Subwoofer Crossover Question

What would be the starting point for Subwoofer integration with a pair of speakers that has the Frequency response below. Any layman explanation for what the -6db at 23Hz signifies and how this might relate to subwoofer crossover into a two channel music system, (two Rel Strata III's) will also be appreciated.

Frequency Response 28Hz to 25kHz ±2dB, -6dB at 23Hz
REL subwoofers are easy to set up and blend with your system. Run your main speakers full range and blend the RELs into your speakers. I would not be concerned much with specs because the room and overall system plays a big part in the balance. This really needs to be done by ear. Read your REL owners manual.
Not what you want to hear perhaps, but if your speakers are only down 6db at 23hz I question the value of using subs at all. There is a lot of information 'down 6db at 23 hz'. Now if you really meant down 6db at 32hz then subs really can help. There is little information much below 32hz and, as Rrog mentioned, your room and set up plays a major role in bass frequency response.

What subs can do really well though is help smooth out the bass frequency response. This is accomplished by placing the subs in other locations than the mains and, often out of phase as well. The ear is not as sensitive to the frequency variations as one might think except in a gross manner. I would (and have over the years) use a SPL meter (Radio Shack has one which will do well enough and its cheap) and a test record with 1/3d octave tone (such as produced by Stereophile), placing the SPL meter at the listening position, charting the FR of the mains at this location, and as Rrog suggested running the mains full range and the subs crossed over as low as possible. The object then is to flatten the bass FR response by either/or/and moving the subs, changing the cross over points, and the volume of the sub, remembering that those subs can be effective placed anywhere in the room that they might add/or subtract to the bass FR. They don't need to be up front with the mains, in fact, in my experience they can sound quite good located on side walls.

FWIW if your speakers were down 6db at 32 hz I would probably start out with the cross over set at 60hz. In theory at least as the frequency response level doubles (i.e. 32hz to 60hz)and the power level double (i.e. down 6db to down 3db is a doubling of volume) so the suggested cross over point in theory would be down 3db at 60 hz. But experiment, you want to keep the cross over point as low as possible. If set too high the subs will start introducing higher frequencies into the sound and screw up things imaging etc. Not too effective a way of explaining this I think, but hope you will get the idea. There are some excellent books available on this subject.
I agree. I run my Maggie 1.7s full range and my SVS subs crossover at 40 Hz. That seemed very low to me, but it was a factory, recommendation and it works beautifully. I have a Antimode on each sub and I run them is stereo. That made a big improvement over mono. For a while you will likely have them running too high and too loud, but you will find music with not much bass sounding better due to imaging. You will have a good time exploring new limits in your system. Many opine subs would sound better if driven from the power amp, not taking away any power, but making a better match to the amps' own sound quality. If you don't go with room correction, this is another way to play with the sound. Enjoy!
Well I just re-read your original post - I don't know how I missed your description of the spec's on FR which have your speakers down 2db at 28hz and 6db at 23 hz.

This is a remarkable FR! Unless you are trying to correct room response issues by locating the subs in locations that will fill in nulls heard at the listening position I would think that subs will do more to screw up the sound than improve it. -2 db and -6db isn't much actual volume wise, and would be considered a very shallow slope. That assumes however that you want a flat FR. Certainly if you are trying to increase/elevate the bass response with out changing the frequencies above say 100hz then the subs can do it, but keep the cross over point at its lowest, or close thereto. Have fun.

You make some excellent points but the spec on his speakers
are +/- 2db down to 28hz so they could not be down 6db at 32hz.

With that said I concur with your following statement.

"Not what you want to hear perhaps, but if your speakers are only down 6db at 23hz I question the value of using subs at all."

OTOH, if the OP uses the speakers for Home Theater or listens a lot to organ music.....

At this point it would be helpful if Matt would tell us what he feels is missing.
When a spec states something as + or - 2db it means that a product (speakers in your case) will only increase or lose volume by the specified 2db between the lowest and highest frequency's stated. So in your case, between the very low frequency of 28hz and the very high frequency of 25khz the speakers will only add or subtract 2db from the music sent to them.

DB's or decibels is a measurement of volume or loudness. 1db is considered the smallest amount of change in loudness that humans can hear. However in practice 10db to most people sounds like twice as loud. So 6db would be half way.

If you have ever messed with something that has traditional bass and treble knobs, 6db would be the same as turning the knob about half way.

I just looked at Matt's system and he already HAS the REL's, he's not looking for advise on if he should add them to his system. I apologize for my misunderstanding the question.

So at this point it would be helpful to know how the subs are currently hooked up.

One line of thinking is that subs can relieve mains and the amps that drive them from extreme LF duty. Subs can also help smooth LF response in room. THX recommends a crossover of 80 Hz, a frequency low enough that its source should not be localized. Whatever the setting, the goal is to not have any speaker identified as a source of sound within the sound stage. You do not want to be aware of the subs.

The frequency response of a speaker usually is measured in some sort of anechoic environment. (Rooms with deep anechoic ability are expensive to build.) The 3 dB down point often is used as an indicator of the useful frequency range of the speaker, but its actual response will be a function of your room.

I'd suggest finding a way to audition at home a DSpeaker Antimode product.
There is very little music below 30Hz, much kess 23Hz. I would not spend $ on a sub snd instead in an amp which matches well with your speakers. Also I would optimize the room and be certain the room is behaving correctly.
+1like to Jallen and to Newbee.
The often overlooked detail with subs is that they are not time aligned with the rest of the drivers and this why one well designed box is better unless a sub has been designed for the accompanying speakers. This is why so many subs have one-note-sub reputations. The low freq. detail is more clear only with time alignment. Can a sub work? Sure, but not a first choice for music (imho)unless needed due to a speaker low freq. limitation. Jallen
Thanks for all the help. I have had the rels for some time and when I purchased the Aerial's about six months ago I automatically rebooked the Strata III's back into the system without listening to the Aerial's without them.

Jirenman, specific to your question have each sub hooked up to the back of the speakers with a customized Neutrik connectors that were made for me by a buddy of mine who subsequently went to work for Cary Audio as their director of product development. I have had the connectors over 4 years, and had them made shortly after purchasing the second sub.

After reading all of the above post's, I have taken Newbee's suggestion and now have the Rel's crossed over as low as they can go at 22 HZ. My initial impression is that the overall presentation has cleared up considerably, and I feel like I am hearing some additional details that had previously been obscured. This weekend I'll listen without the subs and evaluate with and without them.

Thanks again to everyone for all of the quality responses.
Which Aerial speakets? I have 10T's powered by 4 quicksilver monos and using plasma super tweeters crossed over at 3500k. Very enjoyable.
Aerial 7T's.
I use Rel sub also. Most people set crossover to high. In your case the crossover at about 25 hz should work well. Sub in a system is not only deeper, tighter bass. It affects mids and treble also. There is more micro detail, more air, the soundstage is more open gents. When you turn off a sub during listen session you realize how much sound you miss without it.