Jump to content
Sign in to follow this  
Ricci

Ideas for new ways to display data

Recommended Posts

Ricci    652

We are hopefully going to do a bit of a revamp to the site in the next 6 months or so and we have a lot of ideas.

 

One new comparison chart that I want to add is an SPL per cubic liter of cabinet metric. This would be based at the same 12, 1/3rd octave center frequencies as currently used for the burst testing. The burst SPL would be considered for each system at each bandwidth and a value assigned based on the SPL and the total external volume of the system. This way it would give a relative value of power density at each bandwidth. Should be interesting to see small systems compared to huge horns and the like in this manner. I haven't quite worked out the exact comparative formula yet. Since SPL is a log function it will likely require converting to Pa and back. Shouldn't be too bad though. Anyone want to take a stab at a normalized formula?

 

Below is an idea for a different type of distortion graph that was suggested by Nathan Funk at Funk Audio.

Not exactly easy to put together right now and it's just kludged together in excel at the moment but something could be automated to make it faster I'm sure. Basically the distortion captured during the long term sweep measurements from each system are charted at a single frequency as it increases with the increased output of the device during the sweeps rather than over the whole bandwidth during a single sweep. The sweeps themselves are only measured at increases of 5dB typically so a few data points will be used to extrapolate the rest of the data between to fill the curves in. Judging from the rough results here it looks like this is not an issue. It does make comparison easier but also only represents a very tiny slice of the bandwidth. Still I think it is worth adding something like this possibly though.

 

Here are a few charts showing a collection of drivers tested in the standard sealed cabs with the data shown in the manner detailed above at 10, 12.5, 16 and 20Hz.

 

Suggestions? Thoughts?

 

10Hz

post-5-0-32573700-1450904649_thumb.png

 

12.5Hz

post-5-0-02024400-1450904653_thumb.png

 

16Hz

post-5-0-08329200-1450904656_thumb.png

 

20Hz

post-5-0-92087900-1450904658_thumb.png

 

 

Share this post


Link to post
Share on other sites
Diogenes    9

Very information dense and it seems it could get out of hand in a hurry unless there's a way to select which drivers to show, but it tells a lot at a glance. Fwiw, I like it, but as an addition to, not substitution for the already pretty clear way you present data.

 

Admit it, you just wanted to show off how awesome that Rockford Fosgate driver is.  ;)

Share this post


Link to post
Share on other sites
SME    210

We are hopefully going to do a bit of a revamp to the site in the next 6 months or so and we have a lot of ideas.

 

One new comparison chart that I want to add is an SPL per cubic liter of cabinet metric. This would be based at the same 12, 1/3rd octave center frequencies as currently used for the burst testing. The burst SPL would be considered for each system at each bandwidth and a value assigned based on the SPL and the total external volume of the system. This way it would give a relative value of power density at each bandwidth. Should be interesting to see small systems compared to huge horns and the like in this manner. I haven't quite worked out the exact comparative formula yet. Since SPL is a log function it will likely require converting to Pa and back. Shouldn't be too bad though. Anyone want to take a stab at a normalized formula?

 

Hi Ricci.  This sounds awesome!  I'd be glad to help contribute my mathematical and acoustic knowledge to this problem.  I practically do conversions between dB SPL and Pa in my sleep.  However, I'm not exactly certain what what you are trying to achieve with your formula.  Should efficiency enter into the picture?  Without considering efficiency and assuming unlimited amp power, most sealed box systems are likely to perform almost the same, especially at the bottom end where everything is excursion limited anyway.  I'm thinking you may be more interested in efficiency per liter.  But really, I guess it depends on the application.

 

I really like your ideas for the distortion graphs and see no issues with your approach.  If your plotting system supports B-spline interpolation, you may be able to get curves that are more smooth and more accurate at the same time, but you'll want to verify that the fits make sense.  For example, some kinds of spline fits assume that either the data points or their derivatives (i.e. slopes) go to zero at the ends of the graph, so that's something to watch out for.

