I just want to add that I think the B and BX sound quite different to my ears.
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I'm sorry I listened.....
- Thread starter ShawnStones
- Start date
I just want to add that I think the B and BX sound quite different to my ears.
- Feb 12, 2006
- 61,029
- 5
- 220,900
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
I'm a little bit hesitant chiming in on this, but a couple of you guys asked some technical questions privately regarding this specific subject...
Regarding how amps are rated, there's not only the rated load impedance but also the duty cycle of the signal used. Very few amps will deliver full rated sine wave (or pink noise) power for hours and hours, because normal music is nothing like this type of signal and to do so would add both cost and a lot of weight to the amp. The designer of the amp must be familiar with the profiles of a typical bass player's signal and be comfortable estimating (and testing for) "reasonable" worst case conditions. While the safety agencys look at the 1/8-rated power for testing purposes, and this is pretty typical of unclipped full range signal such as a PA amp, when a bass player is digging in and using compression, distortion, etc. this 1/8-power number is really no longer a reasonable or realistic estimate. It's up to the designer to know enough about real world conditions to come up with their own criteria. For my designs, I rely on 30 years of touring pro audio experience to know what you players will do with your gear and plan accordingly. The downside to this is that the more thermal headroom designed into the amp, the greater the cost.
Real world conditions also include speaker cabinets that may be rated with a nominal impedance of say 4 ohms but when you run a real impedance sweep over them you discover that some manufacturers have some dirty little secrets and there can be a significant area where the impedance dips well below the nominal rating. This can really be detrimental to the health of any amplifier, and could be caused by a poor choice of driver parameters or crossover design (especially in a 3 way cabinet where there are high current bandpass filters involved). I recently came across a speaker with a poorly designed crossover, there was a resonance in the bandpass filter that caused the amp to oscillate. Not all amps would do this, but several amps by different manufacturers did and one was destroyed. The problem was that a damping resistor was missed in the design of the crossover filter!!!
I am currently fighting for a client of mine with a well known pro audio company who released a product that carried an 8 ohm nominal rating but almost 3 octaves dropped into the mid 5 ohm range. When driving what he thought was a nominal 2 ohm load on one channel of a large Crown amp, it would get hot and shut down. The amp cheched out fine, there shouldn't have been any issue but the problem persisted. I dove into analyzing the speaker and was horrified by what was really going on. His net load on the channel was around 1.4 ohms under sweep conditions test, well beyond the reasonable expectation of any amp. When I inspected the LF drivers, they were in fact 4 ohm nominal drivers rated that way by the driver manufacturer, when I contacted the cabinet manufacturer they gave me a BS song and dance about how I didn't understand how speakers worked "little boy". Turns out this has indeed been a known problem that they have chosen to ignore, they now know who I am and that I have the same engineering background as they do in this industry, they told me that there was no fix, they stand by the 8 ohm rating even though their own impedance plot duplicates mine showing clearly a nominal 4 ohm rating is justified. They will not correct this problem, so the customer is screwed. He will re-label the cabinets as 4 ohm and sell them. I will no longer recommend products by this company.
So, I would not assume that the problem is with the amp before investigating all other possibilities. It's likely that there are other causes, maybe a combination of things that are pushing the thermal limits over the edge. I recommend that you give the amp manufacturer a call, explain the situation, and ask for somebody in the engineering support area to help you with your problem. You might get better information this way rather than dealing with a sales or marketing guy.
Regarding how amps are rated, there's not only the rated load impedance but also the duty cycle of the signal used. Very few amps will deliver full rated sine wave (or pink noise) power for hours and hours, because normal music is nothing like this type of signal and to do so would add both cost and a lot of weight to the amp. The designer of the amp must be familiar with the profiles of a typical bass player's signal and be comfortable estimating (and testing for) "reasonable" worst case conditions. While the safety agencys look at the 1/8-rated power for testing purposes, and this is pretty typical of unclipped full range signal such as a PA amp, when a bass player is digging in and using compression, distortion, etc. this 1/8-power number is really no longer a reasonable or realistic estimate. It's up to the designer to know enough about real world conditions to come up with their own criteria. For my designs, I rely on 30 years of touring pro audio experience to know what you players will do with your gear and plan accordingly. The downside to this is that the more thermal headroom designed into the amp, the greater the cost.
