Height of the impedance peaks for Woofer in bass reflex design

[spintonik]

Hi!

I tried quite hard to find more information about this from the forum - but no luck. Still I believe I ask pretty simple question, (one I should now already), so lets keep it short:

When I measure the raw driver's electrical impedance in two-way, vented loudspeaker cabinets I have built, I usually see quite high impedance peaks for the woofer, around speaker vent tuning frequency.

In design (2-way, 11 liters with 2x 5,25 mid woofers and tweeter) I made last time, woofer DCR (without crossover) was about 7 Ohms, upper impedance peak (110Hz or so), was over 40 Ohms, Lower 30 Ohms or so.

If I compare that to for instance Seas DIY guidelines, many of them have significantly lower impedance peaks, despite DCR level is very similar. Troels Graevesen, in other hand, seems to be able to achieve very high peaks in many of his Scan-Speak designs, but his SEAS designs are lower.

I am keen to assume that there would not be absolute right in this, but:

What does this all signify? Where does this difference come from and can you control it somehow in cabinet acoustics?

Thanks in advance!

-Mikko

 

[Baseballbat]

SEAS drivers often use aluminum voice coil bobbins, so their Qms ist quite low. Scan-Speak uses glass fibre or Kapton (recently even Titanium, I believe), and their Qms is high. That's the reason. Try with your favourite simulation program.

 

[DrBoar]

Damping material also adds resistive losses. Compared to an empty box
Adding damping material in the box will lower the peak hights.
Adding damping material in the vent will make the dip between the two peaks less deep.