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Your Home Theater ULF Score - Page 5

post #121 of 1882
Thread Starter 
Quote:
Originally Posted by bossobass View Post

Hi Dom,

Great stuff, thanks for the efforts.

My problem is in the assumption that each SI-18 (or equivalent) is equally powered.

The SI reference being used for these calcs was powered by a K10 on a 220V/50A line. eek.gif

It's not realistic to assume that (for example) a system of 8 of them would each have its own K10/220V/50A power plant.

It's also not realistic to assume that a system of 1-SI-18+K10/220V/50A would last more than one sitting of WOTW in my 3500 cubes HT at any sort of spirited playback level.

I think that your formula will only work accurately with commercial subs, using a commercial subs results as the reference.

I apologize for this post in that I usually I have some alternative choices or an equalizer to the existing formula, but in this case I don't because I haven't had enough time recently to do much extra-carricular thinking. I've just been watching the greatest MWB ever made and enjoying the heck out of it. cool.gif

Anyway, keep up the great work and hopefully this will evolve into a world class standard for actual use in actual rooms... something that has always been sorely lacking for the general sub-buyeing public.

Damn you Bosso...good point. :)

 

You're right, there's a lot more variables when it comes to DIY...power, amp rolloff, box size, etc.

 

As I mentioned before, it's not a perfect metric, and not meant to be. However, for DIY the power piece could have a significant impact on output and the resulting SI conversion ratio. 

 

For now what this means is that commercial scores are pretty good. For DIY, the scores are more of the 'max potential' of your HT system. Some that use fp14000 are probably very close to max. Those that use EP4000s, could be down a bit depending on driver, box, efficiency, etc.

 

I still think it puts folks in the general ballpark (and serves the purpose of this thread) to give others an idea of their ULF perspective, but agree that DIY could use some more refining.

 

Interested in hearing thoughts from others on how to make DIY more accurate...(again it won't be ever truly representative, but we could probably figure out a way to get it closer to commercial scoring).

post #122 of 1882
Thread Starter 
Quote:
Originally Posted by bossobass View Post

I've just been watching the greatest MWB ever made and enjoying the heck out of it. cool.gif

BTW, what MWB mean?

post #123 of 1882
So what happens if you use 600 watts for the SI which it is rated for? When I compare drivers in Winisd I use the amount of power which each reaches x-max at 5 hz.
post #124 of 1882
Quote:
Originally Posted by dominguez1 View Post

BTW, what MWB mean?

Sorry: Movies With Bass. The last few days I've watched, Thor, Iron Man II, Total Recall, Bourne Legacy, The Dark Knight Rises and Star Trek. tongue.gif

MKT,

Yes, it will have to be something like that. You could even double the rated power and be more realistic than a K10/220V/50A. Josh uses very small boxes for his driver tests, otherwise, most of the drivers would end up dead. The 18s go in 4 cubes and the 15s in 2 cubes for all of the testing. So, maybe a model to .707 with rated power X2? I dunno, but in any case, it's a great idea and should be pursued until a consensus is reached. cool.gif
post #125 of 1882
The voltages used to produce the cea-2010 and max burst output are listed for most DIY systems. Very very few can take the full brunt of that amp below 30Hz even in a small sealed enclosure without being blown apart. In the case of the SI driver it took about 60-80volts to produce the deep bass numbers. 120volts had it to the point of cracking the bottom plate. Also one thing to consider is since cea-2010 has distortion thresholds this is not necessarily the maximum output of the system. Some have had another 6dB or more left in the deep bass but with drastically increase distortion. Once you place the unit in room the boost in deep bass relative to the upper bass will in general lower the deep bass distortion quite a bit but the typical peaks and nulls in the upper bass range will also have dramatic effects on the distortion harmonics. That all being the case and considering the fact that different systems have varying amounts and variance in the relative levels of the harmonics that comprise the distortion, each sub could see a different amount of gain or loss if tested for maximum output outdoors versus in room with a set distortion threshold similar to cea-2010. It doesn't really matter a whole lot for the purposes of the exercise here but it is something to think about when bench racing bass systems.
post #126 of 1882
Thread Starter 
Quote:
Originally Posted by bossobass View Post


