Phil Starr

FWIW Bill is absolutely right, as is LukeFRC. It's possible to make a 15 go down to 20hz and to make one that is 99dB/W but you couldn't do both at the same time. To be efficient you need a light cone and a short voice coil, to be deep you need a heavy cone and a long voice coil. You can get efficiency up by using a huge magnet but at huge cost. Even then you would eventually overdamp the speaker leading to a loss of low end. All speakers tail off in their response at both ends. Bass tails off at about 12dB/octave in a sealed cab and usually 24dB/octave in a ported cab. This means they all produce some output at 20Hz, just that it is too little to be of any use. In any case your bass goes down to 41hz for a 4string and 30ish for a 5 so there is no need for lower. Excursion also doubles for each extra octave so you'd have to halve the power rating if it really did go that low. It's a dishonest claim really 1dB is pretty much the smallest change in volume you can detect, so 0.6db won't be noticed. If you like your sound then only the 2x10 will give you more of it, The 15 will change your sound. You'd have to try it out to find out if you like the change or not.

Sorry, speakers I'm OK with but I'm no expert on any particular bit of DSP. I really can't tell you if one manufacturer has done a good job and another not so much. A couple of observations though. Signal processing is something we've been doing for as long as there has been amplified music. Doing it digitally should be no different to making the same changes with analogue processing other than it should be easier and cheaper. If some analogue gear currently sounds 'better' than digital then this is temporary, the digital processing will get better and cheaper eventually overtaking it. My taste is for as little processing as possible, nothing on my mixing desk ever goes past 2 o'clock, reverb sparing and little or no compression. The thing is with digital that once you have a really fast computer controlling your sound your options are almost unlimited. As many channels of eq as you like, all parametric if you want, filter any frequency you want, let the computer kill feedback or do your eq for you, protect the speakers , apply compression to any channel or split the signal and compress each part differntly etc etc. Now this promises sonic perfection, but if the organic bit operating the knobs (or even the software developer) gets it wrong the opportunities to sound nasty multiply as well. I'm open minded about it really, excited by the possibilities but not yet impressed by the amp/speaker simulations on offer for example. It'll come but I think we aren't quite there so far. I'd love DSP on my PA though. If I was mixing out in the audience I might be able to out compete the DSP (or not) but stuck up on stage with a bass in hand it's pretty difficult to think I could adjust the eq as the room acoustics change because of the audience coming in or kill feedback effectively. Most of us don't have the luxury of a sound engineer so DSP frees us to concentrate on the music.

Thanks for the article, should have remembered that really because there was a long thread on this a while ago. It probably wasn't the best example to choose I think the rest of what I said is about right though. One of the advantages of this DSP approach is that you are far less likely to blow your speakers through over excursion in return for very little signal distortion/loss of sound.

[quote name='Dad3353' timestamp='1403978439' post='2488307'] It mounts up very quickly, as (in theory...), twice the volume needs 10 x the power, so a 50w amp becomes 500w. The next stage up (twice more volume...) would be 5 kW. We see those in PA systems. [/quote] This is right, you can just tell a 1dB rise and really you need 3dB to be able to say that an amp is appreciably louder. That takes twice the power. So going from 75W to 150w doesn't seem like much but going from 200-400W is exactly the same 3dB step. The real reason is (I suspect) that amplifier watts are so much cheaper nowadays, especially allowing for inflation. I've been toying with buying one of the TC amps and the RH750 is only about £100 more than the 450, 30p per watt! We'd have bought 750W amps years ago but they weren't affordable, and we couldn't have lifted them. Modern speakers, by and large are less efficient, trading low bass and excursion for efficiency. They will handle more power though.

