I use two subs with my SC's, both are NHT SW2's, which have outboard amps. I have the subs on spiked amp stands, with cushioned auto wheel rings under the subs. How I came to that configuration is a long story, but they work very well. The only way you are going to know if two are better then one is to try them together. Purchase where you can get a return accommodation with full refund within 30 days. If one works, take the other back.
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I had these speakers in an open living room/dining room/hallway like yours, and the REL Storm III I had worked superbly. Like REL recommends, I had the crossover way down and I never had the gain up past 12 o'clock. This setup worked perfectly for me. I am not sure what the current day equivalent to the Storm III is, but someone is selling a used Strata III (smaller sub but still probably would work in your room) for cheap on this site. Also you can get a T-5 or T-7 from Music Direct or Audio Advisor, both for under $1000. I would definitely investigate those. And no, you will not need two. I am speaking about 2-channel audio listening, not home theater and LFE.
As SC53 noted, a well implemented subwoofer usually does not need to be set at high gain and/or high crossover frequency. This is particularly true when music, and not home theater special effects, is a priority.
Multiple subwoofers are used to get a more even bass response, it is NOT generally utilized to get more bass. This issue was discussed extensively in this forum a few days ago; see:
You don't "need" two, but the results are usually better with two or more.
Thanks much for the replies guys. I'm so glad to hear that I may be able to still use the One SCs. I love their tonality and imaging. I'll start looking for a REL sub.
With your setups, you did not pass the lows to the monitors, just the subs? I can see this would put much less demand on the ProAcs.
I only listen to 2 channel music, jazz.
The REL "high level" connection via the Neutrik Speakon cable connects directly to the speaker terminals of your power amp for the most balanced implementation possible of the subwoofer. The Neutrik cable has three strands, yellow, red and black; the yellow and red connect to the positive terminals of your amp, the black is a ground that connects to a negative terminal. That's all you have to do before you start listening and tuning the dials on the REL. By all means plan to use this connection, not the "low level" RCA-type connections to the REL. It will come with a detailed manual explaining all this.
The only issue you'll have using a REL as mentioned by others is the additional stress on the monitors due to the larger space (assuming you drive them harder than in the smaller room).
Ideally, the little monitors should be high-passed as you noted in your question.
I would skip the REL and look for a sub with a builtin high-pass filter. SVS offers such subs. Velodyne does as well, though it's a first order filter last time I looked. Martin Logan's subs used to have a high pass filter; I haven't looked in a long time. Hsu Research offers an external sub crossover (bass management unit).
Velodyne has models with parametric EQ, which would be an advantage over the other subs I mentioned.
Thanks again guys.
Sc53 is the Neutrik made by REL or is it separate?
Erik, I wish I coujld afford a D30R right now. I've spent some time listening to the D40R, it was magical. Has to be in my future though.
Bob, yes I am worried about that stress. While sending some bass energy to the sub will help, still it's a big space and I do listen loud. My RM9 will easily overwhelm the One SCs. I guess I'll just have to find out. If I end up selling the ProAcs the sub will be useful anyway. I wonder if it would be useful to set the high pass at a higher frequency? The woofers in the One SC are small.
Velodyne makes the SMS-1. Don't know if it has a parametric or if it differs from Hsu's network. What is the advantage of a built in high pass vs. the REL with an external?
Jim, yes REL provides the Neutrik cable, although you can also buy after-market upgrades too. I had one made by somebody here on Audiogon some years ago, now I see that Kimber makes one specifically for REL subs, I think Signal Cable has one too. Try the standard one first, and follow the tuning procedure in the REL manual. Setting the crossover LOW (perhaps counter-intuitive with such small monitor) works better 90% of the time, but your room and ears and music will be the guide.
If you are concerned about overdriving the main speakers, you should go with a fully active crossover/subwoofer system that actually cuts off the main speakers below the crossover point. With such a setup, the best sound will most likely be with the crossover set at a quite low frequency, as others have mentioned above. I almost always find that for music, a low crossover point sounds better.
I haven't listened to that many subwoofers, but, of those I heard, I liked the Martin Logan subwoofers that I heard coupled to quite small Totem monitors.
While the REL does not cut off the main speakers in the low frequency, I have been impressed with how easily REL subwoofers can be integrated into a system.
REL subs were originally designed to be used with essentially full range speakers. Thus, their low pass filter has a lower frequency range than most other subs and their frequency response is shifted to a lower bass region and their clean output is more limited than other subs.
