Phil Starr

Good question. I've also come across situations where the PA is set up with a smiley face on the graphic as a starting point. Please don't listen to this advice. I came across it only a few weeks ago when an inexperienced guy hired in a PA where we were playing. We had a BBC engineer on the monitor mix and the hirer on the FOH. Result was the on-stage sound was glorious and FOH a bassy mush throughout the whole day. So you want your PA to sound like what you are feeding in. The graphic is only there to adjust for room acoustics IMO. If you want the bass or kick louder turn them up in the mix. If the bass sounds thin then adjust it with the channel controls so it doesn't. Don't boost both if you only want to affect one of them. The trouble is that a lot of these 'rules of thumb' date from the times when PA and backline were in their infancy. If your PA was composed of underpowered amps and WEM 4x10's and you were mixing with the bass coming through a guitarists 4x12 boosting the bass and treble made some sort of sense, though replacing drivers was routine as a result.

Here's the thing though, and this has only just occurred to me re-reading my own post. Turning up the bass and treble at means that you are effectively turning the mids down relative to the two extremes. The equal loudness curves show that just turning up the volume sounds like you are turning down the mid balance. Ever had that experience of a band being really loud but somehow not being able to pick yourself out of a mix? Well the mids are what you need to hear yourself and a nasal mid balanced sound always sounds awful at home but a better fit once you are mixed in with a band. Equal loudness could be most of the reason for that. Especially if everyone else is turning up at the same time. That's why I love these discussions, I'll be mulling over that all day, and i now feel stupid for not having thought about it before

Back on track, I did warn you I like a graph. This next one is probably familiar and I think the 'science' reason behind the 'smiley face' eq so many amps have when the controls are all set to noon. Each curve measures how much energy you need at each frequency to make sounds equally loud. Effectively it draws where you'd need to set the graphic to get a flat sound. You'll notice there isn't watt in sight, sound is measured in decibels. The easiest line to explain is the 'threshold' line. In this case 0db is set at the quietist sound you can hear with all the other decibels set relative to that. Originally the first measurement was taken at 1kHz so that is where zero was set, a bit like setting 0 as the lowest temperature they could get at the time at the bottom of the Fahrenheit scale. So this is why we like a smiley face eq. If you look at all the lines they show a broad dip in the middle with lots of extra volume to get you to hear the bass and treble as loud. And let's face it when you only had two tone controls on the radiogram you only ever boosted you never cut. Looking carefully to hear 40Hz (bottom E) at all you need 50db of bass boost. That's 100,000x the power! If you look at the other extreme at 100Phon (about the level of sound where the drummer sits in a rock band) you only need 20db of boost. The bass sounds 30db louder and only needs 1000x the power. Subjectively it will sound 8x louder relative to that 1kHz mid. So turning up the volume of anything amplified makes it sound like you've boosted the bass and treble and here's the punchline: boosting the bass and treble at any frequency makes an amp sound like a bigger more impressive amp. I wonder why anyone would want to do that in a showroom situation

OK it looks like I'm going to have to do this What about the shape? As John has said the only consideration so far has been to match the Ashdown After 8 in shape. That's pretty niche so I can change the shape to a more conventional one. Less cube more Golden Ratio. this would cut down any potential resonant modes inside the cab and potentially clean up the sound a little and it would also help portability as a deep cab can bank against your legs. On the minus side it looks quite cute as it is and is so small anyway that portability isn't really an issue as it would be with a larger cab. I suspect this will also be used for home practice a lot of the time. what shape has the most room appeal, something with the minimum height or something with the smallest footprint?

I'm looking at using REW which is free and pretty powerful. It's also fairly well supported and there are plenty of instructional videos on You Tube. Any 2 in/2 out interface should work and I'm probably going to use my USB mixing desk. REW lets you do a calibration plot so if the interface does have any artefacts they can be allowed for. There might be a problem with connecting some BTL (bridged) amps to earth but most DI boxes should let you fix that. Currently John is doing his measurements with an oscilloscope and other software. I'm not sure if that is an issue, if they lead to different results then we can investigate. The only other issue I can think of is all agreeing a protocol so data can be collected and compared. For measurement I think 20-20kHz measurements at low power makes sense and REW allows you to centre results at 0db. Displaying results as a graph is useful but a table summarising results would also be good as a quick reference (-3db points, frequency range, rate of roll off, centre and size of any frequency anomalies) Ideally it would be good to make the data files themselves available to anyone who wants them. I've no idea about how they are stored. I'm no expert on this so any help/suggestions are very welcome. We might need to take this across to another thread if this takes off

That's a shame, I'd have loved to have a listen to your combo but when i get back from setting up for the shootout it had already disappeared. Maybe next year.

OK it is starting to look like a plan, it might take a while to sort out the easiest way to do it and write a how to guide but worth doing. I'll have a chat with John when he gets over his covid and I'll have a good look myself. That might take a while as we have a couple of new band members to rehearse in but it could be an interesting project.

