Do voltage limits change with cabinet design?

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tvent
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Do voltage limits change with cabinet design?

#1 Post by tvent »

I limit my 3012LF loaded T39's as per the plans at 50-55v, depending on high-pass & number of cabinets I'm using.

I recently built some Simplex 12's also using 3012LF's. If using the Simplex for general PA use, should I set the limiters to the same voltage limit since it is the same driver, same voice coil, and same xmax, or does the cabinet design come in to play? (I do assume the direct radiator design of the SImplex will distort and sound bad well before I hit that limit.)

Is it complex to calculate the voltage limit of a given driver? I wouldn't mind knowing this info for my Jacks and Wedgehorns, and I think it'd be just good general info to have.
I've tried to search on this, but haven't really found a clear answer.
Any help is greatly appreciated.

Thanks,
Tim
Built:
4 x WH10 melded
4 x WH8 melded
2 x Jack15 melded
2 x Simplex 12 w/BGH-25 for Bass
1 x Simplex Tiltback (powered PPA800DSP) for Keys
2 x SLA Pro
Bought:
6 x T39 20" 3012LF loaded

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Bill Fitzmaurice
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Re: Do voltage limits change with cabinet design?

#2 Post by Bill Fitzmaurice »

Voltage limits are determined by the voice coil thermal rating or the mechanical excursion limit, whichever is lower. Mechanical excursion is different in every cab. We generally don't worry about the mechanical limits in any of the full range cabs, as you'll hear them distort long before you'll damage them. With tops you'll almost always reach the thermal rating long before the mechanical limit. All the folded horn subs have limit voltages in the plans because with those you won't hear distortion before they'll be damaged.

tvent
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Joined: Sun Sep 26, 2010 4:29 pm
Location: Helena, AR

Re: Do voltage limits change with cabinet design?

#3 Post by tvent »

Thanks for the reply Bill.

I often loan out speakers to my kid's school and leave them in the hands of whoever is there to operate them.
They have proven to be a bit less careful than I would be.

I can't remember if I had Beta's or Delta's loaded up, but the school did a pretty good job of completely disintegrating the spiders and voice coils on the pair while loaded in a pair of Jack 15's. I'm pretty sure there had to be open flames for some length of time.
Now I have finally put 3015's in the cabs, so the abuse threshold should be raised a bit, but should I invoke some sort of safety for those with no common sense? (admittedly, I realize I'M the one without common sense for continuing to loan them out - but...)

Is there a mathematical rule I want to follow or just hook it all up here at the house and set the limiters just lower than where I hear it start to distort by ear?

Thanks,
Tim
Built:
4 x WH10 melded
4 x WH8 melded
2 x Jack15 melded
2 x Simplex 12 w/BGH-25 for Bass
1 x Simplex Tiltback (powered PPA800DSP) for Keys
2 x SLA Pro
Bought:
6 x T39 20" 3012LF loaded

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Tom Smit
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Location: Sarnia, Ont. Canada

Re: Do voltage limits change with cabinet design?

#4 Post by Tom Smit »

Perhaps 5v lower than when you hear distortion.
TomS

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Bill Fitzmaurice
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Re: Do voltage limits change with cabinet design?

#5 Post by Bill Fitzmaurice »

Unless you're the one operating them limiting will do you no good, the people using them will find a way to change it. Never loan or rent out anything you won't mind getting back broken.

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BrentEvans
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Re: Do voltage limits change with cabinet design?

#6 Post by BrentEvans »

Bill Fitzmaurice wrote: Sat Oct 13, 2018 8:59 pm Unless you're the one operating them limiting will do you no good, the people using them will find a way to change it. Never loan or rent out anything you won't mind getting back broken.
Or, they’ll keep turning everything up that makes it “louder” and run the whole thing into clip for so long it burns up anyway.

If they are burning up gear, someone needs to sign a contract that guarantees payment of repair or replacement charges.

There are a very select few people who get to use my A or B rig gear without me (or one of the people on the list) being present. I can think of four people that are on that list. And I do this for a living full time. I do have a couple of systems i’ll Let out of my sight for a while. Like the bose stuff. I kind of want someone to blow that up.
99% of the time, things that aren't already being done aren't being done because they don't work. The other 1% is split evenly between fools and geniuses.

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Bill Fitzmaurice
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Re: Do voltage limits change with cabinet design?

#7 Post by Bill Fitzmaurice »

BrentEvans wrote: Sun Oct 14, 2018 10:57 am Like the bose stuff. I kind of want someone to blow that up.
:hyper: :hyper: :hyper: :hyper: :hyper: :hyper: :hyper: :hyper: :hyper: :hyper: :hyper: :hyper:

tvent
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Location: Helena, AR

Re: Do voltage limits change with cabinet design?

#8 Post by tvent »

Bill Fitzmaurice wrote: Sat Oct 13, 2018 8:59 pm Unless you're the one operating them limiting will do you no good, the people using them will find a way to change it. Never loan or rent out anything you won't mind getting back broken.
Yes, that is certainly correct. The last time I went to pick up gear there my amp's DSP had been switched to DSP OFF.
BrentEvans wrote: Sun Oct 14, 2018 10:57 am If they are burning up gear, someone needs to sign a contract that guarantees payment of repair or replacement charges.

