will a SUB help

[PaulRain]

I was just wondering......
in the case of treated room as much as I can due to the dimensions and obstacles, and having problems on the <100Hz caused by LBIR that I probably can't solve with trapping (for the above reasons)......
I was asking my self, will a sub help on fixing nulls under 100hz......
filtering the signal from the monitors, LBIR should not be an issue (caused from them) and a sub can me moved around a little more to get the right spot.....
At the moment this is just a thought wanted to know your opinion.
thanks

[SörenHjalmarsson]

The subwoofer is merely an extension of your main speakers, not a tool for reducing acoustic distortions. If the subwoofer is inexpertly calibrated however, it will introduce acoustic distortions of it's own.



MVH
Sören

[tINY]

A single sub and a filter set will cure most ills for a single position (if you like to lock your head in a vice...).

If you are willing to buy 2 subs and play around a bit, you can get decent results for a reasonably wide area (mix position with some slop).



-tINY

[PaulRain]

I'm most concerned about the sound at the listening position, the room is kind of small and if anybody else is in the room with me is more likely for recordings....
at the moment changing the listening position yield to very different response anyway.
@Sören: what do you mean with "If the subwoofer is inexpertly calibrated"?
position?
Maybe my idea it to much simplistic and I miss the point but in my small sick brain I was thinking that finding the right position for a sub is maybe easyer because it could be moved around more than the other two monitors

[SörenHjalmarsson]

Originally Posted by PaulRain

@Sören: what do you mean with "If the subwoofer is inexpertly calibrated"?

What i mean is that by dividing your bandwith into separate High and Low frequency devices, you might be introducing as many problems as you are solving...

Sure, a separate LF transducer will enable you to change your boundary inteferences somewhat, but that does not mean that all the virtual images will magically disappear - only that the relationship between the boundaries and a certain part of the bandwidth will change, depending on where you place the sub...

Further more: besides virtual sources you will also have three (or more) real sources that needs to be aligned with respect to time, in regards to the listening position (i.e. they all have to be either physically or electronically 'equidistant' to your ears). If they aren't properly integrated there will be a difference in path length between the spaced sources and you will get destructive cancellations and polar lobing, just like you would with the boundary related problems... and after you've established the placement and crossover frequency, you will also need to calibrate the output level of the device(s) - to get a linear frequency response...


MVH
Sören

[Kjell Gudmonsson]

Originally Posted by tINY

A single sub and a filter set will cure most ills for a single position (if you like to lock your head in a vice...).

If you are willing to buy 2 subs and play around a bit, you can get decent results for a reasonably wide area (mix position with some slop).



-tINY

+1. two subs is always the way to go. And yes, low frequencies ARE directional.

[Jens Eklund]

Originally Posted by Kjell Gudmonsson

And yes, low frequencies ARE directional.

?

Any wave motion has direction but a speaker will be omni directional at low frequencies and if in the modal region, you’ll struggle to hear where it’s coming from. It’s a completely different story that you might be able to hear where the sub is located since it will produce frequencies (wind noise if ported, distortion, vibrations etc.) above the modal region that will give it away, but if only playing say 45 Hz, it would be close to impossible to locate unless the room is big.

[PaulRain]

any more thoughts on this?
During summer vacations I will increase the treatment in my room with tuned panel absorbers but I still think I won't be able to solve the LBIR issue coming from the back wall.....
the SUB idea is still there, even if I did understood it's a little bit tricky and not easy to setup.

[SörenHjalmarsson]

Originally Posted by PaulRain

I was just wondering......
in the case of treated room as much as I can due to the dimensions and obstacles, and having problems on the <100Hz caused by LBIR that I probably can't solve with trapping (for the above reasons)......
I was asking my self, will a sub help on fixing nulls under 100hz......
filtering the signal from the monitors, LBIR should not be an issue (caused from them) and a sub can me moved around a little more to get the right spot.....
At the moment this is just a thought wanted to know your opinion.
thanks

Paul,

This shouldn't be too difficult to investigate. Move your main speaker(s) around in the front of the room, if there is no place in which the LF response is better, a subwoofer probably won't help... If there IS a place in which the LF response has improved, then that's where your subwoofer needs to be placed (provided that this placement enables you to align the sub(s) with the main speakers).

