Impedance amp see's

[cubdenno 0]

Not really sure what I am asking here but here goes.

I am running a TC3000 15"DVC sub. Each coil is 2ohms. I am running this parallel to a SAZ1500d for a 1 ohm load. With no music this specs out at about a perfect 1 ohm at the box terminals. Now whem I measure resistance while music is playing using my trusty calibrated Fluke 87 DMM, The lowest I am seeing resistance-wise is above 3 ohms. It never gets below and of course we are not going to discuss the high point. This is all done on a 60-20 htz sweep. So one of my questions is, does this mean that my sub is at most only getting 500 ish watts? I suppose what I need to do next is measure voltage and current. Was just doing some testing with my son before we build his box. And had no way of explaining what was really happening. Any input would be great. As always, just trying to learn.

Edited November 3, 2008 by sundownz

[ANeonRider 3]

Impedance changes with frequency & heat...

[BKOLFO4 29]

How are you measuring the impedance?

Is the sub in a box when you measure?

Brian

[cubdenno 0]

I understand that, but does that mean that it is possible to actually add a matching woofer to get a more closely realistic during music impedance? And heat may have been a minute factor but this was taken in the morning, 50 ish degrees and on cold equipment with about 30 percent volume. So am not concerned about the heat.

[cubdenno 0]

How are you measuring the impedance?

Is the sub in a box when you measure?

Brian

Fluke 87 multimeter. Measured at the box terminals and at the amp. Yes sub is in a box. I understand that the box "loads" the woofer or vice versa... Whatever the sub box combo becomes the load. Not that I am doing this as I don't have room but, does that mean I could do a two woofer combination, all thing being equal in my car, which wooferwise would be a .5 ohm load, but when in a box seeing music would be a minimum of about 1.55 ohms.

[sundownz 197]

Simply measuring resistance while playing isn't really accurate - measure current and voltage and calculate it that way.

It is quite normal for impedance to shift like that. That is why many people can get away with running such low "nominal" loads.

[BKOLFO4 29]

Simply measuring resistance while playing isn't really accurate - measure current and voltage and calculate it that way.

It is quite normal for impedance to shift like that. That is why many people can get away with running such low "nominal" loads.

x2

To measure it, you need to measure voltage and current, or measure voltage across a known load in series with the woofer and calculate voltage and current across the driver.

[cubdenno 0]

Well I grabbed the trusty fluke i410 digital clamp. Now measuring DC current, (And a thought just hit me, should I have put it on the negative?) I measured a max peak of 93 amps of draw at the battery playing a two step remix by DJ Unk. My boy had it in there. I measured AC current at the box at 19 amps.My two little ones were bugging me to come inside so I did not hook up another multimeter to check voltage. Now some things I did notice was that in my installation I am running 2 seperate runs of wire off the amp to each coil. These wires were warm and the banana plugs i use to connect the box were warm as well. I will upgrade the wire and redo the connections this weekend plus I will be able to do both voltage and current tests. All I can say is this combination of amp and sub puts out a ton of sound.

[lee 2]

You'll have to clamp output using A/C current and voltage. With those you will be able to figure out resistance. Clamping the power wire in D/C will show what the amp pulls from the electrical.

[AlpineAndy 3]

To measure your Impedence you need to use the clamp meter on AC current on the speaker wire goin to your sub. If your meter is not a true RMS clamp meter you will not get an accurate reading unless you play a 60hz tone. You really should use tones instead of music to get an accurate reading anyway! Voltage/Current=Resistance

Edited November 6, 2008 by AlpineAndy

[cubdenno 0]

You'll have to clamp output using A/C current and voltage. With those you will be able to figure out resistance. Clamping the power wire in D/C will show what the amp pulls from the electrical.

Yeah, I am going to do just that. Any advise to see what the whole system pulls? Pink noise?

[lee 2]

You can play around with it as you wish. It's cool to have a more info than not, it's up to you

[cubdenno 0]

Yeah I suppose. This whole thing got started with my kid. I have a few of the old Autosound 2000 tech briefs. There was discussion regarding Richard Clark GN. We were looking at what he said was needed to actually get the actual power rated out of an amp and how most amps could not actually do it. Which got me wondering what mine was actually putting out. Cause damn it pounds!!

[lee 2]

It is in the human nature to be curious and want to find out, isnt it?

[cubdenno 0]

It is in the human nature to be curious and want to find out, isnt it?

