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Author Topic: Lab Sub handling  (Read 18030 times)

Keith Broughton

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Re: Lab Sub handling
« Reply #10 on: November 16, 2013, 08:52:01 am »

Most class D amps would LOVE to be able to produce sine waves for a couple of seconds.  If you look at the specs-you will see full power for "typically" 0.08 seconds  (80ms) before dropping down..
Something good to be said about the old Crown VZ5000 "welders"  ;)
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Art Welter

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Re: Lab Sub handling
« Reply #11 on: November 16, 2013, 02:28:37 pm »

What voltage would xmax be at 30hz?
20hz?
10hz?

I don't think the class d amps with pwm power supplies can provide full power at lower frequencies for more than a few seconds at a time into very low impedances without voltage being time-limited and dropping to a fraction of that rated power with test signals or some dub step synth tone.
Xmax of the Lab 12 is 13mm regardless of frequency.
The voltage required to reach Xmax varies with frequency as you can see in the simulation in post # 3.
I wouldn't put huge faith in the excursion sim below Fc (around 40 Hz) but at 10-20 Hz looks like 46 volts or so would hit Xmax, around 44 at 30, and only 30 or so at 35 Hz.

The SpeakerPower class D amps can deliver full power for around 4 seconds.
The SP1-4000 (4000W/2 ohm, 2400W/4, 1300W/8) weighs only 7 lbs.
It is a nice choice for a pair of Lab 12 (one LabHorn), and will handle four Lab 12, though at that low of an impedance (near 1 ohm at the impedance minima) the breaker will trip with extended full power LF.
It does have plenty of power to smoke the Labs if sine wave type material is played.
Even with pink noise, the SP1-4000 just below clip/limit will induce a couple dB of thermal compression in the Lab 12.
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Benjamin Goulart

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Re: Lab Sub handling
« Reply #12 on: November 19, 2013, 06:22:56 am »

Xmax of the Lab 12 is 13mm regardless of frequency.
The voltage required to reach Xmax varies with frequency as you can see in the simulation in post # 3.
I wouldn't put huge faith in the excursion sim below Fc (around 40 Hz) but at 10-20 Hz looks like 46 volts or so would hit Xmax, around 44 at 30, and only 30 or so at 35 Hz.


So you think the excursion is probably more below 30hz than the simulation is predicting? 

I was not expecting that sudden peak in excursion at 34hz.  Is that normal for a driver in a horn?
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Art Welter

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Re: Lab Sub handling
« Reply #13 on: November 19, 2013, 11:24:28 am »

So you think the excursion is probably more below 30hz than the simulation is predicting? 

I was not expecting that sudden peak in excursion at 34hz.  Is that normal for a driver in a horn?
The excursion is probably less below 30Hz than the sim, both the small chamber and the Lab 12 suspension are putting the "brakes" on excursion.
FLH typically have the greatest excursion around Fc, so yes, normal, but again, may be a bit exaggerated.
That said, the sim may be a few Hz high from what I recall the measured low corner of the LabHorn is.

Hornresp is a great predictive software (really great considering it is free- thanks David McBean!) but the dips and peaks in impedance, frequency response, and excursion are all a bit sharper than in real speakers.

Of course, short of putting a little video camera in the throat or a Lexan window and measuring excursion, about all you have for to go on for FLH  ;).

Art
« Last Edit: November 19, 2013, 11:33:07 am by Art Welter »
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Benjamin Goulart

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Re: Lab Sub handling
« Reply #14 on: November 19, 2013, 12:31:00 pm »

So then, the greatest xmax points would be around 35hz and 60hz?  I heard below the Fc the Lab12 drivers behave like in free air.  And I always thought xmax skyrocketed in the deep bass on all woofers if allowed to.

Does the xmax graph matter that it's RMS voltage?  If I'm using this to set limiters in the amp's DSP, should I be using sqrt 2 * RMSvolts?  If I do that, 58.5 Vrms (the predicted xmax it looks like for 60hz, assuming 1.3 * 10mm =13mm and 1.3 * 45V = 58.5V is correct methodology) comes out to about 82V peak value... which is exactly the maximum default stereo output of my nu3000 DSP's hard cap (82Vp).  And since they are current-limited to only a few seconds at low impedances & low frequencies with sine-wave-like signals, maybe I don't even need a lower limited voltage for thermal reasons... assuming I have a 48dB Butterworth at 35hz, which will halve the average voltage the Labhorns see at 35hz with program content (-3dB at the corner freq, and assuming half the voltage actually halves the excursion), right?  A 35hz test signal cranked way the hell up could still exceed xmax if the gain compensated for the filters, but assuming I or no one else do that, are these rational limits?

