Moderators Kindness Posted August 14, 2008 Moderators Share Posted August 14, 2008 I receive a lot of private messages asking me about pairing amps and cabinets, some regarding specific pairings and some just looking for general guidance. I also have responded haphazardly to threads and posts where a fellow forum member may mention they are "pushing 3,000 watts into a "Brand X" 4x10. I figured I'd use this thread to consolidate some of what I've written. First, no thread about amp and cabinet pairings would be complete without a discussion of "underpowering" a cabinet. The short story, there is no such thing as underpowering a cabinet. When someone uses that phrase, you need to question whether the speaker/writer actually understands the subject matter. Agedhorse's thread in the FAQ regarding speaker failure explains the two mechanisms for speaker failure, both caused by sending too much power to a cabinet. If you haven't already, read and re-read this thread until you understand it. You don't need any technical background to understand the concepts as they are presented, so if you don't understand the entirety of that post, you may want to ask questions about where you are falling off track. Once you understand everything written in that thread, you'll be well equipped in understanding your gear. Agedhorse's Speaker Failure Thread Got it? Good. One of the questions I am asked the most is some variation of this: "I have "Brand/Model A" amp. What cabinet will handle the "X" watts from my amp?" The real question isn't what cabinet will take the wattage from your head, but which cabinet will produce volume/tone sufficient to meet your needs with your amp. You can have an enormously powerful amp and a cabinet that can't handle much power, but if you are achieving your desired tone and volume everything is just fine, you just might be carrying around more power than you need. Speaking of more power than you need, what about the guys playing with huge power amps into standard bass cabinet? Does anyone actually use 2,000 watts into a typical 4x10? Nope. No one. There just aren't bass cabinets that can actually handle that much power. Remember from the FAQ post linked above, there are two limits to cabinets, thermal limits and mechanical limits. Nearly every commercial bass cabinet is actually displacement limited (mechanically limited) - not thermally limited. What the heck does this mean? Go back to Agedhorse's post and reread the mechanical limit section. In short, due to the mechanical limits of a cabinet, it is not uncommon for a bass cabinet to start farting out in the bass region at about 1/4 the published thermal rating of the cabinet. Your 1,000 watt 4x10 probably can't handle much more than 200-300 watts below 100 Hz. Crank the volume, boost the bass and bask in the flubbiness. How am I going to know if I am exceeding the cabinet's mechanical limits? If you are listening to your cabinet you should be able to tell when it is farting out and you should dial the amp back. If it sounds good, it is. If you are interested in learning more about these limits, download WinISD and start modeling cabinets. If you have questions about that, post them and I'll help. Then why do I need a 2,000 watt power amp to get sufficient volume out of my cabinet? Many bass specific preamps are incapable of driving the power amp to full power. Power amps have an "input sensitivity" which is the voltage required to drive the amp to full power. If the preamp cannot output sufficient voltage, you will not be making use of the full power of the amp regardless of volume/gain settings. Thus, if your components aren't well matched (and it is often difficult to even find published specifications to make the determination) you might think you have your 2,000 watt amp on full go, but you might only be driving 200 watts. If you put a mixer or preamp in front of the amp to boost the signal, you might find you've been carrying a lot more reserve power than you expected. Lots of people want to know what equipment they need to be as loud as they want to be. Many know that doubling the power or doubling the displacement will give you a 3 dB increase in volume. +10 dB is generally accepted as "sounding twice as loud." In order to achieve a +10 dB increase, you need ten times the power or just over eight times the displacement (eight times the displacement is +9 dB). In other words, a 1x12 at 50 watts may be twice as loud as the same 1 x 12 at 5 watts. Similarly, eight of the same 1x12s may be twice as loud at 5 watts as the 1 x 12 at 5 watts. One of the reasons adding speaker displacement is generally a great way to boost volume is that most solid state amps will deliver more power to a lower impedance. Therefore, if you take a typical 1x12 on a solid state amp and add another 1x12, you have both doubled the displacement and (approximately) the power for a +6dB gain. +6 dB isn't double the volume, but it is a noticeable change. The other reason is power compression. Many speakers do not operate linearly within the range of power we use to drive them. In many cases the first 50 watts to the cabinet have a much greater effect than the next 50 watts. When you split the amps power into a greater number of drivers, you reduce the effects of power compression. Lastly, a little something about sensitivity ratings. I sometimes get asked something like: Cabinet A is 103 dB/w/m and Cabinet B is 99 dB/w/m - this means Cabinet A is louder, right? Well... it means that even if the specs can be trusted that Cabinet A is louder with an input of 1 watt. It doesn't tell you anything about what happens when you turn up. Maybe cabinet A will start farting out at a much lower power level than cabinet B. So even though it takes more power for Cabinet B to get loud, it might be that Cabinet B has a higher maximum output. Then again, maybe not. The point is, those specs are more related to how power hungry a cabinet may be, not how loud the cabinet can get. (In practice they tend to connote how mid oriented a cabinet is. Generally speaking, the higher the sensitivity cabinet will tend to be more mid oriented.) Hopefully these few short paragraphs are helpful in some way. They are just thoughts off the top of my head based on common questions I get and I would be happy to expand on any of them if anyone has questions. Link to comment Share on other sites More sharing options...
