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tipo1000 11th September 2007 06:52 AM

"Distorted" step response
 
2 Attachment(s)
Hi, I'm new in this group.

What should I think about this "distorted" step response graph I took from my 10" subwoofer? Does it indicate something, like broken element, or is it normal? What that "double peak" means it has?

I thought that step response is always smooth like in this one (graph below) I took from woofer of my shelf speaker. Both were taken in near field.


Thanks, Tipo

phase_accurate 11th September 2007 07:28 AM

It may sound strange at first but the upper step response is nicer than the lower one !

The distortion that you see is either cone resonance or maybe from the reflex tunnel (though the step response reminds me from a cloded box). Has it been taken without crossvover ?
This resonance can be reduced significantly as soon as its source has been determined.

BTW: The reason why I like the upper response more than the lower one (probably reflex, isn't it ?) is because it has less overshoot.

Regards

Charles

Svante 11th September 2007 09:23 PM

I would like to see the frequency response.

The step response is IMO much less informative.

tipo1000 12th September 2007 05:03 AM

2 Attachment(s)
Attached is freq response and step response curves for both closed and vented configurations.

Box is 40l, tube 340/66mm, element Peerless 10" XLS. I simply closed box by putting foam into tube.

There's practically no difference between closed and vented step responses.

Speakers sounds and "feels" good. I'm just curious why step response is "distorted". I don't have questions about freq resp.

There' s no crossover/filter/EQ in measured system.

Thanks, Tipo

phase_accurate 12th September 2007 06:22 AM

Quote:

Speakers sounds and "feels" good. I'm just curious why step response is "distorted". I don't have questions about freq resp.There' s no crossover/filter/EQ in measured system.
1.) Sound and feels good: Everything is OK.

2.) Distorted step response and frequency response: They are depending on each other. The ripples you see on the step response are caused by very the uneven response above 500 Hz.

3.) As soon as you measure this SUB-woofer with a lowpass in front most of the ripple will be gone.

Regards

Charles

Svante 12th September 2007 05:37 PM

Quote:

Originally posted by tipo1000
Attached is freq response and step response curves for both closed and vented configurations.

Box is 40l, tube 340/66mm, element Peerless 10" XLS. I simply closed box by putting foam into tube.

There's practically no difference between closed and vented step responses.

Speakers sounds and "feels" good. I'm just curious why step response is "distorted". I don't have questions about freq resp.

There' s no crossover/filter/EQ in measured system.

Thanks, Tipo

Ah, this is a close field measurement, near the woofer?

That is clearly visible in the frequency response, but not in the step response. The port is tuned to ~21 Hz, and the port contribution is neglected (due to the close field measurement).

Am I right?

DSP_Geek 12th September 2007 06:54 PM

Quote:

Originally posted by phase_accurate


1.) Sound and feels good: Everything is OK.

2.) Distorted step response and frequency response: They are depending on each other. The ripples you see on the step response are caused by very the uneven response above 500 Hz.

3.) As soon as you measure this SUB-woofer with a lowpass in front most of the ripple will be gone.


And you can even tell it's around 500 Hz by figuring out the period of the step response ripples. They're about 1.8 milliseconds (ms), indicating a problem around 550 Hz (period of 2 ms). Lo and behold, the response graph shows a narrow and deep null there, indicating a high-Q resonance. I wouldn't worry about it, since the subwoofer crossover should be many dB down by then.

Phase_accurate liked the first step response, even though it looked a bit grungy, because the grunge is well outside the passband and the time response is otherwise well damped. The second step response has ringing around 10 ms, hinting at a resonance around 100 Hz. That will be noticeable in a subwoofer.

tipo1000 12th September 2007 10:21 PM

2 Attachment(s)
Thank you all for answers! Everything cleared out!

Svante: Yes, it is near field meaurement. I didn't include port measurement, but here it just for curiosity.

Thanks, Tipo

Svante 13th September 2007 06:03 AM

OT: am I also right in that the port is not positioned very close to the driver? (Testing an hypothesis of my own here)

phase_accurate 13th September 2007 06:08 AM

My guess is that same as Svante's. And we can also see the source of the ripple ! ;)

Regards

Charles


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