 

By the way, the technical term for filling in between data points as you are doing here is called interpolation.  Extrapolation refers instead to extending curves beyond the last point in a data set.  As you can imagine, extrapolated figures are a lot more likely to give erroneous results, which is why they are typically frowned upon.

Share this post


Link to post
Share on other sites
3ll3d00d    72

 

Here are a few charts showing a collection of drivers tested in the standard sealed cabs with the data shown in the manner detailed above at 10, 12.5, 16 and 20Hz.

 

Suggestions? Thoughts?

 

I tend to find line charts visually quite misleading as your eye is drawn to the outliers rather than the data points, not sure if there is a sensible way to avoid this here though.

 

I suspect that a comparative chart would be good though, i.e. pick a driver as the baseline and then show a.n.other driver as the delta to that baseline.

 

You could also turn that into a surface plot to enable the different frequencies to be pulled into 1 chart. I would think this would be particularly useful when comparing two drivers. You could look at the REW eq window for an example of this in action, the waterfall plot in that screen allows you to overlay the before and after waterfall and you can then reasonably easily the key points of difference.

 

A directivity sonogram or speclab captures are some other examples (albeit 2D examples) of such 3d plots.

 

Also who doesn't like 3d charts? We expect an IRIX interface here :D

Share this post


Link to post
Share on other sites
shadyJ    19

Hello Josh,

 

As you well know, THD is not a great metric for assessing how clean a subwoofer sounds. Still, it's better than nothing. I am not sure that comparing individual harmonics make sense either, I am not sure how useful that would be. This might be ridiculous, but what about using some kind of harmonic-dependent threshold for long-term output, something like CEA-2010? YOU could probably establish a more sensible metric than the Consumer Electronics Association anyway, you would be surprised at how arbitrary the CEA-2010 thresholds are. They are not based on rigorous experiments. It would take more work to create graphs from your own distortion threshold formula, but it would be an interesting project. 

Share this post


Link to post
Share on other sites
Infrasonic    153

Hey! That's a pretty sweet new way to quantify these subs performance. SPL per cubic foot. I love it!

 

I can't think of many (any?) suggestions for new tests, I'm sorry to say.

 

Maybe bring back spectral contamination tests but I believe those were originally nixed from DB tests because you said (paraphrasing) "too hard on a driver" of a test to do. IIRC.

 

Erm, that's all I can think of at the moment.

 

Ummm....

 

 

Ship all the systems to me when you're done testing? Yes. Yes. That sounds good.

Share this post


Link to post
Share on other sites
Ricci    652

Very information dense and it seems it could get out of hand in a hurry unless there's a way to select which drivers to show, but it tells a lot at a glance. Fwiw, I like it, but as an addition to, not substitution for the already pretty clear way you present data.

 

Admit it, you just wanted to show off how awesome that Rockford Fosgate driver is.  ;)

 

The charts I showed are just what I whipped up in excel to see how it would look. I had them done a long time ago and kind of forgot about them. I was adding the RF driver and thought I'd go ahead and post something about it. The T3 19 sure does do well though huh? :D  If something like this was added to the forum it would be similar to the comparable graphs we have now. You would only be able to compare 2 systems at a time not 10+ like I had on these.

Share this post


Link to post
Share on other sites
Ricci    652

Hello Josh,

 

As you well know, THD is not a great metric for assessing how clean a subwoofer sounds. Still, it's better than nothing. I am not sure that comparing individual harmonics make sense either, I am not sure how useful that would be. This might be ridiculous, but what about using some kind of harmonic-dependent threshold for long-term output, something like CEA-2010? YOU could probably establish a more sensible metric than the Consumer Electronics Association anyway, you would be surprised at how arbitrary the CEA-2010 thresholds are. They are not based on rigorous experiments. It would take more work to create graphs from your own distortion threshold formula, but it would be an interesting project. 

