Subwoofer Question

If properly placed and dialed in it shouldn’t. 

That's what I was thinking. Those frequencies are supposed to be non directional right?

Yes, it did for me. No matter where I placed it, I could always tell it's location even when the crossover was set at 40hz.  It bothered me to the point of getting a second sub to balance it. Happy now.

Yes, this is why I often say a Stereo Pair of Subs, located near your mains, front firing to get the directionality/imaging that exists, i.e. where's the Jazz Bass Player?

you get fundamentals, harmonics, and overtones, i.e. 60/120/180/240 ....

diminishing in volume while increasing in directionality.

https://www.google.com/search?q=fundamentals+and+overtones&oq=fundamentals+and+overtones&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIKCAEQABgKGBYYHjIICAIQABgWGB4yCAgDEAAYFhgeMggIBBAAGBYYHjIICAUQABgWGB4yDQgGEAAYhgMYgAQYigXSAQg3Mzg4ajBqN6gCALACAA&sourceid=chrome&ie=UTF-8

Had one sub, now two. Amazing difference,

@elliottbnewcombjr 

I understand that all notes have harmonics, but any harmonic above 60 Hz, (the op's crossover point) will be reproduced by his mains and not the sub, so I wouldn't think he would get directional cues from the harmonics, from the sub? The mains, yes, but not the sub. What am I getting wrong?

@wsrrsw 

Had two subs, now four. Amazing difference,

That sounds like it could be a relative phase issue.  Check polarity on all speaker and amp connections, including the sub.

To be clear, the OP was asking about imaging being pulled to one side.  Properly set up and set at 60Hz the imaging and image placement from your main speakers won’t be affected (other than imaging improvements subs can provide) but you may sense more weight or pressure coming from the area where the sub is located depending on placement, which is a major reason why two subs are much preferred to one along with better dealing with room issues, lower distortion, etc..  But that’s separate from imaging from your main speakers, so voices and other instruments should still appear where they normally do, and if not then that’s a sub setup problem. 

@soix Thanks. Pretty much confirms my thinking. I will mess around with my sub's placement and see what that does... 

the cone of the driver that makes the fundamental ALSO makes the overtones. They are not generated electronically, they are generated physically, relative to the fundamental

whichever driver initiates a movement also makes the harmonics

watch this short video, 

https://www.youtube.com/watch?v=EeEspQ6-Gzk&t=35s

this video is longer but perhaps easier to understand

https://www.youtube.com/watch?v=Wx_kugSemfY

In case it helps, here’s a method to find the best locations for a sub(s) in your room…

https://www.audioholics.com/home-theater-connection/crawling-for-bass-subwoofer-placement

Here are some steps from Paradigm how to adjust sub settings (after you’ve found proper placement) that I’ve found to be simple and effective…

1. Turn the Subwoofer Level control completely counterclockwise to its minimum; 2. Turn the Subwoofer Cut-Off Frequency control clockwise to its highest frequency (i.e. 150 Hz). 3. Set the Phase Alignment Control to 0°; 4. While you listen to a bass music or video selection in your primary listening area, have an assistant turn up the Subwoofer Level control until the subwoofer can be clearly heard; 5. Have an assistant try the Phase Alignment control until you hear the most bass. Your subwoofer and front speakers are now in phase. Do not change phase alignment again unless you move the subwoofer or the front speakers to a different location in the room or move or remove large items of furniture or room furnishings (i.e. carpet, draperies, etc.) 6. Turn the Subwoofer Level control completely counterclockwise to its minimum. 7. Turn the Subwoofer Cut-Off Frequency control completely counter-clockwise to its lowest frequency (i.e. 50 Hz); 8. Slowly rotate the Subwoofer Level control until you match the subwoofer output level with the level of your front speakers. Bass should be clearly audible, but not intrusive; NOTE: If using an A/V receiver or processor to control crossover setting, skip the next step and set the subwoofer cutoff frequency control to ‘Bypass.’ 9. Slowly rotate the Subwoofer Cut-Off Frequency control until you hear the best subwoofer/main speaker blend. If the sound is too ‘thin,’ you have not set the frequency high enough; if the sound becomes ‘boomy’ you have set the frequency too high. Adjust until you find the most natural balance.  The sub should not draw attention to itself.

