SEAS-22_Snell-E3

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SEAS-22 - or
Revival of Snell Type E/III
Copyright 2024 © Troels Gravesen

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DRIVERS CROSSOVER CABINET WORKSHOP PICS

MEASUREMENTS SPEAKER-KIT CROSSOVER LAYOUT

Doing a test of vintage Snell E-III, I couldn't help thinking SEAS CA22RNY. I have used it in my SEAS 3W-Classic mkII. A classic coated paper cone driver with good sensitivity and good frequency response, that doesn't take much equalisation.
A two-way from an efficient 8" midbass driver and a great tweeter not costing a fortune; it doesn't get much simpler and it is highly cost-efficient. A lot of good sound from modest investment.
The concept is very familiar to me as I have used it extensively in my range of speaker based on my JA8008-HMQ driver. Having a middle-sized driver doing it all up to lower treble range does its thing in terms of coherence and transparency.
Obviously I picked the ScanSpeak D2608/913000, a tweeter I have used in so many constructions for its excellent performance and due to it's properties the high-slope crossover can be made from few components.
In addition to this, an impedance profile that doesn't go lower than 7.0 Ohms, thus a true "8-Ohm" speaker, something owners of smaller tube amps will love. My 32 wpc EAR-861 loves it!
It's all very classic, and have you never made a pair of speakers before, this may be the place to start. I started here many years ago and today we have drivers far better than back then. And most importantly, today we can make much better crossovers with sota measuring equipment, simulation software and premium crossover components, none of these things even existing at that time.
Also the box spells simplicity. A rectangular box made from premium Baltic birch with good bracing does it, quite a lot better than the Snell chipboard enclosure, although the E/III really wasn't that bad except for the damping that wasn't quite up to what one could expect from Snell. Maybe the workers had to leave early that day just leaving a roll of polyester damping thrown into the cabinet.
Having had the Snell Type E/III at first hand, I can assure you this construction by far exceeds the performance of the original, deeper bass, better transparency, better everything.
Moving the finished speakers to my living room proved another step up from my small workshop. Having a good 8" driver doing it all until lower treble has its benefits. Stunning transparency, smooth treble and very good bass indeed. Actually a speaker I could live with solely. Really? Honestly, yes. Exceptional midrange, great bass and smooth treble, what's not to like? I have speakers that can do better this and that, but all speakers are compromises, but if cost, performance and an easy build was my priority, then I'm all in.

Basics:
2-driver speaker.
Dimensions: 32 x 26 x 90 cm, WxDxH.
System sensitivity: 90 dB/2.8V/1 meter.
Impedance: 8 Ohms.
Power requirement: 10+ watts/channel depending on how loud you play and room size.

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
http://www.troelsgravesen.dk/Placement-of-ports.htm

DRIVERS
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Download specs here: D2608/913000 CA22RNY

CROSSOVER
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The crossover features a LR4 topology made from as few components as possible due to the natural roll-off of drivers. Basically the same as the Snell-EIII. Those looking for a "coil and a cap", look elsewhere. I don't subscribe to "less is more". All things come at a cost and all speakers are compromises.

CABINET
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Cabinets were made from 20 mm Baltic birch and the 100 mm base from 25 mm solid oak. The base to get the speaker up to a reasonable height with regard to listening position incl. adjustable feet.
The internal volume was reduced a little compared to the Snell-EIII as it is really a little too big for such an 8" driver. It's the balance of bass extension and progressive more sloppy bass the bigger volume we use.
I placed the crossover on the rear panel behind midbass driver, but can also be placed at the bottom support as we now have the opportunity to get the crossover out of the box. Probably not a big deal, but when possible, why not. And it gives easy access to the crossover for possible tweaking if you might have other ideas of crossover components. They are few and may be subject to experimentation. Current crossover uses premium components and you have to dig deep in your pockets to possible improve the performance.
After finishing the speaker I decided to make a 80 mm base support and at the same time tilt the cabinet 5 deg. Your choice what you will do.

I made the support from 30 mm solid oak.

My base support have these dimensions. Tilt is 5 deg.

Workshop pics
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All pieces cut in the rough.
What I always do before starting cutting the panels to size, I sand the panels, grade 270, and give the panels a thick coat of lacquer. This reduce edge ripping and it prevents glue from penetrating the outer veneer leaving bright spots in the final finish. After cutting the panels to size, I even give the edges a coat of lacquer to prevent glue saturating the edges, leaving bright spots.

Braces in the rough before cut to final size. Yes, I do the holes with the router. I'm sure you know this already because you did follow all the links suggested at the beginning of this page :-)

Not much to show from a simple rectangular box, but here some shots.
And the sides/top/bottom are NOT laminates. What you see is rebates.
The vertical strips on front and back have no structural function. Just for minimising waste.

Chamfer midbass driver hole, just 45 deg. at 10 mm depth.

Next felt damping:

Cover all internal panels except rear panel behind midbass driver, where the crossover will be.

Inner side of front panel.

Left: Acoustilux at bottom, 2 sheets 50 x 50 cm.
Right: One sheet 20 x 60 cm covering rear and sides in port compartment.

Left: Midbass compartment, 2 layers of 25 x 50 cm covering crossover and sides.
Right: 1 pcs 50 x 50 cm stuffed behind tweeter.

For two speakers:
4 pcs 50 x 50 cm
2 pcs 60 x 20 cm
4 pcs 25 x 50 cm
2 pcs 50 x 50 cm
Total 4.6 meter of 50 cm width, 2.3 sqm. 2.5 sqm supplied with kit.

Left: Very first: Does reality live up to simulation? It does. The rest is fine-tuning.
Right: Add some Superfix to port hole and insert port.

First time set-up with prototype crossovers.
Give them some 10 hours break-in.

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.

Frequency response of CA22RNY on actual baffle.
Nice and smooth roll-off.

Frequency response of D2608/913000 tweeter on actual baffle.

Final frequency response of speaker measured at 0.5 meter distance at a height between the two drivers.

Final system impedance. Minimum 7.0 Ohm @ 140 Hz.

Measurements showing the point of crossover, 2 kHz, a little below the Snell-E/III and a lot smoother profiles.

Speaker dispersion @ 0, 10, 20 and 30 deg. off-axis.

SPEAKER-KIT
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To configure a DIY kit and get a written offer including shipping cost, please use the DIY kit configurator in the Jantzen Audio website:

https://jantzen-audio.com/diy-kits/

All technical questions to troels.gravesen@hotmail.com