Moderators ThudMaker Posted August 14, 2008 Moderators Share Posted August 14, 2008 Great post, Kindness. Link to comment Share on other sites More sharing options...
Members Trauma_Luna Posted August 14, 2008 Members Share Posted August 14, 2008 this MUST be a FAQ, answered a lot of questions to me, thanks Kindness Link to comment Share on other sites More sharing options...
Members King Kashue Posted August 14, 2008 Members Share Posted August 14, 2008 I just want to figure out how to keep the amp gnomes from letting all the magic smoke out of my amps... Yet you've provided me no gnome guidance...useless...completely useless... Link to comment Share on other sites More sharing options...
Members T. Alan Smith Posted August 14, 2008 Members Share Posted August 14, 2008 Great post, Kindness. What HE said! Link to comment Share on other sites More sharing options...
Members catphish Posted August 14, 2008 Members Share Posted August 14, 2008 there is no such thing as underpowering a cabinet. . I think the confusion is similar to the way people toss out that audiologists say using only one ear plug you increase the risk of damaging your hearing. It's not that using one ear plug is gonna hurt your ears, but you're brain says I need to hear more and your more likely to turn up and then increase the stress on the one unplugged ear. It's not that under powering your amp hurts the speakers, but being under powered for the situation you run the risk of hurting your speakers due to human nature. Great thread. Link to comment Share on other sites More sharing options...
Moderators Kindness Posted August 14, 2008 Author Moderators Share Posted August 14, 2008 I just want to figure out how to keep the amp gnomes from letting all the magic smoke out of my amps... Yet you've provided me no gnome guidance...useless...completely useless... Feed the gnomes. Keep them happy. Take them to the zoo on a nice summer day. Link to comment Share on other sites More sharing options...
Members catphish Posted August 14, 2008 Members Share Posted August 14, 2008 Feed the gnomes. Keep them happy. Take them to the zoo on a nice summer day. but DO NOT take them to the monkey house, trust me. Link to comment Share on other sites More sharing options...
Moderators Kindness Posted August 14, 2008 Author Moderators Share Posted August 14, 2008 but DO NOT take them to the monkey house, trust me. Link to comment Share on other sites More sharing options...
Members T. Alan Smith Posted August 14, 2008 Members Share Posted August 14, 2008 but DO NOT take them to the monkey house, trust me. Really?? My gnomes thought the monkeys were delicious. Link to comment Share on other sites More sharing options...
Members RSBro Posted August 14, 2008 Members Share Posted August 14, 2008 I think the confusion is similar to the way people toss out that audiologists say using only one ear plug you increase the risk of damaging your hearing. It's not that using one ear plug is gonna hurt your ears, but you're brain says I need to hear more and your more likely to turn up and then increase the stress on the one unplugged ear. It's not that under powering your amp hurts the speakers, but being under powered for the situation you run the risk of hurting your speakers due to human nature. Great thread. This is what I try to explain to people who do this also, especially if you play more than one set. Your ears become fatigued very quickly (especially for us bassists) and if you make it a habit, this is a potential consequence. Link to comment Share on other sites More sharing options...
Members catphish Posted August 14, 2008 Members Share Posted August 14, 2008 Really?? My gnomes thought the monkeys were delicious. ...but expensive. I still owe Brookfield zoo $700k Link to comment Share on other sites More sharing options...
Members chunky-b Posted August 14, 2008 Members Share Posted August 14, 2008 ...but expensive. I still owe Brookfield zoo $700k That's why the monkey exhibit was closed last time I was there. The gnomes got hungry!! Link to comment Share on other sites More sharing options...
Members T. Alan Smith Posted August 14, 2008 Members Share Posted August 14, 2008 ...but expensive. I still owe Brookfield zoo $700k Doesn't Beam work at the Shedd? Maybe we can get a discount there for seafood. Link to comment Share on other sites More sharing options...
Members JacieFB Posted August 14, 2008 Members Share Posted August 14, 2008 So I hear about available PA Power "needing to be greater than what the speakers can handle". Is this also a misconception? In fact, I hear it in reference to PA gear more than anything. Also, I hear of guitarists speaking of using cabinet distortion...especially with a more vintage-esque setup. Is there a "safe" level of pushing the speakers beyond the safe level? I know, sounds like a dumb question. The engineer in me assumes that you're just pushing your equipment to an earlier failure. I wonder if there is anything else going on and if it's worth discussing in this thread. Thanks for the thread, Kindness. Link to comment Share on other sites More sharing options...