In both cases you really should have someone else to help to get best results. 

Keep in mind that the 60Hz crossover setting isn't a cliff.  There is some slope to that rolloff above 60Hz and those upper frequencies the sub is playing can be additive to the same frequencies the mains are playing.

I'd set the crossover on the sub lower to something like 40Hz and see how it goes first.

Just curious, what speakers are you pairing them with, how big is the room, what gear are you using and are you high pass filtering your mains? Some other info there could help to dial in your setup.

@paradisecom is right in that a xo point @60hz doesn't stop your sub from playing and adding @240hz. Albeit probably 20db down or so, it will still add to what the mains are doing. Combinebthat with the likelihood of a 200hz room mode and you have some extra weight in that region for sure. I'd be willing to bet if you measured on REW a L with sub vs R with sub, the side where the sub is placed will be 1-2db higher under 500hz. Try centering your sub between mains, and perhaps lower your xo point. Other option would be using dsp to hard 4th (or higher) order filter to build that xo point to be a cliff where Gandalf shouts "You Shall Not Pass". After you try that for a weekend, just buy a second sub. I upgraded my single Rythmik 12" sub to a pair of Rythmik F8, and I now have perfect stereo imaging  with very good separation with high pass filter around 150hz and raising spl measured down to 9hz in my small room. With bass notes, it's a strength in numbers thing. 

-Lloyd

Hi Loyd, Check out my virtual system. All the answers to your questions are there. Thank you! Im going to lower my crossover point. My speakers go down to 44Hz so I can go lower.

Two subs are always better than one!!!!   

Yeah given the space and how you have the speakers set up in that doorway so to speak, moving sub to dead center isn't really an option. Now, if you run your system with the sub off, everything is dead center perfect balance? Have you measured your system's response with the left + sub vs right + sub to see if perhaps it's a phase issue on one speaker causing a null at a certain frequency? I've seen that before where sub is perfectly set for one speaker, but absolutely detrimental to the other channel. It's maddening. I'm sure there's an acceptable setup option available. Also try pulling your sub away from the corner a pinch. If it is not only located on one side, but is corner loading that side, it'll be exasperating those heightened frequencies. But worst case scenario there's always another REL t7 on sale somewhere....... lol.

Agree strongly with the comments above (a) to check phasing and (b) that the crossover is not a cliff. Confessed as the owner of stereo T7/x's

Yes as many have shared.  I have stereo subs with my 2 main systems.  A pair of subs with a pair of speakers in 2.2 setups.  Sounds like the subs and speakers are all in one, so I can’t pick out the subs location when listening.  A second properly placed sub should solve your issue.  Good luck! 

A crosssover is not a cliff, so other fundamentals of slightly higher frequencies, lets pick 80hz  (at progressively diminishing volumes) are simultaneously originating from the sub’s location, and each fundamental brings it’s own set of harmonics, 160, 240, 320, ..... ALL lower in volume, yet ALL higher frequencies, ALL becoming progressively narrower, more directional.... 

When the ear can locate a harmonic’s location, the brain can ’find’ the origin of the fundamental.

Near crossover points, and as frequencies transcend, you can have both the sub’s cone, and the main’s woofer’s cone both making the same fundamental and series of harmonics. To retain directionality, to get the benefit of imaging, it is better to locate a stereo pair of front firing subs adjacent to the mains. I don’t llike ports, if so, also front firing to preserve/enhance imaging.

My speakers have 15" woofers with monster magnets, to both move and stop the cone (they weigh 37 lbs each) I think of them as built-in subs. People with true subs and sub arrays certainly have more lows than me, but I benefit from the bass imaging they create.

we read all the time that bass is omni-directional, but that's out in a cow pasture.

the conflict, in a listening space is, one sub, let's get the extension but not know it's location

two subs, let's get the benefit of extension AND imaging.

array, well that's for the big dogs for true extension added to large full range systems

My little 5.1 video system, I have 1 sub with a 1000 watt amp, right next to me, facing the TV, primarily to get Jurassic Park Dinosaur Stomps ...

Those frequencies can be directional due to intensity/level/loudness.  If the frequecies for the sub are recorded stronger in one channel or the other it will pull the image toward the sub.

