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[Aaron Montgomery]

I am building a Tuba 60 box with 2 Eminence LAB12's inside. I have the plans and am looking at amps and subs now. The LAB 12 has a 6ohm and a 4ohm option. I believe an 8 as well but not 100% sure. What i need is help with how to wire these speakers together to get the correct impedance for the amp. i was thinking the 4ohm version and a Behringer iNuke 3000 which pushes 880w at 4ohms. But I'm unsure of how to achieve this exactly. My common sense tells me to have 1 channel to each speaker. But if memory serves me right thats not correct and i need to run them in parallel to achieve 4 ohm and not 8 from the iNuke. Any help with this subject is appreciated. Have some experience with car audio subwoofers/amps but its been a long time since I've done any DIY audio period. Thanks in advance.

[Ivan Beaver]

I am building a Tuba 60 box with 2 Eminence LAB12's inside. I have the plans and am looking at amps and subs now. The LAB 12 has a 6ohm and a 4ohm option. I believe an 8 as well but not 100% sure. What i need is help with how to wire these speakers together to get the correct impedance for the amp. i was thinking the 4ohm version and a Behringer iNuke 3000 which pushes 880w at 4ohms. But I'm unsure of how to achieve this exactly. My common sense tells me to have 1 channel to each speaker. But if memory serves me right thats not correct and i need to run them in parallel to achieve 4 ohm and not 8 from the iNuke. Any help with this subject is appreciated. Have some experience with car audio subwoofers/amps but its been a long time since I've done any DIY audio period. Thanks in advance.

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[Ivan Beaver]

I am building a Tuba 60 box with 2 Eminence LAB12's inside. I have the plans and am looking at amps and subs now. The LAB 12 has a 6ohm and a 4ohm option. I believe an 8 as well but not 100% sure. What i need is help with how to wire these speakers together to get the correct impedance for the amp. i was thinking the 4ohm version and a Behringer iNuke 3000 which pushes 880w at 4ohms. But I'm unsure of how to achieve this exactly. My common sense tells me to have 1 channel to each speaker. But if memory serves me right thats not correct and i need to run them in parallel to achieve 4 ohm and not 8 from the iNuke. Any help with this subject is appreciated. Have some experience with car audio subwoofers/amps but its been a long time since I've done any DIY audio period. Thanks in advance.

Just because a loudspeaker driver has a rated impedance, DOES NOT mean that is the load that the amp sees-ESPECIALLY with horn loaded drivers.

In some cases (of extreme horn loading) the impedance the amp "sees" is actually twice that of the drivers rating.

So you might have a higher impedance than what you think.

I am not aware of the lab12 being available in different impedances-but I have not looked in years.

It also depends on how well the particular amp can deliver power into certain impedances.

The best and most surefire way is to run an amp channel per driver.

Amps LOVE higher impedances and the power supplies can deliver power longer with higher impedance loads.

[Aaron Montgomery]

Just because a loudspeaker driver has a rated impedance, DOES NOT mean that is the load that the amp sees-ESPECIALLY with horn loaded drivers.

In some cases (of extreme horn loading) the impedance the amp "sees" is actually twice that of the drivers rating.

So you might have a higher impedance than what you think.

I am not aware of the lab12 being available in different impedances-but I have not looked in years.

It also depends on how well the particular amp can deliver power into certain impedances.

The best and most surefire way is to run an amp channel per driver.

Amps LOVE higher impedances and the power supplies can deliver power longer with higher impedance loads.

After reviewing the plans i have made a change to the design. I will instead be building 2 boxes with one sub per box. Rather than the two subs in one big box. So i will in fact be using one sub per amp channel. The plans call for the 6ohm LAB12s. Stating that with the volume of the box it will draw 8ohms. So i guess my question was answered in part by reviewing the plans.

However im still a little a little un-confident with amp purchase and use. The rms wattage is 400, Max is 800. Should i be looking for an amp that is above 2x450watts @ 8 ohm and under 2x800 watts @ 8 ohm? or can it be above 800 watts/channel @ 8 ohms? would a 2x500 watts @8 ohm have to work too hard at higher volume and/or really deep bass? Also is "Program Power" a fancy word  for max wattage?

[Len Zenith Jr]

Here is an impedance plot of a dual lab12, 29" width, T60 wired in parallel:


Your plans state that you must hard limit your amplifier to 50 volts so what you need is an amplifier that can output 50 volts or slightly more to get full power from the T60. That is about 312 watts RMS into 8 ohms if you are looking at amplifier spec sheets. Also, why don't you ask these questions on the BFM forum where users that are familiar with the plans and design can help you better? Also, use the regular 6ohm Lab12, the 4 ohm version, the Lab12C has different T/S specs and won't work as well. The inuke 3000   has about a 47 volt output under load so it is OK but I'd rather get a bigger amp so that it wouldn't be ran full tilt boogie all the time, perhaps the 6000 with the built in DSP.

[Aaron Montgomery]

Here is an impedance plot of a dual lab12, 29" width, T60 wired in parallel:


Your plans state that you must hard limit your amplifier to 50 volts so what you need is an amplifier that can output 50 volts or slightly more to get full power from the T60. That is about 312 watts RMS into 8 ohms if you are looking at amplifier spec sheets. Also, why don't you ask these questions on the BFM forum where users that are familiar with the plans and design can help you better? Also, use the regular 6ohm Lab12, the 4 ohm version, the Lab12C has different T/S specs and won't work as well. The inuke 3000   has about a 47 volt output under load so it is OK but I'd rather get a bigger amp so that it wouldn't be ran full tilt boogie all the time, perhaps the 6000 with the built in DSP.

