The importance of time alignment for subwoofers

[Thomas savage]

When I had Meridian DSP5000s and a pair of D1500 subs, I used them as Tom does, next to my main speakers, effectively creating a larger loudspeaker. However, the D1500 subs didn't have and provision for delay, just crossover frequency, level and polarity. I even thought of standing the DSP5000s on the subs, to get better horizontal alignment, but that raised the tweeters too high.

What I don't understand is why should having subs next to the main loudspeakers be any different from just having larger loudspeakers, i.e. why should the subs be sited elsewhere?
I appreciate that introducing delays to the mains might then correct the path-length difference, but that then introduces latency which may or may not matter, depending on whether there's any video sync involved, but also whatever path-length difference is set, that's only good for the one listener at the central position. Room correction similarly can't correct for every point in the room. It can either do it right for one listener, so-so for several listeners or possibly make it rather worse for some room locations.

S.

Hallelujah, thanks serge

 

[watchnerd]

Yes the sub 6 allows you to input a measurement of distance between the mains and the sub.. so many ( like my REL’s) seem to ignore it. Well they give you a polarity knob, Iv got 0 degrees and 180 .

One of the Dynaudio engineers, the British bearded hipster dude who seems to be the lead subwoofer acoustician, said in one of the interviews that it is important for the speakers and subs to all be aligned as if they're sitting on the surface of a sphere, with the listener in the middle.

That might have been for 2.1, though, as he gave a different answer when speaking of multiple subs.

 

[Purité Audio]

When I had Meridian DSP5000s and a pair of D1500 subs, I used them as Tom does, next to my main speakers, effectively creating a larger loudspeaker. However, the D1500 subs didn't have and provision for delay, just crossover frequency, level and polarity. I even thought of standing the DSP5000s on the subs, to get better horizontal alignment, but that raised the tweeters too high.

What I don't understand is why should having subs next to the main loudspeakers be any different from just having larger loudspeakers, i.e. why should the subs be sited elsewhere?
I appreciate that introducing delays to the mains might then correct the path-length difference, but that then introduces latency which may or may not matter, depending on whether there's any video sync involved, but also whatever path-length difference is set, that's only good for the one listener at the central position. Room correction similarly can't correct for every point in the room. It can either do it right for one listener, so-so for several listeners or possibly make it rather worse for some room locations.

S.

If your speakers were pulled a long way into the room and you place the subs underneath/ beside the direct versus rear radiated/delayed bass may become an issue, if you have your subs near the boundary there will be less delay but some/more reinforcement.
Keith

 

[mitchco]

I find time aligning subs important to the over all impact of the sound. Technically, if you use REW to measure and switch to a step response it will show if the subs are time aligned with the mains. However, time aligning subs is really difficult due to the natural low pass of the sub, as it takes time to peak. This leads to additional delay - typically 3 to 4 ms. Additionally, if you run a sub sweep that ends at 300 Hz, the sub will appear to have more delay than if the sweep is run to 1 kHz. Personally, I have tried many methods for time aligning subs, and have found only 1 DSP package that does this correctly and reliably. That's Audiolense and there is a review of it on CA, but there will be another review in the New Year showing how to integrate subs that are time aligned. For me it is all about the impact/transient response of the system.

 

[Thomas savage]

One of the Dynaudio engineers, the British bearded hipster dude who seems to be the lead subwoofer acoustician, said in one of the interviews that it is important for the speakers and subs to all be aligned as if they're sitting on the surface of a sphere, with the listener in the middle.

That might have been for 2.1, though, as he gave a different answer when speaking of multiple subs.

He was extremely hipster, in a knee jerk reaction I reached for my baseball bat...

 

[sergeauckland]

One of the Dynaudio engineers, the British bearded hipster dude who seems to be the lead subwoofer acoustician, said in one of the interviews that it is important for the speakers and subs to all be aligned as if they're sitting on the surface of a sphere, with the listener in the middle.

That might have been for 2.1, though, as he gave a different answer when speaking of multiple subs.

Whether 2.0, 2.1, 4.0 or 5.1, It seems to me that the speakers should all be aligned on one circle, with the listener in the middle. The standard for 2.0 is an equilateral triangle, the standard for 4.0 is a square, the standard for 5.1 is a 60° lateral spread for the fronts, a 120° spread for the rears, all on the same circle. As to where the 0.1 channel goes......

By the way, why have a 0.1 channel, why not just have 5 bloody great 'speakers!
S.

 

[Fitzcaraldo215]

Whether 2.0, 2.1, 4.0 or 5.1, It seems to me that the speakers should all be aligned on one circle, with the listener in the middle. The standard for 2.0 is an equilateral triangle, the standard for 4.0 is a square, the standard for 5.1 is a 60° lateral spread for the fronts, a 120° spread for the rears, all on the same circle. As to where the 0.1 channel goes......

