Powering your BFM rig....

[jcmbowman]

There's been some debate on this, and then the thread got locked (probably because the debate had nothing whatsoever to do with the original question...)
I'm not trying to drag out a flame war, I really want to explore this further to see what everyone else may think about this...


The biggest limitation on my T36-based system is the amount of output at the lowest frequencies. If I'm running a very demanding setup I set the HPF for the subs at 35hz. For lower-power situations I sometimes go as low as 25hz. The amount of cone excursion at 25hz when running at 100-200 watts is very close to the Xmax limitations of the driver, so even a momentary peak of 600+ watts would almost certainly destroy one or all of my sub drivers.

Admittedly, I run sound for some very demanding events. Maximum bass extension and output is critical, and when you throw in the fact that I'm generally doing sound reinforcement for a series of other DJs each of which may decide to twist that bass EQ knob on the DJ mixer all the way to +20dB at a moment's notice, a hard limiter is absolutely critical. In addition, the different tracks the DJs play may vary in bass level by as much as 30 or 40dB from track to track. Over-excursion is a real and constant danger, and it's only the appropriate usage of compression and limiting that allows me to step away from the board/amp rack for more than 30 seconds at a time without fearing that I might lose a significant chunk of change.

(As a side note, I have visually observed the cone excursion on those low notes by way of a friend's wireless infrared spy cam that we mounted inside on of the driver chambers. A 30hz sine wave at 50 Volts causes that cone to move a WHOLE LOT. That's about 200 watts into that driver in that cab. And before anyone contends that a sine wave is not indicative of a real bass note, synthesizer-generated sine waves are one of the most commonly-used bass tones used in the kinds of electronic music I do sound for. Sorry, no footage - the spy camera self-destructed before we could hit record on the feed. It only made it about 3 seconds...)

For the record, I rent a rack of iT4000s on a regular basis, and I use both the on-board thermal and peak limiters to protect my gear. The peak is set to 450 watts at 12ohms, the thermal is set to ~300 watts. If and when I have several hundred dollars to burn (that isn't already allocated to the rainy day fund, the SWMBO brownie point fund, the kid's college fund, etc...) I may take it upon myself to try running with a higher peak limiter and see what happens.

There are a lot of people out there who run their systems differently--i.e. with a good thermal limiter set to the RMS rating of the speaker, and a peak limit set to 2x or 3x that value. Most of these people, however, are running commercially built cabinets. I have yet to hear of anyone doing the same thing with BFM cabinets in the real world. Because these speakers are not rolling off an assembly line with the tolerances and QA of mass production almost all BFM boxes currently in use are unique one-of-a-kind boxes. Even if rigorous testing could be done for each of the designs to determine where exactly that line between maximum output and driver destruction is, that line would most likely be different for each individual box due to the variances in construction. Add on top of that the fact that horn-loading a driver completely changes it's response characteristics. What may be perfectly safe for a driver in a typical front-loaded direct radiator cab may not be in a horn-loaded enclosure. Regardless, we don't have those real-world testing numbers, all we have is the theory, and the person who understands the theory of these designs the best, because he's the one who invented them, has said that it's best to use a peak limiter, and to set it no higher than the RMS rating of the driver.

I guess what I'm saying is: There are all kinds of trade-offs when it comes to DIY speakers. Yes, I have access to levels of bass and sub-bass output and extension that would have cost me an arm and a leg otherwise (and weighed at LEAST 4x as much). One of the trade-offs is that I had to take the time to build them myself. If one of the other trade-offs is that I can't push them as hard as I could a commercial cab because there are no real-world numbers for where the driver failure point is, I'm Okay with that. (especially since the sensitivity more than makes up for that loss of output...) At the same time, I'm always open to any way that I can increase the output of my system without endangering my investment.


How is everyone else powering their speakers? (As in - what kind of limiting are you using, etc...)

[Landl.livesound]

Hey John,

Got to do a quick read through, but plan to read through it even more tonight.

But I would say it was a well thought-out response that addresses some things that hadn't been in the past, in the trade-offs, and trade-off in price point and performance.

And like you mention once you get down to 30hz on many of these designs it seems like the driver is going to be flapping like crazy. (reason for using an appropriate HPF on your subs.)


I would personally be more concerned on what the driver/design does within it intended bandwidth. (Say probably 40-100hz for most of the designs, where I believe the driver should not "un-load")

I do find it surprising that you mention a T36 with a 3015 will take physical damage with 600 watt split second peak, but I guess that is one of the trade-offs you mention with a bang-to-buck DIY.



As for a quick what I do, I use no limiters on my system. Tried some peak limiters that are built into cheaper DSP's but they just didn't sound that good if they would actually end up having to do something in the future, plus I realized I had no need for them since the peak voltage the amps I was using couldn't even damage the driver physically, and that I should be more worried about burning out the VC from too much average power. Which I then realized a peak limiter isn't the right tool for the job.

