The 27TBCD/GB-DXT is an aluminium/magnesium alloy dome tweeter with a DXT® (Diffracton Expansion Technology) lens.

The DXT® tweeter addresses the major issues regarding directivity control in traditional loudspeaker designs. DXT® solves several well-known issues regarding; directivity control, off-axis response, integration with midrange units and baffle diffractions.

From approximately 7 kHz the diffraction edges begin to work. At the very high frequencies the DXT® uses up to 3rd order diffraction to expand the sound field. At lower frequencies the DXT® tweeter operates as a waveguide to narrow the mid-band dispersion.

Stiff and stable rear chamber with optimal acoustic damping allows the tweeter to be used with moderately low crossover frequencies. A fine mesh grid protects the diaphragm.

Seas spec. sheet:
27TBCD/GB-DXT (H1499)
DXT Technology
DXT Website

T/S Parameters:


Lower resonance frequency than the official SEAS specification and showing a 5% variation between the two driver unit samples.









The DXT tweeter doesn’t use ferro-fluid in the magnetic gap. The double peak in the impedance plot indicates some sort of cavity resonance. The impedance plot shows a slight variation between the two driver unit samples. Overall a good consistency between the two samples.








Frequency measurement conditions:

The tweeter is measured mounted in a 14 liter Dayton Audio enclosure (PartsExpress part #302-721) baffle with the following conditions:

Baffle size (WxH): 21,59×35,56cm (8,5″x14″)

Driver position: Mounted on center-line with driver unit center 8cm from the top of the baffle.

Mic position: 1m distance, on tweeter-axis.

Smoothing: 1/24 octave smoothing applied.

0deg tweeter-axis:
Sample 1 = Blue
Sample 2 = Red

Virtually the same frequency response between the two samples except for some sort of cancelation for sample 1 at 21kHz. Between 1.5-4kHz the baffle diffraction is noticed as dips and peaks in the frequency response. This is reduced in the off-axis measurements.

The tweeter has a sharp peak centered at 27kHz which is caused by the hard dome cone break-up. This cone break-up behavior is very common among hard dome tweeters and is often noticed as increased odd-order distortion between 5-10kHz, depending where the cone breakup occurs. Many people refers this as “sounding metallic”, while others claim it can’t be heard.

0deg = Blue
15deg = Red
22.5deg = Green

30deg = Blue
45deg = Red
60deg = Green

Thanks to the DXT lens the tweeter has a remarkable controlled off-axis response and frequency dispersion!



 Measurement setup:

  •     Tweeter near-field measurement at 10cm
  •     Frequency Range Tweeter: 500-10000Hz
  •     Baffle size WxH: 21,59×35,56cm (8,5″x14″)

The distortion measurements are done in near-field and the amplifier output level was adjusted for each driver so that the fundamental is 85dB at 1m and 90dB at 1m. This setting simulates normal to medium-high listening levels.

85dB @ 1m (click on picture to zoom)

Left = Sample 1

Right = Sample 2


90dB @ 1m (click on picture to zoom)

Left = Sample 1

Right = Sample 2


The odd-order harmonics are very low throughout the tweeters usable frequency range. The harmless 2nd order harmonics is a bit elevated compared to the odd-order harmonics.

Unfortunately however, due to the measurement setup these distortion plots don’t tell the whole truth about this tweeters distortion profile. The cone break-up at 27kHz causes a rise in the distortion profile at 13.5kHz for the second-order, 9kHz for the third-order and 5.4kHz for the fifth-order harmonics and so on.

These distortion spikes will contribute to the tweeters sound character. Some people call it “metallic sound”, other think it adds additional resolution and details to the sound. I say it’s a matter of personal preferences and taste, if it’s good or not

To sum up, this is a very interesting and affordable low distortion tweeter. Thanks to the DXT lens it has an exceptional controlled off-axis response and frequency dispersion. The DXT tweeter can be used down to 2kHz, perhaps even lower than with an appropriate steep filter.