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Juspur 18th October 2012 12:35 PM

The portable, cheap, fullrange-driver open baffle
Hi folks
Let me introduce a fast, cheap - and surprisingly fun & listenable project :D

- a great weekend project !!! :eek:
The driver is a modified 8" fullrange driver (Monacor SP-205/8)

The loudspeaker is designed to stand on the floor, and in a small room (up to about 15-16 m2 / 150-160 square feet). It is necessary to stand on the floor in order to get enough bass support. The baffle is suppported with an angle bracket on the back - which you can adjust up and down to find the vertical baffle angle, you think sounds best.

If you enjoy "live"-sound, this may just be the perfect fit.
In addition, the speaker is quite portable, and sounds better than small PC speakers, especially if you are playing loud, and just want a fair amount of bass ...

A little further images to stimulate the appetite...

What you actually do is to cut off the Whizzer-cone with a large pair of scissors. Cut in a spiral and cut several pieces. Do not worry - it's NOT difficult - and the job is easily done. The original function of the whizzer cone is to provide more treble - but whizzer cones in general sounds awful IMHO.
The Monacor SP-205/8 with original whizzer cone
Closeup: Monacor SP-205/8 without whizzer cone

You simply just have to saw a 18.0 cm / 7" hole for the Monacor in the middle of the plate, mount the driver, speaker terminals, cables and the hinge bracket with a single screw. I have attached a handle - your funkyness decides whether that's a good or bad idea :D

Why is just the Monacor SP-205/8 used?
- When creating open baffle speakers, it's important that the driver you want to play bass has a high Qts, high sensitivity, low fs and a nice xmax. Normally a Qts around 0.7 is recommended as being ideal. A lower Qts makes the speaker roll off faster in the bass-region (ie less bass), a higher Qts causes the driver to roll off more gentle (more bass). Monacor SP-205/8 is in a German forum measured to have a Qts of about 2.5, which is pretty wild high.

"Normally" you can not make that narrow baffles (10" baffles), and get any bass. But this high Qts makes the speaker roll off very slow. The sensitivity is around 94 dB, so you can easily use even the smallest amplifiers (I use myself a TriPath 2020 amp with good results and high SPL).

I have tried to make an informal test of the low frequency curves using Online Tone Generator - Generate free low frequency tones to test your subwoofer.. And the level is disappearing below 80 Hz.

But, when playing music, I don't feel that I lack bass - what there is, is both sufficient and nuanced. Try these samples from Dieter Ilg's album "Bass" with acoustic bass here: Bass, Dieter Ilg (Arrang.) - WiMP

For each speaker, use
- 1 Monacor SP-205/8 full range driver (which you must modify - you must remove the whizzer cone). The device costs about 15-20 US$, and can be found cheaply on eBay - eine der größten deutschen Shopping-Websites
- 1 piece of wood, 25.5 x 25.5 cm (10" x 10") for baffle,
- 1 set of speaker terminals and some cable + screws.
- 1 angle bracket so the speaker can stand safely.
- Drill, Jigsaw, long scissors, soldering iron, screwdriver

Good luck - I'm looking forward for your feedback :D

Godzilla 18th October 2012 01:12 PM

I think this is very cool. Do you use two or just one for mono?

sreten 18th October 2012 01:29 PM


Fold out wings also acting as the stand will help the bass somewhat.

rgds, sreten.

Juspur 18th October 2012 02:17 PM


Originally Posted by Godzilla (
I think this is very cool. Do you use two or just one for mono?

Hi Godz
I've made two. Excellent imaging and 3d-room :-)

Juspur 18th October 2012 02:28 PM


Originally Posted by sreten (

Fold out wings also acting as the stand will help the bass somewhat.

rgds, sreten.

Yep - thank's for the advice :)

mondogenerator 18th October 2012 05:13 PM

cool. I finally know what to do with these visaton ws25

norman bates 18th October 2012 11:02 PM

I can't see the pictures.

soundaatma 19th October 2012 12:16 AM

The Betsy is another great candidate for similar low cost OB applications. No mods needed, perhaps slight BSC and it sounds just great....almost full range.:D

zman01 19th October 2012 02:29 AM

Smart project!

owen 19th October 2012 04:41 AM

Simple, and effective!


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