That is strange, especially when you were able to set the crossover on the sub to 25Hz. My experience is that with subs properly positioned and calibrated imaging improves and the soundstage expands and think that should be no different with your Harbeths. I’m perplexed.
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,
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So was I. But to my ears I lost air and soundstage openness with the sub even at a 25 Hz crossover. I’m just sensitive to that area of the frequency range. Probably 60-120 Hz. Not subtle to me. I did experience a minor soundstage expansion and slight improvement of depth but again at the expense of openness. Also with the sub a perceptible warming of strings. Less ethereal and airy. The image slightly more forward. When I turned off the sub it was like someone turned on the lights over the orchestra. It was more airy. Don’t know what to tell you but I’ve been experimenting with this for a year. I just prefer the overall sonic with the Harbeth without the sub. I really wanted the sub to work. |
As I mentioned recently elsewhere. That has been my experience with subs-woofers as well. In addition to two subs I used to have a low frequency subwoofer equalizer... so it did not operate on the main speakers. Still the same problem, bumps somewhere... and lack of coherence. I was really happy and stunned with my then new Sonus Faber Amati Traditional without subwoofers. I suddenly understood what coherence sounded like. The Amati are about flat to 28hz, so I really don’t feel I am missing anything and the character of the sound is beautifully homogeneous. So, I got rid of the subs and are really happy. If at some point I want more bass, I’ll upgrade to Sonus Faber Lilium (20hz - 20khz). |
Couple of things. I've heard these effects and heard them solved. I suspect one of these issues:
Of course, the easiest solution is to start with measurements. You gentlemen have run into something I've known for a while, that subs don't alays just drop into place and can require significant work to integrate. The audiophile habit of trying to configure speakers and subs by spec instead of measuring how they are performing IN ROOM makes it very difficult. Best of luck,
Erik |
@soix +1 Unlike your dramatically rolled off -6dB sub-bass woofer the first step when switching to a -3dB subwoofer is to simply drop the sub into one of YOUR rooms strongest standing wave bass modes. Unfortunately most manufactures of subwoofers simply don't get this critical first step. JL Audio is no exception.
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I had the same speaker with an SVS 16 and thought it really helped steady the image and deepen the experience. Mayne my hearing is off and I didn't notice the nuances, or maybe room dependent as it mostly is. Some of those Rel subs are not rated very low. I suppose it's a niche to make a sub that only goes down to 35hz, but for my purposes I'd say you want something more like the s812 with those speakers. My issue with the C7's were with volume. They play loud but once you throw a little bass at them and the driver would bottom out. Other than that I loved them. The clarity and energy with the lack of fatigue or aggression is great. |
Proper sub integration takes a lot of time and effort. If you are a seasoned audio aficionado and have lived long without subs, it becomes easier to understand when subs add smearing and cause issues more than help. In my experience, this is not just about the crossover point and slope, but also equally as much to do with phase and time alignment, and maybe even more so. The challenge with REL is that integration of their subs is typically limited to adjusting the crossover and positioning them, as phase is limited to 0 or 180 degrees, and most models do not have other features such as delay or parametric EQ. If you were to play with subs fromPerlisten (I’m an authorized Perlisten dealer, FYI), SVS (previous owner), or Martin Logan, their subs can be dialed in from your listening chair. When you can do this and adjust phase by degree, delay by millisecond, and crossover frequency by Hertz (as well as its slope), you’ll be amazed at how much easier it is to dial the sub into your system and get favorable results. Of course, sub build quality is very important. While SVS does wonders for the money, Perlisten and Martin Logan offer products that are a huge step above. As others have mentioned, many of RELs offerings are meant to operate in the audible range and augment musical information into the subs (e.g. they don’t go that low). To experience the benefits of a wider, deeper soundstage and a more coherent presentation across the entire frequency spectrum (and not just in the lows), the sub should be dialed in using the features mentioned above, but in reality the sub also needs to go down to at least 20Hz, and preferably below. In my reference system, I employ two Perlisten D12s subs. A few of my clients have had me configure swarms of their larger subwoofers. In some cases they are crossed as low as 31-34Hz, and with proper integration in any system I’ve configured subs, you can barely hear them when the amplifier is off. But what they do to eliminate room modes, clean up the entire frequency spectrum, and add immediacy and texture to the sound can be accomplished by little else (BACCH-SP’s DSP innovations come to mind here). |
I use an SVS sub which has very comprehensive DSP over most parameters. Changing the rolloff to 24db instead of 12 makes a huge difference in how it interacts with the mains. I also use a 24db HPF on my mains to reduce the bleed. I tried two subs but found one works better in my room. Integrating a sub takes time and effort. How many, location, filter settings, EQ, and phase all work together in complex ways. It's not much different than setting up your mains. Listening, measuring, trial and error with settings, and sufficient time are all part of the process. |
I have 4 JL Audio F-113’s, all at 40hz crossover at 24db. Two in the front, and two in the back. All have been individually set up at my listening position with the calibrated microphone. I just tried going without the subs, and I do agree there is a little more purity in just using the mains. And now that I think of it, I am using Planar/Dipole speakers, and it has been said that the rear reflection is 180 out of phase with the front sound. In this post someone mentioned about trying the subs out of phase to the mains. At this point, that does seem to be a decent compromise. Once you use subs that are dialed in, it’s hard to go au naturel. So, we shall see how my experimentation goes. ozzy |
With all due respect, if you asked an AI bot, "What is the weakest link in my system?" the answer would be the main speakers. The mains are rolling off at 45hz. That makes for a big ask to get subs to integrate seamlessly. With that in mind there are a couple of things that you can do to optimize what you have working in your room. Pass off your subs at max 45hz with a 24db slope as your already discovered. Phase is a moving target so getting the phase organically in-line without electronic correction is paramount. For a starting point, set your subs outside of the mains, and at least a few inches forward of the mains to compensate for the natural delay of the lower frequency signal. This should help keep the subs from knitting into the mid-bass range and keep things clean. Good luck and cheers. |
