Ohms & Watts

[javj2007]

I want to hook up a monitor system. just wondering if this will work ok. I have a amp thats Servo-260 130 watts @ 4 Ohms per side. And 2 12" monitor speakers that are 8 Ohms 65 watts each daisy chained together. Couple of questions. 1st - Is it going to work, if I just use 1 side of amp in mono for both speakers ? Will I lose any Watts because there are daisy chained together? 2nd - Is the amp to big? Should I get Servo-170 model delivers 85 watts (into 4 ohms) of power per side ??? Any thought on this would help alot.
Thanks

[pdf64]

It depends on how sure you are that feedback can be well controlled - a prolonged burst could blow the speaker/s on the amp you've got whichever way you connect them.
Guess it will do ~70W@8ohm, which may be 100W when overdriven with feedback.
Pete

[Mark Black]

Judging by the wattages mentioned I would guess this would be a studio monitor application?

And by "daisy chained" means the speakers are plugged from one to the next and then to the amp, making them paralleled rather than series-wired?

The two paralleled speakers on one side of the amp should be a fine match, resulting in a total load of 4 ohms (8 + 8 in parallel), and a total wattage capacity of 130W (65 + 65).

It is common practice in a studio environment to use a larger-than-needed amp for better transient response, so no - I would not think the amp is too big.

If the speakers are series-wired and/or we're talking about stage monitors that's a whole different perspective...

[bob p]

Help me out -- I don't understand the connection between amplifier power and transient response. I thought transient response was measured by slew rate and rise time, and not by power output.

[defaced]

Don't want the transients to clip.

[eschertron]

I want to hook up a monitor system. just wondering if this will work ok. I have a amp thats Servo-260 130 watts @ 4 Ohms per side. And 2 12" monitor speakers that are 8 Ohms 65 watts each daisy chained together. Couple of questions. 1st - Is it going to work, if I just use 1 side of amp in mono for both speakers ? Will I lose any Watts because there are daisy chained together? 2nd - Is the amp to big? Should I get Servo-170 model delivers 85 watts (into 4 ohms) of power per side ??? Any thought on this would help alot.
Thanks

Just so I have this straight - from reading your other threads - you have a concert monitor system: board, amp, and speakers that you want the singer and guitar player to use during performance (a good practice rig by itself) so they can hear the vocals. Am I right so far? Are you planning to put guitar signal through the monitor? How much?

For vocals only, I'd say your system as described should be fine. And I'm guessing that the power amp has volume knobs that allow you to set *less than full* power when you choose. I say that because it's important to optimize the signal chain from front to back, please don't make the mistake of turning the amp all the way up and depend on the mixing board channels to keep the volume controlled. It's too easy for a mistake to be made that results in serious damage to the equipment (and possibly your hearing!). Get a decent signal on each channel and then push the faders up to the "zero" line (the nominal reference line for 100% signal) on both the channels that you're using and what ever aux send faders/knobs that you have. Then carefully adjust the amp's volume for what you want to hear. You can always tweak later, as you go, but start from a known safe position.

If you are putting anything other than vocals through the monitors you might be pushing the limits of the speakers - that is, if you ever get to the point where you've turned the amp's controls all the way up. Mark Black's comment about transient response should be understood to mean that an amp rated at 130W can put out much MORE from brief periods of time. In a live setting, those transients are usually the result of dropping a mike, having a cord yanked out of a guitar, etc etc that can result in screeching distortion and way more power than you want going through your speakers (and ears!). Keeping the controls on the amp as low as you can will help minimize the effects of these unplanned transient spikes.

Good Luck!

[javj2007]

Thanks all of you guys for the awesome feedback on this. Learned alot & again
Thk you

[Mark Black]

Glad to hear you are feeling better about things. Some decent pertinent reading:

JBL :: Technical Library

http://www.rane.com/pdf/ranenotes/Se...l_Controls.pdf

[bob p]

i've got an interesting little story to hijack with about the JBL technical note that Mark referenced above. Back in around 1983 I bought a pair of JBL L96 bookshelf speakers when I moved into my first apartment. I remember paying $700 for them. One of the documents that was included in the speakers' boxes was the JBL technical note entitled, "Danger: Low Power." It's the same note that's linked above.

