TL-CENTER

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TL-CENTER
High-efficiency Center for The Loudspeakers:
TL-1, TL-2, TL-3 and Faital-3WC-15
Copyright 2023 © Troels Gravesen

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DRIVERS CROSSOVER CABINET WORKSHOP PICS MEASUREMENTS SPEAKER-KIT CROSSOVER LAYOUT

There have been requests for a center speaker for the The Loudspeaker-1/-2/-3 and Faital-15, matching the potential of these systems, and none of my existing designs are hardly up to the task, maybe except the 8008-CENTER, but here is a design that will truly match potent, high-efficiency main speakers in a surround system.

The magnificent Faital 6RS140 driver was an easy choice for midrange and the SBAcoustics SB29BAC-C000-4 Beryllium tweeter another easy choice.

For bass there were several options and having quite some experience with the 18 SOUND 10" bass driver, 10NW650, this was tried and found more than suitable. This driver is seriously efficient and we have to use two drivers in series, delivering a healthy impedance above 8 Ohms in the bass region. Most amps will love this.

Having two 10" midbass drivers calls for some cabinet volume and the TL-CENTER is not a small speaker as can be seen below, but so it must be.
Center speakers really do not have to play deep bass and the TL-CENTER may on paper do well down to around 50 Hz and 40Hz including assumed room-gain, but believe me, it can play bass.

Basics:
4-driver speaker.
Dimensions: 90 x 42,5 x 30 cm, WxDxH.
System sensitivity: ~93dB/2.8V/1 meter.
Impedance: 4-8 Ohms.
Power requirement: 30+ watts/channel.

Useful links (Please follow all links before e-mailing!):
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/tips.htm#CONSTRUCTION_OF_CROSSOVERS
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/LCR-RC.htm
http://www.troelsgravesen.dk/Inverted-Polarity.htm
http://www.troelsgravesen.dk/choices.htm

DRIVERS
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SBAcoustics Be-dome: SB29BAC-C000-4, 4 Ohms.

Faital-6RS140, 8 Ohms.

Read the excellent review by Dickason in AudioExpress.

18 SOUND midbass driver: 10NW650, 8 Ohms.

Click images to view large.

Download specs here:

SBAcoustics tweeter: SB29BAC-C000-4
Faital midrange: 6RS140 (8 Ohms)
18 SOUND midbass: 10NW650 (8 Ohms)

CROSSOVER
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Please remember to read this carefully: http://www.troelsgravesen.dk/LCR-RC.htm

CABINET
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Click image to view large.

Cabinet was made from 21 mm Baltic birch and front panel from 25 mm HDF (Valchromat). Chamfering the front panel is optional. You can just make it flat and add a front grill if needed.
On the rear of the midrange compartment drill 5 holes of 15 mm diameter - or make a slot of similar area. Cover on inside with one layer of grey felt glued around the holes. This makes an aperiodic tuning of the midrange.
The ports can be placed as seen on drawing - or in the middle, not critical, but to the outer end to make room for the crossovers next to MT section. See below.
Make ~8 mm holes in vertical panels at bottom of midrange cabinet for wiring and also holes for MT wiring. Seal properly once wires have been added.
Ports are 68 x 120 mm as delivered.

Workshop pics
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The great thing about center speakers is that you only have to make one :-)

Faceting front panel is optional, but looks nice. I decided only to do the sides.

All felt material in place.

Add acoustilux as seen on images. Fasten with 10 mm staples.
Make hole for port (not seen here).

Make 5 pcs 15 mm holes in rear panel towards midrange cabinet - or make slot or similar square area.
This to make an aperiodic tuning for the midrange.

Gluing the front panel.

MEASUREMENTS
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A few comments on MEASUREMENTS before you start interpreting the readings below.
First of all, if we think measurements will tell us how a speaker sounds, we're wrong. The perception of sound is way too subjective to be reflected in any measurements we can perform. A loudspeaker system is meant to give us a satisfying idea of an acoustic event and for some people a pair of 5 USD ear-plugs are enough, others spend 200 kUSD on a truly full-range pair of speakers - and the latter may not be happier than the former.
Measurements may give us an idea of tonal balance of a system, i.e. too much or too little energy in certain areas, although dispersion characteristics play a vital role here. A two-way 7+1 and a three-way 7+4+1 may display similar horizontal dispersion, yet sound very different. Measurements may tell us about bass extension if far-field measurements are merged with near-field measurements. In addition to this, ports may contribute to bass extension. Most of we diy'ers do not have access to an anechoic room for full-range measurements from 20-20000 Hz.
What cannot be seen is what kind of bass performance we get in a given room. Bass performance is highly dependent on in-room placement of your speaker and the same speaker can be boomy in one place and lean in another. Actual SPL level at 1 meter distance and 2.8V input is useful for en estimate of system sensitivity and combined with the impedance profile may give an idea of how powerful an amplifier is needed to drive the speaker to adequate levels.
What measurements do not tell is the very sound of the speaker unless displaying serious linear distortion. The level of transparency, the ability to resolve micro-details, the "speed" of the bass, etc., cannot be derived from these data. Distortion measurements rarely tell much unless seriously bad, and most modern drivers display low distortion within their specified operating range.
Many people put way too much into these graphs and my comments here are only meant as warning against over-interpretation. There are more to good sound than what can be extracted from a few graphs. Every graph needs interpretation in terms of what it means sonically and how it impacts our choice of mating drivers, cabinet and crossover design.
What measurements certainly do not tell is the sonic signature of the speaker, because speaker cones made from polypropylene, aluminum, Kevlar, paper, glass fiber, carbon fiber, magnesium, ceramics or even diamonds all have their way of adding spices to the stew. Nor do measurements tell what impact the quality of the crossover components add to the sound, from state of the art components to the cheapest of coils and caps, they all measure the same if values are correct, yet sound very different.

Basic SPL @ 1 meter, 2.8V.
System sensitivity around 92-93 dB.