Welcome to BassChat Go for used, if you buy sensibly then you will be able to use your bass for a year or two and then if you want sell it and get all your money back. With the amp you will get something that will sound better and encourage you to stick with playing, cheap practice amps are often unrewarding to listen to. £500 is a good budget. the good news is that there are a lot of really excellent budget instruments around, it is almost hard to go wrong and if you spent half of that on it you could get a really usable gigging bass. A lot of us are moving on from old heavy amps and speakers to more modern lightweight gear so again there are bargains out there. I've picked up some real bargains off FB marketplace recently but it is worth buying from the ads here if you see what you want. There is kind of an honour system here and you can also check people's history as sellers so it isn't as unreliable as Evilbay.

. We had hoped to measure a lot more amplifiers. There were plenty there at the bass bash but we simply ran out of time. The result for the Gnome was so unexpected that we spent precious time checking everything over. I had to set up and run a speaker shootout in the main hall and couldn't act as gopher for John. Anyway it was an interesting experiment I think we'll repeat and try to grab more data on other amps. There is free software to do this so if you have a simple two in and two out interface you should be able to do this at home so maybe a few of us could work together and build a database

You are perfectly correct, it could be described any number of ways, but I see it as a shaped response. I'm looking from an engineering perspective and trying to reverse engineer what is going on inside. Any power amp will have a flat response up to whatever frequency that particular amp can manage and flat down to the point where capacitance and inductance filters out the bass. Generally this will be in multiples of 6db/octave. So 6/12/18/24db for ist,2nd.3rd,4th order filters are what I'm looking for. That means the response is shaped from flat, probably in the pre-amp stage and somebody has designed that shaping into the amp. In this case they helpfully quote 400hz as the centre frequency of the mid control so it is set deliberately down by around -4/-6db at 12o/c, turn it up by that much (around 3.30 on the mids) and there will be roughly a straight line between 150 and 1.8khz. That leaves the rising response of 6db between the bass and treble. Clearly that is effectively a cut in the bass and a boost to the top end to give it a bright sound.

You'll have to ask John @Chienmortbb that. I was demonstrating speakers for most of the time whilst he was taking measurements. The aim was to find the 'flat' response though so I'm fairly sure it was flat.

I do feel sorry for manufacturers, they have to do these things even if their engineering instincts tell them not to. Though to be fair a 'sounds good when practicing' button isn't a bad idea Below is the response of the Ashdown RM500, you can see the rest of the measured responses we took HERE So when looking at this I ask three questions. Is there a low end roll off/HPF (where and how quickly)? Is there a high end roll off (same questions)? Are there any irregularities that make the amp non-flat. So roll off I take from the -3db points and the rate of roll off I calculate over 2 octaves from there. The highest sensitivity of this essentially flat amp is around 13db so the minus 3db points are where it crosses the 10db line and the roll off is more or less 6db/octave. Ashdown clearly know what they are doing, -3db at around 50Hz and a gentle roll off is going to give you plenty of bass without overpowering and offers a little protection from idiots blowing speakers. Bass output is almost all in the 100-4,000 Hz range and that is flat with another gentle roll off above that. If you want a midrange dip there is a button and tone controls. The top end roll off will also tame one of the problems with single driver cabs (as opposed to ones with horns and crossovers) where most cone drivers have cone s breaking up in the low KHz region

And as you know any headline or bit of clickbait with a question in the title isn't going to offer an answer For me this is a surprising question, I'm a lot of a nerd, Science trained and I spend my time looking at graphs, numbers, measurements and formulae. I've just hit 4,000 posts and most of them are about speakers and specifically about the technical side of bass amplification I like to share the little bits i know and hope it helps somebody somewhere. I'm just wondering though whether those who do it by feel, by listening and twiddling and doing all the wrong things may have it right. Is FRFR the holy grail of bass? Or is there a technical reason why we are constantly chasing new and better gear other than just GAS? So here is why I think we have a problem. We spent a few hours this Sunday at the SW bass bash measuring amplifier responses. All controls set to noon, as you'd expect that to be more or less flat and the amps would all look the same, but far from it. We were only really interested in answering two questions; did the amps all have built in HPF and was noon really flat. What we found was that the amps we tested varied wildly. The Ashdowns all had built in top end roll off, The Trace Elf had a smiley face response, The Warwick Gnome and the TC BAM had a rising response and most of the amps had irregularities, lumps and bumps in the frequency responses that would be clearly audible. Not one of the amps we measured could be described as 'clean' or hi-fi although some of them have been. Never mind class D or AB the pre-amps alone aren't flat, the tones aren't neutral. Now add in that bass speakers aren't neutral either, we've been measuring these a lot recently and even some really expensive boutique cabs are nowhere near neutral, or natural come to that; have you ever heard an amplified sound that fooled you into thinking you were listening to something real and acoustic? Now I've got loads of thoughts on this but let's look at one example. My Gnome has a crazy response a bass hump centred on 150Hz, a huge midrange suckout at 400Hz and an overall that just rises and rises. Oh and the bottom end is rolled off at 80hz. Fortunately it has a midrange control centred at 400Hz so balance is almost restored if you turn it to 3.30. I'll show you. Now a lot of speakers have a hump at 100hz and also have a mid cut , but not necessarily at 400Hz, they might have a crossover to a horn at 2,500hz which creates a dip there and that horn might also have a rising response up to 10,000Hz and then fall off after that. So now you have two peaks at the bottom end two dips in the middle and heaven knows what at the top. Good luck sorting that out with bass middle and treble controls. And of course you might want a middle drop out but at some other frequency than either the amp offers or the speaker gives. Now here's the thing, I quite like my Gnome, I've been using it a lot though with the mids boosted on my active P and a boutique FRFR bass cab. I've been a bit worried about the amount of mid boost but it's sounded OK and once the gig starts you've other things to worry about. So is it better to know all this stuff, seek the 'truth' and hunt the perfect rig or to live in blissful ignorance and just max out the tone controls until it's time to trade your gear for new in the eternal quest for sound nirvana. What do you think?