By the way, why have a 0.1 channel, why not just have 5 bloody great 'speakers!
S.

Yes, aligned on one sweet-spot-centric circle is what one should do. That is obvious in 2.0, and in Mch the tools to achieve that in DSP via speaker level and distance correction delays are built into even the cheapest Mch AVRs, often via calibration with a supplied mic and calibration routine.

The sub or subs should also follow the same rule, and they do even in cheap AVRs.

Why not just use 5 or more great speakers for Mch without subs? Three reasons, mainly. One, subs can be independently positioned of the main speakers for best bass response in the room without altering imaging by the main speakers at higher frequencies.

Two, it's economics. Big speakers with good bass are disproportionately more expensive than smaller ones. I don't think you can assemble a five big, great speaker setup as inexpensively as a five great small speakers plus subs system with similar quality. My main fronts are big, but I cross them over to the sub at 60-Hz. Incidentally, use of the sub also sounds noticeably better to me than running them full range. In my next system, if ever, all my speakers will be smaller, but top quality.

Three, using a sub is a simple, easy form of biamping, offering potentially less distortion, better power handling, etc. via active xovers.

 

[sergeauckland]

Yes, aligned on one sweet-spot-centric circle is what one should do. That is obvious in 2.0, and in Mch the tools to achieve that in DSP via speaker level and distance correction delays are built into even the cheapest Mch AVRs, often via calibration with a supplied mic and calibration routine.

The sub or subs should also follow the same rule, and they do even in cheap AVRs.

Why not just use 5 or more great speakers for Mch without subs? Three reasons, mainly. One, subs can be independently positioned of the main speakers for best bass response in the room without altering imaging by the main speakers at higher frequencies.

Two, it's economics. Big speakers with good bass are disproportionately more expensive than smaller ones. I don't think you can assemble a five big, great speaker setup as inexpensively as a five great small speakers plus subs system with similar quality. My main fronts are big, but I cross them over to the sub at 60-Hz. Incidentally, use of the sub also sounds noticeably better to me than running them full range. In my next system, if ever, all my speakers will be smaller, but top quality.

Three, using a sub is a simple, easy form of biamping, offering potentially less distortion, better power handling, etc. via active xovers.

5 big actives!

Subs are for wimps.
S.

 

[Purité Audio]

Big actives are certainly more straightforward.
Keith

 

[Blumlein 88]

I wonder if you weren't running the main speakers full range if the difference would have been much smaller? If you run two speakers at a different distance from the listener with overlapping response you will get comb filtering. In this case of sub and main speaker the comb filtering probably would lie above the point where the sub has any real output. It would nevertheless start causing some phasing issues before that point. Another reason using 80 hz might work better than 120 hz. If your subs have a phase adjustment, you might play with that and find a point where having it in the corner isn't a terribly negative effect. Determining when you have managed that something like REW is very valuable and a big time saver. As someone mentioned you can look at step responses for help.

Conventional thinking based upon some psychoacoustic research is our ability to hear timing or phase differences is about gone by 80 hz and drops rapidly below that point. So simply getting level combined response is thought to be most important at 80 hz and below.

 

[Thomas savage]

I wonder if you weren't running the main speakers full range if the difference would have been much smaller? If you run two speakers at a different distance from the listener with overlapping response you will get comb filtering. In this case of sub and main speaker the comb filtering probably would lie above the point where the sub has any real output. It would nevertheless start causing some phasing issues before that point. Another reason using 80 hz might work better than 120 hz. If your subs have a phase adjustment, you might play with that and find a point where having it in the corner isn't a terribly negative effect. Determining when you have managed that something like REW is very valuable and a big time saver. As someone mentioned you can look at step responses for help.

Conventional thinking based upon some psychoacoustic research is our ability to hear timing or phase differences is about gone by 80 hz and drops rapidly below that point. So simply getting level combined response is thought to be most important at 80 hz and below.

Yea that all makes sense, with them where there are so basically acting as one big speaker rather than a main and a sub, subjectively they sound of nothing. I never had any localisation but comb filtering ( subjectively perceived as smearing to me) was happening regardless or crossover Hz when they were further away from the mains. Intuitively Iv always put subs next to my speakers as in the picture but the manual told me to put it in the corner lol.

I am aware of the research regarding directionality becoming less perceptible from/below 80hz , running them where they are ( inline , right next to) my speakers this became a non issue. After some experimentation Natural extension is best served with them running at 120hz.

The room correction box says to run them full range for the calibration, maybe something it does helps blend them in at this unusually high point. Sound is more linear with it set that way, but only with them where they are .

Iv got a few nice bass jazz solos I use, set at 80 there’s a slight hole like a note missing, set at 120 it’s seamless all notes present and blend together like a double bass should. I should switch over to streaming this year so il have a computer and will drill into what’s going on with measurements I can post here.. subjectively it sounds even across the range of a double bass and that’s good enough for me and like Iv said the actual measurements Iv taken don’t revel anything horrendous and with room correction the twin subs on their own measure flat within their designed range.

