Violet DSP Evolution - an Open Baffle Project

[Dan_E10]

twest820,
Thanks for the link on filter design. I'll read deeper in Matlab's docs to see if I can come up with something that might be useable.
Dan

[twest820]

Dan, what's apropos to a crossover's radiation pattern is the behavior of the crossover's electrical outputs relative to each other. Converting one to linear phase and leaving the other warped phase won't preserve phase tracking. To preserve a consistent radiation pattern the FIR patch up you describe will end up applying the same phase correction to the tweeter as was applied to the woofer. So you might as well save yourself the hassle and just light up the active button on the Arbitrator channel.

Managing output phase shifts due to Fs, ports, or acoustic center alignment is a separate set of corrections. You're correct they're important for getting the overall response flat phase, but as a design consideration that's distinct from the radiation pattern effects of switching from one crossover to another. Typically Fs for midranges and tweeters is low enough it doesn't cause signficant phase shifts within their pass or transition bands. Hence Arbitrator's UI assumes the applied port/free air/bandpass phase correction only affects the woofer. That doesn't hold for pro drivers, particularly in four ways, and I'm trying to convince Jan some improvements would be helpful.

SoundEasy has an FFT based crossover emulator. It doesn't do FIR and you have to design a passive crossover and plug in driver models to use it. Good for planning passive crossover builds, very cumbersome as a digital crossover.

[Dan_E10]

Dan, what's apropos to a crossover's radiation pattern is the behavior of the crossover's electrical outputs relative to each other. Converting one to linear phase and leaving the other warped phase won't preserve phase tracking.

Right, my point was not so much that the radiation pattern would be different, but that the frequency response in general would be different. Even if you change both both the electrical high and lowpass sections to linear phase, the phase tracking will be different than with min. phase filters because the electrical portions were probably not symmetric. Their contributions to the final acoustic response was not equal so the new response with linear phase filters could be different.

To preserve a consistent radiation pattern the FIR patch up you describe will end up applying the same phase correction to the tweeter as was applied to the woofer. So you might as well save yourself the hassle and just light up the active button on the Arbitrator channel.

Yeah, point well taken. I haven't used Arbitrator for a while, it's time to do some more A/B comparisons with it again. I was interested in cuibono's filtering setup because he had not been that impressed with Arbitrator but seemed pretty happy with the linear phase filters he's using now.


Dan

[Dan_E10]

cuibono,
I think you mentioned the Tang Band 1320's were just about the right size to cross to your tweeters to balance radiation pattern while not being too small that there are air flow issues at the back of the driver. Did you look at any even smaller drivers than the 1320? If so, which ones and what did you find?
Dan

[twest820]

Originally Posted by Dan_E10

Even if you change both both the electrical high and lowpass sections to linear phase, the phase tracking will be different than with min. phase filters because the electrical portions were probably not symmetric. Their contributions to the final acoustic response was not equal so the new response with linear phase filters could be different.

In the general case, yes, hence my remark about the phase tracking needing to remain the same. Personally most of the crossovers I've encountered are symmetric, with LR2, B3 (Butterworth), LR4, and LR8 being most common.

I took a look at active and passive crossover design and concluded I might as well go direct to digital, but along the way I got the impression the main reason for using asymmetric slopes in analog crossovers is time aligning drivers. That's of limited utility in dipoles as time aligning the front wave degrades back wave alignment; better to get the physical alignment correct. And, with a digital crossover, it's easier to change the channel's delay setting than to vary slope. The other reasons I've seen for asymmetric slopes are reducing component cost and development time and maybe trying to dodge a problematic driver behavior. IMO these don't really apply in digital as the incremental cost of using and tuning higher order crossovers is low.

[cuibono]

Sorry for not responding - I moved last week...

Dan - I've looked quite a bit at 3" drivers, and there are a few I'm interested in. But the thing is, I really doubt that you could use only a 3" driver as a mid in a 3-way. The other thing is that there are no guarantees on the radiation pattern for the 3", so the only way to find out is buy one and measure.

[Dan_E10]

Whoa!

I measured it outdoors, 3.5m in the air, at 1.85m, and it is effectively ungated. 30deg is the listening axis.

I just realized, 3.5m in the air is over 11 ft. high. How did you suspend your speakers and mic that high?

But the thing is, I really doubt that you could use only a 3" driver as a mid in a 3-way. The other thing is that there are no guarantees on the radiation pattern for the 3", so the only way to find out is buy one and measure.

Yeah, at some point soon I'll have to do that. From skimming over this and other threads I'm thinking the Neo3 matched to either the Neo8 or TB1320 is a good place to start with open baffle. On using a 3" driver in a 3 way, I was thinking more along the lines of monopole subs with 3-way dipoles running from somewhere around 100-150Hz. That might allow the use of one or two 8" or 10" drivers to run to a higher crossover point that a 3" driver could handle. Still, that's probably better considered a 4way since the subs might need to run off a different signal that the dipole woofers.
Dan

[cuibono]

Hi Dan - to measure speakers, I basically have a small table with 8' beams for legs. For the mic, I have a camera tripod, the legs of which I taped long poles to. Pretty home made, but works fine. I've taken pictures, just not posted them.

If you only want to go down to 150Hz, there are lots of 8" and 10" possibilities. That is one of the major benefits wrt the mid section of OB speakers - if you split the 150-2500Hz range between two drivers, your selection of appropriate drivers goes from almost nill to almost any.

[wowo101]

cuibono - since my last post to this thread I started my own experimental OB project, and in the course of driver testing I seem to reach every point you already got to. I hope you take my gradually copying your design as a compliment.

At the moment I'm discovering the low end limits of the 1320s, and I'd be very glad to hear about your experiences when driving them at higher SPLs. My own findings are that those little gems turn into nasty little noisemakers when driven below 400 Hz and above 80-85 dB SPL @ 0.5m - can you confirm that? At what levels are you driving your system?

And apart from that: Did you change anything in the setup, or are you still using the 3-way configuration?

Thanks for an update on that!

[cuibono]

Hi Wowo,

The model I use is the w4-1320sj - did you get the same? I haven't had any issue with their low end performance. I drive them really loud.

It looks like you are only judging by measurements, and you're not too sure of your setup. I would check by listening too, before making judgement. I do non-linear distortion tests of the drivers, and had no issue. I didn't save the data, so I can't show it though...

For the last month, I've been away from home at a new job. I'm not currently doing any audio stuff, but a break is okay...

Good luck with your driver. I had serious issues with the TB driver I was using before the 1320sj - it had manufacturing issues - I had 4 of them, and they all had the same issue, some sort of buzz. You might be seeing something similar...