So I just now know where my crest factor is in the program material I am putting through it, I know where the amps I am using clip at, and then use that to figure about how much average power will be going to the driver and if it will have no problem taking it or not. So far, so good!



Sorry for the quick and dirty response and I should have more in-depth comment on tonight!


For me personally, there might not be any really reason to string this out much longer since it seems like you answered the questions I had about durability and such. So it seems like it comes down to knowing how rugged a driver it is. And that seems like a big reason why Bill pushes the very conservative peak limiter settings. Although it might be good for him to educate on why a peak limiter isn't the right tool for the job for limiting the average power going to the driver. But that's for another day!


Thanks for the info, John,

Phil

[SeisTres]

First of all - YAY! for starting a new thread with the correct topic for the discussion instead of have these discussion where they have nothing to do with the original topic and then having to search ALL over the forum to find something that we missed.

But as far as powering, I actually do nothing special. If i dont use the DRPA, then there is no limiting or compression and i just turn up the amp to where it doesnt clip which is a 300watt into 4 ohm.

If i'm using the drpa, i use the hardest limiting option available(which is still not brick wall, mind you), and then bring out the 800 watt into 4 ohm amp and try to average 15-18volts on the titans (bp102) and let the most of the peaks through to around 40-48 volts. Any more and the amp starts clipping, but anymore and the drivers would be very unhappy

[Bill Fitzmaurice]

The amount of cone excursion at 25hz when running at 100-200 watts is very close to the Xmax limitations of the driver, so even a momentary peak of 600+ watts would almost certainly destroy one or all of my sub drivers.

Not at all. When you exceed xmax the driver is in no danger of imminent destruction. Xmech is usually twice xmax, and when that's the case it takes twice the voltage/four times the power to reach xmech as xmax. However, once you reach xmax any additional power applied isn't going to give you more output, it just ends up as more heat in the motor, and if you do that for extended periods that heat will cause driver failure. That's why I recommend limiting amp output to not exceed xmax. As for the increased excursion demand at lower frequencies that's very much offset by the reduced content at those frequencies, so as long as you high pass as recommended there's no need to go more conservative with the limiting.
As for commercial gear, most commercial subs are direct radiators, and when those hit xmax you can hear it, so limiting isn't as critical as it is with folded horns that simply don't distort.

[jcmbowman]

The amount of cone excursion at 25hz when running at 100-200 watts is very close to the Xmax limitations of the driver, so even a momentary peak of 600+ watts would almost certainly destroy one or all of my sub drivers.

Not at all. When you exceed xmax the driver is in no danger of imminent destruction. Xmech is usually twice xmax, and when that's the case it takes twice the voltage/four times the power to reach xmech as xmax. However, once you reach xmax any additional power applied isn't going to give you more output, it just ends up as more heat in the motor, and if you do that for extended periods that heat will cause driver failure. That's why I recommend limiting amp output to not exceed xmax. As for the increased excursion demand at lower frequencies that's very much offset by the reduced content at those frequencies, so as long as you high pass as recommended there's no need to go more conservative with the limiting.
As for commercial gear, most commercial subs are direct radiators, and when those hit xmax you can hear it, so limiting isn't as critical as it is with folded horns that simply don't distort.

Really? Awesome! So I've been extra conservative for no reason.

The plans state to use a HPF of 35hz on the Tuba36. (with a slope of at least 24dB/octave), but that's a bit confusing since it's the section in italics that is quoted from the eminence statement regarding the Lab12/Labsub. For a 30" wide T36 with the 3015LF what would be the recommended HPF?

[SeisTres]

Really? Awesome! So I've been extra conservative for no reason.

The plans state to use a HPF of 35hz on the Tuba36. (with a slope of at least 24dB/octave), but that's a bit confusing since it's the section in italics that is quoted from the eminence statement regarding the Lab12/Labsub. For a 30" wide T36 with the 3015LF what would be the recommended HPF?

I think you might have some older plans since all the plans for prosound subs come with the recommend hpf. But for t36, it is 30hz for less than four, and 25hz for 4+.

[jcmbowman]

Really? Awesome! So I've been extra conservative for no reason.

The plans state to use a HPF of 35hz on the Tuba36. (with a slope of at least 24dB/octave), but that's a bit confusing since it's the section in italics that is quoted from the eminence statement regarding the Lab12/Labsub. For a 30" wide T36 with the 3015LF what would be the recommended HPF?

I think you might have some older plans since all the plans for prosound subs come with the recommend hpf. But for t36, it is 30hz for less than four, and 25hz for 4+.

does it state the recommended slope?

[SeisTres]

does it state the recommended slope?

