Phil Starr

Sorry the 'edumacation' only extended to telling you what an inverter is. Most of the commercial ones are three stage 'near sine wave' and whether they will work with your amp depends upon both the inverter and the amp. The good news is that if your amp has a switch mode power supply then you have a reasonable chance of finding something that works. If you have a Cass D lightweight amp and a friend with a caravan/camper it might be worth seeing if the amp works OK with their 'near sine wave' power supply The other battery solution is to look for a 12V amplifier. The 'bog standard' in car entertainment amps produce about 20w into 4ohms so if you can get an old car stereo with a mini jack input you could have 40W into a couple of 4ohm speakers and there are also cheap and cheerful Chinese stand alone 2x20W 12V amps around. Beyond this there are more powerful in-car amps that produce pretty much any power you want which have switch mode power supplies built in to the amp. I see @Mottlefeeder has pointed you in that direction already. It's not a bad solution if you want something cheap and only need to do this occasionally. It means you can use your usual speakers too. Worth looking at his thread on building a combo. The general problem with running off a battery is how long the charge lasts, It's not a bad idea to look to the most efficient speakers you can find. 3db of extra sensitivity is going to halve your battery use at the same sound levels.

The inverter plugs into a car battery (leisure battery is a spare battery to run a caravan) and turns the battery voltage to mains This one is £31

OK this is effectively our Mk2 cab then, don't tell @steviebut I really liked the SM212/1445 best of all yes you have fairly extensive bracing already, simple cross braces add a lot of stiffness for very little increased mass. Even a simgle batten linking the opposite panels will make a big difference. If you have any offcuts of your batten it would be a matter of moments to cut a batten as a tight fit and test it. Plave it slightly off centre if you can . A single brace will effectively divide the panel in two if you place it centrally and you can simply move the resonance up an octave. If you've ever damped a string over the 12h fret you know what that means.

Well done, I have to say that at this stage I usually spend far too much time playing with a half finished cab just for the joy of making a noise. I've looked at your pics and i like the bracing around the port/horn area which is a particular problem for the 110 we built too. that should be stiffening the back too so long as the front to back brace is firmly fixed. I'm a little suspicious of the frequencies you found resonances at 120Hz is so close to half of 230Hz it's possible energy is being transmitted between the side and rear panels. The easiest solution would be two braces across from side to side. bracing here might well help damp down the rear panel resonance as well. Which compression driver are you using with the horn?

there are a number of advantages of running two cabs at 8ohms The increase in radiating area increases the efficiency so you'll get an extra 3db of sound, this is greater than the roughly 2db you'll lose because your amp will produce less power into 8ohms. You'll double the power handling. The excursion of each speaker will be reduced this is usually the ultimate determinant of how loud the system will go and instead of the peaks taking the speaker into distortion using two will bring them back into their designed operating area. The halving of the power to each speaker will reduce the temperature and resistance of the voice coils at high levels reducing thermal power loss. stacking one speaker on the top of the other will bring the speaker nearer to ear level so you will hear the crucial mids and highs and be hearing more of what the audience will hear It looks cool

It's looking good, time to show the world.😉

Its looking promising, good proportions. As you suspect you'll have to brace. They are big panels for 12mm ply. One place we've had problems with is the baffle particularly between the speaker and port. Plan to have some sort of bracing there and leave plenty of meat to fix to.

G4M listing one in stock https://www.gear4music.com/PA-DJ-and-Lighting/Celestion-CDX1-1070-1-Compression-Driver-8-Ohm/2NRH

If you can take some pictures during the build please. I didn't take many as I never thought it would gather a lot of interest. If you build it I've also used it as a 'bright box' which it does quite well and is fun.

Hi John, the 50mm dimensions are the ones I used in the original combo, because I was using an existing cab I only had space to fit in a tiny port. When i redrew the cab for @RichardH I recalculated the port for the permanent design. It is tuned to the same frequency. The 68mm is the outside dia, inside dia is actually 64mm but it is standard UK downpipe. The bigger dia pipe is better because wind noise in the port is less likely so use that nless there is a good reason not to. I missed this yesterday because I was at rehearsal. I took my 6" cab and Warwick Gnome along to set up as a bit of fun. I've recently built a lightweight cab for our guitarist and I was teasing him about his 'huge' stack. Since it was there anyway I used the House Jam Cab for the first song. Our drummer is pretty loud so I had my usual cab but hidden out of sight (I know, I'm really childish) but didn't need it for the first song or the whole rehearsal. The studio isn't huge maybe 6mx6m but this is mad , I used a bit of compression and some trimming of the bass with my Zoom B1 but backed up against the wall the sound was really just there, sitting in the pocket and plenty loud enough for rehearsal/on stage monitoring. I'm starting to wonder about a 2x6.....

