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Multi-Way Conventional loudspeakers with crossovers

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Old 16th March 2013, 05:38 AM   #111
Stevenn is offline Stevenn  Australia
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Thanks Tony
New graphs produce horribly different response..... why is that?
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Old 16th March 2013, 07:59 AM   #112
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Because they have phase data The frd and zma files without the added phase data make it look like the drivers have perfectly flat phase across their frequency range. This will result in the sim assuming perfect phase alignment if the electrical filter phase matches. This doesn't happen in reality though.

I've been playing around, have moved it to speaker workshop as I find it better for fine tuning. I see why you say the drivers don't match well. The mid is a bit low on efficiency. I dropped the target to 87db and that seems to work better.

I also dropped all of the ancilory (zobels etc) to start off, I will add in if I think necessary.

Going out for dinner now.

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Old 17th March 2013, 12:18 AM   #113
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Hi Steve, could you give me the dimentions of the baffle? also I'm assuming the drivers will be centered, so could you also give the approximate distance from top (or bottom) of the centre of each driver.

As I really struggled to understand phase when I was starting out, I thought that this short youtube clip might help. Sine Waves and Degrees of Phase - YouTube

Basically if two sine waves are 180 deg out of phase they will cancel each other out resulting in a dropout in the sound. If they are in phase they will add together. In between they will either add or subtract to a certain degree.

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Old 17th March 2013, 12:36 AM   #114
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Tony,
Nice examples to simply explain phase angle. Now you have to add the different acoustic centers to multiple devices on a baffle and the time misalignment to the equation and things start to get more complex. Add in the electrical phase angle from a second or third order filter and it gets even more messy. This is why it is so much easier to go with higher order filters such as 4th order as the overlap is much less and the phase angle of 360 degrees takes that out of the equation to an extent. The more you look the more you realize how hard it is to really produce an excellent speaker + crossover design that give the conjugate result that you are looking for.

Steven
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Old 17th March 2013, 08:26 AM   #115
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Yes Steven (KH), I've already got to a point where I was thinking about the driver offset's and the z offsets. These are things that I didn't have to worry about with my MTM's as they were all factored into the actual measurements. All measurements were done on axis with the tweeter (with drivers in their final cabinet), and time zero locked, so vertical and depth offsets were already in the measurements.

I've not tried going about design from the traced measurements in a serious way before, and I can see that whilst it will be better than an off the shelf crossover, I can't see it being as good as if real measurements are taken on the baffle.

Also going back into speaker workshop and playing with the sims, I've realised that getting the phase tracking right was probably the hardest bit, much harder than getting the slope correct, and quite a few iterations were necessary, trying different electrical orders (but still getting the same accoustic slope) was necessary before flat fr AND good phase tracking were achieved.

One thing I found with the hilbert transform was that the phase could be quite different depending on where I start the lower frequency from, this is not giving me a lot of confidence in the phase data.

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Old 17th March 2013, 10:50 AM   #116
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Hi Steve,

first thing I would say definitely has to change is the resonant peak filter on the tweeter. I modeled it it speaker workshop with the values you have in PCD, and it is missing the mark. Attached is a comparison of your pcd one, compared to the one automatically calculated by speaker workshop, and finally the one that resulted when I ran the optimizer in SW for the tweeter circuit I had.

The SW auto one is pretty much optimal as far as flattening the impedance is concerned, the optimizer probably changed it a bit to get the rollof to match the target curve I had better. The circuit diagram shows the SW auto calculated one.

The tweeter doesn't appear to have any ferro fluid (the impedance peak would be much lower if it did) so it probably does need the zobel if you want it to roll off properly, certainly I found it necessary (even though I started without it) to get the tweeter to fit the target curve (which I ended up setting at 4th order L/R at 3Khz).

Tony.
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File Type: png tweeter_zobel_compare.png (25.9 KB, 31 views)
File Type: png tweeter_zobel_SW.png (6.5 KB, 29 views)
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Old 17th March 2013, 11:22 AM   #117
Stevenn is offline Stevenn  Australia
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Thanks Tony
I tried Speakerworkshop and found it virtually incomprehensible to the uninitiated compared with PCD which at last has an intuitive feel to it. After an hour I still had not loaded driver files so I gave up.
Will measure driver centres tomorrow, they are not aligned on same vertical axis. Nothing seems to be straightforward.....
I understand the concept of phase, but as driver data sheets invariably do not display it, I am mystified as to where info is coming from. Nothing seems straightforward! Why don't driver manufacturers talk about it more?

Thanks
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Old 17th March 2013, 10:00 PM   #118
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Tony
Using cartesian co-ordinates in cm from bottom LHS corner:
Woofer - (14,16)
Tweeter - (6.5, 46.5)
MId - (20,37.5)

All co-ords to centre of dustcap. Woofer is aligned with centre vertical line.

Hope this makes sense.
Again, please do not spend much time on this, this is way beyond what i was expecting!

Thanks
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Old 17th March 2013, 10:05 PM   #119
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Don't forget the third co-ordinate.
Depth of speaker to the Voice Coil/Dust cap
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Old 17th March 2013, 10:17 PM   #120
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Hi Steve, don't worry, I've always found that trying to help people increases my own understanding, so it helps me too

On the questions on phase, KindHornman touched on that above, that is one of the reasons for requesting the driver positions. You will notice that PCD has a section where you can enter the relative driver offsets. This is one place where it has an advantage over speaker workshop. What I'm having trouble with at the moment is how I get (very) different phase data depending on where on the freq scale I start the hibert transform.

Speaker workshop is easy once you get the hang of it, but getting there has quite a steep learning curve.

Right click in the left pane and click import to import your driver frd and zma.
go to resource new driver and add a driver. double click it. right click on the graph that comes up and select properties. go to the data tab. click on the question mark beside frequency response and zma and choose the measurements you imported.

You now have a driver that you can add into a network.

I find speaker workshop better for looking at the phase than PCD as I can adjust the graphs more, it's also better for doing notch filters, but pcd will probably be better for your situation

Tony.
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