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Technical Chat for Subwoofers not to be used for asking purchasing choices.

moonfly

Banned
The "Less excursion is best" line as a general argument appears to hinge on 2 points;

that drivers are non linear through a substantial part of their operating range
that the distortion they produce is audible (in a way that has a negative impact on SQ)

Studies of the latter tend to point towards the hearing system being remarkably tolerant of distortion at low frequencies as far as I remember. I have no idea about the former, any data to share on this?

The other question is whether you are hearing (preferring) a change in spectral balance vs any changes in distortion.

Really, it boils down to the basic principle that when a driver isnt moving it creates no distortion, and when it is it does create distortion, with more movement equalling more distortion. Making the basic assumption that less distortion is better, then less excursion is then also automatically better.

Ive made the same arguments as yourself for a long time now, that as long as the threshold of distortion remains sufficiently low, then comparing one system to another is a bit of a moot point. Some people have actually been shown to prefer a certain amount of distortion over output that is too clean.

It might boil down to how particular you are. Ive found through experience that if you work to certain principles, i.e, assume nothing and simply work to reduce distortion as much as possible no matter what, then you wont go wrong, and I like to work that way myself. The figure of 10% distortion is obviously mentioned a lot if you study the field, but its also clear that some in the industry consider this too high (Ken Kriesel for example). There is then also a point I like to consider, and thats the point that I certainly feel there is a difference between obvious and non obvious distortion. Obvious distortion is, well, obvious, it makes you sit up and question what just happened. The less obvious distortion is what you begin to notice over time but cant pick up on as a distinct problem. Its like the difference between loud music, and music thats not loud, when they are actually both played out at the same spl. I wont try explain that Matt, as I know you understand what I mean by that comment. For me, being particular about your distortion in a way more like Ken is tends to help ensure the less obvious distortion issue never rears its ugly head. Obviously, we need to remember that there are several components to this part, and proper system set up and integration can be as big a factor in this as reducing driver distortion components to a minimum.

Ill have a look for some links, but John at AE made a nice post about xmax some 6 years ago now:

Acoustic Elegance • View topic - So What's the Deal with Xmax?



The bit in bold is not true, at least with the usual miniDSP model which provides you with the ability to create a bunch of biquad (IIR) filters. The distinguishing features being that they are computationally cheap and that they can only approximate a linear phase filter (and cannot be used for phase correction). To do that kind of work you need the opendrc model which opens up fir filtering to you (though latency becomes a real issue then).

Sorry Matt, I should have been more specific in general. The LTCs built into something like a DXD accounts for this. Ive not looked into the MiniDSP enough to see how that device deals with this, and wasnt meaning to imply that device would automatically solve these problems. It will however do a much better job than trying to simulate something like a LTC with a bunch of PEQ filters with say a BFD for example.
 
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mattkhan

Distinguished Member
Really, it boils down to the basic principle that when a driver isnt moving it creates no distortion, and when it is it does create distortion, with more movement equalling more distortion. Making the basic assumption that less distortion is better, then less excursion is then also automatically better.
by that definition any sound is distortion :) whether something is theoretically better is irrelevant, it has to be audibly better and without evidence towards that then the above is just cargo cult science. There are obviously other benefits to running multiple subs though & it seems reasonable to suppose that reducing distortion can't hurt so perhaps it is a moot point anyway.

tSorry Matt, I should have been more specific in general. The LTCs built into something like a DXD accounts for this. Ive not looked into the MiniDSP enough to see how that device deals with this, and wasnt meaning to imply that device would automatically solve these problems. It will however do a much better job than trying to simulate something like a LTC with a bunch of PEQ filters with say a BFD for example.
FWIW minidsp filters are biquad filters, you can read details on their site. Their is a biquad filter calculation spreadsheet which is v handy and can be found here. This lets you plug in the to/from values for the LT and it pumps out the biquad filter params. I use this to calculate the LT I use, trivially easy to use.

AIUI phase linearisation using biquads *might* be mathematically possible (or you might get close enough) but I don't believe anyone would do this in practice, you would just use FIR instead (and that means stepping up to the opendrc or using a PC).