Yes, very good point on the BFM forum. lol. I will ask this there as well. Learning alot from you guys over here. Thank you for sharing you knowledge. I, in fact, not based on your voltage suggestion, but based on 8ohm wattage, have set my sights on the iNuke 6000dsp as of yesterday. But your insight to the voltage pretty much locks it down. I think its probably the best option for my budget. More than i want to spend but i also dont want to damage my LAB's. And dont want to HAVE to upgrade the amp for lack of power. I also decided to build 2 smaller Tuba 60's each with one LAB12 instead of building a dual 12 Tuba 60. According to Bill Fitzmaurice himself, 2 single T60's will sound the same as one dual 12 T60. But easier to haul around. Which is the concern i have. Any additional insight or things i should keep in mind, or change, based on the design change? Also, Limiters. Ive read a little about limiters in PA systems limiting the peak power to the sub/speaker(s) to prevent the amp from sending too much power and damaging them. Say, this iNuke 6000 that has a peak of 1600w x2 @8ohms, while LAB12 has a max of 800w, the Limiter will essentially not allow the amp to deliver more than 800w (or as much as it is set to). Similar to a Compressor or Limiter used in production (which i am more familiar with). Is this correct? And, if so, can i buy one as a standalone unit to limit any amp i get, or are they always only built in to the amps themselves? Again thank you. All of your feedback will help me whether with this project or another. Or will be passed on to someone else who needs it. I consider myself pretty highly educated in a lot of things, but a master of nothing. So, i must learn yet another subject from the masters. 

[Aaron Montgomery]

Your plans state that you must hard limit your amplifier to 50 volts so what you need is an amplifier that can output 50 volts or slightly more to get full power from the T60. That is about 312 watts RMS into 8 ohms if you are looking at amplifier spec sheets. Also, why don't you ask these questions on the BFM forum where users that are familiar with the plans and design can help you better? Also, use the regular 6ohm Lab12, the 4 ohm version, the Lab12C has different T/S specs and won't work as well. The inuke 3000   has about a 47 volt output under load so it is OK but I'd rather get a bigger amp so that it wouldn't be ran full tilt boogie all the time, perhaps the 6000 with the built in DSP.
[/quote]

Len, I also have no idea what i am looking at with your image of the impedance plot. lol. Im not sure what to look for or how to decipher it. What is the plot telling me?

[Ivan Beaver]

 Also, Limiters. Ive read a little about limiters in PA systems limiting the peak power to the sub/speaker(s) to prevent the amp from sending too much power and damaging them. Say, this iNuke 6000 that has a peak of 1600w x2 @8ohms, while LAB12 has a max of 800w, the Limiter will essentially not allow the amp to deliver more than 800w (or as much as it is set to). Similar to a Compressor or Limiter used in production (which i am more familiar with). Is this correct? And, if so, can i buy one as a standalone unit to limit any amp i get, or are they always only built in to the amps themselves?

The "issue" with limiters is that they take TIME to react.  This time can either kill the feeling of the sound or not do any good for the heating of the woofers-depending on the type of material.

I personally prefer 3 types of limiters on each channel.

One is for peaks, with a REALLY FAST ( as in 0.1ms) attack time to help limit excursion damage

Another is continuous-which is set for the continuous (not program) rating of the loudspeaker.  The attack time should be about equal to the high pass filter.  So for 50Hz that would be 20ms.

Some people will say this should be twice the highpass filter time and others will say it should be 1/2 the high pass filter time.

I have not had the time nor the budget to tear up a number of speakers with different types of program material to find out.

The most important is the heating limiter.  If you only have one limiter-then use this one.

The attack time should be around 3 seconds for subs, 2 seconds for woofers, 1 second for mids and 0.5second for HF drivers.

The voltage (NOT power-Power should be around 1/4 power) should be set around 1/2 or just over that, of the continuous (not program) rating of the driver.  I used to say 70% (half power), but have recently (due to extensive testing) changed my suggestion and lowered it.

[Len Zenith Jr]

On the impedance graph, the x-axis is frequency, the y-axis is impedance and the blue trace tells you the information. The dual T60 varies from about ~2.8 ohms - ~14 ohms impedance depending on the frequency being played. If you gain anything from that graph it should be that impedance varies with frequency. If a manufacturer says you have an 8 ohm speaker then that is just an average baseline to help you pair it with an amplifier and isn't a concrete number.

Limiters are usually part of a DSP. Whether you have a stand alone unit or it is part of an amplifier doesn't matter. If you are on a budget I would get the one built into the amplifier. You can use one channel of the amp to run both subs, the other to run your tops and the DSP to do your filtering/EQ/limiting. One amp to run the entire system is the cheapest way to get started.

"Any other insights?" Yes, I have 2 dual T60's in an install so the size isn't a problem for me. If I had to move these from place to place and store them in between I would consider something smaller. Bills T45 can do almost everything the T60 can do ... almost. You have to give up 25-30hz but those bottom 5hz DOUBLES the size of the cabinet. How bad do you want that 5hz? I work with PK Sound cabinets designed especially for EDM and even they don't bother going down that low.

[Ivan Beaver]

"Any other insights?" Yes, I have 2 dual T60's in an install so the size isn't a problem for me. If I had to move these from place to place and store them in between I would consider something smaller. Bills T45 can do almost everything the T60 can do ... almost. You have to give up 25-30hz but those bottom 5hz DOUBLES the size of the cabinet. How bad do you want that 5hz? I work with PK Sound cabinets designed especially for EDM and even they don't bother going down that low.

It really depends on the particular music and what the customer wants/needs.

5 or 10Hz down that low IS a big deal-in some cases.  In other cases, it is a waste of size and money.

When you can make the customer really smile- it is worth it.

Of course-as you note-to go lower the size has to go up.  OR the output has to go down.

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