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Ideas for new ways to display data

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It seems quick and easy in a very simple comparison like the one I posted and it is, but what about quickly comparing multiple systems at multiple frequencies with dimensions that are not so evenly divisible? Correct there is nothing done that can't be looked at by anyone with the time but isn't a visual aid and having the work already done and condensed into a simple comparable number worth something?

 

Don't get me wrong, I'm not saying it is worthless but i'm not sure just presenting that data as is would be that helpful, or rather I'm not sure the conclusion that you described (8 of the smaller one is about equal to 1 of the big one) would be that obvious from a simple line graph. It seems like you're getting into modelling territory here and that would benefit from some user input.

 

For example something like the following would be relatively straightforward to code up in javascript

 

Let user pick 2 systems as a baseline, call these A1 and B1

Show a graph that renders it in dB as A1/B1 to show the difference between the two 

Add a control that lets you enter how many instances of each system you have (i.e. to scale up from 1 to 8 in your example), call these A2 and B2

Add another series to the chart rendering A2/B2

Add a control that lets you simulate a difference in power (e.g. perhaps you only have 50% more power)

render A2/B2 again

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You know, way back when we started this site we had a pipe dream of having an advanced simulation program built into the site that ran online and would allow people to save and share files online in a common space. Not sure if that will ever happen.  

 

I'm not sure the APD graph idea would be that useful to most people but I might do it anyway. The idea is to show which systems have the most output for their size and how different types of alignments compare to each other in that aspect. That is all. Some of that can be backed out of simulators like HR easily but that's simulated and not based on real data with all of the warts. BTW this info would be put into a big sortable systems chart like the output averages and burst data are now in addition to the graph that would be in the individual systems measurements.  

 

 

 

Mike,

I like the idea of a radar type graph to show several types of data all at once. That might be something to think about. I've not created those before but it can't be that bad. It would probably have to be an image upload rather than a live comparable graph, though. The question is what data gets put on a graph like that? Anybody want to make some suggestions or take a stab at generating one?  

 

 

 

Updated APD graph in Log (Pa) format. Meant to do that yesterday but missed it trying to get things done in a rush.

 

post-5-0-89960200-1451579236_thumb.png

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I would only add an option to do (PAPD)/(Watts to get that Sound Pressure).  While many HT builds 'from scratch' have more than enough current capacity out of the wall, there are many that will use just what is currently available.  People may find out that horns may be better for them if they can spare the space.

 

JSS

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I was thinking you wanted a metric that would be relatively independent of the particular box chosen.  It looks like instead you want a metric that applies to systems in general.  One fault I see right away is that the same driver put in a smaller box will (almost?) always exhibit more burst pressure per liter.  A HIL-limited sealed sub will drop 3 dB or 0.707 times with a halving of box size, and that will make its apparent output per liter go up.  Of course, what's really happening is that you're using more drivers per liter of space to achieve this, which only supports the old adage of "there's no replacement for displacement".

 

In reality, efficiency does matter, and for a driver in a very small (what I'm calling HIL-limited) sealed box one can expect the acoustic power per liter per electric watt to be fairly similar between boxes of different (very small) sizes.  Note that acoustic power and acoustic pressure are different quantities.  Acoustic power scales with the square of acoustic pressure.  So all else the same, every doubling of SPL is a quadrupling of acoustic power.

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attachicon.gifPAPD SPL Graph Example.png

 

Whether this data is of interest to anyone is the question. It interests me but I cook up weird data like this all the time for my own curiosity. This is clearly a very simple way of looking at it and ignores a lot of issues that would have to be considered. Number one being amplifier power. Are both systems already capable of handling a very large amp? If so, is it really feasible to use 8x the power for the smaller system in this example? At some point efficiency does factor in. (Efficiency actually is tracked in this data for the passive systems above roughly 50 or 63Hz.) However it is ignored in the deep bass and for active, closed loop systems. Perhaps the bigger system A weighs 220lbs and uses a single large driver. What if System B uses a heavy driver itself and already weighs 75lbs despite its small size? 8 of them results in a 600lb system. That may be an issue. Perhaps the system must fire all output from a single enclosure face and this will be impossible with 8 drivers/vents etc... Cost is ignored as well. Perhaps the big system is way too big to consider to begin with? The list of factors for consideration goes on.

 

Thoughts?

Well you have at least my vote for this. I agree that SPL is a lot easier to read, especially in the deep bass. This is of great interest to me because it very effectively demonstrates output per liter.

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The metric I was wanting to show is a little different than just showing the true efficiency. Yes HIL governs the deep bass efficiency of a system but that in turn also limits the theoretical maximum output. In the deep bass the maximum output is usually limited by the driver or vent displacement capabilities these days, rather than the system efficiency since huge amplifier power is cheap. I'm more interested in which systems have more output potential per unit of volume than which ones have more efficiency per unit of volume. Both are important and are linked but perhaps require separate metrics.

