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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,

jfrmusic

Showing 1 response by gournard

gournard
10 posts
 

Dear jfrmusic, this needs to be approached scientifically if you hope to achieve proper integration of subs into your system. You have some really nice kit and it's worth doing what is necessary to hear what it's capable of.

The only way to do this without endless experimentation is to embrace measurement so please download REW (free) and buy a suitable mic. for $100 which will remove the guesswork. There has been some good advice here in certain repects but most of it is all over the place and confusing. Best is to go about things methodically.

Any sub like REL and its ilk are unsuitable for 1 reason: they do not have variable phase. It's also easier and better to use sealed subs which your D108 is and has a natural 12dB/octave roll-off so plug the ports on your speakers which force them to now behave as a sealed box (a good thing)  which decays at 12dB/octave and so match the D108.  I suggest at least 2 subs  which is neccessary to truly smooth out the performance of speakers, extra bass sources (subs) and the huge influence of your room's acoustics. This brings into the picture the importance of plugging the Harbeth's ports. You have effectively removed 2 additional bass sources that resonate at only 1 specific frequency which by definition can not be tuned and will complicate set up. Point: AI has misled you claiming a 12dB slope. Your REL  has a passive radiator which rolls off slightly steeper than a ported design which is 24dB/octve.

Your D108 partnered with a sealed sub like the great value SVS SB 1000 PRO with numerous controls will allow you to achieve the industry standard of +/- 3dB across the spectrum. Without the ability to see the frequency response continually change as you adjust the controls you are left guessing. REW will also display if you have sufficient absorption or perhaps too much. As I mentioned it's a scientific approach which has been well documented. It works. 

A further bonus is the ability to place the subs where you would like them to be which is a function of continuously variable phase. Ignore the advice in posts above to place them behind or in front or whatever. I do recommend starting with 1 sub in a corner, any corner, and the other in the middle of the opposite wall. 

I state with confidence that you will not have a smeared image nor loss of air just the opposite. By using measurement and subs and some absorption you will have effectively removed the damaging effects of your room's acoustics and will hear the acoustics of the event. The audiophools holy grail is it not? surprise

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