OA-Transient II

By Ronald Koot
31 Dec 1995

Technical details

Principle: Terminated line
Impedance: 6 Ohm
Sensivity: 88 dB (2,83 V/ 1 m)

Speaker drivers
Bass-midrange driver: Scan-Speak 18W/8542-05 ; 170 mm paper cone
Tweeter driver: Vifa D27TG-35-06 ; 25 mm dome (called HT-275D2 in NL)

Cabinet
All cabinet parts in 22 mm MDF, and the pieces listed below are for one speaker. Drawings of the cabinets Fig. 1. Drawings of the cabinets.

Front - back : 2 pieces 1000 x 210 mm
Side panels : 2 pieces 1000 x 256 mm
Top panel : 1 piece 166 x 256 mm (with a hole for the line exit)
Internal divider : 1 piece 775 x 166 mm (inclusive a 5 degree angle)
Bottom panels : 1 piece 272 x 166 mm (inclusive a 20 degree angle). 1 piece 138 x 166 mm (inclusive a 20 degree angle)

Damping materials:
Pritex 200 x 166 mm (under the top panel)
Pritex 450 x 166 mm (on the internal divider)
BAF 400 x 166 mm (bottom of the cabinet)
A picture showing placement of the damping materials Fig. 2. Placement of the damping materials.

Crossover
The crossover frequency is 2200 Hz. The filter is 12 dB/Okt Fig. 3. Crossover schematic.

Crossover components:
L1 = 2,2 mH air coil
L2 = 0,39 mH air coil
C1 = 8,2 uF bipolar capacitor
C2 = 8,2 uF bipolar capacitor
C3 = 8,2 uF capacitor MKP
R1 = 5,6 Ohm/ 5 watt resistor
R2 = 2,7 Ohm/ 5 watt resistor

Other components
1 x Terminal
8 x Mounting screws 4 x 20 mm - for the drivers
4 x Mounting screws (countersunk) 4 x 20 mm - for the terminal

Internal cables:
terminal-filter 1 x 1 m 2,5 mm OFC
filter-bass/mid 0,5 x 1 m 2,5 mm OFC
filter-tweeter 0,5 x 1 m 1,5 mm OFC

Description
I developed this design for a small audio firm called Original Audio which had a customer who wanted a design with this driver. This because the customer had bought a large amount of the Scan-speak drivers and wanted to sell them. (The customer sold his whole stock very fast). By the way, everybody is free to use this design for your own personal use.

It uses a 7"Scan-Speak 8542-05 driver and a Vifa Tweeter the D27TG-35-06, in Holland also known as the HT 275D/2 (we use different numbers!). The cabinet is made according to a principle called a terminated line. I know that this is a kind of strange principle to use for such a driver but I had to come up with a reasonable amount of bass (design goal). I have also build this speaker in a bass-reflex box with a net volume of approx. 16 liters. This speaker sounded very analytical in the low freqencies but not as nice as the terminated line, it lacked a bit of natural warmth.

The terminated line which i called Transient II, has a much warmer and still very analytical bass performance. The mid is up-front but it also gives, together with the high, a lot of spaciousness. Transient performance is good. The tweeter gives a little too much at the end of the spectrum which gives the system, when used with certain electronics, a bit of bright, 'harsh' sound.

The damping material is long fiber wool or BAF-wadding (about 400 grams a cubic meter). The drawing, said wool but the BAF is easier to use because it stays in place and do not settle like the wool. The other material called 'Pritex' is a brand name. It's a kind of synthetic foam with an egg shape, it weights about 30 kg a cubic meter and has a height of about 40mm.

If you have any questions or remarks i will be pleased to reply on them.

Ronald Koot

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