Effect of Subwoofer on Power Demands of Main Speakers

[fbczar]

I have TDL Reference Standard speakers. They are rated to have a sensitivity of 87db. They are full range speakers and can reach 16Hz if the room permits. I use an XMC-1. I use Reference Stereo mode occasionally, but I find I often listen in Stereo mode when I want to use Dirac and my Kreisel DXD12012 Subwoofers or Direct mode for the same reason. I am presently considering the purchase of either a pair of XPA-1's or a pair of XPA-1l's. I would like to know how much less power is needed for my main speakers when I use a subwoofer crossed over at 80Hz than when I am using them full range. If I were using my main speakers without the subs I think the XPA-1's, even though they cost much more, would be best. On the other hand I think the XPA-1L's would be a better choice if the power they can provide can handle everything above the crossover point with ease. Any advice or ideas?

[jlafrenz]

In my opinion I think you should choose the amplifier that will drive your speakers to full potential assuming that you don't have a sub. This way you know you have enough power. There is magic number (generally speaking) that tells you how much to reduce amplifier power once you add a subwoofer. Your speakers, subwoofer, room and listening preferences all are variables and are not the same in every situation.

I also believe that that the subwoofer should complement the mains, which means it shouldn't necessarily take over for what the mains can produce. It should be an add on to help produce what the mains are unable to.

[knucklehead]

If you drive your mains without a sub then the bigger amps are probably warranted - but only if you like listening at very high SPL. Adding a sub will reduce the power requirements to the mains - a less powerful amp can then be used. The differences between 100w and 200w is 3db. Buying headroom can be very expensive.

[DYohn]

Wow. I've been in this game for more than 40 years now and I don't think I've ever heard that question before. IMO the question has no answer. The acoustic output from the subwoofer has no impact on the power demands of main channel speakers. It's apples and oranges.

[fbczar]

Oct 29, 2015 19:05:14 GMT -5 DYohn said:

Wow. I've been in this game for more than 40 years now and I don't think I've ever heard that question before. IMO the question has no answer. The acoustic output from the subwoofer has no impact on the power demands of main channel speakers. It's apples and oranges.

How is that possible? If the subs are in use everything below 80hz is amplified by the subwoofer so the mains require less power, right? Perhaps I am missing something. Of course, in this hobby logic does not always apply.

[DYohn]

If what you are talking about is dbSPL in the room, you are missing the fact of the main channel high-pass crossover. A properly setup system will cross over between the subs and the mains. But it has nothing to do with amplifier power, it has to do with relative volume levels controlled by your preamp.

[pedrocols]

The lower frequencies (in your question and in your case 80hz and lower) will free your main speakers and amps from having to drive and reproduce that load. Higher frequencies required less power to drive. Someone please correct me if I am wrong.

[KeithL]

In general, using a powered sub and crossovers will reduce the amount of power it takes to run your main speakers satisfactorily, but how much this occurs will depend on the sort of music you listen to.

Movies tend to have lots of very powerful low frequency sound effects, which use a lot of power to reproduce accurately, so diverting that to the sub should reduce that requirement for the main channels considerably (but it's all relative). The same would probably be true if you listen to lots of well-recorded Back organ toccatas, but much less true if you listen to pop or jazz; the lowest string on a bass guitar is well within the range handled by a sub, so how that works out with rock will depend on your favorite band. (Even though that bass guitar will end up being handled partly by the sub, it's movie explosions, and those low organ pedal notes that tend to use the most power.) Assuming that you picked an amp powerful enough to supply the occasional loud peaks in your music without clipping, then you probably have enough power for big solid bass notes as well - unless you like your effects really cranked up. If your amplifier was actually clipping because it was nearing its power limits, then preventing this from happening is of course going to make the rest of the sound it's producing sound better, however, beyond that, simply lowering the amount of power it's asked to deliver won't make much difference to a modern amp. (Back in the old days, a typical 200 watt tube amp would have much lower distortion when running at 50 watts than when running at 100 watts; however, most modern solid state amps, including ours, have very low distortion right up to the point near where they clip, so, as long as the amplifier is not clipping at all, reducing the amount of power you ask it to deliver a little bit doesn't change the way it sounds very much.)

However, even with speakers designed to be full range, the huge cone excursions required to make very low notes very loud can interfere with the speaker's ability to sound its best over the rest of its range. Having a woofer waving around, trying to move enough air to reproduce the bottom note from a pipe organ, will almost certainly interfere with its ability to reproduce other higher frequencies perfectly and cleanly. There are very few speakers that can really reproduce a loud 32 Hz organ note, or the stomp of a T-Rex, without having it affect the way other things being played on that same speaker sound - at least a little bit.

