agedhorse

Yup, insignificant heating issues.

Yes, the air gap will reduce the enclosure heating effects somewhat which is why I keep mentioning worst case.

My calculations show that with 25 degrees C ambient, a 31cm x 31cm x 31cm wood box with nominal 12mm thickness, the final temperature after "forever" (called the asymptotic limit) will be 33 degrees C with an 8 degrees C total temperature rise. This is about what I would expect worst case, pretty much trivial. Here's one handy enclosure calculator, there are several. These sorts of formulas are also used in the heating and air conditioning industry too, the walls will have a thermal resistance, and if playing in the sun there will also be heat gain due to radiation. https://www.powerstream.com/temperature-rise-in-an-electronics-enclosure.htm

There's not much heat involved, the average dissipation is less than 50 watts worst case. Not going to be a problem at <50 watts of dissipation, it would take DAYS to raise the temperature 10 degrees C above ambient.

The amount of heat in the speaker being discussed is insignificant in the big picture

I only have a couple of saddle mounting systems left for those amps. Yes, be VERY careful when "home brewing" any hardware for an amp, I have seen too long screws ruin an amp beyond economical repair (aside from being dangerous).

Yes, it makes perfect sense IMO.

My experience and testing suggests that it's very dependent on the preamp and preamp pedal. There are a good number of pedals that have no issues driving power amps to rated output, the real issue is a shortage of specifications that provide the definitive answer. For example the TwoNotes revolt preamp's MOL is +11dBu (from their specs) and it operates from a standard 12V DC power supply.

Designers certainly sit down with these graphs when developing amps and speakers. They really aren’t intended for end users, especially because of the misunderstanding of the correlation between the graphs and how this translates to end results.

If you can’t understand the specs, than you either need to have somebody help you, by lucky or buy products designed to work together. It’s no different than taking gigs where you need to sight read, if you can’t do it, don’t take the gig and don’t criticize those who do.

Since I spent much of my career in the pro audio industry, there are a lot of misconceptions going around. First, it’s acceptable to power an amp at 2x the RMS rating of a speaker provided there’s is minimal clipping or OD/distortion components in the signal. As soon as distortion is added, no matter where in the signal path, this recommendation changes and the power handling of the speaker and amp (in RMS metrics) should be pretty similar, and for heavier distortion, and heavy compression, the speakers should be capable of greater power handling than the amp provides (by ~50% if you follow the guidelines of some driver manufacturers including JBL). This also assumes that a proper HPF is also used. Crown’s recommendation is being taken out of context when quoted for bass guitar amplification.

Nominal output level doesn't tell you all that much, what's more important is the maximum rated output level of the preamp. Generally, it needs to be about 6dB greater than the rated sensitivity of the amp to be sure you have sufficient drive capability to drive the amp into limiting (most pro audio power amps have internal limiting, and you want to be sure you can drive into this rather than clip the output of the preamp). Also, all numbers need to be expressed as volts rms.

Maybe, but this is the reason for published specs... to be able to answer these kinds of questions without guessing.

Since the Carbines are fan cooled, the orientation is not important PROVIDED the vents are not blocked.

Maybe, but there's no input sensitivity spec anywhere in their documentation so there's no concrete way to know for sure without trying it (or asking the manufacturer what the input sensitivity is for rated output).

In general, pro audio power amps are +4 to +8dBu rated sensitivity with the level controls fully up. Generally you will want 6dB of drive headroom to avoid overdriving the preamp while approaching the clip or limit point of the power amp. Some power amps also have exhibit lower sensitivity when driving unbalanced inputs, and many preamps have 6dB lower maximum output level when driving from unbalanced (or unbalancing via adapters) outputs. These are all things that need to be tested/verified to determine compatibility. It’s not always easy with the limited specs that are often provided.

Read the answers you got from me (and others) on talkbass where you posted the same question.

I would suggest that in general, testing at the preamp out is much safer, and likely to get results that are plenty close enough.

Duplicate post

Yes, in part because speakers were being discussed within this thread as well and the combined measurements of speakers and amps tend to go hand in hand with these discussions.

Yes, you want to be VERY careful with bridged amps, and most class D amps are internally bridged. Most are not protected from a short between 1/2 of the output bridge and ground, this is not the normal way a fault occurs on a speaker out, the protection typically looks at either 1/2 of the bridge or (indirectly) the difference in current between the two halves of the bridge. Also, the level is (or can be) higher than many scopes can handle. This is a common way folks who are new to testing, or are new to electronics, or do electronics as a hobby destroy their laptops or interface (depending on where the interface is located). The fault is large enough that it typically lets the magic smoke out pretty instantaneously and catastrophically. I've been testing class D amps professionally for over 20 years, there are a lot of necessary tricks to get good results and data, especially power and THD data (depending on the modulation scheme and output reconstruction filter type). It's harder than it looks, especially if the numbers need to be accurate.

Beware that it's MUCH easier said than done. It's common for folks who do not do this all the time, with a setup that allows for anechoic measurements 1/2-space measurements (1/2-space is most commonly used for stage speakers because that's the closest approximation of the real world environment) to have errors of between 3 and 6dB SPL. Then they go proclaiming things that are simply not true because they have drawn conclusions based of incorrect and/or inaccurate data, which is unfair to everyone.

What is magnetic plywood?

You have to remember that we are primarily a tube guitar amp company and the marketing/website folks use a template that describes the output stage by what tubes are used (or no tubes at all, which would then be in the case of all the new bass amps "class D" because nobody uses power amp tubes in class D amps). When we used class AB output stages in bass amps, it was described as MOSFET - class AB It's assumed that players purchasing this level of equipment will understand this, and have done their homework by doing at least a little bit of research. There are numerous reviews, videos, forum discussions and even the owner's manual is available on line. In the back of the owner's manual is a tutorial on what class D is and how it works. We even discuss switchmode power supplies. I don't think it's misleading, and in fact in the entire 8 years of the Subway line this is the first time this has come up.

I am going to respond assuming that you have grossly misunderstood the manual rather than being intentionally disrespectful. The manual is crystal clear and accurate in its description of what the amp is and how it works. There is also a block diagram in the back that clearly shows the signal paths throughout the amp. There are also extensive specifications published at the end of the manual. The TT-800 is a 2 channel preamp, with a Boogie channel and a Subway channel. Both channels are tube driven and have tube gain stages. There is switching between the two channels, which then drive an 800 watt RMS class D power amp. If you are looking for an overdriven tone, I would suggest the Boogie channel to start, be sure the gain switch is in the high gain position, start with the channel master at the 9:00 position, all of the eq controls at noon, the high pass filter set to the 10:00 position, and turn the gain up until you hear the overdriven tone. Once you get this, use the channel master volume to set the overall volume of the overdrive tone. This is a starting point. If you have a low output bass or the setup of the bass had greater pole clearance than stock, or you have a light touch, you may not get as much overdrive as another bass with higher output. This channel has roughly the same gain structure as the Bass 400. That said, if this is confusing to you, or you continue to have difficulty understanding this amp, it simply may not be the right amp for you. It’s not as simple as other amps on the market (including the other amps in the Subway line) Another thing you can do is follow the sample settings page, but for overdriven tones, these settings were developed with specific bass types more commonly associated with overdriven and distorted tones. Hope this helps.