The speakers also came with a warranty manual that can still be found on-line. The warranty card said that only low power could damage the speakers, and that JBL speakers were not given a power rating because they could handle any amount of clean power. Evidently, the guys at JBL who wrote that were still living in the old-world of relatively low-powered tube amps and transistor amps, because new electronics were coming onto the scene that had HUGE amounts of power -- enough to incinerate many speakers. That's right, I said incineration -- more on that later.

The next step in satisfying my GAS for audio gear was to replace my 60W Sherwood receiver with a Carver M-1.5t amplifier that could put out 350W RMS per channel into 8 ohms, 600W per channel of "musical program power," or 1.2 kilowatts of peak power for transients. Remember that JBL claimed that low power was the real danger to my speakers, and that my L96 didn't have a maximum power rating because the speakers could handle any amount of clean power...

The Carver M-1.5t proved them wrong. I was playing the following Telarc CD when things went bad:

Everything went fine until the finale of the 1812 Overture, which included HiFi digital reproductions of live cannon blasts. During the performance I heard what sounded like a gunshot, I smelled smoke, and as I turned around to see what had happened, I saw flames beginning to consume my LE10H-1 woofer. I have to give JBL credit for one thing -- the sensory reproduction was real -- I heard what sounded like a gunshot, I smelled smoke, and flames shot out of my woofer. Unfortunately, the JBL speakers were only able to reproduce the program material one time.

Naturally, I filed a warranty claim with JBL, who then refused to provide a warranty recone for the driver under their 5-year warranty program. They claimed that I had abused the speaker. I responded that I had operated within the exact recommendations that they provided in the speaker's documentation: In order to judiciously avoid clipping I had bought an amp with more clean power than I would ever need; the amp even had a clip-detection and limiting circuit built-in so that it would never send a clipped signal to the speaker. I also pointed out that JBL's warranty documentation stated that the speaker didn't have a power rating because it could handle any amount of clean power. I proposed that my driver had to be defective in materials or workmanship because it failed to meet their claimed performance standard related to unlimited clean power handling ability.

The first generation of Carver amps were new on the scene in the 1980s, and they brought obscene amounts of power to the marketplace and a reasonable cost, at a time when speaker manufacturers weren't used to their speakers being powered by amps that had that kind of power on-tap.

To make a long story short, JBL refused the warranty repair and wouldn't even return the driver. From what I could tell, the warranty department passed the driver along to some other department for forensic examination, and the driver had became lost in the process. So not only had I lost a functioning cone and voice coil, I had lost the re-conable basket as well. I had to gripe and moan for over two years, enduring personnel changes along the way, to get my driver returned. JBL refused to return the driver claiming that they didn't have it. I had shipping records and signed delivery confirmation proving that they had received it, and they had no documentation that the driver had ever been shipped back to me. They refused to return the driver until they had performed an exhaustive records search to confirm that they had no documentation that the driver had ever been returned to me. It was obvious that they hoped to drag things on long enough that I would grow weary and give up the fight. I didn't. Eventually they conceded that they could not prove that the driver had ever been returned, so they finally caved-in and sent me a brand-new LE10H-1 driver to replace my lost one.

The moral of the story is that you can't believe everything that's written in that JBL Technical Note: Danger: Low Power. Too much clean power can and will destroy your speakers.

[Steve Conner]

Yep, the laws of thermodynamics trump any manufacturer's technical note.

Most speakers are about 1% efficient, the exception being massive horn-loaded ones. Of the power that goes in from the amp, 1% is turned into sound and the remaining 99% heats up the voice coil. If you put 1.5kW of power into it, it's going to catch fire in a matter of seconds, no matter if the signal is clean or distorted.

