First, some background info: I used my ALTEC 756B/Jensen RP302 combination on JE Labs Style open baffles. To fill in the bottom 2 octaves, I used a powered sub-woofer. After about 10 years with this setup, I decided I wanted to make 2 changes. First, I wanted narrower baffles (the JE Labs are almost 3 feet wide). Second, I wanted integrated woofers (no more separate powered sub-woofer).
After weighing my options and not wanting to give up my ALTEC/Jensen driver combo, I decided to go with the Pure Audio Project (PAP) open baffles and woofers. PAP cut a custom mid-range/tweeter panel for my drivers. This worked exactly as I hoped it would - the PAP baffles are about half as wide as the JE Labs OBs and with two 15" woofers per side, no separate powered sub is needed.
Initially, I bi-amped the PAP woofers off a separate Crown DriveCore 2 amp with built-in DSP crossover. I used the system this way for about a year until recently when I got the idea to see how the system would sound running it full-range with my 8 watt Bottlehead Paramount 300B amps. In order to do this, I purchased a pair of 80hz 4 ohm 12db/octave low-pass filters from Parts Express.
The reason the filters are 4 ohms is because the two 8 ohm woofers per side are wired in parallel. OK, so how did it sound? Not so great at first! The low bass seemed to be missing in action. Then I remembered reading that 12db/octave filters are 180 degrees out-of-phase. I assumed this was causing significant cancellation between the PAP woofers and ALTEC 756Bs.
The simple fix was to wire the woofers out-of-phase (reverse the +/- input connections) and that made all the difference! Now the low bass was back in business. See the photos below for the system setup.
Question 1 - Does wiring the woofers out of phase make sense? Question 2 - What is my speaker system's total impedance? To summarize: each speaker has two 8 ohm woofers wired in parallel and low passed at 80hz with a 4 ohm filter, one 8 ohm ALTEC 756B run full-range directly off the amp and one 16 ohm Jensen RP302 tweeter. A .47uf cap is used to high pass the tweeter.
Edits: 04/18/17This post is made possible by the generous support of people like you and our sponsors:
Topic - Pure Audio Project Open Baffles & 2 Questions - Gerry E. 11:27:52 04/18/17 (11)
- RE: Pure Audio Project Open Baffles & 2 Questions - David Yost 14:46:11 04/21/17 (0)
- What Are The Two 15" Woofers? - thetubeguy1954 05:29:50 04/20/17 (1)
- RE: What Are The Two 15" Woofers? - Gerry E. 11:30:45 04/20/17 (0)
- RE: Pure Audio Project Open Baffles & 2 Questions - TubeDriver 11:58:59 04/19/17 (0)
- RE: Pure Audio Project Open Baffles & 2 Questions - Mick Wolfe 15:53:39 04/18/17 (6)
- RE: Pure Audio Project Open Baffles & 2 Questions - Gerry E. 14:34:06 04/19/17 (5)
- RE: Pure Audio Project Open Baffles & 2 Questions - Mick Wolfe 09:07:23 04/20/17 (0)
- RE: Pure Audio Project Open Baffles & 2 Questions - Tre' 15:03:03 04/19/17 (3)