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"Bass management" in a stereo system. My take.

Chromatischism

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A short while ago I posted about this not being as necessary as some think and got some vigorous pushback. Here I expound a bit more. If I want to use a subwoofer in my stereo system can I use a simple preamp output to drive the sub or do I need "bass management"?

The answer is it depends. First off what is bass management? In an AVR (Audio Video Receiver) it is twofold. One is sending bass from all channels below their crossover points to the subwoofer. Second is routing all signals from the LFE (low frequency effects) channel to the sub only. In a stereo system bass management simply means a crossover. Some preamp and integrated amp subwoofer outputs have a low pass filter (LPF) for the sub and some have this and a high pass filter (HPF) for the main speakers). Some have a full range jack labelled subwoofer which is a full range signal summed to mono. Others have no sub output at all. All powered subwoofers have their own LPF for their driver and and a few have an HPF built in when one uses the speaker level inputs. Most high quality subs do not have speaker level inputs.

So can I run a full range signal to my sub and run my main speakers with no HPF? Sure I can. My subwoofer already has a built in perfectly good crossover. Also my main speakers are designed to be run full range from whatever amplifier they are connected to. I know of no speakers on the market that the manufacturer recommends they be high pass filtered to play properly.

The usual objection to this is that I will get higher distortion from trying to force the woofers in my main speakers to produce frequencies that they can't. This is mostly nonsense. They were designed to be driven full range. Anyone who has played a warped record with no infrasonic filter can tell you that any woofer is fully capable of moving in a pistonic fashion at 2hz, never mind 20hz. The problem with smallish drivers or those with limited excursion is that they don't make a very loud sound at very low frequencies. They move just fine, they just don't talk very loud. Woofer distortion happens at higher frequencies when the cone begins to break up (flex in an uncontrolled fashion).

Others will talk of intermodulation between the ultra low frequencies and the midbass or midrange (depending on whether you have a two drivers or more) This is already cooked into the design. If you like the way your speakers sound then this distortion source is not causing audible problems.

The final potential issue is blending the response of the sub and the mains in the crossover region. This is usually not a big deal. The natural rolloff of bass SPL due to woofer displacement (combination of area and excursion) is a pretty smooth slope. Adding another slope to this with a HPF is not necessarily going to improve things. I have a mid to low priced sub from SVS that has selectable LPF slopes of 6,12,18, and 24db/octave. I can match the natural rolloff of my Imagine T2's pretty well. If we listened in anechoic chambers, perhaps we would want exact matching of crossover slopes between the mains and subs. We do not and a couple of db hump or dip in the crossover region is going to be swamped by the untidy mess that bass response is in home listening rooms.

I write this as I am about to replace an amp containing DSP that I was using to HPF my main speakers and I am wondering what effects this will have. In real terms, nearly nothing. I will need to tweak the subwoofer setting a bit, that's all. Bottom line is if you are shopping for an integrated amplifier or preamp and plan to use a sub, it's nice to have a jack on the back to connect it to but you don't have to narrow your list to only those that have two way crossovers built in. If your subwoofer doesn't have left and right inputs (many do) you may want to use a summing network to create a mono signal from your preamp/amp. Ideally, you want the output you use to be separately buffered so you don't reduce stereo separation in the main outputs when using a passive summing network. Most, if not all, bass in recordings is already summed to mono at subwoofer frequencies so, although I haven't tried this, you could probably just connect one left or right channel to the sub and never notice the difference.
I'd say this is a good summary but there are two more issues not raised here (that I can think of).

1. Modal phase interactions between bass sources
2. Room EQ not knowing what is the naked response of your components so that they can be delayed and equalized with accuracy

IMO/IME it is really the combination of Room Correction and Bass Management that together get better results than you'll get from analog methods. That translates to better bass.
 
