agedhorse

Another ridiculous urban myth that I’ve never seen at a pro gig ever.

No way to accurately predict the outcome.

What’s difficult about his question or the information that was provided? Often, a seemingly simple question doesn’t have a simple accurate answer and since the wrong answer (of an answer that’s out of context) can be dangerous, the additional information is in fact important.

Ok, if the problem returns, Surrey Amps is handling Genz Benz and Mesa repairs for the UK.

My understanding is that T is the designator for time lag or time delay or timed opening fuses. Looking at the IEC standards, there are T, TT (even slower opening), F and FF (even faster opening) but the TT and FF are specialty products that we won't see in the MI industry. These only apply to the 5mm x 20mm fuse type, the 6.3mm x 32mm fuses use different designators.

That's what the regulations say, I am not sure of the date of this data though. .75mm^2 is equivalent to our 19 AWG, and our 18 AWG (slightly larger) cordsets are permitted to be used on 20A branch circuits. This is specifically to prevent fire due to a fault in the cordset, it's not best practice for sizing to a load. In our industry, this is addressed under the safety regulations by providing an equipment located fuse or breaker (called an overcurrent protection device) that is sized in conjunction with the specified IEC cordset size. Since most equipment that we are talking about here is typically protected by a T6.3A or smaller fuse, and will work plenty fine (and safely) with a 75 mm^2 cordset. There are a lot of quirky elements to this topic as you can see. Other countries and regions are even more convoluted.

Not necessarily. Using the Subway 115 and 215 as examples, the 8 ohm 115 is rated at 400 watts RMS, the 4 ohm 215 is rated at 800 warts RMS, when driven from the 2 ohm tap (switch position) each DRIVER receives 1/3 of the ~800 watt rated power or about 260 watts which is well below the rated power handling of the driver in those cabinets. Perfectly safe, perfectly good power match as well. Here's the handy table from the owner's manual, and why I strongly recommend reading the owner's manuals for our products:

There are two DIFFERENT fuses for 2 DIFFERENT reasons. I have to deal with this stuff whenever submitting products for international/CB certification testing. The first (in the UK) is the fuse in the "13A" (BS-1363) plug cap, also referred to colloquially as a kettle cord. This fuse is sized based on the wire size in the mains lead wire. This is because of the unique 30A ring circuit in the UK (and some UK colonized locations) where each receptacle is fed from 2 circuits simultaneously configured in a ring type distribution. This is an efficient way (less copper) to deliver power, but inconvenient for protecting because of the higher available fault current. The UK approved fuse style is BS-1362 which has specific opening and clearing characteristics to comply with the regulations. The second is the equipment protection fuse that is used to protect user, the equipment and external wiring from overload and fire in the event of a fault within the equipment. If it's and external fuse that is intended for user replacement, the fuse value must be printed in a specific format on the back of the equipment (the type, voltage and current... like T3A/250V) which says that it's a 5mm x 20mm time delay fuse, 3 amps, suitable for up to 250 volt operation). There may also be an L or H which signifies low or high clearing capacity. If L or H is not present, either L or H rated fuses may be used. The lowest approved plug cap fuse that I have seen is 3A

It may be that the valve is not seated properly, but it could be other things as well. Where are you located?

It's an astable equilibrium, doesn't take much to push it out of equilibrium which is why class AB was used... it forces the issue to the better side of the compromise.

If you believe all the marketing crap, sure. There are plenty of examples of class B amps that have less distortion than class AB amps, but it's also part of the definition of class B which in practice is impossible to attain, therefore all class B amps are technically either class C (slightly less than 180 degrees conduction angle) or class AB greater than 180 degrees). To achieve exactly 180 degrees is like balancing a marble on the top of a ball. Class AB, B and C are all greater efficiency though, and class C can be rather dreadful at low volumes in particular.

You have a fault within the amp. This can be repaired under the factory service program. If you message me here or on TalkBass, I will send you the service program information.

Except for the fact that it's a class AB power amp. The class A description is with regards to a specific preamp gain stage.

It's not a class A amp, therefore you can rule that out. Some amps have the fans running continuously, some fan's speed track the temperature of a specific component or section, and some fans run intermittently. It depends on the specific design. Sounds like it needs to be serviced by a qualified service tech.

You need to find a better speaker repair guy, those comments are ridiculous. A speaker’s power handling is whatever it’s designed to be by the designer. There are 100 watt 15” drivers and 500 watt 15” drivers, there are 50 watt 10” drivers and there are 300 watt 10” drivers, and I’m talking about mechanical power handling not thermal.

First of all, kWh is a nebulous term because there are some assumptions about discharge rates and depth of discharge that are hard to get accurate data on from marketing brochures. 1. Assume that whatever kWh that is advertised is total capacity, only 80% should be used under most situations. This leaves you with 0.8kWh (800Wh) 2. The power consumption numbers on the PA cabinets are at 1/8 rated maximum output with is similar to driving your PA UNDISTORTED to maximum output. 3. Your MarkBass amp's 300 watts power consumption is calculated (almost always) based on the same or similar metrics, so that number is a good one also. (In reality, it may be quite a bit less, which model is it?) 4. The digital mixer will be right around 100 watts (assuming it's not a "bigger boy" console) The calculations would be: PA cabinets: 3 x 110 = 330 watts Bass amp: 1 x 300 watts = 300 watts Digital mixer: 1 x 100 watts = 100 watts Tube gtr amp: 1 x 150 watts = 150 watts Total = 880 watts which will last about an hour in your application. The maximum power draw of 1800 watts isn't going to be as much of an issue here.

