Phil Starr

What a great question and the answer is actually quite subtle and probably something we all ought to know if we are playing amplified music. Now the first thing is how do we measure loudness? Most people would say 'in decibels' but that's not quite right. The actual measurement of loudness is the phon. More of that later. The decibel is actually a slightly difficult concept and is used to describe slightly different things, it can be used to describe the electrical gain in an amplifier or preamplifier or the sound energy level at a particular point, they are of course closely related but not the same thing. For that reason the decibel (more accurately the Bel isn't accepted as a SI unit though it is regulated and recognised by ISO and IEC). It was initially invented by Bell for measuring the loss along a mile of standard telegraph cable with one decibel being the smallest loss that anyone would notice and 1dB remains the smallest change in volume that anyone will notice. The other way the decibel reflects our hearing is that it is a logarythmic scale. for us to hear a doubling of volume it takes 10x more power. It's a brilliant piece of organic/evolutionary engineering which lets us hear a leaf blowing across a forest floor several meters away but still cope with a herd of elephants charging or even a volcano or landslide. It's not so good when you are buying an amplifier, a 10W amp will give you 10dB over a 1W amp but that will only double the sound level. If you want it four times louder then you need to increase the amp to 100W to get your extra 10dB and then doubling again to eight times louder will need 1000W. Sorry to tell you but moving out your 500W bass amp for an 800W monster gives you just over 1dB extra headroom, only just noticeable and not really worth the expense. Now this is all about gain so far and in telegraph cables you get 1dB loss for each mile mile of cable and in amps doubling the power gives you an extra 3dB of sound. Go back and have a look at BFM's excellent explanation of what happens with 2x10's and 4x10's and you can see what a good deal an extra 6db is compared with the 1dB gained by buying an 800W amp So this is where we move from sound levels to actual loudness, how it sounds to us and the reason why some amps sound louder than others, the mystery or Trace watts if you like. Sound is frequency dependent humans can't hear bass very well, we feel bass when it's loud, our ears aren't much better at picking up bass than the stretch receptors in our guts and on our skin, Similarly we don't hear bats very well or anything much above a few thousand Hz, our hearing is much more sensitive at around 1,000Hz quite high in the midrange and the quietest sounds we can only detect here, the rustle of that leaf blown through the forest. When we remove the measuring microphone and pressure measurements we start again with a new decibel scale. One decibel is now defined differently as the quietest sound we can hear at 1,000Hz, something twice as loud (still at 1,000hz) is 10dB and your bass speaker producing 90db is 1,000,000,000 times louder than that at 1khz with just one watt or less! but at bottom E our hearing has lost most of that energy, deliberately filtered out by the working of the ear and then by the brain. You've lost 30dB or three of those noughts or in terms of hearing the 1.000Hz noise if 8x louder than the fundamental of bottom E. This is where the Phon comes in, it compares all the sound with the 1kHz sounds and allows for all the trickery of the ear/brain interface. Very few people use Phon's, we use decibels because we can measure them and anyone using them knows about Phons and equal loudnessbut there's one big practical thing about knowing all this for musicians. I terms of perception any aplification systen that emphasises the midrange is going to sound louder and for a long time speakers in particular have tended to have huge peaks in the midrange a 6db boost isn't unusual and this can make a cheap 100W amp sound as loud as a really honest high quality 400W amp. Actually the whole of rock'n'roll was founded on that sound so I shouldnt use words like honest, people love this artificial boost and it sounds good to them. The thing for you when buying an amp is to realise that Trace, Orange and many others are made to sound loud for a reason and if your tone rolls off those frequencies you might not be using all that boost. If you've read all this I apologise, I'm such a nerd As a final treat these are the equal loudness curves ISO version

Thanks for this, I will take it as a prod to get me moving on fitting a pair I've had laying around for a few years, I picked them up cheap and loved the idea of neo but the fitting got lost in the hundres and one other things I waste my time with

the idea is to help people by meeting them where they are. Mic cable doesn't mean mic level. I didn't say always lower quality sound, I used the word generally, it's practial advice aimed to helpsomeone struggling to maem head or tail of setting up a PA system for live music who will wonder why the sound engineer would prefer a balanced line. I'm not disagreeing with your comments but sometimes it's good to keep things simple if you want to be helpful. If maybe you read the words you'd have realised I'd allowed for exceptions but decidednot to make it more complex than it need be.

