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Author Topic: Speaker specs question  (Read 2268 times)

duane massey

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Speaker specs question
« on: August 23, 2011, 12:41:24 am »

All right, I need some help understanding what I'm missing here. SRX725 specs state freq response is =/-3db 53hz-20kHz. Graph doesn't seem to bear this out, especially at the top end. Am I just confused?
http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=825
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Duane Massey
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George Friedman-Jimenez

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Re: Speaker specs question
« Reply #1 on: August 23, 2011, 03:27:53 am »

On the graph, the max SPL is around 100 dB, so the +/- 3dB frequency response range should end where the SPL drops below 6 dB less than that, ie at 94 dB. At the low end this looks like around 65 Hz. At the high end it looks like around 14 kHz. So my reading of the graph is that the +/- 3 dB range is (being generous) from 65 Hz to 14 kHz, not 53 Hz to 20 kHz. The -10 dB range looks like about 40 Hz to 18 kHz, again narrower than the claimed 37 Hz - 20 kHz range. Can anyone fill us in on what kind of mathematical magic JBL might be using to calculate their claimed frequency response and frequency range?
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David Parker

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Re: Speaker specs question
« Reply #2 on: August 23, 2011, 06:49:32 am »

All right, I need some help understanding what I'm missing here. SRX725 specs state freq response is =/-3db 53hz-20kHz. Graph doesn't seem to bear this out, especially at the top end. Am I just confused?
http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=825

one thing I noticed is that in the schematic, the two 15's are wired parallel. A lot of 2-15 cabs have a passive lo pass on the bottom 15 which takes the mids out of it. Some have said that that is to keep comb filtering down, but I have always believed it was to level out the eq response. At any rate, these have the 15's wired parallel, both 15's getting the same signal.
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Todd Rasmussen

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Re: Speaker specs question
« Reply #3 on: August 23, 2011, 08:31:51 am »

On the graph, the max SPL is around 100 dB, so the +/- 3dB frequency response range should end where the SPL drops below 6 dB less than that, ie at 94 dB. At the low end this looks like around 65 Hz. At the high end it looks like around 14 kHz. So my reading of the graph is that the +/- 3 dB range is (being generous) from 65 Hz to 14 kHz, not 53 Hz to 20 kHz. The -10 dB range looks like about 40 Hz to 18 kHz, again narrower than the claimed 37 Hz - 20 kHz range. Can anyone fill us in on what kind of mathematical magic JBL might be using to calculate their claimed frequency response and frequency range?

I'm not quite as familiar with sound reinforcement speaker specs/methods but, with home audio speakers, the published frequency response is typically with respect to 1 watt of input power.
« Last Edit: August 23, 2011, 08:33:33 am by Todd Rasmussen »
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Paul G. OBrien

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Re: Speaker specs question
« Reply #4 on: August 23, 2011, 09:39:33 am »

All right, I need some help understanding what I'm missing here. SRX725 specs state freq response is =/-3db 53hz-20kHz. Graph doesn't seem to bear this out, especially at the top end. Am I just confused?
http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=825

I'm probably being overly cynical but I suspect the response graphs are provided by the engineering dept and the print specs are generated by the marketing department.
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George Friedman-Jimenez

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Re: Speaker specs question
« Reply #5 on: August 23, 2011, 03:52:12 pm »

I'm not quite as familiar with sound reinforcement speaker specs/methods but, with home audio speakers, the published frequency response is typically with respect to 1 watt of input power.
Within the power range of the speaker, the SPL output is pretty close to linearly related to the input power. The SHAPE of the frequency response curve (relative SPL by frequency), and thus the frequency range and frequency response should be reasonably independent of input power, while the absolute output SPL would vary with the input power.
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duane massey

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Re: Speaker specs question
« Reply #6 on: August 23, 2011, 05:59:10 pm »

I always figured freq response was freq response, regardless of power. I'm more concerned about the apparent conflict between the +/-3db spec vs the graph, certainly looks like there is a bigger roll-off towards the top end.

Not just these speakers, not JBL either. That's my question, and I suspect Paul is correct.
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Duane Massey
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Houston, Texas

Benjamin Krumholz

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Re: Speaker specs question
« Reply #7 on: August 23, 2011, 06:35:31 pm »

I always figured freq response was freq response, regardless of power. I'm more concerned about the apparent conflict between the +/-3db spec vs the graph, certainly looks like there is a bigger roll-off towards the top end.

Not just these speakers, not JBL either. That's my question, and I suspect Paul is correct.

Exactly! Frequency response ratings from manufactures are not at max SPL! All i see in this graph is at 84-90dB they have it..
There is a great article by Heartly Peavey about speaker ratings  http://www.peavey.com/monitor/pvpapers/index.cfm
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Todd Rasmussen

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Re: Speaker specs question
« Reply #8 on: August 23, 2011, 07:42:49 pm »

I always figured freq response was freq response, regardless of power. I'm more concerned about the apparent conflict between the +/-3db spec vs the graph, certainly looks like there is a bigger roll-off towards the top end.

Not just these speakers, not JBL either. That's my question, and I suspect Paul is correct.

No, frequency response is not frequency response regardless of power.

I've posed a couple questions to JBL about my old SR-4732As and they've obliged me with answers in a pretty timely manner. Perhaps that's the way to go, rather than postulate.
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Brad Weber

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Re: Speaker specs question
« Reply #9 on: August 24, 2011, 06:32:42 am »

I always figured freq response was freq response, regardless of power. I'm more concerned about the apparent conflict between the +/-3db spec vs the graph, certainly looks like there is a bigger roll-off towards the top end.

Not just these speakers, not JBL either. That's my question, and I suspect Paul is correct.

No, frequency response is not frequency response regardless of power.
To the point that some people, including some who perform the tests for several speaker manufacturers, support the concept that a speaker's power rating (or maximum input voltage) should be determined by when a readily audible (3dB) change in the response occurs.  Apparently their experience is that this would actually result in lower ratings for many speakers, and thus may be difficult to get some manufacturers to support.
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ProSoundWeb Community

Re: Speaker specs question
« Reply #9 on: August 24, 2011, 06:32:42 am »


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