 

Actually there is study that has been put into the thresholds established as the limits for CEA-2010. There are various papers available on harmonic distortion, masking and bass frequencies. It is by no means perfect as has been discussed a few times. There is no doubt that even large amounts of distortion up to 15-20% o the first 2 harmonics are not that easily noticed in the bass range. Especially with complex content with upper frequency masking. Mechanical or non harmonic noises are much more distracting to me personally. Still some sort of standard is better than nothing. On that we agree. I'm not going to get to the point of comparing individual harmonics. That would be a lot of work and practically difficult with the current tools available without investing significant time and resources. At the end of the day I don't know if it would be that useful either. However I still feel that distortion is a useful metric to look at and compare and my preference is for as low of distortion as possible.

Share this post


Link to post
Share on other sites
Ricci    652

You could also turn that into a surface plot to enable the different frequencies to be pulled into 1 chart. I would think this would be particularly useful when comparing two drivers. You could look at the REW eq window for an example of this in action, the waterfall plot in that screen allows you to overlay the before and after waterfall and you can then reasonably easily the key points of difference.

 

A directivity sonogram or speclab captures are some other examples (albeit 2D examples) of such 3d plots.

 

Also who doesn't like 3d charts? We expect an IRIX interface here :D

 

Hmmm...I have to admit a 3d plot with frequency, SPL and THD would be great. Not sure how feasible this is but it can't hurt to poke around.

 

 

 

 

Hi Ricci.  This sounds awesome!  I'd be glad to help contribute my mathematical and acoustic knowledge to this problem.  I practically do conversions between dB SPL and Pa in my sleep.  However, I'm not exactly certain what what you are trying to achieve with your formula.  Should efficiency enter into the picture?  Without considering efficiency and assuming unlimited amp power, most sealed box systems are likely to perform almost the same, especially at the bottom end where everything is excursion limited anyway.  I'm thinking you may be more interested in efficiency per liter.  But really, I guess it depends on the application.

 

I really like your ideas for the distortion graphs and see no issues with your approach.  If your plotting system supports B-spline interpolation, you may be able to get curves that are more smooth and more accurate at the same time, but you'll want to verify that the fits make sense.  For example, some kinds of spline fits assume that either the data points or their derivatives (i.e. slopes) go to zero at the ends of the graph, so that's something to watch out for.

 

By the way, the technical term for filling in between data points as you are doing here is called interpolation.  Extrapolation refers instead to extending curves beyond the last point in a data set.  As you can imagine, extrapolated figures are a lot more likely to give erroneous results, which is why they are typically frowned upon.

 

Haha...You got me on a technicality there. Good catch. Say it with me, interpolation...

It should work well. Depending on how the data would be uploaded and displayed it shouldn't be difficult to smooth the data and curve fit it better. I don't think that'll be a big issue.  

 

About the SPL / cubic liter / frequency metric.

I believe it makes sense to limit the bandwidths to those that are commonly driver or port displacement limited and also affected by Hoffman's iron law. I'm thinking 40Hz and lower or possibly 31.5Hz and lower. The basic idea is some sort of metric that gauges how hard each system is pushing up against HIL in the deep bass. At the upper bass frequencies where the limitation is often amplifier related rather than displacement a different formula would be needed.

Share this post


Link to post
Share on other sites
3ll3d00d    72

Hmmm...I have to admit a 3d plot with frequency, SPL and THD would be great. Not sure how feasible this is but it can't hurt to poke around.

A quick google says highcharts doesn't do such plots so I can give you an example using gnuplot if you want to generate some static images. 

