Sub integration issues e.g. less bass at some settings.

KingKrell

Novice Member
I have a BK XLS2000 sub set up as a music sub for CDs with the hi-level input. It goes down to 17hz. My AE Aelite (mains) speakers go down to 34hz. My room is not huge, but I got the BK a few years ago as it was one of the fastest in a reasonable price range and it helped bolster the bass.

Since the introduction of a Benchmark DAC 1, the integration and behaviour of the sub has change somewhat. I have noticed that with the sub off, bass is tight and much more extended and very directional. It sounds very, very good in the sweet spot now. In fact the sweet spot is enhanced in all frequencies.

Now, if I turn on my sub and slowly turn up the gain, it gets to a point where the bass lowers a few db. I tried this a few times and it definitely occurs. If I simply turn off the sub, bass will rise on the mains again. If I turn up the bass to match the loss in bass from the mains to match what it was, the bass is not as tight and warmer, but thick/solid sounding as the sub bass is being heard - this appears too high as it should blend. It's as if the sub is cancelling out the mains slightly and then replacing the bass with it's own which is not as tight, but thicker as I match for the lost bass. To be honest, the sub seems to offer no extension in the way it used to...

I thought it might be the phase setting, but changing the phase only really changes the volume and makes the sound thicken even more. it's best on 0. If I lower the cut-off the same thing happens, but tightness improves as the cut off lowers. However, the bass reduction is still occurring.

I'm wondering whether I'm better off without the sub as the sweet spot is a lot better since the introduction of the DAC 1!

Interestingly, if I walk away with the sub on, bass carries well throughout the room (and the house too). With the sub off and if you walk away the bass reduces a fair bit. If you walk far away, such as into the hall, bass comes back a bit but it doesn't carry much. This is good, in that I can listen at high volumes without annoying other family members, but bad in that it sounds worse if you want music on whilst you are doing something about the house.

Questions:

Why does the sub reduce/cancel out the bass at certain gain levels? :confused:
Why does the sub bass travel so much better around the house? It seems I'm between a rock and a hard place here – tightness vs dispersion. Can't I have both? :rolleyes:
 

[unique]

Standard Member
I kinda have same as u with my bk200.

Any >40 hz the bk produces is just bad, very bad.
Since im only using bk's xover its ****ing my main speakers tight bass aswell..
hopeing an amp with subw.out will help me fix this (so i can boost <40hz without ****ing my mains, then again the sub doesnt seem to have that much power so i will probably get a load of distortion then.. mm why did i buy it without listening to it beforehand.. relying on opinions from forums can be a bad idea i noticed :oops: )

The cancel out stuff you have, i do not notice much. Have you tried placing your sub near your front speakers? If their wide appart certain frequencys will always be blocked cuz of the wave lenghts..
 

AngelEyes

Distinguished Member
Ok chaps fear not, you haven't bought a duffer you are just suffering from one or more symtoms of incorrect setup. This is not a criticism of you at all, as subwoofer setup can be a complete nightmare to get right, especially without any measuring equipment. Anyone who thinks they can seemlessly integrate a sub with a pair of full range speakers in the average room is aving a laff. :D

Ok lets dispel some myths, any speaker or subwoofer manufacturers claims of output are usually tosh so don't expect 17hz from the BK or 34hz from the AEs at any kind of apreciable volume.

Having one bass radiator in a room causes interactions with the room (reflections and standing waves) in the sub frequencies that can lead to cancelations as well as concentrations of bass. This can be heard as quiet or loud boomy areas in the room. The room itself already has these troublesome 'nodes' with a single sub radiator, add two more (by asking the speakers to dig really deep) and you can see how things can get very messy. This can end up with muddy slow, bloated or just plain 'missing' bass.

In order to keep things simple I would recommend trying a higher crossover frequency, say 80hz, this leaves the speakers and stereo amp less to do, reducing distortion and allowing the sub to do what it does best and cater for the sub frequencies. Don't kid yourself that a full range speaker is good at producing deep bass, it isn't and it will be distorting like crazy if you force it too. Raising the crossover will also reduce the interactiosn between the 3 radiators to slightly higher frequencies which tend to be less problematic.

