agedhorse

The send impedance isn't going to matter much, it's the return impedance that dictates the effectiveness (based on orders of magnitude and the position of the elements in the circuit.) It's a good exercise to do the math, then it becomes obvious WHY. Return input impedances run anywhere between 10k and 100k, there will be a lot of effect at 10k and almost none at 100k.

A 56k resistor is series will work ok with some amps and not with other amps depending on the topology of the loop. I was just pointing g out a more correct solution for those who care about such things.

Neither, those topologies are used for impedance matched networks. All you need is a simple voltage divider.

Using a resistor like that depends entirely on the input and output impedance of the effects circuit. Generally, a more predictable result comes from a true series/shunt pad where the variables are defined almost entirely by the external circuitry rather than varying based on what is inside the amp.

If there are no bleeders designed into the circuit, or if there is a failure with the bleeder circuit, caps can store charge for a surprisingly long time if there's no load (like a typical plate circuit).

This is something that sound guys deal with daily.

The answer is in part that "it depends", but in practice far field cabinets that are designed to work together (reasonably similar math and phase response) generally will not have any more negative impact on the audience sound than "perfectly matched" speakers as these differences are WAY too far to the right of the decimal point to be a significant factor. I'm sure somebody could dream up some wild combination that would be a factor, but I'm talking about REASONABLE choices here.

I should have qualified my comment, because the smallest venues I typically work in start at about 1000 seats. A bass player fighting the sound guy in larger venues is absurd because the sound difference out in the house is SO different than what it typically is on stage (especially in proscenium houses). Also the tools I have in a typical PA are MUCH different (typically) than even the biggest bass rigs. multiple double 18" subs alone completely change the low frequency extension equation. Often a player will want more extension than what their on stage rigs are capable of, so they will boost the low end in an attempt to get more extension, yet all this does is generally muddy things up (especially on stage). The better choice is to allow the PA to do the heavy lifting and concentrate on their stage sound and how the entire band is impacted by it. With a little bit of coordination, often the sub bleed from the PA will fill in the missing lowest octave just fine on stage anyway.

Wait a minute, that's not true at all. The amps are the same width, the holes are in the same locations. The rack ears are identical, with the exception of the size of the screw holes which are about 0.1mm smaller in diameter. The holes on the rack ears can be opened up with a suitable size drill bit.

Of course the quality of the sound will vary from venue to venue, it will do this even if you have a single cabinet. Each venue has completely different acoustic properties, different absorption coefficients, different boundary conditions, and different combinations of path lengths. The PA and a (qualified) FOH engineer will take the bass signal off the stage and do what is necessary to work in the acoustic environment of the auditorium which will always be different than what is happening on stage. The better the engineer, the better the translation of the desired stage sound to the audience... and it has to happen in context with the rest of the mix also.

Everything within the Subway line is (of course).

There are a LOT of differences, including just about every parameter that applies to compliance, resonance, moving mass and then there's the design differences that account for cone (and suspension) break-up. Generally, the frequency that the high frequency rolloff occurs is quite a bit higher than with a bass speaker, and HOW it rolls off is different too.

It's not a crap shoot because there are manufacturers who do know what they are doing, and have a well established track record of doing so without issues.

It also allowed for the blood to pool at the front, sparing much backstage inconvenience

Yes, it is a myth when the speakers are designed with this in mind (and have the engineering/math to back it up). None of the efficiency equations contain any variables related to the size of the driver. Mixing drivers CAN be problematic, but it doesn't have to be problematic and in fact can provide the (knowledgeable, skilled) designer the ability to develop a range of voicings that is not possible (or practical) with a single driver.

In practice it MAY cause issues IF the cabinets were not designed with similar acoustic properties. This means sensitivity, power balance, phase response, complementary voicing, etc. The issues of acoustic summing occurs regardless of similarity of the speakers, it relates to identical speakers also, based on the number of point sources and the distance between the sources. Then there is the (usually) greater issue of boundary conditions, how the reflections within the room combine and the frequencies that each boundary act on (and at what level). The myth of only combining identical speakers without the considerations of all underlying factors that affect the summed response needs to be put to bed rather than be perpetuated.

If the Roland amp states that using the headphone out as a recording or aux output, that means that the designers determined that it was safe to do so. Different circuits can behave in unpredictable ways when used in ways the designer did not intend. This is why using a headphone output MAY not be safe unless stated so by the manufacturer.

Part absurd myth with a little bit of truth too. IF the speakers are designed to work together, that means sensitivity, power handling, phase response, complimentary voicing, then the combination may be better than 2 identical speakers. Of course, this can not be assumed, nor taken for granted. Where cabinets were not designed (in the engineering sense) to work together, it will be a total crapshoot.

Do not use a headphone out except for headphones. Some are not intended to be ground referenced and can either cause noise problems or in some instances damage. You can use a post-modeling line output into the effects return of the amp that is connected to the speaker. Check the owner’s manual to see if there may be other (safe) ways.

In general, unless there is a problem that can be traced to a bad tube, I recommend leaving well enough alone.

I see an awful lot of perfectly good tubes replaced, sometimes causing more problems than leaving well enough alone. For every player who is convinced a tube is "worn out", another player thinks that “bad tube” is the “best tube ever”.

At reasonable volume, a pair of Eon 515's should work pretty well (not ideal but certainly not garbage either). How exactly are you trying to us them, and how do you have things connected? I suspect that you have a connection/interface problem rather than the problem you think (unless you already damaged the speakers).

This is why I always recommend verifying that when buying any used cabinet you always check that the driver is original to the cabinet (the driver the manufacturer designed the cabinet around) and that the cabinet/crossover hasn't been screwed with. I see with enough regularity cases where the original driver was expensive and was either swapped out with a cheaper driver (and the original driver sold), or that the original driver was damaged and rather than spend the money they just slapped a cheap driver in the box. If the modification to your cabinet was done by somebody knowledgeable, you might be ok, but that will take a little research and effort to sort out.

I missed the date, hence their comments and conclusions being wrong for the times. 20 years ago, there were challenges, but electronic technology (especially power semiconductors) have come a long way since then.

All this talk of the "good 'ol days", how many of you were actually there in the good 'ol days, where hyperbole and bravado meant more that actual measured specs? First of all, when bravado claims about Trace amps being able to deliver XXX watts peak... for ALL amps regardless of brand, peak power equals exactly 2x the "RMS" power, so the AH-250 better be able to deliver 500 watts peak or it's not able to deliver 250 watts RMS. Next, since I worked for one of the companies that owned Trace before selling back to he original directors, I have more technical experience than most do about the product line. I looked up the technical docs I have for the AH-250 and the Vsat across the FETs is about 2 volts, add to this another 3V of sag at 4 ohms and you have a maximum voltage swing of 41 volts peak or 29V RMS. This equates to 210 watts RMS continuous, and with a 20msec burst rating of ~32V RMS or 256 watts RMS (burst). This is real world, and burst ratings were often used because they do represent how an amp feels. While Trace made an elegantly designed (IMO) product (especially for the time), there were stumbles in the execution throughout the company's life that resulted in reoccurring reliability issues that required a significant amount of correction. In fact, with NO real world losses (impossible to achieve) the maximum power of this power amp is a little more than 265 watts RMS. This is 530 watts peak, and not achievable with real world losses.