Phil Starr

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.

Hi @RhythmJunkyWelcome to BassChat

Ok good question I'll give the answer in two parts. The volume of the cab is very important as it has frequency dependant elements and non-frequency dependant effects. It acts as a mass on the back of the cone, a spring and a sponge and that is in any speaker cab. In a ported there is the added complication as it acts as part of a tuned couplet with the port. The conventional theory on speaker design changes all these things into resistive, capacitative and indictive elements and crunches all the elements of the cab and the driver to balance them all out into a workable cab. The volume and the tuning of the cab have all been calculated to match the speakers we use and then we've built and tried them to make sure they meet the specs we started out to achieve. The shape of this volume matters far less than the volume and tuning, the differences caused by shape will be less noticeable and some will be below our ability to detect them. The real issue with changing the shape of the cab are resonances. It's quite possible for a resonating panel to put out as much sound as the speaker and you can both hear and measure resonances. There are also resonances in the air of the cab and in the port itself. The frequency of the resonances are set by the dimensions of the panels, their flexibility and their masses. If you are sticking to plywood as in all our designs then it's only the dimensions of the panels that are changing so you'll be shifting the resonances upwards with smaller dimensions and down with longer ones. The worst thing you can do is to repeat dimensions so panels all resonate at the same time. The worst shape is a cube and the ideal is one which sticks to the golden ratio (roughly 1.6:1) The advantage of using a ready made design like ours is that a lot of this work is done for you. In the later designs cab resonances have been looked at and bracing suggested where needed. The joy of a self build however is that you can personalise your build and let's face it there are only a limited number of options open to you if everything is to fit in. You'd probably have to be very unlucky to hit a truly awful resonance and so long as you know to look you can always find the resonances with your fingertips and knowing about them gives you the chance to deal with them by bracing the panel concerned.

I think it is a question of a design choice. You can design a flat response speaker and then use eq/modelling to get the sound you want and that is how the Mk3 was designed. Or you can decide to 'voice' the speaker to make a satisfying sound 'out of the box'. Different people prefer different approaches. I don't think it's about right or wrong, for me it is abut what works. It isn't really about efficiency or wasting power. the blue line (higher tuning) shows an extra 2db at 100Hz and the red and extra 2db at 40Hz, so which is louder? They are both the same sensitivity for the majority of their response. I designed the MK1 to give a satisfying result for a first time builder and gigged it extensively to check that it worked in a band situation. The secondary aim of these threads is to de-mystify cab design, there are lots of these little tweaks in commercial designs where the compromises are made for you. When it comes to something simple like this where blocking a couple of ports lets you hear the difference at home and decide for yourself then it's a perfectly sensible thing to ask and try out. @Gottastopbuyinggear might well decide the decisions I took all those years ago weren't right for his needs today.

Bugera Veyron? Meets your spec except for price. It's only 800W not 2,000 but it is 800W

Hi John, I wonder whether this belongs in an amplifier thread. In many ways this looks like another amp like the Gnome/BAM/Elf, if so it's a remarkably cheap option but it's roughly the same size and power output. As it happens I'm sitting here looking at a little power amp board based on the TDA8954 which will give this sort of power given the right voltage, it cost £10.35, I bought a preamp at the same time for £6.54 of course it needs a power supply and a case but it isn't hard to see how cheaply switch mode stuff can be built. Last year I repaired a Behringer active monitor with a replacement plate amp. That cost me less than £100 and that had two amps in it, nominally 250W for bass and 50w for the tweeter and that included most of a case and the power supply. I suppose I'm saying it can be done and if you get Thomann's three year warranty why not try it? I'll be mainly running my Gnome of a B1 too.

Yes i remember gigging with the prototypes, they could be overwhelming My drummer at the time once repeatedly asked me to turn it up, so I did, at the end of the first set he said 'I couldn't hear my effing snare drum' covering one port won't be enough to make a real difference try going down to two. This is what it will do to frequency response The trouble is that it also affects power handling and potentially port noise. this is power handling. 180W @70Hz isn't too bad but you need to know

Some of you will have noticed that I am (very slowly) trying to archive the BC designs so that people can go on building them. What has become apparent is that many of the parts have become unavailable though substitutes are always coming through as well. I'm going to tweak the designs as I go and one of the things I will do is move to only using standard building pipes as ports as the pre formed ones only seem to have short runs. The horns too have short lives it seems. I'll double check but I think the Mk1 was very slightly bigger than the Mk2/3, Both nominally 50l but I allowed slightly more 'extra' space in the Mk1 to allow for extra intrusions into the cab. So long as you use the Mk1 ports in the Mk 1 cab and Mk2 ports with Mk2 cab it won't be an issue. The shape was a result of requests that the cab should take an old heavy iron 19" amp with no overhang. My intention is to do an 'easy build' version of Stevie's mk3 shape cab as a revision for the Mk1 and that will go up eventually. In the meantime you can build the Mk3 shaped cab without a horn if you want. Retrofitting a horn has always been an option though you'll need a new baffle as I didn't leave enough space for the specified horn in the Mk1. The horn/crossover for the Celestion 1445 version of the Mk2 is still up on the thread and that was my favourite combination. Stevie is our crossover expert but I don't think changing the cab will make a significant difference at the crossover point but changing the horn or compression driver will as he pays a lot of attention to anomalies here and is very careful about the matching of horn and driver . @Gottastopbuyinggear I'm not sure why you would want to build a Mk1 with a higher tuning? Stevie and I differed over the preferred tuning and it is possible to come up with a series of tunings that will work well each achieving different compromises. There's a lot of discussion about it in the original thread I believe. The effects are complex and affect power handling, excursion and the shape of the response well away from the tuning frequency. We did listening tests too before we settled on the recommended tuning. There's lots of good reasons for tweaking the tuning but it certainly isn't as simple as taking out a bit of bass by tuning higher. Let me know what you are trying to achieve and we can see what the options are, you might be better off reducing the size of the cab for example. There's a lot of psychoacoustics involved too, just adding the horn will make your cab sound less bass heavy.

This is possibly the bit to look at first. The way to keep the vocals 'pristine' is to keep the level of bass reaching the vocal mics to an absolute minimum. What you want is for the audience to hear both the bas and the vocals and everything else clearly in exactly the right amounts. That's not about keeping it out of the PA it's about getting nice clean signals to the PA. The perfect solution for vocals is no backline at all, no sound bouncing around the stage and being picked up jumbled by the vocal mics. Ideally use in-ears but next best thing use your wedge monitors for bass. If you have to have a bass amp on stage use it for your own monitoring and keep it as low as possible. As to the new speaker without technical details we can't really tell you what sized cab sealed or otherwise would work well. Can you get the TS parameters for the speaker?

The marginal cost of a combi that would keep us all happy isn't that great but Neutrik would want their cut I guess and £10 on a £120 amp is significant. You'd think that Trace would want to distance themselves from their much cheaper competitors though.