The MAIN reason for employing subwoofer(s), is to extend the frequency response/bandwidth of the main speakers - however, sometimes the optimal position for the LF and HF behaviors aren't the same (assuming a pair of full range speakers) and you therefore need to be able to move the high and low drivers independently... that's where deviding a part of the bandwidth into separate LF device(s) might help...

Just remember that when you change the position of an LF transducer, several boundary interferences will change (not just the LBIR) and become better or worse... and the remaining problems will STILL need to be adressed with the proper treatment - not to mension the signal alignment between the sub(s) and the L/R speakers, in regards to the listening position...

Further more... if you 'only' use one subwoofer, it will need to be integrated with one, or both of the main speakers (so that the time difference between the mains and the sub is the same, at the listening position) however, there are some limitations to using a single sub... sometimes (due to issues with uneven modal distribution) the optimal position of the sub might differ for each main speaker, and therefore (among other things), a better option is to employ TWO subwoofers - and individually align them to each of the main speakers. Another reason for using separate subs (one for each of the L/R channels) is that it offers a more realistic soundstage and unified image - not to mension more headroom and less distortion...


MVH
Sören

[boggy]

Originally Posted by PaulRain

I was just wondering......
in the case of treated room as much as I can due to the dimensions and obstacles, and having problems on the <100Hz caused by LBIR that I probably can't solve with trapping (for the above reasons)......

Classic acoustic treatment is a best way to get good bass response, with or
without subwoofer. Try to improve your LF response with better, or more
basstraps, and better speaker positioning.

Originally Posted by PaulRain

I was asking my self, will a sub help on fixing nulls under 100hz......
filtering the signal from the monitors, LBIR should not be an issue (caused from them) and a sub can me moved around a little more to get the right spot.....
At the moment this is just a thought wanted to know your opinion.
thanks

Nulls in response below 100Hz are a results of phase cancellation because room
boundaries, and if you add subwoofer, it will suffer from same phase
cancelations too. Small position movements helps sometimes, but you will get
phase differences between subwoofer and loudspeakers if you move only
subwoofer independently.... then, if you need a good response, you must
move complete system trying to preserve same phase differences between
loudspeaker and subwoofer.

Generally, this is a question about loudspeaker positioning AND bass treatment
in room... subwoofer has no business here, other than extending SPL below
100-150Hz.

BTW, loudspeaker really isn't directional below 100-150Hz, but it still have its own
phase response at this frequencies.

Independent amplitude/phase adjusting of two subwoofers for stereo reproduction
is easier, with better results.


Best regards,

Bogic Petrovic

[ggegan]

Originally Posted by boggy

Small position movements helps sometimes, but you will get phase differences between subwoofer and loudspeakers if you move only subwoofer independently.... then, if you need a good response, you must move complete system trying to preserve same phase differences between
loudspeaker and subwoofer.

Bogic Petrovic

Just a question - why not use delay to time align the subwoofer and the satellites at the crossover frequency? I suppose that is a compromise solution, but in my situation the best position for the sub meant that it and the satellites were not equidistant from the listening position, so I didn't see an alternative. The crossovers in my BSS Soundweb have built in delays available, which I assumed were for this purpose. It did seem to work pretty darn well for me.

[boggy]

Originally Posted by ggegan

Just a question - why not use delay to time align the subwoofer and the satellites at the crossover frequency? I know that is a compromise solution, but in my situation, the best position for the sub meant that it and the satellites were not equidistant from the listening position, so I didn't see an alternative. However, it did seem to work pretty darn well for me.

It's possible, but he must not move his ears. One delay is valid for single ears position (or two) if subwoofer isn't in same plane with other drivers (or near to other drivers)... for other (ears) positions measured delay isn't valid anymore. Acoustic addition isn't that simple like electrical signal addition.
I get best results when subwoofer is practically third driver, fixed with two way loudspeaker, and drivers are in same plane (or woofers are on box sides)... but this is basically a three way loudspeaker, not two way with sub.

Cheers,

Bogic

[tINY]

Originally Posted by boggy

It's possible, but he must not move his ears. One delay is valid for single ears position (or two) if subwoofer isn't in same plane with other drivers (or near to other drivers)... for other (ears) positions measured delay isn't valid anymore. Acoustic addition isn't that simple like electrical signal addition.

