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post #1 of 17 Old 08-06-2013, 08:47 PM - Thread Starter
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when modeling drivers in winISD, and setting up xmax, eq and cone excursion, should I be making it so that PEAK power is hitting xmax, or RMS power is hitting xmax? For example if a driver is hitting xmax at 900 W according to winISD, is that 900W rms or 900W peak? Should I be looking at apparent power, again is that peak or RMS? How exactly do I balance it properly, is there a specific strategy for setting up linkwitz transforms? What exactly happens if a driver goes past xmax?

I can model the drivers well and can design the boxes, and stuff, I just am not sure how to properly set up the EQ part of it to get it flat, and to get the most out of the low end, and to make sure it's not going to wreck the driver.
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post #2 of 17 Old 08-06-2013, 10:29 PM
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"For example if a driver is hitting xmax at 900 W according to winISD, is that 900W rms or 900W peak?"

its 900 watts.

"What exactly happens if a driver goes past xmax?"

that depends on the driver. some will have a ton of overshoot, some run out of gas just past xmax. xdamage, xdam, xlimit, xlim, are all additional measures for the point past xmax where the driver may actually start to get into trouble. sometimes a driver "hard bottoms" voice coil former hits the back plate and sometimes it "soft bottoms" which is just the soft parts being stretched really hard. neither is ideal and it really depends on the driver.

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post #3 of 17 Old 08-07-2013, 07:09 AM
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Originally Posted by WagBoss View Post

when modeling drivers in winISD, and setting up xmax, eq and cone excursion, should I be making it so that PEAK power is hitting xmax, or RMS power is hitting xmax?
RMS. Engineering always uses RMS. Peak is used by marketing departments.
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What exactly happens if a driver goes past xmax?
With more power applied you don't get more output in the lower frequencies, you do get more output in the higher frequencies, and that results in high level harmonic distortion.

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post #4 of 17 Old 08-07-2013, 07:29 AM - Thread Starter
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LTD what do you mean by that, RMS I take?

Not sure what you mean on your 2nd answer Bill, the extra power would be applied with a linkwitz transform so it would only give more power to the low frequencies, so I wouldn't get more output in higher frequencies.

Is there an advanced tutorial for setting up a linkwitz transform to make it perfect for the driver excursion, box size and amplifier power?

What I've been doing is setting a transform to basically put the driver to xmax at all frequencies below 20 hz, then checking the apparent power to make sure it's not going way over the power handling of the driver. Is this the best order to do it? I assume power handling is more forgiving than xmax, so it's better to design based on xmax?
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post #5 of 17 Old 08-07-2013, 08:15 AM
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Originally Posted by WagBoss View Post

Not sure what you mean on your 2nd answer Bill, the extra power would be applied with a linkwitz transform so it would only give more power to the low frequencies, so I wouldn't get more output in higher frequencies.
WinISD doesn't have the capability of showing what happens to output when you exceed xmax, but HornResp does. Check it out.
Linkwitz transform or not, if you hit xmax in a sealed box at, say, 30Hz at 100w, and then apply 400w, you'll get no additional output at 30Hz, while getting 6dB additional at 60Hz.

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post #6 of 17 Old 08-07-2013, 10:26 AM
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Originally Posted by WagBoss View Post

when modeling drivers in winISD, and setting up xmax, eq and cone excursion, should I be making it so that PEAK power is hitting xmax, or RMS power is hitting xmax?
RMS. Engineering always uses RMS. Peak is used by marketing departments.

Engineers understand how their tools work first....

WinISD shouldn't be labeling the input amplitude as "input power" because really, under the hood, the program is immediately converting the "power" to an RMS voltage, and then doing the calculations. If you want to know the actual power, then you need to look at the "amplifier apparent load power" which is taking into account the impedance of the resultant system.

Also, WinISD is already taking into account the conversion from RMS to Peak for the cone excursion:
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Cone excursion is calculated by first determining volume velocity through driver. Then, volume velocity is integrated, and the result is then divided by Sd to get cone excursion. Still, we need to scale result by sqrt(2) if we want to get peak value and 2·sqrt(2) if we want peak-to-peak value.
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Cone excursion shows how much driver cone moves with sinusoidal excitation at chosen powerlevel. The powerlevel is controlled in "plot"-tab. The power applied can be related to excitation voltage with following relation: Eg=sqrt(P·Re), or P=Eg²/Re where Eg is the RMS voltage applied to driver's terminals, P is the input power in watts and Re is the DC resistance of the voice coil. Please note that there is few different ways to express this value. WinISD can be configured to show RMS, Peak, Peak-to-peak (p-p) values of the cone excursion. RMS value is defined just as RMS value of any sine waveform. Peak value is the difference between zero and the maximum value of sinusoidal waveform. Peak-to-peak is twice the peak value, i.e. difference between minimum and maximum point of waveform. The peak value is perhaps a most practical expression, because driver parameter Xmax indicates how much cone can be deflected from it's rest position linearly, in either direction.

