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[Silas Pradetto]

I measured this with my new WT3 system today, it's just one LAB sitting on the floor with a stage deck sitting on top (it's being used as a work table).

I'll check singles and doubles soon in a more proper location.

[Art Welter]

According to your impedance chart, there is as almost as much below the 4 ohm line as above in the usual 30- 80 Hz sub range.
Looks like calling it by the nominal 3 ohm is the safe bet, calling it a four ohm load is pushing it a bit.

Evidently the impedance figures you have quoted before are some sort of average over the frequency band.

You can revise any sensitivity figures based on a 6 ohm impedance down 3 dB..



With an amp capable of more output at two ohms than four ohms it would be very easy to tear up the cones below the horn cutoff frequency, where the impedance is lowest, and the power delivered would be at its maximum.

[Silas Pradetto]

I wish there was a way for the WT3 program to give me an impedance average over a specified frequency range. I bet the average from 30 to 100Hz is above 4 ohms.

Yes, the measurements I've reported before are the Itech's reported average from the passband they're being powered over, and they also have to be powered over a certain voltage threshold to get a reading. I'm not sure what the threshold is.

I want to do a block of two LABs, and also power the LABs with some sine waves for a couple minutes to heat them up, then measure again. I usually see the Itech average hover at 3 ohms for a pair when being driven pretty hard, so we'll see what I get.

I've always wanted to see impedance of my speakers, so now I can. I'm going to be measuring the entire shop of speakers soon, hopefully today  


Edit: Also, seeing how low some of the impedance dips are, it would be an obvious reason that lower end amps have a hard time pushing LABs, especially in bridge mode. It would also explain why even on Itechs, one LAB per channel sounds better than two.

[Ivan Beaver]

Silas Pradetto wrote on Wed, 18 August 2010 15:01

I wish there was a way for the WT3 program to give me an impedance average over a specified frequency range. I bet the average from 30 to 100Hz is above 4 ohms. Yes, the measurements I've reported before are the Itech's reported average from the passband they're being powered over, and they also have to be powered over a certain voltage threshold to get a reading. I'm not sure what the threshold is. I want to do a block of two LABs, and also power the LABs with some sine waves for a couple minutes to heat them up, then measure again. I usually see the Itech average hover at 3 ohms for a pair when being driven pretty hard, so we'll see what I get. I've always wanted to see impedance of my speakers, so now I can. I'm going to be measuring the entire shop of speakers soon, hopefully today   Edit: Also, seeing how low some of the impedance dips are, it would be an obvious reason that lower end amps have a hard time pushing LABs, especially in bridge mode. It would also explain why even on Itechs, one LAB per channel sounds better than two.

And yet another example of trying to use a "simple" number to decribe a complex measurement-such as impedance.

It depends on where the kick is tuned-but the impedance could be pretty high at that point-which means the subs would be pounding away-yet not producing much heat.  That is a good thing.

I would say that if you averaged between 30 and 100Hz, the impedance would be higher than 4 ohms.  But some amps don't like "averages-the minimum could cause them not to be so "happy".

[Art Welter]

Ivan Beaver wrote on Wed, 18 August 2010 15:10

Silas Pradetto wrote on Wed, 18 August 2010 15:01 I wish there was a way for the WT3 program to give me an impedance average over a specified frequency range. I bet the average from 30 to 100Hz is above 4 ohms. Yes, the measurements I've reported before are the Itech's reported average from the passband they're being powered over, and they also have to be powered over a certain voltage threshold to get a reading. I'm not sure what the threshold is. I want to do a block of two LABs, and also power the LABs with some sine waves for a couple minutes to heat them up, then measure again. I usually see the Itech average hover at 3 ohms for a pair when being driven pretty hard, so we'll see what I get. I've always wanted to see impedance of my speakers, so now I can. I'm going to be measuring the entire shop of speakers soon, hopefully today   Edit: Also, seeing how low some of the impedance dips are, it would be an obvious reason that lower end amps have a hard time pushing LABs, especially in bridge mode. It would also explain why even on Itechs, one LAB per channel sounds better than two. And yet another example of trying to use a "simple" number to decribe a complex measurement-such as impedance. It depends on where the kick is tuned-but the impedance could be pretty high at that point-which means the subs would be pounding away-yet not producing much heat.  That is a good thing. I would say that if you averaged between 30 and 100Hz, the impedance would be higher than 4 ohms.  But some amps don't like "averages-the minimum could cause them not to be so "happy".

