Bill Fitzmaurice

[quote name='KiLLaGoD' post='314511' date='Oct 25 2008, 09:19 AM']Maybe I've got the wrong idea here but I've always been told that where possible you should use a power amp matched to the speaker cabs wattage exactly.[/quote] Been told by whom? Certainly not a quailfied engineer. Anywhere from a 2:1 to a 1:2 amp power to speaker power rating is well within the useble range in most cases. A 2:1 amp power to speaker power ratio won't hurt speakers, assuming one has enough sense to turn the volume control down if the speakers distort, while a 1:2 ratio is usually adequate to drive the speakers to their full output capacity, as that capacity is determined by the excursion limit of the cones, not the thermal power rating. The only immutable rule is that there is no immutable rule.

This is the source of the controversy: [url="http://www.jblpro.com/pub/technote/lowpower.pdf"]http://www.jblpro.com/pub/technote/lowpower.pdf[/url] Those who actually comprehend the Queen's English will note that the underpowering caveat applies only to 'High Frequency Components', ie., tweeters. Those who do not have completely subverted the intent of the document, arriving at the conclusion posted on the Sweetwater site.

[quote name='Mr. Foxen' post='310797' date='Oct 20 2008, 04:15 PM']Occurred to me that the speaker is effectively in a very small enclosure of its own.[/quote]It's for reactance annulling. [quote]Exactly, I was making the point that just because something is old-fashioned or lo-fi doesn't make it no good.[/quote]No argument, my point is that this old behemoth can be beat. and seriously so, by a modern cab literally half its size and weight. Restoring it is like restoring a 50 year old luxury car that gets 10 miles to the gallon. There is value in so doing, but from the standpoint of practicality you wouldn't want to use it for your primary mode of transport.

[quote name='Thunderhead' post='310536' date='Oct 20 2008, 10:56 AM']so you probably shouldn't spend too much time trying to analyse it.[/quote]Or salvage it, except possibly for sentimental value. The number of things wrong with that horn design far exceed the number of things about it that are correct. Circa 1970 it was a fine cab, as the driver technology of that time was so primitive by today's standards that even a mediocre horn was far better than everything else then available. But modern driver technology and advances in both horn design and direct radiating cabinet design have relegated it to curiousity status.

[quote name='Thunderhead' post='309962' date='Oct 19 2008, 01:26 PM']Up-rate the bass drivers so they can take anything the amp can throw at them, even distorted. Yes, I know you're not supposed to distort a PA, and NORMALLY (assuming an intelligent sound engineer) it's actually safer to use less speaker capability than the amp can deliver so the amp doesn't get driven into distortion... but that relies on the sound engineer actually listening for the distortion and not doing it! If musicians are in control, you need to assume the worst . Pick bass drivers which can handle more than double the RMS power of the amp (per channel) - preferably even more - and if possible use one impedance step above the amp's minimum load too, so it cannot deliver as much power - ie use 8-ohm speakers if the amp can drive 4 ohms per channel, or two 16s if it's a mono amp with a 4-ohm minimum load... these are harder to find in PA type speakers though. Yes, this does reduce the efficiency of the system and you won't get as much volume as you think it should be capable of... that's the idea! If it matters, I've also done a lot of repair work for rehearsal studios over the years and this is the only guaranteed way to prevent damage, both for instrument amps as well as PA cabs. If you deliberately under-load the amp, you'll also help prevent power stage damage too. (Don't do this with valve guitar amps though, they don't like to be underloaded.) If this is not what they want to do (high-powered drivers are more expensive), you may need to modify the amps so there is a signal level pad (fitted internally) between the preamp and the power amp - this will stop the amp reaching full power if you arrange it so the preamp goes into distortion earlier than the power amp. This is a simple kind of brick-wall limiter, really. With all these methods you may still need to increase the protection on the tweeters too, since reducing the volume of the amp and making it distort sooner will still have the usual effect. Increasing the value and power handling of the crossover resistor will help - it will also reduce the HF response of the cabs which is probably an advantage in helping with feedback in confined spaces. As you can guess we are not talking ideal solutions for great performance and sound quality here . Just over-engineering to the point it's difficult to break things .[/quote] That seems an awful lot to go through when a $100 limiter is all that's required. As far as using lower powered amps goes, that invites overdriving them to clipping, and clipping has the nasty habit of taking out tweeters, even when they're supposedly protected. Another tried and true remedy is a hefty damage deposit. Abuse is far less likely to occur when there's a penalty for doing damage.

[quote name='tempo' post='309688' date='Oct 19 2008, 05:21 AM']Would a hi-pass filter not help?[/quote] Yes, it would, and for that reason it should be standard equipment. But it won't prevent overpowering of the drivers.

