Confused: Setting Limiter: How to convert volts to DBU?

[Kevin James]

I have been told I am not setting my limiter correctly if I am only converting the watts to volts and NOT converting the volts to DBU so I have a couple questions.

1. How DO you convert the volts to DBU? I was given an example but it seems I’m either missing something or looking at it totally wrong. The formula I was given is 20 log which is v/.775 = dbu, and the example I was given is and 1800 watt 8ohm cabinet which is: Square root of 1800 x 8 = 120volts, 120/.775 = 43dbu. But that doesn’t make ANY sense to me… if I divide the 120 volts by .775 I get 154… not 43. What am I missing?????

2. How would I set a limiter to a specific dbu? I know how to set to a specific voltage with a volt meter, but I haven’t got a clue how to set to a certain dbu.

Any help would be much appreciated.

[Sydney]

http://www.sengpielaudio.com/calculator-db-volt.htm
http://www.sengpielaudio.com/calculator-volt.htm



Try 20 . log (120/.7746) Instead

[Bill Fitzmaurice]

I have been told I am not setting my limiter correctly if I am only converting the watts to volts and NOT converting the volts to DBU

Not by a knowledgeable source. If you read the amps output in volts you don't need to know the dBu value.

[Kevin James]

I have been told I am not setting my limiter correctly if I am only converting the watts to volts and NOT converting the volts to DBU

Not by a knowledgeable source. If you read the amps output in volts you don't need to know the dBu value.

Yeah thats what I thought.... I mean I can use a volt meter to tell me what the voltage is coming from the amp outputs.. I don't know anything thats going to tell me what the dbu is

Thanks Bill. One more question though, you mention on DJF that the voltages are in the plans. Was that something added recently? My copy of the plans is over 2 yearsd old and I have to search for it but I'm wondering if its even in my copy since its that old.

[bgavin]

One more question though, you mention on DJF that the voltages are in the plans. Was that something added recently?

Yes

[Kevin James]

One more question though, you mention on DJF that the voltages are in the plans. Was that something added recently?

Yes

So does that mean I need to buy a new copy or is there an update peogram for people that bought plans already?

[Bill Fitzmaurice]

One more question though, you mention on DJF that the voltages are in the plans. Was that something added recently?

Yes

So does that mean I need to buy a new copy or is there an update peogram for people that bought plans already?

Got a question? Look here first!

[Kevin James]

OK sorry about that. I tried sending you a PM with the purchase date and email address the plans were sent to but the mesage is stuck in my outbox and will not actually send. Any ideas why it wont send?

[David Carter]

OK sorry about that. I tried sending you a PM with the purchase date and email address the plans were sent to but the mesage is stuck in my outbox and will not actually send. Any ideas why it wont send?

I had that same question a while back, and it turns out that it does send the message, but it shows like it's in your outbox until the recipient opens the message.

[Kevin James]

OK sorry about that. I tried sending you a PM with the purchase date and email address the plans were sent to but the mesage is stuck in my outbox and will not actually send. Any ideas why it wont send?

I had that same question a while back, and it turns out that it does send the message, but it shows like it's in your outbox until the recipient opens the message.

OK cool. Thanks for the info, it was driving me insane

Unfortunatl;y I tried resending it a couple times so now I think Bill's gonna have multiple copies in his inbox... oops... but hey thats kinda of a wierd way for the pms to work so whatever.

[Kevin James]

A few more technical questions about setting the limiter for the Tuba 36.

So I know the limiter should be set to give the driver a maximum of 60 volts. I also know that 60 volt figure comes from taking the 450 watt rating of the driver and multiplying that by the impedance of the driver which is 8ohms which gives me 3600, and then taking the square root of 3600 which is 60.

I also know that when you put the driver in a Tuba it adds 4 ohms to the over all resistance so in the case of a single driver/single cabinet you still have a 450 watt driver but the overall impedance is now 12 ohms instead of 8 ohms. What I need to know is how that difference in impedance between the raw driver and the loaded driver effects setting the limiter as well as how it effects selecting an amp.

Here are the questions I have:

1. If I am looking for an amp to drive the cabinet,(In this case I’m looking at a QSC PLX3602 in stereo mode with anywhere between 1 and 3 cabinets per channel depending on the gig size) and I want to know how many volts the amp can give it unlimited vs how many volts I need to limit it to see how much headroom I have how would I figure the volts on the amp side….. by the 8 ohm rating of the driver or the 12 ohm rating of the cab?

2. When setting the limiter do I just run a signal to the amp with no actual load plugged in and set the voltage that way with a volt meter on the outputs or would I need to actually plug a cab into the amp (which would have the cops at my door in 2 minutes flat )

3. If a load has to be plugged in can I use something like this?
http://www.parts-express.com/pe/showdet ... er=019-020
or
http://www.parts-express.com/pe/showdet ... er=019-030

[Tom Smit]

Here you go...http://www.billfitzmaurice.net/phpBB3/v ... =17&t=8709
And do it without the speakers hooked up.

[DJPhatman]

Kevin, the voltage does not change when adding loads to amp channels, except when using a series circuit. 1, 2, or 3 cabs in parallel will get 60VRMS max. The amperage goes up, not the voltage. When you series wire drivers, the voltage gets split between the drivers, meaning 2 drivers wired in series would take 120VRMS to reach their thermal limits. Ohm's Law teaches that there is a balance between load (impedance), power (volts) and draw (amperage). More load means more draw is required to maintain power level.