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Author Topic: Understanding speaker specs  (Read 13169 times)

AllenDeneau

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Understanding speaker specs
« on: January 21, 2013, 03:36:24 PM »

As I was reading another thread it has become even more apparent to me that I know some, but certainly not as much as I would like, about most things, LOL, but especially, about speaker specs.

I have an old Peavey SP system consisting of SP2G's and SP118 subs. This question really isn't necessarily speaker specific but, more of an understanding relating to my speaker. Below will be a pic taken from my manual showing the frequency response graph. I understand what it's saying BUT, as dumb as this may sound, what frequencies do each vertical line represent? By counting it shows a total of 28 vertical lines, that must mean it's a 27 band eq?

According to the Yamaha Handbook it says that the lowest 3 frequencies are excluded from the 31 band in an 28 band eq. So am I to presume that 20, 25 and 31.5 are not reporesented in this graph?

Since I usually have a parametric or a 31 band eq, what I know is: a 31 band eq is a 1/3 octave eq, meaning every octave has 3 bands of eq for control. Every 10th frequency is a decade which divides the 31 bands into 3 decades. It appears to me the 10 to the powers, on the chart, are the decade frequencies of 200Hz, 2,000Hz and 20,000Hz BUT again, which of the 31 frequencies are missing from the 31 band eq that would tune that speaker?

So my biggest questions in relation to that graph and those specs are:
1. Which frequencies do the vertical lines represent being that a 1/3 octave eq has 31 bands and the graph has 27?
2. Why do the numbers start with 2 in each decade? (I feel like I should or do know that already)
3. Why does the spacing between the graphs vertical lines decrease when the frequencies increase?
4. Shouldn't that freq chart allow me to equalize that speaker box pretty close to flat by using that chart as a starting point? That'll allow me to account for the driver issues withing the box than to eq for the room a bit quicker?

I feel like a total bonehead asking this but it's driving me nuts and I can't seem to come up with a definite answer, at least I don't think I have.

Sorry and thanks for the help...

OK, one last question somewhat related to this subject...

Every octave is a doubling of frequency, so why do 31 band eq's shallow up their frequencies in the 2nd decade of the graph? 20, 40, 80, 160, 31.5, 630, 1.25, etc...

Even after they shallow up a bit, say 31.5 to 630, they're not exactly doubling until they get back to 2.5 to 5K. Ok, I guess I know they'll still control the same frequencies but why did the center frequencies move from exact double to just a bit off?

Weird or sad that all these years I never noticed or cared or thought about this until now...

Thanks
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Allen D.
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Joseph D. Macry

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Re: Understanding speaker specs
« Reply #1 on: January 21, 2013, 04:24:48 PM »

10-superscript-2 is 10 to the 2nd power = 100 Hz. Line to the left of that are 20 through 90 Hz.
10-3 (sorry, I can't type superscript) is 1000 HZ. Left of that are 200 through 900. 10-4 is 10,000 and the highest line is 20KHz.

So the vertical lines here are 20, 30, 40 ... 100, 200, 300, 400 ... 1K, 2K, 3K, 4K ... 10K, 20K.
True, these are not the 1/3 octave bands as found on most 31-band graphic EQs.

Graphic EQ bands generally center on ISO standard frequencies which are *approximately* 1/3 octave apart. When comparing to this plot, you may have to interpolate a bit. For instance, look between 600 and 700 to find response at 630Hz.

The vertical lines get closer as freq goes up because it is a logarithmic (base 10) plot.

Do not simply use this plot to set your graphic EQ. Use it to compare with other speakers, and to get an idea of the behavior of the speaker IN ITSELF. Your actual response will vary with the room, other gear in the signal chain, environmental factors etc etc. EQ according to RTA reading (or your ears, if very good and experienced) of pink noise played through the actual system in place.
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Tim McCulloch

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Re: Understanding speaker specs
« Reply #2 on: January 21, 2013, 04:32:08 PM »

Macry beat me to it, and in fewer words... :)
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AllenDeneau

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Re: Understanding speaker specs
« Reply #3 on: January 21, 2013, 04:39:01 PM »

10-superscript-2 is 10 to the 2nd power = 100 Hz. Line to the left of that are 20 through 90 Hz.
10-3 (sorry, I can't type superscript) is 1000 HZ. Left of that are 200 through 900. 10-4 is 10,000 and the highest line is 20KHz.

