Dual woofer OB configurations, which and why?

[oktyabr]

Since you're looking at a two way (wide band and woofer) I'd suggest the miniDSP 2X4 board. 2 in and 4 out for $120 to your door. I think for another $20 you can get the version with the case, but this is DIY anyways! The nice thing is if/when you decide to go 3-way, or add subs, you can add another board to it. There's also a digital in board. For $300 I've got a 4-way digital in active crossover.......

You can also create filters for the miniDSP with REW, and someone is working on some Excel spreadsheets for custom biquad filters. There are also several currently available....

I've been using miniDSPs for a year now and and am quite happy with their capabilities and sound.

Thanks! I did take a look at the miniDSP product once... I'll have to look again

 

[Pano]

Wow. Has anyone priced passive components lately (rhetorical question, I'm sure)?!?!?

Yes.

Expect to spend a lot on the crossover. Copper is $$$ these days so the big inductors needed for OB will cost you.

FWIW, I found it very difficult to get good results on OB using the DCX. Maybe I just didn't understand what I was doing - OB crossovers are strange - but using a big coil on the woofer always gave better results. For more normal box speakers, it was much easier.

Basically, you have to set the woofer crossover point much lower than your desired acoustic point. Because of the rising response, you need the low point to flatten it. I found that near impossible to do with EQ and shelving filters, tho I don't know why.

 

[Radugazon]

.....but using a big coil on the woofer always gave better results....

Maybe because the Qts skyrockets with the (20 mH and more ?) inductor . BTW, I have to trust you but don't understand why you can't cope with this when using the DSP.

Or is it that in despite of a correct (and correctly) measured response you feel that something is going wrong ? Here I must confess similar thoughts. I had H frames that always colored the sound whatever I did with the DSP.
Solution : no more OB and it's going fine.

 

[natehansen66]

FWIW, I found it very difficult to get good results on OB using the DCX. Maybe I just didn't understand what I was doing - OB crossovers are strange - but using a big coil on the woofer always gave better results. For more normal box speakers, it was much easier.

Interesting..........to me it's quite easy! High shelf centered at about 200hz of anywhere from -6 to -12 db flattens it nicely, and a high q notch to flatten the peak. Standard crossover implementation from there............Although, I cut me teeth in "speaker design" with active filtering and open baffle speakers.

Gimme a box to work with and I'd be clueless

 

[oktyabr]

Yes.


FWIW, I found it very difficult to get good results on OB using the DCX. Maybe I just didn't understand what I was doing - OB crossovers are strange - but using a big coil on the woofer always gave better results. For more normal box speakers, it was much easier.

Basically, you have to set the woofer crossover point much lower than your desired acoustic point. Because of the rising response, you need the low point to flatten it. I found that near impossible to do with EQ and shelving filters, tho I don't know why.

Nice to hear an opposing view on the actives, particularly the DCX. Ok, DCX with enough XLR-RCA adapters to work with my system, approx: $330

 

[oktyabr]

My passive crossover construction kit should include enough components to make at least low pass (x2) for the 18" Goldwood H-Frames (125Hz), the 15" Eminence Alpha in an open baffle (200Hz), U-frame (150Hz?) and H-frame (125Hz), and maybe the GRS 15" (???) in any the above as well. Since the only one of those solutions I think will make me happy using only one driver per channel is the 18" then I need enough components to go 8 ohm OR 4 ohm in case I double up the Alphas or GRS (open baffle or some frame thing).

My next goal is to try and come up with a "shopping" list, what someone would want to have in their parts drawer, to come up with a low pass for any of the above. I'm going to work on that now. If anyone wants to chime in with a similar shopping list I would sure love to hear it!

Any consensus on electrolytic caps in the low pass? How about 400v vs. 250v?

Thanks in advance.

 

[oktyabr]

MJK specifies for a single Alpha in a plain OB:
Solen 68uF 400V Polypropylene Capacitor @$27.29 x2 = 54.58
Erse Super Q 9.0mH 16 AWG 500W Inductor @$24.77 x2 = 49.54

in parallel (4 Ohm) that would be twice as much on the caps and half as much on the inductors (?) or $109.16 in caps and what recommended for an inductor?

For the GW 18" H-Frame he suggests LR2@100Hz and the parts list is:
Erse Super Q 9.0mH 16 AWG 500W Inductor @ $29.29 x2 = 58.58
and an Erse 150uF 400v (3%) cap which I can't find. PE stocks the Solen 100uF 400v (5%) for $38.81 and a Solen 51uF 400V for $19.65 that combined is $58.46 or $116.92 for both sides. Erse stocks their PulseX in 400v that could be combined as well (just no 150uF)... And their 100uF 400v is only $26.12

Help?

 

[adason]

i found bipolar (non-polarized) electrolytic capacitors for crossovers in woofer section absolutely adequate
no need for expensive exotic, save the money for better midrange and tweeter where it really matters
100V Non-Polarized Crossover Capacitors at Parts Express

 

[oktyabr]

Thanks for the help and tips so far guys!

I have another question... what happens to OB bass when the OB is elevated? I have fairly dense carpet and wonder if using carpet spikes would be good, bad or just ugly?

I've also read posts about better bass from H-frames if they are weighted down and I've been considering building the bottom base of the OB (probably H-Frame) in two layers and sandwiching a thin cavity between them to be filled with lead shot or the like. Has any one experimented with raising the back slightly to put more weight on the leading edge/point of contact with the floor?

 

[Rudolf]

I have another question... what happens to OB bass when the OB is elevated?

If it is just a few cm or about one inch, I can't see what could be wrong about it.

I've also read posts about better bass from H-frames if they are weighted down and I've been considering building the bottom base of the OB (probably H-Frame) in two layers and sandwiching a thin cavity between them to be filled with lead shot or the like.

Have you ever watched how Tokyos skyscrapers are secured against earthquakes? Skyscrapers aren't tipped over by the quake wakes, but crushed by resonances. To keep the buildings from resonating/rocking, a big (counter)weight is hung up high in the building. So the best strategy is to put as much weight as reasonable ON TOP of the H frame - not at the bottom!

Rudolf

 

[mondogenerator]

This ripole/loading interests me and ive often thought the visaton WS25 would be a good alternative to others, and reasonably priced for us folks in Europe.

Maybe also the W250 is worth a look?

http://www.visaton.de/en/chassis_zubehoer/tiefton/w250_8.html

35Eu each isnt too bad

 

[oktyabr]

@ Rudolf

Makes good sense! I was also looking at the design of James D. take on the Quasar (mkI)... the bottom almost seems to bridge putting the weight at point of contact on the front edge and at the very back. I wondered if better floor coupling was the reason and also the reason I asked about carpet spikes.

As for the weight your analogy makes good sense! Actually others have said to weight them at the top too. I'll just build my sandwich on the top instead of the bottom and fill each one with 20lbs or so of lead shot I have laying around. Might have sourced some 1" thick marble too

@ mondogenerator

I know the visaton drivers certainly have their fan club, at least the B200. If the others were available to me here in the 'states I'd certainly be considering them too.