[mresseguie]

I hope I can pose this in a clear manner. I've read a bunch on speakers and subwoofers, but I have a question about the interaction between the L/R speakers, the sub, and the preamp. Here goes:

Let's say I have a pair of speakers that play down to 50Hz. I want more bass, so I decide to add a subwoofer (GR Research/Rythmik sub) to the mix. I set the subwoofer cut off at 100 Hz. Is there some sort of signal that travels from the subwoofer to the preamp to the L/R speakers telling the L/R speakers to play no lower than 100Hz?

If there is no such signal, is there any way to control the output of the L/R speakers manually? For example, could a toggle switch be added to the back cover? [Switch it on when you do not use the sub; switch it off when you do use the sub.] Does anything like this exist?

My apologies if these are silly or naive questions.

Thanks to all who offer their thoughts.

Michael

[JLM]

Proper setup varies with the gear.  All the scenarios listed below allows volume control from your pre/integrated amp.

Virtually all A/V receivers and some stereo preamps/integrated amps have a subwoofer output (low level, RCA connection) of some sort (often called LFE = Low Frequency Effects).  Most of those are set to a given crossover frequency (80 Hz is very popular and the THX movie standard) so that the sub only gets the below 80 Hz signals and the mains (what the Brits call your main speakers) get the rest.  This scenario relieves the mains of bass output which is many cases allow their midrange to "open up" (sound better) and gain headroom (play louder before distortion).

The next option is where stereo preamps have two sets outputs or integrates that have a separate low level (RCA) outputs that the subwoofer can be connected to.   No crossover here, so you dial in the subwoofer high frequency filter to blend with the mains.  Don't get confused by trying to use "tape outputs" where the output is fixed at full volume.

If your pre/integrated or A/V receiver lacks either of these options, look for a subwoofer that has high power (speaker connections) input and a high power (again speaker connections) output to the mains (quite popular) and run the amp to the subwoofer.  Some purists cringe at this option and would prefer to connect two pair of speaker cables to the amp, one to the subwoofer and the other to the main.  But this can cause low impedance loading on the amp that can stress/overload it.

With some powered/active speakers a subwoofer output is provided on the mains, so you only need a pre-amp (and a 2nd interconnect cable) and the signal is routed from pre to mains to subwoofer.  Alternately many professional subwoofers have low power (RCA/XLR) outputs to the typical powered/active mains so the signal is routed from pre to subwoofer to mains.

The 80 Hz crossover is a good/workable starting point for most systems.  Bass frequencies travel in waves, not rays and so cannot be located by ear.  Tiny mains may require crossovers much higher but that can get into midrange frequencies and you could hear sound coming from the subwoofer and the mains (smearing the imaging).  Achieving a proper blending of subwoofer(s) to the mains (frequency and proper location) has filled many threads at AC and beyond. 


Regarding switching the subwoofer on and off: 

Every A/V receiver is different, but there should be a menu option for running without the sub.  On a stereo pre-amp with a subwoofer output you many just need to unplug it.  Some subwoofers might allow you to pass a signal through while it's turned off.  I'm sure you could find a switch box of some sort where both subwoofer and mains connect to the amp via speaker cables.  Of course you could just turn the sub off.


Confused yet?   

[mresseguie]

JLM,

"Virtually all A/V receivers and some stereo preamps/integrated amps have a subwoofer output (low level, RCA connection) of some sort (often called LFE = Low Frequency Effects).  Most of those are set to a given crossover frequency (80 Hz is very popular and the THX movie standard) so that the sub only gets the below 80 Hz signals and the mains (what the Brits call your main speakers) get the rest.  This scenario relieves the mains of bass output which is many cases allow their midrange to "open up" (sound better) and gain headroom (play louder before distortion)."

Thank you. You know, I've known this for some time, but I was never entirely certain the mains would cease producing the sound below 80 Hz (or whatever is the setting).

Cool. I'm getting to like this hobby even though I'm forever playing catch-up.

[corndog71]

Don't feel too bad.  I've been in this hobby for 20 years and I too still feel like I'm catching up. 

