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Author Topic: What does an simple SPL number tell you anyway?  (Read 4698 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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Ivan Beaver
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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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Ivan Beaver
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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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Ivan Beaver
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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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Ivan Beaver
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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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Ivan Beaver

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Re: What does an simple SPL number tell you anyway?
« Reply #10 on: June 01, 2017, 07:42:07 am »


So trying to describe something with a simple SPL meter reading often falls short of what the actual experience is.
I have done a couple of shows lately that had some "interesting SPL reading".

These were what you would call "hardcore" type shows in which you would expect the levels to be pretty high.  Hardcore nasty rap-metal bands etc.

There is no SPL limit in the venues, and the systems still had plenty of headroom left.

I let the operators run it as they wanted-unless they would be close to causing damage-which they were not, so I never said anything about the levels.

Keep in mind that there was plenty of low deep freq available-so the energy was there.

The levels at FOH A slow (which seems to be popular these days-it never used to be------Oh well) was around 101-102dB.

Not what you would expect from that type of show, yet the FOH guys and the audiences were happy (and impressed), yet the measured SPL was not as high as at some other shows.

I think this is a good thing, especially when you consider that your ears didn't ring.  Unless of course you like that sort of thing :P

The simple SPL is not always an indicator of the "fun factor" of the overall sound.

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Scott Bolt

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Re: What does an simple SPL number tell you anyway?
« Reply #11 on: June 01, 2017, 09:47:47 am »

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.
I can see that with speakers like Danley.

Lots of speakers have a relatively high cross-over to the horn (1-3K).  I think in these designs the horn isn't as stressed.  The lower you go, the more power it takes to get SPL out.

Seems like (could be a wrong perception) that it is more difficult to prevent distortion in HF than LF though?

I totally agree with you that the "fun" factor is totally missed in an SPL reading!
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Ivan Beaver

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Re: What does an simple SPL number tell you anyway?
« Reply #12 on: June 01, 2017, 10:08:57 am »


Seems like (could be a wrong perception) that it is more difficult to prevent distortion in HF than LF though?


There are 2 things to consider when discussing harmonic distortion (the addition of harmonic related freq to the fundamental).

The first is the fundamental freq, the second is the freq of the actual harmonics.

In the case of most of our products, the distortion components are "mechanically/physically" reduced due to the physical low pass filters that are in front of the low and mid drivers.

So any distortion components produced by the drivers (above the low pass freq) are reduced.  This is kind of like how the muffler on your car works.

So lets say the woofers operate up to 300Hz.  If you put a 200Hz tone in, then the harmonics (400,600,800 etc) are reduced AFTER they are created.

You cannot do this with processing, only after the sound exits from the driver.

The HF driver does nto have such a low pass-because it needs to go higher.

However, the harmonic distortion of the driver (especially as you go up in freq) become less of an issue-simply because your ears can't hear them (out of our hearing range).

When you have a lot of horn gain at the lower freq of the HF driver, you end up with a lot of "extra level" that you need to "throw away"-via eq or higher xover freq.

When that range is reduced in level going to the driver, then the driver is going to have a lot less distortion, than a driver that is on a small horn that does not have this gain.

In some cases, we are "throwing away" 15dB of gain.  this means that at those freq, the driver is getting 1/20th to 1/40th of the power at the higher freq.  So the distortion is lower at those freq, and those freq are the ones that will have harmonic content that we can hear. At 2Khz you will have harmonics of 4K-6K-8K-10K etc.

Also remember that the particular harmonics sound different (pleasing) to our ears.

The even harmonics are not distracting.  The odd harmonics are the "bad ones".  So fortunately the odd ones are higher in freq-so they are either out of our range of hearing or start to be in the acoustic low pass filters and reduced.
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Lance Hallmark

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Re: What does an simple SPL number tell you anyway?
« Reply #13 on: June 01, 2017, 10:46:57 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.

THIS is what so many people don't get when you are talking about higher quality sound systems. Just did a 14 hour show of House music this weekend with zero ear fatigue and never felt that the sound was ever overpowering. Lower quality speakers would have you thinking it's too loud and bring on the headaches and ringing.
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George Friedman-Jimenez

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Re: What does an simple SPL number tell you anyway?
« Reply #14 on: June 01, 2017, 12:06:28 pm »

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.

