Sensitivity vs Impedance Plots?

johninCR · 23rd November 2004, 01:39 PM

This question is related to a horn but I think it applies to all speakers.

At the low cutoff of my horn the FR plot shows a peak in response, however, the impedance spikes at this same point. What is the real outcome of this? Does the peak in response actually get negated because the amplifier can't deliver the same power due to the increase impedance?

Lusso5 · 23rd November 2004, 02:34 PM

Is the peak at/around driver FS?

Impedance will rise as the frequency approches FS, where it is most resistive.

I'm not a horn guy, but the driver's increased efficiency at FS, coupled with the horn must have something to do with your spike in SPL. Typically you won't see that in any boxed alignment.

BillFitzmaurice · 23rd November 2004, 11:24 PM

The impedance spike is normal at the horn fc; it's one way of knowing where the fc is. It has nothing to do with the driver fs per se. There will also be a peak at the rear chamber fb, unless the horn is perfectly reactance annulled, in which case the fb and fc are identical and there is only one peak.

johninCR · 23rd November 2004, 11:47 PM

Quote:

Originally posted by BillFitzmaurice
The impedance spike is normal at the horn fc; it's one way of knowing where the fc is. It has nothing to do with the driver fs per se. There will also be a peak at the rear chamber fb, unless the horn is perfectly reactance annulled, in which case the fb and fc are identical and there is only one peak.

I understand it has nothing to do with Fs. HornRESP calls it electrical impedance and it goes up to about 20 ohms at the 40hz spike with my low impedance wiring scheme. This is a concern to me because I use one of Decware's amps that prefers low impedance and won't put out even 1 watt per channel into a 20 ohm load. Does that mean my response will drop off severely right at 40hz ?

Jim York · 24th November 2004, 12:11 AM

The amp will be just fine. The spike also coincides with where the system operates most efficiently. Reponse will fall off below fc at 12dB/octave from the horn component, and another 12dB per octave kicks in below fb of the rear chamber.

johninCR · 24th November 2004, 12:40 AM

I guess I did it right. Only 1 spike in impedance and the rolloff below 40hz looks more like 24db per octave. Thanks for the help.

23rd November 2004, 01:39 PM	#1
johninCR diyAudio Member Join Date: Apr 2004 Location: Costa Rica	Sensitivity vs Impedance Plots? This question is related to a horn but I think it applies to all speakers. At the low cutoff of my horn the FR plot shows a peak in response, however, the impedance spikes at this same point. What is the real outcome of this? Does the peak in response actually get negated because the amplifier can't deliver the same power due to the increase impedance? __________________ Everyone has a photographic memory. It's just that most are out of film.

24th November 2004, 12:40 AM	#6
johninCR diyAudio Member Join Date: Apr 2004 Location: Costa Rica	I guess I did it right. Only 1 spike in impedance and the rolloff below 40hz looks more like 24db per octave. Thanks for the help. __________________ Everyone has a photographic memory. It's just that most are out of film.

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23rd November 2004, 02:34 PM	#2
Lusso5 diyAudio Member Join Date: Jul 2003 Location: Houston, TX	Is the peak at/around driver FS? Impedance will rise as the frequency approches FS, where it is most resistive. I'm not a horn guy, but the driver's increased efficiency at FS, coupled with the horn must have something to do with your spike in SPL. Typically you won't see that in any boxed alignment.

23rd November 2004, 11:24 PM	#3
BillFitzmaurice Banned Join Date: May 2004 Location: New Hampshire	The impedance spike is normal at the horn fc; it's one way of knowing where the fc is. It has nothing to do with the driver fs per se. There will also be a peak at the rear chamber fb, unless the horn is perfectly reactance annulled, in which case the fb and fc are identical and there is only one peak.

24th November 2004, 12:11 AM	#5
Jim York Banned Join Date: Oct 2004	The amp will be just fine. The spike also coincides with where the system operates most efficiently. Reponse will fall off below fc at 12dB/octave from the horn component, and another 12dB per octave kicks in below fb of the rear chamber.

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