Theoretically, yes.

But, if the two drivers are within a meter of each other and the cross-over is low, the audible effect in a small room is nearly impossible to hear.



-tINY

[boggy]

Originally Posted by tINY

Theoretically, yes.

But, if the two drivers are within a meter of each other and the cross-over is low, the audible effect in a small room is nearly impossible to hear.
........

I don't agree. From my experience anything more than 1ft. can be easily audible by skilled professionals that visits gearslutz forum.

Fortunately, I found this online document written by Siegfried Linkwitz where you can find useful info about this question, something like this:
With crossover frequency at 100Hz, and 12dB/oct LR2 crossover filters (worst example),
- 3ms (~1m) delay between causes about 6dB dip at about 150Hz,
- 2ms (~2 feet) causes 3dB dip at more than 200Hz, or
- 1ms (~1 foot) cause about 1dB dip at 400Hz.

Or part quoted from original text:

Not surprisingly the +23deg of additional highpass phase has little influence on the summed response, but anything more than a foot of path length difference between woofer-to-listener and midrange-to-listener causes severe dips in frequency response in the two octaves above the crossover frequency. This can be smoothed out somewhat with added delay of 1 ms in the midrange channel, but larger amounts of delay correction require multiple 1st order allpass sections.

[Bolding is by me]

Hope that clarifies the matter.

Cheers

Bogic

[tINY]

This is theoretical, free-space calculations with theoretically tuned filters and "perfect" transducers....

Once you account for the reflections off the back wall, the peaking or frequency mismatch of the real filters (on purpose) and the lag of the transducers involved, you will find that analysis is far more complicated and tuning is quite effective.

...and that's not even considering the psycho-acoustics involved where people adapt to the room (except for ringing).




-tINY

[DanDan]

This may seem OT but perhaps not.
I was comparing some kick drums the other day.
I placed one in the null of the first length mode, i.e. the centre of the room, facing lengthways. Thin sound.
Turned it 90 degrees, now perpendicular to the length mode.
Enormous sub rich sound.
I'm still pondering the implications of this, and how it may apply to sub woofers.
Maybe they too are more directional than we have assumed, in terms of stimulating modes. There may be intriguing possibilities with the new deliberately directional subs.
We are talking 30 something Hertz here, there is no way I would have considered this drum directional at such frequencies.
Thoughts?

DD

[ggegan]

Originally Posted by DanDan

This may seem OT but perhaps not.
I was comparing some kick drums the other day.
I placed one in the null of the first length mode, i.e. the centre of the room, facing lengthways. Thin sound.
Turned it 90 degrees, now perpendicular to the length mode.
Enormous sub rich sound.
I'm still pondering the implications of this, and how it may apply to sub woofers.
Maybe they too are more directional than we have assumed, in terms of stimulating modes. There may be intriguing possibilities with the new deliberately directional subs.
We are talking 30 something Hertz here, there is no way I would have considered this drum directional at such frequencies.
Thoughts?

DD

A mixer I work with has a 5.1 TV mix room that uses bass management. Bob Hodas tuned the room and wound up placing the sub off to one side, facing away from the console towards the side wall. Turns out that was the best orientation for that particular room.

[Paul Spencer]

Adding a sub can help with the dips that are related to room modes. Here is an example:



You will have peaks and dips in any position, but the trick is to find positions that when combined will remove the dips. I would argue that the most accurate bass you can get will involve multiple bass sources, placement, calibration, treatment and EQ. The handy thing about subs is that there is a lot more placement flexibility. Sometimes you can get a better result by overlapping rather than crossing over.

In that example I put a high pass on the mains at 60 Hz so that they run just low enough to help with the 70 Hz dip. If the sub runs up high enough it can also help with the 84 Hz dip that the mains have. The result takes care of all dips below 100 Hz. What remains are some midbass peaks that are then reduced with EQ. When combined with serious bass trappage, the steady state response looks good and the decay shows modal ringing under control.

[boggy]

Originally Posted by Paul Spencer

Adding a sub can help with the dips that are related to room modes. Here is an example:



.............
In that example I put a high pass on the mains at 60 Hz so that they run just low enough to help with the 70 Hz dip. If the sub runs up high enough it can also help with the 84 Hz dip that the mains have. The result takes care of all dips below 100 Hz. What remains are some midbass peaks that are then reduced with EQ. When combined with serious bass trappage, the steady state response looks good and the decay shows modal ringing under control.

