Bill Fitzmaurice

[quote name='escholl' post='1306283' date='Jul 16 2011, 06:16 PM']The ratio of harmonics does not, however, depend upon length.[/quote]I've found that it does, though I've only done very rudimentary testing just to satisfy my curiosity.

[quote name='fatback' post='1306026' date='Jul 16 2011, 12:35 PM']Presumably it's the longer scale length that's allowing for the different harmonics? How does that work?[/quote]The longer the scale the higher the fundamental to harmonic ratio in the waveform. A string doesn't reach its full potential for fundamental output until it's 1/4 wavelength long. At 30 Hz that's 9 feet, so you'd need one really big bass to create a strong 30 Hz tone.

[quote name='ShergoldSnickers' post='1305827' date='Jul 16 2011, 09:31 AM']Does the constriction of the hole immediately in front of the speaker on the top shell - and not shown properly in my rough from memory illustration - serve any purpose other than to speed up air 'squirted' into the resonant chamber in order to excite it? Surely this constriction would radically alter the behaviour of the cone as it is now impeded more by having to move air through a constricted hole? Edit: Also wondering about how much distortion this set-up would introduce to any otherwise pure signal. [url="http://www.avforums.com/forums/attachments/subwoofers-tactile-transducers/237169d1303471020-graham-holliman-infrasonic-generator-graham-holliman.pdf"]Link to original plans for this cabinet[/url][/quote]The size of the hole is part of the tuning mechanism. The size of the hole has far less to do with the driver excursion than the volume of the chamber. The THD of this box would be similar to a standard bass reflex with similar specs. BTW, the tapering of the ducts would seem to be an attempt at adding some horn loading, but duct length and exit area preclude that, both being far too small. As my colleague George Augsperger would say [i]"There are many ways to build a bass reflex. This is one of them."[/i]

[quote name='ShergoldSnickers' post='1305621' date='Jul 16 2011, 06:33 AM'][/quote]It's a bass reflex cab, nothing special or unusual except for the external driver mounting, and that serves no purpose, it could be inside with the same result. In current parlance it would be called an LLT, for Long (duct length) Low Tuning. The designer was totally in error with regard to the rounding of corners. Ten to forty foot wavelengths aren't the least bit hindered by hard corners.

[quote name='Phil Starr' post='1305381' date='Jul 15 2011, 07:49 PM']Fair comment, I should have said there is little point in doing this with your computer speakers. Even with decent hi-fi speakers you will get some audible harmonics but it does give you an idea of just how low the fundamental of bottom E is and it's usually a shock to people who hear it for the first time.[/quote]Not as much of shock as it is to have a speaker putting out 15Hz at 100dB and you can't hear it, nor would you even be aware of it if not for a meter telling you it's there. And that's why even for home theater LFE I don't even think about going below 20Hz.

[quote name='Phil Starr' post='1303710' date='Jul 14 2011, 11:29 AM']There are loads of signal generators online and if you are deeply boring (like me)it is quite interesting to listen to a 40Hz (roughly bottom E) pure tone and realise just how low that is. If your speakers can go that low of course.[/quote]You may still be hearing a lot of harmonics, as your speakers create them. If you play a pristine 40 Hz or lower sine wave through a capable speaker with very low THD you can't even discern pitch.

[quote name='tim126' post='1303547' date='Jul 14 2011, 09:12 AM']Now I have heard about harmonic frequencies and stuff (not sure I understood it, mind you!)... but, putting it in really dumb terms, if the bottom B is producing a frequency below the rated/stated capabilities of the amp and the cab, how come I can still hear it when I play it?... .[/quote]Because you're mainly hearing said harmonics. They dominate the output below roughly 80Hz. You perceive the fundamental being louder than it is as the second harmonic is the same note an octave up. And what you perceive as 'deep bass' is typically an octave higher than you think it is.

[quote name='jmsjabb' post='1303228' date='Jul 14 2011, 04:38 AM']The amp is a Markbass F1 and it will run with an Ashdown ABM210[/quote]Get another ABM210. It will work better than adding a fifteen, especially if you rotate the cabs 90 degrees to place all the drivers on a vertical line.

You must provide the specs on the amp as well, which impacts sensitivity, response and excursion requirements.

[quote name='Balcro' post='1295388' date='Jul 6 2011, 06:13 PM']Further to your post No. #14 above:- Wooks79 has a SS power amp section to his SVT3 Pro and its operated into a vented cabinet, which displays that typical double peak impedance (red-line) plot. Therefore from your explanation, can it be assumed that amp will be reasonably comfortable under such conditions? Balcro.[/quote]SS is generally fine with all vented cabs, not so much with sealed cabs when run at the amp minimum load rating. The opposite is true of tubes. They'll run into a dead short without complaint, but aren't happy with some vented cabs, especially those with very low Q drivers, which have very high peak impedance values. Now defunct Basson is an example, well known for bragging on their very low Q drivers with 20 pound magnets, almost as well known for their cabs toasting output transformers as a result of same.

[quote name='Balcro' post='1294629' date='Jul 6 2011, 07:29 AM']Reading between the lines, I think Bill is cautiously referring to the potential for damage that may occur to the amplifier if your amp is not capable of operating into a 4 Ohm load.[/quote]Not quite. Load figures are only vast generalizations, based on the DCR of the drivers used. Even with the same nominal load rating different cabs have very different loads, even when using the same drivers, as shown here: This shows the same driver in a sealed and vented cab. A tube amp will be much happier with the lower average impedance load of the sealed cab, SS will be happier with the higher average impedance load of the vented cab. The inverse is also the case, and is likely the source of Ampeg's problem with its Micro VR SS head and sealed 2x10 cabs.