[Edit: I misspoke about the -3dB corner freq halving the voltage.  -6dB would halve the voltage.  Linkwitz-Riley or a parametric would do the trick.]

I've run the pair in stereo this way a few times (assumed the amps were underpowered from prior Labhorn user posts everywhere), with or without parametric EQ to flatten it, and even tried the Dynamic EQ to further reduce the lowest range when it's very cranked.  DEG: -15dB, 30 or 35hz, LP12, 1:10, and a variety of threshold settings.  I think the Dynamic EQ thing did make it sound cleaner at loud volumes and gave me peace of mind.  But if you're right about below 30hz not really being the worst xmax range, then it may have only sounded cleaner because the room was shaking a little less or there was more available power (or power supply swing) for the rest of the range.   I'm mostly worried about using these in a live situation either with bands or with crazy-ass live dubstep producers having use of my system.  I'm wondering what the proper safety voltage limit is per sub in such situations.

[Edit: Mechanical safety concerns would be xlim, which doesn't account for overheating.  But xmax is the linear excursion range that sounds good before nonlinearity sets in.  55Vrms produces xlim at 35hz according to the graph, or 77.8V peak, if a lone single-band signal made it through.  The below 45Vp calculation is the xmax voltage limit at 35hz.]

And I was also curious when I do have these plugged in at home, what voltage limit is safe to use when having no HPF on it at all... or if that's even safe at any voltage.  If the graphs are either correct or conservative, and my math is right above, wouldn't that mean a Labhorn could handle about 45Vp ((from 13mm/18mm)*45Vrms * sqrt 2) without any filters and not be at too much threat of getting damaged?

So maybe if I'm using them unfiltered at home, or letting a band or young synth head play through them,  then 45Vp limiting is safe.  But if I'm babysitting them the whole time or DJing through them, then the default 82Vp hard limit is alright per Labhorn?  You mentioned some Crests incidentally prevent thermal limits, which I assume is also due to the Class D amp design & switching/PWM power supply.

[Edit: Meant Crown here, not Crest.]

If my thinking/math or whatever is wrong, please let me know.  Assuming halving the voltage linearly halves the excursion compared to the graphs is a pretty big assumption, not to mention this live PA thing is very new territory for me. 

Oh, and thanks for everyone's input so far.

The excursion is probably less below 30Hz than the sim, both the small chamber and the Lab 12 suspension are putting the "brakes" on excursion.
FLH typically have the greatest excursion around Fc, so yes, normal, but again, may be a bit exaggerated.
That said, the sim may be a few Hz high from what I recall the measured low corner of the LabHorn is.

Hornresp is a great predictive software (really great considering it is free- thanks David McBean!) but the dips and peaks in impedance, frequency response, and excursion are all a bit sharper than in real speakers.

Of course, short of putting a little video camera in the throat or a Lexan window and measuring excursion, about all you have for to go on for FLH  ;).

Art
« Last Edit: December 11, 2013, 09:27:17 am by Benjamin Goulart »
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Art Welter

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Re: Lab Sub handling
« Reply #15 on: November 20, 2013, 09:47:26 am »

1)So then, the greatest xmax points would be around 35hz and 60hz?
 
2)I heard below the Fc the Lab12 drivers behave like in free air.  And I always thought xmax skyrocketed in the deep bass on all woofers if allowed to.

3)Does the xmax graph matter that it's RMS voltage?  If I'm using this to set limiters in the amp's DSP, should I be using sqrt 2 * RMSvolts?   A 35hz test signal cranked way the hell up could still exceed xmax if the gain compensated for the filters, but assuming I or no one else do that, are these rational limits?

3)I'm mostly worried about using these in a live situation either with bands or with crazy-ass live dubstep producers having use of my system.  I'm wondering what the proper safety voltage limit is per sub in such situations.

