Impedance Too Low for 4ohm Amp?

[Wushuliu]

Working on a design with Eclipse W6520R woofers. DATS impedance sweep attached of current XO. Does this qualify as 4ohm amp friendly? (Edit: forum posting has really become a PITA since the 'upgrade'.)

[tomzarbo]

I'll take a stab at it...

If you look at the graph and the dip your crosshair is on, that range from 100 to 200 Hz is hovering under 3 ohms.
I bet if you were to play sine sweeps at a louder volume, some 4 ohm amps might go into protect mode if a 80-240 Hz test tone was ALL that was playing. From about 90 to 340 Hz you're safe in the 4 ohm range.
This stuff is somewhat academic because we don't play sine sweeps... except when trying out new subwoofers to see if we can knock stuff off of shelves several rooms away. Music will be easier than sweeps by a humungous amount...

It is a bit low, and maybe right up to the line if not almost crossing it... but I think it might just be okay under most conditions. It really depends on the amp as well. Some smaller ones might 'click off' and go into protect, while some others will go all day with no complaints.

Could you possibly 'twiddle' with the components somewhat to get the DC resistance up a bit higher? Slightly smaller air cores instead of laminate cores, etc.? Usually we're trying to do the opposite with woofers, but in this case a little more resistance would be nice, I agree.

Hopefully some more experienced guys will be able to give you a bit more insight on why/why not on this crossover.

Best of luck with this!
TomZ

[Millstonemike]

You might want to post the XO. There's several "gurus" here that could pinpoint problem area(s) and suggest improvements.

[craigk]

Depends how good of amp you have. Any descent amp should have no problem with this.

[isaeagle4031]

Please post your crossover. The load there isn't horrible for a decent amp, but it is a bit low.

The 50Hz Fb is a bit high for the W6520R. It can do that easily sealed. That tune may result in boomy bottom end.

[Wushuliu]

Please post your crossover. The load there isn't horrible for a decent amp, but it is a bit low.

The 50Hz Fb is a bit high for the W6520R. It can do that easily sealed. That tune may result in boomy bottom end.

XO attached. Work in prog. MTM with Satori TW29R for my PE .75cu cabs. Using 6in PVC elbow for ports so yes a touch boomy for the enclosure but in my current space away from walls it's fine. Not worried about my amp per se since it's a Class D that hits 2ohm no prob, but I was curious if by typical standards this was '4 ohm' friendly.

[jhollander]

Not sure what the woofer LCR is doing

[Wushuliu]

Not sure what the woofer LCR is doing

Taming a peak (attached)

[Wolf]

You don't have a DCR input for your tweeter coil. Besides that, I'd be leery of the impedance below tuning. If you have a DC coupled source and amp, and there is any DC offset in your musical cuts, you really could blow up some stuff with that load at low freqs if the amp is not stable lower than 4 ohms.
Later,
Wolf

[jhollander]

Might pick up a bit if you dump the woofer LCR and add a 1 uF cap across the the 1.24 mH inductor

[isaeagle4031]

Agree John. And with these woofers in series, a 1.24mh seems small when considering bsc.

[Wushuliu]

Agree John. And with these woofers in series, a 1.24mh seems small when considering bsc.

They are in parallel, that's why I posed the question. Sorry, should have been more clear. Playing with WinPCD doesn't show any meaningful change with or without the RLC or swapping with 1uf on the inductor...

[isaeagle4031]

Well that answers why the impedance is so low! These are 4ohm nominal drivers. Being in parallel, the inductor size makes sense now. Try a smaller cap, .67-.33uf. Both methods work, but less parts (less$)

[Wolf]

I disagree with John and Chuck on losing the LCR. That is in a range above the xover point, and is already swamped by the LP filter and has a rising impedance. I also assumed they were in parallel having a DCR of about 2.5 ohms at the bottom end. Once you figure in added coil DCR, that's about right, and having a 3 ohm load yields approximately 0.6mH w/o BSC for the range he is rolling it off. I think 1.24mH is actually pretty close.

I also do not advise using a tank cap of 1.0uF, as that will allow quite a bit of ripple in the upper treble to be reinstated. I'd start with a 0.1uF for most cases. It is also something that does not always work as well as a true LCR to short out the breakup occurrence.

Later,
Wolf

[isaeagle4031]

Ben, what is the LCR going to accomplish here that the cap won't? The breakup on the W6520R is really pretty benign and the cap is more than sufficient to bring it well below audibility, particularly at this crossover point. I simmed for both when I built Mike's Redemption, A .47 cap nuked the breakup along with the 1.5k crossover point and is certainly not audible. The LCR did the same thing, just with more parts.