For a lot of people, huge amplifier power is not cheap. Consider that your average person spends probably $2-300 on a Best Buy sound system for their home theater. Especially if you're limited to a 15A circuit, whatever you have left over dedicated to the subwoofers won't be able to run most of these systems to their very limit. Dividing that remainder between 3-4 subs for a Geddes setup, and now the small-signal behavior of these systems becomes very relevant. I think it would be extremely useful to have both efficiency/volume and max output/volume.

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Radar plots are easy, you just need to normalize the data relative to each other so the scales are the same. Excel can handle them, and the math isn't bad.

 

Metrics? Pick any of them. Compare systems, drivers, whatever. Cost, power handling, extension, size, 1W efficiency, take your pick. Just normalize things in a consistent manner. Make the "good" things normalize to a big score when more is better, but invert things when a lower score represents better. Power handling and efficiency? More is better so higher numbers are good. Extension? Lower numbers are better, so 1/extension might be a better approach, DC would be an unobtainable result, just like the real world.... Size? Smaller = better, so a 1/volume might be appropriate too. Cost is easy, bigger cost is something that's universally understood. Still, it has to be normalized, so the ceiling value is simply the highest one to date.

 

Lots of ways to do this. Shoot me an email if you want to see some examples.

 

If I could attach pictures, I would.... I can't seen to manage that here, at least not consistently.

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are you looking to determine output density for the subs that were measured or determining the output density in an ideally sized cab for each driver?

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are you looking to determine output density for the subs that were measured or determining the output density in an ideally sized cab for each driver?

 

Potential output density assuming unlimited amplifier or close. Important for working within defined space or shape limits. Sort of a way to investigate the effective utilization of minimum space to meet the system requirements.

 

Another cross section of this would be the actual system efficiency regardless of system size, but that will need to be looked at separately. More important for systems with space but limited budget.

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Added graphs for the normalized burst output per liter. This will only be used for finished amplifier/driver/cab systems with appropriate limiting and amplifier reserves built in. Won't be used for K20 tests with passive cabs for obvious reasons after looking at the data. Currently the graphs are not comparable. Need to make some changes to the site to get them setup as a directly comparable graph.

 

Will be adding...

 Calculated 1 watt efficiency for all passive systems.

Calculated power applied curve during the long term measurements for all passive systems

Possibly calculated current applied as well.

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Added graphs for the normalized burst output per liter. This will only be used for finished amplifier/driver/cab systems with appropriate limiting and amplifier reserves built in. Won't be used for K20 tests with passive cabs for obvious reasons after looking at the data. Currently the graphs are not comparable. Need to make some changes to the site to get them setup as a directly comparable graph.

 

Will be adding...

 Calculated 1 watt efficiency for all passive systems.

Calculated power applied curve during the long term measurements for all passive systems

Possibly calculated current applied as well.

 

How hard would it be to put the output per L in the comparable charts section?

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How hard would it be to put the output per L in the comparable charts section?

 

 

That's what I meant in my post above. Eventually it will be and also in the comparable graphs tab but it requires some changes to the backend of the site, which I do not handle. It'll get done at some point.

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That's what I meant in my post above. Eventually it will be and also in the comparable graphs tab but it requires some changes to the backend of the site, which I do not handle. It'll get done at some point.

Sorry I misread that part, and thought it meant something else.

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Welcome to the forum.

Been registered for a couple years now, I was sure I had posted before, I guess not. Well I am posting, now you'll never get ride of me B)

 

It is nice to see new graphs coming, mainly I like to see things to help people who aren't as technically minded compare products in aspects they care about and understand. Like the one you just added. And something like what has also been discussed output/$ at given frequencies, and distortion compare would be nice but that one does get complicated.

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I look forward to seeing the new graphs.

 

About those efficiency figures.  In the thread for Luke's 8 X 21" build, I alluded to the idea that the power dissipated in the woofer voice coil is not necessarily the same as the power (or current) demand from the amp.  I admit, my knowledge is not strong here, so if there are any amp experts around who can chime in about this, I'd like to hear it.

 

As I understand it, with class AB amps at least, reactive power is dissipated in the output devices.  This has two implications:

  1. The reactive power is wasted, which makes the load look lower in impedance to the amp.
  2. The heat produced by dissipating that energy puts more thermal stress on the amp.

I'm not sure how often #2 is really an issue, at least with raw drivers that don't use passive crossover components.  I believe #1 may matter a little bit.   I think it would be interesting to be able to at least see how much power is demanded from the amp.

 

With that said, I don't know how class D amps work in this respect.  I have heard of bus pumping being a problem, related to the management of reactive power, but I don't really understand what happens to that power when a class D amp is used in a bridged configuration, which of course, alleviates the bus pumping problems.

 

Any thoughts?

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Digital amp topologies typically can recycle the energy from back EMF. Drivers with higher efficiency typically generate higher levels of back EMF as well. I am not strong on this subject either though. I know just enough to be dangerous. Perhaps someone with a higher level training in amplifier kung-fu will read and chime in.

