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WinISD question - System Input Power

5091 Views 15 Replies 10 Participants Last post by smcmillan2, Sep 10, 2019

Aural_Sex

Discussion Starter · Sep 9, 2019

I'm just getting deeper into playing with modeling tools, so I apologize if this is a silly question. I'm doing some modeling with the UM18-22 that will be paired with the NX6000D. When entering specs for testing it gives the option to change the System Input Power which, of course, has significant impacts on the model. My question is whether it is best practice to:

1. Put the RMS of the driver
2. Put the maximum/peak of the driver
3. Put the RMS of the amp
4. Put the maximum/peak of the amp

I appreciate the collective knowledge - cheers!

1 - 16 of 16 Posts

lknhomeaudio

· #2 · Sep 9, 2019

I use RMS of the driver, because I listen to a lot of heavy, long bass songs and movies.

If a person listened mostly to rock music (or similar), they could probably get away with modelling/running closer to max power of the driver.

But of course, if you are amp limited, then use RMS power of the amp.

Zarkoff500

· #3 · Sep 9, 2019

I also look at apparent amplifier power, excursion and port velocity (if appropriate) to see the bigger picture of the enclosure/driver. If sealed you can sometimes go up in power, if vented, sometimes down or down to keep port velocities in check.

noah katz

· #4 · Sep 9, 2019

Use available amp power, not driver capability, as that's determined by Pe in driver parameters.

Under the Signal option is Advanced; there you can select "SPL graph is Xmax limited" to take that into account (as an aside, that overpredicts capabilities since it assumes only a single frequency, whereas all freq of a broadband signal add to excursion).

Reactions: 1

Aural_Sex

Discussion Starter · #5 · Sep 9, 2019

lknhomeaudio said:
I use RMS of the driver, because I listen to a lot of heavy, long bass songs and movies.

If a person listened mostly to rock music (or similar), they could probably get away with modelling/running closer to max power of the driver.

But of course, if you are amp limited, then use RMS power of the amp.

That's where my head is at as well.

Zarkoff500 said:
I also look at apparent amplifier power, excursion and port velocity (if appropriate) to see the bigger picture of the enclosure/driver. If sealed you can sometimes go up in power, if vented, sometimes down or down to keep port velocities in check.

You nailed it - I'm really focusing on port velocity which is highly dependent on the power. I can get by within parameters with 1000W; however, if I go the 3000W available it blows the velocity sky high (and would toast the driver).

noah katz said:
Use available amp power, not driver capability, as that's determined by Pe in driver parameters.

Under the Signal option is Advanced; there you can select "SPL graph is Xmax limited" to take that into account (as an aside, that overpredicts capabilities since it assumes only a single frequency, whereas all freq of a broadband signal add to excursion).

If I go this route I run into the issue that this amp can deliver a helluvalot more than the driver can handle. It makes it look like velocity is at 34 m/s (3000W) instead of a manageable 20 m/s (1000w).

Sangui

· #6 · Sep 9, 2019

I'm trying to model the same driver and will be using NX6000D as well. Here are some of my thought/observation on learning the model software and from reading through other forum posts (there are so many posts to read).

I don't think the rated 3000W @4ohm is considered realistic; the actual output may be somewhere around 60% of the rating, or ~2000W @4ohm, which coincidentally lines up with the UM18's rating for 2000W peak.

The back of my NX6000D lists 120V ~ 60hz and 620W. In my experience, that data would indicate that the amp will only pull maximum ~5 amps from the outlet. (Some forum threads have people installing dedicated 20amp circuits for the amp, which I do not understand yet.) The difference between 620W input and 6000W output would presumably be met by capacitors in the amp that could help meet peak demand. If only 620W max can come into the amp, then 620W would be the RMS output as well (probably reduced further by efficiency losses).

In my winISD model, I seem to be hitting cone excursion Xmax at around 1000W input signal for lower tunes, 11-15 hz. A sealed box appears to allow 1400W input signal before hitting Xmax. My winISD models are showing more 10hz SPL output for a box tune at 12hz with 1000W input versus a sealed box with 1400W input.

winISD lets you add a high pass filter in the 'Filters' section. I'm trying 4th and 2nd order BW @ 14-17 hz, to try and mimic the recommendations in the MartySub thread. This filter prevents the excursion from blowing up at low frequencies.

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noah katz

· #7 · Sep 9, 2019

Aural_Sex said:
If I go this route I run into the issue that this amp can deliver a helluvalot more than the driver can handle. It makes it look like velocity is at 34 m/s (3000W) instead of a manageable 20 m/s (1000w).

Hmm, I haven't used WinISD in quite awhile, and don't remember if Pe puts a hard limit on how much input power is allowed.

I thought it did, but from what you say, I guess not.

lknhomeaudio

· #8 · Sep 9, 2019

noah katz said:
Hmm, I haven't used WinISD in quite awhile, and don't remember if Pe puts a hard limit on how much input power is allowed.

I thought it did, but from what you say, I guess not.

