Speaker Positioning: Bass or Imaging?

[FrantzM]

It was in jest ... What's slope you're using ...

 

[DonH50]

I am pretty sure that 43.141592654... is the one and only frequency for you, Steve.

 

[vinylphilemag]

I am pretty sure that 43.141592654... is the one and only frequency for you, Steve.

Also known as "forty-pi".

 

[DonH50]

I like it! I just thought it was irrational...

 

[Nyal Mellor]

Nyal

It seems counter-intuitive. I do however believe that running the mains full range AND adding subwoofers provide the smoothest response possible... I have seen the response in my own case getting better by adding a third subwoofer.. This system is not more nor am I able to retrieve the graphs ... I can however point to some other people who have performed similar experiences ... or to the papers of Floyd Toole and Sean Olive. I would have liked Earl Geddes to chime in since the protocol I used was his , a variation on the multi subwoofers from Olive and Toole for producing better bass response in a room ...
My point is anecdotal. I have gotten the best bass with speakers that could hit 25 Hz in my room with autority .. the addition of 3 subwoofers, one corner placed and not EQ, strangely produced the best bass I have had in my system, actually in most systems. Steve here use EQ'd Gotham to supplement his full range running X-2 and believe me both aurally and measurable his bass is excellent .. I actually believe he would have gotten even better results by using a higher crossover point; something that in I would found to be anathema to high End reproduction only a few years ago ... 43 Hz is Ok but higher might produce better results ..
it's not simply a matter of the bass absorption in the room ... more subs result in better bass, smoother , more extended more integrated ...
The trick become : Place the mains wherever they image best , then add subs to bring the bass smooth and integrated ...

I will PM Earl Geddes and see if he's willing to explain his method here ...he's done it somewhere in this forum but very succinctly ...


P.S. Steve please, leave your system alone .. It took you months to get to that level of bass integration .. Don't listen to me ... .... .... .... ...
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....... but slightly higher(50?, 60?) ... might even be better

Of course one can try running subs over the full range speakers without a crossover (I think that is your point?). This may or may not produce good results, wheras the method of matching speaker roll of and low frequency extension point with the sub XO is pretty much always going to work, even when you are using a cheaper sub like a Velodyne DD model with Avalon or Wilson speakers.

 

[terryj]

My AVR and sub do have (independent) phase compensation, a topic I touched on elsewhere and agree is critical to matching sub and mains.

ah yes, I remember we left that one 'hanging'.

I think you responded to me when I said sumthin along the lines of 'aligning timing', and you mentioned phase.

Are they not interchangeable concepts??

If I've got it wrong, well I'm here to learn.

(curious, most of you guys with dsp here I presume are from the states, and it seem that the weapon of choice is the tact. I'm from aus, and I use the deqx. Haha, much like seans thoughts about different countries having different tastes, why is the tact so prevalent over there and the deqx 'rare', and the opposite over here?? I only know one tact owner in aus)

anyway, that was a bit off topic. The hardest thing with integrating subs (assuming the quality of the sub is not the restricting factor), for me, is the timing. (don then countered with phase, which to me down 'there' are the same thing??) Any sort of 'double thump' will be a dead give away. Maybe not to location, but certainly to poor integration.

get it right, and you can't tell the sub is on. Then the job is finished.

I feel a bit silly stating the bleedin obvious.

I can get close with appropriate delays to the appropriate channels (using measurement), but only in the last few days have I found something extra that seems to work for me.

the last 'few mm' of refinement can be done by ear, and it revolves around where the apparent bass comes from. My mains prob go down to forty or so, can't remember right now, so of course the bass comes from the front, as it should.

My subs are behind me, probably around thirty degrees, so this last little bit of delay adjustment is to tweak until the bass most solidly comes from the front, where it should be.

Dunno if it applies to these low frequencies, but sort of the 'bass precedence effect'. If the bass has been pulled back slightly from it's frontal position, then (to me anyway, my own crackpot theory) that means the subs (behind me remember) are firing too early, ie it is pulling the bass backwards. Delay it slightly (again, rough work done by measurements, fine work by ear) so the bass goes back to where it should be.

that's possibly completely bonkers, but at least it helps me convince myself!

 

[FrantzM]

Of course one can try running subs over the full range speakers without a crossover (I think that is your point?). This may or may not produce good results, wheras the method of matching speaker roll of and low frequency extension point with the sub XO is pretty much always going to work, even when you are using a cheaper sub like a Velodyne DD model with Avalon or Wilson speakers.

Nyal

The last part of your paragraph is puzzling to me ... "always going to work"?

Now why wouldn't a Velodyne DD work with any speakers , even the most expensive ones? One could even argue that in term of low frequency extension a Velodyne DD (not my favorite sub by the way buta decent one nonetheless) will always match or surpass several very expensive speakers ...