 

For the data I'm going to be representing for efficiency/power/current it will all be calculated from the measurements of the impedance and system SPL. It will not consider things like "real" vs "apparent" power, back EMF, phase angle, impedance shifting due to heating and non linearity in the drivers, etc. I don't have that data for all of the current systems tested and it would simply be too much work to start gathering it  for new ones. So understand that while the data at lower drive levels should be close to real it is likely to veer off at higher power from what is actual. At least it will all be roughly comparable though.

 

Nathan,

I am planning to add the distortion chart idea but it will take some time as well.

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Digital amp topologies typically can recycle the energy from back EMF. Drivers with higher efficiency typically generate higher levels of back EMF as well. I am not strong on this subject either though. I know just enough to be dangerous. Perhaps someone with a higher level training in amplifier kung-fu will read and chime in.

 

Sure I can chime in! When bus-pumping is taking place, you basically want to make sure the front tires have a slightly higher PSI than the rear tires so when the brakes are applied, you get the best slowing results...the slowing is amplified. 

 

EMF can be entirely done away with by wearing tinfoil hats while driving the bus.

 

I hope this helps.

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Sure I can chime in! When bus-pumping is taking place, you basically want to make sure the front tires have a slightly higher PSI than the rear tires so when the brakes are applied, you get the best slowing results...the slowing is amplified. 

 

EMF can be entirely done away with by wearing tinfoil hats while driving the bus.

 

I hope this helps.

 

Clearly your amplifier kungfu is grand master level.

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Sure I can chime in! When bus-pumping is taking place, you basically want to make sure the front tires have a slightly higher PSI than the rear tires so when the brakes are applied, you get the best slowing results...the slowing is amplified. 

 

EMF can be entirely done away with by wearing tinfoil hats while driving the bus.

 

I hope this helps.

 

For a short while when I was younger, I had a job driving city buses.  I was surprised more than once to experience how easy it was to hydroplane a bus, easier IIRC than any cars I've driven.  And yeah, a few newer models had anti-lock breaks.  Talk about pumping!  I'd literally watch the air pressure meter drop furiously wiggle from full to half full in a few seconds.

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Josh,

 

How about putting up the output per liter graph for passive systems too but only up to the highest driver(distortion/excursion) limited frequency, then just show a straight line above that, as that is often the absolute most amount of power that should be run on the driver/system in question, and so that would indicate a reasonably fair comparison to other DIY and even commercial subs

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I've been working on some of what's discussed in this thread for a while. New ways to present data, etc...

 

One quick thing I want to run by everyone is the possibility of posting the burst data as the current format of 2m, rms calculation with the averages in basic SPL format which favors systems with deeper, more uniform over a wider bandwidth output capabilities and also the same data as 1m peak (+9dB from the usual reported here) with the averages done with conversion to Pascals which results in higher numbers that tend to favor systems with less uniform response more. The second way is the way some mfg's report it.

 

I'm torn a bit on this. It wouldn't take much effort and I'd like to think it would help clear up confusion for less knowledgeable people who may not understand the differences in the differing ways the data is reported. Then again it may just confuse people even more. I also don't want to encourage reporting the data like that as it mostly just inflates the numbers and favors systems that are loud but not necessarily very strong in the deep bass or uniform in output.

 

Thoughts?

 

 

 

Josh,

 

How about putting up the output per liter graph for passive systems too but only up to the highest driver(distortion/excursion) limited frequency, then just show a straight line above that, as that is often the absolute most amount of power that should be run on the driver/system in question, and so that would indicate a reasonably fair comparison to other DIY and even commercial subs

 

That's possible. I have to get in depth with some of this data and perhaps look at it limited like that. One issue is knowing what the output would be with that limited amount of voltage. I'm not comfortable doing a bunch of calculations or assumptions of what it should or might be. That would leave only having the frequencies where the driver excursion is a limitation for the passive systems. I'm better with that but still not happy. Perhaps I could use the max long term sweeps for the passive systems since that is a known voltage level that won't beat the drivers to death mechanically that tests the whole bandwidth. Technically that level of power might still be able to cook them in most cases if something even worse than the sine wave sweeps comes along, like Blown Sub-driver (Sorry I mean Lone Survivor),  but it's about the best compromise I think.

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Maybe it would be easier to simply write an article with an outline on what means what and explain all these things clearly in a way that makes sense to the less experienced.

 

That to me seems like a LOT less work and would service the issue equally as well.

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Maybe it would be easier to simply write an article with an outline on what means what and explain all these things clearly in a way that makes sense to the less experienced.

 

That to me seems like a LOT less work and would service the issue equally as well.

 

Myself and others have already done that a number of times. No it wasn't officially an article here or whatever but even if it was I don't think it would help.

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Myself and others have already done that a number of times. No it wasn't officially an article here or whatever but even if it was I don't think it would help.

It wouldn't hurt though (to have a reference article on the subject alongside the reference dataset).

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