ScanSpeak MUN17-3W
Copyright 2017 © Troels Gravesen

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DRIVERS   CROSSOVER    CABINET    MEASUREMENTS    SPEAKER-KIT     CROSSOVER LAYOUT

This speaker was designed for the ScanSpeak trade visitor exhibition at the Munich 2017 High-End event. The primary product here is the 28W/4878T00 bass driver, filling the gap between the 26W and 32W bass drivers.
The midrange driver is a variant of the 18M/4631T00 driver, but here in an 8 Ohm version, better suited the target system sensitivity. Maybe the kind ScanSpeak guys got tired of hearing my grumpy comments to the abundance of 4 Ohms midrange drivers and made an 8 Ohm version. I'm happy! For tweeter there was no doubt it had to be the Be dome D2908/714000. Only constraints to the design was a closed box for the bass driver. Everything else was up to my imagination.

Let's start with the bass driver. This is a sandwich cone driver with a whopping 3" voice coil and 4 Ohms impedance. Sensitivity is 88.3 dB/2.8V as an average of response at 300-1000 Hz. A closed box of 40 litres makes F3 = 42 Hz. Not bad at all - and we're going to extend this by tweaking the Hypex modules driving the unit. Further TS data below.
40 litre is not a whole lot, thus allows for a very compact design. Overall dimensions are 100 x 34 x 30 cm - and there's a grille for the MT section. High WAF! I didn't make a grille for the bass driver, but obviously no problem in doing so.

This is the first time I use the 18M midrange drivers and only reason for not doing so was the 4 Ohm impedance requiring excessive attenuation to fit any ~88-89 dB design. It may be prejudice, but I don't like excessive attenuation for midrange drivers. Even the 8 Ohm version would by standard crossover design require some attenuation, but here - after quite a lot of modeling - I decided to use a baffle step compensation circuit to control amplitude and get the target SPL.

   
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Sound:
This 18M came as a pleasant surprise! It surely rivals my favourite AudioTechnology 18H52 for midrange. It has all the virtues of a high-quality midrange with superb detail, transparency and an overall ear-friendly presentation. With regard to frequency response it's probably the smoothest 6" midrange driver on the market, making crossover work very easy. The low-pass section of a midrange crossover can often be a real pain, rolling off too fast or we can't get the damned thing stopping again. Not this one.
I render this speaker in the top three of any speaker I've ever made. The midrange-treble transparency is astonishing to my ears.

As can be guessed from the crossover layout we only need 66 uF series capacitors for the midrange saving us some 150 EUR compared to most of my larger 3-/4-ways requiring 88 uF with the same 200 Hz point of crossover. Tuning the bass roll-off was easy as we can manipulate the  driver to our liking in the Hypex software. The 28W sandwich cone, the closed box and the Hypex module delivers a firm and punchy bass and  I can't tell how it overall sounds as it makes no sense describing sound. Even if I wrote a book on the sound, you wouldn't know until you heard it yourself.

Only limitation I can point to is the quality of the amplifier you put in front of the midrange-tweeter. Be prepared you can feed it the best money can buy and you don't need humongous amounts of watt to drive the MT section. Some 20+ high-quality watts can do. My GlowMaster just loves this MT section with its fairly high impedance profile!

 

Basics:
You're likely to let go of 3100 EUR for Hypex modules and drivers. On top of this crossover components and cabinet materials.
3-way speaker from 11" + 7" + 1" drivers.
System sensitivity: 88 dB/2.8V/1 meter.
Impedance: 4 Ohms for bass, 8 Ohms for MT section, minimum 5.5 Ohms @ 400 Hz.
Point of crossover: 200 and 2,000 Hz.
Power requirement: 20+ watts/channel.
Pre-amp: Line stage for running the Hypex modules.
Power handling: A lot! Please also read this: http://www.troelsgravesen.dk/power-handling.htm, and remember any burned driver is a misused driver. Having a dedicated plate amp for the bass, means you can have a smaller amplifier for the midrange/tweeter, e.g. 20-40 wpc.

As always: Any change to front panel design and drivers' placement and you need a new crossover and I can't help.
Please do read before asking questions: http://www.troelsgravesen.dk/crossovers.htm

 


The terminals next to the Hypex are connected to the channel 1 amplifier for feeding the MT section if needed.