[quote name='Subthumper' post='309583' date='Oct 18 2008, 06:48 PM']Is a fuse sufficient? Or is there a way other than using an amp with a self limiting system?[/quote] Fuses don't work. A brickwall limiter set so that the amp cannot deliver too much power no matter what is the only foolproof protection.

[quote name='escholl' post='300756' date='Oct 6 2008, 02:39 PM']so basically where the others would have a dip in frequency response around 70-80 Hz, as limited by their power handling at that frequency, the one modeled in red doesn't, and it additionally has a significantly better output down to around 40 Hz...with the end result being a broader, smoother frequency response at high output? or something?[/quote] Pretty much. The other boxes all have limited output capabilities at the frequency where the dip appears, and in the low end, but that will not show up on a standard small signal SPL chart.

[quote name='escholl' post='299994' date='Oct 5 2008, 12:24 PM']Say the cab could put out 128dB at 100 Hz, and 136 dB at 1kHz (as an example)....but due the varying sensitivity with frequency range of whatever particular driver, it may reach that 136 dB with only 500 watts of power, but need 2 kW to reach 128dB at 100 Hz....or something along those lines.[/quote]A dilemma indeed, and a very real one, until you realize that differential is only 6dB, and that's on average a quarter turn of an EQ knob. EQ makes it possible to get pretty much anything you want out of a cab, so long as the cab has the ability to make use of the power that EQing results in giving it. In any event, you'll sooner see a man on Mars than you will frequency response or maximum SPL charts from the manufacturers.

[quote name='escholl' post='299868' date='Oct 5 2008, 08:23 AM']err...maybe it's just me, but those graphs don't say that much to me on their own. A graph of frequency response and/or sensitivity/vs frequency, would really be a bit more informative. any chance of that?[/quote] The maximum SPL chart is far more informative than a FRD. FRD shows what the cab will do with low level input, but what a cab will do with 1 watt doesn't say what it will do with 100 watts or more. Admiittedly having manufacturers provide FRD would be a giant leap in the right direction, but ulitmately the max SPL chart tells us what most of us are really interested in, which is how loud the cab will actually go.

[quote name='Mr. Foxen' post='299038' date='Oct 3 2008, 07:16 PM']Dunno if this is a lucky score or an extra wardrobe. Figuring its a lot like a 18" folded horn a lá Acoustic 361. Think the 150W is wrong from the valves I can see. Anyone know anything about these? Or feel the urge to pick it up and drive it to my practice space. [url="http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=170266941211"]http://cgi.ebay.co.uk/ws/eBayISAPI.dll?Vie...em=170266941211[/url][/quote] Valve amp technology hasn't had a significant change since roughly 1969, so a 30 year old amp is just as good as a new one from a technological standpoint. But speaker technology more than ten years old is dodgy, and more than 20 is a dinosaur.

[quote name='alexclaber' post='291733' date='Sep 25 2008, 08:05 AM']Continuing to meander off-topic, how much sense does this chart make? Red = The Big One Orange = The Compact Blue ~ Epifani UL410 Green ~ Schroeder 1212L It's showing maximum output in dB SPL as limited by both excursion limited or program power handling. Alex[/quote] It's informative, if not entirely accurate, as calculated maximum SPL doesn't take into account thermal power compression. But since every manufacturer who publishes maximum SPL ratings doesn't factor in the mechanical compression caused by xmax it's still a far better representation of a real world result.

[quote name='alexclaber' post='294354' date='Sep 29 2008, 05:04 AM']Exactly! Alex[/quote] Also, the PDN 15sb40 is not a good choice for an electric bass cab.

[quote name='alexclaber' post='294059' date='Sep 28 2008, 01:30 PM']Have you already bought the drivers? Alex[/quote] What Alex didn't say but should have is "I hope not". Aside from a ten and a fifteen not being the best combination, choosing drivers first and then a cab to go with them isn't the road to a successful build. The cab design and appropriate drivers to be used with it should be decided upon simultaneously.

[quote name='david_l_perry' post='291033' date='Sep 24 2008, 12:00 PM']If you are talking about the wedghorn 10, its [i]massive[/i]....[/quote]I wouldn't say 4 cu ft and 35 pounds is massive, though it's not exactly a shrimp either. But if you want to go low and loud small isn't part of the equation.

