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Ideas for new ways to display data


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#41 SME

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Posted 04 March 2016 - 05:15 AM

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?



#42 Ricci

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Posted 04 March 2016 - 04:42 PM

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.



#43 BeastAudio

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Posted 04 March 2016 - 06:28 PM

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.



#44 Ricci

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Posted 04 March 2016 - 08:11 PM

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.



#45 SME

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Posted 05 March 2016 - 05:54 AM

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.



#46 Funk Audio

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Posted 06 March 2016 - 08:54 PM

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



#47 Ricci

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Posted 30 September 2016 - 07:02 PM

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.



#48 Infrasonic

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Posted 30 September 2016 - 07:08 PM

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.



#49 Ricci

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Posted 30 September 2016 - 07:20 PM

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.



#50 3ll3d00d

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Posted 30 September 2016 - 10:04 PM

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).

#51 shadyJ

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Posted 01 October 2016 - 01:33 AM

I think averages should just be avoided. Averaging in dB will weigh down the average to the lower value, and averaging in Pa will pull the numbers up. To get an idea of the sub's performance at a glance, the best thing to do is what you are already doing; using comparative graphs. There is just no great way to boil down the performance of a certain frequency band with a single number, but graphs can do it all with a single image. 


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#52 SME

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Posted 01 October 2016 - 09:59 AM

I agree that doing an average like this is not a good idea.  There's no real fair way to do it.  Everyone would have his/her own criterion for weighting the data.  And in fact, those of us who would actually care about how that average was calculated would not find it useful anyway.  Such numbers are only likely to be "helpful" to the sort of people who start forum threads with "I have $500 to spend.  Which subwoofer should I buy?" and no other details.


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#53 Kyle

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Posted 02 October 2016 - 03:15 AM

"There's no real fair way to do it" -- this is the truth. The passive systems with 10k+ amps wil always have an advantage in the upper bass where active systems are always power limited. I think we'll do some nice filters for the chart view so we can compare active vs active and passive vs passive if users want.


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#54 Ricci

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Posted 03 October 2016 - 03:05 PM

Doing away with the burst averages entirely certainly would avoid a lot of the issues. Sounds good to me. B)

Should we get rid of the long term sweep averages as well? I'm thinking yes...

I never see anyone discussing those and when I do it's an email from someone who is confused and trying to compare it to 1m burst data from somewhere else. Taking them away solves the problem with minimal effort. The correct way is to pull up the full bandwidth measurement and compare and we already have that data capability built in.

 

Just to illustrate how confusing some of this is here is some of the M.A.U.L. data using the various reporting methods.

 

Normal 2m "rms" method for reporting THD limited burst SPL used here at DB.

 

20Hz = 128.6

25Hz = 130.6

31.5Hz=133.1

40Hz = 135.8

50Hz = 138.3

63Hz = 141.4

 

Of course the 1 meter "peak" results would be 9dB higher which is easy to understand at least.

20Hz = 137.6

25Hz = 139.6

31.5Hz=142.1

40Hz = 144.8

50Hz = 147.3

63Hz = 150.4

 

Example simple SPL averages using the 2m data normally used here. Of course the 1m peak results would be 9dB higher.

 20-31.5Hz=130.8 (139.8dB 1m peak)

40-63Hz = 138.5 (147.5dB 1m peak)

 

Here are the same results averaged in pascals.

 20-31.5Hz=131 (140dB 1m peak)

40-63Hz = 138.8 (147.8dB 1m peak)

 

We can see that the results using Pa averaging are just a hair higher in this case. They are always higher than averaging using SPL. It doesn't amount to much here because the M.A.U.L. is actually quite uniform in output over these ranges. Varying by 12.8dB from 20Hz to 63Hz which seems like a lot but it is actually not that much. With systems having a decently uniform output the Pa averaging doesn't boost the output averages that much so it isn't a big deal. Let's look at a system which is not as uniform in output though.