You really need to invest in an SPL meter, BK sell one of the best on the market for a good price so it is worth a look. What you need to do is determine your ideal listening position and tune the sub to best suit your rooms nuances. Forget being able to hear the same 'bass' all round the room or all round the house, it just won't happen, sorry. :(

You can use the SPL meter preferably with a PC and Room EQ Wizard to plot a frequency response for your listening position in your room. By moving the subwoofer or the listening position sometimes only a few inches, you can dramatically improve the bass and produce a much smoother curve.

Unfortunately a lot of rooms are either not flexible enough (few positions SWMBO will let you place a sub) or have a really bad frequency responce and some EQ is required. REW will show you exactly which frequencies are giving you problems and if you connect low level then a relatively cheap tool like the BFD can cure this for you. For high level users you would probably have to opt for a Velodyne SMS-1 which being more expensive than the XLS200 is probably not viable in this case...

Sub position can still make a massive difference and if you don't want the hassle or expense of using a PC then you can download some test tones and burn them to a CD and plot a relatively crude but still useful room curve using the SPL meter.

If you can persevere you should be able to transform your sub into a musical treat :smashin:

Adam
 

AngelEyes

Distinguished Member
[unique];6986068 said:
Any >40 hz the bk produces is just bad, very bad.
I would suggest this may be due to setup/position as the BK is well renowned for going deeper than 40hz with no problems.

[unique];6986068 said:
Since im only using bk's xover its ****ing my main speakers tight bass aswell..
hopeing an amp with subw.out will help me fix this (so i can boost <40hz without ****ing my mains, then again the sub doesnt seem to have that much power so i will probably get a load of distortion then.. mm why did i buy it without listening to it beforehand.. relying on opinions from forums can be a bad idea i noticed :oops: )
Subs should come with a warning: 'Do not plonk down in room and expect to work perfectly'. They are hard to setup and people really should be told this, if you read the forums enough I would hope you would have known this already, if not you can either give it a go or give in :D

[unique];6986068 said:
Have you tried placing your sub near your front speakers? If their wide appart certain frequencys will always be blocked cuz of the wave lenghts..
Not sure what you are getting at here :confused: but there is truth in the fact that positioning is key :smashin:

Adam
 

Member 96948

Distinguished Member
Why does the sub reduce/cancel out the bass at certain gain levels? :confused:
Why does the sub bass travel so much better around the house? It seems I'm between a rock and a hard place here &#8211; tightness vs dispersion. Can't I have both? :rolleyes:
One word; Positioning.

In an ideal world, the musical signal would emanate perfectly in phase and therefore in time from all of the speakers drive units. In practice, two frequencies don't even arrive in phase from the same drive unit as fluctuations in impedance cause related shifts. By the time you add in additional electrical components in the form of a crossover and another driver with it's own set of issues and it's not unusual to see a single loudspeaker with swings of 90deg in phase over very small ranges in frequency.

Consider now the signal leaving a preamplifier and passing through two separate amplifiers with their own separate drive units and it's not to big a leap to suspect there maybe some phase issues. The difference is that, this time, one of the speakers is producing frequencies that overlap with the other, without the benefit of a carefully designed and integrated crossover like a two way speaker has.

Where the frequency range of two speakers, or sub and speakers in this instance, overlaps and there is a phase disparity, you will get a cancellation. No amount of turning the subs gain up will boost the dip in the frequency response, in fact it can deepen the cancellation. What increasing the gain will do, is boost the subs output at the frequencies either side of the response. This is quite probably where the speakers are managing quite nicely by themselves, thus muddying the bass quality with excessive bass output and two slightly out of sync signals.

Sound familiar?

Actually, I've painted the nice simple version that would happen if you were sat listening in the middle of a field. By the time you introduce walls and ceilings, a single bass frequency can be 20dB down and yet 2ft away, be 20dB up with only a subwoofer playing by itself. Throw in two more sources of overlapping bass and you can see that it just got complicated and entirely unpredictable.

So, positioning.

With that lot in mind, it can be seen that whilst placing the sub between, or near, the main speakers with the phase set to '0' is a logical place to start, it may be pretty far from the best place for that room/setup.

Phase is related to distance. Lets say you have a big phase induced cancellation right in the middle of your crossover region, which for the sake of argument is the 34hz mentioned above. We shall assume that the cancellation is as big as it can be at that frequency which would mean 180deg out of phase, or half a wavelength. Half a wavelength at 34Hz is 5m which would involve a rather large change of position for the sub to correct the difference.