[quote name='alexclaber' post='290308' date='Sep 23 2008, 03:37 PM']Based on my experience most bass cabs, whether lightweight or heavyweight are underbraced and underdamped. Tilt an Acme cab up and it won't go anywhere because it's really solidly built and properly braced, despite the high excursion woofers creating far more internal pressure than on a run of the mill cab. Alex[/quote] +1. Well designed and constructed cabs don't vibrate, poorly designed and built cabs do. One place where manufacturers cut corners de riguer is with bracing, as it can't be seen. The same applies to internal damping. [quote name='The Funk' post='290159' date='Sep 23 2008, 12:46 PM']Is this a stupid question: does this mean generally that the smaller the speaker the greater the dispersion BUT the smaller the speaker the higher the frequency range AND the higher the frequency range the smaller the dispersion?[/quote] Yes. The main reason for the necessity of using multiple drivers of different sizes is that small drivers can't go low, and large drivers can't deliver wide dispersion at higher frequencies.

[quote name='escholl' post='286611' date='Sep 18 2008, 08:45 AM']that does make sense. where did the myth come from then?...because it seems quite widely known.[/quote]Probably from the fact that most neo drivers are upper end, with better engineering and therefore better midrange response than the cheaper OEM variety drivers. While some may find the superior midrange of high end drivers too 'midrangey' for their taste, based mainly on what they're used to, accomodating tonal tastes is why amps have tone controls.

[quote name='KevB' post='286581' date='Sep 18 2008, 08:11 AM']need 8ohm units really to match the other speakers..[/quote]No, because to do it properly you need an electronic crossover and a separate amp to drive the subs. Passive crossovers of the sort used in the Wharfedale are only good for low power situations, and won't cut it on PA. I'd pass on the Wharfedale as the cost of its passive crossover is wasted money that should be invested in a crossover and amp.

[quote name='Zach' post='285843' date='Sep 17 2008, 08:38 AM']I've heard this midrange bias mentioned several times in reference to neo's, and i just can't fathom the reason behind it.[/quote]You're quite correct. There are many factors behind how a particular driver sounds, but the magnet material is not one of them. If a driver that's strong in the mids happens to have a neo magnet, or vis-versa if you choose, it's purely coincidental. A driver has strong mids because its designer configured it to do so.

[quote name='stingrayfan' post='285265' date='Sep 16 2008, 12:50 PM']Must be economics. At the moment, they're limited to more top end stuff[/quote] The main advantage is the reduction in shipping costs, of both the drivers and the finished cabs. Trimming a 22 pound driver to 10 pounds is a lot more important to a manufacturer's bottom line than trimming a 6 pound driver down to 5.

[quote name='Merton' post='284990' date='Sep 16 2008, 08:44 AM']But will it have any bearing on the phase relationships at f3 etc, if one is rear-ported and one front-ported?[/quote]No.

[quote name='phil_the_bassist' post='282968' date='Sep 12 2008, 06:04 PM']is there any advantage (like more oomph/better response/power handling etc) to runnin one cab off the Ext.Cab. socket of the other?[/quote] No. You lose current capacity that way. Run two cords from the head, though in truth the difference would be barely measureable and likely inaudable.

[quote name='Mr. Foxen' post='280676' date='Sep 9 2008, 03:45 PM']Right, since we shed a guitarist I suddenly have some space to fill in the higher end. Thus far I've been all about the low doom rumble, and I don't want to lose that. So: I have a Firebass head with a crossover, the current plan is to run the high out into a JCM600 guitar head into a 4x12 (or possibly 2x12) cab. For bass cabs I have a nice 4x10 and a couple of not so great (serviceable) 1x15s. Thus on the bottom I have a choice of 2 15s or a 15 and a 4x10, or one of any. This is a loud dense bassy band that tunes down to A mind.[/quote]Use the two 15s on the bottom. On the top more than 1x12 is overkill. A vertically aligned 2x10 would be far better.

[quote name='Fraktal' post='280105' date='Sep 8 2008, 07:57 PM']Beyma... Extremely underrated speakers, Im positively surprised someone has mentioned them. Powerful, tough and reliable, even cheap here in Spain since thats where they are made, no clue about international prices.[/quote] Their prices in the US are prohibitively high, which is unfortunate.

[quote name='SMART' post='279980' date='Sep 8 2008, 03:42 PM']Glockenklang only offers 10" neos at this time as they feel the current crop of 12's and 15's etc in neo format simply can't hack it.[/quote] IMO the Eminence 3015 and 3015 LF drivers are the best full range and sub woofer fifteens made today, period. There are many other very nice neo drivers of all sizes from not only Eminence but also JBL, Beyma and B&C amongst others, with far better specs than the ceramic magnet drivers they replaced in their respective lines. The only non-neo driver I still recommend is the Eminence BP102.