Home Theater Forum and Systems banner

1 - 6 of 6 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter #1
Hi,

I recently made some impedance measurements on a 18" bass-reflex enclosure, with 4 successive mechanical arrangements.
The following measurements were performed in exactly the same conditions.
You observe that the floors of the curves are different, and by far.
What could be the explanation ?

Regards

Pascal
 

Attachments

·
Premium Member
Joined
·
6,711 Posts
That's usually due to having the input leads swapped, adding an offset equal to the sense resistor. Should be able to correct it by swapping the leads or changing the input channel which has been selected in the Soundcard preferences.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #3
Hello,

Thank you for the quick reply.
But the right explanation is probably somewhere else : there was absolutely no change in the settings between my four measurements.
The sense resistor is 22 Ohms, measurements made with four sweeps.
Maybe the input level was too low ?

Pascal
 

·
Premium Member
Joined
·
6,711 Posts
Some soundcards/PCs do not maintain synchronisation across multiple sweeps, it is best to use single sweeps in most circumstances.
 

·
Registered
Joined
·
14 Posts
Discussion Starter #5
Thank you, I'll try this.
But it seems to me that I had already encountered the problem before, with successive measurements using one single sweep (REW v5.19 beta 7).

Pascal
 

·
Premium Member
Joined
·
6,711 Posts
If you are measuring at high levels would get some thermal effects, but would not expect such a large change. Does the time between measurements make a difference?
 
1 - 6 of 6 Posts
Top