Share this post


Link to post
Share on other sites
shadyJ    19

Actually there is study that has been put into the thresholds established as the limits for CEA-2010. There are various papers available on harmonic distortion, masking and bass frequencies. It is by no means perfect as has been discussed a few times. There is no doubt that even large amounts of distortion up to 15-20% o the first 2 harmonics are not that easily noticed in the bass range. Especially with complex content with upper frequency masking. Mechanical or non harmonic noises are much more distracting to me personally. Still some sort of standard is better than nothing. On that we agree. I'm not going to get to the point of comparing individual harmonics. That would be a lot of work and practically difficult with the current tools available without investing significant time and resources. At the end of the day I don't know if it would be that useful either. However I still feel that distortion is a useful metric to look at and compare and my preference is for as low of distortion as possible.

The research that CEA-2010-A is based on is D.E.L. Shorter's 1949 study for BBC "An Investigation Into Non-linear Distortion First Interim Report" and Eric Benjamin's and Louis Fielder's 1988 study "Subwoofer performance for accurate reproduction of music." If you go over those papers, you can see that they are not at all adequate for understanding the audibility of distortion in bass frequencies. They were intended as a 'starter' studies to prompt further research, and they were not intended to be the final word on that subject. CEA-2010-A sort of uses Shorter's suggested weighting scheme for its thresholds (obtained by multiplying the nth harmonic by n2/4), but that is largely guesswork as to how humans might be sensitive to distortion in low frequencies- it is not based on anything like comprehensive testing. Benjamin and Fielder's research only used 4 subjects with some Stax headphones if I remember right. Floyd Toole had some interesting comments on it, but it is really just a 'nascent' study for that subject which was not followed up with any serious research. Anyway, I am not trying to be argumentative, I am just saying the research in this area is very sparse, and CEA-2010-A distortion thresholds are essentially based on guesswork as far as I can see, not hard evidence.

 

The idea of the 3d plot of THD vs SPL would be pretty great. That would be a nice visual depiction of the way drivers misbehave at the edges of their performance. Such a plot might be interesting with CEA data too. If I remember right, Ed Mullen has remarked that CEA-2010 fail thresholds do give a pretty good indication of when the driver has reached its xmax. In your experience, would you say that CEA-2010 thresholds tend to correspond to xmax limits?

  • Like 2

Share this post


Link to post
Share on other sites
Ricci    652

Shady,

yes I would say that it does seem to track the "useful" excursion limits or output limits pretty closely. Sometimes it seems to limit a bit early and other times the subwoofer may have changed in tone or character noticeably indicating some type of audible distortion or non linearity. In general though it seems close so I'd agree with Ed. There are a few other papers out there if you really dig but none of them is what I'd call comprehensive. Really with this type of subjective data, which could vary drastically from individual to individual, how could there be something comprehensive?

 

BTW. It's been planned to remove the CEA-2010 label from everything here for a while, for a few reasons which I don't feel like going into. It's going to take a LOT of work so I haven't done it yet but it will happen. The testing or data, won't change at all, just the labeling. 

Share this post


Link to post
Share on other sites
shadyJ    19

Whatever other research exists in the audibility of distortion, it must really be obscure, at least in regards to harmonic distortion. When I asked Charlie Hughes, who is chairman of the CEA standards committee, what research was used to establish the distortion thresholds in CEA-2010-A, he said the Shorter paper and the Fielder/Benjamin paper. As for relabeling from CEA-2010, whatever the reason, I am sure they are good reasons. I am looking forward to where ever you take the data-bass website, I know it will be in a sensible direction. 

Share this post


Link to post
Share on other sites
SME    210
About the SPL / cubic liter / frequency metric.

I believe it makes sense to limit the bandwidths to those that are commonly driver or port displacement limited and also affected by Hoffman's iron law. I'm thinking 40Hz and lower or possibly 31.5Hz and lower. The basic idea is some sort of metric that gauges how hard each system is pushing up against HIL in the deep bass. At the upper bass frequencies where the limitation is often amplifier related rather than displacement a different formula would be needed.

