Speaker Impedance revisited

[3db]

Most everyone on here knows or can agree that speaker impedance is a function of frequency and is constantly changing with the signal source. I'm also realizing how inadequate manufacturer specs when it comes to rating speaker impedance. Even when manufacturers state a minimum impedance drop, they are still omitting the two most important specifications; a.) The frequency at which that mininmum impedance drop occurs and also what the phase angle is at that minimum impedance. If the phase angle is small or negligible enough and that impedance drop occured at frequencies out of the bass region, I'm guessing that many more receivers would be able to drive loudspeakers without having to get a beast of an amp.

My question are these;
1.) When SM (speaker manufacturers) model their products impedance curve, are they using just a single signal that is swept from 20Hz to 20KHz?
2.) If two or more frequencies are being applied to the speaker, is the impedance calculated to be the vector sum of the impedance of the speaker for each given frequency contained in the signal?
3.) Does the minimum impedance of the speaker always correlate with the max phase angle?

 

[highfigh]

I think you're basically saying that you want the speaker manufacturers to list specs that a minute percentage of their customers A) want, B) care about and C) understand. For the vast majority of speakers, this will be completely unnecessary because their market doesn't care about these specs at all. If you want the high end manufacturers to state these, good luck- they tend to not be very willing to give out many details. Most amps are fine with most speakers and the speakers that give amplifiers fits will have a reputation for it. speaker designers used to avoid large variations in impedance (e.g., crossover point at least one octave above the free air resonance or using an impedance compensation network) to keep the amp from being damaged, becoming unstable or going into protection.

If you were to contact some speaker manufacturers, I doubt that you'll find anyone who will want to discuss this for any length of time.

As far as your questions, if they aren't using LEAP (which uses a sweep, AFAIK) or something like it, you'll have to ask each one.

 

[Rickster71]

FWIW
I agree about inadequate manufacturer specs when it comes to rating speaker impedance.

I would think the problem is mostly relegated to 2.0 listening.
With a 5.1 setup and the LF going to the sub, the receiver doesn't deal with the crazy impedance drop and phase angles. The LF's are really where this situation puts the most stress on an amp.

I wouldn't rely 100% on a manufacturers specs anyway.
Just hope the speaker is reviewed and check the impedance drop and phase angles there.

 

[3db]

FWIW
I agree about inadequate manufacturer specs when it comes to rating speaker impedance.

I would think the problem is mostly relegated to 2.0 listening.
With a 5.1 setup and the LF going to the sub, the receiver doesn't deal with the crazy impedance drop and phase angles. The LF's are really where this situation puts the most stress on an amp.

I wouldn't rely 100% on a manufacturers specs anyway.
Just hope the speaker is reviewed and check the impedance drop and phase angles there.

Umm what does FWIW mean?

 

[fredk]

For What Its Worth and that would be my .02 worth.

 

[highfigh]

For What Its Worth and that would be my .02 worth.

Are those OFC pennies? If not, they're not worth the copper used to plate the zinc.

 

[Rickster71]

Umm what does FWIW mean?

It was bound to happen, once I got my NetLingo dictionary, with thousands of computer and Internet terms.

 

[R-Carpenter]

Most everyone on here knows or can agree that speaker impedance is a function of frequency and is constantly changing with the signal source. I'm also realizing how inadequate manufacturer specs when it comes to rating speaker impedance. Even when manufacturers state a minimum impedance drop, they are still omitting the two most important specifications; a.) The frequency at which that mininmum impedance drop occurs and also what the phase angle is at that minimum impedance. If the phase angle is small or negligible enough and that impedance drop occured at frequencies out of the bass region, I'm guessing that many more receivers would be able to drive loudspeakers without having to get a beast of an amp.

My question are these;
1.) When SM (speaker manufacturers) model their products impedance curve, are they using just a single signal that is swept from 20Hz to 20KHz?
2.) If two or more frequencies are being applied to the speaker, is the impedance calculated to be the vector sum of the impedance of the speaker for each given frequency contained in the signal?
3.) Does the minimum impedance of the speaker always correlate with the max phase angle?

The impedance of a single driver or a multi driver speaker system is measured throughout 20-20k and then ballparked. There's no speaker out there with flat 4ohm or 8ohm impedance. There's a lot of factors involved and your regular consumer will not be able to make sense of it anyway.
You 6ohm woofer can have an impedance jump to 60ohm at FS, go back to 5ohm in midband and have an inductive coil raise to 15 ohm. Then you deal with additional impedance of the crossover components and their interaction with other drivers.
I would pay more attention to Frequency response charts and possibly off axis response and distortion parameters.