Thanks for that. I'm always ridiculously pleased when a build makes it's first sounds, even more so when it is someone else's. That Faital is a nice driver but recommending something when other people's tastes and needs vary so much is always a bit of a risk. Really looking forward to seeing the pics,

@anrque how is your build going?

There's loads of resources out there but as a practical, working source of advice The Loudspeaker Design Cookbook by Vance Dickason is as good as it gets, TBH nowadays it's my bible, I read a lot of the more technical stuff years ago but don't go into that level of detail in building and designing speakers. It's my go to when I want to check advice I give here is correct as far as it goes.

That looks a lot better, you'd need to think about how the pipe butts up against the flare as that joint would need to be as smooth as possible. Think as if you were designing the aerodynamics of a car, Any sharp joins are going to cause wind noise and drag. Maybe a collar running outside the flare and the pipe? You'd also want to slim down the front flange unless you intend recessing it into the baffle. This is now looking like a really interesting project.

Hmm it's 50 years since I did any fluid mechanics but there's not enough of a radius on that design to make any difference to the air flow inside that port so the only advantage IMO is that the length is continuously variable. though the lip covering any problems in cutting a hole in the baffle will improve the finish. To be honest it's a lot quicker to cut lengths of pipe

I think you've answered your own question here. I don't consider myself much of a musician but there are people out there with apparently no idea. I was a late starter to music, still suffer from imposter syndrome and I'm still pathetically grateful to anyone who will have me in their band but there have been a few occasions where I've felt we've been letting the audience down and I'm never going there again. I've a really lovely friend who plays keys and he's partnered with a woman with a truly great rock voice but he can't keep time and has an inability to listen to the rest of the band. I haven't the heart to tell either of them but I think every musician in the area knows the problem and we are all letting them hang on to their dreams whilst making our excuses. Excuses you will have to make. If you are going to stand up in front of other people I think you owe it to them to take it seriously whatever level you are playing at.

You should add maybe 8 litres for the speaker and port. if you can flare the port at both ends it reduces the sudden pressure changes and ultimately the turbulence you get which causes port noises at high levels. However it will also mean that if the tuning is out you can't easily change the length of the port to re-tune. I suppose one answer will be to make the flares so that they are designed to push fit into the end of a standard soil pipe. That would be quite neat and there might even be a small market for them However I've never had a problem with port noises in a band setting, even with smaller ports than these which should be better than the original Peavey ports anyway, if it's important to you and you have expertise then give it a go but it's a luxury touch not essential IMO. Adding a tweeter will change the sound of the speaker. That's complex because of the way we hear sound and because the changes will depend upon the exact characteristics of both the speaker and the compression driver/horn that you choose. If you like the sound of what you have then do you want to change the sound. Crossover design is complex and still requires a lot of trial and error and ideally proper measuring equipment. You can buy a generic crossover but it will only be very approximate. I can talk you through some of the design problems but I'm not really an expert. To be fair a lot of commercial cabs with horns don't have well designed crossovers so you can get something that 'works' from a generic crossover and you might like the sound. It doesn't have to be 'honest' to sound good. There are pluses though in having a horn. A 15 is very directional in the mids and tops so what you here and what the audience hear wont be the same. The upper range is all coming with the cone under break-up conditions when the cone is no longer a pure piston and as such is distorted and often slightly louder on axis than the bass. It's part of what gives 15's their lovely old school sound. Get the horn and crossover right and you'll get a much more modern flat response. More like a bass played through headphones. It's up to you really but you could just build the cab but leave space on the baffle (front board) to retro fit a horn if you later decide it's a must have.

I'm not familiar with the Scorpion itself, all my Peavey experience is with the Black Widow speaker which looks to be similar. The dust cap which you get on every speaker (just about) is usually just a fabric or paper dome stuck down onto the middle of the cone , primarily to stop dust and crud getting into the magnet/coil. The foam is/was found inside the back of the magnet if I remember. I haven't had that problem. Like the BW you can remove the magnet off the back of the scorpion and see inside and clean out any debris. If your speaker sounds good and doesn't make any 'off' sounds then you probably don't have a problem to solve. So I'm recommending a 55litre cab with a 4" soil pipe forming a port, you only need 7.3cm length though. Are you confident enough to work out the panel sizes yourself? This might be useful it has instructions for taking the magnet off. Be gentle with the voice coil though, it's easy to damage with a big heavy magnet.