 

Here's the Bic PL-200 THD limited burst data

 

20Hz = 84.0 (93dB 1m peak)

25Hz = 96.2 (105.2dB 1m peak)

31.5Hz=102.5 (111.5dB 1m peak)

40Hz = 107.7 (116.7dB 1m peak)

50Hz = 110.4 (119.4dB 1m peak)

63Hz = 108.1 (117.1dB 1m peak)

 

Averages of above PL-200 data as presented here. 2m, rms, straight averaging of SPL

 20-31.5Hz= 94.2

40-63Hz = 108.7

 

Averages of the same data but reported at 1m, peak, with Pa averaging

 20-31.5Hz= 106.1

40-63Hz = 117.8

 

In this case the 20-31.5Hz average is greatly boosted by 2.8dB by using Pa averaging. The PL-200 does have a wide variance over that bandwidth but it is by no means alone or the worst offender. There are many systems that have been tested that are similar. I believe that everywhere else reporting averages or most everywhere else anyway are using this Pa averaging method. It is better to simply look at the discrete frequencies individually rather than lump them together as averages in those cases IMHO. If you compare to another system that has much more uniform output down to deeper frequencies but do not look at the discrete bandwidths and only the averages when comparing systems, it would appear that the less uniform system is more comparable in deep bass output than it actually is.

 

Does anyone have a counterpoint or think we should keep any averages at all after the next big update?


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#55 Kyle

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Posted 03 October 2016 - 06:08 PM

I agree because its also less work for me with the new site.


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#56 Kyle

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Posted 03 October 2016 - 06:10 PM

The new site is going to have a lot more rich experience anyway, and the comparing tools will be much better. I'm also thinking about adding a quick graph mode where any user can just add plot points and it will save the data to a hash key in the db and you can pass the link around, or edit it further similar to https://jsfiddle.net/, but with graphs, not code.



#57 lukeamdman

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Posted 03 October 2016 - 07:20 PM

What I liked about the 2m RMS value was that it was a little "closer" to reality, especially below 30hz when you factor in room gain.  Those numbers were actually reachable.  Add 9db and they're way out of reach. 



#58 Ricci

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Posted 04 October 2016 - 01:45 PM

What I liked about the 2m RMS value was that it was a little "closer" to reality, especially below 30hz when you factor in room gain.  Those numbers were actually reachable.  Add 9db and they're way out of reach. 

 

Yep. I have some data for powered subs in my current room vs outdoors and it matches up well. You see some wild variation up near 80-125Hz as you would expect from a single sub subject to the acoustics of a typical domestic sized room. The output tracks quite well overall from 25-70Hz and starts showing some gain at 20Hz (3dB roughly)and it increases steadily down to 10Hz and below (10dB or more). About what should be expected in general.

 

That leads to a good question. Since we are tossing out output averages...Should we entertain the idea of listing the burst data as both the standard way and the +9dB, 1m peak method? I'm thinking we don't and we perhaps just put a banner or note on the data that states that it is reported as 2 meter rms (Add 9dB for 1m peak equivalency) or something to that effect.

 

We will be listing the distortion limited burst data as usual and adding the maximum burst output with no regard for THD which I have for most systems. I'll usually run the system until it stops getting louder, THD reaches 100%, or I hear some sort of "BAD" noise indicating self destruction is nigh. Generally the extra output is in the deep bass frequencies below the system impedance maximum as can be seen on the static burst data images. The data is useful from my perspective as it shows what the actual dynamic maximum of the system is. Some of the higher inductance drivers for example fail in the deep bass for distortion a good 6dB or more below their useful excursion limits. For those drivers the distortion limited results aren't really a good indicator of how much displacement the driver truly has. When you place a sub in a room as compared to outdoors the THD often drops dramatically in the deep bass. Some powered subs have gone from being distortion limited during the 12.5 or 16Hz burst, a good 8dB below their maximum output outdoors, to producing a "pass" distortion result at very nearly full output in my room.


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#59 lukeamdman

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Posted 04 October 2016 - 03:13 PM

That leads to a good question. Since we are tossing out output averages...Should we entertain the idea of listing the burst data as both the standard way and the +9dB, 1m peak method? I'm thinking we don't and we perhaps just put a banner or note on the data that states that it is reported as 2 meter rms (Add 9dB for 1m peak equivalency) or something to that effect.

 

YES. 



#60 Kyle

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Posted 04 October 2016 - 10:17 PM

YES. 

 

We can just have a toggle button that adds 9dB to each value in the table. Two different views of the same data.






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