Nice

[quote name='Spike Vincent' timestamp='1403254634' post='2481130'] I would be highly dubious of ANY speaker that has a claimed SPL of 118db. [/quote] You may be muddling the max SPL with sensitivity which is the output at one watt. If the figures are accurate then this speaker is 95dB @ 1W and 118 @ 200W although they may be quoting the figure for both speakers together. [quote name='The Admiral' timestamp='1403261026' post='2481221'] I've used a set of these for a couple of street parties and they've been great. http://www.gak.co.uk/en/yamaha-stagepas-300/7920?gclid=CI39oO2giL8CFagewwodZGEAjg They are also a really portable solution for an acoustic gig and they are typical Yamaha quality, so if you were thinking of buying, you could do a lot worse. Not £150, but the current GAK deal is great value, but I'd also suggest, it depends what you are running through them : if it's a young DJ wanting to thump out earth moving drum and bass, then that's a non starter, but for background or even sensible levels for some party music, they will be fine I would think. They also hold their value really well, with a second hand set going, with the bag (which is well worth getting), and stands for £275 recently. Also very compact and fit easily into the back of a hatchback. [/quote] I have one of these setups, they do an excellent job and the midrange and treble will be much cleaner but they are limited in volume and bass. max output is 112dB only

Skytec are well enough known and the same speakers are sold under a whole lot of badges. If you buy the base level own brand speakers from almost anyone they will come from the same factory in china. The standard practice is to quote power as RMS,program and max doubling the power in each case, these are 200W RMS. For this price you get a piezo tweeter and a driver with a tiny magnet and short voice coil. Piezo tweeters work but aren't ever great sounding. The small magnet means low efficiency, no deep bass and a bass hump which sounds really thumpy. The efficiency is raised by the short voice coil but this means excursion is limited so trning the bass or volume up overloads the speaker. The speaker is rated as 118dB which is a lot louder than your hi fi but only enough for an acoustic act in a pub. These things are remarkably good value for money and this is a very cheap price for them. They'll sound Ok so long as you don't turn them up too high and do a job, They are remarkably well built for the price. Just don't expect too much and you'll be pleasantly surprised. I'd happily give you £100 for them after so i can nick the amplifiers to convert my monitors to actives, actually £150 for two 200W plate amps, hmmm. Get your friend to pm me if you do want to sell.

Enlarge the thumbnails for a good insight into what we are all saying. that shallow roll off for the sealed box is almost a mirror image of the standard bass control. 12dB of bass boost at 80hz would give you a pretty flat response, boost the bass by 6db with the sealed cab and that lump at 100Hz will become embarrassing. With a parametric and patience you might be able to eq but it's not going to be something you do between songs shallow roll off and no lumps and bumps are a real bonus. However with this speaker the roll off is from much to high a point, 300Hz right in what I think of as midrange. Applying 12db of bass boost means demanding 16 times the power. If you are running at a conservative 50W then you are going to need 800w from that lightweight head which your little 10 isn't going to be very happy about.. Far better to let the ports do the work with this speaker and get something else if you want a sealed box.

Hi Chris, what are you trying to get out of this and what do you want to preserve? Is it the sound or the look or the authentic original speaker. Taking the driver out will obviously preserve it but the cab won't be original any more and the sound will change. You could take it out temporarily I suppose and returrn the cab to original condition should you wish to sell. Putting any other driver in will change the sound. As you've found out no-one makes a wide range 18 any more and you wouldn't use a box that size with most 18's currently sold. A modern 15 would outperform your 18 in every way except it won't sound like the original. your box would work well with a wide range of 15's and you could fit a second panel (baffle) behind the original to fix the new speaker to without having major surgery on your vintage cab.

Just looked at your speaker, it isn't really ideal for a sealed box as Q=0.31 is really too low for a sealed box design. It's going to roll off from quite high up and sound really thin in any practical sized box.

Bill is right of course but there are some other advantages to a sealed cab. The gradual roll off is easier to eq, especially if your cab is well damped (with Q=0.7 or less). I'm also finding a lot of cleaning up your sound is about avoiding exciting room resonances, ie rolling off the bass. If the cab does this as part of its design then it can be very effective. The problem with the loss of 3-6dB of bass below say 80Hz that you'll get is that you need more power and your speakers can easily end up running out of excursion if you start to eq extra bass. You can improve the 'bassiness' of your sound by rolling of a little treble and maybe adding some upper mids to add a little brightness. Many cheap drivers have this midrange peak anyway so pack, say, eight of these into a sealed box and you solve the excursion problem, roll of the treble, oh wait a minute......

