Bill Fitzmaurice

[quote name='Leonard Smalls' timestamp='1387812011' post='2316000'] The flat response part is the difficult bit with horns! From my experience of hifi horn speakers, unless the horn is seriously well-designed it can sound properly honky - as if you'd cupped your hands and shouted through them. Fair enough, it's louder and therefore more efficient, but not necessarily accurate... [/quote]Read this: [url="http://www.avsforum.com/t/1353217/speaker-shootout"]http://www.avsforum....peaker-shootout[/url] Or the first page, anyway. The DR200 and DR250 are my designs, fully horn loaded, not just the tweeters. True, EQ is an absolute necessity, but that's true of all speakers, let alone high sensitivity pro-sound horns, because there are no rooms with flat response. Not that I recommend pro-sound PA cabs for home stereo/theater, this guys system is overkill to the nth degree. But there's no such thing as horn 'honk' with a well designed horn, be it a tweeter or a subwoofer. There are a lot of poorly done horns, though, so the notion is understandable.

[quote name='Beer of the Bass' timestamp='1387733045' post='2315006'] I wonder if one of these horn tweeter designs would still come out ahead if the blind test included a fuzz pedal, or other distortion effects? [/quote]No worse than any tweeter equipped cab, and with the ability to roll off above 3.5kHz, probably a lot better.

[quote name='bassman7755' timestamp='1387726850' post='2314919']why-arent-more-bass-cabs-designed-like-this [/quote]Because they don't look like every other cab. Bass players aren't quite as bad as guitar'd players when it comes to buying with their eyes rather than their ears, but they come close. The ideal cab showroom would have all cabs hidden behind a scrim, so that you couldn't see the cabs you were trying, you could only hear them. Said showroom wouldn't stay in business a week. [quote]Its almost there is some unwritten law against using a large flared horn in a "bass" speaker, when surely it is the obviously thing to do when designing a flat response 2-way system ?[/quote]Obvious to who? Duke approached the design with a clean sheet of paper and a real engineers perspective: [i]How do I make the best speaker possible for this application? [/i]That's diametrically opposed to the standard of most companies, which is: [i]What do we make these look like so that they'll sell. [/i]

[quote name='Jus Lukin' timestamp='1387568987' post='2313569'] Ok, cool, thanks Bill. So could I put words in your mouth to suggest that the Alpha 12s would sound much like a Fender speaker, but with better spec?[/quote]+1, the midrange response is quite similar, but with a lower Fs and 2.4mm versus 1mm xmax the lows are what we wished we could have had from Jensens. The only way I was ever able to get a clean low E back then was after I went from two Fender 2x12 cabs to a pair of 4x12 Kustom column speakers, that would have been 1968. [quote]Also, do you think the same might apply to a Marshall, for that snarling grit they put out [/quote]Safe bet.

[quote name='bumnote' timestamp='1387564740' post='2313503'] What about the phil jones 5" jobbies? I originally thought it was a gimmick but it works really well. I would love to try on of the big rigs with 24 or more speakers [/quote]Displacement is displacement, whether you get there with one large driver or a whole bunch of little ones. Using smaller drivers offers the potential advantages of higher frequency response and broader dispersion, but only if you use them correctly. That means either arraying them vertically or, if clustered, bandwidth limiting, so that only the innermost drivers operate to the top of their range, while the drivers to either side are progressively low passed to lower and lower frequencies the further they are from the cabinet center. PJ doesn't do the former, I don't know if they do the latter. The disadvantage to smaller drivers is cost, as for a given displacement using larger drivers generally costs less per cubic centimeter of Vd.

[quote] putting a pair of Jensen C12Ks in a Fender style sealed cab to be pushed with even 50watts of Bassman induced power sounds like it could risk over excursion. [/quote]I had a 65 Bassman with two cabs and still couldn't get a clean low E with any volume. You can get a good vintage tone in a sealed cab with Eminence Alpha 12s, and they have over twice the xmax of C12s. The Beta 12 has plenty of xmax, but doesn't have quite the high mids that the Alpha does. I'd go Alpha if you want more grit, Beta if you want more clean.

