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Old 29th December 2012, 04:18 PM   #331
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Quote:
Originally Posted by Joachim Gerhard View Post
Still i would like to see the Step Response.
Thanks for explaining though.
I found these snapshots from back in April. They aren't very high resolution so I hope they are worth something. Here's the Step Response on the speaker (It says Impulse, but it's actually a Step Response):

Click the image to open in full size.

And here's the Impulse Response on the design axis:

Click the image to open in full size.


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Old 29th December 2012, 10:36 PM   #332
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Hi Joachim, very nice first attempt! very good phase tracking between the drivers. Interesting null, it looks similar to the first iteration of my MTM crossovers null... what was the target crossover freq out of interest?

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Old 30th December 2012, 01:34 AM   #333
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Originally Posted by Jeff B View Post
However, the tweeter axis is typically used as the design and listening axis simply because it is the more directional of the two drivers, especially at the upper end of its frequency range. Midwoofers are usually crossed over before they become directional, but we don't have that luxury with tweeters. If a tweeter is large, like these 29mm SB tweeters then the top octave can roll-off quickly as you move off axis.

Jeff
Thanks Jeff, that makes sense. So tilting the baffle works as HF EQ as well as driver alignment. Joachim has the tweeter firing horizontally, but you have chosen tilt. Should there be much attenuation of tweeter at HF with this amount of tilt?
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Old 30th December 2012, 10:23 AM   #334
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Originally Posted by Richidoo View Post
Thanks Jeff, that makes sense. So tilting the baffle works as HF EQ as well as driver alignment. Joachim has the tweeter firing horizontally, but you have chosen tilt. Should there be much attenuation of tweeter at HF with this amount of tilt?
Not much, it's only 14 degrees. I posted the measured response a few posts up so you can see there's no droop in the top octave at this angle. In reality if I raise the mic and angle it at the tweeter the response would be rising a bit more above 12khz, so the angle does help to flatten the forward radiating energy a tiny bit.
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Old 31st December 2012, 02:52 PM   #335
gornir is offline gornir  Sweden
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Originally Posted by Jeff B View Post

Here's another pic. Only this one shows the old one-piece face plate on the tweeter, but it gives a good idea of the speaker's look.

Click the image to open in full size.

Jeff B.
Jeff,

What's your baffle dimension (baffle width and baffle edge round-over)?

I'm a bit curious because, when I started some simple quick and dirty cross-over simulations based on these measurements I found out that the baffle step where a bit more complicated than usual to take care of, at least when I simulated LR2 filter with 3kHz x-over point and didn't want an excessive amount of components. If I lower the x-over point to about 2.4kHz it looks easier.

When I measured my Satori mid-woofer I used an 24.8cm wide baffle with (r=18mm) round-over for the baffle edges and get a broad hump (+5dB) centered at approximately 800Hz and f/2 at 570 and 1150Hz.

For comparison:

Click the image to open in full size.

Measured @ Tweeter-axis, on-axis.

Blue = Satori MW16P-4 (24,8cm baffle, r=18mm round-over)
Red = ScanSpeak Revelator 15W/4531G00 (21,6cm baffle, r=12mm round-over)
Green = AudioTechnology 15H520613SDK (21,6cm baffle, r=12mm round-over)

Happy New Year!

/Göran
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Old 31st December 2012, 09:12 PM   #336
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Originally Posted by gornir View Post
Jeff,

What's your baffle dimension (baffle width and baffle edge round-over)?

I'm a bit curious because, when I started some simple quick and dirty cross-over simulations based on these measurements I found out that the baffle step where a bit more complicated than usual to take care of, at least when I simulated LR2 filter with 3kHz x-over point and didn't want an excessive amount of components. If I lower the x-over point to about 2.4kHz it looks easier.

When I measured my Satori mid-woofer I used an 24.8cm wide baffle with (r=18mm) round-over for the baffle edges and get a broad hump (+5dB) centered at approximately 800Hz and f/2 at 570 and 1150Hz.

For comparison:

Click the image to open in full size.

Measured @ Tweeter-axis, on-axis.

Blue = Satori MW16P-4 (24,8cm baffle, r=18mm round-over)
Red = ScanSpeak Revelator 15W/4531G00 (21,6cm baffle, r=12mm round-over)
Green = AudioTechnology 15H520613SDK (21,6cm baffle, r=12mm round-over)

Happy New Year!

/Göran
My baffle is 16" tall by 9" wide with 3/4" roundover (40.6 cm x 22.9 cm, 18mm roundover)

I did not find the baffle step to be troublesome at all. However, you will find with a driver like this on this size baffle that the simplest crossover will typically net a crossover point close to 2 kHz or over lower.

I never force a crossover (meaning pick the crossover point in advance and try to force that to be my crossover point). You will find that depending on the woofer and tweeter's natural response, their phase response, and the offset between the drivers, that with certain acoustic slopes there is a natural crossover point that you can arrive at with very simple electrical circuits and achieve the correct phase alignment at the same time. In my case the crossover in my Kairos speaker is a hair under 2 khz (about 1.9kHz, but slopes are gradual in this region).

If I tried a higher crossover point, like 3khz, which I experimented with, then the circuits picked up considerably more elements.

And remember, crossover types like LR2 or LR4 are always a combination of the driver's natural roll-off and the circuit's transfer function. In other words, for an LR4 crossover, if the tweeter is begining to roll-off naturally second order around 1-2 kHz then all you may need is a second order circuit to achieve a perfect LR4 response.