[Quiet Earth]

If your question is asked with your Simaudio integrated and ProAc speakers in mind, I would say don't worry about the crossover point for the ProAc speakers. In other words, don't worry about limiting the low frequencies that the main speakers see. Here is why:

  If your ProAc speakers play loud enough for you in your 13x15 room (and I imagine they do) and all you want to do is add a little more low end, then you won't really gain anything by limiting the low frequencies that the ProAc speakers see. Just let them play full range like they normally do, and add the subwoofer to them using the Pre Out jacks on the back of the Simaudio. To set the level, play a song at a normal listening level. Turn the sub crossover frequency down really low (30Hz?) and gradually adjust the sub's volume control so you just barely notice it. Now the Sim will be the master volume for both the sub and the mains. And if you want to turn off the sub you can do that too.

Keep in mind that your preamp outputs from the Sim come directly off of its volume control pot. So it is a passive, un amplified signal and somewhat fragile. All that really means is the subwoofer's RCA inputs will slightly load down the signal that would otherwise be going entirely into the amplifier section of the Sim. This shouldn't be too much of an issue if you keep your interconnects (to the sub) under 10 feet long. BlueJeans cables sells a very low capacitance RCA cable that would probably work well for this application.

Hope that is useful. Now you have me wanting to do it. 

[mresseguie]

If your question is asked with your Simaudio integrated and ProAc speakers in mind, I would say don't worry about the crossover point for the ProAc speakers. In other words, don't worry about limiting the low frequencies that the main speakers see. Here is why:

  If your ProAc speakers play loud enough for you in your 13x15 room (and I imagine they do) and all you want to do is add a little more low end, then you won't really gain anything by limiting the low frequencies that the ProAc speakers see. Just let them play full range like they normally do, and add the subwoofer to them using the Pre Out jacks on the back of the Simaudio. To set the level, play a song at a normal listening level. Turn the sub crossover frequency down really low (30Hz?) and gradually adjust the sub's volume control so you just barely notice it. Now the Sim will be the master volume for both the sub and the mains. And if you want to turn off the sub you can do that too.

Keep in mind that your preamp outputs from the Sim come directly off of its volume control pot. So it is a passive, un amplified signal and somewhat fragile. All that really means is the subwoofer's RCA inputs will slightly load down the signal that would otherwise be going entirely into the amplifier section of the Sim. This shouldn't be too much of an issue if you keep your interconnects (to the sub) under 10 feet long. BlueJeans cables sells a very low capacitance RCA cable that would probably work well for this application.

Hope that is useful. Now you have me wanting to do it. 

QE,

Yes. It is useful. Thank you!

What prompted me to ask was an interest in adding a subwoofer to my bedroom system, to my main two-channel system with the ProAcs, and to my future speakers. I'm still working out which speakers will those will be, but there is a good chance they will be standmount speakers.

I'm pretty sure I will order either the double 8" subs (GR Research drivers) or the single 12" subs from Rythmik. I plan to buy two matching subwoofers. This way, I can have one in my bedroom and one in HT, or two in HT when I want the extra oomph.

The only time I feel a need for more bass from my ProAcs is when the volume is quite low. That's when I miss the bass.

I have a few months to decide. Our son will move into his new apartment in September sans his current room mates who love LOUD MUSIC no matter how distorted and OOPS....sorry about that blown speaker. I trust my son to take reasonably good care of his new AV123 bookshelf speakers, matching center channel (recently purchased used in Portland for a song), and my old PSB 300 subwoofer driven by my old Denon AVR2113ci. If he blows a speaker, he can find a new one on Craigslist or order a new driver from Danny. The PSB sub is okay, but it is not musical. He won't notice. Rather than my trying to sell my unwanted items, I hand them down to my son who may develop an interest in HiFi someday.

BTW Quiet Earth,

I peaked into your profile and noticed your Audio Note speakers. They look nice. If you feel up to it, I'd love to 'hear' what you have to say about them. I'm unfamiliar with the brand, but I'm willing to bet they sound lovely.