NHT 2.5i review part 6


This is the final part of the NHT 2.5i review. It contains a small summary of my impressions of the loudspeaker and some suggestions on how to fine tune the bass response of the loudspeaker.



NHT 2.5i has not only a high WAF factor, but it is also a very well designed loudspeaker. It has a very smooth frequency response paired with a powerful bass response. The upper midrange and treble is smooth and neutral sounding and leans towards a bright rather than a warm and dark sounding character. This is to some extent masked by the powerful and to some degree exaggerated bass response.

Pair this loudspeaker with warm sounding equipment and you get not only a detailed loudspeaker, but a musical sounding as well. If paired with e.g. a bright sounding amplifier you can get too much details, which in the long run can be fatiguing to listen to.

If I have something to complain about it would be the bass response. If the NHT 2.5i isn’t optimally placed it has a tendency of sounding “boomy” and too bass heavy. This is particularly the case if it’s placed too close to the corners or the back wall. Compared to the larger NHT 2.9 model it has a “party” bass character rather than a neutral one, which of course is a commercial decision made by NHT.

Loudspeaker tuning suggestions:


Here are some suggestions on how to fine tune the loudspeaker.

Disclaimer! This is merely suggestions and I haven’t tested this myself and I don’t guarantee that you will like it, but I think it’s worth trying if you are prepared to experiment.

The cross-over:

2.5i Original cross-over

The NHT 2.5i is a nice and well designed loudspeaker and it makes no sense trying to replace any of the drivers or make any major changes to the cross-over. However, it can be worthwhile to replace some of the cross-over components.

C1 and C2 and R1 are good candidates to experiment with and to replace with new components of your favorite choice.

Don’t buy super high-end components, but e.g. Mundorf Mcap Audiophile MKP caps and MOX resistors or similar components could be an option.  The Mcap Audiophile cap has very tight tolerances of +/- 3%, but often, when measured they have a tolerance in the range  of +/- 1-2%. This is a lot better than the original electrolytic caps in the 2.5i cross-over.

The C2 cap can be replaced with a 100uF and a 33uF connected in parallel with each other.

Bass tuning:

If you think the loudspeaker has too much bass or sounds “boomy” in your setup you have two options:

  1. Put a foam plug or sock in the bass-reflex port.
  2. Change the R3 resistor in the sub-woofer cross-over.

Obviously, the easiest bass tuning to try is to put a foam plug in the bass-reflex port, but that doesn’t really change the bass loudness peak around 75Hz. In order to suppress the 75Hz peak you need to change the value of the R3 resistor.

SIM - Sub Freq R3 tuningSIM - Sub Imp R3 tuning

(click on picture to zoom)

Left: Simulation of the sub-woofer + port nearfield frequency measurement.

Right: Simulation of the sub-woofer impedance response.

The bass response tuning can be made in two ways.

  1. Replace the R3 resistor with a new one.
  2. Add a resistor (R4) and connect it to the sub-woofer driver terminals.


Sub-woofer cross-over tuning:

Change the R3 resistor:

R3 = 15 Ohm (-2dB @ 75Hz)

R3 = 10 Ohm (-3dB @ 75Hz)

Add a R4 resistor:

R4 = 30 Ohm (-2dB @ 75Hz)

R4 = 15 Ohm (-3dB @ 75Hz)



Even considering how old this loudspeaker design is and its use of an older generation of driver units, I still think it has great performance. If you can find a pair second hand in a good condition, don’t hesitate to buy it.

You will have great fun listening to it….. 🙂