Ah Ha! You think, I'll just turn the phase control through 180deg and dial the cancellation out. The problem is the phase control will turn all of the subs frequencies through 180deg, thus shifting the problem somewhere else in the frequency range. It is a useful control, but only in conjunction with positioning the sub as best the rooms layout will allow in the first place.

With an AV systems and especially the latest amps with complex auto setup routines, such phase errors induced by signal delays can be compensated for by applying relative delays between the channels. My sub consistently measures 4.65m away, but I can assure you it's no more than 3.25m to it's furthest extremity for instance.

Again with the complexity of this interaction between speakers, room and sub, it's impossible to predict the likely positions that will provide the smoothest, most integrated response in your room and I'll say now that the popular 'myth' methods promoted by the general hi-fi press (the walk and crawl methods) are woefully inaccurate* ways of tuning bass. All they really do is allow you to find the position suffering the biggest (read loudest) peaks in the sub/rooms response. As you've noticed, these can be whilst standing up and even elsewhere in the house.

Nope, what you need to do is measure whats going on at the listening position, because that's the only place that matters. You can then make informed decisions about where the problem lies and see what differences moving this, or tweaking that makes. Every other method is hit and miss in comparison.

Get yourself a Radio Shack Analogue SPL meter, download some free test tones and see that your room/speakers/sub does. There's nothing wrong with any of your kit, regardless of what others may say, let me make that clear. Once you start measuring though, don't be surprised that what you think is even, tight bass from the speakers turns out to look alarmingly uneven once you see it on a graph. You'd be amazed what we get used to.;)

Russell

*See my blog.

PS. just seen Adams post. Man, I type slow.:rolleyes:
 

AngelEyes

Distinguished Member
PS. just seen Adams post. Man, I type slow.:rolleyes:
I couldn't believe you hadn't replied, classic russ.will territory :D

I will now see how much I got wrong :rolleyes:
 

AngelEyes

Distinguished Member
Oooh Russell, yours was all 'sciency' :D

Adam
 

cribeiro

Novice Member
Type it once, type it clearly and type it ALL!

It saves on confusing queries later.;)

Russell
But why is it that there is always some little difference every time someone comes with a bass problem, which does not permit to use an older write-up :rolleyes:

I also do a good amount of client support in my job, and you never know. Some can handle everything at once, but others need to digest it step by step :suicide:
 

Member 96948

Distinguished Member
That's what paragraphs are for.;)

Anyway, I now have a PC, soundcard and REW; Wait until I start beasting you for advice. That's gonna hurt!

Russell
 

KingKrell

Novice Member
The sub is on the inside of my left speaker and right next to it, both standing out from a corner. The left speaker is out from the corner as less as possible, but it had to be about 60cm (to nearest surface) or so from either wall to sound okay and free from boom. Mains are facing toward the listening position. So, the sub is about a metre in from the left wall at the corner, but in line with the left speaker, about 60cm out.

A downside is I have a through room (front room joined to living room). If you drew a line in the centre, then I'd have a square room, but there is no wall on the right of the right speaker and the dining table is over on the right. So the sub is in the far left hand corner of the rectangular room close-ish to the left wall...

I could possibly wire it over to another corner or near the right speaker nearer the centre of the room where I have a table that could move... The cable might just reach. I put it where it is now, as it seemed to be the best place where I could match it to the left speaker as close as possible. You'd think if it was right next to it I could match it and generate similar reflections? I have a feeling I might have to try the phase again, but with much more minor increments. I was using 1/8th turn steps to test to start with. I had it on 0 phase for ages. Oddly, I never noticed the bass cancellation before until I got the DAC 1. It’s giving me a tighter, different style of bass than before.

Yes, I need to get a meter so work it out properly really! I'm worried that if I can't move the sub anywhere useful it's going to be a painful exercise... :suicide:

As for sub bass, I have tried turning the sub gain right up so I can hear more of the BK's own bass to get a much better idea of how it sounds on its own. Right now, it's not as tight and much warmer sounding so I'm wondering even if I get the balance right my mains will still sound sharper, but maybe not deeper..? I know the XLS2000 is rated a good sub, but it appears it's not going to be as fast and tight as my mains..? However, reviews of the BK claimed it was one of the fastest subs out there. :confused:

You say let the mains do less work, but they are crossovers are fixed as my source amp is stereo only and it's used for music. Alas I can only tweak the sub :mad:
 

cribeiro

Novice Member
You say let the mains do less work, but they are crossovers are fixed as my source amp is stereo only and it's used for music. Alas I can only tweak the sub :mad:
Then you need to use the natural roll off of your main speakers as crossover point, or use a line-level crossover.

