Driver Impedance 'kinks' and their implications

[Stevepaul]

Jon,Thomas, others....

Jon, I have been reading with interest your posts both here and over on the Madisound Forum, in regards to your methodology of choosing the correct drivers for your projects. You consistantly bring the importance of the impedance curve into the discussion....most importantly, looking at the kinks, bumps, etc.

After reading your latest post on Madisound, I looked at the Imp. curve of the Audax HM210Z12 (I have 4 of them sitting on the shelf). The have quite a large hump at centered around 375 hz. This shows itself in the Freq.response curve as a large 3.5db dip from 225hz...ending at around 500hz.

Am I too surmise that this woofer would be best used below the impedance kink...ie, below 375hz? Is this impedance kink (which is rather large compared to other woofers I have looked at) an energy storage issue? A cone mode? ?? What are the implications of using this woofer above 375hz?

I am not requesting a specific 'design' question....just looking for a more broad based understanding of this issue.

On a separate note...Another interesting observation is that rigid coned woofers, at approximately half the frequency of their major breakup region...they have a spike in their distortion products. For example, on the Excel W15, the major breakup region is around 6K...but, distortion spikes in the 2.5-3k range. Which would cause a designer to consider crossing over these types of woofers with steep slopes at a minimum of half of their major breakup frequency. Would this be another 'guideline' (albiet, broadbased) when considering various drivers?

I am a fan of rigid drivers (both tweeters,mids, woofs) and am looking to get better at my hobby. Thanks for anything you can offer.

Have a good weekend guys! :B
Steve Paul

[ThomasW]

Am I too surmise that this woofer would be best used below the impedance kink...ie, below 375hz?

:T

Would this be another 'guideline' (albiet, broadbased) when considering various drivers?

sort of :T

There's a good deal of info about our design techniques woven into Jon's 3 part AudioXpress article (hint, hint). And some info we simply don't provide to the public. But in a nutshell, here's some of the 'beef' without "spilling the beans" ...... :wink:

To get the 'best' performance from any given driver, use XO points a full octave below any glitches in the impedance plot. And if the glitches are 'big', be sure to use high order XO's. Failure to follow these guidelines will result in 'garbage' from the glitches degrading the overall SQ ... 8)

Note that this is one reason we frown upon the use of first order or series XO's.

Finally, there are people that ridicule 'cloning' or reverse engineering speaker designs. That's too bad, because when people do engage in that practice, it can be quite beneficial to their learning curve. Understand that one doesn't need to actually build the speaker, to obtain the knowledge. :wink:

[JonMarsh]

Yeah, what Thomas said....



Eight inch drivers can be a real mixed bag. A surprising number of them have cone or surround resonance issues at relatively low frequencies.

Many/most of them I would only use in a three way system- including those Audax.

By dint of the high order elliptic cauer filter which emulates an 8th order L-R for the first 40-50 dB of attenuation, I get away with running HiVI 8's or 6's in two ways- and get pretty good results.

Here's the nearfield sweep of the HiVi M8a at center, mid to edge, and edge. This is taken at about 1" from the cone surface, which is why the SPL is so high.




The impedance curve has no kinks until 2.5 khz, where the peak is.

I think there's a reason RBH, Revel, TC-Sounds, and many other "professional" speaker companies use an inverted dome cone.

~Jon

[Stevepaul]

Thanks Guys!

Thanks for all the information Thomas and Jon.

The more I learn....the less I know. As an engineer, I always want to know everything so that I make the best decision. But, there are so many different ways to make sound...2-ways, 3-ways, fullranges, 4-ways...subs, no subs. Each has their own tradeoffs.

Hopefully, this fall, my hobby money will be back up to where I can start playing again! Gotta' give them ARVO's a try!

Thanks again!
Steve

[JonMarsh]

Thanks for all the information Thomas and Jon.

The more I learn....the less I know. As an engineer, I always want to know everything so that I make the best decision. But, there are so many different ways to make sound...2-ways, 3-ways, fullranges, 4-ways...subs, no subs. Each has their own tradeoffs.

Man, is that ever true.... the closest thing, in my opinion, to true creativity, is just finding a better set of tradeoffs for meeting your needs and preferences. That's how the original M8 two ways came about, through four iterationis, and their lineal descendents, the M8ta and the Arvo's.

Now, I've been working on a new power amp design the last year and half... man, could I tell you some stories... :E actaully, it's not even "new", just a total refit concept for classic Aragon amplifiers- some of my friends and I just have too many of them to toss them out, but need to improve on some aspects of the performance... :B