DRIVERS
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Download specs: 28W/4878-T00   18M/8631-T00    D2908/714000

 

    
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CROSSOVER
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CABINET
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The cabinets were made from 20 mm Baltic birch and 25 mm black MDF for the front panel of the midrange-tweeter section. The bass cab is simplicity itself. 60 x 34 x 30 cm. Make a compartment for the Hypex module to be sealed off from the heavy pressure of bass driver. Brace it well! I wouldn't hesitate to recommend 25 mm MDF all over, just extend depth to make some 38-40 liter net volume.

As always you have to stick to the front panel dimensions and drivers' layout of the MT section to make the crossover work as intended! Too many think there's free ride here - and there isn't! Any change and you need a new crossover - and I can't help. Please read this file carefully: http://www.troelsgravesen.dk/crossovers.htm I've seen some sad examples recently of people spending 3+ kEUR and changing the design to such extent they for sure never hear what it was supposed to. Acoustics can't be fooled.
The front panel chamfering here was made on a table saw, but can be made very simple from only chisel, planer and sandpaper - and elbow grease! Read here.

 


Follow the design of the MT cab carefully! Important for frequency response and crossover.


 

Go to: Hypex PSC2.400 modules


Workshop images


The bass cab was made from 20 mm BB and I used 19 mm black MDF for top and bottom.
I suggest adding further bracing to the top panel.


To the right the lower brace. Holes are Ø135, 55 and 75 mm.


Left: MT frequency response during crossover development.


Trying out the MT section after gluing.

   
Left: MT section ready for lacquer.Right: Prototype MT rear panel. Follow instruction (drawing) and make one brace allowing crossovers for tweeter and midrange to be mounted on rear panel.


Front grille was made from 19x30 mm fillets of black MDF glued with epoxy. Lower front bar was 12 mm MDF.

 

Cabinet damping:

Bass cabinet: Add 8 mm felt to all internal panels. Add 4 layers of 30 mm acoustilux at the bottom and two layers behind and bass driver and on top of the cabinet.
MT cabinet: Add 8 mm felt to all internal panels except rear panel. Add two layers of acoustiux on top of crossover.

Port: 50 x 145 mm. Cut a piece of 12 x 20 cm acoustilux and stuff the port (= aperiodic tuning).

 

 
Left: Prototype crossovers. Different from the final crossover layout. I hadn't realised the size of the caps....
Right: Living room fine-tuning.

 


I use 8x8 mm neo magnets for holding the grille frame in place.

 

 


MEASUREMENTS
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Everything that can be counted does not necessarily count; everything that counts cannot necessarily be counted". Albert Einstein.

A few comments on MEASUREMENTS before you start interpreting all 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. 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 us 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.


Left: SPL from bass driver, no crossover. Right: Bass response driven from Hypex.


Left: SPL og bass, MT section and summed response. Right: Impedance of MT section.

 
Left: CSD of MT section.


Left and right speaker. Quite a matched pair. Tweeter at highest attenuation.


Horizontal dispersion at 0, 10, 20, 30 and 40 deg. off-axis.
Very even frequency response up to 10 kHz over a 60 deg. window.


Something we rarely see: Vertical dispersion.
Here measured at 0.5 m distance at a height starting at the lower edge of the 18M driver (red) up to the upper edge of the cabinet (blue)
(red-green-orange-yellow-blue)


Front grilles usually ruin the party, but here we have the response at 0 (red) and 10 deg. (green) off-axis.
Listening at e.g. 10 deg. off-axis provides a rather smooth response.


Same again, here at 0, 10, 20, 30 and 40 deg. off-axis with front grille.

 




Speakers at ScanSpeak demo room in Videbaek
Gamut frontend.

SPEAKER-KIT
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All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark.

Download Complete Kit Sale Presentations (pdf file):

All technical questions to troels.gravesen@hotmail.com

All questions regarding purchase of kits, please mail Jantzen Audio at contact@jantzen-audio.com


CROSSOVER-LAYOUT
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Layout for tweeter

 

Layout for midrange

 


Speaker wiring, MT section

 


Placement of crossover on MT rear panel