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Speakers' resonant frequencies
Old 6th August 2020
  #1
Lives for gear
Lightbulb Speakers' resonant frequencies

I don't know too much about speakers tech data.

I was eyeing a pair of Dynaudio BM 15 A.
https://www.dynaudio.com/professiona...15a#tech-specs

We can read 'Resonance Frequency: 39Hz'.

So I googled what is resonance frequency, and I read here
https://www.proaudioland.com/news/th...ant-frequency/

'If you've ever taken a look at the specs a speaker you've probably noticed that they are labeled with a certain frequency, 55Hz or 75Hz for example. This parameter is known as the speaker's resonant frequency. Every object in the world has a resonant frequency. That's the frequency that the object will sound, or resonate, when struck. A lightweight object will generally have a higher resonant frequency than a heavy object. The weight of the object, however, is not the only determinant of resonant frequency as the density of the object also contributes a role.

This rating is important for speakers in particular for a couple of reasons. First, it is used to prevent a cabinet from ‘ringing’. If a note is played through a speaker and that note is at the resonant frequency of the speaker, the speaker cabinet will radiate that sound. With a loudspeaker, the mass of the moving parts and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. Over the years, manufacturers have worked to deaden their cabinets in a variety of ways.

The other reason this rating is important has to do with sound. As a general rule of thumb, a lower resonant frequency indicates a speaker that would be better suited for low-frequency reproduction than a one with a higher frequency. For example, a 55Hz speaker usually offers a deeper, bassier tone with slightly laid back upper mids while a 75Hz model raises the resonant frequency a bit, which affects the deepest lows, but also will tighten things up a bit on the bottom and bring out the upper midrange. It should be noted that this is not always the case though, because other parameters affect the ultimate performance as well'


Is that definition correct?

I presume the lower the better...the more expansive as well?

If mass defines res. frequency, which means that adding more mass to the speaker will lower that frequency, right?

Thanks a lot for reading!
Old 6th August 2020
  #2
Lives for gear
 

The definition is correct.
You can of course alter the frequency resonse with an EQ, DSP etc.
If the speaker can take a beating and the amp has enough power you can get lower freqs out of the enclosure.
But you move a volume of air with a surface (the speaker membrane) so there is a quadratic ratio and a small speaker has to make large excursion to keep up with a bigger speaker.

The definition of the sound I do not fully agree; when there is less low you get a thighter sound is of course bull****, there is less masking but you want a linear freq response so you don't mix in to much lows.
Old 6th August 2020
  #3
Lives for gear
Quote:
Originally Posted by JayPee View Post
...
Is that definition correct?

I presume the lower the better...the more expansive as well?

If mass defines res. frequency, which means that adding more mass to the speaker will lower that frequency, right?

...
I liked most of that descriptive definition snip except for the part about the resonant frequency of the speaker triggering cabinet resonances. I think a better way to say it is that sometimes the cabinet resonance frequency is close to the woofer's natural resonance (Fs in the Thiele/Small parameters) and that can cause additional troubles in the overall performance of the speaker/cabinet combination.

In my experience, the design objective of all cabinets is to prevent them from resonating at all. If concrete was a practical material for making cabinets, it would be preferred for its anti-vibrational nature. The last two pairs of custom cabinets I've made have been done with a constrained layer of 30-lb roofing felt, as the "meat" in a sandwich of 3/4-inch thick MDF.

The resonant frequency of the woofer is used as a design parameter for ported cabinets to enhance the output of the speaker below its natural resonance, thereby achieving better (lower frequency) bass response for a given diameter of speaker. Sealed woofer designs depend on an inherently low resonant frequency, as bass output declines rapidly in a sealed design when driven to produce frequencies below the resonant (Fs) value.

As noted in another response in this thread, adding mass to the cone (as an experiment) would indeed lower the resonant frequency of the woofer. Adding mass as an effort at enhancing the performance of the speaker is an errand that should *not* be taken.
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