Titan 48

[gdougherty]

Would reduced strength of the woofer not throw sensitivity out of whack?

[Sydney]

That makes sense, without a magnet it would behave like a coil.
Less or no flux, and the magnetic field generated by the energized coil has less to attract to, and repel from.
If you had a woofer with a blown coil & you suspected the magnet was damaged, and you had a similar working unit, it should be easy to get an idea on the relative strength, by comparison.
This might prevent a wasted recone on a bad magnet.

[Dave Non-Zero]

I am one of those, 'operators in error' having toasted a couple of t48 3015s. let dj loose on system without proper limiting and far too large an amp. Crown K2 bridged into 2 cabs. (2400w) lookin again at the blown speaker it looks to me like the voice coil jumped out the magnet. I will post pics if anyone is interested?

[James R]

So based on what I've read it's far better to run a T48 loaded with 3015's voltage limited. So if the single 3015 is rated at 450w and it gets a 10 ohm load. That would be 67 volts it could take , but it's sound like around 60 volts 360 watts is safer correct? I have 2 older QSC USA 900's that I bridge now at a 4 ohm load to achieve ( on paper ) 1500 watts. That figures out to 77.4 volts

[Mikey]

So based on what I've read it's far better to run a T48 loaded with 3015's voltage limited. So if the single 3015 is rated at 450w and it gets a 10 ohm load. That would be 67 volts it could take , but it's sound like around 60 volts 360 watts is safer correct? I have 2 older QSC USA 900's that I bridge now at a 4 ohm load to achieve ( on paper ) 1500 watts. That figures out to 77.4 volts

After reading a recent post by moo, I'm really starting to take over-powering and it's subsequent heat much more seriously...

I came across this Info on another site recently:

Years ago I did a M_ean T_ime B_efore F_ailure (MTBF) on an amplifier that claimed to double its power going from 8 to 4 and again from 4 to 2 ohms (it did). Based on the junction temperatures of the transistors the MTBF at 8 ohms was 10,000 hours, at 4 ohms it was 625 hours, and at 2 ohms it was 39 hours.

MTBF is such that even though the amp won't blow up today or tomorrow, the life is shortened. How much? A typical amp will have a MTBF about 16X longer at 4 ohms vs 2 ohms.
The big PA companies in the states will run 2 ohms in the mids and highs, but run 4 ohms in the low end. There is a reason for that.

This makes thing much clearer regarding running amps at 2 ohms.
It is clear that not all amps are equal, and that some will take punishment more than others, and that more expensive and heavier built amps will have a longer life-span.

If you run the amp at 4 ohms and keep it out of the Red it should last for years. -
At 2 ohms near its limits - it will last for days.

Bridging your amp into your two T48s, you're at 5ohms (nominal), but given the 3015LF's Re of 5.31ohms, you have impedence dips below the amp's rated minumum (4ohms, bridged). So, you're pushing your amp right to the edge of it's bridged performance.

Other somewhat-related concepts are finally really sinking into my head, too (finally)...

* Bill has been preaching for years that if you need more output, add more cabinets.

* A few weeks ago, he made another gem of a statement that I WISH I could find, which "sorta" said that, for horns, it's not about pushing expensive drivers to their limits, it's about using cheap drivers and more horns ... my VERY vague recollection/interpretation of what he said.

* "The Point Of Diminishing Returns", in relation to drivers, is often mentioned, and has been broken-down in detail in order to prove to people just how foolish it is to throw a lot of power at a driver.

* Heat damage to drivers has also been frequently mentioned for many years here. Most recently, the issue of heat damage to neo magnets has been a topic of concern.

Once I started inter-twining these concepts, and scientifically-proven facts, it all finally became crystal clear to me ... I saw the big picture. I hope that others will grasp the over-all concept faster than I did.

Thank you to all of the very knowledgeable folks who have contributed all of this very useful and valuable information. It's not falling on deaf ears!

[WB]

Based on the junction temperatures of the transistors the MTBF at 8 ohms was 10,000 hours, at 4 ohms it was 625 hours, and at 2 ohms it was 39 hours.