The impedance average may well be above 4 ohms averaged between 30 and 100Hz, but the low points in the pass band determine what impedance you need to work with, averaging in high peaks to arrive at a nominal impedance would give you an inflated figure.

The IEC standard (IEC60268-3) allows any impedance above the rated value, but limits the impedance below. It does not allow the rated impedance to fall below the 80 % of the nominal value at any frequency down to and including DC.

Rating a speaker at 4 ohms when it has  a 3 ohm low is a no no according to IEC60268-3, when it goes to 2.25 ohms, even more so.

One more thing to think about when writing spec sheets, TH-118 cough cough...

[Ivan Beaver]

Art Welter wrote on Wed, 18 August 2010 17:36

Ivan Beaver wrote on Wed, 18 August 2010 15:10 Silas Pradetto wrote on Wed, 18 August 2010 15:01 I wish there was a way for the WT3 program to give me an impedance average over a specified frequency range. I bet the average from 30 to 100Hz is above 4 ohms. Yes, the measurements I've reported before are the Itech's reported average from the passband they're being powered over, and they also have to be powered over a certain voltage threshold to get a reading. I'm not sure what the threshold is. I want to do a block of two LABs, and also power the LABs with some sine waves for a couple minutes to heat them up, then measure again. I usually see the Itech average hover at 3 ohms for a pair when being driven pretty hard, so we'll see what I get. I've always wanted to see impedance of my speakers, so now I can. I'm going to be measuring the entire shop of speakers soon, hopefully today   Edit: Also, seeing how low some of the impedance dips are, it would be an obvious reason that lower end amps have a hard time pushing LABs, especially in bridge mode. It would also explain why even on Itechs, one LAB per channel sounds better than two. And yet another example of trying to use a "simple" number to decribe a complex measurement-such as impedance. It depends on where the kick is tuned-but the impedance could be pretty high at that point-which means the subs would be pounding away-yet not producing much heat.  That is a good thing. I would say that if you averaged between 30 and 100Hz, the impedance would be higher than 4 ohms.  But some amps don't like "averages-the minimum could cause them not to be so "happy". The impedance average may well be above 4 ohms averaged between 30 and 100Hz, but the low points in the pass band determine what impedance you need to work with, averaging in high peaks to arrive at a nominal impedance would give you an inflated figure. The IEC standard (IEC60268-3) allows any impedance above the rated value, but limits the impedance below. It does not allow the rated impedance to fall below the 80 % of the nominal value at any frequency down to and including DC. Rating a speaker at 4 ohms when it has  a 3 ohm low is a no no according to IEC60268-3, when it goes to 2.25 ohms, even more so. One more thing to think about when writing spec sheets, TH-118 cough cough...

Part of the problem is-have you ever seen a loudspeaker rated as having a nominal impedance of say 3.6 ohms?

No-almost without exception (yes there are a very few) loudspeakers are rated for 4-8-16 ohms. You would not believe how many people are "confused" by the non standard numbers.

Oh course most manufacturers only give a single number-do not show a graph-or list an actual minimum impedance-so who knows what the ACTUAL impedance should be on most products.

If you look at the actual impedance of the TH118 (top graph below) you will see that most of it is well above 4 ohms.  I know that doesn't "fit" the standard-but does give a better idea of the actual load to an amp.

Take for example the SH50.  We used to rate it for 6 ohms.  But I was getting calls ALL the time with people wondering what size amp they should use on it-because they could not find a 6 ohm wattage rating on the amp manufacturers site.

So we changed it to 4 ohms-and now nobody is confused

If you look at the bottom graph you will see that the 6 ohm rating more accurately describes the actual load presented to the amp.

But some people just can't figure it out.  I guess that is one reason many manufacturers only give a simple number.   It reduces the phone calls.