I find the room acoustics are too often the biggest factor in 'nice' bass, sometimes with the right amp to match the room you get a sweet combination and it just sings. then you take the amp somewhere else and the magic dies. I much prefer my J bass to play, and love the depth, but sadly my American Deluxe P bass just does the job better and sounds good with the band. I suspect your usual set up is just overwhelming with bass because of exciting room resonances. It's so frustrating, I love wallowing in the deeps but have to roll it off nearly all the time.

Don't worry too much, it's very likely that you will end up building a cab that is smaller than that needed to get the very best out of this speaker. Building a small cab is going to have two effects, it will raise the lower cutoff for the speaker and may create a bass 'hump' in output around the 100Hz mark. On the plus side too small a cab improves power handling. Before we had T/S we just used to tune the cab to the speakers resonant frequency. You can find this if you have a signal generator (they have these on-line) and a multimeter as the impedance of the speaker rises to a maximum at resonance. Alternatively you can just tune the cab to 40-50Hz and it will probably work, albeit at less than optimum. If you can get the data or find an original cab then all well and good, if not try finding a cab as near as possible in size to the one you remember copy the dimensions and tune it to 40Hz. WinISD will cough up the port dimensions for this. I wouldn't advise this for a new driver but you don't have a lot to lose. Be careful about how much power you put through it and use a bass filter like the thumpinator if you have one and the speaker should be fine.

if you use the same area and length the cab will be tuned to the same frequency. I'm using round ports for prototyping but the finished design will be slot ported to keep the construction as simple as possible.

Hi Luke, you'll have to wait until Stevie comes on for practical experience, I've never used them. I've not noticed chuffing as a problem with restricted port areas in PA sytems or bass speakers so I've given it little thought. However I roll off the lowest frequencies when I play to avoid room resonances and over excursion muddying the sound so I wouldn't expect to notice. It has been a problem in hi fi designs I've listened to though because of the more critical response to distortions in these speakers. The problem we're addressing here is twofold. Because we have chosen a high Xmax/excursion driver there is going to be more air moving through the port than most speakers of this size and the air speed becomes a significant fraction of the speed of sound creating turbulence. This leads to the practical problem. the cabs are small and have modest dimensions. if you increase the port area then the port has to be longer and it meets the back of the cab. You can bend the port but this was meant to be a simple build and a bent port introduces resonance problems. It can also increase the size of the cab. The solution Stevie suggested is to use a flared port. the reduced turbulance means less noise from a smaller port. Its a neat solution but means more expense and sourcing problems for anyone building the cab. What we hope to resolve with the prototypes is what port velocity we are prepared to live with. Mach 0.05 is the generally recognised upper limit (17m/s) but there are discussions between 15 and 20m/s. http://www.hometheatershack.com/forums/diy-subwoofers-general-discussion/24897-port-velocity-goals-aims-what-side-effects-high-port-velocity.html This is a good illustration for the non-technical of the sorts of design compromises involved in any bass cab design. You can build a basic box and it will work, but there are all sorts of tweaks you can make to get a bit more undistorted sound out and problems at extremes of use that you can avoid.

