SEA-CENTER-EXCEL

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SEAS-CENTER-EXCEL
Copyright 2022 © Troels Gravesen

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DRIVERS CROSSOVER CABINET WORKSHOP PICS MEASUREMENTS SPEAKER-KIT CROSSOVER LAYOUT

From time to time, speaker constructions may need an update and while the SEAS-CENTER-PRESTIGE stay the same, being a low-cost entry model, this EXCEL version could need an overhaul - and possibly a slightly better tweeter, not least matching the new W12CY006 edge-coated midrange driver. Due to its far better frequency response, I wanted to fine-tune the mid-tweeter section one more time.

This kit only comes with the new W12CY006 midrange driver, but for bass you can choose either the W18NX001 or the new W18NX003, the latter enhancing power handling and dynamics. Not a big deal for a center speaker, but as the crossover for both drivers is the same, both options will be available and the W18NX001 is significantly cheaper. You will have to live with the W12CY006 black center plug with the W18NX001 drivers having an alu finish.

For tweeter I picked the ScanSpeak D2608/913000 because it offers an unprecedented quality/price performance.

The crossover topology is the basically the same as before, 2nd order for bass low-pass and midrange high-pass and 4th order for mid tweeter as we need best possible vertical and horizontal dispersion as we would like to have the same sound from any place in a 4-seater sofa.

The cabinet has been simplified with a standard 68 mm vent. Chamfering the front panel, as seen on drawing, is optional - but it looks nice and can be done by hand, chisel and sandpaper.

SEAS-CENTER-EXCEL with W18NX001 midbass drivers.

SEAS-CENTER-EXCEL with W18NX003 midbass drivers.

Basics:
4-driver speaker.
Dimensions: 65 x 37-39 x 25 cm, WxDxH. Depth depends on your choice of front panel thickness.
System sensitivity: 91 dB/2.8V/1 meter.
Impedance: 4-8 Ohms.
Power requirement: 20+ watts/channel.
Power handling: 200 watts.
Please also read: http://www.troelsgravesen.dk/power-handling.htm, and remember any burned driver is a misused driver.

Useful links (Please read before writing!):
http://www.troelsgravesen.dk/tips.htm
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/LCR-RC.htm
http://www.troelsgravesen.dk/Inverted-Polarity.htm

FAQ (Please read before writing!):
You cannot change cabinet front panel dimensions and drivers' placement without needing a new crossover - and I cannot help.
You cannot use any other drivers with the crossover specified.
http://www.troelsgravesen.dk/crossovers.htm
http://www.troelsgravesen.dk/choices.htm

DRIVERS
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ScanSpeak D2608/913000 tweeter.

SEAS W12CY006 edge-coated midrange driver.

Midbass option 1: SEAS W18NX001 driver.

Midbass option 2: SEAS W18NX003 driver.
Read here what you get from the W18NX003.

Download specs here:

D2608/913000 W12CY006 W18NX001 W18NX003

CROSSOVER
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Pay notice tweeter and midrange connected with inverted polarity.

CABINET
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Cabinet made from 20 mm Baltic birch. Use 19-22 mm Baltic birch, MDF, HDF, or similar high-density material.
I used 15 mm for the two vertical braces and sloped midrange panel.
Faceting the front panel is optional.
You can make the cabinet with vertical front panel if placed high. Depth 340 mm without front panel.

Workshop pics
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I used 35 mm for the front panel, 25+10 mm HDF, thus special precautions needs taken with regard to the midrange driver as it would choke on a straight mounting hole.

Start chamfering 45 deg. down to around 10 mm from rebate edge. This makes the midrange breathe - but still not enough.

Set up boundaries for your router and remove some 12-15 mm with a straight router bit.

Above to the left what it should look like. Now the midrange can breathe.
If we didn't we'd have huge irregularities in frequency response due to acoustic resistance on rear radiation.

Cover all internal panels with felt except rear panel behind midbass drivers, where the crossovers must be placed.

Front panel was added three coats of water based before glued to the cabinets.

Place a piece of ~40 x 50 cm acoustilux behind midbass driver as seen on photo.
Stuff the mid cabinet with 80-100 grams wool.

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.

Horizontal dispersion at 0, 10, 20 and 30 deg. off-axis (red/green/orange/purple respectively).