And of course, if the drivers are on a flat baffle, then asymmetrical roll-offs are usually required to compensate for the relative offset of acoustic centers and arrive at good phase tracking (within the crosover region).

Jeff
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Old 1st January 2013, 12:53 PM   #337
gornir is offline gornir  Sweden
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Quote:
My baffle is 16" tall by 9" wide with 3/4" roundover (40.6 cm x 22.9 cm, 18mm roundover)
Thanks for the info!

Quote:
I did not find the baffle step to be troublesome at all. However, you will find with a driver like this on this size baffle that the simplest crossover will typically net a crossover point close to 2 kHz or over lower.

I never force a crossover (meaning pick the crossover point in advance and try to force that to be my crossover point). You will find that depending on the woofer and tweeter's natural response, their phase response, and the offset between the drivers, that with certain acoustic slopes there is a natural crossover point that you can arrive at with very simple electrical circuits and achieve the correct phase alignment at the same time. In my case the crossover in my Kairos speaker is a hair under 2 khz (about 1.9kHz, but slopes are gradual in this region).
Complicated was perhaps a strong word, I would say a bit tricky since I were hoping not to need to equalizing the remaining hump with a LCR circuit (L2+C1+R1), but again this is purely experimental at this stage. See picture 2 and 3.

Quote:
If I tried a higher crossover point, like 3khz, which I experimented with, then the circuits picked up considerably more elements.

And remember, crossover types like LR2 or LR4 are always a combination of the driver's natural roll-off and the circuit's transfer function. In other words, for an LR4 crossover, if the tweeter is begining to roll-off naturally second order around 1-2 kHz then all you may need is a second order circuit to achieve a perfect LR4 response.

And of course, if the drivers are on a flat baffle, then asymmetrical roll-offs are usually required to compensate for the relative offset of acoustic centers and arrive at good phase tracking (within the crosover region).
I haven’t yet finally decided which tweeter to use in combination with the Satori mid-woofer, but I’ve tested a couple of ScanSpeak tweeters on the same baffle, hence the experimental 2.4kHz x-over which seems viable with one of them using a stepped baffle and yes, all your advices is a nice good sum-up of things among others to consider in the chosen design.

Picture 2: Experimental 2.4kHz LR2 x-over
Picture 3: Mid-woofer 15deg off-axis, effect of LCR

Sorry Joachim it wasn’t my intention to hijack your thread, but I was a bit curious and thought it was interesting to compare the different baffle dimensions we used, yours 30cm wide baffle and Jeffs 22.9cm and my 24.8cm.

/Göran
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File Type: jpg Picture2.jpg (16.7 KB, 180 views)
File Type: jpg Picture3.jpg (191.1 KB, 228 views)
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Old 1st January 2013, 09:15 PM   #338
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Göran, do not worry, your experiments are interesting and helpful.
Jeff, great work you did.
I placed the crossover at ca.2.1kHz. Yes it seems to be that lower crossover points work better with the Satori Mid-Woofer. I prefer lower crossover points anyway to stay out of the problem zone in the upper range.
The Satori is very extended but does not work as a perfect piston any more higher up.
Fortunately modern tweeters are quite extended in the deeper regions too.
Yes, the DIY version of the cabinet i designed has a straight baffle with the woofer on a thinker baffle but the professionally made cabinets made by SB will have an angled baffled, not much different then Jeffs design. I posted a rendering of that version some time ago.
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Old 1st January 2013, 09:42 PM   #339
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Originally Posted by Jeff B View Post
And remember, crossover types like LR2 or LR4 are always a combination of the driver's natural roll-off and the circuit's transfer function. In other words, for an LR4 crossover, if the tweeter is begining to roll-off naturally second order around 1-2 kHz then all you may need is a second order circuit to achieve a perfect LR4 response.
I understand what you are saying, you are looking at the amplitude slopes, shaping them as would LR4 electrical filters acting on drivers with no rolloff.

But true LR crossovers also have coherent phase between the crossed drivers. If you replace half the electrical filter with acoustic rolloff don't you lose that phase coherency? A 4th order electrical filter twists the phase faster than 2nd order electrical. I can understand that the rising inductance of the woofer coil adds some phase in the right direction, but does it change fast enough to match an electrical 4th order filter? I understand the low end roll off of the tweeter to be caused by decreasing acoustic impedance which I think will not affect its phase at all, but resonance affects phase. So is it really a true Linkwitz-Riley 4 crossover since phase is not necessarily coherent all the way through the filter band? Or is it?

I see this point made occasionally, that acoustic slope is what matters, but I never had opportunity to ask for clarification about phase until now. It is rare to have accomplished designers willing to share their expertise as you guys are here. Thanks!
Rich
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Old 1st January 2013, 09:57 PM   #340
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Yes, it is the acoustic response that matters. That has the consequence that the crossover schematic does not look like a textbook example at all.
I have made L/R4 and L/R2 filters many times where the phase matched over a very wide range. I do that usually with LSP-CAD and do the rest by trimming with hand while watching the individual phase window.
Here is a picture how the prototype box looks at the moment. I will round the edges and sink in the drivers. After this i will fine tune the crossover.
When the factory made cabinets come i will have to fine tune again.
While Jeff has made a phase linear version and Göran is working on an L/R4 i will stick to the L/R2. We have a lot of options then.
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