[quote name='LukeFRC' timestamp='1387220716' post='2309566'] Hmmm I think the back side is being treated as a horn of some kind. [/quote]They claim that it's a waveguide, based on the fact that it's tapered. A taper does not a waveguide or horn make. It's a tapered ducted port. [quote]I would be very interested to know what the 'cost no object' BFM solution would look like, if you cared to design it. [/quote]Simplexx is a cost no object bass reflex. There's only so much you can do with a bass reflex. You can load it with more expensive drivers, but otherwise that's about it. [quote]There is a niche for high performance bass reflex cabs, currently occupied (IMO) by Audiokinesis, Acme, BF, Baer, Greenboy, etc,[/quote]What makes them different than more pedestrian options, like Peavey and Ampeg, is the use of premium drivers, like the Eminence Kappalites. The engineering isn't all that different, other than those that use midrange drivers instead of tweeters. I received my Kappalite samples six months before they went on the market, I had bass reflex prototypes using them a year before Greenboy put anything out, and I designed one of the best reviewed 1x12/1x5 cabs that uses an OEM Kappalite 12 (I can't say which, as the first thing you sign when taking on a design contract is a non-disclosure agreement, as no company wants it known that they employ independent designers). I don't use a Kappalite loaded bass reflex myself, I use a Jack 12 Lite. I introduced Simplexx because I had many requests for an easy to build design that still met my quality standards, not because bass reflex is better than or even equal to what I already offered.

[quote name='brensabre79' timestamp='1387469442' post='2312360'] [url="http://www.ebay.co.uk/itm/like/400617627560?hlpht=true&ops=true&viphx=1&lpid=95&device=c&adtype=pla&crdt=0&ff3=1&ff11=ICEP3.0.0&ff12=67&ff13=80&ff14=95&ff19=0"]Here's[/url] one under £70. [/quote]Unfortunately its specs are quite the opposite of those needed. if the OP wants a worthwhile driver he needs to spec match it as close as possible to the Delta Pro 15. If he doesn't care how it sounds or if it will last more than three notes that's a different story.

The original driver is an OEM variant of the Eminence Delta Pro 15.

[quote name='LukeFRC' timestamp='1387147740' post='2308823'] stumbled upon the physics defying cabs and tried to work out what on earth they were talking about... [/quote]What they've done is to take a bass reflex cab and put a reflector inside that directs the driver rear wave out the ports. It's been known since the 1940s that if you do that the front and rear waves will meet at various angles of phase, resulting in major reponse peaks and valleys. And since the 1940s bass reflex cabs have used damping inside the cab to prevent that, allowing only bass frequencies close to the port tuning frequency to come from the port. Damping the rear wave is one of the most basic tenets of speaker design, but these guys have managed not to learn that. The other feature they use is cross-fired drivers, but that's hardly new or unique. They use extremely expensive drivers, so their prices are off the charts. But they look cool.

[quote name='LukeFRC' timestamp='1387137630' post='2308598'] +1 I didn't even realise until yesterday Bill wasn't on TB anymore, no idea why (I don't want to know)[/quote] Explained here: http://billfitzmaurice.info/forum/viewtopic.php?f=7&t=18092 [quote]Mind you TB is an odd place I was reading all this hype for some "vortex" speakers and then went and looked at other more pro audio design forums... different response there!... [/quote]Those speakers attempt to defy the laws of acoustics. They fail in that attempt. But as our President Lincoln famously said (and probably paraphrased Shakespeare in so doing) you can fool some of the people all of the time. [quote]When designing a three way or two way full range system, how do you decide where to cross over? When polar response starts to drop off at the woofer[/quote]That's the primary concern, or should be anyway, but you do have to balance it against cost, as the lower you cross over the more expensive the components, not just for the driver but also the horn and crossover components. In a cost no object design I'd go even lower than I did with the Simplexx, but for most builders cost is an object. Most commercial cabs go too far in the other direction where that's concerned, and cross over way too high. Oddly enough the only ones who benefit from their cost savings are themselves.

[quote name='xgsjx' timestamp='1387101526' post='2308142'] A couple of weeks ago, my guitarists found out what dispersion is when the room we hired had a 4x12 guitar cab, stood right in front of it & kept turning it up because he couldn't hear himself. I suggested that he move further away & he stepped forward & to the side. He still thought he was quiet. The other guitarist pulled him over to where he was standing, straight across from the cab & he stood there for the rest of the sesh (& turned down too). [/quote]Not the sharpest tacks in the bin they are. I once mixed a band where the guitar player insisted that he not be mic'd. As I knew would be the case he couldn't be heard outside of a small cone shaped area directly in front of his cab. First break he asked how he sounded. I told him I didn't know, since ge wasn't in the PA I couldn't hear him. His solution? Turn his amp up. Needless to say that did not improve matters a whit. Go to a guitar forum and you see them go on forever about this speaker, that pedal, these strings, those picks, all in search of a magical tone that will make them the next Clapton, yet most are profoundly clueless about how to get said tone heard by more than 15% of the audience. The best player I've seen since Mike Bloomfield is John Mayall's current guitarist. His Fender Twin is aimed across the stage at the drummer. He doesn't hear it directly, like the audience he hears it through the PA.