If your mains are rated to ~44Hz anechoic, then they cab be benefitting from some room gain, as well.  That, coupled with the subs crossover set way to high and you'll have a problem.  For proper handoff from the mains to the sub, you'll probably find that the crossover will be much lower than what it is now.  Probably something in the ~30's Hz range.  In addition to that, if you get the crossover set properly, you can then increase the volume a click or 2 to aid in finding the lower bass notes that you might not be hearing now.  Try that after you get the crossover finalized, though.

Those frequencies can be directional due to intensity/level/loudness.  If the frequecies for the sub are recorded stronger in one channel or the other it will pull the image toward the sub.

@emuagogo  No.  Just…no.  If the sub is properly located and calibrated it will not pull images toward the sub, and if it does that’s because of very poor setup by someone who has no idea what they’re doing.

Thanks to everyone who helped me figure this out.

I lowered my crossover to what Im guessing is around 40 Hz and that solved the problem. I was probably getting overlap from 50-75 Hz and surprisingly that’s enough to pull my imaging over about a foot. I know, super nit picky but the way my room is set up if the center image is off you can tell. Visually. And that was bugging me!  I know, enjoy the music, well now I can...

Congrats!  Glad to hear all is well. 

as a data point to the thread for me it was different with different subwoofers.  even with low xo , e.g. 45 hz and steep 28db slope my SVS SB 3000 was directional and pulled the image.  

REL T9i was also directional.  

JL Audio D110 placed in a corner was not directional.  

may be caused by enclosure resonance.  

as a data point to the thread for me it was different with different subwoofers.  even with low xo , e.g. 45 hz and steep 28db slope my SVS SB 3000 was directional and pulled the image.  

REL T9i was also directional.  

JL Audio D110 placed in a corner was not directional.  

i believe the issue may be caused by enclosure resonance well above 80 hz.   

@elliottbnewcombjr 

the cone of the driver that makes the fundamental ALSO makes the overtones. They are not generated electronically, they are generated physically, relative to the fundamental

Whatever gave you that idea?  Your first video is no help at all.  Don’t you understand that the harmonics are part of the audio signal which is separated into frequency ranges by crossovers?

Yes, harmonics are not (usually) generated electronically, they are generated by the originating instrument and are what gives each instrument its sound signature.

When a piano, for example, plays a low note, the fundamental may be sent to the sub-woofer but the first harmonic will go to the woofer, the second harmonic maybe to a mid-range driver and some very high harmonics will be handled by the tweeter.

They are absolutely not all handled by the cone of the sub-woofer.

There are special considerations.  If the sub-woofer cone does not follow pistonic motion, but experiences cone breakup, these will show as nasty higher frequencies generated by the sub-woofer cone.

As several others have pointed out, cross-overs are not brick-wall filters so there is some bleed through of higher frequencies.

Some distortion is generated electronically and is sometimes encouraged, for example in valve amplifiers

If you can 'locate' the single sub easily, then of course it affects the imaging.  Even if it does not technically 'pull the image' to one side, the ears  ability to locate the bass affects the image in your brain.  If properly set up, a single sub can often still easily be located.  Just close your eyes and listen.  If you can point right to the sub, it it not nearly as ideal as two subs.  In both of my listening spaces, my pairs of subs are located well off the the sides and are not even easily seen from my listening positions. Placing them here made a huge difference compared to right beside my speakers, but it was for decreasing booming not imaging issues.  Congrats on turning the lowpass filter down to help!

yes harmonics in the airwaves are captured electronically during recording, any sound will be, and the crossover will subsequently send different frequencies to different drivers

but whatever is vibrating is what creates BOTH the fundamentals and harmonics, and, when you re-create an electronic signal into sound, you make something vibrate,

and

the thing (any thing) that vibrates creates both fundamentals and simultaneously creates a new set of harmonics, again, each time,

look at the patterns created by harmonics in the sand on the flat stiff steel plates. (far stiffer than any lightweight beryllium coated stiffened cone).

@elliottbnewcombjr 

the thing (any thing) that vibrates creates both fundamentals and simultaneously creates a new set of harmonics, again, each time

Not if it vibrates as a pure sine wave, when there are no harmonics.  You would be better off looking at Fourier analysis which shows that any repeating waveform can be represented by a set of sine waves - the fundamental and the odd harmonics.