This is the sentence that hit home for me. I used to poo-poo 2 ohm load concerns in the past. Not anymore.

[Sydney]

having toasted a couple of t48 3015s...limiting and far too large an amp. Crown K2 bridged into 2 cabs. (2400w) ... I will post pics if anyone is interested?

Dave Non-Zero
I'd like to see the post mortum...
I'll show them to a friend who just acquired 2 Crown Macro2400 amps ( for $175 ea ) and plans to bring them on-line soon.
As kind of a nudge to get a limiter.

[DJPhatman]

I'll show them to a friend who just acquired 2 Crown Macro2400 amps ( for $175 ea ) and plans to bring them on-line soon.
As kind of a nudge to get a limiter.

Thats not "acquired"! That is theft!

[Sydney]

That is theft!

Actually it was an auction ( bank theft ).
22 Crown amps when for the same price. A Yahamha M4000 40 chl console went for $60!
A Kurzweil piano for $350
A Fender Twin went for $45, etc, etc, etc...
BTW - Anyone want an older Soundcraft 32 channel console? ( keeping the Soundcraft Spirit monitor 40 )
( I'm hoping to get a bunch of 2206 CHEAP )
Syd

[thijs666]

* "The Point Of Diminishing Returns", in relation to drivers, is often mentioned, and has been broken-down in detail in order to prove to people just how foolish it is to throw a lot of power at a driver.

* Heat damage to drivers has also been frequently mentioned for many years here. Most recently, the issue of heat damage to neo magnets has been a topic of concern.

Once I started inter-twining these concepts, and scientifically-proven facts, it all finally became crystal clear to me ... I saw the big picture. I hope that others will grasp the over-all concept faster than I did.

For technical background on the subject of power compression and why more power isn't very helpfull, read this from Elliott Sound Products

... Seriously, read it

Yes, it's a lot of text, but it sure is worth the time reading

[Mikey]

For technical background on the subject of power compression and why more power isn't very helpfull, read this from Elliott Sound Products

Just read it. You're right, it's a good read!

I didn't realize how many ways that energy is lost in the entire electrical to acoustical conversion. It definately reinforces the fact that using horn-loaded cabs to convert more of what is left by the time energy reaches the cone is the logical thing to do. It also made me realize that v-coupling to gain 3db is much more of a benefit than I had previously taken into perspective.

The explained impact on passive crossovers was very informative. I never realized just how little power to the drivers it takes to throw a system using passive crossovers out of whack.

I bookmarked the page, and I'll definately be reading that a few more times, as I'm sure there is yet more to learn from all of it. Thanks very much! That's definately very useful information.

[Sydney]

Ron Elliott has one of my favorite sites - as soon as I came across it I bookmarked it.
He updates frequently ( he just added an article on PS regulation ).
I had lost count of the time I've referred to the article thijs666 mentioned.
Other favorite articles:
Phase Angle Vs. Transistor Dissipation
http://sound.westhost.com/patd.htm
Semiconductor Safe Operating Area
http://sound.westhost.com/soa.htm
These articles further explains the dynamic AC interaction between amp and speakers - which is not a simple DC resistive system.

[Mark Coward]

Bridging your amp into your two T48s, you're at 5ohms (nominal), but given the 3015LF's Re of 5.31ohms, you have impedence dips below the amp's rated minumum (4ohms, bridged). So, you're pushing your amp right to the edge of it's bridged performance.

I agree with most of your other statements, but this is supposition on your part and has not been proven in actual usage. All drivers have a minimum impedance that is lower than the nominal/average, which occurs at a specific frequency. But that does not mean that he would be pushing the amp "right to the edge of it's bridged performance." Theoretically if you have "musical" content that is a pure sine wave at this frequency, with no other signal present, then the minimum impedance might be a factor. But in actual use by Live SR and DJ, there is a much wider bandwidth of content and the nominal speaker impedances and amp ratings generally provide safe operating guidelines. I'm not sure which amp the quote above referenced, but many modern amps are designed to safely run 2 ohm loads.

