# Impedance Curve, does it matter for essque?



## onebadmonte (Sep 4, 2008)

Howdy all. I've got a little time on my hands and have a couple of widgets at my disposal. I'm running Stevens Audio Full Body horns in my ride and have a few compression drivers to try out. The compression drivers I've collected so far are the Stevens Audio Pro Drive, Dayton Audio D250P-8, and the DIY Sound Group DNA-360. I've head them here and there, but not long enough to decide which are the best for me. I've got one of those Dayton Audio DATS thingies, so I decided to test out my compression drivers and see what the impedance curve looks like with and without the horn body. I figure I'd share them and spur some discussion on how important the impedance curve is regarding sound quality. 

Lets start off with some measurements of the drivers without the horn.

Up first is a compression driver making a strong showing in the home theater scene, the DIY Sound Group DNA-360.


Here is the DNA-360 in my scientific testing lab.


Up next is Dayton Audio's offering the D250P-8


The Dayton driver going through the ringer.


Lastly the Stevens Audio Pro Driver.


The Pro Driver being tested.


Now lets see the drivers tested with the horn body installed.

First up is the DNA-360. This is what it looks like on the horn body.


Up close of the DNA-360 driver.


Here is the setup in the testing facility.


This is what the DATS had to say about the DNA-360 in the Stevens Audio Full size horn body.


Up next the Dayton D250P-8 installed on the horn.


Here is a close up of the D250P-8.


This is the Dayton driver getting tested.


Here is what the Dayton D250P-8's impedance curve looks like when installed on the Stevens Audio full size horn body.


Lastly the Stevens Audio Pro Driver on the horn body.


Up close and personal with the Pro Driver.


The Pro Drive getting it's turn through the test rig.


The results of the Pro Driver.


For ****s and giggles here is my Electro Voice DH1A driver on a AutoTech 350Hz Tractrix Horn body going through the test rig.


The results of the EV.




Here are some side by sides of the D250P-8, DNA-360, and the Pro Driver.


Any thoughts?


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## hessdawg (Feb 20, 2007)

Would like so hear Eric Stevens thoughts on this


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## Hanatsu (Nov 9, 2010)

The impedance and the impedance phase is electrical measurements that only the amplifier "sees". Unless it's a difficult load and the amplifier starts to act weird, it doesn't affect anything. Well, that's not really correct to say either, the impedance is inversely proportional to the amount of power the amplifier will feed the drivers and might affect the frequency response unless we talking about an ordinary free air resonance. Don't know if this applies to horns as I have limited knowledge of this topic.


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## Eric Stevens (Dec 29, 2007)

The impedance curve can tell you a lot of things with a HLCD, compression driver, or other speaker. Smoother is better in most if not all cases. The magnitude of peaks at resonance points are not part of the smooth statement.

It is more useful to also have the frequency response graph along with the impedance curve.

The magnitude of the peaks is a function of motor strength.

Smoothness in the higher frequencies shows behavior of the diaphragm.

The DNA driver appears to possibly have a problem (possibly rubbing or foreign material in the VC gap) as the higher peak in its free air impedance curve show a double peak.

easier to draw conclusions with frequency response data.


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## Patrick Bateman (Sep 11, 2006)

A few years back Geddes mentioned that he could get clones of the B&C drivers in China for about $25. He passed on the opportunity, as the quality of the B&C drivers was higher. Basically the Chinese drivers looked identical, but didn't measure identical.

A couple years after that, we started to see clones pop up. The Denovo and Dayton drivers are clones. 

These measurements are a great example of what Geddes was talking about. Take a look at the impedance curve of Eric's compression driver and the Dayton compression driver. *Eric's product just crushes the Dayton.* In particular, look at the wiggles in the top two octaves. Those 'wiggles' will manifest themselves as peaks and dips in the frequency response. Basically there's something going on that's creating a series of resonant peaks in the impedance curve. See those peaks at 8 and 9khz? That means the compression driver will draw a bit less power at those frequencies.

