What is the audible result of damping?

[Art Welter]

Re: What is the audible result of damping?

For a voltage drive amplifier,
The transfer function from Voltage to displacement, given a simplified linear model, has a Q value

Q = sqrt(km)/(b + (BL)^2/Re)

So what I've noticed over the years, BL will typically be the dominate factor in pro-audio systems. For example, High BL speakers will have an over damped frequency response, rolling off at around 6dB/oct way above Fs of the system. Adding series resistance can be quite noticeable if you start sticking large values in there.

Adding excessive amounts of series resistance could, cause the cabinet tuning to go bad on an HP enclosure. Normally when the Q gets big the Frequency response will become under damped, which is what we perceive as that "floppy" sound.

I haven't tried it yet, but if a passive network is built to compensate for the resonance in a HF driver, adding the series resistance could cause the network to not function properly anymore at the crossover region.

Obviously there are a lot more variables involved in the total Voltage/SPL transfer function. But the simplified model does match what you will observe if you grab a variety of magnets and resistors.


PS. This is also why if you start taking passive networks out of boxes and converting them to biamp you should also be checking the porting on the enclosure.

Mark,

Cabinet tuning, Fb, is determined by the volume of the box, and length and diameter of the port. Fb is independent of the speaker's Fs, it is a Helmholtz resonance.

Whether the box has one, two or four speakers, high or low BL, series coils, speakers or wire, the Fb remains the same.

After reading Jay's posts #16 and #18, I'd suspect the problems he mentions are faulty passive crossover components, or partially burned 15" voice coil, or both.
The low damping factor would just make the speakers sound bad, but not different at different drive levels.

 

[Jay Barracato]

Mark,

Cabinet tuning, Fb, is determined by the volume of the box, and length and diameter of the port. Fb is independent of the speaker's Fs, it is a Helmholtz resonance.

Whether the box has one, two or four speakers, high or low BL, series coils, speakers or wire, the Fb remains the same.

After reading Jay's posts #16 and #18, I'd suspect the problems he mentions are faulty passive crossover components, or partially burned 15" voice coil, or both.
The low damping factor would just make the speakers sound bad, but not different at different drive levels.

I am leaning towards that point of view myself. The speakers are fairly close together in a very lively room. It is very possible that I did not hear the problem with one speaker because it was masked by the other speaker plus room reflections. Some quick measurements will show if it needs to go back to EAW.

Then when that is resolved I can suggest appropriate sized cables.

 

[Mark DeArman]

Re: What is the audible result of damping?

Mark,

Cabinet tuning, Fb, is determined by the volume of the box, and length and diameter of the port. Fb is independent of the speaker's Fs, it is a Helmholtz resonance.

Whether the box has one, two or four speakers, high or low BL, series coils, speakers or wire, the Fb remains the same.

After reading Jay's posts #16 and #18, I'd suspect the problems he mentions are faulty passive crossover components, or partially burned 15" voice coil, or both.
The low damping factor would just make the speakers sound bad, but not different at different drive levels.

Who was talking about Fb or Fs?

Oops, I clicked quick reply.

Not talking about Fs or Fb, I was talking about Q of the speaker or Q of the system. Both of which involve BL, Re...

 

[Art Welter]

Re: What is the audible result of damping?

Who was talking about Fb or Fs?

Mark,
In Post #13, you wrote:

"High BL speakers will have an over damped frequency response, rolling off at around 6dB/oct way above Fs of the system…. PS. This is also why if you start taking passive networks out of boxes and converting them to biamp you should also be checking the porting on the enclosure."

Fs of system, whatever that means.
"Porting on the enclosure" is known as Fb.

Sounds like you were talking about Fb and Fs as well as Q of the system to me..

Cheers,

Art

 

[Mark DeArman]

Re: What is the audible result of damping?

Mark,
In Post #13, you wrote:

"High BL speakers will have an over damped frequency response, rolling off at around 6dB/oct way above Fs of the system…. PS. This is also why if you start taking passive networks out of boxes and converting them to biamp you should also be checking the porting on the enclosure."

Fs of system, whatever that means.
"Porting on the enclosure" is known as Fb.

Sounds like you were talking about Fb and Fs as well as Q of the system to me..

Cheers,

Art

Art, I'm not sure how I could have been any more clear, but I will try.

I started with an equation which models a behavior:
Q = sqrt(km)/(b + (BL)^2/Re)

And then, talked about implications of that equation. I guess I did assume some basic knowledge of small signal parameters. In response to your comments above:

I normally use Fs to represent the resonance of a speaker or a system, this might be confusing. I'll use F0, f0 or w0 for resonance of an individual component. Can we can agree that Fb will be the resonance of the enclosure/speaker system as related to Vas of the enclosure? If not, I'm not sure where your definition of Fb comes from?

#1
"The roll off above Fs", in fact does not have anything to do with Fs (even though I used Fs in the sentence of the original post) but with the Q of the loudspeaker. High BL leads to a very small Q, wide bandwidth, which results in an over damped SPL response. I did not think the use of the word Fs would be confusing, since I am talking about the Q equation.

#2
"Porting of the enclosure" is not just about Fb, but also about the total Q of the system. I'm not sure about you, but when building enclosures, I don't just look at the 'tuning' (meaning Fb) frequency when determining the porting. I am not talking about the tuning frequency in my original post. Changing Re will not change the value Fb of the enclosure/speaker system (small signal), but will change the Q of the system.

(edit) Well this is only true in the small signal sense. Fb changes with drive level in general soo.

Now to be fair I could have used a different word than 'tuning' later on in my post. I guess a lot of people call it 'alignment' when talking about the shape of the SPL response desired by adjusting the Q of a HP enclosure.

PS. Again, I know looking at the model for a single speaker not in an enclosure, is an over simplification, but it DOES bear well on what you will observe for a system when you modify the variables.

PPS. I'm done replying to this thread. This is way off topic now. If you want to investigate small signal models yourself go ahead. I'm not going to waste anymore time arguing over semantic issues when all of the models are well published. As are all of the more recent models which take large signals into account. Just search AES.

Mark DeArman