I just can't see being overly concerned about damaging an amp, imagining a worst case scenario. The amp failures that I have seen have been few and far between. Look on this forum, there have been a number of posts about blown drivers, I don't recall a single post about a blown power amp. This has been my experience over some 30 odd years as well, I've seen lots of blown drivers but very few amp failures. The amp problems I have seen have most often been new or relatively new units, like Tim A's recent amp purchase, most likely a manufacturing defect.

It's taken me a long time to understand and believe Bill's information about power compression, maximum SPL, and overpowering drivers. When I first built Tubas & DR's, I was running them with 2xRMS or more because I thought that was how the "pros" did it. I was probably thinking something like "Bill's just a wuss, let's throw some serious juice into them." Thankfully I didn't blow any drivers.

There are folks who are opposed to running amps with 2 ohm loads, but there are many amps that work dependably in this fashion. More often it's a 4 ohm bridged load, running one amp per 2x18 sub or 2x12 top. But now I understand that you don't need to run 1,500w RMS cabs with 3,000 watts of power. IMHO, Bill's designs are more suitable for running 2 ohm per side on a capable amp, since we only want/need about 300w per driver in most cases. I'm thinking something like 8 - T48's and 8 - DR280's running on just one pair of QSC PLX3602 or Crown XTi 4000 amps. Can you imagine the amp racks it would take to power an equivalent JBL SRX setup?

[Sydney]

Examining the specs provided by reliable amp manufacturers: The criteria for achieving those large 2 ohms power numbers are much less stringent than the 4 and 8 ohm values - usually a relaxed EIA rating at a single frequency and distortion an order of magnitude greater ( ex 1khz and 1% distortion measured for short duration ) NOT evenly across all the bandpass at low distortion over a period of time. Copy writers love these numbers - they impress and sell units. But if you look carefully in the fine print, there are warnings and disclaimers about 2 ohm loads, and many issue stern statements that in bridged mode - 4 ohm is the limit.

As Ron Elliot points out ( and many amp designers know ) "All of this has happened in perhaps 10 milliseconds, and the case is not even warm. This phenomenon is called "second breakdown" (or secondary breakdown), and is the single greatest reason for transistor failure in a working circuit." It does not take several seconds of a pure sine wave - but a few cycles. A 60Hz signal has a cycle of 1/60 of a second ( .016sec ). 4 cycles = .067sec. This duration is far too fast for a fuse or over current protection to react. Amps may not fail outright, but they are being stressed.

As one who has built and repaired amps since the early 70's, I have seen plenty of amp failures. After all a repairman - like a coroner is going to see more than their share of dead bodies. Service guys usually don't do forensics, or a case history - they just fix. There are some things that are indicators of chronic mis-abuse. Usually it is not a single catastrophic event , but a long pattern of slow degradation that prematurely ages and burns parts out of spec, until failure.
Just today I read a posting ( on an amp forum ) about a Peavey 2600 that caught fire. The amp had been in operation for hours, the owner confessed to his habit of running the amp "warm". He wondered if "perhaps he pushed it too hard"

Ron Elliot's articles can seem incomprehensible if you don't have a background in electronics ( especially AC and amplifiers ), but the bottom line is Heat is the enemy.
It doesn't matter if an amp gets hot because of inadequate heat dissipation, from a blocked or inadequate heat sink, a failed fan, poor air circulation, summer sun or excessive current from low impedance: Amp life is shortened.

[Mikey]

Mark, most larger amps are typically rated to 2 ohms stereo, 4 ohms bridged. By this point, most of us are aware of "nominal" impedence, minimum impedence, and the constant varying impedence of a system under operation. Practically speaking, combined speakers calculated to be 5ohms, nominal, are just a hair away from 4 ohms. Their actual difference in operation in comparison to speakers combined to a nominal 4ohms will be miniscule. So, yes, the amp would be pushed "right to the edge of it's bridged performance." In light of recent technical information presented on this forum regarding the ill effects of heat on amplifiers, it seems to me that it would be irresposnsible at this point to continue to condone running amps at or near their minimum impedence load.

That being said, I ran my Peavey CS800s at 2ohms per channel for over 2 decades, and they reliably kicked ass. I guess I was ignorant and lucky.