Hi Luke, I've been on holiday and then my computer crashed terminally so I've been off the boil Just to recap and bring everyone up to date I've built two prototypes out of 12mm lightweight ply and have been using them at practice. I've now installed some bracing which has tamed the rather alarming resonances of the panels and tightened up the sound. I quite like the way they sound now. I've agreed with my co conspirators to do some testing before we release a final design. Three issues need to be resolved, the cab tuning, the port area and the wall material. The current cabs are built with four pipe ports that can be blocked off and altered in length to achieve different tuning. basically I proposed a 40Hz tuning which gives us lower excursion at extreme bass and keeps it within the speakers damage limit up to 300W others have been suggesting a 50Hz tuning which gives a touch more bass and power handling above the extremes. we need to see if there is an audible difference and if it makes any difference in actual use. the port area issue is about balancing the avoidance of wind noise against ease of construction. Big ports are quieter but can pose construction problems or we could buy expensive(ish) flared ports. If we can use something small and simple we will, but the best way of seeing how far we can push it is to try out different set ups. At some stage i want to open up the chance to try the speakers to basschatters to feed into the design

Interesting, that looks like a fairly significant crossover. Did you consider using something simpler like the 'bright box' approach with just a simple 6db/octave high pass filter to the midrange and no filtering on the bass driver? Obviously that would lead to some comb filtering effects and it would be almost impossible to get a flat response but it would be a lot cheaper and simpler and you would get the extra frequencies and dispersion from your midrange driver. How did you decide on the crossover frequency? I assume there are a few octaves of overlap.

Yep half the volume is right. the shape matters in that it affects the resonances in the cab, avoid haveing any two measurements being similar and a cube is the worst possible shape for a cab. However cabs are a compromise and with small cabs there is a real problem in squeezing in a 10" dia speaker into a few litres and making an easy to carry shape, so few practical cabs are the 'right' shape and you may have to put up with a few resonances.

I haven't modelled these but they look a bargain at the moment http://www.bluearan.com/index.php?id=PAUE15350N&browsemode=category

I think that's a great question. Cab design has concentrated on all the stuff below 200Hz because that's the bit the mathematical models and design software address. The bit the box designers control. Then I go in to gigs and roll off the lower frequencies to get the best sound for the band. It's obviously better to have a perfect sound and then shape the lower end but the expensive and bulky bit of amplifying bass is the bottom octave which we can barely hear. If you've not done this before it is worth listening to 41 and 31 Hz http://plasticity.szynalski.com/tone-generator.htm if you start at 1000Hz and scan down the sound disappears, you can't really hear low B fundamental in any practical sense, so why do we make such a fuss? To make it a fair test use headphones, your computer speakers won't go that low in all probability.

Two very simple things: It doesn't matter where the controls are pointed, it's the sound coming out that matters. Read Alex's article on gain at the top of this forum. You haven't buggered your amp. What has probably happened is that it got hot. You did two things, cutting the mids made it sound quieter because we hear mids well and bass poorly (damn those guitards). Boosting the volume to compensate and then boosting bass demanded extra power. Your amp can do this for a while (half an hour apparently) and then it starts to overheat, all your resistances rise with temp and protection circuits activate and the available power falls. the amp is protected but sounds s**t. You turn it off, it cools down and you are back to normal probably. I have no idea if the speaker will take this, it just depends. If you want certain tones the cost is extra power and usually more or bigger speakers, or perhaps a bit of both.

You'd want one of these if you had the space http://blog.sciencemuseum.org.uk/insight/2014/04/24/in-search-of-perfect-sound-introducing-britains-largest-horn-loudspeaker/

Volt make some well regarded hi-fi drivers, the price has always deterred me from looking at them. the one you link to is not really suitable as a bass speaker, it is an overdamped (Q 0.27) driver specifically designed to go into a satellite system for a PA. It rolls off in frequency above 80Hz so is designed to work with a subwoofer. Oh and the Xmax is 4mm the higher figure is the maximum excursion before it destroys itself sometimes called Xlim Your Beymas go further before distorting.

Glad it has worked out for you. The other big difference will be in the excursion, those Beymas will handle deep, loud bass much better, unless you crank them you won't notice it so much but it's nice to know it's there. It'd be really nice to know what you think of the sound after living with them for a few weeks, we all inevitably tweak things until we get the sound we like and that takes time.

[quote name='Happy Jack' timestamp='1400065122' post='2450323'] I'm guessing that was supposed to be "omnidirectional"? [/quote]oops