With low power you want a hgher Q driver that delivers a humped midbass response, for adequate output. With high power you want adequate xmax to handle it, whereas with low power high xmax is unwarranted. And then there's the matter of impedance, being sure that it's appropriate for the amp. That's far more complicated than it seems on the surface; Ampeg is having some major problems with their mini-stack, as the load offered by a pair of the 2x10s is fundamentally at odds with the needs of the amp.

Still need your amp specifics, as which you'll use makes a big difference.

[quote name='Blademan_98' post='1291260' date='Jul 3 2011, 01:16 PM']He must be a drummer though as he wore no gloves or mask [/quote] More likely a bass player, we're used to being ignored. Not a guitar'd player, though, or he'd have smiled for the camera.

[quote name='jonno1981' post='1291004' date='Jul 3 2011, 09:10 AM']This is a re-post from a friend of mine who had a break in at his rehearsal studios last night. Watch out for any secondhand Mag300 heads going cheap around berkshire......If anyone recognises the guy please send Jay a message.[/quote] He'd get a better result posting the actual video feed, rather than a video of a video. I assume the police have used the video to get a still photo of the w***er for a 'Wanted, Dead or Alive' poster. And the way these things work chances are better than even he's a client of your friend, not a very bright one judging by the apparent lack of gloves.

Technically any Gamma 12s are NOS, new old stock. Production of them ceased a number of years ago.

[quote name='51m0n' post='1287713' date='Jun 30 2011, 08:52 AM']you will still get boundary effect with the bottom 2, maybe even 3 speakers and the floor.[/quote] You will get the full boundary loading effect with all the drivers, as they will be spaced close enough together to fully mutually couple in the bass frequencies, essentially operating as one large driver.

[quote name='Thurbs' post='1287595' date='Jun 30 2011, 07:48 AM']You could put them both on their sides to arrange the drivers vertically and watch the middle of the audiance wonder where all the bass has gone... [url="http://www.astralsound.com/bass_pattern.htm"]http://www.astralsound.com/bass_pattern.htm[/url][/quote] Methinks you misunderstand the link you posted, as it (correctly) states exactly the opposite of what you seem to think it states. Those diagrams show the overhead view of the stage and audience, and display why cabs (and individual drivers) should not be horizontally arrayed.

[quote name='muttley' post='1286649' date='Jun 29 2011, 11:57 AM']Yes, I knew about the dominance of neo in PA. It's not [i]that[/i] long that I've been out of the industry . But for MI, do you mean non-guitar applications?[/quote]Guitar is the one area where neo has not yet made major inroads, because most guitar drivers don't use very large magnets nor have high xmax values.

The Ampeg driver has 4.7mm xmax, the 2510 4.2mm. That gives them virtually identical output capability.

[quote name='muttley' post='1286462' date='Jun 29 2011, 09:26 AM']I've been out of the game for a few years now so don't know what the latest thought is on neo[/quote] More than a few I'd say. Neo has owned the high end PA genre ($5k and up per cab) for a decade, musical instruments for the last five years. But as of recently the price has skyrocketed due to predatory trade practices by the Chinese. And Eminence didn't get to be the #1 driver manufacturer in the world by producing crap.

[quote name='Neuroscar' post='1286020' date='Jun 29 2011, 02:25 AM']Im thinking about making my own 15" cab[/quote]Only do so if all of this makes perfect sense and you know how to make use of it: [url="http://www.eminence.com/support/understanding-loudspeaker-data/"]http://www.eminence.com/support/understand...udspeaker-data/[/url] [url="http://www.linearteam.dk/default.aspx?pageid=winisd"]http://www.linearteam.dk/default.aspx?pageid=winisd[/url]

[quote name='Lozz196' post='1285850' date='Jun 28 2011, 05:51 PM']Ok, been doing a bit of reading over on T*lkb*ss, and there seems to be a fair appreciation for Eminence Basslite S2010s. I`ve also found out from Eden that the speakers in my cab are their Chinese made cones. So, would the Basslites be an improvement, and offer me a tone nearer to that of an Ampeg than what I have now?[/quote] Impossible to say without either seeing response charts for both (Eden does not publish any, as it would reveal their SPL claims to be rubbish) or having cabs with both drivers side by side.

[quote name='Merton' post='1284755' date='Jun 27 2011, 05:49 PM']Sorry for going OT here but when did Eden stop making their own drivers? Was it around the time of the US Music takover or when David left?[/quote]Eden's a bit cryptic, so I can't say for sure if they're still making any ceramic drivers or have gone completely to Eminence, but their staple driver was the 1060, and they now use the 1040 in Nemesis, probably Eminence. Their Neo is Eminence. The Ampeg drivers aren't all that heavy, 6.7 pounds, so four of them are only eight pounds heavier than four neo tens. Any other weight difference would be in the cab.

[quote name='Lozz196' post='1284593' date='Jun 27 2011, 03:44 PM']I`m thinking of changing the speaker cones in my Eden Nemesis 410, to either Eminence BP102 or B102 cones, to try and get a more Ampeggy sound, figuring that as Ampeg use Eminence speakers, that is logical[/quote] The cab and driver must be matched to work well. With older Edens when they made their own drivers you really needed to use Eden replacements. They now use Eminence, so there's probably nothing to be gained by swapping them. As far as what Ampeg uses, they bear no resemblance to either the BP102 or B102. The B810 is a direct replacement, but if you don't have a sealed cab you won't get Ampeg tone. And the cab is only half the equation. It takes an Ampeg head as well.