Bill Fitzmaurice

[quote name='Phil Starr' post='1181809' date='Mar 30 2011, 03:00 AM']'Normal' speakers operating in a sealed cab change the air pressure as they move to and fro'. putting a second speaker behind with an air chamber means the radiating speaker is operating under constant pressure (hence the name) and promises more linear movement of the cone and higher fidelity. Linn made particularly successful speakers this way.[/quote]In those respects isobarics operate exactly the same as single driver systems. Some early designers may not have realized how they worked and made erroneous assumptions. Technically what happens with isobaric loading is that with two drivers Vas is halved, and along with it net cabinet volume. But Vd remains the same, as only the area of one cone is exposed to the air, so SPL remains the same as with one driver.

[quote name='Mr. Foxen' post='1181761' date='Mar 29 2011, 07:56 PM']Any idea how the Ampeg thing measured up in practice? Commercial failure/success is more down to garish colour schemes and dubious marketing than anything practical.[/quote] I've only seen them in pictures. The look was OK, the 134 pound weight a wee bit off-putting.

[quote name='Mr. Foxen' post='1181529' date='Mar 29 2011, 05:11 PM']I think in the days when speaker motor power was limited it was a fair advantage, but not so much now.[/quote]It was advantageous 30 years ago and more when driver technology made it necessary for cabs to be very large to reach very low. And then it was applied pretty much to hi-fi woofers and subs, not electric bass cabs, explaining why they weren't employed in them. Ampeg made one, and it was a commercial failure.

[quote name='plankspanker' post='1181464' date='Mar 29 2011, 04:34 PM']...I can't see what the problem is with this but no doubt the purists will throw their hands up in horror.[/quote]Not the ones with a clue. Your setup is preferable to having them both 8 ohms, where the 175 watt rating of the 210 would be the weak link in the chain.

[quote name='phil.i.stein' post='1176590' date='Mar 25 2011, 05:31 PM']i just read that article, i must've missed that issue of bgm. a great way of visualising the 'maths/music' as a concept or relationship. i love it when science boffs like Alex both educate and consolidate your own experience/knowledge at the same time. i would love to see a cool visual (artistic) interpretation of the harmonic spectrum, be it western or otherwise..[/quote] [url="http://www.talkbass.com/forum/f15/bass-frequency-waterfall-plots-what-they-mean-rigs-510749/"]http://www.talkbass.com/forum/f15/bass-fre...an-rigs-510749/[/url]

[quote name='fonzoooroo' post='1159617' date='Mar 12 2011, 12:48 PM']Excellent. Thanks for that reply - It's cleared a lot up![/quote] Somewhat OT, but not completely, I once reviewed a book entitled 'How to Build Speakers' or something of the sort. It wasn't a DIY book, it was a tutorial for potential production managers on how to set up a speaker building factory/assembly line. It was written by a chap who owned a fairly successful speaker company in the 1980s. In the book he admitted that he didn't know anything about acoustical engineering, nor did any of his employees. He got his designs the old fashioned way: he copied them from other companies. Trouble was, he didn't copy JBL or EV or the like, he copied others who apparently didn't know any more than he did. He didn't care how they sounded, he only cared if they looked right, as he knew that's what sold speakers. He was right.

[quote name='voxpop' post='1159356' date='Mar 12 2011, 09:47 AM']Thanks for the info...........[/quote] As for a driver for it, standard box modeling software cannot easily be used. A more sophisticated program like AkAbak or Hornresp is required, unless you can find someone with the requisite gear and expertise to measure the cab impedance. Then you can find out its resonant frequency and use that along with a standard box program to model different drivers in it.

[quote name='voxpop' post='1159019' date='Mar 12 2011, 04:25 AM']I dont think it is a true horn design. Its more of a large vented port the exits the back of the drive unit and vents into a large area at the base of the cab. This kind of cab was very popular in the 1980's....I am sure someone could explain the design and why it went out of fashion.[/quote] Correct. It resembles a rear-loaded folded horn, but it's at best half the required size to function as one. Even a 50 Hz horn is no less than six feet long. Many cabs of this sort were produced in the 60s and 70s by companies who had no trained acoustical engineers on staff. They scaled down real folded horns, like the Jensen Imperial and JBL Keele bins, not realizing that you can't do that with a successful result, and what you end up with is a bass reflex cab with a flared duct. The result was no better than any other bass reflex cab. But as well engineered bass reflex cabs didn't come along until roughly 1975 they did hold their own until then. Interestingly these faux horns were produced by some very well known companies, including Sunn and Music Man, and no, they did not have trained acoustical engineers on staff. Sunn advertised the 200S as a rear loaded folded horn, and it was anything but. Designer Conrad Sundholm admitted that he called it a rear loaded folded horn after seeing the term used, though he had no idea what a rear loaded folded horn actually looked like or how they worked.

[quote name='fonzoooroo' post='1157631' date='Mar 11 2011, 03:28 AM']I recenty got hold of a "COMPACT Sound MKII" 1x15" folded horn cab. What do you think?[/quote]'compact' and '1x15 folded horn' is an oxymoron. Pics and dimensions will reveal if any improvement is possible.

[quote name='chris_b' post='1156230' date='Mar 10 2011, 03:51 AM']OK, that's good to know. I thought it was nearer 12".[/quote] Not hardly. In fact, if the cab is a bit too close to the wall the space between the wall and cab becomes, in effect, part of the cab, and the low end is further extended. That allows you to back off a bit on the low EQ, giving more headroom out of both the amp and speakers. In theory the best port location is down-firing, the cab on feet of specific height. It's possible to make the space between the cab and floor act as an extension of the cab, allowing the cab to be made smaller. But that removes the option of tilting the cab back to better hear the mids.

