?  System voicing that is diametrically opposed to what you *need* is often difficult to fully un-do...  These are considerations that don't show up on a spec sheet and the best you can hope for without an audition is an honest review from another user who is familiar with your intended use.

Attributed to Mark Twain-  "There are three kinds of lies.  Lies, damn lies, and spec sheets statistics."
Agreed.

Actual side by side is among the best ways to listen to loudspeakers.

Something else that doesn't show up on spec sheets is "what does it sound like at that SPL?"

What about distortion?

Just because a loudspeaker can produce a specific SPL does NOT mean you want to listen to it at that SPL.

And sound quality can be very subjective.

Different people look for different things.  Some want clean accurate etc.

Others look to use the system as a tool to inflect pain upon the audience (no, I did not make that up).  I know several people who feel the sound system should hurt you between the eyes or icepick in the forehead type sound.

Others like a really screwed up freq response because it has a "particular" sound.

Other feel that combfiltering is "the way a sound system is supposed to sound"

Those don't come across on the spec sheets
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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!

Scott Bolt

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Re: What does an simple SPL number tell you anyway?
« Reply #5 on: May 31, 2017, 09:56:30 pm »

Ivan,

Yea, it is clear from your readings that the "ice pick in the ear" frequencies are louder in the flat readings .... and that A vs C really emphasizes it.

Not sure what you guys have found, but IME it is nearly always the woofer driver that limits first.  The HF driver seems to be able to make loud noise without limiting (based on when my own powered speakers limit ... ie on bass notes in the frequency range of the woofer in the top box).

Another very difficult to quantify attribute is the distortion of the HF driver.  While it is possible to make a cheep and very LOUD tweeter, it seems like it is expensive to make one that is nice sounding at higher output levels and which has low distortion.

One of my least favorite tweeters was that God awful JBL EON 1st generation tweeter in the plastic grey box.  Ick!

Tim,

I have made it a hobby to personally audition speakers ;)  Since I retired my amp rack and passive speaker systems, I have been very active in auditioning the newest powered speakers.  The latest trend seems to be that you can have decent sound at a low price, but it won't get very loud, and wont stay looking nice .... OR you can spend quite a bit more money for a speaker that will sound good, get loud (and still sound good) and stay looking nice (good finish).

I do wish there were some better measurement to classify pro audio speaker output with.  My go-to method is to listen to many reviews on forums, and when lots of them agree that something is "good", go track it down (hopefully one of my friends locally in a band will have one, or a friend in live sound rental) and audition it.  Kind a hard to put a number on that though :)
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Scott Bolt

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Re: What does an simple SPL number tell you anyway?
« Reply #6 on: May 31, 2017, 09:59:24 pm »

Oh, and I agree.  A/B is the absolute best way of auditioning a speaker.  The one thing that I think gets missed when this is done is that you should eq each speaker separately to your taste, THEN A/B them.

Sometimes the best POTENTIAL sounding speaker is not the same as the one that sounds best at its default voicing.
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George Friedman-Jimenez

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Re: What does an simple SPL number tell you anyway?
« Reply #7 on: June 01, 2017, 06:15:56 am »

Agreed that single number SPLs in speaker specs lend themselves to fudging and misleading comparisons. Single number SPL measurements do have some uses, however. For example, prevention of hearing loss depends on knowing SPLs (mainly A weighted) and limiting time of exposure to high SPLs. A second example is, when A/B auditioning speakers, I like to do at least a quick listen at SPLs similar to real life levels, which means listening from a pretty long distance away and matching the SPLs pretty closely. There is a tendency to perceive the louder speaker as sounding better and even a small SPL difference can have this effect. Also, I like to A/B compare single speakers, not pairs. I have noticed some salespeople in MI stores like to start out playing a pair of one model vs a pair of the other. This adds complicating variables to the comparison, such as different distances from the drivers (which affects SPLs), interference (comb filtering), room acoustics and stereo vs mono sources.
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Ivan Beaver

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Re: What does an simple SPL number tell you anyway?
« Reply #8 on: June 01, 2017, 07:27:58 am »



Not sure what you guys have found, but IME it is nearly always the woofer driver that limits first.  The HF driver seems to be able to make loud noise without limiting (based on when my own powered speakers limit ... ie on bass notes in the frequency range of the woofer in the top box).


Actually it really depends on the cabinet.

In almost all of the Danley designs, the HF is the "weak link" due to the fact that the horn loading gives so much extra gain to the low and mids.
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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!

Ivan Beaver

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Re: What does an simple SPL number tell you anyway?
« Reply #9 on: June 01, 2017, 07:34:13 am »

Here is a fun experiment to play-when talking about SPL meter readings and how it sounds.

Take a 3 (or 4) way tri/quad amped system and turn it up to a good comfortable pretty loud level-but still easily listenable.

Now mute everything but the HF (keep the levels the same).

What do you do?  You IMMEDIATELY cover your ears because it is to "loud" and hurts.

But why?  The actual SPL measured is LOWER than before, when you could listen to it.

And the highs will sound really nasty, yet they were clean before.

It is not just the "simple SPL", but rather the balance of the sound/freq ranges that make a HUGE difference in how we perceive loudness.

Our perception of loudness can be VERY different than reality

So trying to describe something with a simple SPL meter reading often falls short of what the actual experience is.

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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: What does an simple SPL number tell you anyway?
« Reply #9 on: June 01, 2017, 07:34:13 am »


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