Sorry: Movies With Bass. The last few days I've watched, Thor, Iron Man II, Total Recall, Bourne Legacy, The Dark Knight Rises and Star Trek. tongue.gif

MKT,

Yes, it will have to be something like that. You could even double the rated power and be more realistic than a K10/220V/50A. Josh uses very small boxes for his driver tests, otherwise, most of the drivers would end up dead. The 18s go in 4 cubes and the 15s in 2 cubes for all of the testing. So, maybe a model to .707 with rated power X2? I dunno, but in any case, it's a great idea and should be pursued until a consensus is reached. cool.gif

MWB week...nice. Of the above movies, I'd have to say my ULF favorite was Total Recall...great ULF movie!

 

Where did you come up with the .707 number? Just curious what that meant.

post #127 of 1882
Thread Starter 
Quote:
Originally Posted by Ricci View Post

The voltages used to produce the cea-2010 and max burst output are listed for most DIY systems. Very very few can take the full brunt of that amp below 30Hz even in a small sealed enclosure without being blown apart. In the case of the SI driver it took about 60-80volts to produce the deep bass numbers. 120volts had it to the point of cracking the bottom plate. Also one thing to consider is since cea-2010 has distortion thresholds this is not necessarily the maximum output of the system. Some have had another 6dB or more left in the deep bass but with drastically increase distortion. Once you place the unit in room the boost in deep bass relative to the upper bass will in general lower the deep bass distortion quite a bit but the typical peaks and nulls in the upper bass range will also have dramatic effects on the distortion harmonics. That all being the case and considering the fact that different systems have varying amounts and variance in the relative levels of the harmonics that comprise the distortion, each sub could see a different amount of gain or loss if tested for maximum output outdoors versus in room with a set distortion threshold similar to cea-2010. It doesn't really matter a whole lot for the purposes of the exercise here but it is something to think about when bench racing bass systems.

Thanks for chiming in Josh.

 

So, if I understand this correctly:

 

graph

 

So, at 10hz, it takes 57V to produce the 89.2 SPL output.

 

So, using 4ohms as the resistance (I know 4 is not exact):

 

P = V^2 / R

 

57^2 / 4 = ~812watts @ 10hz?

 

I'm assuming that the clone can produce this wattage at this frequency. Can an EP4000 produce this? Obviously, this wattage requirement is also a function of the size of the box...the larger the box, the less watts needed, so that throws in another variable compared to commercial score as box size can vary.

post #128 of 1882
Quote:
Originally Posted by Ricci View Post

The voltages used to produce the cea-2010 and max burst output are listed for most DIY systems. Very very few can take the full brunt of that amp below 30Hz even in a small sealed enclosure without being blown apart. In the case of the SI driver it took about 60-80volts to produce the deep bass numbers. 120volts had it to the point of cracking the bottom plate. Also one thing to consider is since cea-2010 has distortion thresholds this is not necessarily the maximum output of the system. Some have had another 6dB or more left in the deep bass but with drastically increase distortion. Once you place the unit in room the boost in deep bass relative to the upper bass will in general lower the deep bass distortion quite a bit but the typical peaks and nulls in the upper bass range will also have dramatic effects on the distortion harmonics. That all being the case and considering the fact that different systems have varying amounts and variance in the relative levels of the harmonics that comprise the distortion, each sub could see a different amount of gain or loss if tested for maximum output outdoors versus in room with a set distortion threshold similar to cea-2010. It doesn't really matter a whole lot for the purposes of the exercise here but it is something to think about when bench racing bass systems.

Hi Josh,

I've done almost 100% of my tests in-room, 3500 cubes. Open to the rest of the house or closed to the rest of the house makes little difference, if any in my results.

I've tested nearly 100 drivers with lots of different amplifiers over 13 years time. I use an average of 10dB boost L/T to get the response flat to below 5 Hz at the seats with room gain.