[quote name='xgsjx' timestamp='1387069801' post='2308013'] What I meant was that a driver's diameter doesn't mean it has a particular sound. [/quote]+1. Within reason you can get pretty much the same result with any cone size from an eight to an eighteen, with the single exception of the dispersion angle. It isn't all that practical to get 30Hz out of eights, or 4kHz out of eighteens, but it can be done. There is absolutely no characteristic ten vs twelve vs fifteen sound.

[quote name='xgsjx' timestamp='1387014944' post='2307384'] Cone size makes no difference to the sound. [/quote]Cone size has a direct effect on the angle of dispersion. When the cone is one wavelength or more across dispersion narrows; a cone that's too large for the frequency being radiated is what causes beaming. While larger cones tend to have better low frequency response, and smaller cones tend to have better high frequency response, those are not absolutes. Dispersion is, and it's the primary reason why midranges are smaller than woofers, and tweeters smaller than midranges. A relevent point is that when two drivers are placed side by side the horizontal dispersion is the same as if they were one driver twice their size. Thus a pair of tens side by side have the horizontal dispersion of a twenty inch driver, explaining why a fifteen can have better highs off-axis than a two ten cab. Twelves side by side are even worse. Almost every guitar player running cabs with side by side twelves complains about beaming, as do those in the audience in front of them who get their heads taken off by even an AC 30, let along a stack, while those standing to the side can't hear them at all. The physics involved are quite simple, but few guitarists have a clue how speakers work, beyond "you plug an amp into them".

[quote name='nottswarwick' timestamp='1386967530' post='2307073'] Any thoughts? [/quote]Most tweeters don't do anything below 4kHz, and most players don't have a lot of content in their tone above 6kHz, so getting along without them you don't lose much. What most players can benefit from is better response between 2kHz and 5kHz, where midrange drivers operate. But midrange drivers and their crossovers are more expensive than tweeters, so they're rarely seen.

[quote name='jimbobothy' timestamp='1386522066' post='2300992'] Any suggestions please? [/quote]If it farts out turn down.

[quote name='Grangur' timestamp='1386166089' po [quote]st='2296627'] Is this normal for a combo speaker to only take half volume? [/quote]It is. Combos tend not to use the highest quality drivers, and the cabinet size concessions made to keep the rig light and portable are reflected in limited low frequency output capability.

[quote name='flyfisher' timestamp='1386063296' post='2295071'] While not disputing tweeter sensitivity to excess harmonic distortion, is this really a practical issue with modern gear? Is the THD figure for modern amps really so excessive these days that it could damage a properly rated tweeter, even at full volume?[/quote]The THD figure you see listed for amps is what's used as a benchmark when measuring the amp output. That might be anywhere from 0.1 to 1% THD on average. By no means is that the limit to the THD that they can produce. If you crank the amp, or boost the signal level going in to the amp, you can easily reach 20% THD and more. That's how guitar players get their tone, and for that matter why guitar amps never use tweeters, because they'd never last through even one gig. Bass players tend to use amps large enough that they don't have to crank them to get loud enough, but not all do. And bass players who use distortion devices tend to cook their tweeters. [quote]Also, do cab manufacturers not include any simple filter protection for their tweeters? It would be fairly easy to roll off the frequency response above, say, 25khz [/quote]25kHz isn't the problem. Everything a tweeter reproduces is harmonics. A tweeter normally sees only 5% of the broadband power content. That means a tweeter in a 400w rig normally will never receive more than 20w. When you go from 5% THD to 15% THD the level of the harmonics goes up by 10dB. The tweeter that normally is called on to handle 20w now might be gettting 200w. Magic smoke ensues. Woofers aren't phased by the increased harmonics since they would be able to handle 400w anyway.

