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).

Mauhorn-2

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.)

Mauhorn-1

Mauhorn-3

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. solid-angles 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.

Mau-IV-Flare

(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.

Mauhorn 4

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.

Mauhorn 2

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.

Mau IV 001

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

PM2C

Lowther PM2C.

.

fa22rcz

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!

PS. You can see the Mauhorns pictured in my Tractrix 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.

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8 thoughts on “Mauhorn IV

  1. Pingback: Mauhorn IV update | D a r k L a n t e r n

  2. Lovely article. I wonder, did you ever get to make the V? I am looking in to the V based on your article, but can not find any more information, designs other than the image you have posted here.

    • Hi Jonathan – I have never constructed the Mau V. There was some info on the web, but I have not checked for a while. Andreas’ dimensions above are pretty much all he had & all you need. The Mau V horn is longer than the Mau IV & is more exponential flare & tends to produce deeper bass, but bear in mind that, in order to maintain small cabinet size, both these horns are compromised in mouth size – this means that LF response will be truncated & a bit lumpy. However, if placed near room corners, the LF balance is quite satisfying – depending of course on the mid-HF driver & its response too.

      Keep me posted on progress, if you decide to build!
      Cheers, Owen

      • Owen
        Apologies, I didn’t realise you had replied and was about to contact you again.

        I have been reviewing and thinking about the execution of the project. The size of the throat (2.5cm x 26cm = 65cmsq), so the frequency is low (900Hz), and the mouth is 1.69msq, so lowest frequency even in a corner is circa 300Hz… I realise now it is the unit that is playing the full range and the horn is back filling/colouring the sound. Silly boy.

        So, I have also been thinking, if I am going to make these then I shouldn’t skimp on the unit, so looking at the PM4 A rather than the PM7 A, especially as it is the unit that will determine the overall quality of reproduction. I have not spoken to Lowther yet to get the low down on the differences and benefits, if any between these units. The Qes is about 4 times better on the PM4 A. A concern is the amount of hardware at the back of the 4. Do you know the reasoning and any calculations to determine the back chamber size, or is it “just enough” space for the driver?

        Have also been thinking bout reducing the depth to reduce the “intrusion” in to the room, and the how:

        So for depth reduction, I was thinking about using less width for the throat and taking the throat from the centre of the back chamber and having it circa 2.5cm x 2.5cm (1.387kHz), then taking that to the back at an angle, and then returning the “funnel” back to the back of he back chamber again, in parallel and then back toward the back of the cabinet and then the 1st down funnel down one side, not the back and then up the other before following the final 5 chambers where the original plan runs from back to front, if that makes sense. This will increase the horn length (increase LF) to about 5m, as well as introduce a higher frequency, more back pressure and reduced cabinet depth. It will be more complex to make, which is why I am still “thinking” about it.

        To increase the low frequency, I was also thinking of increasing the sides at the bottom and following the mouth plan of the IV to make it at least 70cm, thus getting the same LF as you mentioned you got. The attached shows a red dotted line where I want to horizontally fold the top channel and run the two rear channels down one side and up the other (blue)… But still working on the idea and how I can create it, if at all.

        Thoughts. Will this ruin the unit? I should add that I intend to use 4 x Kef B139s mounted under the floor using the underfloor space as the cabinet (seen this done in the roof, but not floor, though I think under floor would be better as it is more rigid and better sealed). This will be my sub woofer from 100Hz down. These will be run off a Quad 33 and 303 – an expensive active crossover/filter. And a super tweeter, AudioSmile Supertweeter MKII, which runs in parallel to the horn.

        When does a Mauhorn V not become a Mauhorn V….

        Best Jonathan

    • Whoa Jonathan – that’s a complete new design!
      Remember:
      – The Mauhorn designs are exponential-hypex flares that have been ‘truncated’ at the mouth end in order to maintain acceptable size. So LF output will be compromised, ie limited & lumpy.
      – However, truncated horns like this (see also Big Fun Horn) achieve greater LF performance by being room corner-loaded.
      – The throat does not function like the mouth, its size 0.25 – 0.5 of driver Sd (Dinsdale) provides pressure-damping to the driver. It also assists as a bandpass filter.
      – The back-chamber vol. combined with throat area determine low pass characteristic (Dinsdale again). Chamber vol. is also useful in ‘throat reactance annulling’ (see Edgar).

      The PM4 is a much more powerful driver & was designed by Voigt to be used with a front horn – it’s upper range ‘shelving’ is more pronounced & needs the lower mid lift that a front horn would provide. Hence, why PM7/6A are used with these cabinets without fronthorn loading. The PM4 also has a ‘magnet stand’ attached to support the huge magnet & needs a sufficiently deep & flat chamber.