Members puckdude66 Posted August 14, 2008 Members Share Posted August 14, 2008 Thank you very much Kindness!! I've realized just how little I really understand about my equipment by just being on these boards that last few days. This post and the ohm faq have really opened my eyes to exactly how the heads and cabs go together. I really appreciate all of you sharing your knowledge with the rest of us. Link to comment Share on other sites More sharing options...
Members GreaserMatt Posted August 14, 2008 Members Share Posted August 14, 2008 Kindness for prez... Link to comment Share on other sites More sharing options...
Members T. Alan Smith Posted August 14, 2008 Members Share Posted August 14, 2008 I really appreciate all of you sharing your knowledge with the rest of us. Yup. Gnomes n monkeys=bad business. Link to comment Share on other sites More sharing options...
Moderators Kindness Posted August 14, 2008 Author Moderators Share Posted August 14, 2008 Also, I hear of guitarists speaking of using cabinet distortion...especially with a more vintage-esque setup. Is there a "safe" level of pushing the speakers beyond the safe level? I know, sounds like a dumb question. The engineer in me assumes that you're just pushing your equipment to an earlier failure. I wonder if there is anything else going on and if it's worth discussing in this thread. There are plenty of examples of cabinets that are routinely pushed past their linear limits, but run below their absolute limits. This is where the amp has pushed the speaker into distortion, but not so far that the mechanical structure of the speaker is damaged. There is a lot more that can be said in a lot more technical language, but I'm not sure how much info you are looking for. Basically, yes, you can run the cabinet past its linear response and you will be safe as long as you don't exceed its mechanical limits. For example, right at the threshold of farting, most cabinets will be okay, but once you cross that threshold it will be harder to know how far you can push it before you hit the absolute limit. Link to comment Share on other sites More sharing options...
Moderators Kindness Posted August 14, 2008 Author Moderators Share Posted August 14, 2008 Thank you very much Kindness!! I've realized just how little I really understand about my equipment by just being on these boards that last few days. This post and the ohm faq have really opened my eyes to exactly how the heads and cabs go together. I really appreciate all of you sharing your knowledge with the rest of us. I'm glad you're learning something. There are plenty of posters on this forum that will get you up to speed. Don't be afraid to ask questions! Link to comment Share on other sites More sharing options...
Members RSBro Posted August 14, 2008 Members Share Posted August 14, 2008 IMPE I found once I got the "Ohmness Doctrine" down, much more makes sense, as far as speaker "loudness" and excursion, as well as amp efficiency/performance. Link to comment Share on other sites More sharing options...
Members JacieFB Posted August 14, 2008 Members Share Posted August 14, 2008 Misconception. If the PA power needed to be higher than what the speakers can handle, you could never turn the amp down... I think I said that wrong. I just meant, well, if you've got 2 cabs rated at 250 watts, you need more than 500 watts to power them "properly". You did answer the question though. The myth carries over into the PA world as well. That's a pretty good description of what I was talking about with regard to guitar speakers, too. The only time I've seen it work and liked the results was a former guitarist that I played with. He had a 150 Triple Rectifier that he used with a 100 watt Marshall cab. He didn't get crazy with it, but just a little bit of pushing that cab beyond what it was supposed to be pushed gave it a nice powerful "thwoosh" to it--better than the ever-dark-sounding Rectifier cabs. Sounded like liquid ass when you tried to record it, though. Link to comment Share on other sites More sharing options...
Moderators Kindness Posted August 14, 2008 Author Moderators Share Posted August 14, 2008 That's a pretty good description of what I was talking about with regard to guitar speakers, too. The only time I've seen it work and liked the results was a former guitarist that I played with. He had a 150 Triple Rectifier that he used with a 100 watt Marshall cab. He didn't get crazy with it, but just a little bit of pushing that cab beyond what it was supposed to be pushed gave it a nice powerful "thwoosh" to it--better than the ever-dark-sounding Rectifier cabs. Sounded like liquid ass when you tried to record it, though. I recently sent a PM to a forum regular explaining to him why he likes his particular bass cabinets so much in a rock setting. The answer is that they are actually guitar speakers in a well tuned cabinet that allows the speakers to be run past their linear limits and create a nice thick distortion in the low mids that absolutely kicks ass for what he uses them for. The speakers literally start distorting at 20 watts below 100 Hz. The cabinet is designed in a way that allows the user to overload the speakers in the bass region without allowing them to be ripped to shreds. Link to comment Share on other sites More sharing options...
Members Renfield Posted August 14, 2008 Members Share Posted August 14, 2008 Well done, and I second that this should be FAQ'd. Link to comment Share on other sites More sharing options...
Members King Kashue Posted August 14, 2008 Members Share Posted August 14, 2008 Well done, and I second that this should be FAQ'd. As should his set-up thread, but that one isn't despite several calls for it... Link to comment Share on other sites More sharing options...
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