The effect on the frequency response might be subtle. But this is an excellent example of why you can't just rely on frequency response measurements. You really gotta look at that impedance curve. It will show you things the frequency response won't.

You should see the CSD and impedance plots of a ribbon. They're gorgeous.


I don't know what's inside Eric's compression driver, but I'd be willing to bet it uses a smaller and/or lighter diaphragm. The big heavy mylar drivers of the B&C clones aren't a huge issue on a properly sized horn. But car audio horns are dramatically undersized, so they tend to have smoother response when the diaphragm is smaller/lighter. (Small *and* light is better, but you can also get away with just lighter. For instance, the TAD drivers have a large diaphragm but it is a light diaphragm. Beryllium is much lighter than mylar.)


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## thehatedguy (May 4, 2007)

Not to mention ALL of the DE250 clones have a LOT less motor and sensitivity than the original B&C drivers.

I'm not that impressed with the ZMA data on the clones...Eric's drivers are pretty resistive compared to the other two, and those bumps in the impedance data can cause IME some funkiness in the sound.

But it would be helpful like Eric said to have some FR data to go a long with impedance data...and I would wonder what/how things change once they are properly coupled to the dash of a vehicle.


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## onebadmonte (Sep 4, 2008)

Thanks for the insight fellas. I'll try to get some reponse graphs to go along with these impedance curves to keep the discussion going.


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## thehatedguy (May 4, 2007)

The thing that bothers me about the Denovo drivers is that you can't easily get replacement diaphrams for them. Erich doesn't stock them, or didn't the last time that I looked. 

Folks have had pretty bad QC issues with the Dayton drivers too. Which is odd because Dayton is or has been pretty well known for good consistency with their cone and dome drivers.


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## Patrick Bateman (Sep 11, 2006)

onebadmonte said:


> Thanks for the insight fellas. I'll try to get some reponse graphs to go along with these impedance curves to keep the discussion going.











Here's a measurement of the JBL 2408H-1 screwed into Pyle's clone of JBL's PT waveguide. (Pyle PH612.) I put a cap in series to keep from blowing it up, 1mfd. Total cost is about $140 and it's almost as flat as a dome tweeter. I can see why Zilch was such a fan of these. I don't like the Selenium compression drivers, but this waveguide is great. Blue curve is on-axis, red is 45 degrees off axis. Looks like it will sound better cross-fired.


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## subwoofery (Nov 9, 2008)

I asked on DIYAudio but no answer, what difference in using a 1mfd VS a 3mfd? 

Kelvin


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## Patrick Bateman (Sep 11, 2006)

subwoofery said:


> I asked on DIYAudio but no answer, what difference in using a 1mfd VS a 3mfd?
> 
> Kelvin


With an 8ohm tweeter a 1mfd cap sets a first order lowpass at 20khz.
With an 8ohm tweeter a 3mfd cap sets a frist order lowpass at 7khz.

Calculator is here: http://www.carstereo.com/help/Articles.cfm?id=8

Basically I set the 'corner' up at 20khz. The combination of the natural rolloff of a compression driver and the first order filter gets 'flatt-ish' response to about 2khz.

You still need EQ to totally flatten it out, but a single cap will get you close to flat. If I'd put the corner at 7khz I'd have more output overall, but the top end would be decaying. (Because my 1mfd cap is basically 'complementary' to the natural response of a compression driver.)


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## subwoofery (Nov 9, 2008)

Patrick Bateman said:


> With an 8ohm tweeter a 1mfd cap sets a first order lowpass at 20khz.
> With an 8ohm tweeter a 3mfd cap sets a frist order lowpass at 7khz.
> 
> Calculator is here: Car Audio - Crossover Network Design Formulas & Calculator (1st Order Butterworth)
> ...


I think you meant to say Highpass, correct? 

Kelvin


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## Patrick Bateman (Sep 11, 2006)

subwoofery said:


> I think you meant to say Highpass, correct?
> 
> Kelvin


Correct! Thanks.


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