Real world conditions also include speaker cabinets that may be rated with a nominal impedance of say 4 ohms but when you run a real impedance sweep over them you discover that some manufacturers have some dirty little secrets and there can be a significant area where the impedance dips well below the nominal rating. This can really be detrimental to the health of any amplifier, and could be caused by a poor choice of driver parameters or crossover design (especially in a 3 way cabinet where there are high current bandpass filters involved). I recently came across a speaker with a poorly designed crossover, there was a resonance in the bandpass filter that caused the amp to oscillate. Not all amps would do this, but several amps by different manufacturers did and one was destroyed. The problem was that a damping resistor was missed in the design of the crossover filter!!!
I am currently fighting for a client of mine with a well known pro audio company who released a product that carried an 8 ohm nominal rating but almost 3 octaves dropped into the mid 5 ohm range. When driving what he thought was a nominal 2 ohm load on one channel of a large Crown amp, it would get hot and shut down. The amp cheched out fine, there shouldn't have been any issue but the problem persisted. I dove into analyzing the speaker and was horrified by what was really going on. His net load on the channel was around 1.4 ohms under sweep conditions test, well beyond the reasonable expectation of any amp. When I inspected the LF drivers, they were in fact 4 ohm nominal drivers rated that way by the driver manufacturer, when I contacted the cabinet manufacturer they gave me a BS song and dance about how I didn't understand how speakers worked "little boy". Turns out this has indeed been a known problem that they have chosen to ignore, they now know who I am and that I have the same engineering background as they do in this industry, they told me that there was no fix, they stand by the 8 ohm rating even though their own impedance plot duplicates mine showing clearly a nominal 4 ohm rating is justified. They will not correct this problem, so the customer is screwed. He will re-label the cabinets as 4 ohm and sell them. I will no longer recommend products by this company.
So, I would not assume that the problem is with the amp before investigating all other possibilities. It's likely that there are other causes, maybe a combination of things that are pushing the thermal limits over the edge. I recommend that you give the amp manufacturer a call, explain the situation, and ask for somebody in the engineering support area to help you with your problem. You might get better information this way rather than dealing with a sales or marketing guy.
No, most of the heads I've used have been a strait forward 4 ohms, no bridging. I did use a Peavey CS3000 power amp with a few different pre's for a while, and I did run that bridged at 4 ohms.
I don't think this is an issue with impedance ratings or cabs. It most likely has to do with the power supply for it. Could be an issue with how much it's getting from the wall vs. what it needs to get before shutting down or perhaps the protective feature is too sensitive. Just guess on my part but I think you're looking in the wrong direction.
I alluded to this in a post above, but my guess would be that this could vary widely among different bass players. So an amp that performs perfectly fine with a player with a soft touch will be shutting down on a player who thumps very hard or, as you said, maybe uses compression to raise the average signal level.
What are your thoughts on how much of a factor this may be in general, and can you give insight as to how much leeway you have in building that type of headroom into your amps designs to accommodate those differences?
Rhetorical question: I wonder how many engineers have their hands tied, being pressured into developing a 1,200 watt amp at a specific (low) cost, when in fact it's not possible to make a "true" 1,200 watt amp and the numbers must be fudged to get it in under that price point.
all i will say is that i had pro bass 500 head back in the early 90s and it went thermal on me all the time......... so its kinda odd to hear someone else having issues that I had. I sold it as is to a local guy - he knew the prob with it - and he said he could fix it --- he had the same issues with the head and unloaded it, so it wasnt just me running it wrong... it was just a bad unit.... and the DI sounded absolutely horrible.
- Feb 12, 2006
- 61,029
- 5
- 220,900
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
This is indeed a big factor, and amps that are marketed towards the hard player or are likely to be embraced by them should be designed for more electro-thermal headroom than amps targeted for say the church, jazz or folk markets. For example, I use different duty cycle criteria for the acosutic amp designs than I do the bass amp designs.
I think it's a big factor, and getting bigger. In the products that I design, I have pretty much complete control over how much headroom, protection circuit latitude, etc that is needed. This is one thing about offering productsfor sale that have a 3 year transferrable warranty, if there's a problem, it's our problem so clearly it's best for all concerned to get it right the first time. I think this applies to all companies who offer liberal warranties. As example of a company whose products are well backed up by warranty is QSC.
Hands being tied is pretty common.. In general, the drive towards lower and lower priced amps, along with smaller and lighter weight has led to more and more compromises being forced upon the designers of many (not all) companies. A good example of this can be seen by the rush to get lightweight SMPS - class d micro amps to market. While we had been working on the concept, technology and reliability for quite a few years (behind the scenes) and were one of the very first to market with the Shuttle line, we feared the flood to follow by competing companies would compromise reliability and bring a bad reputation to the micro-amp product catagory in general... lumping the good product in with the bad. This did happen, and there are those of you out there that assume that ALL microamps suffer from reliability problems when this is patently untrue. What is true is that SOME manufacturer's amps do indeed suffer from constant problems but there are also manufacturers out there who produce very high quality, high reliability product.