[quote name='ML94' timestamp='1385849982' post='2292925'] As the title says I'm interested in knowing what could happen if I underpower my cabs. At the moment I have a 600w Genz rig, both at 300W and head being a powerful 600w amp. What if I powered my 600w cabs with a 500w amp. What would the consequences be ? [/quote]For the woofers, nothing. If you have tweeters they can be damaged by too much harmonic content, and excess harmonic content is what's created when an amp (or any device in the signal chain, including fuzz pedals) is pushed to clipping. You're far more likely to push a smaller amp to clipping than a larger one, and the smaller it is the more likely that scenario.

[quote name='bassmachine2112' timestamp='1385898049' post='2293237'] I must echo the comment about how they sound in the mix ,that,s where they shine. [/quote]That has nothing to do with the isobaric design, and everything to do with what's inside, which is this: http://www.bluearan.com/index.php?id=EMIDLIT2510&browsemode=category There are many other sources for Deltalite II 2510 loaded cabs, and if they're not isobaric then a 2x10 will be as loud as a 2x10, not a 1x10.

Related to the OPs original question is if you can get higher sensitivity ported than sealed while maintaining the same response why wouldn't you? This is why: The blue trace is a ported ten with EBP 138, the black a sealed ten with EBP 80, both are 1.5cu ft cabs. At 50Hz, where demands on the amp and driver are the highest, the ported cab has 6dB higher sensitivity. That means it would take two of the sealed to match one of the ported. One reason one might prefer the sealed is if one doesn't care for the stronger low end of the ported. But that's why amps have all those knobs and sliders. Using those devices one can get the same response as sealed, with a major difference, that being headroom in the amp is increased while driver excursion is decreased by using EQ to reduce low frequency output. The other reason why one might prefer sealed is that the reduced amp headroom and increased excursion demands on the driver with sealed will result in a dirtier tone. If that's what you're after all well and good, but if not you should reconsider bias against ported.

[quote name='LawrenceH' timestamp='1385681328' post='2291228'] Your own example is a good one for showing exactly what I'm talking about. Yes, the slope rolls off steeper below 30 just as physics says it must. [/quote] So? That being well below the passband it's moot.[quote] With this particular example the increased sensitivity above that means the group delays between the two cabs will diverge at a much higher frequency ie the transient response of the ported cab will be poorer. [/quote]In this particular case GD of the vented cab is significant only below 40Hz, so it is also moot. GD at 50Hz is 4 and 6ms respectively, putting both well below the threshold of audibility, and GD of the two above 100Hz is identical.

[quote name='LawrenceH' timestamp='1385679616' post='2291203'] Yes, it does mean exactly that. Unless the 'laws of physics' you so humbly equate yourself to are markedly different to everyone else's. You can get it the same in a limited bandwidth, which is what I said at the beginning. You can't get the final slope of a ported cab below resonance to roll off at 12dB/oct no matter how many magical beans you buy from mysterious old men you meet on the way to speaker markets. [/quote]This is a chart of the Ampeg SVT driver, ported in blue, sealed in red, in the same net volume. Of course the gross volume of the ported is larger, to account for the duct, but the increased sensitivity makes that worthwhile. The ported does have a higher roll off slope below 30Hz, but that's hardly of any consequence. This also answers the OPs question regarding what the same driver may do sealed or ported, in this case with a driver that has a moderate EBP that allows it to function in both.

[quote name='LawrenceH' timestamp='1385676173' post='2291136'] The sum of the driver/port below resonance will be a 24dB/oct slope. Always. [/quote]That doesn't mean one cannot realize the same result with vented and sealed, just that one must possess the necessary design skills to do so.

[quote name='LawrenceH' timestamp='1385671086' post='2291055'] I am always puzzled when I see people say that you can design a ported cab to give the LF response of a sealed cabinet, [/quote]You can. I don't know why you'd want to, but it's not all that difficult, if the driver specs are amenable. [quote]In hi-fi, I also think mid-range leakage from ports can be a difficult issue to solve completely satisfactorily as well. [/quote]I've never found it an issue at all. [quote]I don't know why (I'm sure someone on here could explain) but a sealed cab seems to be an especially good match with a valve head. [/quote]Because the impedance peak of a sealed cab with high Q drivers tends to be much lower than the peaks of a vented cab with low Q drivers, and valves don't deal well with high impedance loads. [quote]How does the same driver react in sealed and ported cabs?[/quote]Not all that well, as a driver that works best in a ported cab has a high EBP, that which works best sealed has a low EBP, so putting either into the other is a round hole/square peg situation.