Bill Fitzmaurice

[quote name='Magic Matt' timestamp='1410264681' post='2547594'] So, I'm looking to get the most output I can over 50Hz, but avoid getting the 41Hz low E dropping too far down that steep slope, otherwise it will be much weaker than the other notes... yes? [/quote]No. While the low E note has a fundamental of 41Hz most of its content is in the harmonics. For reference, a Fridge f3 is 58Hz. No one complains about how it handles the low E.

Low 'E' is 41 Hz. Most amps have a high pass filter built in to prevent over-excursion below 40Hz. Maximum output above 50Hz is what matters.

[quote name='Chienmortbb' timestamp='1410215722' post='2547311'] Got to also say the AC30 bass was a POS. [/quote]So were 60s Fenders that were basically guitar rigs without reverb. Best guitar amp ever? '59 Bassman... with outboard reverb.

[quote name='Magic Matt' timestamp='1410136424' post='2546529'] Ok... but if tuning the cab lower gets rid of the hump, and doesn't seem to make a huge difference to SPL on the graph... why is that bad? ...can't I just turn the amp up a tiny bit more to compensate? (I expect I'm missing something crucial here, but I don't know what) [/quote]Look at the Maximum Power and Maximum SPL charts.

[quote name='karlfer' timestamp='1410170694' post='2546682'] I always thought a bit more speaker watts than amp watts, so with the Carvin I would have looked min 800watts cabs. [/quote]Most cabs reach maximum driver excursion at no more than half their rated power, so that's all you need to get full output from them. You can have more power on tap if you wish, but you simply won't use it. The same applies to PA. Where PA differs to some extent is with respect to high frequency drivers. They can be harmed by clipping, so plenty of amp power used to be a necessity to prevent that, but clipping is very effectively prevented with electronic limiting, something which was not an option when this was written: http://www.jblpro.com/pub/technote/lowpower.pdf As for the link's take on guitar speakers, he misses that by an even wider margin. Most guitar drivers have such short xmax, 1mm or less, that they reach maximum uncompressed output in the lows with only 10-15w input. The power required where guitars get most their decibel output, between 500 and 2kHz, is quite low, and doesn't require massive driver capacity to handle it. Anyone doubting that has never been on the receiving end of a Vox AC-30.

The problem is that it's incorrect, because like most laymen he's considering watts and that's not what matters. Voltage swing and driver excursion are. Suffice it to say that where watts are concerned if your amp is rated anywhere between one half and twice what your speakers are rated for you're fine.

[quote name='Magic Matt' timestamp='1410126455' post='2546474'] Ok, so I downloaded WinISD Pro and tried to put the parameters in direct from the spec sheet.... same as I had in WinISD... [url="http://www.eminence.com/pdf/Basslite_C2515.pdf"]http://www.eminence....slite_C2515.pdf[/url] This happens... ...oh. Bugger. Now I don't know what to do. [/quote]That's because WinISD is more accurate in the spec calculation than Eminence, going to more decimal places. Only put in as many specs as required, let WinISD calculate the rest. That means Qes,Qms,Vas, Fs, Re, Le, Sd, Xmax and Pe. As for eliminating the hump, you do that by using the correct size cab. Since you're undersizing the box you'll have to live with the hump.

Why tune so low? Maximum output demands, even for a low F# six string, lie between 40 and 70Hz, so you should be looking at the maximum SPL chart to find the tuning that gives the best result in that range. Tuning lower than 40Hz robs you of maximum output in the 40-70Hz bandwidth, and it makes the cab larger than it needs to be. If you have a 4 string you should be tuning even higher, 45-50Hz.

[quote name='Magic Matt' timestamp='1410084748' post='2545885'] It'll be a simple box, rectangular bass port, 130 litre, tuned to 25Hz Recommendations please? [/quote]How did you arrive at that? The C2515 models to the flattest possible response in 412L tuned to 33Hz. That's silly large, of course, but points out why one should think thrice about using the C2515. It can work in 130L, but you wouldn't tune it at 25Hz. 40Hz is the lowest you'd want to go. 25Hz would make the port unmanageably long, and would cause a serious loss of maximum output, while there's no benefit to be gained from tuning that low.

[quote name='bonzodog' timestamp='1409911065' post='2544474'] Very glad I started this thread as there is clearly difference of opinion which I find interesting. [/quote]Well, there's science and there's speculation. Science will win that battle every time.

[quote name='Marky L' timestamp='1409836488' post='2543796'] I currently run ..a 2x10 cab ...rated at 8ohms. I fancy adding a 4x10 8ohm to the 2X10. I can't see what probs I would have. [/quote]The drivers in the 210 would see twice the power as those in the 410, making the excursion capability of the 210 drivers the weak link in the chain. Looking at it from another perspective, what you'd be able to get out of the system wouldn't be all that much different than what you would get out of a matched pair of 8 ohm 210s. The additional output capability of the 410 wouldn't be of much use with the 210 holding it back.

[quote name='mart3442' timestamp='1406894967' post='2515679'] I'll tell that to my friend with the fried amp...... [/quote]His amp may be fried, but it had nothing to do with the lack of the speaker. When in standby mode there is no current flowing to the tube plates. That's why no sound comes from the amp when in standby. If there's no current there's no potential for damage. He might as well have claimed that he blew the engine in his car by pressing the gas pedal to the floor...whilst the ignition was off.

[quote name='spacey' timestamp='1409599335' post='2541410'] The trouble is a lot of of 2x10 are 4ohm and end up doing the lions share of the work if the 4x10 is 8ohm [/quote]That's because of the manufacturers conceding to the "I want to get all the watts out of my amp" syndrome. A 16 ohm 2x10 would be best, allowing you to use up to four of them if you wish, or to pair one or even two of them with an 8 ohm 4x10. But even though it would be the dodgy amp that couldn't drive a 16 ohm 2x10 to full output no manufacturer is going to produce them, because the average player doesn't know that, and would never buy a 16 ohm cab.