Strangely, audiophiles tend to inhabit the frequency domain and talk about bass, midrange and treble, whereas in real life sound exists in the time domain which gives rise to discussions about Prat.

You can mathematically convert that repeating waveform into a set of frequencies using a Fourier transform.  You can also take the frequency set and convert it back to (almost) the original waveform.

There is an unfortunate glitch as the original waveform approaches a square wave in form.  The reconstructed waveform has a sharp spike surrounded by ripples.  You can see these as fringes if you look at sharp edges in a magnified digital photograph from a compressed file.

Huh?

No. But unless the subwoofer is next to you, you're best bet is a second matching sub placed elsewhere to offset room modes and standing waves. You don't want to be sitting in a peak or null.

So a second sub eliminates peaks and nulls or just decreases the chances of a listener sitting in one? 

@maprik What type of source program or test tone was used in the spectrum analyzed graph at the bottom of your equipment list?

Did it provide a flat output say from 10HZ on up? 

Does the graph display your speakers and sub-bass woofer output simultaneously or just the speaker output?

@m-db That’s white noise from a Stereophile system test cd. I believe its flat from 20hz to 20khz. The graph is my speakers only without the sub. I will do one with the subwoofer. 

I have tried this, using 1 subwoofer. if you have non-treated room, and the system is not in synergy it will not matter. 

But if you have a well-treated room and the synergy of your speakers are dialed in, Then Yes, it will matter. 

For me, having dual subs enable me to position the sound stage such I can hear the bass drums or cello playing the correct sound stage placement. not just bass, but correct bass alignment and spatial location of the instrument. 

heck, i started to think bass was just bass. but after the dual subs and room treatment. the musical presentation was leaps and bounds better with just 1 sub,

but I always say, YMMV.

As always, much misinformation regarding subs and how to set them up. I see the ridiculous crawl method being suggested again and again. This is not optimal, if you find a spot where it sounds good it will probably not be where you would like and furthermore you have no idea where the accompanying null/s will be so the whole sound will change as you move around in and out of peaks and nulls. I recommend disregarding that entire article from audioholics and forget about crawling around the floor. This could lead to divorce, insanity and getting bitten by the dog.

How to avoid crawling:  If you're going to add seperate bass sources (subs) then do it properly and this means knowing where in terms of frequency and amplitude the peaks and nulls are and getting rid of them. A minimum of 2 subs are required and the best and also easiest way is by usuing subs that are sealed and they must have variable phase (timing) adjustment which will allow you to place them where you like. Ported subs can work but will take a lot more effort and still not be as good. The ported units are more suitable for home theater but I would still choose sealed for the superior bass performance. A port resonates at only one frequency and by definition is frequency invarient so therefore untunable. Subs like REL which do not provide continuous phase adjustment should be avoided if you want the smoothest  response. 0-180 phase flip will not get you there. I'm talking about bass performance that is within the industry standard of +/- 3 dB up to the transition frequency (Schroeder) A good place to start is one sub in the front wall corner and the other in the middle of the opposite wall.

How to dial them in:  If you really would like to hear the music you've been missing in the nulls which is cancellation happening, it's a null right? and tame the peaks which is the only reason you hear people say the sub just did not work no matter what they tried or it's boomy or slow then you need to measure. There simply is no such thing as a slow or boomy sub. What gives this impression are the excessively large peaks taking much longer to decay. Peaks and nulls are your biggest enemy and I can assure you crawling will not tame the peaks nor fill in the nulls. I'm sure by now you have all heard of the free download REW you just need a mic. Get started it's easier than you think and will provide real time information where you can watch the frequency plot of your room change before your eyes as you adjust parameters on the subs. Measurement will remove the guesswork and also reveal the decay across the spectrum which if you choose can be treated with damping.

The result of this will astonish you so do it right and stop crawling around the floor, it's creepy.

As others have already said, the low pass filter on a sub determines at what rate the sub's output vs. frequency rolls off. If the sub is set at 60Hz and has a 1st-order low pass filter, 120Hz will be reproduced at only 6dB down from 60Hz, 180Hz at 12dB down. In contrast, with a 4th-order filter and a setting of 60Hz, 6dB down is not reached until 240Hz.

