Lots of decent ones but you need to tell us more about your system and your budget.
I listen to classical music almost exclusively. I have a jlAudio f113 in one system and, in the other, two Paradigms: a Servo-15 and a Sub-15.
"Music in the Round"
Senior Contributing Editor, Stereophile
I would say most good recordings go down to 27-28hz as the Double bass and piano can go that low. Most good full range speakers can handle most of this but a "real" subwoofer can add a sense of weight to the music. I find that it is a fine line between the sub being too loud or not adding to the music. It takes me a long time to dial in a sub to work with Classical music where it does not sound like a subwoofer is playing. I will say, I have gone through a lot of subs, (about 10) all were returned or giving away to friends. I'm a cheap person so I have not bought a sub over $700 cdn.
In the showroom it's really hard to test a sub for classical music as most of the time the sub is set too high. I also find that you need to be familiar with your main speakers and know their limits as all the bass should sound like it is coming from the speakers. One should walk into a room and think that you are listening to full range speakers with no sub, the music should just sound heavy. When I play with my orchestra, I can feel the double bass vibrations in the floor and I would love the recreate that in my home. You will need a “fast” sub with low distortion. One of the only subs that worked for me years ago in a showroom was Paradigm’s servo 15 v1, I loved the fact that you could not hear it. The room just felt heavy and pressurized. That sub was too expensive for me at the time so I got a ported sub and ended up returning it.
Recently, I listened to the paradigm’s sub 1 (or 2, the big one) and the Sub 25 (discontinued) and I did not like them. I will say it was most likely because of the setup, as it was in a home theater setting. I’m sure I might get those to work with more time and totally changing their settings. That same day in their music showroom I had the pleasure of listening to the Rel R-328 it sounded so clean and I feel in love with the sound from the first note. At times it did seem like some notes were missing but again I was listening cold without knowing what the main speakers could do.
My only advice to you is the music should never sound fake; the music should be gentle; the bass drum should be felt in the chest with no distortion; you should feel the double bass notes. If you have bookshelf speakers people should be looking at them in awe and say "holy crap those speakers are great". Not "WOW, where’s the sub that bass is cool".
Tell us your system and budget. And it would help us to know what type of classical music also.
Update: Google rosemary5858 and you'll see the same name posting on a dozen sites in the last few days. It's only a matter of time before you'll get a hit when you enter that name here:
The Laws of Physics aren't swayed by opinion.
plus or minus what? If they really are only minus even 6 dB that low, you might not need much, although IME there are "realism" sounds below the fundamentals of even deep instruments. LEading edge transients, etc. Some claim to be able to hear the hall better with deep bass present. And, critically, how loudly do you listen. Deep bass requires a lot of excursion as you get louder and you may find that the bass cannot keep up if you play loudly.
IMO, ideally a sub that is flat or at least no more than minus 6 dB down to 20 Hz and capable of whatever SPL you need is likely to be a revalation on at least some recordings.
I can hear down to only 25 Hz as I’m getting older.... I’m running a basic 2 channel setup so I have no room correction or EQ. I’m just looking to feel/hear something that will play 16 Hz to 50 Hz. All the subs I tried could play louder than my speakers but I don’t care about that. If I match my speakers and sub at 80 hz the sub adds nothing so I end up thinking, “what is the point of a subs if it can’t play lower than my speakers”. Plus the sound of most of the subs I tried sound sloppy. If I crossed over at 80 hz I just hated the sound. I listen to large scale orchestral works, and of course a little bit of everything.
My experience with Hifi is limited. (My experience within live Orchestras is considerable, almost always from the 2nd best listening position- Concertmaster). I have been told that the issue, especially with 2-way speakers of high quality, is the woofer attempting to drive low frequency and mid-frequencies at the same time. It might appear "clean and strong" in a normal sine-wave Frequency Response curve, but when you start to drive a whole lot of different frequencies at the same time, the character of individual instruments (and voice) begins to suffer.
I will be looking for a Sub after I become dissatisfied with my mains- and I expect to be dissatisfied, at least a bit. It's possible that my under-$600 budget will be unable to match the sound of using my soon-to-arrive Ascend Sierra-1 fronts alone (2.0 versus 2.1). However, if I raised my budget, I am almost certain that I could obtain a more realistic experience. I'll SWAG that my crossover will be somewhat higher than you used, and I'll also be using Audessy XT to provide an initial calibration. Without applying some EQ to remove the low-frequency content from your Mains, I'd expect to hear as you did- the subs good for nothing except adding a lot of bombastic mush.
My musical preferences are challenging: Mahler, Shostakovich, and similar.
Poorly scripted recordings at the sound board level will bury frequencies behind other frequencies creating mush at the recording level and poorly integrated subwoofer reproduction will do the same by killing or reinforcing frequencies due to sound wave interaction with a room's acoustics; subwoofer caused mush.
I've seen folks with back-to-back concert grands in their living room, recording their efforts on an $80.00 cassette player. So the real question becomes, how often is the listener beset upon by "critical listening" vs music being background to a human gathering of sorts? Is the music being reproduced, the main course or in real terms, is music being used as background noise, intended to fill in the sonic gaps of a gathering of minds at an after show party? In real terms, how will the listener be using the subwoofer system?
The point of the above ramblings, is the individual working with quality recordings being reproduced by a thoughtfully integrated subwoofer system or is this just a bunch of wine and cheese heads enjoying an evening of wine and hors d'oeuvres?
For your entertainment: Kyung Wha Chung: Vivaldi: "The Four Seasons" About eight minutes into "Summer."
What to take away from the above piece? Is the individual listening to a piece of compressed trash where information has been removed from the recording? Who's the artist? What's a listener's sensitivities toward the artist's recording they're listening to? What are the overall skill sets bring brought to the reproduction process? What are the long and shortcomings of the recording venue? Et cetera. Just saying, if one link is weak in the entirety of the recording/playback system, then the reproduction process will continue to be weak from that point on and can only be further weakened.