This is really sort of a trick question..... The amount of amplifier power your main speakers will need to reproduce music properly without compressing the dynamics of your music or clipping anything will depend mostly on the efficiency of your speakers, the size of your room, what you listen to, and how loudly you listen to it. Adding a sub isn't going to alter this overall equation as much as you might think. The main reason to add a sub is to allow your main speakers to sound better by removing the need for them to reproduce those difficult to reproduce very low notes. (The difference in audible loudness between a 250 watt amp and a 500 watt amp is really very small; and adding a sub isn't going to make a huge difference there. Depending on your main speakers, adding a sub may well make a much bigger difference than doubling the power of your main amps.)

Because how much difference it makes depends so much on your main speakers and your particular needs, I would urge anyone making this decision to consider the two things separately.....

1) How much amplifier power do you need on your main channels?

2) Would adding a sub enable your main speakers to sound better?

[stlaudiofan1]

Oct 30, 2015 12:04:00 GMT -5 KeithL said:

In general, using a powered sub and crossovers will reduce the amount of power it takes to run your main speakers satisfactorily, but how much this occurs will depend on the sort of music you listen to.

Movies tend to have lots of very powerful low frequency sound effects, which use a lot of power to reproduce accurately, so diverting that to the sub should reduce that requirement for the main channels considerably (but it's all relative). The same would probably be true if you listen to lots of well-recorded Back organ toccatas, but much less true if you listen to pop or jazz; the lowest string on a bass guitar is well within the range handled by a sub, so how that works out with rock will depend on your favorite band. (Even though that bass guitar will end up being handled partly by the sub, it's movie explosions, and those low organ pedal notes that tend to use the most power.) Assuming that you picked an amp powerful enough to supply the occasional loud peaks in your music without clipping, then you probably have enough power for big solid bass notes as well - unless you like your effects really cranked up. If your amplifier was actually clipping because it was nearing its power limits, then preventing this from happening is of course going to make the rest of the sound it's producing sound better, however, beyond that, simply lowering the amount of power it's asked to deliver won't make much difference to a modern amp. (Back in the old days, a typical 200 watt tube amp would have much lower distortion when running at 50 watts than when running at 100 watts; however, most modern solid state amps, including ours, have very low distortion right up to the point near where they clip, so, as long as the amplifier is not clipping at all, reducing the amount of power you ask it to deliver a little bit doesn't change the way it sounds very much.)

However, even with speakers designed to be full range, the huge cone excursions required to make very low notes very loud can interfere with the speaker's ability to sound its best over the rest of its range. Having a woofer waving around, trying to move enough air to reproduce the bottom note from a pipe organ, will almost certainly interfere with its ability to reproduce other higher frequencies perfectly and cleanly. There are very few speakers that can really reproduce a loud 32 Hz organ note, or the stomp of a T-Rex, without having it affect the way other things being played on that same speaker sound - at least a little bit.

This is really sort of a trick question..... The amount of amplifier power your main speakers will need to reproduce music properly without compressing the dynamics of your music or clipping anything will depend mostly on the efficiency of your speakers, the size of your room, what you listen to, and how loudly you listen to it. Adding a sub isn't going to alter this overall equation as much as you might think. The main reason to add a sub is to allow your main speakers to sound better by removing the need for them to reproduce those difficult to reproduce very low notes. (The difference in audible loudness between a 250 watt amp and a 500 watt amp is really very small; and adding a sub isn't going to make a huge difference there. Depending on your main speakers, adding a sub may well make a much bigger difference than doubling the power of your main amps.)

Because how much difference it makes depends so much on your main speakers and your particular needs, I would urge anyone making this decision to consider the two things separately.....

1) How much amplifier power do you need on your main channels?

2) Would adding a sub enable your main speakers to sound better?

Thanks for the explanation.  I find that Totem Forest speakers sound much better using the XSP-1 with a sub verses full differential mode without a sub.  It logically seems that 2 way speakers, where the low frequency drivers have to cover more frequency spectrum, would have an increase potential for benefit.

[smarties]

A few factors

1) Using bass management in your speakers will help with reducing the demands on those amplifiers. Instead of using full range, say small 80hz (ignorning if the speakers bass response)

2) A speaker may have incredibly low impedance down low, my speakers are 4ohm nominal but around 40-60hz they drop down to 2.2-2.4 ohm. So you need a good amp. If you don't have a good amp, then using bass management will help here again.

3) Depends what speakers you actually have. Standmounts + sub may be better than the speakers trying to play full range. But if you have floorstanders with excellent bass response you may prefer this over floorstander + sub. But then whether for music or movies. And taking into considering your amplifier..

How much power you need varies. Depeneding on room size/distance to speaker, efficiency of speaker.
Speaker impedance is also part of power requirement, as lower impedance speakers require more current from the amp, although more power output from the amp increases, but only if the amp is able to do it. So needs a good power supply.