If you want to maximize power handling of any box, then adjust the box parameters so that cone excursion is kept at minimum value possible. Of course the transfer function magnitude graph should be taken into consideration also. In closed box, the minimum excursion is obtained, when enclosure is as small as possible. Same basically applies to vented box, but there is a local minimum at port tuning frequency.

When comparing graphs between programs, please note that many programs give the RMS excursion which is "wrong", in my opinion. I have seen some programs, where the calculated excursion is RMS value, and limit is shown as peak. That gives over-optimistic power handling impression. Please also note that this graph doesn't take nonlinearities into consideration. But it let's you see when the nonlinearities are becoming too great.

All of these descriptions came directly out of the WinISD help file.

Btw, the Maximum SPL plot takes into account the Power and Excursion Limits of the system - just the same as Hornresp:
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Maximum SPL graph is a combination of SPL and maximum power graphs. It tells how loud particular design is able to play, considering Xmax and Pe restrictions. If calculated power to reach Xmax is greater than Pe, then Pe is taken as input power to the driver. With this, you can easily visualize potential of particular design. Please note that it doesn't apply to room or in-car environment, what could change things quite a bit. It is useful as an comparison tool, e.g. comparing same driver in closed or vented box.
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What I've been doing is setting a transform to basically put the driver to xmax at all frequencies below 20 hz, then checking the apparent power to make sure it's not going way over the power handling of the driver. Is this the best order to do it? I assume power handling is more forgiving than xmax, so it's better to design based on xmax?

With power handling, you just turn down the volume to reduce the power....keep in mind that a 3dB change in output level (which is really quite small) will cut the power needs in half....so don't get too hung up on the power numbers.

The way I would approach your problem is take a look at the Maximum SPL plot, and you will see a line decaying at 12dB/octave starting at the point where the maximum power reaches the maximum excursion of the system....and then below that point, you will always be excursion limited.

In the excursion limited region, you can pick the lowest frequency you want reproduced, and then the maxSPL plot shows you the maximum SPL you can have with a flat frequency response. Then you would design your filter such that your frequency response is flat to that frequency, and you've now set the safe bandwidth/maxSPL tradeoff of your system. In the process, you're giving up maxSPL at the higher frequencies unless you set the gain structure of your system such that you can exceed Xmax at the lower frequencies.

Now if you wanted to minimize the solution size of your system, then you could decrease the size of the enclosure until the maximum power achieves the maximum excursion at the lowest frequency you want to reproduce...

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post #7 of 17 Old 08-07-2013, 10:32 AM
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Harmonic distortion is additional energy in the harmonics, or octaves above the fundamental. So your fundamental frequency doesn't get louder once you reach xmax but the higher frequencies do due to the increase in harmonic distortion. Distortion is simply energy that is not in the original signal and harmonic distorion is energy that appears in octaves above the frequency in the signal.

Program material is not single frequency sine waves at 0db ref. It is a complex waveform typically with no single frequency greater than say -3db from the total energy of the waveform. 3db is half the power, so if a design can take 50% of the driver's RMS without exceeding xmax is probably a safe design in that it will not exceed xmax with program material. It will also be an efficient design that can be driven to near it's full potential before cooking a voice coil.

The caveat is that most of us run more than our drivers RMS power handling because program content for movies is periodic and not continuous. You are unlikely to cook a voice coil with an amp with 2x the driver's RMS.

The ideal design is some compromise of these.
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post #8 of 17 Old 08-07-2013, 10:45 AM - Thread Starter
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Originally Posted by nograveconcern View Post

Harmonic distortion is additional energy in the harmonics, or octaves above the fundamental. So your fundamental frequency doesn't get louder once you reach xmax but the higher frequencies do due to the increase in harmonic distortion. Distortion is simply energy that is not in the original signal and harmonic distorion is energy that appears in octaves above the frequency in the signal.

Program material is not single frequency sine waves at 0db ref. It is a complex waveform typically with no single frequency greater than say -3db from the total energy of the waveform. 3db is half the power, so if a design can take 50% of the driver's RMS without exceeding xmax is probably a safe design in that it will not exceed xmax with program material. It will also be an efficient design that can be driven to near it's full potential before cooking a voice coil.

The caveat is that most of us run more than our drivers RMS power handling because program content for movies is periodic and not continuous. You are unlikely to cook a voice coil with an amp with 2x the driver's RMS.

The ideal design is some compromise of these.