In my experience, there has been no single driver system that would last 1 day driven by a K10 on a 220V/50A line without exercising extreme caution and pushing nowhere near the limits of that kind of available power. I seriously doubt that my experiences are different from reality in any room using any driver.

Rob (notnyt) has a 14K clone in stereo per pair of LMS-U; 4 amps, each on a 120V/30A home run, 8 drivers. If he instead had 8 X K10, each on a 220V/50A line and each driving a single LMS-U, that would require a caution flag for sure. If he had a single LMS-U and 1-K10 on a 220V/50A line, that would require a broom and a dust pan.

You run tests to 10 Hz. WOTW extends that test to the bottom of the signal chain. In my case, that's -3dB @ 3 Hz @ 10X the level @ 30 Hz.

Now, imagine Rob has a quad of LMS-U wired for a single 4 ohm load and used a single 14K, bridged. If he used that system for a month, then switched to a K10/220V/50A power plant, he'd see at least +6dB of amp headroom and he'd immediately report the difference in performance.

That's the trouble with DIY. There are no standards for any facet of it. What amp, what load, what juice, what voltage, what boost curve, what limiters, what filters, what box volume, what smoothing EQ, what signal chain roll off... all a mystery.

But, one thing that isn't a mystery is this: no one in the history of DIY subs has driven a single driver system with a K10 on a dedicated 220V/50A line.

I think MKT is on to something. The US standard is 120V/15A. What would an upgrade to 120V/20A mean in terms of actual performance? 120V/30A? Can these converted amplifiers even handle that much current? 220V/16A?
post #129 of 1882
Quote:
Originally Posted by dominguez1 View Post

Thanks for chiming in Josh.

So, if I understand this correctly:

SI%20HT18%20SEAL%20CEA2010.PNG

So, at 10hz, it takes 57V to produce the 89.2 SPL output.

So, using 4ohms as the resistance (I know 4 is not exact):

P = V^2 / R

57^2 / 4 = ~812watts @ 10hz?

I'm assuming that the clone can produce this wattage at this frequency. Can an EP4000 produce this? Obviously, this wattage requirement is also a function of the size of the box...the larger the box, the less watts needed, so that throws in another variable compared to commercial score as box size can vary.

Yes.

See my post before this one.

Also, look at the max w/no THD limit. 5KW @ 10 Hz. End users have no idea what THD they're producing and don't care. They push the sub to its limits to "see what this puppy can do".

Now, look at the amp limited numbers above 30 Hz.

At 63 Hz the impedance curve shows 6.3 ohms. Josh fed the driver a noise burst tone at 283 volts. That's nearly 13,000 watts. Not a likely scenario for a DIYer because if he did have that much power available to a single SI-18, he wouldn't be able to instantaneously lower that input level at 5 Hz during movie playback and his driver would be stopped in Mexico for speeding.
post #130 of 1882
Quote:
Originally Posted by bossobass 
If he had a single LMS-U and 1-K10 on a 220V/50A line, that would require a broom and a dust pan.
......
At 63 Hz the impedance curve shows 6.3 ohms. Josh fed the driver a noise burst tone at 283 volts. That's nearly 13,000 watts. Not a likely scenario for a DIYer because if he did have that much power available to a single SI-18, he wouldn't be able to instantaneously lower that input level at 5 Hz during movie playback and his driver would be stopped in Mexico for speeding.