Just adding a sub to your system does not reduce the bass load on your monitors. They will still receive a full range signal and you'll still adjust the SPL based on the midrange and treble you hear.
What I suggest you consider is adding a sub in such a way that you will be converting your 2-way monitors into a 3-way system with a movable bass driver. The only way to accomplish this is via bass management.
Velodyne's SMS-1 is a standalone external digital PEQ device similar to what's built into their Digital Drive subs. Hsu bass management controller is an analog device and does not do any EQ.
As in all things there are trade-offs between an external BMC and a high-pass filter built into a sub. Cabling is much simpler with an external device. You simply insert it between the preamp and amp. Cost is much higher with an external device. Those high pass filters built into the plate amp are effectively free.
Typical high-pass filter settings are around 80 Hz. Based on the FR graph I saw of your speakers at the Stereophile site, 80 Hz may be too low.
Since the woofer is so small in your speakers, the slope of the filters needs some consideration. Higher order would be better. Velodyne's first order will still keep quite a bit of bass on the monitors.
Setting the crossover LOW (perhaps counter-intuitive with such small monitor) works better 90% of the time, but your room and ears and music will be the guide.Setting the low pass filter low with small monitors will create a discontinuity in the frequency response. The idea is to create a smooth FR across the region that encompasses the sub's response and the main speakers. You do that by raising the low pass filter to meet the response of the main speakers.
Thanks so much everyone for the great help.
Bob, so I'm on a hunt for a crossover. I knew about the SMS but not it's cutoff range. Makes me think I may have to choose between having a too-low cutoff or going full range on the ProAcs. I wonder if there is also the consideeration of how high the subs work well, if I'm trying for a high cutoff.
Any ideas on where to find a crossover with high enough range? Perhaps I could have one built?
Bob, this is from the SMS-1 manual. What do you think about being able to find a good crossover with the ProAcs and a sub?
16 - Digital Drive SMS-1 Users Manual
All six presets contain the following fields:
Low Pass Crossover Frequency and Slope
Adjust the upper limit of your subwoofers frequency
response. Select a crossover setting, in increments of 1, between 15Hz and 199Hz and slope at 6, 12,
18, 24, 30, 36, 42 and 48 dB/octave.
The product I wish was still in production is the NHT X2 filter, but I guess there just wasn't enough demand.
Analog options are subs with builtin high-pass filters, like SVS, or the Hsu sub crossover. I think the Hsu device is over priced, though I paid close to $1K for an M&K unit about a decade ago. Hsu also has a reasonably priced external high-pass filter.
I'd give the SVS SB-2000 some consideration. It's very similar to the SB-12 Plus I used in my office system several years ago. I used its high-pass filter with KRK VXT6 active monitors. It's a 2nd order filter fixed at 80 Hz.
If you're so inclined, there's the miniDSP product that would be interesting. Kal reviewed one of their products in Stereophile a while back.
Jim, re the SMS-1. What you quoted is the low-pass filter features.
On page 7 of the manual:
OUTPUT These RCA connectors incorporate the use of an 80Hz 6 dB/octave slope high pass crossover.
First order slope wouldn't be my first choice.
I'm guessing Marchand is still in business:
I have no experience with any of his products.
I believe the new JLAudio E-Sub has high-passed outputs:
I couldn't justify the price.
Bob, thanks so much for the great info and pointers. I'll have some work to do to thoroughly check them out.
With the RM9 I felt I was pushing the One SCs to their conservatively safe limit in my 11x12 room. I think if I try to run them full range in my much bigger new space it will be too much for them, so I do need to find a satisfactory way to divert the lows to take advantage of 1/f power spectra. I also agree that 80 is too low due to the small woofers in the ProAcs. As well as that first order is not going to be decisive enough. I took a glance at Marchand and that looks promising. I run JL in my car, and the amp has a good tone, if dry compared to my tubes. Shouldn't matter on the sub.
I do wish it was not so difficult to find a very nice pair of Response 2.5s.
Thanks so much.
Sarah (Sc53) noticed I said I wished I could find some 2:5s. Well she saw a pair for sale here and let me know and I now own an absolutely flawless pair of 2.5s in oak, purchased from Frank in Phoenix. A much more satisfactory solution than trying to get the One SCs to handle the big area with their small woofers and a sub.Thanks again for all the comments everyone.
Thanks Sarah and Frank!