The higher the crossover frequency chosen, the more steep should the low pass filter be (1st-order is 6dB/octave, 2nd-order 12dB, 3rd-order 18dB, 4th-order 24dB). And of course the lower the crossover frequency, the more shallow can be the low pass filter. Conversely, the steeper low pass filter, the higher can be the crossover filter. When I spoke with Roger Modjeski (Music Reference) about mating subs with the Quad ESL, he told me he used a 4th-order filter and a crossover frequency of 100Hz with his.

I am a +1 on having two subwoofers.
Transformed so many different anomalies in my system. I have one up front with the LCR and then the other back behind me about 12-14 feet away.  

After using an active crossover and 4 passive woofers I built based on a design by Roger Modjeski I decided to try active subwoofers and purchased 4 KEF KC62 subs with balanced force drivers. KEF has an interesting take on setting LP and HP filters that you can read here: 

https://us.kef.com/blogs/news/understanding-lpf-and-hpf-settings?srsltid=AfmBOoofYdV0rzjlbr3BQq-70TAKqvj5oU1Qz-pdCBZRW6kppBi5c54c

Setting the LP and HP at different frequencies worked well with my box speakers, but not so much with my Quad ESL which have a resonance peak at 90 Hz, so setting HP and LP at 100 Hz was ideal. As the KEF article states with a 4th order filter the highest attenuation of the signal will be -24 dB at one octave above for the LP and one octave below for the HP. So for 60 Hz that will be either 120 Hz and 30 Hz.

So a second sub eliminates peaks and nulls or just decreases the chances of a listener sitting in one? 

Watch this.

https://www.youtube.com/watch?v=RE6g2IawzSQ

Read these.

https://www.harman.com/documents/multsubs_0.pdf

https://www.acousticsciences.com/wp-content/uploads/2024/11/Soundoctor-Barry-Ober-sub-integration.pdf

@maprik, to directly answer your question:  Could having just one subwoofer (REL T/7x)with the crossover set around 60hz pull my image to the side that the sub is on?

 Rereading my long post I realised that I did not specifically address this concern of yours so I apologise for that. If the sub has been properly set up regardless of where it is positioned it will not skew the image, the variable phase adjustment/timing and smoothing of the response will deal with this and this is why I try and impress upon everybody the importance of being able to measure. It's not expensive nor difficult to do and there are many youtube tutorials and articles on how to proceed. The best way forward is to read articles from the likes of Toole, Welti and Geddes. Dr. Earl Geddes actually wrote his thesis on this very topic and I suggest you take heed of their teachings. The posts in this thread are I'm sure all well intended but for someone new to acoustics it would appear confusing and daunting. It's not. It's thoroughly investigated science and proven in practice and all within your reach. 

The cost of the mic. which is about the same as a meal for two will be the most valuable cost effective purchase anyone can get and is IMO the only way to dial them in. The measurement system does a lot more than help position the subs it will provide a waterfall plot of the time it takes for the  sound to decay by a certain amount. If your room has a lot of hard surfaces and bare windows the sound from the seakers will take a long time to deay creating a confused smeared image with loss of detail.

This is scientifically based and not subjective in behaviour. It is difficult to conceptualise the damage strong early reflections cause which can be dealt with by placing some broad-band absorbers in the right place. Again measurement is necessary where the decay is computed for you by the amazing App REW which will provide the time it takes for the sound to decay by 60dB across the spectrum known as RT60 usually about 300ms for domestic listening rooms. RT60 depends on the intended use and volume of the space. Tables can be found online and the times will differ depending on whether it's for a lecture room, school, church etc. 

Getting a smooth frequency and decay response is paramount and I state with confidence that a modest system dialed in as per the above will get you a more immersive and rewarding experience than a big $$$ system not dialed in. All for the cost of a mic. and if necessary which it usually is some absorption.

Hope this was helpful and good luck.

If you place sub 1/7th of each dimension into the room and place near the listening position on an isolation platform, you'll be within the wave launch of the low frequencies and the direction of those notes will be perceived as coming from the mains sprakers that are producing the harmonics that are directional. The 1/7 puts the sub in the spot that's least suseptable to room harmonicas at low frequencies.

Wow. AMAZING advice! Thank you so much for sharing your experiences and knowledge! For now, reducing my crossover on the REL to around 40Hz has eliminated the problem. I spent a few hours finding the perfect spot for the sub using trial and error and a friend. I see a second T/7x in my future though (I mean why not?)