I chuckled when I read these. tongue.gif
post #131 of 1882
Dave is exactly right and I've been trying to explain this for awhile...Do not assume you can get the burst output levels recorded for the DIY systems full bandwidth as the power inputs ramp up dramatically as the test frequency gets higher. The commercial systems are just that a finished system that is safe. The DIY tests are more of a test of what the driver can do and to give an idea of how to utilize it in a finished system. I want the driver to be the limiting factor for those not the amp since that is the case. As Dave says having the power on tap that I do for the tests equals a time bomb of exploded drivers waiting to happen. I have to be very careful during testing or that is exactly what happens as in the case of Huskers UXL18 and a few others. So for example if you look at the SI driver test it is right at the verge of hard bottoming with a 95 volt input at 31.5Hz. Using an amp with anymore potential voltage swing than that could potentially mechanically damage the driver with the right signal so you would want to use somewhat less than that for safety. That also says nothing of long term thermal handling which depending on the signal and duration could fry the coil potentially. Though that is usually less of an issue in a HT or home audio playback system. Also the excursion relationship will change with different alignments and box sizes. When looking at the DIY systems I would suggest finding the lowest max voltage input at any frequency on the chart and use the nominal system impedance to calculate power input and match with an amp that is rated a bit under that power at least. For resonant or non sealed systems a high pass must be used to limit voltage into the system below tuning for safety and you should look at the lowest max voltage at and above tuning instead.
post #132 of 1882
Quote:
Originally Posted by bossobass View Post

That's the trouble with DIY. There are no standards for any facet of it. What amp, what load, what juice, what voltage, what boost curve, what limiters, what filters, what box volume, what smoothing EQ, what signal chain roll off... all a mystery.

As much as I love stuff like this, all of the reasons above make this type of scoring tally extremely arbitrary. Why don't we simplify since it's such a rough system as it is?

Let's make this a simpler "game" where we add up the total displacement of the drivers in the system (in ft^3) and compare that with the room's volume.

Simple as that. Since ULF (3-20Hz) is the name of the game, we don't need to worry about alignment. What one system gains at 20Hz due to a port, it loses at 10Hz because of a highpass. What the GJALLARHORN gains from 16-20Hz over the sealed LMS-5400 it loses where it's completely filtered (15Hz HPF) and it's <10Hz ULF is non-existent.

If desired, it would also be interesting to throw a third number in- external volume of system enclosures. Now we can compare how much air your system moves versus how large your room is versus how much of the room your system occupies.

Any other ideas?
post #133 of 1882
Thread Starter 
Quote:
Originally Posted by Ricci View Post

 When looking at the DIY systems I would suggest finding the lowest max voltage input at any frequency on the chart and use the nominal system impedance to calculate power input and match with an amp that is rated a bit under that power at least. For resonant or non sealed systems a high pass must be used to limit voltage into the system below tuning for safety and you should look at the lowest max voltage at and above tuning instead.

Thanks Josh and Bosso. This is great discussion.

 

So, what I attempted to do below is use the minimum power across the bandwidth, as that would be the limiting factor. I tried it with volts, but when I factored in ohms using Josh's impedance curve, the min volt actually equated to more power at some frequencies that it could handle under CEA.

 

EDIT: Changed logarithmic calculation changing chart and spreadsheet (e.g. half the power = 3db down)

 

 

 

Using 304 watts, I then ultimately calculate the new output based on using only 304 watts.

 

What this means is, during movies and music, unlike Josh's tests, we cannot control the power being fed to the sub by each frequency. Therefore, we should match an amp up that can only produce the minimum power of any frequency before going outside of CEA standards (in this case 304 watts).

 

The 304watts seems very low; mainly because of the impedance at 31.5hz being 29.7 ohms. Perhaps I'm using the impedance curve incorrectly? The watt to db conversion is logarithmic:

 

L = 10 Log(x), where L is db and (x) is the "1 - % difference ratio" in the chart above.

 

I've attached my excel spreadsheet for those interested.

 

SI Min Power Output v2.xls 28k .xls file


Edited by dominguez1 - 9/2/13 at 8:25am
post #134 of 1882
Quote:
Originally Posted by dominguez1 View Post

So, what I attempted to do below is use the minimum power across the bandwidth, as that would be the limiting factor. I tried it with volts, but when I factored in ohms using Josh's impedance curve, the min volt actually equated to more power at some frequencies that it could handle under CEA.




Using 304 watts, I then ultimately calculate the new output based on using only 304 watts.

What this means is, during movies and music, unlike Josh's tests, we cannot control the power being fed to the sub by each frequency. Therefore, we should match an amp up that can only produce the minimum power of any frequency before going outside of CEA standards (in this case 304 watts).