When designing though, do you look at the apparent power or the input signal power? My signal input could be 600 watts but after doing a L/T everything below 20 hz is 1200 watts.
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post #9 of 17 Old 08-07-2013, 10:50 AM
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Always use apparent power for determining thermal limits.

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post #10 of 17 Old 08-07-2013, 10:55 AM - Thread Starter
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What about for excursion limits?
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post #11 of 17 Old 08-07-2013, 11:25 AM
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op, be sure that you understand what mike said in post #6 as that is pretty key to understanding what exactly is going on with respect to "power".

"Always use apparent power for determining thermal limits."

that would be right if that is what the manufacturers did for testing the subs. unfortunately, there is no standard and it is really all over the map with most of them providing some sort of rough range of power suitability. if they just tested the driver at the impedance minimum with a known test signal for a known duration that would help a lot and is what many pro audio companies do.

"What about for excursion limits?"

what is your question (beyond the obvious answer "look at the excursion tab in winisd")?

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post #12 of 17 Old 08-07-2013, 11:28 AM
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"When designing though, do you look at the apparent power or the input signal power? My signal input could be 600 watts but after doing a L/T everything below 20 hz is 1200 watts."

right. that is because equalization is not "free power". when you increase the signal, you increase the power. the maximum equalization that you can put on a system is limited by the amplifier output power. one way to see this is to create a winisd file for your driver and enclosure and set the input power at whatever your amp is rated for. then create a second file which has your equalization applied. no matter how much equalization you apply to the second file, it can never exceed the limit of the first one.

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post #13 of 17 Old 08-07-2013, 11:31 AM - Thread Starter
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I'm not worried about thermal limits. I'm just trying to figure out how much of a L/T I can put on the 20 hz and below of a sealed subwoofer without bottoming it out.
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post #14 of 17 Old 08-07-2013, 12:21 PM
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Quote:
Originally Posted by WagBoss View Post

What about for excursion limits?

This is where the MaxSPL plot will help you out....it basically tells you what the maximum SPL is for each frequency - which is usually limited by excursion at the lowest frequencies (unless your enclosure is crazy small).

Maybe it'd help to put it in step form:
  1. Pick the bandwidth you want from the system.
  2. Go to the MaxSPL chart and find the lowest point within that bandwidth. Draw a horizontal line (or just remember the SPL number).
  3. Go to the SPL chart and modify the input power until the highest part of your passband matches the lowest point in the MaxSPL chart.
  4. Modify your filter until your filter shape fits within the MaxSPL limits (you may need to adjust your input power since you'll be boosting at some frequencies)
  5. After this is completed, the Apparent Power will tell you how much amplifier you need, and the Excursion chart shows you how things approach the limit.

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post #15 of 17 Old 08-07-2013, 12:33 PM
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I'm just trying to figure out how much of a L/T I can put on the 20 hz and below of a sealed subwoofer without bottoming it out.
Just what the chart shows. if it's 600 watts, it's 600 watts. If you take 600 watts and add 6dB of EQ boost it isn't 600 watts anymore, it's 2400 watts, and you've probably toasted your driver, or amp, or both. There's nothing magic about L/T, the driver can only give what its xmax will allow. If that's not enough you need to add another cab, or go vented.

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post #16 of 17 Old 08-07-2013, 02:32 PM - Thread Starter
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Originally Posted by MBentz View Post

This is where the MaxSPL plot will help you out....it basically tells you what the maximum SPL is for each frequency - which is usually limited by excursion at the lowest frequencies (unless your enclosure is crazy small).

Maybe it'd help to put it in step form:
  1. Pick the bandwidth you want from the system.
  2. Go to the MaxSPL chart and find the lowest point within that bandwidth. Draw a horizontal line (or just remember the SPL number).
  3. Go to the SPL chart and modify the input power until the highest part of your passband matches the lowest point in the MaxSPL chart.
  4. Modify your filter until your filter shape fits within the MaxSPL limits (you may need to adjust your input power since you'll be boosting at some frequencies)
  5. After this is completed, the Apparent Power will tell you how much amplifier you need, and the Excursion chart shows you how things approach the limit.

Thanks, that's exactly what I was looking for. I guess what would be best when actually EQ'ing a sub would be to measure and then make sure the EQ curve that REW sets will not put it over power or excursion. Then I could implement an L/T until it hits max excursion if it already isn't in the lower freqs.
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post #17 of 17 Old 08-07-2013, 03:13 PM
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Then I could implement an L/T until it hits max excursion if it already isn't in the lower freqs.
Or don't bother with it at all. WinISD shows half space anechoic, and between boundary loading and cabin gain most subs will correct in-room to flat with just EQ. L/T is mainly useful if you actually only have half-space loading, no cabin gain, and you don't have EQ.

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