So the vertical lines here are 20, 30, 40 ... 100, 200, 300, 400 ... 1K, 2K, 3K, 4K ... 10K, 20K.
True, these are not the 1/3 octave bands as found on most 31-band graphic EQs.

Graphic EQ bands generally center on ISO standard frequencies which are *approximately* 1/3 octave apart. When comparing to this plot, you may have to interpolate a bit. For instance, look between 600 and 700 to find response at 630Hz.

The vertical lines get closer as freq goes up because it is a logarithmic (base 10) plot.

Do not simply use this plot to set your graphic EQ. Use it to compare with other speakers, and to get an idea of the behavior of the speaker IN ITSELF. Your actual response will vary with the room, other gear in the signal chain, environmental factors etc etc. EQ according to RTA reading (or your ears, if very good and experienced) of pink noise played through the actual system in place.

Thanks Joseph, that was helpful. Wonder why they don't measure and publish these specs as related to a 1/3 octave eq?

I undertood the center on ISO I guess I was just curious as to why they change as the frequencies go higher?

I knew I should've known that it was logarithmic :(

I agree that it shouldn't be the guide to set your eq but with a new speaker you're not used to I'd think it'll give you some sort of baseling reference to get you close to flat then using the ear to tune to the room etc... No? I've never used it but during my time staring at it I began to think, well, that's a pretty good start for flattening out major dips or peaks.. Maybe not huh?

Thanks.
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Allen D.
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Paul G. OBrien

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Re: Understanding speaker specs
« Reply #4 on: January 21, 2013, 05:07:22 PM »

Wonder why they don't measure and publish these specs as related to a 1/3 octave eq?
Because a 1/3 octave EQ is a pretty bad tool to try and correct a speakers response with, ideally you want the fully adjustable notch and shelving filters found in a DSP processor. But even with that and an RTA display to look at you're not going to get a ruler flat response no matter how many filters you apply, and that's because speaker response is a product of the amplitude and phase response of the drivers and crossover components and how all that interacts with the room it's in, so you simply cannot correct that with an amplitude only device like an EQ... and that's ignoring the phase altering side effects of those EQ filters that you have no control over.
« Last Edit: January 21, 2013, 05:09:40 PM by Paul G. OBrien »
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AllenDeneau

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Re: Understanding speaker specs
« Reply #5 on: January 21, 2013, 05:39:50 PM »

Because a 1/3 octave EQ is a pretty bad tool to try and correct a speakers response with, ideally you want the fully adjustable notch and shelving filters found in a DSP processor. But even with that and an RTA display to look at you're not going to get a ruler flat response no matter how many filters you apply, and that's because speaker response is a product of the amplitude and phase response of the drivers and crossover components and how all that interacts with the room it's in, so you simply cannot correct that with an amplitude only device like an EQ... and that's ignoring the phase altering side effects of those EQ filters that you have no control over.

Great info, thanks Paul.

PS. I sent you a pm, about the sub question post I had, did you get it?
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Allen D.
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Scott Bolt

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Re: Understanding speaker specs
« Reply #6 on: January 21, 2013, 10:02:41 PM »

As I was reading another thread it has become even more apparent to me that I know some, but certainly not as much as I would like, about most things, LOL, but especially, about speaker specs.

I have an old Peavey SP system consisting of SP2G's and SP118 subs. This question really isn't necessarily speaker specific but, more of an understanding relating to my speaker. Below will be a pic taken from my manual showing the frequency response graph. I understand what it's saying BUT, as dumb as this may sound, what frequencies do each vertical line represent? By counting it shows a total of 28 vertical lines, that must mean it's a 27 band eq?