The 304watts seems very low; mainly because of the impedance at 31.5hz being 29.7 ohms. Perhaps I'm using the impedance curve incorrectly? SI Min Power Output v2.xls 28k .xls file
I am confused... (easily done tongue.gif lol)

Does that therefore mean that we shouldn't be powering SIs with more than 304 watts across the range because to do so would bottom the subs out at the frequency that the 304 watts occurs at, due to the amp not being able to control its power output accurately enough? Which would be half their rated power?

Or is that just in the box that Josh was testing with?

As I'm working towards a quad SI18 build in 13-15cuft in total, powered by a CV5000, am I just going to tear my cones from the surrounds as soon as I fire it up?!?


My WinISD modelling of 15cuft and no box filling suggests xmax at around 8Hz and a 'power seen by the amp' curve that drops to 600w or so at around the impedance peak, which then rises quite steeply to around 4500w at each end of a 1-200Hz X-axis (haven't got the graphs to hand on this computer) so I was hoping that with signal chain roll off and the fact that EQing and room gain should hopefully reduce bottom-end demands on the amp and drivers, all would be fine...

If the above is the case (re: 304w applied across the whole range for safety) I don't see how popalock's and carp's builds work if they're giving each driver 1000w+ RMS across their full bandwidth!
Edited by MemX - 9/2/13 at 12:02pm
post #135 of 1882
When adding so many drivers the sensitivity increases and you won't use nearly as much power. The systems I have build don't require much power at all considering the output.
post #136 of 1882
Quote:
Originally Posted by Ricci View Post

Dave is exactly right and I've been trying to explain this for awhile...Do not assume you can get the burst output levels recorded for the DIY systems full bandwidth as the power inputs ramp up dramatically as the test frequency gets higher. The commercial systems are just that a finished system that is safe. The DIY tests are more of a test of what the driver can do and to give an idea of how to utilize it in a finished system. I want the driver to be the limiting factor for those not the amp since that is the case. As Dave says having the power on tap that I do for the tests equals a time bomb of exploded drivers waiting to happen. I have to be very careful during testing or that is exactly what happens as in the case of Huskers UXL18 and a few others. So for example if you look at the SI driver test it is right at the verge of hard bottoming with a 95 volt input at 31.5Hz. Using an amp with anymore potential voltage swing than that could potentially mechanically damage the driver with the right signal so you would want to use somewhat less than that for safety. That also says nothing of long term thermal handling which depending on the signal and duration could fry the coil potentially. Though that is usually less of an issue in a HT or home audio playback system. Also the excursion relationship will change with different alignments and box sizes. When looking at the DIY systems I would suggest finding the lowest max voltage input at any frequency on the chart and use the nominal system impedance to calculate power input and match with an amp that is rated a bit under that power at least. For resonant or non sealed systems a high pass must be used to limit voltage into the system below tuning for safety and you should look at the lowest max voltage at and above tuning instead.

Josh, do you think the long term output graphs are representative of what can be expected of any system for pro sound usage where systems are abused for 10 hours or more? Will the systems handle that thermally?

I can't see the impedance graph of this -

http://www.data-bass.com/data?page=system&id=72&mset=78

Is it uploaded? Or is something wrong with my browser...

Also are you ever going to test a LAB horn? I am curious to see the numbers on this one.
post #137 of 1882
Dominguez,

Re post #138...
Amplifiers are not constant power or current devices. They operate off of constant voltage. Power and current vary wildly with frequency due to the changes in impedance of the speaker system. The voltage does not. Because of this amplifiers should really be rated by voltage and current capabilities not power. Assuming 95 volts in as a max input signal the minimum impedance is what should be looked at as this will be the heaviest current load on the amplifier. Assuming a 4 ohm nominal impedance 95 volts in results in a current of 23.75A and roughly 2250w. A far cry from 300w. So an amplifier rated at 2000w peak into 4 ohms would be getting close to the danger zone. Remember halving the power only results in 3dB less output in theory and if the system is being stretched to its limits the output is compressing and not responding in a linear manner to power increases so in actuality you may only lose 2dB with an amp of half the power if the speaker system is close to it's limits. The Cea-2010 bursts and long term sweeps are supposed to find the limits of the system which always involve compression due to thermal heating, loss of motor force, loss of suspension linearity in the driver etc...So you cannot calculate down from the maximum spl and drive levels recorded because it will not account for compression effects.
post #138 of 1882
Thread Starter 
Quote:
Originally Posted by Ricci View Post

