Howdy!
I'm going to built a 3-way involving:
Peerless 830868
Vida TC9FD
ScanSpeak D2010/851300
The enclosure will be made of 4mm (9mm for front/back baffle) plywood, 4mm MDF and 8-16mm of bitumen laminated together. No bitumen on front and back baffle. So a thin-wall construction, no bracing. The front and back wall will be screwed on. Enclosure will be about 22l, tuned around 30Hz. The F3 point is around 65Hz. This will get low group delay but a bit more bass extension than closed. Enclosure dimensions will be around 226x300x478 (WxDxH) on the outside. Mid enclosure will be a 12cm diameter steel half-sphere damped with bitumen, around 1l volume. Mid and tweet will be off-center, enclosure width is the width of woofer flange.
I've got measurement gear, so I'll figure the XO when the enclosure is done. Currently thinking about 700Hz&5000Hz XO points, but we'll see. XRK971 proved in his experiments that the little Vifa full-range works perfectly well surface mounted, so I'll surface mount woofer and mid, and flush mount the tweeter. With the lower crossover point, Troels proved in his site that time-alignment of acoustic centers does not matter. With the higher point, I tried to measure the acoustic centers by analyzing the impulse responses of TC9FD and D2010 yesterday; they were remarkably close together. Flush mounting should be sufficient to align them, and I can tilt the speaker if it needs to increase.
So this thread is a sanity check before I order the boards cut and start building. Is there anything I missed and should consider before I embark on this journey?
I'm going to built a 3-way involving:
Peerless 830868
Vida TC9FD
ScanSpeak D2010/851300
The enclosure will be made of 4mm (9mm for front/back baffle) plywood, 4mm MDF and 8-16mm of bitumen laminated together. No bitumen on front and back baffle. So a thin-wall construction, no bracing. The front and back wall will be screwed on. Enclosure will be about 22l, tuned around 30Hz. The F3 point is around 65Hz. This will get low group delay but a bit more bass extension than closed. Enclosure dimensions will be around 226x300x478 (WxDxH) on the outside. Mid enclosure will be a 12cm diameter steel half-sphere damped with bitumen, around 1l volume. Mid and tweet will be off-center, enclosure width is the width of woofer flange.
I've got measurement gear, so I'll figure the XO when the enclosure is done. Currently thinking about 700Hz&5000Hz XO points, but we'll see. XRK971 proved in his experiments that the little Vifa full-range works perfectly well surface mounted, so I'll surface mount woofer and mid, and flush mount the tweeter. With the lower crossover point, Troels proved in his site that time-alignment of acoustic centers does not matter. With the higher point, I tried to measure the acoustic centers by analyzing the impulse responses of TC9FD and D2010 yesterday; they were remarkably close together. Flush mounting should be sufficient to align them, and I can tilt the speaker if it needs to increase.
So this thread is a sanity check before I order the boards cut and start building. Is there anything I missed and should consider before I embark on this journey?
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IMHO not a good choice of drivers. In particular the woofer-mid couple, as you have to fully correct the baffle step effect on the woofer only to have it padded down to the mid! (90 vs 84 dB).
Another point of attention is the box/tuning, as 22L is way to small for the woofer if you also want a low tuning, you end up with a too long tube (and it won't really act as you expect), or with air chuffing.
Last, I won't cross the mid higher than 4KHz, for proper dispersion and lobing.
All in all, if you really need a box no bigger than 22L, I'd opt for a 6.5" driver for better bass extension, or a closed box for a 8" driver.
Ralf
Another point of attention is the box/tuning, as 22L is way to small for the woofer if you also want a low tuning, you end up with a too long tube (and it won't really act as you expect), or with air chuffing.
Last, I won't cross the mid higher than 4KHz, for proper dispersion and lobing.
All in all, if you really need a box no bigger than 22L, I'd opt for a 6.5" driver for better bass extension, or a closed box for a 8" driver.
Ralf
Not in stores around here. Besides, the drivers for this project are already in hand
Closed is also a possibility. I don't have to get spectacular bass out of these, as they will be used with a subwoofer anyhow. I have also wondered about the TC9FD and woofer coupling. Need to test and measure more. The woofer enclosure size was based solely on keeping group delay down.
About lobing, it's bound to happen with any higher crossover point. It's physically impossible to get the tweeter and mid so close to eachother that you cancel it unless you go coaxial.
If you use a sub I really don't understand why the complexity of a 3-way, you would be better with a 2-way with a 5"+1" drivers (cheaper and smaller).
That's true, but you aren't forced to a so high crossover point, 3.5-4KHz would work better, and you could also use a small faceplate tweeter.
With drivers already purchased it is a little too late to ask for a sanity check ;-)
Ralf
I usually buy my drivers second-hand for half the price or less. If the project is not suitable they go back into storage to wait for better ideas. So not a large financial investment
The idea of the thread is mainly to check what can be done with the things I already have.
About tweeter lobing: if the XO for example is set to 10k, the tweeter will lobe terribly. Even in 3k, the tweet-mid CTC distance should be under 2,8cm, which in practice is impossible. For a figure-of-eight lobe, it would still have to be about 5,6cm. Very hard to achieve. Practically, the only reasonable solution would either be a FAST or an XO around 1k to a waveguide-loaded tweeter. Still, speakers exist with higher XO points and they seem to work and measure well.
The idea of the thread is mainly to check what can be done with the things I already have.
About tweeter lobing: if the XO for example is set to 10k, the tweeter will lobe terribly. Even in 3k, the tweet-mid CTC distance should be under 2,8cm, which in practice is impossible. For a figure-of-eight lobe, it would still have to be about 5,6cm. Very hard to achieve. Practically, the only reasonable solution would either be a FAST or an XO around 1k to a waveguide-loaded tweeter. Still, speakers exist with higher XO points and they seem to work and measure well.
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