I don't think you can use @stevie's crossover design as it was specifically designed for the two drivers he used. Without giving too much detail he desings by having a target frequency response for each driver so they can be integrated smoothly. Having designed them using theory he then measures to response and repeatedly modifies the high and low pass filters until both do exactly what he wants. He then runs more tests to see that they integrate the way he wants. The Eminence 3012HO has a very different response around the crossover frequency to the Faital driver he designed for. Having said that very few if any manufactured musical instrument cabs go to such trouble so you acn get a workable result by using a proprietry crossover or by building a crossover based upon classical theory. There are online crossover design programs which will calculate the values for you. I've been happy with the results of these designs in the past

OK balanced is usually connected by a mic cable with three connections, it's noise cancelling so you can run long cables without picking up any electrical noise in the room. It feeds into a mic input on the mixing desk. unbalanced has only two connections and is usually connected by a jack to jack instrument lead, if you run long cables then it will pick up electrical noises and generally you'd expect lower quality sound. Your DI in the amp is effectively just another Aux out or FX out and probably the sound engineer would take this output and use a DI box to convert it to a balanced mic level signal. Depending upon their skill set and how long they have for a set up that is. It's probably important to know whether this DI is a pre or post signal. The pre signal is straight out of your bass with no processing by the amp. A post signal will have the tone you set up but crucially means any change in volume you make will also change the volume in the PA and mess up the FOH mix. There may also be a switch so you can change between a pre and post output. I think you probably are going to have to trust your sound engineer to get on with things. You can't really have one band member being able to change the front of house sound even if it is the bassist Just show them your DI and let them choose whether to use it or their own gear.

I'd imagine that any decent sound engineer who is going to be sniffy about feeds will have a box full of their favourite DI's and will split the signal for you. If the Di on your GK is a jack then you need to know if it is a balanced output TRS or an unbalanced TS connection which will probably be too noisy to be ideal

I think going forward in stages is the best strategy. If you like the sound then why undertake surgery on the cab. If you do want to port it then I'd port the back not the front. The cab was originally 'ported' by those cutouts in the back of the cab and personally I'd go for building ports based on extending them if I wanted a reflex cab. You can make ports of any shape with papier-mache I'm conservative with projects like this, a bit like The Repair Shop I don't mind the 'unfashionable' mid century look of the old cutout and I'd be thinking in terms of how I might be finishing the cab before taking a saw to the front. Perhaps ironically it's the look Bugera were going for in your other amp there. The colours of the Bell and Howell and even the grille cloth are a bit reminiscient of the old WEM Dominator amps. What a fun little project!

Nice one @David Morison just the information the OP needs. @Bone Idol The graphs show the advantagesof porting the cab. Crucially the -3db point reduces to around 70Hz which means all the second harmonic down to E is reproduced strongly. You've also got an extra 3db from around 110Hz which is significant. The mixed blessing is that you have roughly a 1db hump in response centred around 120Hz. This will give an artificial warmth to the bass sound which many bassists like and a roughtly half of us don't. The long and short of it is that you are going to get more bass if you port it and it's more than enough for you to hear a real difference. Whether you will prefer the lighter sound of the sealed cab or the fuller sound of the ported version is to an extent a matter of taste.