Nope, no slope, but it does mention the DRPA and the Behringer one, and the DRPA only has 24db, not 48, so I'm guessing 24 is fine, and 48 if you have it.

[Bill Fitzmaurice]

does it state the recommended slope?

24dB is preferred, 18dB is OK. If your filter is only 12dB leave it at 30 Hz.

[Ron K]

HPF set at 32-35 Hz 48 db butterworth slope.

I dont ever use limiters.

I do not supply for DJs.

I always use at least 2xs the rated Continuous power for drivers sometimes 3xs depending on what types of crest factor I'm running. The genre usually will determine the crest needed. 10-24db is average.

FOH is usually delayed to the backline.

BEs are welcome to run the rig but unless I know the very well and trust them they will be monitored.

Monitor land runs a bit different.

Always a separate monitor engineer.

HPFs at 45 hz. 2xs rated power.I almost never need more then that.

No limiters and absolutely no effects in the wedges.

FWIW open vocal mic channels usually have a peak stop limiter on them but its a very conservative setting.Usually the only thing that hits them is dropping the mic and the occasional screamer.!

[Landl.livesound]

The amount of cone excursion at 25hz when running at 100-200 watts is very close to the Xmax limitations of the driver, so even a momentary peak of 600+ watts would almost certainly destroy one or all of my sub drivers.

Not at all. When you exceed xmax the driver is in no danger of imminent destruction. Xmech is usually twice xmax, and when that's the case it takes twice the voltage/four times the power to reach xmech as xmax. However, once you reach xmax any additional power applied isn't going to give you more output, it just ends up as more heat in the motor, and if you do that for extended periods that heat will cause driver failure. That's why I recommend limiting amp output to not exceed xmax. As for the increased excursion demand at lower frequencies that's very much offset by the reduced content at those frequencies, so as long as you high pass as recommended there's no need to go more conservative with the limiting.
As for commercial gear, most commercial subs are direct radiators, and when those hit xmax you can hear it, so limiting isn't as critical as it is with folded horns that simply don't distort.

Really? Awesome! So I've been extra conservative for no reason.

The plans state to use a HPF of 35hz on the Tuba36. (with a slope of at least 24dB/octave), but that's a bit confusing since it's the section in italics that is quoted from the eminence statement regarding the Lab12/Labsub. For a 30" wide T36 with the 3015LF what would be the recommended HPF?

Well, I am glad we cleared that up! I was really wondering why the 3015 was so fragile that a 600 watt peak would physically destroy it.

So, yes, John it does make sense to power the 3015 with an iTech in the 800-1000 range with no problem. Set your thermal limiter to ~350 watts like you have been and set your 4th order 35hz HPF and you should be well protected. (You can even feel free to set the peak limiter to keep the amp out of clipping if you would like)


The thing that is confusing is that the heating power is the average long term power you are putting into your subs, and that is the power that causes power compression. The super quick peaks are usually not much of a problem for a well built driver as long as those peaks aren't causing mechanical damage.

Plus those peaks many times will add to the peak SPL, which you will get more SPL out of your sub since it is just very quick peaks. Those peaks will then help add to the impact of the material being played back, and those peaks are what helps keep those dynanics of our signal in-tact.

And as Bill said though once your average signal gets deep into power compression, you won't gain much more average SPL. Again though since each driver handles power compression differently, some are better than others. But those peaks aren't the power that is heating the driver up, so I say don't cut them off, get an amp that can reproduce them, and turn up the tunes!


Take Care!
Phil

[RayAbbitt]

OK, after reading the posts in this thread (and the previous locked thread) along with a lot of previous postings covering much of the same, I've finally had to go read the I-Tech and I-Tech HD manuals because a lot of what people were saying really seemed to be repeating misconceptions. (Didn't anybody read the thread about RTFM?)

1. I-Tech's thermal limiter is NOT there to protect your speakers, it is there to protect the amplifier. It is only adjustable for percentage of max temperature OF THE AMPLIFIER. Other than that, the I-Tech has only peak and average (rms) limiters.

2. The I-Tech HD series has (in addition to the above) "transducer thermal limiting" I have a feeling this may not be as useful as it seems unless you happen to be using speakers with orange badges on them. In Crown's words:

Transducer Thermal Limiting
This limits the long-term output power of the amplifier to what the loudspeaker load can handle
without overheating and going into thermal compression. You can set the thermal level at which the
thermal limiter engages, the thermal response time and thermal voltage. Your loudspeaker
manufacturer might be able to provide this information. Meters show the amplifier output level in
dBFS; and peak, rms, and total gain reduction.

Conclusions:

1. Apparently nobody bothers to check out the manuals before they buy. And they get their specs from advertising and Guitar Center rather than checking out the real specs on the manufacturers site.

