Since I am already using an active crossover system with two SS amps, the choice for the full range driver opens up to just about any available 3" or 4" model. In reality the choice of full range driver could also include many 6" and even 8" models. The lure of an inexpensive two way OB design with enough flexibility to not lock me into a single driver combination convinced me to finally build this experimental OB system late last summer. Baffle Construction Details : Over the years, I have accumulated a nice stash of veneered plywood in various sizes and thicknesses. Digging through my collection, I found enough scrap pieces to build this 20" wide by 38" tall OB speaker system. Recognizing that I wanted to try a variety of full range drivers, each requiring a different diameter cut-out and pattern of mounting screws, I devised an easily removable baffle arrangement.

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It became somewhat nasal and thin bodied. Compared to no capacitor, the uF solution worked best, but it was still slightly more pronounced in the higher frequencies. The conclusion is to run the Visaton B unfiltered for critical listening, then I might have a switch connecting uF in party mode when I expect high sound levels. Tolvan Edge software should show me what is going on with this shape of baffle.

I also plan to test them with HolmImpuse to see if I get a reasonable frequency curve. The next step is veneering the front and finding a suitable speaker cloth. The veneer I used had a really large knot at one end. I decided to align the knot in the center of the panels to make a reference to the sound pressure from the speakers. The panels were cut to size, then veneer and panels were sprayed with contact glue. Once the glue had dried minutes the veneer was rolled on with a 10kg aluminum bolt that was lying around the shop.

Here are the speakers with a first look at the panels. While I am waiting for the speaker cloth to arrive from Tube Town in Germany, I have been exploring ways of smoothing the rising response of the Visatons high end. My first approach is digital filtering. Although not as well described, technically, to assure you of high fidelity processing, Hijack has far greater flexibility than PureMusic. Hijack Audio Pro is based on plugins. The big deal maker, apart from price is that I can work on global sound out from the Mac, instead of just iTunes, and yes, they are mac Grill cloth arrived!

I cut a front panel of 9mm plywood. Stapled the grill cloth along two edges taking care to keep the treads lined up. Then using as much force as I could, stretched the grill and stapled the other two sides. The whole process took about 50 minutes per panel, and my fingers hurt! The grill was tight enough to bounce a coin about 10cm in the air.

On the rear side I tried spraying the metal grill with gold paint. It worked out very well. I have not decided if I will make a rear frame like on the Wharfedales. Here they are for the first time in my living room.

But they are making nice music. There is a light hiss and the strong highs of the Visatons otherwise everything sounds good. Now the time has come to explore filtering the Visatons rising highs. There is a careful trade-of to be made. Unfiltered the Visatons sound very clear and revealing, but on the irritating side. Once you start dropping the highs, things very quickly turn woolen and uninteresting. The result however is to just take the edge of the annoying highs of the Visatons using a parallel notch filter centered at Hz, damping 2 — 3dB.

Things are still clear and open, but the irritating part is gone, and I have not lowered the SPL to much to drive the speaker with a small amp. Translating these values into physical components I chose the values 0. Using mh-audio. The notch filter is installed and working as planned. The dotted lines are the phase, while the full line is frequency. The sudden fall-off at 10kHz is due to the sound card stopping there.

The frequency plot i smoothed to 6dB increments. A raw plot is hairier. The measurement is done in my livingroom with one edge of the speaker along a solid wood railing to a staircase. This accounts for the rising bass. There is a worrisome dip from — Hz otherwise I am happy with the result.

It can not simulate two drivers with different diameter in the free version of the EDGE, so in stead of mm and mm diameter I have chosen mm diameter for both. Otherwise dimensions and speaker layout are the same. Comparing the two frequency curves you can see that Edge predicts an earlier increase and fall off in the low frequencies, than I have measured.

Factors contributing to the difference are that EDGE does not take speaker element and crossover characteristics into account, and that the baffle was bigger because it was standing by a one meter high wall.

Room gain accounts for the rise in the lower frequencies. The longer baffle moves the simulated peak down to about Hz. Listening impressions from this filter configuration: Lowpass Hz to the Eminence Notch filter centered on Hz -3dB from Hz There is still some mid freq. Phase cancellation my contribute to the Hz dip. I would like to try a second order filter according to Kings OB design paper possibly with a higher crossover frequency.

The parallel notch filter takes the edge of the Visatons, I might experiment with more attenuation, just for fun. As the speakers are today they sound strong in the low frequencies, they have a forward mid to high without being annoying. The result is a lively engaging speaker, that rocks, plays classic music an female jazz voices just as well. So I have ordered parts for a second order filter for the Alpha Similar values to what Martin King recommends in this illustration from his paper see above.

Later I will test it and post a new curve. UPDATE 17 august I have been busy with RC planes and helicopters since december, so there has been little progress here, but today I installed the second order lowpass for the Alpha 15 and the notch filter for the Visaton.

It tried out several resistor values of dampening, but ended with a carefull 2 ohm to just take the edge of the Visaton top, without loosing any trebble distinction. Share this:.


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