Again it comes back to whether any resulting phase shift (of an LT built on biquads vs an analogue LT) is audible, given that you're typically going to be affecting <35Hz here then that has to be v much in doubt. Indeed nothing I've read on LTs suggests this as a problem but I can't say I researched it exhaustively. If you really want to avoid it then you are going to need to use an analogue LT or a PC as your source (using something like rephase for example if you want to avoid spending money on something like acourate/audiolense/dirac).
 

moonfly

Banned
by that definition any sound is distortion :) whether something is theoretically better is irrelevant, it has to be audibly better and without evidence towards that then the above is just cargo cult science. There are obviously other benefits to running multiple subs though & it seems reasonable to suppose that reducing distortion can't hurt so perhaps it is a moot point anyway.
I wouldnt classify any sound as distortion, only sound produced that wasnt intended. Id you want to produce 20hz, but the non linear action of the driver results in harmonics being produced, then those harmonics are what you would quantify as distortion. The CEA measurement system works on that basis for example. Im certainly with you on cult science, but by the same token, if its simple to take steps that are known to definitely help in the reduction of distortion, then why wouldnt you employ them as a matter of course. Its one of those things were I consider it building in headroom, and thats a positive move IMHO.

FWIW minidsp filters are biquad filters, you can read details on their site. Their is a biquad filter calculation spreadsheet which is v handy and can be found here. This lets you plug in the to/from values for the LT and it pumps out the biquad filter params. I use this to calculate the LT I use, trivially easy to use.

AIUI phase linearisation using biquads *might* be mathematically possible (or you might get close enough) but I don't believe anyone would do this in practice, you would just use FIR instead (and that means stepping up to the opendrc or using a PC).

Again it comes back to whether any resulting phase shift (of an LT built on biquads vs an analogue LT) is audible, given that you're typically going to be affecting <35Hz here then that has to be v much in doubt. Indeed nothing I've read on LTs suggests this as a problem but I can't say I researched it exhaustively. If you really want to avoid it then you are going to need to use an analogue LT or a PC as your source (using something like rephase for example if you want to avoid spending money on something like acourate/audiolense/dirac).
Its a while since I looked over the MiniDSP stuff. I want to use it because its a compact solution, and I want to test the effectiveness of it when using REW. Audibility of eq is no doubt open to debate, and I would tend to agree with you that given the working range, then any negative effects are likely to be minimal at best. It will be my first play with a MiniDSP, so we'll see how it goes.
 

mattkhan

Distinguished Member
I wouldnt classify any sound as distortion, only sound produced that wasnt intended. Id you want to produce 20hz, but the non linear action of the driver results in harmonics being produced, then those harmonics are what you would quantify as distortion. The CEA measurement system works on that basis for example. Im certainly with you on cult science, but by the same token, if its simple to take steps that are known to definitely help in the reduction of distortion, then why wouldnt you employ them as a matter of course. Its one of those things were I consider it building in headroom, and thats a positive move IMHO.
Minor digression but this reminds me a lot of the power amp discussion. You'll get some people saying amps sound the same unless they are clipping, others saying yes but they clip more often than you think & still others saying don't be silly, of course they sound different.

Anyway it comes back to (at least) 2 questions;

when does the action of the driver become non linear?
how often does that happen when reproducing material you listen to at the levels you want to listen at?

If your system can deal with what you're asking it at less than audible levels of distortion then adding more subs to reduce distortion further is just throwing money at a problem that doesn't exist.

i.e.

adding in headroom = good
adding in more headroom than you'll ever need = arguably a waste of money unless it brings other benefits

Its a while since I looked over the MiniDSP stuff. I want to use it because its a compact solution, and I want to test the effectiveness of it when using REW. Audibility of eq is no doubt open to debate, and I would tend to agree with you that given the working range, then any negative effects are likely to be minimal at best. It will be my first play with a MiniDSP, so we'll see how it goes.
just to be clear... I am not questioning the audibility of eq in general, just the audibility of phase shifts below ~35Hz (i.e. where most of an LT will be operating).

which minidsp will you be getting?
 

Matyam

Active Member
Its good to have moonfly back the jeremy Clarkson of av bass keep sticking it up the AA s balance is good.Or nigel farage even , if theyre slagging you off the better your doing good job
 

moonfly

Banned
Lol, that's one way of looking at it.

1507160_269822796525910_1780573970_n.jpg
 
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moonfly

Banned
Minor digression but this reminds me a lot of the power amp discussion. You'll get some people saying amps sound the same unless they are clipping, others saying yes but they clip more often than you think & still others saying don't be silly, of course they sound different.

Anyway it comes back to (at least) 2 questions;

when does the action of the driver become non linear?
how often does that happen when reproducing material you listen to at the levels you want to listen at?

