A key point to keep in mind is that both Altec and BBC produce actual, real studio monitors. The two come from different directions: Altec came from theater sound into the studio and the home, predominantly in large spaces common in the US. BBC monitors were designed for the studio, both fixed and mobile and made their way into the domestic environment. This was in the typically smaller spaces common in the UK. Interestingly, the smallest Altec studio monitor, the 9849 is about the same size as the largest BBC Monitors, such as the LS5/8 or similar speakers like the Harbeth 40.2.
I think a fair matchup would be an optimized Altec 9849 and a Harbeth 40.2. The Altec could use the @je2a3 network or an iteration of the 32343 network that @Salectric prefers. I would lean toward an optimized 32343 and would also choose a 414-8C. I suspect the 414-8C would offer a flatter midbass at the expense of efficiency and high end roll off. I would need to use the LF network.
In another thread, a member modeled the 414-8C in the 414 and 9849 enclosures. The 414 showed what should be a satisfying midbass hump before falling off below 50hz. The 9849 low end response modeled a lot like a sealed box enclosure. I would imagine it would do best with room boundary reinforcement. No real hump, but a more gradual falloff in bass.
While researching large BBC monitors, I stumbled across this BBC Research Department Technilogical Report. A very interesting look at the development of the second series of BBC LS5 large monitors. You can see the BBC frequency response (and dispersion) that JE loves. You can also find some other details that ring a bell of familiarity. The LS5/5 crossover was built with autoformers in the crossover to isolate the filter network from the load presented to the amplifier. Joe Roberts also advocates this approach, using a loading resistor to set a firm impedance for the amp to work into.
Here’s some discussion about recreating a large BBC monitor.
I think a fair matchup would be an optimized Altec 9849 and a Harbeth 40.2. The Altec could use the @je2a3 network or an iteration of the 32343 network that @Salectric prefers. I would lean toward an optimized 32343 and would also choose a 414-8C. I suspect the 414-8C would offer a flatter midbass at the expense of efficiency and high end roll off. I would need to use the LF network.
In another thread, a member modeled the 414-8C in the 414 and 9849 enclosures. The 414 showed what should be a satisfying midbass hump before falling off below 50hz. The 9849 low end response modeled a lot like a sealed box enclosure. I would imagine it would do best with room boundary reinforcement. No real hump, but a more gradual falloff in bass.
While researching large BBC monitors, I stumbled across this BBC Research Department Technilogical Report. A very interesting look at the development of the second series of BBC LS5 large monitors. You can see the BBC frequency response (and dispersion) that JE loves. You can also find some other details that ring a bell of familiarity. The LS5/5 crossover was built with autoformers in the crossover to isolate the filter network from the load presented to the amplifier. Joe Roberts also advocates this approach, using a loading resistor to set a firm impedance for the amp to work into.
Here’s some discussion about recreating a large BBC monitor.