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Old 5th October 2007, 08:34 AM   #1
BHTX is offline BHTX  United States
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Default My plans for SEAS coax with Dayton RSS265HF

Just ordered a set of Seas T18RE/XFCTV2 (H1333) coaxials with crossovers earlier this evening, specifically the "Seas Loki Coaxial Kit without Cabinets" from Madisound, with the intention of ordering up to 5 more once I'm certain on a design and things get rolling.
http://www.madisound.com/catalog/pro...3377eab36f44a6

So far, the best option I can find for my intended use (both music & home theater) seems to be a large tower, with 4 Dayton RSS265HF-4's per side in separate 1 cubic foot sealed chambers with a Linkwitz transform, actively crossed somewhere between 200-300 Hz LR4. Each pair of woofers will be driven by one channel of my Mackie FR series amplifiers... so a 2 ohm load to each amplifier channel (which I don't particularly care for, but oh well). The Seas drivers will be in their own .25-.30 cubic foot sealed chambers as well.

I've always owned the larger beefy subwoofer drivers out there (20-30mm+ xmax), but I think I'm beginning to stray away from all that mess. I had originally planned on doing something a little bit smaller for the left and right channels and using separate subwoofers, but I think I've come to realize that using any kind of a woofer as just a woofer (depending on its frequency response tho), rather than crossing them so low (40-80 Hz) like subwoofers might yield lower group delay, better integration with the other drivers, and just an overall better sound. However, I'm not completely certain of this, and have only come to this conclusion as an observation during modeling. I find this very interesting, and would like to confirm it and get other people's opinions.

If it's not already obvious, I've never designed or built a crossover, hence my reason for ordering the Seas drivers with the crossovers from Madisound. As previously mentioned, these will be used with an active crossover for the Dayton RS woofers. I don't think doing this will cause any problems, will it? As for the passive crossover itself, I'm not exactly sure of the components and design, but I'm pretty sure it's just a simple 2nd order without BSC. I have no idea of the xover point to the tweeter. Any ideas? Also, I did come across another crossover design several weeks ago somewhere on the web for these coaxials that was supposedly really good. I think the guy was pretty well-known too, but I can't seem to find a link at the moment. Anyway, I probably wouldn't be interested in doing that right now, but would definitely consider it in the future.

Now, on to my biggest question.. I've attempted to use several of the free little modeling software programs over the years, and unfortunately, due to my lack of knowledge the one I feel most comfortable with and have used the most is WinISD Pro. From what I can tell, this program isn't too accurate at times, and is only really useful for woofers. However, one thing I've been trying to read up on lately is phase between drivers in multiway loudspeaker systems. Like I said, I'm pretty sure it's not very accurate, but I've observed that it seems tough sometimes to line up the phase plot so that the lines cross right at the crossover freq, especially when VC inductance and all the other parameters are entered. It usually seems like the higher the xover point, the better. Why is that? Is this the least bit accurate? Won't the passive crossover on the Seas coaxial slightly affect the phase between the Seas mid-woofer and the Dayton woofers?? If I add a 2nd order Butterworth lowpass at 2 KHz on the Seas woofer, the phase between it and the Daytons shows to line up perfectly when I cross them at 300 Hz. Without the 2nd order lowpass on the Seas woofer, it's 5-10 degrees off and doesn't cross until about 500 Hz. I'm guessing this is normal? Regardless, the Dayton RSS265HF looks far better on this phase plot than anything else I've tried with the Seas H1333. Anybody mind explaining to me what's going on here? Is this actually important/accurate? I'm guessing that it might become less of an issue at lower frequencies anyway, but how low?

As always, any answers/thoughts/opinions/suggestions would be greatly appreciated.

Thanks,
Brandin
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Old 5th October 2007, 01:18 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

You cannot use those programs in the midrange.

Download the trial version of Basta! and play with that.

http://www.tolvan.com/basta/

It does seem the crossover has no BSC - which you will actively
have to fix - hopefully it has accounted for baffle ripple effects.

/sreten.
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