There are a very select few people who get to use my A or B rig gear without me (or one of the people on the list) being present. Like the bose stuff. I kind of want someone to blow that up.
The school was pretty good about replacing the damaged drivers. In fact, they insisted I invoice them. I only charged them the actual cost of replacement components.
Another guy who blew a couple of drivers has "promised" to pay, but has been slow to pony up any $$ (and I was really doing him a favor.)
I'm not really in the rental side of things, but I do loan/rent (for cheap) on rare occasion.
If I'm going to continue, I guess I should get a credit card swiper and do a pre-auth until they return the gear in good shape.
BrentEvans wrote: Sun Oct 14, 2018 10:57 am Like the bose stuff. I kind of want someone to blow that up.
Yeah, that's pretty funny right there Brent (but expensive!)
I do like my little portable rechargeable-battery Bose bluetooth speaker though. It comes in handy.
The sound isolating headphones are also nice for drowning people out (and for checking rough audio levels coming from streaming services in the middle of a noisy event... helps mask the latency you'd get with traditional headphones. Not perfect, but usable.)
Built:
4 x WH10 melded
4 x WH8 melded
2 x Jack15 melded
2 x Simplex 12 w/BGH-25 for Bass
1 x Simplex Tiltback (powered PPA800DSP) for Keys
2 x SLA Pro
Bought:
6 x T39 20" 3012LF loaded

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BrentEvans
Posts: 3044
Joined: Thu Oct 09, 2008 10:38 am
Location: Salisbury, NC

Re: Do voltage limits change with cabinet design?

#9 Post by BrentEvans »

tvent wrote: Mon Oct 15, 2018 12:03 pm

Yeah, that's pretty funny right there Brent (but expensive!)
I do like my little portable rechargeable-battery Bose bluetooth speaker though. It comes in handy.
The sound isolating headphones are also nice for drowning people out (and for checking rough audio levels coming from streaming services in the middle of a noisy event... helps mask the latency you'd get with traditional headphones. Not perfect, but usable.)
You know what’s funny though, is that the stuff is very hard to damage. I’ve run it pretty hard from time time time. I have a pair of 802-iii cabs and a pair of MA12 (and a 502B that’s one of my shop system subs). They can take loads of power, way more than advertised, and when they break up, it’s so nasty no one in their right mind would keep going. I inherited all of it with a business I bought out a while back so it’s not like I paid anything close to retail for the stuff, and it always sounds great (because sound comes from the little logos on the front, you know).

It’s not what I take with me most of the time. Or really, ever.
99% of the time, things that aren't already being done aren't being done because they don't work. The other 1% is split evenly between fools and geniuses.

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Bill Fitzmaurice
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Re: Do voltage limits change with cabinet design?

#10 Post by Bill Fitzmaurice »

BrentEvans wrote: Mon Oct 15, 2018 1:58 pm when they break up, it’s so nasty no one in their right mind would keep going.
My assumption is that the responsible culprits are teenagers, which explains that. :noob:

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BrentEvans
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Re: Do voltage limits change with cabinet design?

#11 Post by BrentEvans »

Bill Fitzmaurice wrote: Mon Oct 15, 2018 2:14 pm
BrentEvans wrote: Mon Oct 15, 2018 1:58 pm when they break up, it’s so nasty no one in their right mind would keep going.
My assumption is that the responsible culprits are teenagers, which explains that. :noob:
Well... I hooked them up to my IPR7500 sub amps once to see how much they could take... they took it all until I was hard into the DDT limiters. So I guess you could say that was teenage of me to try... :chainsaw:

The 802s actually have a fuse that will pop long before the cabs are damaged or distorted. The 7500s can’t pop the fuses. It took bridged RMX5050s to do that.

The MA12s distort at about 70-80v, and the breakup sounds almost like static.

Bear in mind, these haven’t blown up yet. I only know about the limits because I was trying to see what they could handle before I sent them out of my sight.
99% of the time, things that aren't already being done aren't being done because they don't work. The other 1% is split evenly between fools and geniuses.

AcousticScience
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Re: Do voltage limits change with cabinet design?

#12 Post by AcousticScience »

To be honest a voltage limit doesn't do an awful lot for a continuous thermal situation unless it's set so low that a continuous sine wave can pass at any frequency without ever overheating the driver. This means that you don't get as much out of the cab. Voltage limits are best for making sure you don't exceed a safe driver displacement.

The only things that can damage my sound system are:
Going below the high pass on the subwoofers (the cones move like crazy tested at lower power and probably dented voice coil if I did it at high power).
Lowering the high pass on the Omnitop 12.
Also a high frequency sine wave (at ear melting levels) could damage the compression drivers with 40-70 watt power handling. Deafening levels of distorted twangy bass guitar might put more load on the compression drivers.
Other than that it can safely be blasted as loud as it will go.
I'm not sure if playing a 40Hz sine wave for several minutes would eventually overheat the subwoofers (after knocking everything off my shelves and my landlord 30m away complaining about his house vibrating)

The DDT on a Peavey IPR1600 comes in at between 40-50V (depending on impedance) and all my gear can handle this without a limiter. A larger amp I would need to limit the subwoofers. I worked out a voltage maximum on my subwoofers because I looked at the diaphragm displacement curve and kept increasing voltage in the settings until part of the curve (the middle of the pass band) exceeded Xmax.
I know in older plans the limits for a 3012lf was set to 60 Volts in a Titan 39 but has since been reduced. 60 Volts to my vented 12 subwoofers will exceed Xmax and come close to Xlim of 14mm, so the horn does reduce displacement. Bass reflex does cool a driver better than a horn chamber though.

I once bought a fried P-Audio E18-600s with a completely black coil so I would advise against buying second hand Ebay speakers. :cussing:

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