If your system can deal with what you're asking it at less than audible levels of distortion then adding more subs to reduce distortion further is just throwing money at a problem that doesn't exist.

i.e.

adding in headroom = good
adding in more headroom than you'll ever need = arguably a waste of money unless it brings other benefits

The bit in bold is probably the real meat of the discussion. Ive been saying these same things for a long time Matt, particularly when discussing comparisons between different products. The main reason I run two subs is for the eq benefits, though for now they are stacked. There are other effects, increased spl ability at the low end being a big factor, and having that ability while still maintaining low cone travel that remains within the low distortion threshold. You then have to consider the differences between one large radiating cone vs multiple smaller ones spread out. In a stack they are close enough to essentially act as one, but the dispersion pattern is different.

Whether or not an individual prefers one way or another boils down to subjectivity. Again, my system is built upon the principles of headroom. Distortion in some forms has been shown to be desirable by some, but distortion has different forms and effects. One reason the DXDs are designed to have very low distortion is for improved transient response, rather than to prevent pops and farts. The research suggests that very good transient response is dependant on very low distortion. Now very tiny amount of distortion are for all intents and purposes undetectable by ear, but the cumulative effects on transient response, and therefore the accuracy and detail of the bass produced, are considered by some industry leaders (Ken is a good example) to be the bigger issue at play. If you consider that even very small amounts of distortion around the fundamental frequencies trying to be reproduced, while not immediately obvious, will cause a softening of the leading and trailing edges of those sounds. If this happens a lot over the entire operating range of the subwoofer, then you end up with a subwoofer that sounds less detailed and accurate.

Thats what the theory and research would suggest. This is the main reason for employing multiple drivers into a system. The less your cones are travelling, the more these kinds of effects are reduced, and the better the transient response of the system will be. In turn, more drivers means a more efficient system in terms of power use, which again leads to less work for the amps to do and the same lowering of minute distortions that can reduce accuracy and detail.

This is the basis on which I operate. If you look at only your spl requirement, its reasonably easy to see a single 15 can in many cases provide that spl. Adding in more in that regard would seem to be a waste of money, but if you consider the above to be accurate, then its not really the additional spl your chasing when you system begins to far exceed the spl capability you actually need and your employing multiple drivers into the system.
 

mattkhan

Distinguished Member
If you consider that even very small amounts of distortion around the fundamental frequencies trying to be reproduced, while not immediately obvious, will cause a softening of the leading and trailing edges of those sounds. If this happens a lot over the entire operating range of the subwoofer, then you end up with a subwoofer that sounds less detailed and accurate.

Thats what the theory and research would suggest.
does it though? any links to hand pointing at such research?

Certainly on paper it makes sense with respect to how a speaker works but does it make sense with respect to how we hear? Most research I've seen on the subject demonstrates that only higher order distortion (say 5th and up) is really noticeable; Masking is often given as the primary mechanism for this (though the subject appears relatively lightly researched). Meanwhile temporal distortion seems to be largely accounted for by the precedence effect albeit that can have an impact on perception of directional cues (which doesn't seem especially relevant to the normal operating range of a subwoofer). I've seen it said that low levels of distortion only come through via prolonged listening as a perception of fatigue but nothing more detailed than that.

Another factor, as ever, is the room. It seems like the tiny levels of distortion being referred to here would be swamped by the behaviour of the room & in particular a room that has no treatment in it to combat decay times. I find it fairly hard to believe that a room showing typical lounge decay times (easily >600ms) at ULF is one that is going to be revealing of v low level differences in the various types of distortion that you could be present.
 

mainaman

Well-known Member
As good as the SP4 is,especially at its price point,its sensitivity and load ratings seem rather demanding,even for today's "watts are cheap" market.

Too bad that the TC Sounds 18" driver is almost double the price as is the Aurasound.The Volt 18" however doesnt seem to have ultra xmax and very low FS,but its great in the PMC and MJ products,costs less than 400 pounds,doesnt need thousands of watts to get going and its linear past its rated limits.

I know that the Volt wont provide the same earth shattering bass as a well fed SP4 would,but would it be far behind?I reckon a DIY project with a plate amp and relatively compact sealed box could be done for just 700-800 pounds.
 

mattkhan

Distinguished Member
Which driver is that? Do you have a link?

To be fair, this is peculiar to my setup as it will be a massive pain to run another cable to where the sub is. If I did then finding an amp to power it would be pretty easy. This is not to say it isn't power hungry or that there might be more cost effective drivers, just that I am the one making life difficult (or interesting depending on your perspective!!) for myself.
 

mainaman

Well-known Member
Which driver is that? Do you have a link?

