First crossover attempt - what do you think?

[ChaoticKinesis]

Hello all.
This is my first attempt at a speaker design and I would like to know what you think. I intend to use the Peerless 831990 woofer on sale at Madisound and the Seas 27TDFC in an MTM configuration. A possible crossover is attached below and I would like to know your thoughts on it.

My main concern is the impedance phase angle, because I understand that that should not rise or fall as much as it does here (+/- 50 degrees). For some reason every design iteration so far, which has been a dozen or so, has not been better in this regard. I'd like to know what I'm doing wrong for this to be happening, when I see so many designs that are +/- 20 degrees. Though my knowledge of electronics is not great, don't be afraid to throw a somewhat technical explanation out at me, if that's what is necessary.

For the record, I'm using manufacturer's data with the FRD tools and SW for crossover design. And the single woofer in the network diagram is actually the response of a network consisting of the two woofers parallelled.

Thanks in advance!
Dave

[ChaoticKinesis]

Well over 100 views and still no reply? Basically I'd just like to know if this impedance curve is something I should be wary about for the sake of my amp. Is the problem in the crossover design or is it inherent in the drivers themeselves (doubt that)?

Dave

[Tommythecat]

What amp?

[ChaoticKinesis]

It's an HK230 receiver.

[Dennis H]

Impedance phase angle is just another way of looking at how much the impedance changes with frequency. It shouldn't be a problem for most modern amps. If it concerns you, you could always put a Zobel (series LCR) across the input terminals to flatten out the impedance peak.

[ChaoticKinesis]

Thanks Dennis.

[jkrutke]

Hello,

If you're using manufacturer's data, is it infinite baffle? If yes, did you sum in baffle step and diffraction for the tweeter?

In most LR4 usages with the Seas, 2 components and an L-pad will do fine. If you need 3 components to hit LR4 slopes, I'm guessing you didn't add in diffraction.

Given the 1.5mH into the paralleled woofers, Id say you did it for the woofer, but be aware you have to do it for the tweeter also.

And now that I've mentioned the diffraction affecting the tweeter's curve, be aware that you can't model MTM cavity effect. (yet) you have to measure it.

The FRD tools are nice and the price is right, but eventually you should shoot for measuring your own drivers in your enclosure if you want to have accurate results.

Regards,
John

[Marzen]

John, what's cavity effect & how do you ID this when measuring?
Thanks,
Ward

[ChaoticKinesis]

John, the data is infinite baffle and I summed in diffraction and baffle step using the Baffle Diffraction Simulator. Regarding the tweeter network, second order electrical gave me about 20dB/octave roll off, so not quite LR4 and response was not as smooth through the passband as with third order. I guess I'm going to play with that some more now to see if I can improve that.

I too would like to know more about cavity effect as that is not anything I've heard of before.

Dave

[jkrutke]

I too would like to know more about cavity effect as that is not anything I've heard of before.

That's right, it takes me a month to answer a question.

All speaker systems with cone woofers and dome tweeters have cavity effect to some extent. It's barely visible in smallish TM designs but can be up to a 6 dB dip to peak variance in the worst case, which is an MTM with driver placement that amplifies baffle diffraction ripple.

Digging through my directory of speaker measurements, (gah, ever have that problem that when you open a directory, it's so big that windows has to take 30 seconds to view the contents) here's an MTM attached. The dip at 4kHz and peak at 5kHz are primarily cavity effect. It's center frequency and amplitude can vary based on surround design, cone profile, driver position, and it's combination with diffraction ripple which may have effects at the same frquencies or may cancel out at the design axis.

Cavity effect works the same as baffle diffraction - the sound wave from the tweeter follows the baffle and releases when it hits the woofer cone edge and/or surround.

But I guess the point is that there is nothing out there that models this, and it's the main inaccuracy issue with current baffle diffraction simulators. (and midbass inaccuracy because none model cabinet depth) The good news is that it often smooths out off axis in much the same way that baffle diffraction changes off axis.

It can be worked around in the crossover design. You can't get rid of it without a lot of complexity and causing issues off axis, but you do want to minimize peaks on the design listening axis in favor of dips. Dips are much less audible.

[augerpro]

When you measure this is it just one driver being driven (say an MTM), or all three and this is the summed response at 1 or 2 meters?

Would an acoustic treatment like felt or something on the baffle help with this?