According to the Yamaha Handbook it says that the lowest 3 frequencies are excluded from the 31 band in an 28 band eq. So am I to presume that 20, 25 and 31.5 are not reporesented in this graph?

Since I usually have a parametric or a 31 band eq, what I know is: a 31 band eq is a 1/3 octave eq, meaning every octave has 3 bands of eq for control. Every 10th frequency is a decade which divides the 31 bands into 3 decades. It appears to me the 10 to the powers, on the chart, are the decade frequencies of 200Hz, 2,000Hz and 20,000Hz BUT again, which of the 31 frequencies are missing from the 31 band eq that would tune that speaker?

So my biggest questions in relation to that graph and those specs are:
1. Which frequencies do the vertical lines represent being that a 1/3 octave eq has 31 bands and the graph has 27?
2. Why do the numbers start with 2 in each decade? (I feel like I should or do know that already)
3. Why does the spacing between the graphs vertical lines decrease when the frequencies increase?
4. Shouldn't that freq chart allow me to equalize that speaker box pretty close to flat by using that chart as a starting point? That'll allow me to account for the driver issues withing the box than to eq for the room a bit quicker?

I feel like a total bonehead asking this but it's driving me nuts and I can't seem to come up with a definite answer, at least I don't think I have.

Sorry and thanks for the help...

OK, one last question somewhat related to this subject...

Every octave is a doubling of frequency, so why do 31 band eq's shallow up their frequencies in the 2nd decade of the graph? 20, 40, 80, 160, 31.5, 630, 1.25, etc...

Even after they shallow up a bit, say 31.5 to 630, they're not exactly doubling until they get back to 2.5 to 5K. Ok, I guess I know they'll still control the same frequencies but why did the center frequencies move from exact double to just a bit off?

Weird or sad that all these years I never noticed or cared or thought about this until now...

Thanks

As an aside ..... YUCK!  That is a pretty bad frequency response ;)
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Paul G. OBrien

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Re: Understanding speaker specs
« Reply #7 on: January 21, 2013, 11:22:39 PM »

PS. I sent you a pm, about the sub question post I had, did you get it?
Nothing in my inbox....
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David Morison

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Re: Understanding speaker specs
« Reply #8 on: January 22, 2013, 07:34:01 AM »

I agree that it shouldn't be the guide to set your eq but with a new speaker you're not used to I'd think it'll give you some sort of baseling reference to get you close to flat then using the ear to tune to the room etc... No? I've never used it but during my time staring at it I began to think, well, that's a pretty good start for flattening out major dips or peaks.. Maybe not huh?

Thanks.

To expand a little on what Paul said (and making wild assed assumptions to make this example work...), lets say you looked at that graph and decided to boost 1k6 on your graphic EQ to try and flatten the response there.

The problem is you don't know what's causing that dip there. If the crossover point of the box happens to be around there, then one possible cause for the dip would be a phase (or polarity) difference between the Mid and High drivers, causing cancellation of the acoustic output of the adjacent devices. If that is the case, then that phase/polarity difference will continue to cause cancellations even if you do stick a stronger signal in to the box at those frequencies, so you'll be making your amp and drivers work harder to no avail.
HTH,
David.

Edit - Absent Apostrophe Added
« Last Edit: January 22, 2013, 05:19:00 PM by David Morison »
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Frederik Rosenkjær

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Re: Understanding speaker specs
« Reply #9 on: January 22, 2013, 08:56:21 AM »

As an aside ..... YUCK!  That is a pretty bad frequency response ;)

Perhaps, if you're used to looking at smoothed graphs - if it is the unsmoothed plot of speaker I wouldn't consider it particularly bad?
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ProSoundWeb Community

Re: Understanding speaker specs
« Reply #9 on: January 22, 2013, 08:56:21 AM »


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