To be fair, this is peculiar to my setup as it will be a massive pain to run another cable to where the sub is. If I did then finding an amp to power it would be pretty easy. This is not to say it isn't power hungry or that there might be more cost effective drivers, just that I am the one making life difficult (or interesting depending on your perspective!!) for myself.

Volt Loudspeakers | RV4504 (18″)

Volt Loudspeakers | RV4514 (18″) that's the horn version

MJ Acoustics. Reference 800 MkII.

XB3 | PMC Loudspeakers that's the 15'',though

It's an USC discussion,but it would be interesting to compare the SP4 with other 15 and 18'' drivers.The Volt can get going with a 500-1000W plate.The SP4s(and the USC Subs) are a bargain,considering the performance,but a DIY project with the Volt could be done with half the budget,compared to a SP4 based one.
 

mattkhan

Distinguished Member
Volt Loudspeakers | RV4504 (18″)

Volt Loudspeakers | RV4514 (18″) that's the horn version

MJ Acoustics. Reference 800 MkII.

XB3 | PMC Loudspeakers that's the 15'',though

It's an USC discussion,but it would be interesting to compare the SP4 with other 15 and 18'' drivers.The Volt can get going with a 500-1000W plate.The SP4s(and the USC Subs) are a bargain,considering the performance,but a DIY project with the Volt could be done with half the budget,compared to a SP4 based one.
that driver is designed to go in a vented enclosure so it is not a like for like comparison.
 

mainaman

Well-known Member
that driver is designed to go in a vented enclosure so it is not a like for like comparison.

But the MJ design is not vented.
 

mattkhan

Distinguished Member
More twiddling today, I can get 102dB before the amp clips with CEA-2010 tones at 16, 20, 25Hz. I now need to decide whether to buy a different amp or live with it.

Interestingly the 3rd harmonic distortion in the 16Hz tone was just over the allowed -15dB limit & was certainly colouring the tone to my (protected) ears.

16Hz

upload_2014-4-28_15-38-16.png


20Hz

upload_2014-4-28_15-52-24.png


Interesting the way it changes from 2nd to 3rd harmonic as you go below 20Hz.
 

scottthehat

Distinguished Member
Just how much more can the driver give. How much power is the focus suppose to have.
 

mattkhan

Distinguished Member
Just how much more can the driver give. How much power is the focus suppose to have.
If models are to be believed, maybe 10dB more. I don't have an accurate figure for room gain so it's hard to say for sure.

How much it has at these frequencies and for more sustained loads is unknown. This is the norm for pro amps btw, you have to spend more (generally a lot more) to get full bandwidth ratings and high power levels.
 

scottthehat

Distinguished Member
Interesting for sure I expected more.
How much is the driver moving.

Does it clip a lot on films.
 

mattkhan

Distinguished Member
Interesting for sure I expected more.
How much is the driver moving.

Does it clip a lot on films.
Can't see how much it is moving as it is DF.

If you play loud enough then it clips with normal (bass heavy) content. You can only hear this directly with the main amp off so it is impossible to tell with the mains on. I am not sure you would notice it in normal use as you would have to hear the absence of something and that is quite hard, if not impossible, to do.
 

mattkhan

Distinguished Member
@Geckosteve swapped my Focux D6 for a D12 today & we listened to a few clips from the AVS Reference disc (Master & Commander, Terminator Salvation, Cloverfield) to check how it sounds.

Initial impressions are that it's quite a serious uptick over the D6, I am reasonably confident in saying this as a keyboard on my lap was vibrating during parts of the Terminator Salvation clip. In fact, if anything I need to turn the sub down a notch. I need to do some more listening/testing to be sure but it seems promising.
 

scottthehat

Distinguished Member
@Geckosteve swapped my Focux D6 for a D12 today & we listened to a few clips from the AVS Reference disc (Master & Commander, Terminator Salvation, Cloverfield) to check how it sounds.

Initial impressions are that it's quite a serious uptick over the D6, I am reasonably confident in saying this as a keyboard on my lap was vibrating during parts of the Terminator Salvation clip. In fact, if anything I need to turn the sub down a notch. I need to do some more listening/testing to be sure but it seems promising.
What's the difference in power and price Matt.
 

mattkhan

Distinguished Member
the bridged 4ohm peak power available from a D12 is a pretty ridiculous 7.2kW, I have no idea how much this translates to under more sustained load of course. It's obviously not going to be 7.2kW though!
 

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