No my point is that it seems to me and people who know much more than I about the subject ( Earl Geddes of Gedlee Inc for one but also Sean Olive and Floyd Toole of Harman International) that the multiplicity of LF sources in a room tend to create a smoother distribution of room nodes, IOW reduces the level differences between peaks and valleys, resulting in smoother in-room bass response ... Thus the use of at leat 3 subs and in the case of full range mains that brings the number of LF sources in the room to 5 ... It works extremely well in my experience and that of others

 

[DonH50]

Time vs. Phase

@terryj re. timing and phasing: While they are often used interchangeably, strictly speaking they are not, at least in my world (of engineers, radios, radars, and such). They are related, but there is frequency dependence to consider. I am going back to basics, not to be patronizing, but because it's how I think things through, please forgive.

A single tone can be represented by a sine wave function as
Vout = A * sin(2*pi*f*t+ phi) + os where
A = amplitude
pi = 3.141592654...
f = frequency
phi = phase
os = offset (usually a d.c. value; life gets ugly when it's not static!)

Time comes into the equation a little differently than phase, though both modify the value of the sine wave. If I am comparing two signals, then if they are both phase-shifted by the same amount they will line up perfectly in time always only if they are at the same frequency. Now, since by definition the crossover frequency is a single frequency, at that point adjusting the phase or the time (delay) will line everything up. So, in the context of a discussion on crossovers, you are right. As we move away from the crossover frequency, however, things no longer line up with just a phase shift. In the real world, this doesn't really matter for a subwoofer (imo, and how much it matters for higher frequencies is a matter of debate).

In applications where pulse integrity and time of arrival is critical, e.g. radar systems, the quest for a true time delay (e.g. a time delay that is constant for all frequencies) has been a long and hard road. Analog circuits typically use phase shift to add delay, mucking with two things at once and smearing broadband signals. Many compensation schemes have been used, but digital signal processing offers true time delay once the signals are sampled and is the current best solution.

HTH - Don

 

[Nyal Mellor]

Frantz

I fully agree with the theory behind adding a 'mulitiplicity of LF sources', however there is more to the equation - it is not just about LF frequency extension. It is also about group delay. Now there is some debate about the audibility of this but my theory is that if you play sub and mains over each other then differences in group delay between the two systems can change the perceived clarity and articulation in the bass.

 

[VernNeal]

1234567890
1234567890X

If these numbers represented the front of an average listening room usually a speaker with a subwoofer sounds best on the second row(out from the wall) at postion 3 and 7 slightly toed in. The sub sounds best between 5/6, but are very room dependant. My JL Audio speaker sounds best at point X at a 45 degree angle. Do not be afraid to experiment.

 

[audioguy]

I'm not Chuck, but the TacT will only manage 2 subs, unless they're slaved in some fashion. What I'm trying to sort out is, if Audyssey Sub flattens the response and then one uses a non-flat curve in the TacT (i.e. one with some LFtilt-up, as is common), the TacT is correcting the Audyssey corrections!

What say ye, Chuck?

Sort of. The Audyssey SuBEQ corrected response is literally a flat line (see below). Since the SubEQ is normally used with some SSP that has Audyssey Pro and one needs Audyssey Pro for the SubEQ anyway, the desired target curve is created in the SSP. That is, you first run Audyssey Pro on the SubEQ and THEN run the Audyssey Pro on the SSP. If I connect the SubEQ to my TacT (the SubEQ now storing the filters that will provide the flat curve below), I then use a TacT target curve to end up with the final result.

The first two graphs below show the before and after using the SubEQ. This represents measurements from 15 locations so if I were to take a single measurement at the main LP, it would not look exactly like this (and doesn't). The 3rd and 4th charts show the before and after running Audyssey Pro and applying a Target Curve. The before curve should look like the after curve from the previous photo but since the measurements were not taken in the EXACT same positions, there are some differences.

So when I am using the TacT for 2 channel, I will start off with the sub FR looking something like the SubEQ corrected photo above.

Remember, this is all part of trying to find the best low bass sound I can for two channel. I don't know yet if this is it or not. (Sure looks purtty on paper tho !!!)

Now that you are totally confused ......

 

[RUR]

Chuck, the top-most, uncorrected appears to show about 2dB down @ 100Hz (assuming I'm reading the scales correctly!). Third from top shows Audyssey corrected to ~1/3dB down @ 100Hz and bottom-most shows final, TacT imposed slope as -1dB down @ 100Hz.

If I've got all that right, the TacT is partially uncorrecting (or recorrecting - choose your verb) some of what Audyssey has done. A circuitous path, but those end measurements should be all that matters.

Ken

 

[audioguy]

Actually none of these are the TacT. The bottom curve is Audyssey Pro thru my Onkyo which in turn is connected to the SubEQ. The dotted lines are approx 5db (I think). So the very very top chart would say that the subs are down about 8db at 100Hz.

This target curve (last chart) is for movies where I am trying to add a bit of "oomph" at the lower most end of the spectrum. When I set the trims, I always adjust for gain to match at the cross over.

The TacT target curves I will use (later tonight) are the ones you sent me and a few of my own.

 

[RUR]

Ah, gotcha! After you've tried out some curves, post your thoughts over in the TacT sub-forum so we're not derailing this thread. ;-) Have fun!