This is not just perception. The ear has a reflex, the stapedius reflex, that responds to loud sounds by tensing the stapedius muscle, which mechanically reduces the conduction of sound from the ear drum to the cochlea (inner ear). Low frequencies trigger the reflex, high frequencies do not, so when you filter out the LF from your music, you remove the trigger for the reflex and actually allow more HF sound into the inner ear. So while the actual measured SPL is lower, the HF energy making it to the inner ear is higher.
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Josh Ricci

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Re: What does an simple SPL number tell you anyway?
« Reply #15 on: June 05, 2017, 10:30:14 am »

This is not just perception. The ear has a reflex, the stapedius reflex, that responds to loud sounds by tensing the stapedius muscle, which mechanically reduces the conduction of sound from the ear drum to the cochlea (inner ear). Low frequencies trigger the reflex, high frequencies do not, so when you filter out the LF from your music, you remove the trigger for the reflex and actually allow more HF sound into the inner ear. So while the actual measured SPL is lower, the HF energy making it to the inner ear is higher.

Well...I have learned something new today. Thanks for posting this.  :)

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Re: What does an simple SPL number tell you anyway?
« Reply #16 on: March 03, 2020, 08:04:37 pm »

I loved this thread.  I learned so much.  Ivan rocks!
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Yoel Klein

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Re: What does an simple SPL number tell you anyway?
« Reply #17 on: March 03, 2020, 10:20:13 pm »

I loved this thread.  I learned so much.  Ivan rocks!
Thanks Ivan, I love these knowledge and it makes so much sense.
There is one factor I noticed with Danley speakers, and I named it “The Danley Effect”. Lol..
Because when you hear a non Danley box at lets say 100db, you perceive it as loud and full of energy and your happy.  Now play a Danley box, same content, same level, and you will feel like its missing volume... and tend to gain in up more, but you will never feel this brick of sound surrounding your ears, only until you turn it up so loud that your head begins hurting, that is when you realize that your listening to 8x the volume..  and I think this is because the Danley sounds so refined and so clean, which allows your ears to tolerate a much much higher volume. 
Which I call this the Danley effect...
« Last Edit: March 03, 2020, 10:22:22 pm by Yoel Klein »
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duane massey

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Re: What does an simple SPL number tell you anyway?
« Reply #18 on: March 03, 2020, 10:56:12 pm »

Many years ago I attempted to come up with meaningful measurements on a cabinet we had been building for a number of years. Did some research on how JBL, Community, etc, did their measurements. Made as accurate a measurement as we could, and the numbers were somewhat disappointing. Went back and read the marketing literature from the "big boys" and realized that (a) they didn't talk about the actual measurements, just the +/- 10db readings and/or calculated peaks, and (b) none of our clients would ever read the specs anyway, as we typically sold our boxes by doing onsite demos. The numbers don't tell you how the box sounds. I build very few boxes now, and my back & knees are grateful.
Great post, Ivan, as always.
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Duane Massey
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Mac Kerr

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Re: What does an simple SPL number tell you anyway?
« Reply #19 on: March 03, 2020, 11:36:44 pm »

Amazing how a Russian troll posting to this thread before being discovered and removed has resurrected a 3 year old zombie.

Mac
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Robert Lofgren

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Re: What does an simple SPL number tell you anyway?
« Reply #20 on: March 04, 2020, 04:11:32 am »

So heavy bass actually saves our ears? I need more subs!

This is not just perception. The ear has a reflex, the stapedius reflex, that responds to loud sounds by tensing the stapedius muscle, which mechanically reduces the conduction of sound from the ear drum to the cochlea (inner ear). Low frequencies trigger the reflex, high frequencies do not, so when you filter out the LF from your music, you remove the trigger for the reflex and actually allow more HF sound into the inner ear. So while the actual measured SPL is lower, the HF energy making it to the inner ear is higher.
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Scott Bolt

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Re: What does an simple SPL number tell you anyway?
« Reply #21 on: March 04, 2020, 06:33:12 pm »

Amazing how a Russian troll posting to this thread before being discovered and removed has resurrected a 3 year old zombie.

Mac
That is ironic ;)

Still a great thread though!
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ProSoundWeb Community

Re: What does an simple SPL number tell you anyway?
« Reply #21 on: March 04, 2020, 06:33:12 pm »


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