These as every build I do are a labor of love. To bring dance partners together and by that I mean bringing components together. I think the most overlooked component in any system is the conductor...I mean the crossover. My analogy is the woofers, mid range, tweeter/horn, and horn driver are the musicians. No matter how great the musician and you could have a room full of them, it will sound like chaos...until the Mistro or conductor steps into the room. He will delegate how and when each instrument comes in. I found this out, but I had to find out by trial and much error. But with patients, I overcame the inherent problems vintage speaker builder encounter, or at least I encountered. But I found the sweet spot! And when I use my ultimate bass test album War with Eric Burden the song "Low Rider" I get earth shattering, sharp, concise bass that is capable of rattling my dual pained windows and wake the cows! But for some mysterious reason these new (new to me that is) Altec 515B's in cabinets I built to Altec 612 specification...well sorta, you could actually just barely squeeze a 612 cabinet into mine with a quarter in here to spare and a half inch there, not to mention I used 1inch wood that I made with 3/4in MDF and a 1/4in hardwood...we'll call it vernier, glued and screwed to make the 1in wood I would use. Anyway I paired the 515B's with the 511B horns and the 802's for horn drivers, and tied this all together with some (believe it or not) NOS Altec N-500-D crossovers. And even though they sound great, they could not hold a candlestick to my first build which were a little bit larger cabinet 34X30X24inches stuffed with 2 woofers Altec 416's and Altec 803's (a 416 and 803 in each cab) woofers with 1004B 10 celled horns driven by Altec 288 drivers, tied together with Altec's N-800-D's, and I was to say the least...disappointed. Oh and did I mention that all of the components with the exception of the crossovers, 1004B/288 and 515B's are all Heathkit by Altec, I don't think Heathkit ever did a 515, at least not that I'm aware of. but they did do 511B horns with much nicer welds and finish work and also in my opinion built a much tighter spec'd 416 and 803. So I now know that the 515B's are not that much more of a woofer than the little brothers 803 and 416 and in that order 515, 803, 416, and the 803/416 beats hands down.