MY REFERENCE SYSTEM - Bo Hansson

To be able to make good recordings, it’s important to have a good listening system to judge the work. In this case, a room was specially built with non-parallel walls and a soft ceiling to reduce highQ resonances.
The speaker system was inspired by articles in Hi-Fi News in 1966 written by Rex Baldock, who was a leading star for many of us amateur speaker makers. I visited Rex together with my friend Hubert Shutrick in the beginning of the 70s to listen to his system, and I was very impressed. Hubert is a professor of mathematics and was more prepared to absorb the message in the article ”Acoustic Compensation” written by Rex. Hubert helped me with the calculations, to make the bass horns and room work together, in the system I built in 1972.

The bass system consists of two 6 meter long bass horns built of bricks and concrete. The opening comes up underneath the couch. The horn has hyperbolic expansion and goes down to 18 Hz; you can’t hear very much down there but it shakes you and the window glass.
The bass horns are equipped with a pair of 15” Klangfilm drivers; they have an open air resonance of about 80 Hz which is lowered to about 20 Hz when fitted in the horns.

Pictures of the bass horn from the opening in the room 3,4 and 5 and from the cellar pictures 10, 11 and 12At the same distance as the length of the bass horns 6 meters away, the midrange-treble is fitted. It is similar to the midrange horn in Lowter Audiovector equipped with a pair of Lowther PM 4 , and mirroring to the sidewalls as it’s aimed to do. This has come out of my contact with Donald Chave, Lowther Manufacturing, but was originally inspired by an article by John Crabbe in a book ”Five speakers and how to built them”.

I think it is from a series of articles from HiFi News from the late 60s, but that was before I knew about the magazine. Pictures of the midrange/treblehorns 1 and 2.
The midrange-treble is driven by an Opus3 Candela valve amplifier, and the bass horns by a British made, Richardsons valve amplifier which I bought i during a visit to the UK. A simple 2nd order Hp and LP filter on the input on each amplifier takes care of a x-over at 150Hz. Pictures 5 and 6.
I listen mostly to analog records and master tapes. I have thousands of classical vinyl records but not more than 50 CDs!

Picture 1
Program sources are Opus3 Continuo turntable with Cantus tonearm, connected to my nuvistor phono stage and a Stax SR12, (but it is just the cabinet since the electric circiutry is totally rebuilt). The headphone amplifier is still there since I’m using electrostatic headphones for editing/mastering our recordings e.t.c.
The rest is a Dynatuner and a Sony El-7 Elcaset, sometime used for documentations when I don’t need to take the whole recording setup with me, and finally a Nakamichi 682 cassette tape recorder.
Picture 8
The mastering is made on a Telefunken M15 tape recorder and previously on a Meridian CD-R 1 recorder. The Meridian sounds very good to my ears and I plan to use it as an AD-DA converter together with the Macintosh computer and TC Spark editing software. Picture 9.

The recording eqipment is very simple- but efficient. All Opus3/Rauna recordings are made in acoustic environments with just one stereo microphone. We record all sorts of acoustic music from solo instruments, harpsichord, recorder, piano, singer e.t.c, to full symphonic band orchestras or large romantic style organs with huge bandwith and dynamics. A word to those who want to make good recordings or pictures - ”dont care that much about the brand on the equipment but on the result” (Henri Cartier-Bressons, photographer)

The microphone, like most of the equipment I use, was built by myself. The diaphragms are rectangular types (supplied by Pearl, a Swedish microphone manufacturer) and the amplifier is of my own design, with nuvistors and transformers (supplied by Lundahl transformer in Sweden). The goal in mind with this mic is to obtain a very wide pickup area with high sensitivity (no proximity compensation).

The microphone amplifier is a fully balanced, totally nuvistor equipped with transformers on the in and outputs.
Tape recorders used in the field are two Telefunken M28Cs, very much rebuilt and modified. They are extremely reliable and keep performing even after rough handling. Another reason for using the M28 is that it’s moveable and easy to repair in the field --- which has been necessary a few times. Yes the playback is better on an M15 but is good enough on the M28 and the record amplifier is, in comparison with other analog tape recorders, still one of the best sounding in the business.

Pictures 13-17
Most of the monitoring/listening during a recording session is done with electrostatic headphones, but for a proper setup I’m using speakers from my own production, and at the present, Opus3 Chaconne II is in use. We need to use reference speakers in order to make the setup work. That’s the only way to enable proper positioning of the musicians and microphone in order to evaluate the balance between direct sound and reverbated sound.
During the recording they are used mostly to listen for musical mistakes and unwanted disturbances which are easier to detect with good headphones.

This recording eqipment has been used for hundreds of records, concert documentations and recording sessions.