You bet! plus I hate having equipment and tools not being used. I love to tinker!! Plus this little exercise has shown me I went undersized on speakerwire to the sub!

[cubdenno 0]

I was able to measure my setup today.

52 volts

17.4 amps

this was a 50 hertz tone

900ish watts to the sub is what I calculated.

Wow. Guess I have a bit of head room...

Jacob, this now makes me wonder when most manufacturers of amps rate their amps capability to drive low impedance loads, are they figuring in this rise in impedance into the overall picture? I was noticing a guy that was driving a .25 ohm speaker load that actually when the impedance rise was factored in was .95 ohms. This figured into my situation of an almost 4 times rise.

Edited November 30, 2008 by cubdenno

[80INCHES 0]

so from what ive gathered based on the test u have done so far..the saz1500d will put out 900ish watts at 3ohms.(after impedance rise)...that is sooooooooooooooooooooo koooooooooooooooooooool

sundown ftw!!!!!!!!!!!!!!!!!!!!!!!!!!!!1

80

[cubdenno 0]

That is better than Cool. Impressive, awesome, kickass comes to mind. Plus this is from a stock Toyota electrical system. Stock battery and 80 amp alt.

[95Honda 486]

Ughh...

OK, "Impedance rise" is a made up term and means nothing. There is no such thing and whoever coined it is a moron....

There is however, an "impedance curve" of a loudspeaker, and this goes both UP and DOWN in impedance magnitude, hence the word "curve" and not "rise"

The DCR of a voice coil has absolutely nothing whatsover to do with the impedance that will be presented to the amp. I almost wish people didn't know how to hook the test leads of a DMM up to loudspeaker terminals, all it does is confuse most everyone.... Never, ever, ever under ANY circumstances will the impedance of a loudspeaker be near the DCR. It is impossible...

Impedance ratings of a driver are an average rating. That is why they are rated in whole numbers like 1, 2 or 4 ohm. Even though people say they do all the time, nobody has a dual 1.87 ohm subwoofer.... They have a dual 2 ohm subwoofer. And nobody has a sub that measures a little low at "1.6 ohms"...... They just don't have any idea what they are measuring...

The only accurate way to measure impednace is with some kind of bridge. If you don't have an impedance bridge, use a RMS voltage and clamp meter, you need to take about 50 measurements between 20 and 60 Hz.....

[cubdenno 0]

The only accurate way to measure impednace is with some kind of bridge. If you don't have an impedance bridge, use a RMS voltage and clamp meter, you need to take about 50 measurements between 20 and 60 Hz.....

That is something I can do. The test I did was at 50 hertz set up on repeat. I let it do about 25 or 30 passes. Every time it was 52 and 17.4 or really close to those that it didn't matter. Now I can do the 20 -60 hertz sweeps no problem. And my equipment is in fact true RMS. On the initial sweep when I ran the 20-80 hertz, What I found was the variation of impedance. I understand what you were explaining, and I knew that "X" ohm speaker is not really that resistance when music is applied.

But if you know the lowest resistance your amp is going to see in the band of frequencies it is going to play, does that info allow you to factor that as the true impedance the amp will see? And lets say that the dcr is .25 ohms but the actual resistance with signal is 1.1 ohms as the lowest, is that going to smoke the amp with daily use? Or are amp manufacturers figuring this impedance rise (sorry I know you don't like that word.) to get the minimum impedance for the amps? ex: 4 4ohm speakers parallel for 1 ohm dcr with rise 3.5 ohms real world. (I just pulled these numbers out of the air)

Edited December 1, 2008 by cubdenno

[95Honda 486]

Amplifier manufacturer's have no idea, or even care, about loudspeaker impedance curves. When they rate an amplifier, it is into a purely resistive load (i.e. a load resister). This is completely different than a loudspeaker load. Loudspeakers do not have "resistance" they have "impedance". You never measure the "resistance" of a loudspeaker, you ONLY measure the "impedance" because it is a reactive load.

The amplifiers are spec'd into a resistive load because it is a repeatable, comparable way to rate an amplifer. Hooking an amplifier up to a loudspeaker is a horrible way to get comparison due to the different impedance magnitudes and phase angles.

So to answer your question, NO. Amplifier manufacturers don't take any of this (loudspeaker impednace curve) into consideration. They tell you the minimum impedance the amplifier is stable to into a purely resistive load and it is YOUR responsibility to know if you have dipped below this threshold.

Also, please don't forget that loudspeakers have "impedance" they DO NOT have "resistance".....