2. Anybody buying an I-Tech because of the "thermal limiter" isn't getting what they think they are unless they buy an I-Tech HD.

3. These amplifiers have lots of neat features. The I-Tech HD series is a large upgrade from the original I-Tech, but for most of us we will never use all of the capabilities of either.

Lest you think I have something against Crown, I still use CE1000 and CE2000 amps on a regular basis. If they weren't so damn heavy, I'd probably buy some more of them.

References
I-Tech Manual
I-Tech HD Manual

-ray

[Landl.livesound]

OK, after reading the posts in this thread (and the previous locked thread) along with a lot of previous postings covering much of the same, I've finally had to go read the I-Tech and I-Tech HD manuals because a lot of what people were saying really seemed to be repeating misconceptions. (Didn't anybody read the thread about RTFM?)

1. I-Tech's thermal limiter is NOT there to protect your speakers, it is there to protect the amplifier. It is only adjustable for percentage of max temperature OF THE AMPLIFIER. Other than that, the I-Tech has only peak and average (rms) limiters.

2. The I-Tech HD series has (in addition to the above) "transducer thermal limiting" I have a feeling this may not be as useful as it seems unless you happen to be using speakers with orange badges on them. In Crown's words:

Transducer Thermal Limiting
This limits the long-term output power of the amplifier to what the loudspeaker load can handle
without overheating and going into thermal compression. You can set the thermal level at which the
thermal limiter engages, the thermal response time and thermal voltage. Your loudspeaker
manufacturer might be able to provide this information. Meters show the amplifier output level in
dBFS; and peak, rms, and total gain reduction.

Conclusions:

1. Apparently nobody bothers to check out the manuals before they buy. And they get their specs from advertising and Guitar Center rather than checking out the real specs on the manufacturers site.

2. Anybody buying an I-Tech because of the "thermal limiter" isn't getting what they think they are unless they buy an I-Tech HD.

3. These amplifiers have lots of neat features. The I-Tech HD series is a large upgrade from the original I-Tech, but for most of us we will never use all of the capabilities of either.

Lest you think I have something against Crown, I still use CE1000 and CE2000 amps on a regular basis. If they weren't so damn heavy, I'd probably buy some more of them.

References
I-Tech Manual
I-Tech HD Manual

-ray

Hey Ray,
Actually what you quoted from the manual above is exactly what it is supposed to do and why it is so useful. Yes that is what the thermal limiter in the amp is built in to do. It is there for you to set to help keep the average long term voltage going to the driver below a certain level.


You quoted it right here:

"Transducer Thermal Limiting
This limits the long-term output power of the amplifier to what the loudspeaker load can handle
without overheating and going into thermal compression. You can set the thermal level at which the
thermal limiter engages, the thermal response time and thermal voltage. Your loudspeaker
manufacturer might be able to provide this information. Meters show the amplifier output level in
dBFS; and peak, rms, and total gain reduction."

That is exactly what you want a thermal limiter to do. You want it to keep you out of the point where the VC coil will heat up to the point where it gets close to failing.


And yes the original iTech's had a thermal limiter in them as well as the newer "HD" ones. (As John would be able to tell you as well as he used the thermal limiters in the non-HD iTech's.)


The iTech limiters are some of the best in the commercial pro audio world right now. And a big reason of that is because it is built into the amp and can monitor the actual long term average and peak voltage it is actually putting out. (Not like a DSP that has no feedback loop)

There are no perfect limiters right now, and probably won't ever be. The closest we get are the proprietary units with a system like Meyer and D&B that have everything set for a certain system. But the iTech limiters are one of the better choices in "outboard" limiting right now.


Myself, like Ron K, don't use limiters right now, but if I did I would want something very similar to what is built into the iTech's.


Take Care!
Phil

[ben.in.salzburg]

Are the I-tech amplifiers affordable for the weekend warrior type?

I suspect many would be put off by the cost. Thermal limiters which can control the temperature of the voice coil are entirely new to me, but sound fantastic.
If money were no option, the I-tech amplifiers look to be an excellent option.

My amps are pro, but economical, no more than 350 a piece. They have clipping protecting, low pass and thermal protection.
Therefore if I want limiting, working with a separate limiter is the only economical option for part-time sound guys like myself. And I do want limiting for when DJs get to play with my gear.

Re. Meyer sound - Are BFM designs competing with Meyer sound? I suspect they could, sound quality-wise. However, the DIY aspect may not satisfy the technical riders for larger events. I often wonder how best to go about making the BFM meet rider requirements of bands and agents... Sorry to go off on a tangent!

Ben

[Bill Fitzmaurice]

I often wonder how best to go about making the BFM meet rider requirements of bands and agents...

Your personal reputation. No one cares what you're using if you know how to use it.