The loudspeaker system 2025

After testing ceramic drivers in my Monitor 4 and, more recently, the Purifi-Audio / Mundorf AMT combination, I can confidently say I’ve experienced some of the most innovative developments in loudspeaker driver design.

These drivers deliver exceptional micro-detail and remarkably low distortion that would have been unthinkable years ago with paper cones. However, the resulting sound may still become fatiguing over long listening sessions.

Recently, I came across an advert for a brand-new set of unused speakers with characteristics that make them particularly interesting for building a three-way system with the my active H-frame subwoofer.

The mid-woofer cone is not made of exotic materials, yet it is also not ordinary paper. As a result, it tends to inherit some of the characteristics of more advanced cone designs, but with fewer breakup issues.

This driver was also used by Troels Gravesen in one of his projects, and he speaks very highly of its performance.

TWEETER

Seas 27TDFC

Nominal Impedance: 6 Ohm
Sensitivity at 2.83V/1m: 90 dB
Recommended Frequency Range: 1500 - 25000 Hz
Free Air Resonance: 550 Hz

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Data sheet
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The 27TDFC is a high definition precoated fabric dome tweeter with a wide, soft polymer surround and a rear chamber.
Sonotex precoated fabric diaphragm with high consistency and excellent stability against variations in air humidity.
Sonomax surround for low resonance and excellent mechanical linearity.
Voice coil windings immersed in magnetic fluid increase short term power handling capacity and reduce the compression at high power levels. Stiff and stable rear chamber with optimal acoustic damping allows the tweeter to be used with moderately low crossover frequencies.

MID-WOOFER

Seas ER18RNX

6.5 inch bass-midrange

Recommended Frequency Range: 45 - 3000 Hz

Characteristic Sensitivity (2,83V, 1m): 88.5 dB

Free Air Resonance: 37 Hz

Datasheet

The ER18RNX is a 6,5’’ cone driver, developed for use as a long throw high fidelity woofer or woofer/midrange unit.
Edge coated reed/paper pulp cone together with perfectly matched moving parts gives a smooth, extended frequency response.
Bumped back plate in the magnet system, together with the very long and light weight copper clad aluminum voice coil, allow extreme coil excursion with low distortion.
Heavy copper ring below the T-shaped pole piece will reduce nonlinear and modulation distortion. 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.

There are some differences on parameters that probably depend by the DATS errors, I will make other tests about.

Parameter	Parameter Typ	Value	Measured	Unit
Zn	Nominal impedance	8	8	ohm
RDC	DC resistance	5,9	6.5	ohm
Le	Voice Coil inductance	0,67	0.21	mH
fs	Resonance frequency	37	47.8	Hz
Qms	Mechanical Q factor	1,58	2.07
Qes	Electrical Q factor	0,39	0.55
Qts	Total Q factor	0,32	0.44
Vas	Equivalent volume	32	18.2	L
Sd	Effective piston area	136	136	cm2
D	Effective piston diameter	13	13	cm
Bl	Force factor	7.2		N/A
Mms	Moving mass	14	14	g
Cms	Suspension compliance	1,3		mm/N

Follows the simulation with WinISD using the declared and measured parameters on the same bass-reflex box.

THE BOX DESIGN

The front panel is much larger than the rear box to have a very wide baffle to reduce the lateral dispersion at mid-to-high frequencies.

The front panel is also tilted about 8 degrees to align the offset of the emission centers of the 2 drivers.

The internal volume of this box is:

220mm * 150mm * 321mm = 10.6lt

2.6lt more than simulation but in small boxes we have to consider the volume of the magnets and the cone.

The internal walls of the box were covered with an acoustic absorbent ORsilent Lite purchased from Leroy Merlin.

- Main material: Polyurethane

- Thickness (in mm) 20

- Lambda (in w/mK) 0.038

- Density (in kg/m³) 100

LOW FREQUENCY

The low frequencies from 20 to 100 Hz approximately are guaranteed by an 18" woofer mounted in an amplified and equalized dipole H-frame.

The extreme H-frame subwoofer

MEASUREMENTS AND CROSSOVER

Here I am in my living room where the reflections on the walls are controlled with 10 panels model 3D by Acustica Italia.

I will use a miniDSP UMIK-1 Omni-Directional USB Measurement Calibrated Microphone and the Dayton DATS V3 Computer Based Audio Component Test System for the impedance measurement.

This crossover is the result of a long series of measurements of the frequency response and several listening sessions with a my friend who makes live recordings.

Here is a measurement with the Extreme H-frame subwoofer at 20cm at a height of only 55cm so above the sub.

Follow the measurement at 50cm.