driver FR, driver + PR, speaker RF questions

Hello,

I wanted to ask something about speakers, especially FR response graph.

I’ve attached a scan of speaker data sheet for reference

The speaker is rated down to 35hz, yet from the graph, the curve starts to go down after about 80hz. By 55hz it’s already 3db down. By 35hz we are down almost 10db.

1) So my question is - If FR is down by 10db at certain frequency, is it still considered that the speaker is cable of reproducing that frequency?
I looked up a lot of speakers specs - all of them are at least 10gb down at the lowest frequency they are recommended for, so it seems typical practice.

In other words- if speaker outputs 35hz, but it’s 10db down (that’s half perceptive volume if I’m not mistaken) - is it still considered that the speaker can reproduce down to 35hz adequately?
as a listener, can you still adequately enjoy 35hz content even if its -10db?

i did come to my own conclusion that Flat FR is less important (to me), more important for me are room acoustics, stereo image, stage.
but idk - 10db difference seems a lot...


2) Additional question - my speakers have PR in the design. How much realistically does PR extend low range? (You can draw a line on the graph I attached if you want - even better). like -10db at 30hz? or like -10db at 25hz (not happening probably, but you get the idea - i'm trying to understand what realistically can be expected).
i understand that it all depends on the build, and box, and other factors... but if its at all possible to predict - what can i anticipate?

specifically regarding this speaker - my box is about 80L, rectangular, almost no stuffing inside.
that's the original box (its not my DIY), its pretty close to philips (the driver manufacturer) design recommendations. PR is also matched model to the driver i'm speaking of, also 12'', its a guess, but i think it has the same mass, and same RF as the active woofer - they look identical on the outside, same line of product range.

in other words, generally speaking - in simple enclosure built, with PR being same size, RF, and mass as the active woofer - how much low end extension can one typically expect?

3) the driver ive attached has RF of 22hz - from what ive seen compared to other woofers, its pretty low. typically ive seen FR of 30-45hz.
is RF an indicator i should pay attention to, when choosing speaker driver?
based on speakers FR graphs that i compared, i can't say i see anything different between speaker with 22hz RF, and speaker with 40hz RF.
but nonetheless the spec is there, so it must have some importance.
question is - is it, and how significant is it, when choosing a driver.


although i'm asking about specific driver here, its more as an example, i'm trying to generally understand speaker driver specs, and to understand what to look for when choosing one in the future.

Thanks
Vadim
 

Attachments

  • AD12200 graph.pdf
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  • AD12200W specs.pdf
    114.2 KB · Views: 14

Lojzek

Member
2012-02-10 12:12 pm
Croatia
There is information lacking, Qes, Qms values. Attach impedance plot of the unit in free air. Whenever you have an SPL plot, there usually is info on the measurement conditions and if the unit was in some kind of a cabinet. The early roll-off in the bass could mean the driver was on an "infinite" baffle and depending on Q values, the roll-off is more or less pronounced which is a normal thing. You would want to load the driver by placing it in an appropriate cabinet volume and type. This one is obviously optimized for a vented one, hence PR loaded. The simulation of the PR and the cabinet can be done, only the data to do that should be available.
 
There is information lacking, Qes, Qms values. Attach impedance plot of the unit in free air. Whenever you have an SPL plot, there usually is info on the measurement conditions and if the unit was in some kind of a cabinet. The early roll-off in the bass could mean the driver was on an "infinite" baffle and depending on Q values, the roll-off is more or less pronounced which is a normal thing. You would want to load the driver by placing it in an appropriate cabinet volume and type. This one is obviously optimized for a vented one, hence PR loaded. The simulation of the PR and the cabinet can be done, only the data to do that should be available.

i found the info on the measurement conditions, i should have included this page scan as well, anyway it reads:

FREQUENCY RESPONSE CURVES (see Fig. 2)
Curve a: Sound pressure measured in anechoic room, loudspeaker mounted in 80 I enclosure.
Curves d2 and d3: 2nd and 3rd harmonic distortion, measured at the operating power of 5 W in anechoic room, loudspeaker mounted in sealed 80 I enclosure, filled with 0,5 kg of glass wool.

now regarding Qes, Qms - those are not mentioned anywhere in the spec sheet, unfortunately. as well as impedance curve. im sure there is a way to measure it myself, but ive never done that.
 

Lojzek

Member
2012-02-10 12:12 pm
Croatia
There is a simple way to measure impedance with a single resistor in series with DUT. Either REW or Artalabs LIMP module will suffice. No amplifier required.


edit: employing tsp formulae, Qes seems to compute to about 0.33; Vas=325 litres. I assumed Sd=508cm2
Basically, either a medium sized sealed cabinet or a larger vented/PR one.
 
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