[Leo_Gnardo]

"Danger: Low Power."
The moral of the story is that you can't believe everything that's written in that JBL Technical Note: Danger: Low Power. Too much clean power can and will destroy your speakers.

That was a lousy way for JBL to treat ANY customer.

They did sort of "issue the challenge" in their literature. And how many times I've seen in studios small JBL, Tannoy or those ubiquitous Yamaha NS-10's on a console bridge, powered by a huge BGW, Crown or similar amp (200W + per channel). All surviving very nicely thanks veddy much. When "thunder" is needed, that's what the big speakers are for.

Speakers, and ears, will tolerate a bit of being overdriven. Just a dab of clipping at the attack of a note is easy to see on a 'scope but not so easy to hear.

A "small" amp buzz-sawing out square waves will smoke a voice coil too. Seen many warnings about this one. There's an interesting one on Rich Koerner's "Time Electronics" page, where he refers to the effect of voice coil heating via square wave driven (solid state) amps as "hang time." Tube amps are less of a problem, he says, because generally they store less energy in their power supplies, also can't sustain much of a DC output due to output transformer coupling. Even in my medium size PA I saw the clip lights too many times on Crown D-150's powering horn drivers. Went to a bigger amp - no more clipping.

I've seen PA gear(speakers) catch fire 3 times. Never a good thing. Lucky nobody got hurt & the shows went on. Last I heard Clair Brothers keep a 2x15 wedge on display to show their recruits "what can go wrong." That one was shooting flames at a Humboldt College gig 1981 - the local crew simply unplugged it, picked it up, dragged it out the door & face down in the turf. Crowd thought it was a pyro stunt. Don't try this at home.

[bob p]

That was a lousy way for JBL to treat ANY customer.

I had a lot of respect for JBL prior to that experience, and zero respect for them afterward. They lost me as a customer because of that. I've bought a lot of pro sound gear in the years that followed. None of it was JBL. In contrast, I got fantastic service from the guys at EV, back in the days when EV was still a privately owned company in Buchanan, Michigan. I can't begin to remember how many times I drove up there to have them perform on the spot warranty repairs for blown horn and tweeter drivers.

They did sort of "issue the challenge" in their literature.

I thought the same. Some of the tech notes look they were written by the marketing guys, not by the engineers. Engineers know better than to say things like "unlimited ability to handle clean power." The problem is that when I called them on their claims, they refused to honor their marketing claims. That put an end to a lifetime of use of JBL equipment. I turned my back on them and never looked back. It wasn't too long after that that they became assimilated by KarmanHardon.

During the 2 year down period while the 10" woofer was missing, I had ghetto-rigged a replacement woofer -- I had an EVM-15L in a TL-606 Thiele ported cabinet that I hooked up to the bass feed from the L96 crossover. It didn't have any problems dealing with the output from the Carver amp.

And how many times I've seen in studios small JBL, Tannoy or those ubiquitous Yamaha NS-10's on a console bridge, powered by a huge BGW, Crown or similar amp (200W + per channel). All surviving very nicely thanks veddy much.

To be fair, a proper ProAudio install is going to have a high pass filter in the signal chain that's tuned to a low enough frequency to limit the LF content that gets passed to the amp driving those little speakers. I didn't have any high-pass filtration in my system because after all, it was a home audio setup. Home audio systems typically don't have high pass filters turned to low frequencies on an AUX input, though they might have a rumble filter for a phono input. And when records get made, extreme LF content would be rolled-off during the mastering process, so that the media wouldn't contain any content that could hurt the speakers.

That changed with the advent of the audio CD -- when the CD audio medium was new, recording engineers were competing to see who could produce a recording with greater dynamic range, more extreme LF content, etc. CDs got produced with LF content that was so extreme that any responsible engineer would have rolled it off, but during that time when the CD medium was new, mastering was a bit of a Wild West Show. Signals that never should have made it through the mastering process -- like the digitized cannon blasts -- got put on CDs in order to demonstrate what the new medium was capable of, and quite a few systems got destroyed in the process. I'm sure that I'm not the only guy who blew up his speakers with the Telarc 1812 recording of the cannon.

