New DIY build - asking help interpreting impedance sweep

[eddantes]

Hello all,

I tried to build a small desktop speaker based on DX25 and SB12PFC.

I swept both speakers with the above result. Would anyone be kind to opine on what these sweeps show. They aren't quite alike - any idea why that may be and what I might try to do to fix it - if fixing is needed. They sound OK... a bit bright probably, but I didn't expect much low end.

I haven't measured. I dropped my mic and it looks like I might need another :-(

Here's the Vcad box.

 

[NotInYourHead]

You should check for leaks, misplaced gaskets, etc...Are the speakers secured to the box tightly enough? Both speakers have the same amount of stuffing/lining?
What I'm more concerned about is in the mid-high range. The impedance is like a rollercoaster and there are even more mismatches than in the low-end. You should upload your crossover schematics.

 

[Devnull]

I'd probably pull all the drivers and run DATS on them individually to verify no driver issues. Then mount them in the cabs and run DATS on the SB12PFC. Don't need to rerun DATS on the tweeters because they're sealed. Then hookup the xovers and measure again.

 

[eddantes]

Here's my Vcad impedence sim

The peaks around the port tuning dip are the only real deviations.

Also, I am looking to learn to read the chart - can you point to what you see as problematic?

 

[Devnull]

Might be easier to see the differences if you used a linear scale for the impedance. The two speakers should probably have an impedance response of +- 0.25 ohms.

The green peak around 50 Hz is unusual because it has a flat top and an asymmetrical slope.

The blue trace has a hump around 1200 Hz and has a peak impedance that doesn't match the other trace. If the two tweeters measure the same with DATS then it's an issue with the crossovers. Did you measure the crossover components before you assembled things?

 

[SSS]

To me it looks like that one woofer is slightly different than the other. Further, the reflex pipe might be also slightly different and the damping stuffing also.
So, if you can measure the woofers outside the cabinet you may see a difference in resonance frequency and perhaps other parameters. If both are really same valued then either the cabinet, the x-over and dimensional differences may be the cause.

 

[DVDdoug]

I wouldn't panic. It's the frequency response (and sound) that matters! Also, the also drivers won't be identical... Nothing in real-analog world is...

As long as you have an amp rated for 4-Ohms you'll probably be fine.

They sound OK... a bit bright probably, but I didn't expect much low end.

You can add some resistance to the crossover, in series with the tweeter, to knock-down the highs. But it would be a good idea to get a working measurement mic to confirm what's going-on before you lock-down the design. But I probably wouldn't go by measurements alone and we can't do the kind of measurements that Amir does.

 

[Raj21p]

Your sweeps look normal small differences usually come from driver variance, box sealing, or stuffing. The “bright” sound is likely crossover balance, not an impedance issue.