[quote name='budget bassist' timestamp='1409581179' post='2541105'] if I end up with something that sounds similar to my Ashdown kit [/quote]Setting your sights way too low you are. DIY isn't about equalling off the shelf, it's about kicking the snot out of off the shelf.

[quote name='budget bassist' timestamp='1409576681' post='2541035'] If what you're saying is true, then surely I can't do much worse than an ill-considered mass-manufactured box would be? [/quote]True, but what most newbies set out to do is to basically build the equivalent of an ill considered mass manufactured box, with the intent of doing so at a lower cost. In the end they don't save any money, while mass manufactured boxes aren't worthy of emulation. For that matter I can count on the fingers of one hand the number of boutique manufacturers whose cabs that I'd consider owning, and one of those I did the design work for.

[quote name='budget bassist' timestamp='1409524872' post='2540616'] But how are all the manufacturers using such tiny enclosures and still getting a good sound? [/quote]They aren't. One doesn't have to go to the full optimal size for a driver, but one also should be judicious in how small one goes, as it does affect the result. OTOH most manufacturers aren't concerned with getting the best possible result, they're interested in sales. Average customers don't know anything about Hoffman's Iron Law, and think f3 is a note, not a marker of speaker performance. What they've been led to believe is that one gets the best results from stuffing as many drivers as possible into the smallest box, so that's what said manufacturers give them. Since these customers have never used a truly well designed and built cab they don't know the difference, so the cycle remains unbroken. [quote]half the satisfaction will come from having designed the thing myself! [/quote]One might say the same about a hang glider. Making an error with a speaker may not have as disastrous a potential result, but still you are asking questions that one fully prepared to design their own speaker would not be asking. If you're bound and determined to reinvent the wheel, and repeat the same errors made by all those who came before, you should at least avail yourself of resources such as this: http://techtalk.parts-express.com/showthread.php?219617-The-Speaker-Building-Bible

[quote name='bonzodog' timestamp='1409476765' post='2539951'] However i neither have the room in the house or car for another 410 so was thinking of getting a 210TP as its smaller and thommann still sell them cheap. However I am sure i have read on another thread here that this is not an ideal set up due to the fact you are sending the same power from the amp into each speaker but one is half the size of the other even though the ohms are correct. [/quote]That's correct. For each driver to receive the same signal the impedance of the 210 must be twice that of the 410. The problem is that most manufacturers don't make them that way. If the 210 and 410 have the same impedance then the 210s capacity will determine your maximum clean output. [quote]May look for a used 210XL then as they are 200W rather than a 210TP [/quote] Watts are moot. What matters is driver excursion, and you have no way of knowing what that is. The only way to get a perfect match is to use identical drivers with the 210 twice the impedance of the 410.

[quote name='TheDaivisch' timestamp='1409388214' post='2539183'] P.s. 18 inch Peavey mated to a 30 watt Marshall guitar speaker it is then. [/quote]So long as a crossover is employed that's a much better combination than a twelve and fifteen, though an eight or ten inch guitar driver would have better dispersion. I know you were being facetious, but I'm not.

Tube tone doesn't just come from the pre-amp, it also comes from the power tubes and the output transformer, so a tube pre on its own won't give tube tone. A great deal of what contributes to tube tone is compression, so to emulate it you should have a compressor in your signal chain, preferably not a 'one-knob wonder'.

[quote name='chris_b' timestamp='1409144865' post='2536779'] If the cones are moving as much as you say... [/quote]That's usually an indication that the driver is not spec matched to the cab, something which has been totally overlooked so far in recommendations.

[quote name='Chienmortbb' timestamp='1408570103' post='2531524'] Just wondering about the benefits of a cast aluminium basket. Fane make a good looking 10" Sovereign 10-300 and a virtually identical Sovereign Pro 10-300 and virtually the only difference is that the slightly more expensive Pro has an aluminium basket rather than pressed steel. [/quote]Aluminum is stiffer than steel, so it's usually used with heavier magnet structures that might cause a steel frame to warp. Aluminum is also used with higher power neo magnet drivers for its heat sinking properties, as neo is more sensitive to heat damage than ceramic magnets.

[quote name='lefrash' timestamp='1409078467' post='2536138'] I had a cab that was wired up at 16ohm. I then rewired it to 4ohm. The difference in volume was massive, when everything else was the same. [/quote]6dB, to be exact. That's at small signal levels. The difference between 4 and 8 would be 3dB, also at small signal levels. At the full displacement limited power capability of the drivers there won't be any difference, because it's driver cone excursion that limits how loud they can go. So long as you have enough power to push the drivers to full excursion you won't get any benefit from a lower impedance load. As to how much power it takes to push drivers to full excursion, on average only 40% of their thermal rating. In short, a low impedance load is only beneficial if you have an amp that's seriously anemic.

[quote name='aj5string' timestamp='1409063104' post='2535924'] Head gives 250w into 8ohms and 500w into 4ohms. Will it actually much quieter in practice running at 8ohms instead of 4?[/quote]No. The primary factors in how loud a cab will go is frequency response, sensitivity and driver displacement. Power and impedance are only minor players in the overall equation result.

[quote name='weepaul' timestamp='1408889725' post='2534334'] Would there be any issues with the cab ? [/quote]Not as long as you don't crank it to the point of high distortion.

Definition minimum: The [i]lowest[/i] acceptable value. 8 is higher than 4, so no worries.