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Review: Atohm GT2 HD

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The Atohm GT2-HD is an elegant floorstanding speaker which has curved sides and is slightly tilted backward. Its cabinet is composed of 22mm-thick MDF panels reinforced by several internal brackets. At the speaker’s base, two metal baseplates with a hole drilled in the middle allow low frequencies produced by the large bass-reflex resonator located beneath the speaker to circulate freely. The Atohm GT2’s finish (rosewood for our test model) is superb, with a beautiful, thick coat of glossy lacquer. The drivers in the upper third section of the front panel are protected by a magnetic grill fitted with acoustic fabric.

The Atohm GT2’s frequency response ranges from 40Hz to 30kHz, for a sensitivity of 90 dB and a nominal impedance of 6 Ohms.

Atohm GT2: Made in France and handcrafted

Atohm builds its own drivers, giving it an edge over competing brands which often have no other choice than to use drivers which are not completely adapted to their needs. Of course, drivers may be built to respect a distinct set of specifications, but possibilities are nonetheless limited. By designing its own drivers, Atohm has free rein to adapt the cone, surround, voice coil and enclosure to meet its specific needs. Notably those implied by the presence of a first-order crossover filter.

Test Atohm GT2

The Atohm GT2-HD speaker’s 6” low-medium driver

What is a crossover filter?

A crossover filter is a set of passive electronic components (inductors, capacitors, resistors) which keep the driver from reproducing certain frequencies. Indeed, a bass driver should not reproduce highs (it isn’t good at doing so) and a tweeter should not reproduce lows (also not its forte and its voice coil would be quickly damaged). In addition, crossover filters prevent drivers from restituting the same frequency ranges (mids, for example), which would result in an unbalanced listening experience.

The crossover filter allows adjustments to be made to the drivers’ sensitivity, at the very least that of the tweeter, which always produces a greater output than the low-frequency drivers.

In practice, to keep a bass driver from restituting higher frequencies, an inductor is placed on the signal path. To keep the driver from restituting lower frequencies, a capacitor is placed on this same path. The values of the inductor (in millihenrys) and the capacitor (in microfarads), determine the frequency above and below which the audio signal is attenuated. This cutoff frequency is combined with a roll-off slope expressed in decibels per octave. For first-order crossover filters (with a single component), attenuation is set at 6 dB per octave.

Test Atohm GT2

The Atohm logo conceals a hollow cavity which may be filled with sand in order to add weight to the speaker and improve its efficiency in the low register.

Atohm uses a first-order crossover filter to keep signal loss to a minimum, whereas the use of filters of other orders (2nd, 3rd, 4th, etc.), which combine more components in order to offer superior attenuation rates (12 dB, 18 dB, 24 dB per octave), results in a less clear and dynamic sound due to greater signal loss. If filters with steep slopes are often used, this is to ensure better protection for the tweeter or better control of mids and highs for certain bass drivers.

The first-order filter thus comes with two major drawbacks: it doesn’t protect the tweeter very well (moderate attenuation of lows) and it causes signal phase rotation, which impairs sound centering (voices are no longer centered). By building its own drivers, Atohm can integrate these parameters and precisely develop transducers capable of working around them. Result, the pitfalls associated with first-order crossover filters are avoided and the superior transitory regime–a key advantage–is conserved.

Atohm GT2: the tweeter

Is there a risk of damaging the tweeter when cranking up the Atohm GT2-HD’s volume? No, and without getting into the details of its design (Atohm keeps its design secrets under wraps, of course), we can point to its sensitivity of 98 dB for 1 Watt of injected power. To align this output for all low-mid drivers at 90 dB, the speaker’s filter divides the power transmitted by the amplifier by 6 (approximately). If we add 6 dB of attenuation starting from the tweeter’s cutoff frequency (2.5 kHz), the power transferred to the tweeters for low-frequency restitution is negligible.

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The Atohm GT2-HD speaker’s tweeter

The Atohm GT2 speaker’s SD28ND04RD tweeter is a 1” dome model featuring an aluminum coil and an air gap injected with ferrofluid–for improved cooling and higher power handling–in addition to a neodymium magnet. It is equipped with dampening materials at the back to keep backwaves from disrupting the dome’s functioning, notably at high volume. Lastly, the aluminum façade is dimpled to reduce reverberation and optimize sound dispersion beyond the listening axis. This transducer’s frequency range extends from 2.5kHz to 30kHz and offers excellent linearity across the audible spectrum.

Adjustable filtering

The Atohm GT2 speaker is unique in that it allows the listener to adjust its frequency response. In practice, one of three positions may be selected using a dial located above the speaker terminals. The middle position is linear, while the other two change the tweeter’s output by removing 2 dB or adding 3 dB. A wonderful idea which makes it easy to adapt the speaker’s sound to the acoustics of the listening room.