It also depends what use the system is for. For a 2 channel CD playback, with floorstanders, you may not need a subwoofer.
But if it's a home theatre, watching action movies, whether standmount or standrmount then a sub is required. But if your home cinema is just for drama movies and TV, you have floorstander, with half decent amp, you may not need a sub.

But room shape comes into it, a single bass point source would be better than multiple speakers playing low bass.
Also romm correction also comes into it, whether 2 channel (so you have none) or a modern AVR with some type of room correction.

Some people don't like subwoofers in a music system.

So the answer is...maybe - probably. But not a "must have"

Generally in most circumstances good a proper 100W per channel is plenty. I don't think "hmmm I now have a sub therefore I don't need 200W, 100W is ok"

Your question is more from the low end area- area budget AVR's with poor amp stages, that would struggle with full range signal into speakers, therefore re-directing >80 or >100hz means that 40W amp isn't struggling with full range, now just higher frequencies which aren't as demanding.

[Boomzilla]

Hi fbczar!

Mr. DYohn is correct - the SPL in the room (with or without subs) is a function of the gain at the preamplifier stage. Mr. Levkof is also correct - the main amplifier power required decreases as the high-pass crossover point goes up and as your volumes decrease. The transient intermodulation distortion (TIM) of your main speakers also decreases as the cone excursion is reduced.

Now that said, these theoretical "improvements" of removing bass demands from your main speakers are often that - theoretical. Some speakers offer audible improvement when crossed over to a subwoofer. Others don't.

And finally, if your shopping considerations are the XPA-1L vs. the XPA-1 mono blocks, may I encourage you to go with the XPA-1 amplifiers. I've owned the XPA-1L (generation one), and heard both the XPA-1L (generation two) and the XPA-1 (generation two). My preference (and a wide margin) is for the XPA-1.

That said, I bought (instead) the XPA-2, generation two. And to my ears (and in my system) it seems to offer 100% of the sound quality of the XPA-1 amps (and for a LOT less money). Now that said, my speakers are more sensitive than yours, and can easily be driven by less power, so this may not be an accurate comparison.

If you will, try your subs both with and without your speakers crossed over. If you're running your mains full range, you'll have to set the low-pass for the subs using the plate amp on the subs. But if you can get a blend (I could), then the "full-range-mains plus subs" may sound better than using the high / low pass crossover method. Just my personal experience...

Boomzilla

[smarties]

www.hifiengine.com/manual_library/tdl-electronics/reference-standard.shtml


His subs will play low bass louder, and cleaner than those speakers.

So for music I'd try pure direct mode- since he's got good amps and speakers capable of low bass

But for movies, I'd still use bass management. I'd try each 10hz step and listen to what sounds best on the main speakers, playing loud, no booming, no distortion, no port noise/chuffing etc.

For my system my speakers go down to around 45hz, but I've set the crossover for 70hz.

[fbczar]

Mar 5, 2016 11:54:10 GMT -5 smarties said:

www.hifiengine.com/manual_library/tdl-electronics/reference-standard.shtml


His subs will play low bass louder, and cleaner than those speakers.

So for music I'd try pure direct mode- since he's got good amps and speakers capable of low bass

But for movies, I'd still use bass management. I'd try each 10hz step and listen to what sounds best on the main speakers, playing loud, no booming, no distortion, no port noise/chuffing etc.

For my system my speakers go down to around 45hz, but I've set the crossover for 70hz.

Thanks for taking the time to research my TDL Reference Standard speakers and to comment. The TDL's can play down to 16Hz in the right room so they are pretty capable in Reference Stereo mode. The TDL's are exceptional clean, but they cannot match the output of the subwoofers for movies. My stacked pair of DSD-12012 subwoofers are great with music, have been measured to 4Hz in some reviews and  have all kinds of output. I really can't go wrong in any setup available to me, but. I agree with your advice. You are correct that direct mode is a good choice, especially for really dynamic, powerful music. I always use Dirac with movies and cross over at 70Hz. I have been experimenting with Dirac full for music and have been able to get closer to the detail I hear in Reference and Direct mode while keeping the great soundstage Dirac provides. Thanks again for your help.

[Gary Cook]

I started using a sub decades ago for stereo 2.1 music. I had a stereo amp that made 25 WPC in class A, it sounded great but it wasn't really enough power, so I built a 100 WPC stereo Class AB pre map. That had more than enough grunt but it didn't sound as good. An electronics engineer who worked at the same company as I did back then suggested that I try the Class A amp for the left and right channels, build an active cross over and then use the DIY Class AB amp to power a sub woofer. I build an enclosure for a 12" driver and used one channel of the stereo DIY amp to power it. The resulting sound, using the 25 WPC Class A for the L&R, with the cross over around 100 hz, and the 100 WPC Class AB amp for the sub, was a huge improvement. I've used that set up, obviously with different components ever since. Even now I have a Class AB Emotiva XPA-100 power the 17" sub and a pair of Emotiva XPA-1L's that I run in Class A for 2.1 stereo music. The L&R 35 WPC + Sub 400 WPC is plenty and the sound quality is fantastic.