I agree with you about overlapping, and graphs looks promising, really... but, it will be much better for forum, if you may show us a measured summed response in a room, like some final result, when subwofer and main loudspeaker works in same time, not only their separated responses. I'm really sorry if I ask too much.

Cheers

Boggy

[cborg]

I've treated dips as well below 100Hz experimenting with a single sub by setting the phase relationship (options with this sub was 90, 180 and 270).
For one speaker, two speakers, two speakers and a sub the dip was there.
After adjusting phase it was 15-20 dB better. Not completely cured but within +/- 5dB of the low end response. (small room 3 x 4,5 meters)

[Paul Spencer]

Boggy, no problem. I no longer have access to those speakers, but I had a look and managed to find this:



The black line is combined and some EQ was added. It was done some time ago so I don't recall all the details. You can see the 70 Hz dip is much improved. I don't suggest this is the ultimate result, but it does illustrate the point.

Now do you notice what happens either side of the 70 Hz dip? You see some lower Q peaks. Either side of the peak, both mains and subs have a similar level so they sum together quite well, however as you move into the middle of the 70 Hz dip, the sub is quite a bit lower in level so doesn't contribute as much.

[boggy]

Originally Posted by Paul Spencer

Boggy, no problem......

Thank you, Paul!

Originally Posted by Paul Spencer

Now do you notice what happens either side of the 70 Hz dip?.......

Yes, I was expected something similar if we do overlapping without crossover, but non skilled reader possibly can't figure out what you talk about without summing result graph.

Thanks again.

[audiothings]

Dr. Earl Geddes says that the solution lies in multiple subs, and many of the finest minds in the business seem to concur. Of course, he is talking about domestic listening rooms, which, unlike studios, are not highly damped...

The Need for Multiple Subs
Is the low frequency playback in a small room doomed to poor sound? – no, not at all, but it does require a completely new concept and a unique approach that is quite contrary to previous thinking about low frequencies in rooms.
As noted before, the modal situation in a room is a matter of large peaks and dips that basically dominate the audio landscape against which the speakers, as sources, are placed. This landscape is different for every position in the room and for every position of the sub and its entirely different for every room. One cannot approach a problem like this as if there is a singular solution, a one size fits all so to speak. To make a long story short, we must look to statistics to solve this problem. We must look for ways that will reduce the variability of the peaks and dips in both the frequency response as well as the response around the room. The reason for this is that if the response is different at every point then EQing the sound at one point will only make it worse at another point – there is no EQ that can correct the situation except for a single point. On the other hand if we could reduce the variability of this response from point to point then we could apply some EQ and correct the entire problem. Statistically this comes about by using averages – by using multiple LF sources that will average out to a smoother spatial variation which can then be EQ’d for a total global solution. One can obsess about the best locations and number of sources, and papers have been written on this subject, but it all comes down to a simple approach. Use multiple subs placed at fairly random locations in the room – in other words place them wherever you want, just so long as they are not close to one another. It has been shown that this will smooth out the spatial variation of these sources thus allowing for a global EQ’d solution.
The actual implementation of this is in general not trivial, because each sub has gain and phase and low pass filter points that can be set and it only makes sense to set this in a manner that optimizes the frequency response smoothness. In fact, it has been found that, in general, three subs operating in unison with a pair of Summas will yield an acceptably flat frequency response throughout the listening room without the use of any EQ at all. This can, however, only be done with a judicious choice in the parameters of the subs which requires some measurements of the real situation in the actual room. The details of this procedure are beyond the scope of this article, but are available elsewhere. The bottom line is that at low frequencies one is force to smooth out the modal response by using several sources placed throughout the room and optimized to work together as a system. In this way the rather disastrous LF situation found in most rooms can be tamed resulting in a very pleasing sound quality in this most problematic area.

[SörenHjalmarsson]

In short: NO! multiple subs is not the way to smooth out room modes - that is achieved by room topology and treatments... The way to think of subwoofers is as an extension of the frequency response (the bandwidth) nothing more, nothing less...

SAC has tried to explain this many times, along with the Toole topology and the phase knob...