Nope. Just shows peak SPL when people use the "max spl" selection. You can enter 100,000 watts, if you want lol

aron7awol

· #9 · Sep 9, 2019

For a pairing of a UM18 and an NX6000D channel, 1200W makes sense to use because that's both what the driver can handle and roughly what the amp can output @ 4ohms. When modeling this combo, I change Pe to 1200W and Xmax to 25mm (usable excursion). Then if you use the Max SPL graph it will show you output limited to the 1200W and 25mm of excursion.

reference level

· #10 · Sep 9, 2019

Aural_Sex said:
If I go this route I run into the issue that this amp can deliver a helluvalot more than the driver can handle. It makes it look like velocity is at 34 m/s (3000W) instead of a manageable 20 m/s (1000w).

I have always input half of the max amp power (-3db) when looking at the port airspeed tab. If that says 17-22 m/s it's good enough.

My reasoning being that if you are wringing out the last n'th of performance out of your subs, any port chuffing will be masked by sheer output/distortion/clipping and stuff in the room making more noise than the port.

Obviously if you have room to make the port longer and wider, just do that. But when you get to a 40"+ long port you have to sacrifice the port resonance frequency being lower for a lower port airspeed. That isn't much of an issue if you are using a 60-80hz lpf and are never going to raise it.

As an example: Off the top of my head, I think notnyt's boxes have a 60in vent length with 107hz port resonance and he uses a 70hz lpf with no chuffing issues. Rule of thumb is that port resonance should be twice or more than the crossover frequency.

Remember that port shape, quantity, and tuning frequency all affect the air velocity that chuffing/port compression happens. One big round port with flares on both ends is the ideal shape. Slot ports that are wider than tall with no flares are the worst.

https://www.subwoofer-builder.com/flare-testing.htm

Use the full amp power for the excursion graphs.
But even the excursion may be fudged a bit too if you have a bottomless driver like the B&C's that have the spider as the limiting factor instead of clanking the voice coil on the backplate in the motor. It will not go as far past xmax as the model says.

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zeus33

· #11 · Sep 9, 2019

Sangui said:
The back of my NX6000D lists 120V ~ 60hz and 620W. In my experience, that data would indicate that the amp will only pull maximum ~5 amps from the outlet. (Some forum threads have people installing dedicated 20amp circuits for the amp, which I do not understand yet.) The difference between 620W input and 6000W output would presumably be met by capacitors in the amp that could help meet peak demand. If only 620W max can come into the amp, then 620W would be the RMS output as well (probably reduced further by efficiency losses).

Look more closely at that rating. That's at 1/8 power. Even though the Behringers are pretty efficient, they aren't 100%. Even if they were, they can't create power. They will always consume more than they put out. IIRC, they are around 90% efficient.

Power consumption @ 4 Ω,
1⁄8 rated power

Sangui

· #12 · Sep 10, 2019

zeus33 said:
Look more closely at that rating. That's at 1/8 power. Even though the Behringers are pretty efficient, they aren't 100%.

Power consumption @ 4 Ω,
1⁄8 rated power

Not sure whether you're trying to say that this amp can pull 8 * 620 watts = 4960 Watts out of a wall outlet? The most you should be able to pull out of the standard type of NEMA 5-15 wall outlet is 15A * 120 V = 1800 watts.

Transient output could be whichever number you believe is correct: the 3000 watts (mfg number), 2480w (mfg number from 620*8/2), 2000w (from martysub faq), or 1200w (from aron7; his number may be specific to using the UM18 driver).

Aural_Sex

Discussion Starter · #13 · Sep 10, 2019

The long and short that I'm getting from these responses is that there is no hard and fast rule for System Input Power - just best guess based on available power mitigated by whichever is the more capable device.

zeus33

· #14 · Sep 10, 2019

Sangui said:
Not sure whether you're trying to say that this amp can pull 8 * 620 watts = 4960 Watts out of a wall outlet?

The most you should be able to pull out of the standard type of NEMA 5-15 wall outlet is 15A * 120 V = 1800 watts.

No, I'm telling you to pay attention to what you are reading. You were implying that the amp would only pull 5 amps from the circuit. That's not true. That's not at full power.

This is not true either. If you listen to sine waves for long periods of time, then yes, a 15 amp breaker will open around 15 amps. Movies and music (except for dubstep) all have peaks. It's not a constant draw. The internal capacitors can help with burst power, but breakers can provide WAY more than their rated power for a few seconds. Look up time-current curves.

Augerhandle

· #15 · Sep 10, 2019

I modeled with cone excursion as the limiting factor. Turn up the power to hit xmax, tweak other settings, return to excursion to check that xmax is not exceeded, rinse, repeat. I then buy the amp that matches the sub's requirements.

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smcmillan2

· #16 · Sep 10, 2019

Augerhandle said:
I modeled with cone excursion as the limiting factor. Turn up the power to hit xmax, tweak other settings, return to excursion to check that xmax is not exceeded, rinse, repeat.

This is my method as well. Keeping excursion/port velocity (if applicable) in check.

Augerhandle said:
I then buy the amp that matches the sub's requirements.

Or, if amp is already in hand and full power is not required, setting a limiter based on the modelling.

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