That sounds like an interesting project

Well having a quick look there seems to be nothing remarkable about these cabs, looking at the range of MB offer I'm guessing these are going to be their base range speakers in terms of price. There's a couple of mentions of value for money and suchlike amongst the hype. The modular aspect is just a reaction to us downsizing and going for rigs that are just acting as on-stage monitors. You only have to go through the pages here to see that the increasingly normal rig is a 12" cab with a second for 2 'bigger' gigs or when PA support isn't good enough. A few of us are going down to 1x10's with a second held in reserve and there have been plenty o quite long threads asking about 2x12's or two 1x12's. Most of the advice seems to be along the lines of get one of these then add a second identical cab if you need it. MB are just reacting to a market BC is helping to create. Even our own BassChat self build designs are sometimes being built as one cab with a tweeter and one underneath without and people are combining Barefaced cabs (other brands are available) in a one with one without combination. Markbass seem to have a marketing model based upon lots of choice of similar products with small differences, look at the variations of the MBII/III 300/500 amp that are available. The 1x10 200W cab in a 30litre box is completely unremarkable, we've just published our own version of a 200W 1x10 with or without a tweeter a few months back. In the end it will depend upon what it sounds like and what it sells for. @MoJoKe may have more information. My only beef is the 4x10 picture, if you do buy them a vertical stack with the tweeter at ear level please That arrangement looks so wrong!

Again there is a difference in concept between the 'natural' roll off of an amplifier and the deliberate removal of the lower frequencies to protect the speaker and clean up the sound using a specially designed circuit. If the amp is built in it would make no sense to allow the amp to drive the speaker into a place where it could be damaged, one of the advantages of active systems over passive. Reliability is essential to the manufacturer both in terms o reputation and in repair costs so making active speakers fool proof just makes total sense for sellers and customers Increasingly people are using DSP to protect the speakers in powered PA amps. There are a whole series of parameters that can be monitored to make sure none of the drivers goes outside it's design limits. Even cheap as chips Behringers with DSP offer really high levels of speaker protection. My PA amps have the option of setting HPF frequencies and roll off rates as well as hard and soft limiting and crossover frequencies letting me protect my passive speakers and all of this is pre-set to match the drivers in most active speakers nowadays. It makes a bit of a nonsense of the 1000W PA speaker claim. The amps may well be capable of short term power at this level but the DSP makes sure that inappropriate power never reaches the speaker but hey, we are getting near total reliability and are able to drive the system as hard as it will go with no worries about breaking anything so it's all good.

Fair disclosure, my chart was just calculated, not measured, and based upon the oft quoted 24db/octave 30Hz claim. I should probably have said Thumpinator type filter. I also don't know why he's being coy, it's a bit late to copyright a frequency or a 4th order filter and a matter of minutes to just measure the response.

I don't think it's likely to be a filter as such (without any knowledge at all about the ABM's design) Any series capacitor in an amplifiers circuit will act as an HPF. They are frequently used for decoupling DC voltages where you want the signal to pass but need to block the voltage in one part of the circuit from affecting another. One of the things the designer will have to calculate is what effect each has on the overall frequency response of the amp. Someone with very good hearing can detect sounds between 20-20,000Hz so many amps were designed with a target of below 20Hz as the -3db point. If Dave Green is sold on HPF then it may be deliberately designed into the CTM, if so then another good reason to go Ashdown.

That makes sense o your comments then as Al said why not get in touch and see what they have to say

The trick is to remove all the troublesome stuff that causes problems without taking away anything that makes the bass sound good. Easier said than done of course but there's a balance to be struck and it's usually something around 30-40Hz as the -3db point and 24db/octave filtering which is sharper than the natural roll off of most amps. There are multiple reasons for doing this and the optimum will vary. Mixing live I've filtered out everything below 50Hz and no-one has noticed once the bass is in te mix. Anyway here is the problem. This is the excursion of a typical speaker at 200W in a ported cab. As you can see the cone moves further as the frequency falls. The port takes over at 40Hz and below that the cone is flapping about madly. For this speaker the most it can move is about 4mm and then it leaves the safety of the magnetic gap. Below 100Hz it's pretty much into distortion at 200W and that is going to distort everything, not just the bass. Below the port tuning it's crazy, the cone can't physically move 25mm in both directions and you'll end up with a damaged speaker. All this to make frequencies you can't hear. Below is the excursion with a Thumpinator