Dominguez,

Re post #138...
Amplifiers are not constant power or current devices. They operate off of constant voltage. Power and current vary wildly with frequency due to the changes in impedance of the speaker system. The voltage does not. Because of this amplifiers should really be rated by voltage and current capabilities not power. Assuming 95 volts in as a max input signal the minimum impedance is what should be looked at as this will be the heaviest current load on the amplifier. Assuming a 4 ohm nominal impedance 95 volts in results in a current of 23.75A and roughly 2250w. A far cry from 300w. So an amplifier rated at 2000w peak into 4 ohms would be getting close to the danger zone. Remember halving the power only results in 3dB less output in theory and if the system is being stretched to its limits the output is compressing and not responding in a linear manner to power increases so in actuality you may only lose 2dB with an amp of half the power if the speaker system is close to it's limits. The Cea-2010 bursts and long term sweeps are supposed to find the limits of the system which always involve compression due to thermal heating, loss of motor force, loss of suspension linearity in the driver etc...So you cannot calculate down from the maximum spl and drive levels recorded because it will not account for compression effects.

Sorry Josh if this is 101 stuff...but hopefully others are learning with me. :)

 

If volts are constant, than wouldn't 53 (@12.5hz) volts be the max volts in to ensure all frequencies meet the CEA standard in anechoic environment? I believe you mentioned this before.

 

The power at 53v using the nominal impedance of 4 would equate to ~702 watts? 95v from 20hz on down appears from the chart that this would be too much for the driver to meet CEA?

post #139 of 1882
Refer back to my previous posts an Bosso's last couple. I am not discussing prescribing to Cea-2010 but safely matching the driver with an amplifier that will not be able to instantaneously blow the driver if the volume is excessive but will still allow maximum peak dynamic performance from it. In the cab the SI was tested in anymore than 90-95 volts input can be dangerous to the driver at some worst case frequencies.
post #140 of 1882
Thread Starter 
Quote:
Originally Posted by nfraso View Post

As much as I love stuff like this, all of the reasons above make this type of scoring tally extremely arbitrary. Why don't we simplify since it's such a rough system as it is?

Let's make this a simpler "game" where we add up the total displacement of the drivers in the system (in ft^3) and compare that with the room's volume.

Simple as that. Since ULF (3-20Hz) is the name of the game, we don't need to worry about alignment. What one system gains at 20Hz due to a port, it loses at 10Hz because of a highpass. What the GJALLARHORN gains from 16-20Hz over the sealed LMS-5400 it loses where it's completely filtered (15Hz HPF) and it's <10Hz ULF is non-existent.

If desired, it would also be interesting to throw a third number in- external volume of system enclosures. Now we can compare how much air your system moves versus how large your room is versus how much of the room your system occupies.

Any other ideas?
I'd say that if the commercial subs would list there xmax capabilities of their driver, this would get us closer...however, they typically are not readily available, and thus we do not get the complete displacement story unlike DIY.

Good idea though...let's keep the ideas coming. I think I have a good compromise in my head, but am holding off on suggesting it until we play out this DIY metric a bit more...
post #141 of 1882
Thread Starter 
Quote:
Originally Posted by Ricci View Post

Refer back to my previous posts an Bosso's last couple. I am not discussing prescribing to Cea-2010 but safely matching the driver with an amplifier that will not be able to instantaneously blow the driver if the volume is excessive but will still allow maximum peak dynamic performance from it. In the cab the SI was tested in anymore than 90-95 volts input can be dangerous to the driver at some worst case frequencies.
I think I have a good grasp of yours and Bosso's posts...in room real world content is much different than CEA...(at least I think I get it). Therefore, mating an amp just based on CEA would leave a lot on the table regarding clean output in-room potentially.