I ended up loaning that CD to someone and never worried about getting it back.

I've seen PA gear(speakers) catch fire 3 times. Never a good thing. Lucky nobody got hurt & the shows went on. Last I heard Clair Brothers keep a 2x15 wedge on display to show their recruits "what can go wrong." That one was shooting flames at a Humboldt College gig 1981 - the local crew simply unplugged it, picked it up, dragged it out the door & face down in the turf. Crowd thought it was a pyro stunt. Don't try this at home.

I've run into lots of people who didn't believe me when I told the story about the speaker catching fire. Evidently outside of the pro audio environment people have never heard of this happening, but in pro audio everyone who's been around long enough has seen it happen at least once.

[km6xz]

Help me out -- I don't understand the connection between amplifier power and transient response. I thought transient response was measured by slew rate and rise time, and not by power output.

Slew rate is related to voltage swing versus frequency of the highest sinewave frequency to be amplified. That given, the relationship of minimum slew rate to handle a given high frequency limit is SR>(2pi*Freq)*Vpk which shows that of two amplifiers with the same high frequency response limit, the higher voltage swing unit will have higher slew rate.
For signals of equal amplitude, the higher power amp which satisfies the conditions above, will have a faster transit response.
This assumes two amps with the same end to end bandpass capability. Mark's comment is realistic.

[km6xz]

The whole issue of speaker driver power is illogical.
Speakers which have lower mass, and less excursion can have tighter tolerances between the voice coil and pole piece so need less power for a given sound pressure level output than a high power speaker that has a high mass VC in order to dissipate the additional power to move its higher mass. Couple that reduction in efficiency with the need to widen the gap of the pole piece(which greatly lowers flux density impinging on the VC) to allow more deviation in voice coil positioning the higher mass coil requires(and further excursion) and you have a race between higher power countering ever lower efficiencies of high power capable drivers.
They kept pace with each other(power available vs power needed to push a cone that could handle the added power) for a while, until Class D amps made every low cost powered mixer to generate 1200watts or more. Now power is cheaper to generate than speakers to tolerate it, and all along(except in the lowest frequencies) loudness has not increased. Anyone who connected their 6 transistor radio with 600mw output to a Klipsch corner horn back in the 50s or 60s knows what efficiency is. To get the same sound pressure level in the low mids to high frequencies, many hundreds of watts is needed.
My first BIG amp was 60 watts and that was enough to have the police visit my home a number of times. They drove a couple large acoustic labyrinth using KEF oval drivers. Later, I replaced the upper mid and hf drivers with Heil Air Motion Transformers which increased efficiency and top end to 35khz. They were some of the first home made prototypes for that driver.
We designed and built a large touring system for the Jethro Tull Aqualung tour back in the 70 that used electronic cross-overs, with molded folded horns for the bottom and flare horns for mids and arrays of SEAS tweeters for top end, and 24 amplifiers. All that was unheard of in pro audio at the time. Neither were the home made house console that featured balanced line transformerless inputs and switchable meter ballistics(Vu or PPM which was more popular in Europe) All home made. The amps were basically modified Dyna-120s with a single power supply for each rack. 60 watts per channel and it filled some pretty big venues. By the way, we did have a speaker fire in Dallas with that low power. It was probably the first touring system with Hi-Fi performance which is what Ian Anderson wanted. His flute never sounded great with the traditional Altec multicellular horns that were the mainstays of concert sound back then.

With all the power and size of system changes over the years, upper 1 meter SPL is still around 134db or a bit higher per cab, same as it was 40 years ago with 50-75 watts.

[Steve Conner]

I always thought the best way to protect a speaker would be to make it so efficient that your ears would bleed before it overheated.

I think the real issue is money, high efficiency drivers need precision engineering and expensive magnets, but Class-D power is cheap. The situation we have now is probably optimal in terms of SPL per dollar spent on gear, at least in terms of the sticker price. SPL per total cost of ownership might tell a different story.