fairaudio: Despite having been in business for 30 years, the brand Blumenhofer Acoustics seems rather newer. How come?


Thomas Blumenhofer: The brand is newer. It launched officially in 2006. But that doesn’t imply an earlier vacuum. It really all began at the end of the seventies when I installed a proper system in my rusty VW Beetle. It got real loud but remained rusty.


fairaudio: Could you parcel your audio biography into chapters and if so, what remains of the earlier focus?


Thomas Blumenhofer: Hobby eventually became profession. Hifi and pro audio both factored from the very beginning. Older audiophiles might remember my collaboration with Willie Bauer of dps turntable fame. Our omni FJ Om speaker is the final survivor of those days. I initially was very active in pro, meaning the design, construction and installation of sound systems in discos and concert halls. If you visit the Deutsche Theater in Munich, you’re listening to a Blumenhofer installation. We’re a bit  proud of that. If you go for a beer afterwards in the Löwenbraukeller, you’ll run into us again. During a specific period when we were known as Blumenhofer & Schraub, there wasn’t a disco or club in the area we weren’t involved in. Another interesting sector —remember, we’re in Bavaria—were marching bands. They were clueless about acoustics so (laughs) we helped. Man, I can’t count the beer tents I helped set up.


Today I’ve given up personally installing pro systems. Done 'em far too long. But I still help design them and occasionally even build custom sound reinforcement speakers. In the 80s, it was car audio but that’s died since and we left that sector in the mid 90s. But it was an interesting period. We nabbed a number of SPL medals. Our record was 177.7dB. Since then I’m fully focused on home hifi. I want to translate my experience of years’ worth of stage and concert experience into the home. Here the famous live factor is tantamount and that’s why my speakers look as they do.
fairaudio: They're huge.


Thomas Blumenhofer: You mean the Clara Luna?


fairaudio: Yeah. What’s that monster weigh?


Thomas Blumenhofer: About 170kg each. Some people have high standards.


fairaudio: Others couldn’t swing the financing. They're a mean €95.000 the pair if I got it right?

Thomas Blumenhofer: Given the immense R&D cycle and hand-made built-to-order fabrication in Germany, such an excusive design can’t be calculated any other way. Incidentally, we’re working on something even bigger temporarily christened Little Big Horn. Trust me, there’s demand or we’d not go there.


fairaudio: Sounds like an Indian Chief.

Thomas Blumenhofer: (Laughs) Kinda. For bass we run twin 65cm units in a corner horn configuration. The midrange horn mouth is ca. 1.80m in height and 1 meter in width and loaded by six 20cm drivers. The treble will likely be based on a TAD unit. Given the size, this obviously will be a modular system. I doubt we’ll exceed one ton in mass though. [The treble horn in the photo is for show only. The actual unit will be rather more ambitious and bigger.]
fairaudio: Let’s forget about the big boys and cover a range most can still aspire to. You presently have three ranges in the catalog, the smaller Satellite, the central Fun and the bigger Genuin. But I’m somehow confused by the pricing scheme (from €1.500 to €35.000/pr) since one Fun model is significantly more expensive than the smallest Genuin.


Thomas Blumenhofer: It doesn't work like that. The different ranges aren’t sorted by price but technical concept. The price is simply a function of build cost. The Satellites are traditional and without horns. The Fun models are full horns, i.e. upper horns with back-loaded woofers. The Genuins combine upper horns with bass reflex bass.


fairaudio: And why the split into full horns and ported designs?


Thomas Blumenhofer: If the room is appropriate and the customer pays attention to setup, I personally believe that full horns can achieve better results particularly in the speed and impulse response of the bass. Air coupling is more direct which accelerates bass and improves precision. But setup is critical. Not that the Fun models are fussy but the bass-reflex Genuin models are even easier to place.


With comparable bass enclosures, a bass reflex design is less complicated to build than a back-loaded horn and hence more cost-effective. So it’s sensible to offer both. A one-size-fits-all approach doesn’t exist, never mind that certain people find good horn bass... well, let’s say unusual. It’s not just a matter of room and money but also personal taste. No surprise there.


fairaudio: So specific offerings to meet specific tastes. No unifying design philosophy then?


Thomas Blumenhofer: That’s not how I’d put it. There’s common ground beneath all my speakers. Whether that makes it philosophy is another matter. I’d probably call it the same signature.


fairaudio: Like how?


Thomas Blumenhofer: I’d have to cover certain fundamentals to answer that.


fairaudio: By all means.


Thomas Blumenhofer: Okay. Technical concepts, measurements and such are valid necessary tools. But the beginning or better, my ideal, is live music. Many say that. So it sounds trite to mention it. I’ve spent half my life around live music on a daily basis however. I think I know what it sounds like. When musicians perform in front of me, there’s a particular sensation of presence. Live music is simply there without hesitation and conveys a bevy of emotions put out by the performers. This sense of unmitigated presence is, in my opinion, the foundation of live music. My concern is how to transfer that into the living room. That’s my signature. All my speakers pursue the same goal and depending on limitations set by size, price and so forth, inform specific design decisions.

fairaudio: What are the core requirements your speakers all must meet?


Thomas Blumenhofer: To even approach the live vibe, a speaker must have excellent impulse behavior—traditionally called ‘speed’—and track dynamic changes realistically, i.e. not compress when the orchestra or band get really loud. If dynamic shifts stop at a particular level to homogenize, anyone with still a good fix on the live experience will recognize it as fake. It’s also important to convey very fine dynamic fluctuations. Here it’s helpful when the speaker doesn’t immediately consume 99% of the amplifier’s power. That’s about the medium efficiency for most speakers. So a high sensitivity is important. Given these criteria nearly inevitably desposits you at horns. In my book, they’re most suitable for this purpose.


fairaudio: Well, many relate ‘live’ also to having a violin sound like itself and... er, not everyone associates horns with that.


