stevie

[quote name='xgsjx' timestamp='1349442584' post='1826395'] But then Bill's Titan 48 say's otherwise... That's a 1x15 vs a 2x18. [/quote] That drawing doesn't say anything about 4x10s. All it says is how good Bill Fitzmaurice is with a felt pen.

You can't calculate radiating area accurately from the speaker diameter because the surround accounts for a larger proportion of the speaker diameter the smaller you go. PA 4x10s have around 15% more radiating area that 18s - not a huge difference - but in practice have much lower excursion capabilities. An 18" thus has the potential to move a lot more air than 4 x 10s. The fact that most people believe the opposite to be true is down to their respective efficiency in the midrange.

The Marshall 4x12s from the late sixties didn't produce any true bottom.

[quote name='Wiggybass' timestamp='1349438407' post='1826290'] What are the others? Assuming equivalent amplifier power etc.. [/quote] Alex already mentioned excursion, and it is worth adding that the average 18" PA driver has twice the excursion of the average 10" PA driver. But assuming equivalent amplifier power, the reference efficiency of the driver and the size of the cabinet (or the moving mass to air-load mass ratio).

[quote name='Wiggybass' timestamp='1349437150' post='1826262'] Replacing a single 18 with a 4 x10 should make quite a bit more racket because it will shift a lot more air. If we assume that the whole surface of a cone driver is active in terms of direct air displacement (it isn't quite but let's keep this simple), then one 18" driver has a surface area of roughly 176.71". A single 10" has a radiating area of about 78.54" so four of them working together will have 4 x 78.54" = 316.16" bashing the air out. [/quote] Maybe. Maybe not. It depends on several things and radiating area is only part of it.

[quote name='peteb' timestamp='1349295813' post='1824504'] [color=#222222]I switched from using a SWR 4x10 and a 1x18 to using two matching 4x10s after reading something on here (from Alex I think), which I interpreted as speaker cabs with different size speakers will always be slightly out of phase with each other whereas matching cabs will always have the speakers working together i.e. moving together at the same speed.[/color] [color=#222222]This seemed to make sense to me and it did seem to sound better (or at least more efficient) but had I understood the reasoning for doing so correctly??[/color] [/quote] I'm afraid not. The only reason to change your 18 would have been to increase power handling (although even this is a bit moot). Otherwise, a 1 x 18 will work with a 4 x10 as well as another 4 x 10 – in many cases better, in fact, because 18s don't normally have an extended HF response and are thus less likely to cancel the mids/highs coming from your 4 x 10.

Ashdown should be ashamed of themselves for fitting 3-inch ports in this cab. I know it's a budget cab, but there's really no excuse for this level of penny pinching. I'd really like to see some accurate measurements for this cab to confirm or refute whether they have mis-tuned it. Interesting. I've made lots of 15-inch bass cabs and have found 2 x 4-inch ports perfectly adequate. The vent air velocity graph in my design software agrees. Use Roland's method of enlarging the existing holes and fit two ports with a lip. It will look perfectly pro and will perform much better at volume.

[quote name='Phil Starr' timestamp='1348170480' post='1810454'] Aren't the ports on the back of the Mag? If so how worried are you about how they look? You could probably find a chippy to cut the holes for you for a few quid if you are nervous about it. Get hold of the porting first though, I use black soil pipe or drain pipe mostly. [/quote] Yes, the ports are on the back, which means you are cutting through the vinyl and it really needs to be neat. A port with a lip on it gives you some margin for error, and the hole doesn't need to be perfect. Drain pipe is great on the front behind a grille.

Oops, yes, you're right. Those are the ones. I've no idea what happened to my link.

[quote name='skidder652003' timestamp='1348159310' post='1810220'] something like this? [url="http://www.ebay.co.uk/itm/SPEAKER-CABINET-BASS-REFLEX-TUBE-VENT-SILVER-100X200MM-/190647296824?_trksid=p3284.m263&_trkparms=algo%3DSI%26its%3DI%26itu%3DUCI%252BUA%252BFICS%26otn%3D21%26pmod%3D180963208964%26ps%3D54"]http://www.ebay.co.u...08964%26ps%3D54[/url] [/quote] Much too expensive - and the flange looks very thick. This is the industry-standard 4-inch port tube: http://www.wilmslow-audio.co.uk/100mm-flanged-port-413-p.asp. You should find it cheaper on eBay but I can't find any on there at the moment. Just make sure it's going to be long enough before you start cutting your cabinet.

[quote name='Roland Rock' timestamp='1348156845' post='1810181'] Get a spare piece of MDF and make a 100mm hole in it as normal. Then clamp this onto the baffle so the hole in the MDF is where you want the final hole to be. Recess the bit the bit so it's inside the holesaw, then drill, using the MDF to keep the holesaw in place. [/quote] That's a very neat solution. I wish I'd learned about it before - it could have saved me a lot of hassle:-).

On the basis of Phil's estimate of 150 litres, the Warwick cab looks like it's tuned to just under 50Hz, which is OK. It will work, but the cabinet really is on the big side.

That's perfect, Bremen, if you're drilling into a blank piece of wood, but if you're enlarging a hole there's nothing for your bit to drill into.

I've just upgraded to an all-in-one printer, which means I have a Visioneer USB scanner spare. It's good quality and hasn't had a lot of use. Works on all Windows versions up to XP. Unfortunately, there are no drivers available for Windows 7. Collect from Dorchester area, although I occasionally get up to Shaftesbury and could drop it off/ arrange to meet thereabouts.

Skidder, those look like external measurements to me. We need (accurate) internal measurements for the cab and the ports. Based on an internal volume of 100 litres for the Ashdown, the cab seems to be tuned to around 35Hz, which is much too low. What also concerns me is that the port diameter is too small. You're going to get compression and lack of bass when you turn up loud. You need to open up the port holes to fit two 100mm diameter ports. Otherwise you won't get all the benefits of your superior quality driver. It's not that difficult to do with a jigsaw, by the way, as you can buy ports with lips on them to hide your poor carpentry:-).

That's good news.

Overdriving the power amp can destroy speakers by pumping more power into the speaker voice coils than they are designed for. Using a distortion pedal - or overdriving the preamp - won't. So clipping is not just clipping.

With any good quality 2x12 cab you shouldn't really need anything else - so 4 ohms seems a reasonable enough choice to me.

There would only be a point in retuning the cab if Ashdown got it wrong, i.e. if it's tuned higher than 60Hz. Nothing's impossible, of course, and if the OP posts the cab and port measurements, we can get a rough idea of what's what. I'd be more concerned myself about whether the new driver will fit in the existing hole.

So what measurements did you do?

The crappy drivers that Ashdown fit have a midbass bump no matter what you tune the port to. What was the tuning frequency?

[quote name='skidder652003' timestamp='1348071875' post='1808899'] ah ok, would it maybe be better to put the speaker in the warwick WCA pro 115 cab then? (it has 4 ports at the front) [/quote] Don't use the bigger cab - it will not sound very good, will handle less power and will lack punch - and you will be carrying around an extra 50 litres for no good purpose. Don't worry about the porting too much either although, as Mr Foxen says, if the ports are too small the cab won't sound good at high volumes. You really need two 4" ports in your box because you now have a driver that will handle more power than the original one - but try it and see. You don't need to retune the cab either. We can assume that Ashdown knows how to tune a bass cab. If the driver is suitable for the cab (which it is) the tuning will be fine.