NHT 2.5i review part 1


Recently a friend of mine upgraded his NHT 2.5i loudspeakers to the NHT 2.9 model.  Generously, he now lends me his NHT 2.5i loudspeaker for this review and for me to make a closer inspection on how it has handled the years of use.

I must confess that I’m a bit excited over this task, since I have myself owned several different NHT loudspeakers during the nineties. Even though I haven’t owned a pair of 2.5i specifically, I have listened to them on many occasions during the years, both at stores and in my friends’ homes.

NHT Overview:


NHT means “Now Hear This”, a bold name for a trendsetting loudspeaker company. NHT was created by Christopher Byrne and Ken Kantor in the late eighties and as I understand it, Ken Kantor has been the main designer of the NHT loudspeakers created in the early and mid-nineties.

In 1993 NHT released the flagship loudspeaker model NHT 3.3. It was a large 4-way speaker with a powerful 12” sub-woofer mounted in an acoustic suspension configuration on the side of the loudspeaker enclosure. This 12” ( NHT 1259) driver from “Tonegen”  became very popular among DIY:ers and was used in many DIY designs.

In 1995 the NHT 2.5 loudspeaker was released. It was a scaled down version of the NHT 3.3 with similar design principles, but made to a lower price for a broader commercial market. The initial NHT 2.5 was a 3-way with an 8” sub-woofer on its side and with all drivers units made by “Tonegen”. Not long after, when the supply and quality of the “Tonegen” driver units began to diminish, the upgraded NHT 2.5i came to market 1996.

The upgraded NHT 2.5i loudspeaker used Scandinavian driver units from the Norwegian SEAS (tweeter) and the Danish Peerless (mid-woofer and sub-woofer) loudspeaker manufacturers’.

With the new Scandinavian drivers, the quality control and tolerances could be tighter and as a result the sonic performance improved. In many ways the NHT 2.5i loudspeaker became in the late nineties a trendsetter of a furnishing friendly floor-standing loudspeaker with a high performance/price ratio.

These NHT models from the nineties are rightfully still very popular loudspeakers on the second-hand market. A pair of them in good condition for a reasonable price is very nice performing loudspeakers, even by today’s standards.

NHT 2.5i Technical Specification:


System Type: 3-way floorstand loudspeaker, “Focused Image Geometry” design
Enclosure type: Bass-reflex
Sub-woofer driver unit: Peerless 8” long-throw subwoofer.
Mid-woofer driver unit: Peerless 6.5” polypropylene mid-woofer
Tweeter driver unit: SEAS 1” fluid-cooled aluminum dome tweeter
Cross-over frequency: 3.3kHz and 100Hz.
Cross-over function: Tweeter/Mid-woofer, electrical 12db/octave high-pass and low-pass. Mid-woofer/Sub-woofer 6dB/octave high-pass and 12dB/octave low-pass
Frequency response: 29Hz – 25kHz +/- 3db
Sensitivity: 86db 1m/2.83v
Nominal impedance: 6 Ohms
Minimum impedance: 3,6 Ohms
Weight: 24kg (53lbs)
Enclosure dimensions: (height x width x depth): 96,5×17,8×39,4cm (38″x7″x15,5″)

NHT 2.5i manual

The Enclosure Design:


A unique feature with the NHT 2.5i appearance is the 21 degree toe-in angle, which NHT call “Focused Image Geometry” (see the manual for details). This makes the loudspeaker furnishing friendly to set up with no need for any additional  toe-in.

The 21 degree angled baffle shape greatly increases the ratio of direct-to-reverberant sound, effectively reducing side-wall reflections and concentrating sound in the listening area.

The enclosure is rather slim and in order to have it stand firm and stable it has two metal feet’s mounted. These metal feet can use spikes or as I recommend, a soft feet from Sonic Design.

The tweeter is mounted below the mid-woofer and is slightly off-set inwards on the baffle. Next to the tweeter is a foam pad attached, presumably in order to reduce diffraction.

The effective listening height will typically be at the mid-woofer height or up to 10cm above, depending on the sitting height of the listener.


The Enclosure:


Left: NHT 2.5i

Right: Sequence Three – Grand Reference in test cabinets

The enclosure has a gloss black laminate finish which is both beautiful and rather resistant to scratches, but is very sensitive to fingerprints.  The fingerprints can successfully be removed with a microfiber cloth. I don’t recommend using any chemicals on the laminate, since it usually turns out in a flamelike surface.

The enclosure box itself is made from MDF with an outside layer of a rather thick glossy laminate. In the upper part of the cabinet the mid-woofer is housed in a separate closed box of approximately 5 liters. The mid-woofer closed box is heavily stuffed with damping material. The hole for the cable feedthrough is sealed with a rubber plug and some silicon glue.

The remaining enclosure volume of approximately 30-35 liters is used by the sub-woofer. Contrary to what the manual states, the tweeter isn’t mounted in the same enclosure as the mid-woofer. The tweeter actually shares the same enclosure volume as the side-mounted sub-woofer.

The enclosure is braced with a brace in the middle of the enclosure as well as at the top of the enclosure behind the mid-woofer box section. A role of damping material is placed on top of middle brace in order to minimize internal standing waves. The angled baffle and the mid-woofer box section also contribute to minimizing standing waves issues common for tall floor-standers.

The bass-reflex tube is placed at the back-side of the enclosure and is made of plastic with a 60mm diameter and approximately 155mm length. The bass-reflex tube is flared at both ends in order to reduce vent puffing and port noise.

The screws used for fastening driver units are standard black wooden screws with a Phillips head. The screws holding the sub-woofer driver in place are sturdier than the screws for the tweeter and mid-woofer.

The front covers are made sturdy with a rather thick cloth material. While you can keep the sub-woofer cover fastened at all times, I do recommend removing the front cover when listening for the best sonic performance.

Left: Rotten foam pad.

Middle: Foam pad removed.

Right: New foam pad.

The diffraction foam pad rots over time, but don’t panic, it can be removed with little or no performance impact (see later in the measurement review part).

You can of course replace it by cutting out a similar shaped pad from some foam and glue a fresh pair on.

The 5-way binding post allows for bi-amping and when used in this way it’s possible to drive the sub-woofer with a dedicated sub-amp. The cross-over is mounted on the backside of the binding post.

Overall the enclosure build quality is top notch and it’s rare to see this kind of quality in this modest price range.

Go to NHT 2.5i review part 2