4) If the graphs are either correct or conservative, and my math is right above, wouldn't that mean a Labhorn could handle about 45Vp ((from 13mm/18mm)*45Vrms * sqrt 2) without any filters and not be at too much threat of getting damaged?

5)But if I'm babysitting them the whole time or DJing through them, then the default 82Vp hard limit is alright per Labhorn? 

6)You mentioned some Crests incidentally prevent thermal limits, which I assume is also due to the Class D amp design & switching/PWM power supply.

7)Assuming halving the voltage linearly halves the excursion compared to the graphs is a pretty big assumption, not to mention this live PA thing is very new territory for me. 

1) The Lab 12 Xmax is 13 mm, excursion vs.voltage is greatest  near 35 Hz and around 60 Hz.
The simulation shows what excursion will be for a given voltage, the voltage could be continuous, as in a sine wave, or peak, as in a kick drum or a dropped microphone.

2) Below Fc the output of the LabHorn is similar to Lab 12 speakers in a small sealed cabinet, free air the drivers don't do squat. Given the same voltage, excursion goes up as frequency goes down in a normal sealed box, but the LabHorn is a sealed compression chamber coupled to a horn with a long air column, different from a sealed  or bass reflex box.

3) The safe continuous sine wave voltage is 30, safe peak voltage around 60, depending on frequency.

4) Yes.

5) Depends on the average signal level, 82v peak limiting would not limit a continuous 40v sine wave, which could burn the coils. That said, I don't know if your amp could deliver 30-40 volts for a long enough duration to burn the Lab 12s.

6) That does not make sense, and I have not mentioned Crest amps in this thread.

7) Halving the voltage will halve the excursion at any given frequency, but excursion is not linear with voltage input across the frequency range of the LabHorn.

When the excursion exceeds Xmax, the speakers start to distort. 60 Hz tones will put out 120 Hz (second harmonic), 180Hz (third harmonic) etc. 35 Hz will have harmonics at 70, 105, 140 Hz etc.
Second harmonic distortion is generally highest, but because it is an octave higher, is not all that easy to detect, as octaves sound the same- 40 Hz is the low "E" on a four string bass, 80 Hz the low E on a guitar.

Push the subs hard around 60 Hz with no tops to mask the harmonics and you will become familiar with the sound of distortion, and how loud the subs get before distorting. Use a dB meter (or better, an RTA and a dB meter) and you will become familiar with how loud the subs get before they hit excursion and thermal limits.

Unless you have separate peak and RMS limiters, listening for signs of distress, and backing off level when you hear it is the best way to protect your speakers.

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Benjamin Goulart

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Re: Lab Sub handling
« Reply #16 on: November 20, 2013, 12:13:28 pm »

Sorry, meant Crown class D amps, not Crest.  Reading too much stuff about Crest and the guy who sold me the Labhorns recommending them, I think.  Given how many times I re-edited that post for grammar and such, I'm annoyed I didn't catch that!


6) That does not make sense, and I have not mentioned Crest amps in this thread.

When I said 82Vp would be with me babysitting it, I meant going out of my way not to send test signals and trying to not intentionally push them to the limit.  That would also be with pre-recorded & mastered music, not live dub step producers or live bands.  The latter ones worry me.

From what I can tell, while excursion is not linear across frequency, it is linear at a given frequency as voltage varies up to xmax.  Readings I did last night on the subject seemed to indicate that's the whole point of xmax -- the limit where excursion of the driver is no longer linear with voltage at a given frequency, hence distortion increases.  And then xlim is the point at which it fails; xmech being xlim * 2.  So that makes sense.

By the way, your 30Vrms recommendation for maximum safe sine waves (and I assume live bands and live dub step producer wizards)... is that with HPF or without?

Finally, where are you getting 30Vrms and 60Vp?  30 * sqrt 2 = 42.  Is the conversion for a sine wave different than the formula on Wikipedia or something else I'm missing?  Or are you just considering thermal limits?  Are my excursion calculations wrong when figuring the maximum safe voltage limit of 45Vp WITHOUT a HPF?
« Last Edit: November 20, 2013, 12:22:40 pm by Benjamin Goulart »
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Art Welter

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Re: Lab Sub handling
« Reply #17 on: November 21, 2013, 10:50:39 am »

1)And then xlim is the point at which it fails; xmech being xlim * 2.  So that makes sense.

