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Multi-Way Conventional loudspeakers with crossovers

Designing a Crossover for a Mini Two Way, How Important is Driver Phase Response?
Designing a Crossover for a Mini Two Way, How Important is Driver Phase Response?
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Old 25th May 2016, 05:41 AM   #1
MickyG is offline MickyG  Australia
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Default Designing a Crossover for a Mini Two Way, How Important is Driver Phase Response?

So, I've just recently returned to DIY Speaker building and have a full "kit" for some small monitors already sorted (look at Wayne Jaeschke's DBP HERE). Purchased probably in 2005, if I recall correctly. Yeah, it's been a long time...

But, that's not what my question is about. I have some surpless North Creek Music Systems D25 1" matched tweeters that I'd like to use, very much like Wayne's "PeeCreek" project. Only, since the 850122 wid-woofer is long gone, I've looked into some alternatives.

My best, closest match was the Peerless 830874. I could have gone with the 830883 but hated the silver frame and questionable performance benefit for the price, or even the Nomex version 830875. In the end, the price/performance ratio of the 874 won out. I ordered a pair locally and they've arrived today.

On to my question - I'm not hoping for a drop-in replacement for the old crossovers for the PeeCreek and there are a number of differences between the old driver and the new. I'm getting familiar with PCD again and seem to have worked out a few annoyances (it was built for Excel 2007 after all). However, after tweaking a design and thinking I was the smartest guy ever, I realised I hadn't input any phase data for the drivers.

I went back to Response Modeller and after several attempts, managed to get what I think was an accurate phase curve to import back into PCD.

And then my beautiful response curve fell completely apart...

So here's the question: Is there an accurate source for phase data for a given driver? Furthermore, is there any magic to phase data or can it be determined purely on the FR of a given .frd file? Or .zma for that matter? I'm definitely stumped.

Oh, and if this is the wrong place, please let me know so I can flag it with a mod.

Cheers,
Michael
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Old 25th May 2016, 06:18 AM   #2
eriksquires is offline eriksquires  United States
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Hi Michael,

I usually measure the phase and amplitude at the same time. OmniMic has an option to phase restore an FRD file. This is useful when the data is coming from a picture that has been traced.

The acoustical phase is related to the slope of the FRD data, if I recall, so it can be restored mathematically fairly easily.

The electrical phase however is something else, and I"m not sure if it's possible to phase restore it, nor am I sure it matters. That's something I haven't thought about.

It's very important to have the acoustical phase, but you need to know not only the phase vs. frequency, but also the inter-speaker distance. Please read about measuring that on my blog page here. The speaker's natural response + distance is necessary to compute a crossover's final response accurately.

Also, please check out the LM-1 project I just published. About $470 if you buy the cabinets, about $300 if you build them yourself.

Best,


Erik
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Old 25th May 2016, 06:29 AM   #3
MickyG is offline MickyG  Australia
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Thanks very much for the info Erik!

I should have mentioned I've got a very good grasp on driver distance, driver placement on the baffle, size of baffle, and driver depth. Well, a good grasp on how they all can affect response.

What I specifically wanted to know was how the FRD data can possible predict phase, the way the extraction tools seem to suggest.

I've got one of those little iMMC mics from Dayton audio to play with when I get moving on this little project.

My plan at the moment is to define enclosure completely, cut all the wood for the enclosures and then get to work on the crossover, perhaps even using the measurement analysis tools and mic to do it all in sync.

I'll have a look at your blog and see what else I can soak up. Thanks again!
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Old 25th May 2016, 06:49 AM   #4
eriksquires is offline eriksquires  United States
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Hi Mikael,

Yes, driver phase is pretty tightly related to the frequency response of a driver, so you can rely on phase restoration tools.

Best,

Erik
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Old 25th May 2016, 06:58 AM   #5
MickyG is offline MickyG  Australia
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Fascinating. I understand the whole damping, vs radiator size, vs frequency relation but wasn't sure phase could be "read" from a simple FR curve. I'll have to play around a bit more with the modelling software to see if I can make it all match up with my (limited) knowledge at this point.
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Old 25th May 2016, 07:50 AM   #6
eriksquires is offline eriksquires  United States
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Technically phase its not related to amplitude but to the rate of change of amplitude, if i remember correctly. it has been decades since i studied this.

Best,

Erik
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Old 25th May 2016, 08:51 AM   #7
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by MickyG View Post
I've got one of those little iMMC mics from Dayton audio to play with when I get moving on this little project.
Measuring can be a good idea, as not all of the sound will be coming straight from the driver. A reconstruction may not be all you expect it to be. Additionally, you won't need to worry about driver distances.
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Old 25th May 2016, 11:38 AM   #8
Grasso789 is offline Grasso789  Germany
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Quote:
Originally Posted by eriksquires View Post
Technically phase its not related to amplitude but to the rate of change of amplitude, if i remember correctly.
Yes. In minimum-phase systems, say all systems which have only one signal path (what excludes interference, as interference is due to several signal paths interacting), phase is derivation, steepness, rising/falling angle of the plot of amplitude versus frequency, if both amplitude and frequency are shown on logarithmic scale.

Electroacoustic drivers are minimum-phase at low frequencies. If their size approaches wavelength, it becomes different especially off-axis. It must, for else multi-way loudspeakers would hardly work off-axis at all.
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Old 26th May 2016, 05:54 AM   #9
MickyG is offline MickyG  Australia
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I managed to find some of the PartsExpress catalogue extractions from Clio that someone archived ages ago (HERE).

Why do I need old, archived responses? Because I want to "sanity check" my understanding of PCD first, by using the original drivers in the PeeCreek, along with the details of the original kit, as measured by the designer. Then I can look at the driver phase and see if what I get from extracting the phase, matches up with what the modeled response and measured response showed on the site. Granted it's not exact but if it's ballpark, I will know that my own, new project at least is being put into the simulation correctly.
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Old 6th June 2016, 03:13 AM   #10
MickyG is offline MickyG  Australia
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...Just hit some random key combination and lost a fairly lengthy update to this thread. Oops..

So I'm in the final stages of building and have decided to buy the drivers first, settle on an enclosure (I'll likely be going sealed for better integration with my sub, as well as ease of designing the cabinets). My final task will be to test the drivers mounted in the boxes and then (and only then) will I start working on the crossover design.

This will be the first time I've ever done it this way but I think it's the best way to make sure I get exactly what I want to make this all work best.

I've played around enough with the various Excel tools to get to where I think I'm proficient enough to make this all work out well. Thanks for the pointers and the help so far, all! I'll post a new thread when I start construction.
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