Test Atohm GT2

The Atohm GT2-HD speaker’s sensitivity selector has three positions: -2 dB, 0 dB and +3 dB.

Atohm GT2: bass drivers

The 6” Atohm LD150 bass drivers are carefully crafted and designed to cover lows, mids and highs, theoretically ranging from 20Hz to 2kHz. In practice, these two drivers reproduce lows down to 40Hz thanks to a bass-reflex enclosure. The shape of their core and their copper ring are two of their unique features. This design ensures excellent magnetic efficiency, which allows these Atohm drivers to offer a very linear response curve.

The two drivers are not filtered in the same way: the cutoff frequency (low-pass) for one is set at 150Hz to concentrate energy in the lows, while the second also works in the mids up to about 2.5kHz.

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A large magnet for the Atohm GT2-HD speaker’s low-mids driver

Test Atohm GT2

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The base of the Atohm GT2-HD speaker, in the middle of which is a bass-reflex resonator.

Test conditions

We paired the Atohm GT2 speakers up with a Micromega M One M-100 amplifier and Atohm ZEF Max (2×3 m) cables. During our listening sessions, we used the Micromega M One’s DLNA input for lossless transmission of CD-quality and HD FLAC files.

The terminated Atohm ZEF cables.

Atohm GT2: listening impressions

As we expected, the Atohm GT2 speakers offer very refined sound. Our first impression was one of ease and balance. No register outshines another and we found highs remarkably well placed–discreet but not lackluster–with the default settings selected (0 dB).

We were quickly immersed in the GT2’s sonic universe, and we were immediately convinced that our experience would be an enjoyable one, as the soundstage was precisely arranged in front of us without emphasizing any particular direction.

No need to search for auditory clues in the three registers, the listening experience is reassuring and serene. Very important: the dispersal of the sound is even in terms of width, height and depth, and the different instruments and vocals are precisely placed.

With the tweeter’s settings at -2 dB

The listening experience remained just as enjoyable, with the addition of the highs, which were set further back. As a result, the soundstage gained some depth. With the Micromega M One amplifier, this setting takes hardly any punch away from the Atohm GT2, and it should clearly be reserved for a room with a lot of reverb (not the case for our test) and/or for use with amplifiers which are more expressive in the upper register (Atoll, Marantz, Ice Power amp). Another use for the -2 dB setting: to listen to unbalanced and shrill sound takes.

With the tweeter’s settings at +3 dB

With respect to our room/amplification system, the listening experience was less serene and the the soundstage was less expansive (particularly with regard to depth). We can’t think of an amplifier shy enough in the upper register to benefit from this setting. But… certain old sound takes, notably jazz-oriented ones, will sound clearer and more spacious.

Lows
The 40Hz announced seem to have been reached, but the drivers cannot generate significant acoustic pressure because of their diameter. On the other hand, the articulation is very good and there is a pleasurable linearity to the sound. It didn’t fail to convince us once.

Mids
Very good balance between low-mids and mids, with plenty of control and a total absence of projection. Superbly textured vocals.

Highs
Sharp but discreet with the default setting, good restitution of the different timbres of each instrument.

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The sides of the speaker are not parallel, which serves to eliminate internal vibrations

Conclusion

What we liked

  • The build quality and the finish
  • The possibility to add weight to the speaker (with sand, for example)
  • The tweeter’s adjustable sensitivity settings
  • The tonal balance and the finish quality

What we would have liked

  • Nothing more.

A speaker which puts music–and not itself–first? There is such a thing, and Atohm knows how to make it. With the Atohm GT2, the listener enjoys a neutral but lively sound, realistic timbres and an energy which is evenly dispersed throughout the entire audible spectrum. Depending on its mood or on the sound signature of the electronics paired with it, the Atohm HT2 can even play around with the sensitivity of the speaker. In sum, it offers a meticulously crafted sound while always respecting the artist’s intentions. We highly recommend the Atohm GT2 as a trusted partner for (very) long listening sessions. These speakers get along just as well with the Micromega M One as they do with the Hegel Röst, and they should be paired with an amplifier capable of providing at least 2×70 Watts (20Hz-20kHz). For home theater installations, where the Atohm GT2 are sure to shine, they should be paired with a high-end amplifier such as the Yamaha RX-A3060 or Onkyo TX-RZ1100.

This post is also available in: French

About the author

Tristan Jacquel

Tristan est rédacteur chez Son-Vidéo.com. Passionné de musique, d'acoustique et de high-tech, il réalise notamment les tests matériels pour notre blog.

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