frequency response graphs

[tech.knockout]

This is a basic question, but how can you distinguish a speakers performance against another by looking at a freq resp graph, they are all equally squiggly to me.


http://www.seas.no/kit/FROYMK3.pdf
http://www.seas.no/kit/odinmk3%20måling.pdf
http://www.seas.no/kit/Trym%20måling.pdf

[annex666]

The frequency response graph can tell you some key points that help in the designing of your speaker.

For example the upper and/or lower rolloff is useful as it gives you an idea where the crossover should start to distribute the signal to other drivers in the system.

Also any severe peaks and/or dips will give you an idea of resonance characteristics and will allow you to make compensation circuits.

Ideally a driver should be perfectly flat in the passband (flatish part of the frequency resonse) and roll off gently showing no spurious peaks/dips at all. Due to various effects, both mechanical and electrical, this is far from reality and compensation (to varying degrees depending on your philosophy) must be employed.

A crossover (be it passive or active) is the simplest form of frequency compensation - allowing the poor frequency response of one driver to be improved by sharing frequencies between two (or more) drivers. Although easy (in principle) to do this introduces new problems for example time alignment problems and phase interaction or "lobing" between the two drivers. Again there are many views on different configurations to deal with these problems and each have their own advantages/disadvantages.

Just to make things even more complicated there are also psycho-acoustic effects that come into play - for example the human aoral system will compensate for a non-flat frequency response (to a degree) leading to your ears becoming accustomed to a particular driver/speaker.

At the end of the day it is best to listen to the driver in the configuration you are looking to use as this will give you the best idea of how your ears and brain will interact with the driver - specifications can't (unfortunately) tell you this.

Hope this helps?

[till]

the "Trym" one has the best range, bass from 40Hz or so up, and hights up to more than 20 kHz, but very low efficiency (~83dB)

The other ones have little better efficieny (87dB or so) but range isn´t that broad. Bass starts somewere > 50z and hights starts to fall significantly under 20kHZ.

All show a graph for on axis response and for 30° off axis, the difference tells you about the speaker beams at higher frequencys. Off axis hights roll out from some point on.

All graps may be flatened to look like +- 2 or 3 dB, but if this is true or you can see much from the "peaks" i doubt.

[tech.knockout]

many thanks,

Also any severe peaks and/or dips will give you an idea of resonance characteristics and will allow you to make compensation circuits.

what constitutes a 'severe' dip/peak?

[till]

you will see the real peaks and dips better on a non flattened graph.

[annex666]

You should not see any evidence of cone resonance in a complete loudspeaker as the design should make sure that the crossover point(s) are chosen correctly.

The image below shows part of the frequency responce of the bass driver from the Froy (15cm Magnesium alloy driver) - I have marked on it a line to the right of which you can see severe cone breakup and a large peak where one of the cones resonant modes is excited. The crossover for the Froy makes sure there is sufficient attenuation to the bass driver at this frequency that this has no effect on the sound from it - imagine what the speaker would sound like driven with a full-range signal with that frequency response!


Also note that there is a large difference between electrical and mechanical resonance - the electrical resonance of the driver occurs at a much lower frequency and can be seen as a peak in the impedance graph for the driver. This electrical resonance causes other problems - for example it complicates the design of the crossover (if a passive crossover is used) and a circuit called a notch filter is used to remove the effect of this electrical resonance.

[tech.knockout]

looking more closely at the graphs; I'd say that the trym/froy graphs are more noticably 'squiggly'/'bumpy' than the odin/thor.

I.e. In the Odin graph, the response is pretty 'flat' between 500Hz and 3Khz.
The trym is quite bumpy between 200Hz - 1Khz.

Is these bumps a significant(noticable?) indication to the sound quality?

Or should we just care about those major resonant peaks/dips?

[tech.knockout]

The image below shows part of the frequency responce of the bass driver from the Froy (15cm Magnesium alloy driver) - I have marked on it a line to the right of which you can see severe cone breakup and a large peak where one of the cones resonant modes is excited. The crossover for the Froy makes sure there is sufficient attenuation to the bass driver at this frequency that this has no effect on the sound from it

What about the the huge dip just before the line?