 

[3db]

The impedance of a single driver or a multi driver speaker system is measured throughout 20-20k and then ballparked. There's no speaker out there with flat 4ohm or 8ohm impedance. There's a lot of factors involved and your regular consumer will not be able to make sense of it anyway.
You 6ohm woofer can have an impedance jump to 60ohm at FS, go back to 5ohm in midband and have an inductive coil raise to 15 ohm. Then you deal with additional impedance of the crossover components and their interaction with other drivers.
I would pay more attention to Frequency response charts and possibly off axis response and distortion parameters.

When you say speaker, do you mean driver or impedance measured at the speaker terminals outside the cabinet? PSB's new Imagine towers has been measured to have their impedance drop down to 3.4 ohms (nominally rated for at 4 ohms) at 72 Hz with a negligable phase angle. This is not a big swing in impedance and this is the 3ed time PSB has delivered a fairly flat impedance curve speaker in there Speakers are mostly inductive, crossovers have both inductive and capacitance elements which like I said vary with frequency. A frequency graph will not indicate how difficult a speaker is to drive. Its needed but there's much more info needed, espcially when one is trying to match an amp to a speaker.

 

[R-Carpenter]

The final impedance of the speaker is measured at the terminals. Everything in the speaker, including box volume, standing waves, type of staffing will play a role in the impedance of the system. So you need to know as a speaker designer what it actually does after all set and done.
Single driver impedance is measured as a part of speaker design process in the very beginning.
If you really interested in the subject, I suggest reading D'Appolito's “Measuring Loudspeakers”
This: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-804
is also inexpensive and helpful tool to check the actual impedance of the system.
As to selecting amplifier for the particular speaker system, most of the people will stick to a stated impedance a speaker manufacturer recommendations. Can more information help? Probably but again most of the people are not going to bother researching this subject.

 

[highfigh]

When you say speaker, do you mean driver or impedance measured at the speaker terminals outside the cabinet? PSB's new Imagine towers has been measured to have their impedance drop down to 3.4 ohms (nominally rated for at 4 ohms) at 72 Hz with a negligable phase angle. This is not a big swing in impedance and this is the 3ed time PSB has delivered a fairly flat impedance curve speaker in there Speakers are mostly inductive, crossovers have both inductive and capacitance elements which like I said vary with frequency. A frequency graph will not indicate how difficult a speaker is to drive. Its needed but there's much more info needed, espcially when one is trying to match an amp to a speaker.

It's not that hard to add a Zobel network ('network' sounding a bit more impressive than it really is) to smooth the impedance and many manufacturers don't bother with it because at Fs, when the driver would start flapping like sheets in the wind if the impedance graph was ruler flat, the coincidental impedance peak keeps it in check.

A frequency response graph is for indicating only the response. If it has an impedance curve as well, it's usually to impress customers who don't have much knowledge of specs and what goes into designing a speaker. Remember- the spec sheets and all of the info that comes from equipment manufacturers comes through the marketing department and not engineering. In most cases, marketing sells the speakers, not how intelligently the products were designed. Buzz words and BS are far more common than legitimate data.

At some point, it becomes time to listen to the music and not the equipment. If a person can't get past minute flaws in the sound, it's their problem, really. Great sound is possible but perfection is not. It's far easier to make mediocre speakers sound good by treating the room than making excellent speakers sound great in a bad room. Too many people who call themselves "audiophile" do little or nothing to/for the room's acoustics and that's a really good way to eliminate any real satisfaction on their system's sound.

If the acoustics are bad, does a flat impedance graph with little phase angle really matter?

 

[3db]

I never implied not to audition a speaker. That is first and foremost. Unfortunately, alot of teh specs are marketing hype with Bose taking it to the extreme. I also understand that alot of pwoplw either don't care or can't understand speaker specs. But for those of us who do , it would be nice to have espcially when trying to mate the amp/rcvr to the speaker.

 

[highfigh]

I never implied not to audition a speaker. That is first and foremost. Unfortunately, alot of teh specs are marketing hype with Bose taking it to the extreme. I also understand that alot of pwoplw either don't care or can't understand speaker specs. But for those of us who do , it would be nice to have espcially when trying to mate the amp/rcvr to the speaker.

OK, if you know the phase angle graph of the speaker and it doesn't look good, will you absolutely not want to listen to it? We all know that many of the old classic designs never posted anything about this, although they were concerned with phase coherence and addressed that in whatever ways were available at the time. If the drivers aren't proprietary, there's a good chance that the phase angle and impedance are on the same graph, the way LEAP shows it and many of the drivers sold by Madisound and Parts Express show this.

The phase angle won't affect the amp, so why not just look for amps that are known to be able to drive difficult loads? That's not a bad "rule of thumb", anyway.