I just stumbled across the time / phase alignment thing via this smearing or comb filtering and thought I’d start a thread on time alignment. If I’d left the things were I normally have them all this would of never come to light.. I thought “ o, what’s going on there then” rather than having some terrible problem I needed help fixing.

 

[iridium]

Might try putting your subs a few feet in front of your main speakers. Then adjust subs incrementally & seating position incrementally for possible good result.

iridium.

 

[Thomas savage]

Might try putting your subs a few feet in front of your main speakers. Then adjust subs incrementally & seating position incrementally for possible good result.

iridium.

Alert danger of faffing ...

 

[edd9000]

Time alignment where? the group delay of a subwoofer and a passive speaker is all over the place. Also, by the time we register sub woofer frequency wavelengths, its already gone modal in the room, so the room and its decay will still dominate.

 

[edd9000]

5 big actives!

Subs are for wimps.
S.

Nice to see you on here Serge. I consider a "sub" something with a specialised sub woofer driver, if you want high spl at very low frequencies and low distortion, it takes something quite special, particularly for home theatre or large rooms.

I tend to like Geddes approach, lots of stuff showing 3 subwoofers distributed round a room produces the most even response over the widest area, with diminishing returns beyond 3.

 

[Thomas savage]

I did stumble on this paragraph in the link I posted earlier in the thread..,


What is the best way to phase align our subwoofers to the mains? There is a hint in the way the question was phrased. I didn’t say time align (and it is not because I am afraid of copyright police). I say phase align because that is precisely what we will do. Simply put, you can’t time align a subwoofer to the mains. Why? because your subwoofers are stretched over time – the highest frequencies in your subwoofer can easily be 10-20 ms ahead of the lowest frequencies. Whatever delay time you choose leaves you with a pair of unsettling realities: (a) you are only aligning the timing for a limited ( I repeat LIMITED) frequency range, and (b) you are only aligning the timing for a limited ( I repeat LIMITED) geographical range of the room. So the first thing we need to come to grips is with is the fact that our solution is by no means a global one. There are two decisions to make: what frequency range do we want to optimize for this limited partnership and at what location.

Let’s begin with the frequency range. What makes the most sense to you? 30 Hz (where the subs are soloists) , 100 Hz (where the mains and subs share the load) of 300 Hz (where the mains are soloists)? This should be obvious. It should be just as obvious that since we have a moving target in time, that there is not one timing that can fit for all.


It carrys on ...

 

[edd9000]

I'm in the measurebate and DSP camp. Without that its just mess around until it sounds good to you over a wide range of material, with luck you will find a good balance but it can be very difficult if not impossible.

 

[Fitzcaraldo215]

I did stumble on this paragraph in the link I posted earlier in the thread..,


What is the best way to phase align our subwoofers to the mains? There is a hint in the way the question was phrased. I didn’t say time align (and it is not because I am afraid of copyright police). I say phase align because that is precisely what we will do. Simply put, you can’t time align a subwoofer to the mains. Why? because your subwoofers are stretched over time – the highest frequencies in your subwoofer can easily be 10-20 ms ahead of the lowest frequencies. Whatever delay time you choose leaves you with a pair of unsettling realities: (a) you are only aligning the timing for a limited ( I repeat LIMITED) frequency range, and (b) you are only aligning the timing for a limited ( I repeat LIMITED) geographical range of the room. So the first thing we need to come to grips is with is the fact that our solution is by no means a global one. There are two decisions to make: what frequency range do we want to optimize for this limited partnership and at what location.

Let’s begin with the frequency range. What makes the most sense to you? 30 Hz (where the subs are soloists) , 100 Hz (where the mains and subs share the load) of 300 Hz (where the mains are soloists)? This should be obvious. It should be just as obvious that since we have a moving target in time, that there is not one timing that can fit for all.


It carry on ...

Not sure I follow. Are you saying the speed of sound in air is different for 80hz vs. 20 hz?

 

[edd9000]

Not sure I follow. Are you saying the speed of sound in air is different for 80hz vs. 20 hz?

Speakers have group delay.

 

[Thomas savage]

Not sure I follow. Are you saying the speed of sound in air is different for 80hz vs. 20 hz?

I’m not saying anything, it’s a quote from the link I posted addressing this topic on the first page of this thread. It seemed to come at it with a reasoning Iv not yet encountered so I posted it as a point of discussion.

Personally Iv no clue as to its validity, seemed intresting .. could be bollocks but I don’t think it is.

Here it is again, take a look https://bobmccarthy.wordpress.com/2...-of-subs-why-i-dont-use-the-impulse-response/

It’s lengthy and there’s a Q&A at the end.