 

Indeed, this is where I thought you were going after all.  Consider this.  Take a driver, put it in a box that's rather small relative to the compliance of the driver, and play it at a frequency well below its sealed box resonance.  In the limit of low frequency vs. resonance and small box vs. driver compliance, the efficiency will exhibit a 3 dB increase per doubling of box size.  (This is true as long as these stated limits hold.)  This is full-on HIL territory.  Note that a drop in output of 3 dB can be compensated for by doubling power input (assuming you have the watts and excursion to spare).  Likewise, a drop in output of 3 dB, while representing a change in level of 0.707X (sqrt of 2) still represents a sound power change of 1/2 X.

 

So I think the figure you want to quote is acoustic efficiency per liter of box (in dB/W/L perhaps) in the limit stated above.  Note that sound power can be quoted in dB just like level can be.  This figure will vary the least between boxes of different sizes, so long as the limits hold true, i.e., small box relative to woofer compliance, frequency low relative to resonance.  The best measurement of this figure will tend to be found when the box is made as small as possible.  It would probably also be good to clarify to the reader how that number is most appropriately used.  In other words, don't do an I.B. mount, and expect to see extraordinary efficiency, since at that point the HIL limits don't apply and it's the woofer suspension that determines the deep bass efficiency.

 

What I expect we will see is that the drivers with the highest B*L/Re will have the best numbers here.

 

Edit: The above is wrong.  Doubling the number of liters will not double the acoustic output *level* in dB.  It will double the absolute acoustic output instead.  So I guess you really do need to use an absolute acoustic power number instead of dB acoustic.  So the formula would look something like this (where V is volume in liters):

 

    <acoutic-power-output-per-L> = 10^(<measured-level-in-dB-@-1W> / 10) / V

 

You would need to instruct to users that they do the following conversion to estimate SPL versus box size:

 

    <SPL> = 20*log10(<acoutic-power-output-per-L> * V)

 

Edit 2: I probably got the bit about suspension stiffness versus box volume wrong.  Feel free to correct me.  Clearly, I need to study more.  ;)

Edited by SME

Share this post


Link to post
Share on other sites
BeastAudio    89

Hey! That's a pretty sweet new way to quantify these subs performance. SPL per cubic foot. I love it!

 

I can't think of many (any?) suggestions for new tests, I'm sorry to say.

 

Maybe bring back spectral contamination tests but I believe those were originally nixed from DB tests because you said (paraphrasing) "too hard on a driver" of a test to do. IIRC.

 

Erm, that's all I can think of at the moment.

 

Ummm....

 

 

Ship all the systems to me when you're done testing? Yes. Yes. That sounds good.

 

 

Where are you going to put it all then?

 

7e7cecb152e8781ff8563b33a3e9bdadc10f3b5e

  • Like 2

Share this post


Link to post
Share on other sites
Ricci    652

SME I may have a chance to look at this briefly on a real computer today. Hopefully.

 

Not sure I follow on the bit with the users doing estimates? Do you mean for systems not tested officially at DB?

Share this post


Link to post
Share on other sites
Contrasseur    17

How about efficiency vs frequency? Use the SPL values from the sweeps to calculate acoustic watts out, and divide V^2 by the impedance values to get electrical watts in. Make the X axis frequency and the Y axis acoustic/electrical watts. This will highlight the comparison between weak motors and extra-strong ones, and at which points in the bandwidth.

 

To make it even more direct-comparison friendly, normalize it to represent electrical watts needed for a certain spl, say 80db or whatever (given zero compression). Since signal processing is so ubiquitous (and often essential) these days, these charts will take unequalized frequency response out of the equation. If you want a given SPL, this chart shows you exactly how much juice a system needs to make it, and at what bandwidth. Now you can see that the 21IPAL can do 100Hz with .02W and the RE XXX needs .5W or whatever. Moving along the X axis you can see how that changes with frequency, so low FS drivers will really shine in the deep bass. All people need to see is the height of the curve, where lower is better. As clear of a comparison as one could have

 

This completely bypasses the problem of comparing a 3.5 Ohm DCR speaker to a 4 Ohm DCR speaker, especially considering neither of them will be 3.5 or 4 ohms in passband. Now instead of having those "basic response" charts to try and compare 1w/1m SPL, we can really see how they measure up in the one thing that they do, which is converting electrical power to acoustical power.