Just for comparison this is the response of the TC BAM with all controls at 12.00. It does show a resemblance to the Gnome and Elf in the midrange dip at 400hz and the generally rising response. The Elf is clearly filtered above 4kHz compared with the other two. The Bam differs in having no HPF filtering out the extreme bass. In between I'd say they show a family resemblance. I don't know how the BAM response was measured as it was borrowed from another forum. I'm sceptical about the response of the bam below 50Hz as I really would expect some sort of roll off to be happening, having said that our measurements weren't calibrated against a known amp so that this should be seen as just an indicative set of measurements.

You might want to have a quick look at this thread, it's about two specific amps but as you can see from the frequency plots they are very far from clean. Difference in sound between TC Bam 200 and Warwick Gnome - Amps and Cabs - Basschat i'm agnostic about the clean versus coloured debate, like passinwind I do quite like the sound of my bass through a desk and straight to headphones but I also love an amp/speaker combination which just sits in the mix.

I've just chased @Chienmortbb for them

We didn't try I'm afraid, our aim was to measure the baked in response of the amps and look for any HPF. If we'd have had more time we would have just measured more amps. I'm sure @Chienmortbb will be along to put up the plots he captured including the Elf

still look like a schoolteacher then

Great to hear from you, and that the cab is still doing good service. I dug mine out the other day and it is still a fine cab.

I found another pic

How portable do you need to be? I use a Zoom B1ON (now the B1four) Great sound, mini jack for aux in and built in drum machine and tuner. Mine runs on rechargeable batteries for a week but you can run it off USB and 9V

I ran the shootout at the SW Bass Bash. Also included were the Barefaced BB2, GR bass 2x12 and an RCF745. It wasn't a scientific double blind test but to make it a fair test I ran all but the RCF off identical PA amps tone controls flat and tried to adjust the volumes to be equal. I deliberately didn't say anything about the speakers so as not to influence the comments.

We looked into a variety of sizes for this design. 20 litres hit the sweet spot and makes this cab work well. You could potentially tune your Laney lower with a smaller diameter port, or swap your 8" speaker for a 6" like the Fane 6-100 as we did in the original House Jam Combo. https://www.basschat.co.uk/topic/442331-a-house-jam-combo/ This is something @Pea Turgh did with his 15W combo https://www.youtube.com/watch?v=2Fp00Cwc9Q8&t=1s adding proper ports would have brough the bass up even more. If you'd rather re-visit your Laney I'm happy to make suggestions as to port sizes that would work. If you only have 15W on tap then port noises aren't likely to be an issue and that is the only problem with a small port diameter.

We had a display of the various Bass Chat designs and other builds at the South West Bass Bash this Sunday. The biggest interest was around the tiny cabs. My House Jam 6 created the usual stir but this little fella created the most interest. It's a single 8" speaker I designed and built with @Chienmortbb to match his souped up Ashdown After 8. The size and shape is a copy of their dimensions but this little chap will handle 200W and produces a very significant amount of bass and sounds like a much bigger cab. People at the bash generally loved the sound and I'm contemplating doing this as another Bass Chat design. It did work really well with double bass as well, many thanks to @TheRev for trying it out for me I was amazed at the interest in the little cabs (nobody paid any attention at all to the lightweight 15 I'd taken along) but I guess other people have the same needs as me. Something small to practice with at home and portable enough to use for semi acoustic work and to drag along to open mic nights and even the odd rehearsal. There aren't a lot of options of commercial cabs this small that sound grown up. This one is roughly a 30cm cube. For home practice this sounds like a much bigger speaker and it would take you easily up to the volume of the average jazz band or a drummer with a compact kit. If there is a load of interest I'll build a second one and put it here with a set of plans for anyone to copy. It's probably a weekend build and would cost you maybe £100. I'd welcome comments from anyone at the bash who tried it or listened to it.

Ha ha, he wishes