      The Maus are proven designs (with design compromises) but a new design really needs consideration from first principles.
      Cheers, Owen

      • Owen
        thank you. Yes, was even wondering at what point it stops being even a Mauhorn at all.
        Useful to know about the PM4 v PM7/6 and chamber. Will look at the references about throat and chamber you mentioned for purely educational purposes.

        I suspected as much re the throat, hence how I started the subject and semi contradicting myself later as a challenge. I have been out of the game for so many decades that I have much to catch up on, with basic comprehension. Given your feedback on the throat and chamber that clears that up for me and also in an instant the ideas to reduce depth by folding the horns in the now unavailable space So that’s good.

        Mouth: I am still keen to explore the LF further before I start. 20 years on there may be further possible development of the basic design. I have some scope to have a little more height and looking in to some of the references (Big Horn Fun) you shared I may be able to squeeze a little more out of the design. Are there any other references you can suggest? Before i “go”, “no go” on the as is…

  3. So, I built them… And even my buddy with the Avant Guard system is very impressed. I have them plugged in to a Leak Stereo 20 that I replaced all the caps and resistors in and an Angel super tweeter pair and underfloor sub woofer, the later two connected to a Quad 33/303 combo system, also modified with the, sadly now gone Audio-Net upgrade. I am currently finalising the build of a plinth for my new Garrard 401, with SME S2 and Denon DL103 and a Trio/Kenwood head amp. I have been ultra busy.

    Anyway the horns – installed Lowther PM5As (I got the hint), and after much research and testing theories and playing with all sorts of tools, decided to extend the length of the horn by 12cm thus extending the range down, by making the horn taller, this also allowed me to increase the size of the mouth slightly too. I also decided that rather than have all those square edges, I would created curves using rigid plasticard (I like building models too and use a lot of this stuff, though normally much finer) and backed it to make it rigid (I was thinking of sand in plastic bags at first) with wood strips and then expanding foam. So now the whole inside looks like a colon. I also rounded the edges of the horn to make it look nicer and get that bit extra out of them.

    They look stunning – even the wife has to agree, and that was a year in the panning in itself. Sound. Well still building the system and I have a lot of work after fine tuning as they are so efficient they are picking up too much noise, and I still only have my old £20 CD/DVD player to play stuff through. BUT, I have been playing and testing and doing what I can and I have had, so far, two very critical audio aficionados also have a good listen and test, and so far all extremely impressed and surprised – I wasn’t, they were. Esp given one has spent £100ks on his system (his stylus costs more than my entire system) and both in purpose build dedicated rooms.

    So my impressions:
    Orchestra/classical music is outstanding. It is so clear and defined and sounds perfectly natural, and as if you were sitting in a room with the orchestra. The horns, hardly need the additional gizmos, they have great range and hardly a criticism. I would say the same applies to what I call all the natural, real instruments, like drums, piano, guitar, brass, strings etc, and voice. they are so detailed and accurate it is exquisite.

    Jazz/Blues, big band, etc.
    Here they start to show some slight fall off. The top end does not quite get there and the bass falls away significantly, though is there and is very accurate, going down very, very low (So far only crudely measured to 25Hz, but not using any proper equipment and that’s the limit of the tools I was using), but the level is low. I think you found the same with the IV but at 35Hz if I recall. A criticism was that the bass timing was not as accurate. However, with the addition of the parallel system giving the additional bass and super tweeter spectrum (up to 55khz), this all goes away and it’s extremely lively and full, and rich. A real delight to listen too, though I will have to attenuate or do something about the Stereo 20 as the noise, mentioned above and the sensitivity v the estimated db efficiency (estimated from some of the tools I used) of the horn makes it ultra sensitive. It goes from 0 to ear splitting in a notch.

    Rock, Metal, Live
    The system is lively and accurate and sounds truly dynamic, but the top and especially the bottom, start to make it sound a little flat. However, again, with the full system running, that is easily rectified and it sounds great.

    Would show some pics but can’t upload. I created the speakers in 3D before the build in Sketchup and also 2D in PowerPoint. I had a friend who runs a printing biz print them off full size for me, along with the cutting templates (HUGE cutting templates). Anyway thought you’d be interested. Still a lot to do. Need to crack on with that turn table.

    • Hi Jonathan – that sounds like an epic build, thanks for sharing, well done!
      The curved bends would undoubtedly be an improvement & also any increased mouth size. I have not played with a PM5.
      Pics – you could post them up on our DarkLantern hifi forum here – http://darklantern.proboards.com (It’s simple to register/join.)
      I look forward to seeing them!
      Cheers, Owen

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