500 Hz IMO,the 411's only go out to 1000Hz they are a medium efficiency woofer and why you need to use the 30904 network with Altec compression drivers.
One Altec speaker these came in was the Barcelona's 873A and they were crossed at 500 Hz...
http://www.lansingheritage.org/image...lona/page2.jpg
http://www.lansingheritage.org/image...nal/page14.jpg
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