 

[R-Carpenter]

Put it this way. You have 2 choices if you are concern with the actual impedance graph of the speaker.
You can A) get a loaner pair from the store and either pay someone with the software to measure it (takes 5 minutes)or use Woofer Tester. Or B) request this information from manufacturer (to which they will probably not respond).
Unfortunately it is a real world situation.
Having a Zobel will slightly flatten impedance but will also affect the phase, so there's no win-win situation and it's all about the character of sound that you are trying to achieve from the combination of drivers, caps, coils and the box aka speaker.

 

[3db]

OK, if you know the phase angle graph of the speaker and it doesn't look good, will you absolutely not want to listen to it? We all know that many of the old classic designs never posted anything about this, although they were concerned with phase coherence and addressed that in whatever ways were available at the time. If the drivers aren't proprietary, there's a good chance that the phase angle and impedance are on the same graph, the way LEAP shows it and many of the drivers sold by Madisound and Parts Express show this.

The phase angle won't affect the amp, so why not just look for amps that are known to be able to drive difficult loads? That's not a bad "rule of thumb", anyway.

Phase angle has everything to do with an amp's ability to drive speakers, much more so than impedance. A very high phase angle wastes the amplifier power. Its common practise for heavy industry to try and bring back lagging phase angles to zereo my deploying motors which have a leading phase angle because big phase angles wastes power, just like it would an amplifier.

 

[3db]

OK, if you know the phase angle graph of the speaker and it doesn't look good, will you absolutely not want to listen to it? .

No, I'm too curious not to listen to it but because I'm on a tight budget and I can't afford an amp able to drive difficult speakers, I would have to pass up on that speaker.

 

[highfigh]

Phase angle has everything to do with an amp's ability to drive speakers, much more so than impedance. A very high phase angle wastes the amplifier power. Its common practise for heavy industry to try and bring back lagging phase angles to zereo my deploying motors which have a leading phase angle because big phase angles wastes power, just like it would an amplifier.

Aside from the fact that we aren't dealing with heavy industry, does the fact that some of the older speakers sound really good mean they accidentally came up with designs with low phase angle, or do you think they just didn't talk about it? I've been in the business for a long time and until fairly recently, I never heard anyone talk about phase angle and in that time, have heard a large number of great sounding speakers of all prices.

Care to lay out the specifics for how much power is wasted by more PA? I'd like to see it.

 

[R-Carpenter]

3db, I drive speakers of my own design with 3k in drivers alone with $160 Behringer 500 amp driving and people are amazed with the sound. I also have dead Krell that I got for the repairs, seating next to it. It is always assumed that Krell is playing.
Just get yourself the best speakers you can afford and don't worry about the amp so much.

 

[3db]

Aside from the fact that we aren't dealing with heavy industry, does the fact that some of the older speakers sound really good mean they accidentally came up with designs with low phase angle, or do you think they just didn't talk about it? I've been in the business for a long time and until fairly recently, I never heard anyone talk about phase angle and in that time, have heard a large number of great sounding speakers of all prices.

Care to lay out the specifics for how much power is wasted by more PA? I'd like to see it.

The paragraph below is taken from this article;

http://www.ece.msstate.edu/courses/design/ece4512/2003_spring/impedance_meter/Revised Problem 2.doc

In addition, extreme impedance phase angles can strain an amplifier. This measurement looks at whether the impedance of the loudspeaker is resistive, inductive, or capacitive at any given frequency. With impedance magnitude, the more severe the phase angle, the more difficult the speaker is to drive. The measurement of impedance magnitude and phase angle will give the user an idea of how to match the speaker to the amplifier. If the speaker has low impedance and a high phase angle, a powerful amplifier delivering high current while remaining stable into low impedances will be needed. If a speaker has higher impedance and a low phase angle, the demand on the amplifier is lessened.

Home Theater alludes to this;
http://www.hometheatermag.com/bootcamp/40//index1.html


http://en.wikipedia.org/wiki/Electrical_characteristics_of_dynamic_loudspeakers

http://www.stereophile.com/features/99/index5.html

Just to be clear, I never stated that a large phase angle had anything to do with how a speaker sounds nor have I ever implied it on this thread. I maintained the fact that impedance, phase angle and minimum impedance would help better match a loudspeaker to an amplifier's drive capability. Thats been my postion in this thread all along.

 

[3db]

3db, I drive speakers of my own design with 3k in drivers alone with $160 Behringer 500 amp driving and people are amazed with the sound. I also have dead Krell that I got for the repairs, seating next to it. It is always assumed that Krell is playing.
Just get yourself the best speakers you can afford and don't worry about the amp so much.

I'm just advocating for better specifications is all