Hope this helps.
Wow, really? If I say that I have owned numerous pieces of Carvin amplification and never had a single problem even in 110+ degree weather then will you be swayed to choose Carvin? This includes amplifiers DCM600, DCM1500, DCM2000, etc. as well as a BX1200 and now a BX500 - never had a *single* problem and they all sound great.
There's more than likely something going on with the rig or environment used by the OP to have the same issue appear with two different units. It's silly to simply dismiss an entire brand because one guy had a problem which did not even specify where/what else he's using.
/\/\/\/\/\/\/\/\
Same experience here..............
I own/have owned (2) HD1800 power amps, DCM1500 power amp, R1000 head, (2) B1500 heads, BX500 head, and numerous cabs from the RL and BRX line.
Never one hiccup or failure, never one thermal shut down, never one blown driver.
Kudos to agedhorse and Genz Benz as a whole for being an amazing part of this board. Brilliant and informative, this is great stuff.
Have to chime in here again. Far be it from me to doubt the experts here, but, I repeat: I have been bridging amps in to 4 ohm loads, on and off, for 30 years without any of them going thermal on me, including Carvin heads and power amps. Maybe something is wrong with those two units, but, to think that it's somehow risky to bridge an amp into a 4 ohm load, ( if it is rated to do so ), with reasonable settings, just does'nt fly in the face of what I have experienced, or any other bass player I know who has done the same thing.
- Feb 12, 2006
- 61,029
- 5
- 220,900
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Provided there is nothing wrong with the speaker, there should be no problem bridging an amp into whatever load it is rated for.
In the big picture though, if you are planning on "driving the snot" out of an amp (greatly exceeding the typical 1/8-power duty cycle), some amps may not be as robust as others depending on the designer's criteria for thermal headroom.
What is the DC resistance of your cabinet? (take a high quality digital ohm meter and measure across the input terminals of your cabinet without the amp connected). This is not the impedance but there are some good rule of thumb ranges that give insight as to what the corresponding nominal impedance is LIKELY to be.
Before I got my BX500, I used to bridge my BX1200 with a BRX10.4 neo cab. I never had one single problem doing so, it sounded great and the head withstood being dropped at least 4 times. Once the head fell out of the back of my Scion XB onto the pavement in the parking lot of the venue we were to play, somersalting 3 times and coming to a rest upside down. I thought to myself that the head was done for, but it performed admirably and to this day still does. Carvin gear has always been very good too me as I mentioned in my previous post sometime back.
I've owned 2 Carvin amps, one in the mid 60s and one about 5 years ago. Both were junk. The mid 60s one sounded great -when it worked - it stayed in the local repair shop more than it stayed with me. The more recent one had very little use and died less than a year after the warranty expired. I also had a Carvin bass that I quickly sold since it had issues also. Never again. 
Carvins customer service will work with you. I'd send the BX1200 back and get the new B2000. I bet they might negotiate a real good price for you after your problems.
Who in the hell would run a pair of mains bridged at 4ohms? Where's your stereo image? That doesn't make any sense and I seriously doubt 80% of anybody does that. Not around here anyway. Good policy is if your amp says 2ohms, stop at 4, or at least 2.67. If it says 4, stop at 8, or at least 5.33 etc. This applies to any amp, no matter how good or bad you think it is. This is to allow for the marketing bimbo's oneupsmanship, keeping up with the Jones'es, etc. I have never burned up an amp be it bass rig, PA or whatever since following this concept. All this "get to the lowest ohms to get the most power, man" is so stupid.
Here is the response and impedance curve of a common driver, the eminence delta15lf.
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The impedance could be as low as 7ohms or as high as 25 or 30 within the useable range of the speaker. This is also the reason there really is no such thing as a stock, "use it on anything" 8ohm crossover. There are only 2 points where the impedance is actually 8ohms. One at roughly 85 hz and another one at about 275. Unless your crossing it at one of those two frequencies, it's not 8ohms anymore. If crossing it at a typical 500hz, you'd start to design your LPF using an impendance of about 12 ohms or so.
You can pick any other driver out there from any company and it'll be just as inconsistent. The 4ohm/8ohm thing is "nominal" impedance. It's a baseline to figure from and good enough to keep you from burning up a reliable amplifier but it's far from what's really going on.