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anotherhobby

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Distortion in the mains will be whatever it was before the subwoofer was introduced to the system.
Yes, without a crossover that is the problem. I used to have a pair of Focal Aria 906's in a large room. When turning it up louder, you could hear distorion in the mid-range of the music (like male singing voice) when the Aria's single mid-bass driver was asked to produce sub 80 Hz bass at the same time. After adding a sub and crossing them over at 80 Hz I was able to play the 906's much louder before the music would distort. Even at moderate volumes, I noticed improved mid-range clarity. I eventually replaced the 906's with 936's, and the mid-range is vastly superior due to the bass crossing over to the lower 3 drivers at 280 Hz. Same concept. In my office I have Revel M105's and it's the same story. Better mid-range due to being crossed over at 80 Hz with subs. The sound quality of bookshelf speakers absolutely benefits from being crossed over with a sub because it off-loads the bass duty of the single driver and in turn improves mid-range clarity.
 

TheBatsEar

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The problem is not with the low bass distortion. The problem is with the (intermodulation) distortions of the mid/lower-mid/upper-bass riding on the low bass that requires high excursions from the driver.
Yes, but that was there before you got the sub.

I think your opponent wants to tell you that a sub makes things better, even if your mains still get the bass signal. And i agree with that.
It's not optimal, but your mains don't get worse when you add a subwoofer.
 

krabapple

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Btw...sending the same bass to mains and sub is still 'bass management'. It's a bm option on every AVR I've ever seen. In Denons, it's called 'LFE+Main'. (Usually not recommended.)



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Pdxwayne

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That’s all true. However, if you like the sound of your speakers before you add the sub, this distortion in the low bass must not really be that audible.
In small, medium, and large rooms, I have noticed the benefits of high pass the speakers. This is because I like my music loud and I like songs with strong sub bass.

I might like the sound of speakers before high pass. But I like them even more after high pass them and adding properly setup sub(s).
 

phoenixdogfan

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Yes, but that was there before you got the sub.

I think your opponent wants to tell you that a sub makes things better, even if your mains still get the bass signal. And i agree with that.
It's not optimal, but your mains don't get worse when you add a subwoofer.
True, the IMD was there before anyone "got the sub." But one of the chief benefits of having a sub, is that it allows the offloading of those lower bass frequencies, and thereby reduces the IMD the smaller midrange (midbass?) driver would otherwise produce. If the OP wants to forego that benefit, that's his own business, of course. But people are just pointing out that he's leaving some performance benefits on the table.

BTW, if someone is only using a PC for a music source, there exists a free software based crossover called DePhonica, which does up to a 2 x 8 crossover with FIR filters. You will need either a program with a WDM driver (like JRiver) or else Asio4all to provide the virtual input, and also at least a 4 channel USB DAC for the conversion. Alternatively, one of the minDSP units would provide the same type of solution in a hardware based solution which will accept both digital and analog sources other than a PC.

Given all the additional expense, I can see why the OP feels he might want to at least try foregoing the high pass, but, at some point, it might not be a bad idea for him to at least listen to a properly crossed over 2 channel system to determine how its sound compares to his own.
 

okaudio

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Btw...sending the same bass to mains and sub is still 'bass management'. It's a bm option on every AVR I've ever seen. In Denons, it's called 'LFE+Main'. (Usually not recommended.)
It can work but depends on multiple factors. LFE + Main is my goto setup for my 2.1 music setup and works great for 99% of my material. For HT movie viewing I switch it off so mains are crossed over at 80hz.
 

Chromatischism

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Yes, without a crossover that is the problem. I used to have a pair of Focal Aria 906's in a large room. When turning it up louder, you could hear distorion in the mid-range of the music (like male singing voice) when the Aria's single mid-bass driver was asked to produce sub 80 Hz bass at the same time. After adding a sub and crossing them over at 80 Hz I was able to play the 906's much louder before the music would distort. Even at moderate volumes, I noticed improved mid-range clarity. I eventually replaced the 906's with 936's, and the mid-range is vastly superior due to the bass crossing over to the lower 3 drivers at 280 Hz. Same concept. In my office I have Revel M105's and it's the same story. Better mid-range due to being crossed over at 80 Hz with subs. The sound quality of bookshelf speakers absolutely benefits from being crossed over with a sub because it off-loads the bass duty of the single driver and in turn improves mid-range clarity.
I noticed the same thing when I took my S400's from full range to crossed to subs. Singing voices were noticeably more clear in modern pop/rock (complex music). It really did sound like distortion was reduced.

To the OP, I don't believe in the idea that any speaker is "designed to run full range" and therefore should never be crossed to a sub. Just about any speaker would benefit.
 