So to answer your question on the positive effect of a sub woofer on the power demands of the main speakers, hell yes. Without the sub woofer there is no way 35 WPC would be enough but when a 400 WPC sub woofer is added it's plenty.


Cheers
Gary

[smarties]

Using high pass can aid if you don't have much power (or speakers are pretty hard to drive down low) ie using a subwoofer with high pass or a external active crossover between pre and power.

Usually you will do this for standmount or bookshelf. Basically it's like what a HTIB system is, full range goes to the "woofer" then inside the box is a crossover, cable from the box to speakers- that audio signal is filtered say >100hz

[Deleted]

Mar 5, 2016 11:43:38 GMT -5 Boomzilla said:

Hi fbczar !

Mr. DYohn is correct - the SPL in the room (with or without subs) is a function of the gain at the preamplifier stage. Mr. Levkof is also correct - the main amplifier power required decreases as the high-pass crossover point goes up and as your volumes decrease. The transient intermodulation distortion (TIM) of your main speakers also decreases as the cone excursion is reduced.

Now that said, these theoretical "improvements" of removing bass demands from your main speakers are often that - theoretical. Some speakers offer audible improvement when crossed over to a subwoofer. Others don't.

And finally, if your shopping considerations are the XPA-1L vs. the XPA-1 mono blocks, may I encourage you to go with the XPA-1 amplifiers. I've owned the XPA-1L (generation one), and heard both the XPA-1L (generation two) and the XPA-1 (generation two). My preference (and a wide margin) is for the XPA-1.

That said, I bought (instead) the XPA-2, generation two. And to my ears (and in my system) it seems to offer 100% of the sound quality of the XPA-1 amps (and for a LOT less money). Now that said, my speakers are more sensitive than yours, and can easily be driven by less power, so this may not be an accurate comparison.

If you will, try your subs both with and without your speakers crossed over. If you're running your mains full range, you'll have to set the low-pass for the subs using the plate amp on the subs. But if you can get a blend (I could), then the "full-range-mains plus subs" may sound better than using the high / low pass crossover method. Just my personal experience...

Boomzilla

   

[leonski]

Oct 29, 2015 19:05:14 GMT -5 DYohn said:

Wow. I've been in this game for more than 40 years now and I don't think I've ever heard that question before. IMO the question has no answer. The acoustic output from the subwoofer has no impact on the power demands of main channel speakers. It's apples and oranges.

For NORMAL (?) music, the distribution of power VS Frequency is sort of known.  The 50:50 power point is ABOUT 350hz.   So, if you were to biamp (line level) at 350hz, both amps would run out of steam at about the same level.   By using a low cut filter to the MAIN speakers, you potentially reduce the demands on the main amp, transferring the power needed over to the sub, which presumably is powered and has its own crossover.  

Below the 50:50 point, power needed by the bass rapidly drops off.  For a crossover of 80hz?   I'd ESTIMATE no more than 15% of full power is needed.   Still and all, quite a bit.   I personally would go NO LOWER than 25% of power to the bass below your cutoff of 80hz.   
What you POTENTIALLY might gain is clarity.   Bass will (as will all frequencies) interfere with one another.   You might have a suckout at one point and a peak at another. Moving around the room might reverse the situation.  Having a sub and main speaker 'overlap' might also induce phase problems.   The bass from my sytem was 'tubby' when either the sub or main speakers (to their limits) were playing alone.   Combined?   Very non-musical bass.   

IMO?   Try it BOTH ways.   Take the time when doing the setup to get it as good as possible.   Make sure everything is 'in phase'.  

In my system, the 2-way main speakers crossover at 600hz. and have a lower limit of 35hz to 38hz 'in room'.    By cutting frequencies below 50 or 60 hz TO the speakers, I cleaned up the bass, reduced stress on the main Amps (a stereo amp per speaker, biamp) and improved musicality.   

With a lower limit on a speaker of 16hz, which is good for non-musical effects and the 3 or4 pipe organs on the PLANET which have a 64' pipe, I'd cross NO HIGHER than maybe 50hz.    Cross the sub at 40hz.  Since these are NOT brick wall filters, there are frequencies both above and below the cross which will be reproduced.   The idea is to have flat response in the passband.   IOW, between the 2 crossover points.    As the sub reduces in level, the main speakers increase.     
I suspect your 16hz speaker level is AT LEAST 12 to 18 db DOWN from a reference Zero.    The idea is to get the frequencies between the 2 crossovers to 'sum flat'. 

If your mains can be biamped, that is another avenue to explore.    For another time and post.