MAUHORN IV

The Mauhorn was designed by Andreas Mau, a German Lowther enthusiast, in around 1995

Actually, Andreas designed 2 similar Mauhorns at that time – the Mauhorn IV (shorter 3.5m long horn, larger driver chamber) and the Mauhorn V (longer 4.5m long horn, smaller driver chamber).

These designs were published in Sound Practices magazine Issue 10. (Excerpts below – Sound Practices, all issues, may still be available on a CDR from eBay.)

These back-loaded horn cabinets were designed for Lowther loudspeaker drivers, but other suitable drivers can be used.

The Mauhorn IV design contains a folded bass-horn inside a cabinet with narrow front profile.

Main design features:

• 3.5m horn length
• 300mm narrow width cabinet – arguably helpful for stereo imaging
• Cabinet external dimensions, 1m height x 0.8m depth
• Relatively compact dimensions for a bass-horn cabinet.
• Designed for near-corner placement, to utilise the room corner for horn-mouth expansion

With corner-loading, the mouth-area of a horn can effectively be increased by 8 times (1/8 sphere, as illustrated below).

Because the design cut-off frequency Fc of the horn is determined by the horn-mouth circumference, a lower frequency can be produced with corner loading.  According to my analysis, the Mauhorn IV horn ‘flare’ or expansion is Hypex (hyberbolic-exponential, Flare Rate M=0.6 – 0.8) with design Fc of around 30Hz.

(In reality, horns usually do not produce output down to their design cut-off frequency (Fc) – actual output is typically around 1/4 octave higher – depending on various factors.. This is referred to as Throat Reactance (ref. Dr Bruce Edgar).)

Of course, a 30Hz horn would require a horn-mouth circumference of Speed-of-Sound/Frequency – ie. 343/30 = 11.43m – or mouth-area 3.3 sq m.  Even with corner loading, a mouth area of 0.4 sq m would be required.  Horn length would need to be 4.8m – 5.0m.

The Mauhorn IV horn length is only 3.5m and mouth size only 0.7 x 0.26m = 0.18 sq m.  So, this horn has been ‘truncated’ – in order to keep the cabinet size reasonably domestically acceptable.

One disadvantage of truncating a horn flare is that bass response will be more bumpy, less smooth.  This is a sonic compromise that Andreas has made, in order to keep the cabinet size down.

Construction:

I built a pair of Mauhorn IVs in 1997.

Because the cabinet sides are parallel, all the internal panels are same width and can be cut to size relatively easily.

The narrow width internal panels also means that rigidity, stiffness is more easily maintained.  However, additional centre-stiffening panels were added – as in Andreas’s own construction.

In my build, I used 18mm (¾”)  Fijian Kauri-faced plywood throughout.  I much prefer the sound of plywood to MDF (Medium Density Fibreboard) or other compressed wood boards.

Plywood has lower weight-to-strength ratio, which is helpful as each cabinet requires almost 1½ sheets of 2.4m x 1.2m plywood and will weigh 36-45kgs each.

All the internal panel edges were radiused/rounded – this may not matter so much at bass frequencies, but will reduce air turbulence and should assist air-flow at the bends.

There is no internal damping material, except on the panel behind the driver – this will reduce reflection back through the driver cone.  I used Deflex sheet, but carpet or such material should also be effective.

The small horn throat (at the driver chamber) and length of the horn. both help to roll off the upper frequencies in the bass horn output.

Drive units:

I originally used Lowther PM2C drive units, but other drivers of similar size and ‘full-range’ type could be used – eg. Fostex, Seas, Tang Band, etc.  Drivers with relatively low Qes are typically recommended for horn-loading

Lowther PM2C.

.

SEAS FA22RCZ is inexpensive and a possible option.

With a horn, it is important to form an air-tight seal between the driver and the cabinet face.  Use a gasket or Blu-Tak, etc.

These drive units are typically very sensitive, so heavy speaker wiring is not necessary.  There is little signal current capacity required.  You could even use single (or double) solid strand, say 0.7 – 0.8mm copper wire.

Sound:

Typically, there is no crossover required – or a minimal notch-filter network sometimes.  So, the upper range front output will be alive and transparent.

Depending on the drive unit, some running-in time will be required before the driver suspension loosens up and bass output develops.  (The Lowthers needed at least 50 hours.)  Start gently with low volumes, before increasing loudness gradually over a few days.

Rough measurements taken, using a test tones through an Audionote Kit One amplifier, showed the Mauhorn IV bass output in-room to be flat to 50Hz, with good output at 40Hz and surprisingly even some audible output at 31.5Hz.

This is not huge bass, but the quality of horn low frequencies is agile and full of tonal colour – this is not one-note bass or ‘tight’ bass without natural harmonics, decay and timbre.

Enjoy!

See also – MAUHORN IV update (Apr 2015).

PS. You can see the Mauhorns pictured in my5Tractrix Midrange Horn page – later I used the Mauhorns for bass output only, with midrange horns on top.

PPS. I would like to try also the Mauhorn V – this is a longer horn and looks like a more exponential flare, which should produce deeper bass.