Share this post


Link to post
Share on other sites
Ricci    652

How about efficiency vs frequency? Use the SPL values from the sweeps to calculate acoustic watts out, and divide V^2 by the impedance values to get electrical watts in. Make the X axis frequency and the Y axis acoustic/electrical watts. This will highlight the comparison between weak motors and extra-strong ones, and at which points in the bandwidth.

 

There are a number of variable factors involved. This type of thing is shown in enclosure simulation software often and it could be backed out of the data I have collected.  A single representation of the calculated efficiency using the impedance curve and the voltage sensitivity could be done relatively easily. What I'd really like to do is a graph showing the results for each system at low, medium and high power though.

 

 

 

To make it even more direct-comparison friendly, normalize it to represent electrical watts needed for a certain spl, say 80db or whatever (given zero compression). Since signal processing is so ubiquitous (and often essential) these days, these charts will take unequalized frequency response out of the equation. If you want a given SPL, this chart shows you exactly how much juice a system needs to make it, and at what bandwidth. Now you can see that the 21IPAL can do 100Hz with .02W and the RE XXX needs .5W or whatever. Moving along the X axis you can see how that changes with frequency, so low FS drivers will really shine in the deep bass. All people need to see is the height of the curve, where lower is better. As clear of a comparison as one could have

 

This completely bypasses the problem of comparing a 3.5 Ohm DCR speaker to a 4 Ohm DCR speaker, especially considering neither of them will be 3.5 or 4 ohms in passband. Now instead of having those "basic response" charts to try and compare 1w/1m SPL, we can really see how they measure up in the one thing that they do, which is converting electrical power to acoustical power.

 

I do like the idea of this.

 

The issues that occur at higher power levels would be difficult to account for without the impedance data to go with it. The impedance curve can change dramatically which greatly affects the power calculation. In the deep bass most of the systems are limited by driver excursion and output compression unrelated to thermal effects. I personally do not put much emphasis on small signal efficiency for bass systems for these reasons. I'd rather look at efficiency at much higher input power. Doesn't have to be right at the limits of the system but something between one quarter to half of the drivers continuous thermal rating seems reasonable for a "medium" or real world use scenario.

 

Really what is needed is the high power impedance curves. I'd like to get back to testing high power impedance but it is a very intensive test, with a different setup, which takes a long time to complete. What would be great is to have the response shape and magnitude, the distortion and the impedance measurement for each applied voltage level. I'm only missing the impedance data. With all of that it is just a matter of using the data to provide whatever information is wanted.

 

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.

Share this post


Link to post
Share on other sites
lilmike    36

Definitely some interesting ideas being kicked around here.

 

I've been thinking about calculating the "area under the curve" through a set bandwidth at a normalized power input as a way to compare different cabinets. I like the idea of considering output and/or extension vs. cabinet volume too. 

 

Not 100% sure how I will go about this yet, but there's got to be a better way to look at the results.

 

How about multiple "scores" plotted on a radar plot? Excel can do these (at least in 2016). Create a consistently calculated metric for extension, efficiency, and output based on the measurements, add volume data, and possibly even driver cost, then plot things on a multi-axis radar plot. Each axis of the plot represents the relative score on each metric, and comparisons between data sets would show the relative strengths and compromises between designs.

 

Interested to see what you come up with here.

Share this post


Link to post
Share on other sites
Ricci    652

Here are a couple of quick example graphs taking a stab at representing acoustic power density. This is my original idea of representing this that I've had for a couple of years. These are using the burst data SPL (dB) which is then converted to Pascal (Pa) and then divided by the volume that the system takes up in liters (L) 

 

This one is shown using the data in Pa. This is the simplest way but I'm leaning away towards converting the data back into (dB) SPL because that's a format more familiar to most who would be looking at it.

