3 way with DX25, FR125S & SDX7

[sfreak]

Slowly bowling over my projects one by one, which is always a nice feeling. Just about finished my PC case (Tas Oak, and watercooled, should be quite good if and when I get the remaining parts), and now I move on to my next project for some new speakers to go with it.

Design criteria are as follows:

*Plays low as I don't have the room for a subwoofer
*Compact design, no wider than 250mm nor higher than 500mm
*Also desk mountable (to a degree) and also will be close to a wall
*Also have the WR/FR125S open baffle, as my experiments in the past with the driver in that config ended up quite pleasant

So I've been running all these designs through my head and on paper last 3 or 4 months. Gone from MTW with the FR on top in open baffle and now settled on TMW with the FR in the middled open baffle to a degree. Willing to use the SDX7 in a vented config, tuned to somewhere between 28 and 34hz.

Be my first real crossover speaker. So got myself a challenge there. Been reading for nearly a year on the subject, but there is only so much you can learn that way, and it all comes down to practice and trial and errors so I've been told.

Since I am yet to see or get any measurements of the SDX7, was thinking crossed over to the FR125S @ 200hz LR 4th order, to minimize the excursion on the FR mainly in OB (Also, x-over point may vary on how it measures). And then crossover with the Vifa DX25 somewhere between 6.5k and 10k. 2nd or 4th order. Might also use the WR125S as I have a pair laying around here with its roll off after 10k.

Also brings me to measurements etc, I think its about time I invested in some hardware and software, was thinking Soundeasy, but I shall do a bit more research into that in the coming weeks. Would be a good investment whatever I end up getting there.

Also, following are some quick models in SketchUp to show what I am going for. The OB space is 12.5cm from front to back, I can only hope that will be enough. Rearward firing port, which I am tossing up whether to have top mounted facing forward. Mainly to minimise reflections off the back wall (Got 10-20cm space).

Any comments or suggestions would be greatly welcomed.

Dan

[sfreak]

And a closed LHS view. See the open side for the FR125S

[Scottmoose]

Short of a full HE setup, that's the way to do it (in XO terms). Your crossover approximations look good to me. Initial one at 200hz, which is the start of the telephone / midband as defined by Bell Labs, which stretches to a minimum of 4Khz (preferably more). So you've no XOs in our most senstive hearing region, which can only be a good thing. From what I've seen of the SDX7 (already designed a couple of boxes for it), it's excellent to about 500Hz; it's really a small bass driver, not a mid-bass, so keeping the XO points low anyway is a good idea. Just watch out for resonances from your semi OB configuration & especially reflections back through the cone. That part will need tweaking IMO. But it looks to me to have some real potential.

[sreten]

Erm........

The way do do it ? At what frequency will the FR12S start to
roll off due to the open baffle ? Around 800 Hz I estimate ...

/sreten.

[Scottmoose]

I was taking the cavity resonance roughly into consideration which should reduce things somewhat. It's not really an OB -more a very short 1/2 wave line with the driver tapped into the middle. We'd have to see response data et al to refine things -please don't read too much into the above, it was only supposed to be a generalised remark about XO points best being kept out of the midband.

Frankly, I'd prefer the 125 to be in a sealed box, but YMMV as ever.

[planet10]

I haven't yet played with the ported SDX7 alignments, but have the recommended ones to draw up, but on 1st pass the ports are quite long. Looks to be quite a good woofer (Al Wooley is very please with it)

It looks to do well in a sealed box too... it can be usable in as small as 7 litres (Q = 0.7, 21 litre, Q = 0,5)

Sreten has a good point about dipole roll-off... in the SDX7/FR126 box i'm working on the FR will be in a small aperiodic box.

dave

[Scottmoose]

Yep, that would be my favourite option too. Or a sealed line, though that might be a trifle larger of course.

[planet10]

14 litre sealed Stealth Woofer or FR125/SDX7 TL are going to be 1st out the gate (TL is higher in the queue, but the sealed is easier and doesn't need approval)

Here are the "official" alignments... there will be drawings for all of these.

Ported (walls lined with stuffing. Subtract 1" from port length for non-flared port)

1 driver
0.5 ft^3 (14 liters) @ 35 Hz (2" flared port 12" long)
1 ft^3 (28 liters) @ 28 Hz (2" flared port 9.5" long) / Extended bass

2 drivers
1 ft^3 (28 liters) @ 35 Hz (3" flared port 13.5" long)
2 ft^3 (56 liters) tuned to 28 Hz (4" flared port 10.5" long) / Extended bass

Sealed (1 pound stuffing / cubic foot)
.707 Qtc ˆ ~.25 cubic feet (7.5 liters) per driver
.577 Qtc - ~.5 cubic feet (14 liters) per driver
.5 Qtc - .75 cubic feet (21 liters) per driver

Scott has done, 1 & 2 driver ML-TL and tapered TL, there will be drawings for those too.

dave

[sfreak]

Well that does raise the question about the roll off of the FR125S. Perhaps I should just go sealed with the FR and worry about dipole later on down the track when I have more room.

I shall look a bit more into it never the less...

[audiobomber]

What's the Qts of the SDX7? I don't see it listed at CSS.