Thomas Blumenhofer:  True. So that precisely was a central concern for my designs. The horn wasn’t to sound like a horn, meaning it was to lack the typical colorations, distortions and reflection issues but retain the assets of speed and dynamics. That’s where the real work began.
A certain weakness for valves seemed quite evident

fairaudio: What distinguishes your horns from others? Geometry, drivers, crossover? What’s the vital difference?


Thomas Blumenhofer: There isn’t one. It’s how a number of parameters interact. I’ve not discovered a silver bullet. It’s lots of little tricks and how one weaves them all together.


fairaudio: Can you get more specific?


Thomas Blumenhofer:  Let’s inspect the treble horn for example. It won’t work if you mount it to a different driver. Okay, it’ll make noise but won’t satisfy. We do use a common compression driver but modify it with, amongst other things, our own compression chamber.


fairaudio: What should I envision?

Thomas Blumenhofer: We take the stock driver, remove its chamber and machine a new one from wood. Ours uses a different profile and as such, acts differently. We even treat the chamber with a special treatment I won’t divulge. But geometry, volume and material of the new chamber are vital to pure and natural timbres. Just as important is the actual driver and the horn. That’s where the interplay and weaving together of these factors enters.  Again, you’d be disappointed if you took our driver and chamber and mounted it to another horn.


fairaudio: What can we say about the horn profile?


Thomas Blumenhofer: It’s quite special and took a lot of work.

fairaudio: I’m somewhat allergic to the work ‘special’ as it doesn’t really say anything.


Thomas Blumenhofer: Quite so. It’s a lot of work to get right. I’m not about to furnish the lazy competition with free ideas.


fairaudio: Well, I didn’t really ask for a schematic.


Thomas Blumenhofer: You need to remember that I don’t enter a fancy formula into some software program and presto, perfection. It’s more that I have an idea according to which things should work. This leads to a prototype, measurements and auditions. Usually it won’t work properly. Now you shave off horn material in certain places and listen again. This could point the way forward. Or things get worse. Back to the beginning. Prototyping is a drawn-out iterative process. For the Clara Luna, I spent four months and considerable capital nailing it. Ditto the pressure chamber and crossover. You might appreciate why I’m deliberately stum on details. Others might by now appreciate why the prices have to be what they are.


fairaudio: You use the term divergent horn. What’s that?

Thomas Blumenhofer: It relates to the folding and expansion ratio of the back horn. In general, this works by loading the rear driver output into a pressure chamber that couples to and thus drives a horn. This horn is folded thrice and 'divergent' relates to its geometry. Each section expands in a linear function but at different flare rates. The sketch shows the basics but obviously is neither to scale nor otherwise accurate.  All this is for the same reasons – to retain horn dynamics but eliminate distortion. Sourcing the right woofer to drive our horn was problematic to get no distortion. So we had to build our own. Again.


fairaudio: You build your own drivers?


Thomas Blumenhofer: Not exactly. Our 17cm and 20cm woofers were jointly developed with Norman Gerkinsmeyer of A.T.E. who supplies them.


fairaudio: What’s special about those?


Thomas Blumenhofer: Let’s start with the problem. The rear of a back-loaded horn driver must withstand considerable forces since it’s supposed to drive a stout air mass. The air column inside the horn exerts real pressure on the diaphragm, albeit asymmetrically. Depending on the position of the membrane, the pressure is different. This pressure variation undermines pistonic linearity above a given frequency. You get partial resonance modes. This causes distortion and reduces sensitivity since part of the driving force is spent on those unwanted modes. No commercial production driver did the job properly – and we tried many.

fairaudio: How do the A.T.E.s go farther?


Thomas Blumenhofer: The secret is in the membrane. Both the 17 and 20cm unit run sandwich layering. With the 20, it’s two layers of paper with a central foam, with the 17 paper becomes foil. These are extremely light but hard membranes which can withstand the internal horn pressures.


fairaudio: On material, I spotted in your downstairs production area bass reflex ports built from MDF and enclosures made from Ply. Wy those choices?
Thomas Blumenhofer: MDF is audible. The problem has to do with resonances.


fairaudio: Okay, but any material resonates. What makes Ply better?

Thomas Blumenhofer: Take a sine wave generator to an MDF box and push up frequencies. At a particular spot usually in the midrange there’ll be a very nasty spike. Ply also has measurable modes but the vital difference is, those are spread over a far broader area, the actual energy is far lower and does not occur in the midband.


fairaudio: The final question – what’s planned for new products? Are existing models due for an overhaul? Is anything new in the pipeline?


Thomas Blumenhofer: I did mention the Little Big Horn Indian Chief already but that’ll be in the works for another year. In the Genuin Series, the FS4 entry-level model is currently being reworked. It’ll be a completely different speaker with the Fun 17 tweeter horn and a bass-reflex woofer.


The Fun Series came out so good, no changes are planned. The final tweaking of the Big Fun ended a year ago with a few tweaks on the crossover and pressure chamber. Finally, there’ll be a 2-way Clara Cinema for the home theater at music-reference quality. And there’s a surprise for the Munich show but it won't be a surprise if I talk about it now...

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Blumenhofer Acoustics website