TNT-Audio inter.views Bert Doppenberg

Inter.view with Bert Doppenberg, from the Lowther Club - Netherlands

TNT-Audio >
Could please introduce yourself to our readers? How did you start to get involved in audio etc.

BD >
I am Bert Doppenberg, 40 years of age and I am living in a nice quiet village in the Netherlands.
I started my hobby with dismantle (demolish mostly) all kind of equipment to see how it works when I was about 15 years old.
I didn't have any money those day's and got the gear from all over the place. I managed to learn a lot and used things out of them for other purposes. I even used the loudspeakers from old radio and TV-sets to built my own loudspeakers for my first (mono) cassette player.
This to get more sound out of it instead of listening to that one tiny built-in speaker.

During the years I managed to spend some real money on items and eventually got more success in creating better sound out off build enclosures. There where all kind of loadings possible AND used for the speakers (Closed, TL, Reflex, Daline, horns, etc.).
I always liked the horn approch most, especially for the low frequencies. If you ever heard a good designed horn for the bass then you'll know that it's the only way to go!

At some time I came accross some Lowther drivers which had something in them I really liked! The openness, detail and capability to play real loud without give in was remarkable and just what I was looking for.
I always wanted to use a front horn on top of my sub horn but couldn't find the right driver that could do this job alone (wide-band) without adding tweeters or fillers. During my search for better sound and all kind of experiments, I learned that each added (or divided) item in the signal path did loose something (coherence, detail, etc.).
So I started experimenting with the Lowther drivers in several not-alike front horns and in between some back loaded horns.

TNT-Audio >
Lowther drivers seem to be all the rage nowadays. One of the reason for this vast interest is because of the popularity of SET, or low powered tube-equipped, HiFi amps.
Could you please tell us which are, according to you, the main "pluses" of this approach (low-powered tube amps + high-sensitivity loudspeakers)?

BD >
Low powered SE tube amplifiers are much less complex then their Solid State (transistors) "brothers". The more simple the design, the less items are used in the signal path.
I stated this before, each extra item is changing the original signal and mostly replaced by something else or completely lost!
An example is the feedback used. Just there to correct something that went wrong in a previous stage somewhere in this same amplifier????

Properly designed amplifiers do not need feedback at all which makes them sound more open, transparant, spatial, etc.. If one needs an amplfier with more power then there must be used more components (parallel tubes and/or transistors, more correcting C's and resistors, etc.).

Okay, the most simple designs like SE tube amplifiers do not have a lot of Watts to give......but what the heck. If you use high sensitive loudspeakers, no problem!
But finding the right high sensitive loudspeaker isn't that simple. Mostly big and ugly or rather expensive...

TNT-Audio >
Do you think are there some serious drawbacks, as colourations of the mid range and lack of deep bass?

BD >
All back loaded horns do suffer from colouration in the low-mids. Mostly because the horn isn't developed right (reflections, resonances) but also due the time delay of these horns.
Deep and powerful bass can be created with a large horn (big mouth and long like the Carfrae), the Hedlund horn is long but the mouth isn't big enough to give the true dynamics in the mid-bass.

TNT-Audio >
To my knowledge, only big, horn-loaded enclosures can make a Lowther sound with good, powerful and deep bass. For example, the Hedlund horn and the Carfrae, just to name the first ones that come to my mind you've just mentioned.
What's your opinion on this topic? What about Voight pipes, TQWT and the like?

BD >
Only big horn-loaded cabinets are able to give deep powerful bass, smaller horns do not go deep (>50Hz) and do not sound complete.
One main drawback of back loaded horns is the length, the longer the horn, the later (time delay) the sound will come out of the horn mouth.
The TQWT (is Voight pipe!) doesn't have enough sensitivity to correct the falling response down in frequency (using Lowther drive units) to create a balanced sound unless the driver is facing up.

TNT-Audio >
Can you summarize the main ideas behind your Oris 150 loudspeaker?

BD >
Preventing the disturbing time-delay problem by adding a seperate sub woofer which is capable to give real deep frequencies in a smaller cabinet without loosing the dynamic feeling (the harmonics of the bass are produced by the horn), correcting the rising response of the Lowther drive units (adding more "body" to the sound), the increased sensitivity (to be able to play louder with the same power delivered by the amplifier or give less dissortion using only half of that power), less problems with reflections due the walls of the listening room (gaining perfect and detailed placement of instruments and vocals in the right proportions).

TNT-Audio >
Suppose you want to build an inexpensive no-crossover loudspeaker that can sound fine with low-powered SETs. Where would you start from?

BD >
Then the Fostex (ACR) FE 103 S in a TQWP or reflex cabinet would be a very nice start.
This driver isn't expensive, has a 92dB sensitivity plays up to 20k and needs no filter. The only drawback is the small cone which makes it almost impossible to have a party with them...

TNT-Audio >
Are you planning to design different horns for other drivers such as ATDs and such?

BD >
Not for the moment. I do not like horns which are too long and having a small throat (using smaller drivers).
Making the horn shorter will rise the lower cross-over with the need for a extra driver, filter, etc....

BD-Design: Sales@bd-design.nl
Homepage: http://www.bd-design.nl

Courtesy by Bert Doppenberg for TNT.