How did you determine that 90-95v was the threshold? Is there data on data-bass in your review (other than commentary) that would point this out? I'm just interested if I can use some of the data you measured in your reviews for other DIY systems and be able to calculate what this max voltage upper limit might be.
post #142 of 1882
See my posts # 136 and 142 and the SI cea-2010 chart that has been posted. The voltages are listed on the right side. Unfortunately I do not have this data short term burst voltage data for some of the older systems but I do have the voltages for the output compression sweeps so you can use that as a maximum upper ceiling before damage.

Also I am working on some sort of metric that graphs output potential per unit of external system volume.
post #143 of 1882
Thread Starter 

Quote:

Originally Posted by Ricci View Post

See my posts # 136 and 142 and the SI cea-2010 chart that has been posted. The voltages are listed on the right side. Unfortunately I do not have this data short term burst voltage data for some of the older systems but I do have the voltages for the output compression sweeps so you can use that as a maximum upper ceiling before damage.

 

Josh or anyone that has been following, let me try and clarify to see if we're on the same page. :) 

 

graph

 

Quote:

Originally Posted by Ricci View Post

So for example if you look at the SI driver test it is right at the verge of hard bottoming with a 95 volt input at 31.5Hz. Using an amp with anymore potential voltage swing than that could potentially mechanically damage the driver with the right signal so you would want to use somewhat less than that for safety. 

 

From strictly using the data in the chart above, can I arrive at this conclusion because 25hz - 50hz were all excursion limited? And since 95v was the lowest voltage, that is the limiting factor? Also, can I also conclude that the frequencies for 20hz and below, those frequencies could all handle 95v because the max (fail) voltage on the very right hand column were all greater than 95v?

 

So from a driver safety perspective, 95v would be the limit; equating to 2256 watts (probably want an amp with a little less power)?

 

Quote:

Originally Posted by Ricci View Post

When looking at the DIY systems I would suggest finding the lowest max voltage input at any frequency on the chart and use the nominal system impedance to calculate power input and match with an amp that is rated a bit under that power at least. For resonant or non sealed systems a high pass must be used to limit voltage into the system below tuning for safety and you should look at the lowest max voltage at and above tuning instead.
 

But from a CEA-2010 standpoint, 95v would be too much. Why? THD for the frequencies of 20hz and below would not meet the CEA standard as indicated in the very right hand column (pass voltage). However, CEA-2010 standards (reflected in the chart above) aren't meant for driver safety, but a THD threshold for max output.

 

So keeping our CEA-2010 lenses on, 53 volts would be the acceptable THD limit to ensure all frequencies are within the standard above? 

 

That being the case:

 

 

702 watts would be the maximum power limit as indicated from the chart above. I do understand your point about compression effects as you get closer to max output, and that backing into the max output number in theory may not yield an exact logarithmic loss (1/2 power = 3db down). However, for the purposes of this thread, I don't believe it needs to be exact, but fairly close.

 

Having said that, the right most column would represent the max output (with a margin of error) if using only 702 watts. Does this sound reasonable? Again, I'm not looking for precision here...just a 'good' enough number in my mind. To me, the numbers look reasonable.

 

SI Min Power Output v3.xls 28k .xls file

 

Quote:
Originally Posted by Ricci View Post

Also I am working on some sort of metric that graphs output potential per unit of external system volume.

^^^ Very cool. I think that would be very useful.

post #144 of 1882
Thread Starter 

So what do you guys think?

 

If it sounds reasonable, I'll go through data-bass and convert the max output numbers for all subs; adjusting the output by using the minimum voltage and power as I did above. I'll then list the power required to get that output for each DIY sub. That way you'll have an idea of what power amp you'll need to achieve this output without blowing up the driver and maintaining CEA-2010 THD standards. Again, not perfect because of box size, etc., but should be better than what we had before.