Hi, from what you are saying you want a pretty competent PA with nothing weighing more than 30lb/13.6kg and the budget is limited. That's a fairly difficult thing to do Your only advantage is that you don't need it immediately so you can take your time and wait for the right bargains to come along. I've run my Behringer amp with a couple of passive Yamaha speakers and it was perfectly competent. I don't know of your Sampsons but there are loads of cheap and good used passive speakers out there so swapping your amp might be the best idea the Behringer might be a good choice. There are loads of other cheap class D PA amps out there too so you may not just be limited to the NX3000.The Thomann amp is not completely undesirable so you might get most of the cost of a used NX3000 back anyway. It might be worth seeing if you can sell it with the Samsons too as a complete PA. People buying their first PA quite like a package if it has leads and stands thrown in Do you want advice on lightening the load. Getting a competent PA speaker at under 30lbs is pretty difficult at any price. The old passive ones tended to have wooden cabs, often heavy Chipboard or MDF so that is difficult and for a 12" system to be loud and have good power handling usually means a fairly hefty magnet again making 30lbs a difficult target. They exist but usually at a price. The other approach to problems lifting is to use a sub or two. they are heavy but stay on the floor and smaller lighter tops become possible. Long term it might be worth looking into a digital mixing desk, you can then ditch the outboard gear. Basically though I wouldn't rush into swapping things around until you have a clear plan of what you are trying to achieve.

I didn't save the simulations but you are of course correct, excursion is greater in a larger cab, directly in proportion to the extra bass. I think 'tears itself apart' might be a little too strong The power handling is reduced might be a bit fairer and of course this is true universally for all speakers in over-sized cabs. The thermal power ratings remain the same of course and since we haven't specified an amp or what the signal looks like the speaker might be perfectly happy. The actual reduction in power handling is dependent upon the mechanics of the speaker itself too and may or may not be significant. I was aiming for something simple to understand without saying anything that wasn't misleading. The truth but not the whole truth maybe

What do you use your PA for? Is it just or mainly vocals or are you putting more through it. Specifically kick drum, bass and keys which is more demanding? Also how loud is your band? That makes a huge difference as to your options. For anyone buying new nowadays I'd say the practical solution is pretty much always active speakers, quick and simple to set up and with DSP almost impossible to destroy in normal use, even the cheap stuff is reliable. With built in class D amps they can be pretty light too. Unless you really cut corners they are probably going to sound better than your Samsons, which you are happy with anyway. I've got the Behringer iNuke whic I think is the NX3000 in a really ugly case, same electronics. From memory it is 250W a side into 8 ohms 350W a side into 4ohms and 700W+ bridged. The same amp as is in the Bugera Veyron I suspect. Anyway it's a perfectly decent amp and not far off my Peavey IPR1600 amps

Without going into the maths the bigger the box the more bass you get from any given speaker. This isn't just offset by the additional problem of transporting something big and heavy; the 'wrong' sized box brings problems withgettinga flat response. Typically an over large box gives a droop in the bass response and is difficult to make flat, a too small from ideal cab will have a much higher resonance and less deep bassbut will give some bass boost around this raised resonant frequency. This happens with all cone speakers and in both reflex (ported) cabs and sealed cabs though the details differ. These are the calculated bass responses of a 10" bass driver in a 40l cab (blue) 20l cab (green) and a 5l cab (red). The medium sized cab in green gives the flattest response and a practical size. The red cab is way too small and -3db (the lower dotted line ) is 150Hz ish way to high to be useful. The large cab in blue has the response gradually falling from 500Hz and clearly isn't flat but crosses the -3db line way lower than the smaller cabs. Generally speaking cheap speakers with weaker magnets work better in huge boxes. A lot of old cabs tend to be large because speaker magnets in the day were weaker and powerful magnet systems were extremely expensive. Cheaper manufacture and better manetic materials have allowed box sizes to be reduced but big old boxes can still be fun and have a sound of their own.

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That's interesting to see inside the cab. for a commercial cab it has a lot of bracing, It would be difficult to adjust the tuning for most people but the folded port isn't unusual in small cabs. No damping material in the cab though? I'll try and get the calcs done this weekend.

I've had a quick look and the cab is roughly 25-28 litres and my guess is tuned to 50Hz. If you want to measure the internal dimensions of the cab and the port dimensions I can check that for you. That is typical for a 10" cab so probably a range of speakers will fit and work OK. I can do a quick check and identify any complete mis-matches with the drivers suggested if you give me those dimensions