SEAS H1499 27TBCD/GB-DXT

Overview:

 

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.

 

 

 

 

 

 

Impedance:

 

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:

 

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!

Distortion:

 

 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. At these frequencies the distortion is elevated about 8-10 times.

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.