Half the power, with incredibly high damping factor,
Or
Twice the power, with very low damping factor.



psst spkrboy

 

Who's definition of 'better' are we using?

 

I knew I was going to get in trouble for not defining better

Lets say... More impact and presence.

 

high damping will result in better control, now that I have stated the obvious...

1/2 the power of what??? 100, 500, 1000 watts?

I would think 250 to 500 watts with a good damping would be enough for our cars unless you want to rock the neighbors...

But what do I know, I use a 5 channel amp!

 

not exactly double
150w with 80 factor
90w with 300 or 800 factor (quoted 300 by someone at the amp company, owners manual says 800)


Lets say the range of bass played is 40hz and up.

 

This is not the simple question it appears at first-glance to be. On top of that, a higher damping factor rating isn't inherently better than a lower one.

The buzz-killer here is that we have no idea how these DF numbers were generated for your amp. Was it a 1kHz sine? Was it 50Hz? Was it broad-spectrum 20-20k? Was it the same for both 4- and 2-ohm ratings? Unfortunately, rating the DF ranks right up there with power and distortion measurements in terms of marketing. You can measure this yourself, and very simply.

Damping factor is not a measure of an amp's ability to control a speaker. It's more accurate (but still not entirely correct) to call it the amp's ability to resist degradation of the signal at the amp's output. It's a ratio of the unloaded output voltage and the difference between the unloaded and loaded voltages. Simplified, it's the amp's ability to resist changes in it's output voltage. Intuitively, you see that the load means everything. Now it gets really complicated when you consider that loudspeakers are not constant ideal resistances. It's even more-so when you consider the effects of any passive filters and the enclosure design.

Questions: What is the amp driving? What DCR? What nominal Z? What Fb? What Rmax? In what sort of enclosure? Through how much and what size wire? Any passive filters?

Frequency, for the most part is irrelevant, although DF changes become more audible as frequency reduces. The large voice coils of a typical subwoofer are far more inclined to produce the back EMF that we need the amp to resist. On a side note... to me, 'better' means more accurate (less distortion... distortion being any change to the signal whatsoever).

This thread has the potential to blossom into some serious tangents, so we'll have to agree to start new threads for significant ones, ok?

 

We'll we're talking about the Dynaudio Mw172, with the 3" voice coil

 

Sorry, not enough information.

All things being equal and treating the driver as an ideal resistance, I'd use 90 wpc. However, these assumptions are unrealistic, since there are so many other variables.

 

Nominal impedance Znom 4 Ω
DC resistance Re 3.2 Ω
Voice coil inductance Le 0.27 mH
Resonance frequency fs 45 Hz
Mechanical Q factor Qms 2.3
Electrical Q factor Qes 0.65
Total Q factor Qts 0.51
Mechanical resistance Rms 2.6 kg/s
Moving mass (incl. air load) Mms 21.4 g
Suspension compliance Cms 0.58 mm/N
Effective cone diameter d 151 mm
Effective piston area Sd 180 cm²
Equivalent volume Vas 27 l
Force factor Bl 5.4 Tm
Recommended frequency range 35 - 3500 Hz

 

Those things are a function of your install.

The easiest thing to do is measure the DF while everything's in the car and hook up appropriately after you have the measurements.

 

You guys make me

Don't get so carried away with complicated explanations.

The amplifier determines DF by reducing the back emf from the speaker. The higher impedance the speaker "system" has, the higher the DF. Plain and simple, the amplifier and speaker wire combine to determine the final total DF. DF is the ratio of output impedance to load impedance. DF=load-impedance/output-impedance. If you cut the speaker impedance in half, you cut the DF in half. The tiny resistance of the wire going to the speaker gets added to the output impedance. This is why a good wire is important for bass. Also why I recommend the higher selection of impedance for speakers that give you a choice. (dual coil)

Example: If speaker is 8 ohms and amplifier is .01, DF will be 800. If speaker is 4 ohms, DF will be 400

 

I almost forgot to answer the original question. Spkrboy has it correct again. Do you want more power than you need or do you want clean, undistorted bass? Lower power alone will improve that, as long as you don't clip the amp. Any speaker will have less distortion at lower volumes, DF is just one small parameter that contributes to it.