JRS

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That’s all true. However, if you like the sound of your speakers before you add the sub, this distortion in the low bass must not really be that audible.
No, it might mean that you were willing to put up with such shortcomings because of the speakers other virtues. Many an electrostatic speaker will fall into that realm. When I am chilling late at night and want to hear something recorded in an intimate setting, I turn the subs off which will also remove the HPF's from the mains. But when I want to get down, I want to get those 18cm drivers out of harms way, and not adding their pathetic little contributions to sub40 grunt. And as we all agree, relieving the main amplifier of those low bass chores will help to steer clear of clipping (that ,might take out a tweeter as well).
 

Chromatischism

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When I am chilling late at night and want to hear something recorded in an intimate setting, I turn the subs off which will also remove the HPF's from the mains.
This is odd to me because if the bass goes away, soundstage is reduced as well. Or do you mean the bass is somehow distracting to you?
 

JRS

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This is odd to me because if the bass goes away, soundstage is reduced as well. Or do you mean the bass is somehow distracting to you?
No, I guess I am one of those weird guys who believe that the coherence of a really fine 2 way is not something to be taken lightly. Sure a standing bass is less palpable, but I'm not talking about going away--perhaps I should have explained myself more clearly, when late at night and listening at lower volumes than I might otherwise, getting rid of the subs reduces transmission to the remainder of the house, and highlights how good the midbass drivers are, with no cost paid in terms of added distortion. In other words the 18cm are playing within their comfort range with an f3 of about 50Hz that I add some electronic assist to. In even more other words, for max fidelity at low listening volumes with quiet nights and my guitar kind of music, the 2 way setup is dandy. Other times, I want the ability to go low and growl. Then the twin 15's backed with a kW can put a smile on the face--more like Brothers in Arms tunes.

EDIT: A use case might be in a setup with the Purifi 6.5. For anything but demanding situations, they are probably all you need, but there are demanding cases that you simply run out of stroke. Whack whack...ouch.
 
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sigbergaudio

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It's relatively common to bump into people who say "I only use my subwoofer for movies, I turn it off when I listen to music."

This is a sign of poor subwoofer integration as in uneven frequency response.

Typical reasons:
  • Lack of EQ on the subwoofer
  • Lack of EQ on the speakers combined with no high pass
  • Both subwoofer and speakers are ported, making for difficult phase integration
  • Some combination of the above
  • All of the above

Can you add a subwoofer to a system without EQ and/or without high pass capabilities? Yes.
Will it work? Sometimes.
Will the alternative be better? Always.
 

MarcosCh

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  • Both subwoofer and speakers are ported, making for difficult phase integration
Could you please elaborate on this one? Would you recommend ported/not ported combinations to newbies like me to make it easier?
 

sigbergaudio

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Could you please elaborate on this one? Would you recommend ported/not ported combinations to newbies like me to make it easier?

In general I would at least recommend sealed speakers. If you have ported speakers you don't have to switch them out, just put a port plug (or a sock) in the ports.
 

MarcosCh

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In general I would at least recommend sealed speakers. If you have ported speakers you don't have to switch them out, just put a port plug (or a sock) in the ports.
I do have ported speakers that i can seal, but because of space limitations i am thinking of a sealed sub. Sealed sub + open soeakers then or still better use the plug? Thanks!
 

sigbergaudio

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I do have ported speakers that i can seal, but because of space limitations i am thinking of a sealed sub. Sealed sub + open soeakers then or still better use the plug? Thanks!

Still better to use the plug.
 

Fidji

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I use an AVR in a 5.1 surround system. I also have a two channels stereo system of preamp/amp/speakers. The post was about integrating a sub in a stereo system, which generally does not include an AVR. Your question seems irrelevant.

I have my stereo as part of multichannel AV setup, with stereo being priority. So I use AV preamp as preamp.
I am actually using my full range fronts (down to 20Hz in room, sealed) with 4 sealed subs, crossed over at 50Hz. DRC up to 250Hz.

Sounds great to me, measures also well.
 

sarumbear

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(3) that there can be extremely localized (within a few inches) nulls/peaks.
I’m not sure how higher than 2000Hz standing waves can occur on a typically furnished listening room. What am I missing?
 
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