The first solution will work, but the second will make a more seamless transition between sub and speakers, and also increase the reserves of your system, reaching louder with better dynamics.
 

KingKrell

Novice Member
Then you need to use the natural roll off of your main speakers as crossover point.
Okay, this has made me think some more. I thought I had taken this approach, but as I now have deeper extended bass reproduction from the mains (due to the DAC 1) I may need to play with phase after the crossover is set to a lower level. When I tried changing phase recently, I put the crossover back up to what is was before, about 55hz. It is indeed the lower bass only that is reducing. It's highly unlikely the 34hz AEs will touch 40hz much so I'll tweak the phase in the lowest 40Hz setting tonight. If no joy here I'll get a meter to reconsider placement...

Thanks everyone - I have some options to try. :)
 

AngelEyes

Distinguished Member
Then you need to use the natural roll off of your main speakers as crossover point, or use a line-level crossover.

The first solution will work, but the second will make a more seamless transition between sub and speakers, and also increase the reserves of your system, reaching louder with better dynamics.
Good point I overlooked.

Once you get an SPL meter and you can actually 'see' what is happening in the room things should start to get easier although be prepared to spend some time to get it right. Room EQ Wizard will save a lot of time in the long run (although it may take a bit to get your head round it) and is far more acurate than a manual plot.

Lots of help available here though :)

Adam
 

KingKrell

Novice Member
I just read a web article saying essentially, that if the cone of the sub faces the same way as the speakers it's 0 phase, and if it's facing away, say on the other side of the room it's 180. My BK is a DF, so I guess it would be somewhere near half way, as the cone is at right angles? I know that as I go throught the range 0-180, it's much louder around around half way.

Oddly, I get some hum at 0 phase, which goes as you turn past 20 or so. No idea why.

Got plenty of things to try now!

One more question - If I use the stock hi-level (long) copper cable that came with the BK. It is worth upgrading this to something fully shielded or shortening it? I wonder if I can get a tighter bass doing this.
 

badbob

Banned
I would set crossover on the subwoofer to 120hz- it'll sound boomy, continue playing music slowly reducing crossover until you're not getting doubling up of bass frequencies. I've just connected a sub to a Hi-Fi, since you're sending full range to both sub and mains needs a bit more fine tuning
 

KingKrell

Novice Member
Lots of help available here though :)
I'm going to try manual (ear meter!) adjustment to see if things improve somewhat. Certainly I'll try and stop the bass cancellation significantly first. If I feel it's improving and feel more confident the subs going to work okay, I'll fine tune with, and invest in or borrow a meter. :smashin:
 

AngelEyes

Distinguished Member
I just read a web article saying essentially, that if the cone of the sub faces the same way as the speakers it's 0 phase, and if it's facing away, say on the other side of the room it's 180. My BK is a DF, so I guess it would be somewhere near half way, as the cone is at right angles? I know that as I go throught the range 0-180, it's much louder around around half way.

Oddly, I get some hum at 0 phase, which goes as you turn past 20 or so. No idea why.

Got plenty of things to try now!

One more question - If I use the stock hi-level (long) copper cable that came with the BK. It is worth upgrading this to something fully shielded or shortening it? I wonder if I can get a tighter bass doing this.
A better quality shielded cable may reduce hum but it won't necessarily improve the bass. If you really want to change, Mark Grant sells fantastic quality cables for sensible money, either in the cable powerbuy or on his website.

I wouldn't get too worked up about the angle of the driver, it is unlikely to make any difference to the phase compared to other things in the room. certainly placing at 90 degrees is not automatically going to be the best position. As suggested you need to get a visual understanding of what is happening in your room, which will make all these questions much easier to answer.

Generally when using REW or my SMS-1 (or even with manual plotting) you should tuen everything to default settings including setting phase to zero. Then move the sub around and see how the response curve improves as you try different locations, a few inches or the other side of the room may be required. Obviously if you have a couple of preferred spots then concentrate on those. As you can imagine manually plotting so many locations would take ages which is why REW is such a time saver.

Anyway after you have found the best location, start adjusting the phase and remeasuring, see if you can improve things further still. After than it should beome apparent if you are likely to need any sort of EQ.