 

Again, this is not in-room output, but ground plane. It's just a reference point to compare against. By limiting the power and changing the output numbers for DIY, it will more closely resemble the commercial metric and thus more comparable as a whole.


Edited by dominguez1 - 9/4/13 at 6:06pm
post #145 of 1882
Thread Starter 

One more thing: note that this thread is about ULF. The power reduction has it most drastic impact on output beginning at 25hz and above. For this metric, those higher frequency output numbers don't really matter.

 

I just don't want folks hung up on how much it reduces output at the top end. It's really not a consideration for this thread.

 

Additionally, this thread is not about determining what amp to choose to match with your system either.

 

The power measurement is a function of the weakest link in the CEA-2010 standard for the DIY sub being measured. Any more juice than that, and the weakest link will break resulting in a fail result with that frequency because it exceeded CEA-2010 standards.

post #146 of 1882
BTW, your chart is using a fixed resistance instead of the measured impedance found on data-bass.com.
If you were to use the curve, you would see the power demands are quite different.

For example:

At the 95V bottleneck,
10.071 Hz = 1.72 kW (5.241R)
12.451 Hz = 1.58 kW (5.721R)
15.930 Hz = 1.35 kW (6.682R)
20.142 Hz = 1.06 kW (8.547R)
24.902 Hz = 668 W (13.502R)
31.494 Hz = 304 W (29.69R)


At the CEA passing voltages,
10.071 Hz = 620 W (57V, 5.241R)
12.451 Hz = 490 W (53V, 5.721R)
15.930 Hz = 503 W (58V, 6.682R)
20.142 Hz = 749 W (80V, 8.547R)
24.902 Hz = 880 W (109V, 13.502R)
31.494 Hz = 304 W (95V, 29.69R)
post #147 of 1882
Quote:
Originally Posted by dominguez1 View Post

So what do you guys think?

I think you've out excelled me...

I'll sit back while you guys work through the details. I'm fine with whatever end result comes about...
post #148 of 1882
Thread Starter 
Quote:
Originally Posted by Oliver Deplace View Post

BTW, your chart is using a fixed resistance instead of the measured impedance found on data-bass.com.
If you were to use the curve, you would see the power demands are quite different.

For example:

At the 95V bottleneck,
10.071 Hz = 1.72 kW (5.241R)
12.451 Hz = 1.58 kW (5.721R)
15.930 Hz = 1.35 kW (6.682R)
20.142 Hz = 1.06 kW (8.547R)
24.902 Hz = 668 W (13.502R)
31.494 Hz = 304 W (29.69R)


At the CEA passing voltages,
10.071 Hz = 620 W (57V, 5.241R)
12.451 Hz = 490 W (53V, 5.721R)
15.930 Hz = 503 W (58V, 6.682R)
20.142 Hz = 749 W (80V, 8.547R)
24.902 Hz = 880 W (109V, 13.502R)
31.494 Hz = 304 W (95V, 29.69R)
Josh mentioned in one of his posts that the only thing that is constant is the voltage. I interpreted this as the measured resistance and current can change depending on the amp. He suggested using the nominal impedance instead to get a better, more general baseline.

If you look back to my original chart, I did use the measured impedance, and that is when josh responded.
post #149 of 1882
That's good then, makes it a lot simpler.
post #150 of 1882
Thread Starter 

Well, I took a look at data-bass DIY subs to see if I convert them all. Unfortunately, only 7 of the DIY subs list the voltage used to obtain the max output at each frequency. 

 

However, it is notable that of the 7 DIY subs, in all cases the lowest voltage was either at the lowest frequency or the second to lowest frequency. Also, typically the average discrepancy at the low end was only 1db when using the min voltage.

 

Point being, the ULF scores would not change significantly anyway.

 

So, understanding that there is a margin of error, I recommend creating categories that are essentially ranges of ULF scores. This way, there is a margin of error built in.

 

More to come...

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