2)By the way, your 30Vrms recommendation for maximum safe sine waves (and I assume live bands and live dub step producer wizards)... is that with HPF or without?

3)Finally, where are you getting 30Vrms and 60Vp?  30 * sqrt 2 = 42.  Is the conversion for a sine wave different than the formula on Wikipedia or something else I'm missing?  Or are you just considering thermal limits?  Are my excursion calculations wrong when figuring the maximum safe voltage limit of 45Vp WITHOUT a HPF?
1) Xlim and Xmech are two terms for the same thing, the excursion limit where damage will occur if exceeded.
Xlim may be around double  Xmax (the Lab 12 has an Xmax of 13mm and Xlim of 22mm) or more, or less- there are some speakers with Xmax of 8mm that the coil will hit the back plate and be destroyed at only 12mm Xlim. A B&C 18TBW100 has an Xmax of 12 mm(Xvar of 14) and Xlim of 28.5.

2) At 30v the speaker won't run in to thermal or excursion limits. With a slow time constant the RMS limiter could allow peaks through that could exceed Xlim, so use of a HPF is still advisable.

3) EIA 426 compressed pink noise has a crest factor of 6 dB, twice the average power of "normal" pink noise, sine waves 3 dB, twice the average power of the EIA 426, so the pair of Lab 12s take 400 watts sine wave, 800 watts EIA 426, and 1600 watts peak, double  EIA 426, called  "music program" on the spec sheet.
I picked an impedance of 2.25 ohms (the approximate impedance minima) for a pair for my calculation.
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Benjamin Goulart

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Re: Lab Sub handling
« Reply #18 on: November 21, 2013, 11:56:28 am »

1) Xlim and Xmech are two terms for the same thing, the excursion limit where damage will occur if exceeded.
Xlim may be around double  Xmax (the Lab 12 has an Xmax of 13mm and Xlim of 22mm) or more, or less- there are some speakers with Xmax of 8mm that the coil will hit the back plate and be destroyed at only 12mm Xlim. A B&C 18TBW100 has an Xmax of 12 mm(Xvar of 14) and Xlim of 28.5.

2) At 30v the speaker won't run in to thermal or excursion limits. With a slow time constant the RMS limiter could allow peaks through that could exceed Xlim, so use of a HPF is still advisable.

3) EIA 426 compressed pink noise has a crest factor of 6 dB, twice the average power of "normal" pink noise, sine waves 3 dB, twice the average power of the EIA 426, so the pair of Lab 12s take 400 watts sine wave, 800 watts EIA 426, and 1600 watts peak, double  EIA 426, called  "music program" on the spec sheet.
I picked an impedance of 2.25 ohms (the approximate impedance minima) for a pair for my calculation.

Isn't a limiter that you set max voltage in Vp going to limit peaks?

The nu 3000 DSP in stereo mode is already hard capped out and limited at 82Vp or so, which is just under 1700 Watts peak at 2 ohms.  So isn't that an appropriate default setting to use if the HPF is on and I'm only playing properly mastered music myself (no live bands or live synth producers)? 

I also use the parametric EQ which is reducing at 35hz (little bleed off below that), boosting at that 45hz-ish dip, few more slight dips and boosts, dip at 90-something, and then boost a little higher up so that the 90hz EQ isn't reducing the filter corner frequency range at 120hz.

Here's what the standalone Behringer software looks like.  You can mess with it even if the amp isn't hooked up.

http://www.behringerdownload.de/iNuke/iNuke_Remote_Connect_V01-1.zip

What Vp setting would you use if there was no HPF and they were just reproducing a movie through them when they're not out?
« Last Edit: November 21, 2013, 12:08:54 pm by Benjamin Goulart »
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Ivan Beaver

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Re: Lab Sub handling
« Reply #19 on: November 21, 2013, 12:04:04 pm »

Isn't a limiter that you set max voltage in Vp going to limit peaks?

H
THere are a number of different limiters-for different purposes.

A peak limiter is a fast attack limiter that stops/reduces mechanical damage (over excursion), a heat limiter (or other names) is a slow attack for long term heating.

A RMS or music limiter is more of an "average" limiter that is between the others.  Its voltage is between them and the attack time is between them.

ANd then there are other that use side chain limiting for different limits at different freq and so forth.

There is no "one size fits all"

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