The ER18RNX (H1456) is a 7” mid-woofer from the Seas Prestige series and is developed for use as a long throw high-fidelity woofer or woofer/midrange unit. It has an edge coated reed/paper pulp cone together with perfectly matched moving parts, which gives a smooth extended frequency response.

It has a bumped back-plate in the magnet system together with a very long and light-weight copper clad aluminium voice coil, which allow extreme coil excursion with low distortion.

A heavy copper ring below the T-shaped pole piece reduces the non-linear and modulation distortion.

An extremely stiff and stable injection molded metal basket keeps the critical components in perfect alignment. Large windows in the basket both above and below the spider reduce sound reflection, air flow noise and cavity resonance to a minimum.

This mid-woofer driver unit is capable of a cross-over frequency up to approximately 2.2kHz, without sacrificing any off-axis frequency response behavior.

SEAS spec sheet: ER18RNX (H1456)

 T/S Parameters:


The T/S parameters are measured both when the driver units are cold and when warmed up with a 1 hour stress stimulus at 5.66V. The warmed up driver units are rested for 2-3 minutes before they are measured.

The manufacturers DC resistance spec of 5.9 Ohm doesn’t seem to be correct or has a typo. It seems that the DC is about 6.5 Ohm. For Seas, the measurements show an unusual large deviation between the two measured samples. In this case, sample two seems to be the deviating driver unit.




Sample 1 = Green

Sample 2 = Blue

Left: Free air impedance measurement “cold” driver units:

Right: Free air impedance measurement “hot” driver units:

The two samples are not a perfect match between each other. Sample two has a higher resonance frequency than sample one. A small bump in the impedance plot can be seen between 0.9-1kHz, indicating some sort of resonance problem.

The resonance frequency is lowered by 1-2Hz in the “hot” measurement, but otherwise they have the same response curve as the “cold” driver units.



The mid-woofer is measured flush-mounted on a baffle with the following conditions:

Baffle size: (WxH): 24,8×35,8cm

Driver position: Mounted on center-line with driver unit center 12,5cm from the bottom of the baffle.

Mic position: 1m distance, 15,5 above driver unit center (tweeter-axis)

Smoothing: No smoothing applied.

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

Nice consistency between the two driver unit samples. Some cone break-ups at 4.8k, 6 and 7.5kHz.

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

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

The mid-woofer has a smooth frequency response within its usable range.



 Measurement setup:

  •     Mid-woofer near-field measurement at 15cm
  •     Frequency Range Mid-woofer: 200-10000Hz
  •     Baffle size WxH: 24,8×35,8cm


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 mid-woofer has very low distortion in the bass region and average distortion in the mid-range region. The cone break-ups at 4.8, 6 and 7.5kHz is most likely the reasons that gives a slightly elevated third-order harmonics in the upper mid-range and lower treble region. This shouldn’t cause any issues when crossed-over below 2kHz.