Adventures With Subwoofers

My System:

Aurender N20

MSB Discrete DAC

Accuphase P4600 Amp
Harbeth C7-ES-XD Speakers

The Harbeth’s are -3db down at 45Hz. They have useful output down to around 35-40Hz. I wanted to fill out the lower octave from 40-30Hz.

I started with two REL T/5X subs I successfully integrated with the ATC 11 speakers I owned previously. They were -6db down at 55Hz.

After weeks of effort with these subs plus an older REL T3 I gave up. No matter what combination of crossover and volume I could not prevent the subs from bleeding into the lower midrange. The result was a loss of air and soundstage openness. Even at the lowest crossover the result was the same. Even voices were affected. I realized that these RELs especially when using the High Level Speaker connection are bass reinforcement and not true subs. I think if I had a way to externally crossover them and use the low level connection they might work as the REL/Harbeths would no longer be doubling the 35-60Hz range. But there would still be overlap in the 70-120Hz range. That would also mean the beautiful Harbeth upper bass and low midrange would now be appropriated by the RELs. So I sold the two T/5X subs and gave the T3 to my grandson for his gaming system.

Then one day I decided to ask ChatGPT why the RELs could not be configured to stay out of the midrange. The AI said it was because the RELs had a crossover slope of 12db per octave and that I should try a sub with a 24db per octave slope and recommended the JL Audio d108.

So with a 30 day return option I tried the D108. After about two weeks of testing I found it much better specifically because I could set the crossover to between 25-30Hz. But in the end I still noticed, to a somewhat lesser degree, the same artifacts especially on voices and soundstage openness. But I really loved the sub itself. Very well made and powerful. So I moved it to my home studio where I had just purchased Genelec monitors and it blended perfectly.

I really don't have an issue with the Harbeth’s low end response as almost all music sits in their range. I listen to predominately Classical and value an open airy soundstage which I get from the Harbeths.  I was hoping by adding a response down to 20-25Hz I might improve soundstage depth and support the lower harmonics. But I strongly prefer their response without subwoofers. I think if I listened to mostly Pop, Jazz, EDM or Soundtracks where I would not notice the soundstage openness as much the subs would work. But I crave that concert hall liveness,