Part 5 of the NHT 2.5i review contains the system impedance and frequency measurements as well as a frequency measurements analysis on the effects of using the tweeter foam pad.
System impedance:
(click on picture to zoom)
Blue: Left loudspeaker
Red: Right Loudspeaker
System impedance minimum of 3.4 Ohm @ 80Hz, which is slightly lower than the specified 3.6 Ohm.
System frequency:
If nothing else is noted in the comments, the following frequency measurements of the NHT 2.5i loudspeaker are made at a 2m distance at mid-woofer height.
All frequency response charts are presented in a 50db scale with 1/24 octave smoothing and the measurements are valid down to 375Hz.
Frequency response on-axis: Frequency response 15deg off-axis:
Blue: Left Loudspeaker @ 2m
Red: Right Loudspeaker @ 2m
(click on picture to zoom)
Left: On-axis, 15 and 21deg off-axis @ 2m
Right: 30, 45 and 60deg off-axis @ 2m
For a commercial design, the NHT 2.5i loudspeaker has a very linear frequency response. The tweeter dome break-up @ 26kHz is well suppressed by the tweeter dome diffuser.
Frequency 10cm above the mid-woofer:
Frequency response on-axis: Frequency response 15deg off-axis:
Blue: Mid-woofer height @ 2m
Red: 10cm above mid-woofer height @ 2m
(click on picture to zoom)
Left: 10cm above mid-woofer, on-axis, 15 and 21deg off-axis @ 2m
Right: 10cm above mid-woofer, 30, 45 and 60deg off-axis @ 2m
The frequency response at the normal listening height (10cm above mid-woofer).
Frequency with and without tweeter foam pad:
Left: Rotten foam pad.
Middle: Foam pad removed.
Right: New foam pad.
1m frequency measurements of the NHT 2.5i tweeter made at mid-woofer height.
(click on picture to zoom)
Top left: On-axis, foam pad (blue) vs no foam pad (red)
Top right: 15deg off-axis, foam pad (blue) vs no foam pad (red)
Lower left: 21deg off-axis, foam pad (blue) vs no foam pad (red)
Lower right: 30deg off-axis, foam pad (blue) vs no foam pad (red)
There is very little difference using the foam pad or not. First at a 30deg off-axis angle we can see some difference.
Most of the baffle diffraction is already reduced by off-set mounting the tweeter on the baffle. Actually, even the mid-woofer is slightly off-set mounted by about 2mm, but this is made in order to make it fit inside of the angled enclosure.
End of review part 5!
Go to NHT 2.5i review part 6