Adam
 

AngelEyes

Distinguished Member
I'm going to try manual (ear meter!) adjustment to see if things improve somewhat. Certainly I'll try and stop the bass cancellation significantly first. If I feel it's improving and feel more confident the subs going to work okay, I'll fine tune with, and invest in or borrow a meter. :smashin:
Seriously, your life will be made so much easier using at the very least an SPL meter I would recommend not wasting your time doing it by ear. You may improve things, you may not and you will likely never know for sure :)
 

Member 96948

Distinguished Member
I just read a web article saying essentially, that if the cone of the sub faces the same way as the speakers it's 0 phase, and if it's facing away, say on the other side of the room it's 180. My BK is a DF, so I guess it would be somewhere near half way, as the cone is at right angles? I know that as I go throught the range 0-180, it's much louder around around half way.
Could you post a link to that article as it would brighten my day.:rotfl:

This is another one of the common misunderstandings with respect to phase; It is in no way affected by which way a driver points. Due to the massive wavelengths of subbass relative to the size of the driver it is, to all intents and purposes omnidirectional. Therefore, the subwoofer can be considered a point source and you will receive just as much bass above it, as below it, as to the side of it.

As far as phase as concerned, it doesn't even matter whether the sub is in front of you or behind you. Imagine the sub 10ft behind you and the speakers 10ft in front of you, both reproducing a single pulse at 50Hz. As long as the pulses are reproduced simultaneously, the two wavefronts will reach you at the same time and thus be in phase.

If a delay as a result of processing or a crossover, or indeed a room reflection were to affect the subs signal causing a delay of a mere 11ms, one signal would reach you precisely half a wavelength late and thus cancel the other. It would be out of phase and it made no difference which way the driver was pointing or was affected by the relative orientation of all the speakers concerned.

Russell
 

Member 96948

Distinguished Member
One more question - If I use the stock hi-level (long) copper cable that came with the BK. It is worth upgrading this to something fully shielded or shortening it? I wonder if I can get a tighter bass doing this.
It will make no difference.

Russell
 

KingKrell

Novice Member
I'll try and find that link about the direction of the cone... It didn't work for me anyway!!! :D

Well, I spent a lot of time playing and found that the phase was about right near to 160-180, so I left it on 180. At 180, the bass seemed to be deeper, delayed and less bouncy than in the 0 position. But, only near 180 did it stop cancelling the mains out, so I left it there. My cut-off works about around the 50hz level. Any higher, it doubles and I get an over-warming affect. It works okay lower but 50Hz just helps that little bit more.

I hardly have to raise the gain, and it's just set slightly below the second notch. The slightest change takes it too high or too low. At low volumes, I can't feel the cone moving at all. Once the volume goes up it starts to move and essentially as soon as I feel it move I can feel it in the listening position. In fact, I can still just about feel it a lower volumes when the sub appears to not move. I guess the phase is keeping the cone inwards more and as it's set quite low on the cut-off, it's moving less.

What the result was is an added 10% or so of extra bass authority rather than extension generally. I can only feel the extension on very bassy tracks. But what it does give me is a great sense of sound stage as the bass 'field' seems to join the speakers together. If I turn the sub off it's not immediately noticeable, but as soon as you turn it back on the music is more involving and less forced, as if the mains are being assisted.

Good stuff! A definite gain! :thumbsup:

One small downside - I think the sub is gaining volume a little bit faster than the main speakers. It could be room acoustics, but at high volumes it sound a little bit too loud. At mid volumes it's about right (how I adjusted it). I guess the sub is responding differently to my speakers. :confused:

I'm on the lookout to borrow a meter to check my settings!
 

The latest video from AVForums

Podcast: Marantz SR7015 & NAD T 778 AVR + Mission LX2 MKII Speaker Reviews, AV & Film News and More

Latest News

Oppo launches S1 and R1 4K smart TVs
  • By Andy Bassett
  • Published
Lithe Audio AirPlay 2 ceiling speakers world's first
  • By Andy Bassett
  • Published
Humax launches AURA 4K Freeview Play Recorder
  • By Andy Bassett
  • Published
Fyne Audio adds new standmounts to F1 speaker range
  • By Andy Bassett
  • Published
Mark Levinson expands 5000 Series with amplifiers and players
  • By Andy Bassett
  • Published
Top Bottom