 

 

post-5-0-57825800-1451505106_thumb.png

 

 

Here is the same data converted back into SPL decibels. This looks better to me intuitively but it's the same data either way.

 

 

post-5-0-57575800-1451505095_thumb.png

 

 

I think something similar would work. Here is what is going on for those who need a bit deeper explanation.

 

The maximum output from a system is being converted into Pa and divided by the total enclosure volume so that we can end up with a base output number either in Pa or dB, per liter of space taken up, for each 1/3rd octave frequency band. The conversion to Pa is needed so that the results are comparable.

 

Here's a simple example.

System A produces 120dB at 25Hz and measures 90x90x60cm (486 liters of space occupied)

System B produces 103dB at 25Hz and measures 43x36.2x39cm ( 60.7 liters of space occupied)

 

System A produced 120 dB which converts to an even 20 Pa

System B produced 103 dB which converts to 2.825 Pa

 

(1 Pa = 94dB / The formula for converting SPL(dB) to Pa is

Pa = [10^(dB/20)]*.00002)

 

We then divide each systems recorded Pa value by the total liters of space it occupies to get the Pa per liter value which we are going to call a acoustic power density rating or APD. Higher numbers are better.

System A =0.0411 Pa per liter. (20Pa / 486L)

System B =0.0465 Pa per liter. (2.825Pa / 60.7L)

 

What does this tell us? System B while smaller offers more potential output per liter of space. It is 1/8th the size of system A and offers far less output one vs one, but a block of 8 takes up the same space and potentially offers a little bit more output than system A.

 

If we convert the results back into SPL it is perhaps easier to digest.

The formula to convert Pa into dB is the reverse of the Pa conversion formula

 

dB = 20*log[Pa/.00002]

 

Applying that we get the following.

System A = 66.3dB per liter

System B =67.3dB per liter

 

To wrap up we have a very large system which offers 17dB more output than a smaller system exactly 1/8th the size. As most know if you double the systems you gain 6dB. Doubling three complete times to get to 8 total of the smaller system B results in an 18dB gain and the same total space being occupied as system A. The result is a 1dB advantage for an octet of system B. This is what the math shows in the final calculated SPL per liter.  

 

One more example of proving out the APD formula. System A was 120dB and 486L. The resulting APD (dB) rating was 66.3dB per liter. At first you may be thinking that can't be correct. Back calculating out how many systems you would need to provide a 53.7dB gain shows that it is in fact 486 total 1 liter systems each with an output of 66.3dB to produce a total of 120dB.

 

 

 

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?

Share this post


Link to post
Share on other sites
3ll3d00d    72

My immediate thought is why do you need to jump through the hoops to determine that having 8 of system B would produce similar output in a similar size space to system A? As you said "if you double the systems you gain 6dB. Doubling three complete times to get to 8 total of the smaller system B results in an 18dB gain".

 

Perhaps I'm being dim but it's not obvious to me what knowledge you gain by going under the covers (so to speak)

Share this post


Link to post
Share on other sites
Ricci    652

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?

 

This is the kind of feedback I want so thanks.

Share this post


Link to post
Share on other sites
lilmike    36

The main challenge you will face with any single metric is relevance to a viewer. For example, you and I have different criteria that matter "most". You're space constrained, I'm more hamstrung by the budget I've got to work within. Who knows what someone else's main concern may be? That's why the radar plot is kinda cool, lots of unrelated metrics can be displayed in the same plot, which makes it simple to do comparisons once all of the data set is normalized to the same benchmark.

 

I do like your approach because it keeps the frequency portion of the data front and center. Of the two you presented, I prefer the first plot, but I'd suggest that you try using a log scale on the vertical axis. In my opinion, changing the presentation via axis scaling is a LOT easier to do than the math, and that also keeps "dB" out of the plot, which will only lead to confusion. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×