Phil Starr

@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

It's odd isn't it? Few amps guitar, bass or hi-fi will go down to DC (0Hz) and our hearing becomes less and less efficient as the frequency drops so we barely hear 50Hz. The best hi-fi amps usually go down to maybe 20Hz and the design of most amps inherently limits the frequency response at both ends. Basically just about all the amps we use have a frequency response that limits the upper and lower frequencies but I don't remember ever seeing anything in an ad or a manual or a bass amp saying what that is. That wouldn't matter if it wasn't so important. The speakers we use can't really handle those low frequencies. The excessive excursion pushes them into distortion, heats up the voice coils of speakers and can reduce the power reserves of the amp itself, but without information there is little we can do to protect our sound or our speakers short of an expensive fx box HPF which might be unnecessary if the amp has sufficient built in. I can't imagine the manufacturers don't know the -3db point for their amps or how quickly the low end rolls off but nobody seems to say.

I did wonder about saying something, it isn't that surprising as to change the impedance you have to change the voice coil at the very least. That could change the excursion levels and a few of the electrical characteristics even if as usual the maker keeps the same magnet and cone. Effectively it becomes a different speaker. That might mean having to tweak the cab to match what are now different drivers or making other minor tweaks to restore the 'sound' of the cab. The differences aren't necessarily that big but in A to B tests our ears are really sensitive. I'm not sure how much tweaking goes on in practice. Sorry can't help with wisdom

Hi Freddie, you might want to read this before looking for an Eden Cab, though there might be some bargains out there too, G4M are listing the EX112 for £199. Apart from that you might want to come back with a budget and indication of what sort of sound you want to achieve and what you will use the cab for.

I'm amazed you've only had one suggestion for the Zoom B1. It's pretty much the perfect practice machine. Studio quality amp and speaker sims, good headphone amp, aux input via mini-jack, tuner, metronome, drum machine a whole collection of good quality fx sims and you can use it live. It also runs for days on batteries or you can use a USB charger or external power supply. I have the B1ON but the B! Four is almost identical but with simpler and more versatile controls. Value for money is off the scale. I've been using mine daily for years too, they don't feel cheap. If mine went I'd simply go and buy another tomorrow.

That's great, the whole point of a self build for me is that you can take control and customise. To get that response I raised the tuning to 55Hz so with two ports you need them to be around 15.5 cm

How far have you got with the build? The port/s will need a bit of adjustment for this speaker. I think the 12PR300 is a good choice for this cab, normally I'd say spend teh extra for the 12PR320 but it really needs a bigger cab to get the best out of it. The only thing you really lose is that the excursion on the 300 isn't as good. You'll end up with a really lightweight portable cab though. One thought though is that I think Stevie's 2-way BC112T mk3 might suit you best of all, maybe even making the GK redundant. It's not the extra top end of the tweeter but the smoothness of the midrange response that you might like. If you went with the 320 you could use that in the new cab. However the 300 in the small cab promises a really lightweight portable solution.

I ran one other speaker the Fane 12-300 Pro because it is on special offer at the moment, and in stock at Blue Aran £64.88. At this point I need to know what you want, is cost the driving factor? Is light weight more important? Do you prefer an old school coloured sound or is clean more important? What are you going to use the speaker for, mainly practice or regular gigging once that returns? How powerful is your amp? This is the Fane (solid line) compared with the 12PR300.

OK I've had a quick look. This is the two Faital's the 12PR300 (green) and the 12Pr320(purple) in the 30l cab with the 12CMV2(red) for comparison. The box is quite small for pretty much any 12" speaker so they all show a hump above 100Hz. The 12PR300 has the flattest response and the Beyma has the biggest hump and is about 1db louder below 100Hz than the others, that's just noticeable. the 2db hump centred on 120Hz is very noticeable and some people like it. The flatter response of the 300 is nice, it will mean it is going to sound cleaner and will take to eq more easily. They aren't terribly different, the bass response is determined by the size or the box which is fairly extreme or a 12. however they all pass my test o the -3db point being below 80Hz meaning they will all give a decent response of the crucial 2nd harmonics of a four string.

Hi Martin, I haven't modelled either the Faital Pro 300 or the 320 in the 30l cab. I'll have a look sometime in the next couple of days and let you know what I think. I did look at the m both in another context and concluded that as a single driver I preferred the look of the top end response of the 320. Anyway Until it's been modelled I'll keep my powder dry. I'll also look to see if there are any other cost effective alternatives.

Hi all @carnabass has saved one of our old designs and is sending me some of our original material as pdf's. We lost a lot of photos of the builds too as Photobucket and other sites disappeared. Do any of you have any old material saved anywhere that might be useful, it could be of your own build even. If you have can you pm me I will go through all of the posts in the long threads but I already know a lot of information has disappeared and screenshots are great but I'm losing some quality by doing everything that way. I'm working to get my micro-cab build up this week. It would be good to get some comments up there about the format so I can learn from mistakes and polish up the other designs as I get to them.

Yeah big call out for Gear4Music. they let me know they aren't expecting any TC Elf stocks in soon. I cancelled the order and they dealt with that promptly. After all the problems with DV247 I'll definitely be looking to G4M in future.