Subwoofer vs. Fullrange
Questions about sub placement
Evening Out My Sub Bass :(
1 or 2 subs?
Monitor Size/Placement in a Bedroom Studio


MVH
Sören

[psykostx]

It's all about the angles baby... let the manufacturers worry about the crossovers and phase. Your job is to buy the speakers that don't have those problems in your space. Subs are neccessary unles you're monitoring REALLY nearfield, but they shouldn't be loud. I stopped caring about the tech crap, let the manufacturers worry about that, if you can't hear problems when there are problems, then YOU got problems.

[PaulRain]

I will read all the discussions linked.....
but my questions was more related to SBIR and LBIR problems not modes.

[DanDan]

I am pretty convinced of the value of two subs based on this.
http://www.harman.com/EN-US/OurCompa...s/multsubs.pdf

(Based on Toole's work)

The optimum spots for two subs turns out to be centre of walls at the floor wall corner.
Pretty much no SBIR issue there.

DD

[Nick Boyd]

Originally Posted by SörenHjalmarsson

SAC has tried to explain this many times, along with the Toole topology and the phase knob... MVH
Sören

This place isn't the same since SAC was banned ...

[Paul Spencer]

Not sure if it's relevant to mention that my interest is mainly in accurate reproduction in the home. I'm here because I see more interest in acoustics around here.

Originally Posted by SörenHjalmarsson

In short: NO! multiple subs is not the way to smooth out room modes - that is achieved by room topology and treatments... The way to think of subwoofers is as an extension of the frequency response (the bandwidth) nothing more, nothing less...

Are you saying:
a) multi subs don't smooth out room modes
or
b) other methods are more appropriate in the studio.

If a) then I will point out that the effectiveness of multi subs has been well established. I can't see that there is really any argument there.

If b) then could you perhaps elaborate a little more?

I see no reason to compare multi subs vs treatment and room design. The two are complementary strategies that can be used together. Bass traps are essential in dealing with modal ringing, but you are often left with peaks and dips because practical levels of bass trapping are often not enough. Multi subs are effective in avoiding mode related dips. You can then bring down the peaks with judicious use of EQ and it has been shown that this can work as well. The end result if you combine all those strategies intelligently and with measurements as a guide is that you can get a better result than just picking some of those strategies.

Originally Posted by psykostx

It's all about the angles baby... let the manufacturers worry about the crossovers and phase. Your job is to buy the speakers that don't have those problems in your space. Subs are neccessary unles you're monitoring REALLY nearfield, but they shouldn't be loud. I stopped caring about the tech crap, let the manufacturers worry about that, if you can't hear problems when there are problems, then YOU got problems.

If you buy a car and expect the manufacturer to drive it for you as well, good luck! If you include a sub in a system, then you need to worry about integration, crossovers and phase. The question I'd ask is if you aren't "worrying about the tech crap" how do you know if you have problems or not? I use both measurements and my ears to tell me when I've got a result I'm happy with. My argument is that you need both to know you have a good result.

Originally Posted by PaulRain

I will read all the discussions linked.....
but my questions was more related to SBIR and LBIR problems not modes.

The distinction is artificial - in reality you are forced to deal with both, and modes are a big part of the decision with how many subs. With just one sub or in fact any speaker with adequate extension, you can find out the potential benefits of multi bass sources. Put the bass speaker in the listening position then move the mic around. With a free program like REW you can overlay all kinds of positions. In about 20 mins you can measure every position you might think to use, then know before even buying a single sub what benefit you might get out of multiple subs. You can look at all the peaks and dips and see if some positions stand out as together smoothing out the dips.

I'm working on a guide for bass integration. It's intended for home audio, but the goal is accurate bass reproduction so a lot of things are shared:

http://www.hifizine.com/2011/06/bass...-guide-part-1/

Many of you will have different opinions on how this might apply in a studio, but may still find it of some use and interest. I wish people had the same level of interest in room issue in home audio, I think it's so often overlooked.

[DanDan]

Hi Soren, you must have found something interesting in contrast to the well accepted Harman White Paper instigated by Toole, in my earlier post.
You quoted SAC as 'explaining'.
That would be an oxymoron, but I did skim your first link and found nothing addressing our point here.
May I ask your own reasoning for saying

NO! multiple subs is not the way to smooth out room modes.

DD