Depends on how long you want the driver to last, how good your judgement is and how lucky you are. I wouldn't recommend it because I see the results of players who think they have better judgement and restraint than they really do. It's even worse when you don't have enough rig for the gig. This leads to poor decisions out of necessity. IF you are careful and respect the limits of the drivers, you might be ok (until you aren't), many players who think they can hear the driver reach its limits but in testing really can't (and miss by a wide margin because some drivers are very benign sounding when overdriven).

At this point I might be more excited than you

In general, most amps, even some tube amps, the sag is almost zero until reaching maximum power. The original question was regarding doubling the power in which case +3dB minus any power compression of the driver is the correct answer. A well designed power supply is a big part of any well designed amp isn't it? It is likely that a 4 ohm driver (not a 4 ohm speaker made up of 8 or 16 ohm drivers) is likely to have a lower sensitivity. This would be a more significant factor in comparative volume, but I did make the clear assumption that all else being equal, therefore +3dB is still the correct answer. Correct, hence my qualification that all other parameters were assumed to be identical.

The formula for beaming is more or less correct in theory for a planer source, but in reality there are many other parameters like cone geometry, material, dust cap shape, attachment points, material, etc. The bet example where the predictions and real world speaker do not agree is the JBL D-130, where the off axis response is easily an octave or two greater than the predictions predict.

Assuming you are comparing one to the other and they are identical other than nominal impedance... The 4 ohm cabinet will be approx. 3dB louder for the same volume setting on the solid state amp, because solid state amps are essentially ideal voltage sources. If you turn the 8 ohm cabinet up 3dB, it will be the same volume as the 4 ohm cabinet.

It depends on how good your judgement and common sense is. I see a fair number of speakers damaged from too much power (generally mechanical damage) because of poor judgement, false sense of security regarding power handling capacity, or an unfortunate accident like a plug partially coming out of the bass. If you are careful it's fine, how careful becomes a judgement issue.

The Yamaha powered speakers are actually quite good, BUT you are right in your assessment of how power and maximum SPL are derived. I am (mostly) familiar with how these seemingly incredible numbers are derived and as you suggested they are too good to be true in the context of the bigger picture of pro audio (at least the pro audio industry that I grew up designing in). You have to look at the actual specs and it will become more clear: The clarity becomes more obvious when you recognize that some years back, Yamaha shifted from their own in-house solutions (which were pretty good but did suffer from some reliability and support issues) to what I consider the gold standard SMPS/class D solution provided by ICEPower. They are using the 700AS2 power module, which at 4 ohms delivers between 800 and 850 watts RMS with only one channel driver (the LF channel) because the HF channel load is virtually zero for all intensive purposes. Since I have run extensive testing on this family of modules and was actually one of the beta evaluators of the module (back when I developed the original Subway D-800 in 2014). The continuous power rating is 850 watts RMS for the LF and 100 watts RMS for the high frequency (limited within the DSP), for ~950 watts RMS system power. Now, taking the peak power of 950 watts rms (Ppeak - 2x Prms) and you have 1900 watts peak, rounded up for "dynamic" marketing speak modifier) and you have 2000 watts "peak dynamic power" For the SPL calculation, they clearly say maximum PEAK SPL, so doing the calculations backwards using peak metrics and IF Yamaha is using peak for SPL as 4x RMS (customary in passive consumer PA speakers) that yields a speaker of 100dB/1W/1M calculated with no power compression assuming it was an unpowered cabinet. The problem with the above is that we are 3dB too high because program power is a made-up number, peak is really 2x the rms value, the cabinet now must be 103dB/1W/1M PEAK SENSITIVITY for this calculation to work out. I would easily believe 100dB/1W/1M (this really is a pretty good speaker with reasonably premium components) but I wouldn't take 103dB/1W/1M at face value without more investigation. Since we customarily use (in my world) or used to use (the marketing world) RMS metrics for sensitivity and SPL, correcting to RMS metrics yields 100dB/1W/1M average sensitivity which is awfully high but "possible". My better guess would be 98dB/1W/1M real world but I don't have one to test. Therefore the CALCULATED maximum average SPL for this speaker will be somewhere between 133dB/950W/1M (assuming they calculated using the 4x multiplier that the prosumer audio folks tend to favor. My educated hunch is that it's between 130 and 133dB but I don't have all of their spec footnotes. I do these calculations an awful lot, it's pretty easy to see what's going on when you live it.

I was unaware of this, hadn’t seen it in other products. I will have to explore this more to see who does and doesn’t do this.

Actually, most manufacturers use 1W/1M for their sensitivity metrics, not 2.83V. This gives more easily comparable sensitivity figures, especially when a manufacturer offers the same cabinet in 4 and 8 ohm versions. With the Ampeg maximum SPL figure, ~3dB of the gain comes from low frequency mutual coupling and ~3dB comes from double the power handling.