[quote name='chris_b' post='1155996' date='Mar 9 2011, 05:31 PM']Rear ports can be a problem on small stages. If there isn't enough room to leave a large enough gap behind the cabs your sound will suffer.[/quote]The required gap tends to be no more than two inches, so I wouldn't base a buy on that fact.

[quote name='chrismuzz' post='1155872' date='Mar 9 2011, 04:25 PM']I've been toying with the idea of adding another cab ontop of my Markbass STD 104 HF, possibly the rear ported 104.. but I've heard it's not advised to combine front and rear ports. Any thoughts?[/quote]Port location doesn't matter unless the two ports in question are a half-wavelength apart. The shortest wavelength radiated by a port is in the vicinity of fifteen feet long, the rest of the math I'll leave to you.

[quote name='Phil Starr' post='1150718' date='Mar 5 2011, 11:56 AM']firstly I don't believe this to be a universal truth, I am sure a lot of valve amps work perfectly happily with a lot of ported speakers. If there is a grain of truth in this I would suspect the interaction between the amp and speaker at low frequencies.[/quote] This impedance chart shows a vented low Qts ten loaded cab, the red trace, versus a sealed high Qts ten loaded cab, the green trace. Both are 8 ohm rated cabs. Believe what you will, but the red trace is a very unhealthy load for a valve amp, and cabs of this sort are well known to blow valves and output transformers. That's not to say that all valve amps and low Qts vented cabs don't get along, but when's the last time you saw a manufacturer post an impedance chart?

'Expert Village'? Expert in what? Plumbing? Certainly not sound.

[quote name='Mr. Foxen' post='1146515' date='Mar 1 2011, 05:19 PM']Just put it somewhere else. The purpose of cabs is to put sound into a room first, amp stand second.[/quote] +1. Worrying more about how the rig looks or stacks instead of how it sounds should be left to guitar'd players.

[quote name='dannybuoy' post='1143155' date='Feb 27 2011, 06:37 AM']I've heard on numerous occasions that valve amps 'like' sealed cabs. Why is this? Do valve amps behave differently when connected to sealed/ported cabs?[/quote]It's not the sealed cab per se, it's the high Q drivers used in them. The result is a lower peak impedance than low Q drivers in vented boxes, which keeps the circuits happy. From a response aspect a high Q sealed cab tends to be more sensitive in the midbass than a vented cab, and that makes the rig subjectively sound louder, a plus with the generally lower power of valve amps. A very high Q speaker is how one can gig with 25-35 watt Ampeg Portaflexes. The downside to high Q sealed cabs is a thin low end compared to vented cabs.

The benefit is that the net volume of the cab, not including the second driver and plenum between them, is halved. The downside is that the output remains the same as that of one driver, and the driver cost is doubled.

[quote name='challxyz' post='1142194' date='Feb 26 2011, 06:28 AM']i'd like to use the 1x15 and the 410 but impedances are not matched,[/quote] In most cases you don't want them matched. The average 1x15 does not have either the thermal or the displacement limited capacity of the average 4x10, so if both are 4 ohm receiving the same power the 1x15 is the weak link in the chain. That's especially the case with a 410HLF Your positive experience with a 2x10/1x15 should be telling you something: it takes two fifteens to make a good match with four tens. The exception to this would be a high excursion 15, such as the Eminence 3015LF.

[quote name='Phil-osopher10' post='1141579' date='Feb 25 2011, 01:42 PM']I recently purchased a 20W combo made by a orange. Would it be fair to judge most orange amps and such on this amp ie. fundamental sound? rather than spending loads and loads trying figure out if they are for me or not?[/quote] You can't judge any brand by the least expensive product they produce, unless their least expensive costs more than what the competition charges for their better products. For instance, I wouldn't call Toyota a producer of bad cars based on the Yaris. But you can't buy a BMW at a Yaris price either.

[quote name='Dronny' post='1140938' date='Feb 25 2011, 05:48 AM']I'm unclear on whether the bass cab would be any use for this...[/quote]It will not, as it probably goes no lower than what the PA tops do. True subwoofers go at least an octave lower than bass cabs.

[url="http://www.ampwares.com/"]http://www.ampwares.com/[/url]

[quote name='fryer' post='1125710' date='Feb 13 2011, 04:54 AM']Hi, I have two 410 cabs. One is a Peavey, 450 w at 4 ohm, and the other is ( or soon will be ) an Epifani, 1,000 w at 4 ohm.[/quote]The power rating of the speakers is moot. Driver displacement determines how much power they can make use of, not the thermal rating. Too bad not one major manufacturer will reveal the displacement limited power of their cabs, though in deference that's partly because most of them don't know themselves. Should you need to separately adjust their volume you can only do so with an amp that has dual independent power amps.

[quote name='dincz' post='1123204' date='Feb 10 2011, 04:03 PM']I realise that vertical stacking reduces the vertical dispersion, but does it also widen horizontal dispersion?[/quote]It does not[quote]if there's less vertical spread then it has to go somewhere else.[/quote]It does, into the audience. Making the source higher extends further out from the source and further down in frequency the zone of the nearfield condition, where SPL drops at a 3dB per doubling of distance from the source rather than the 6dB of the farfield condition. Going from one cab to two doesn't extend the nearfield all that far, but it does extend it, four times further than with one cab to be precise.

[quote name='alexclaber' post='1121592' date='Feb 9 2011, 12:19 PM']Phil's explanation is correct but it's easily misunderstood because it's referring to ALL loudspeakers. If you look at the small subset that represent bass guitar drivers then there's plenty of room for 8"s to go lower than 15"s and 12"s to have more mids than 10"s.[/quote] True. The fact of the matter is that drivers created for use in electric bass speakers have similar specs, because they're all intended to work within the same bandwidth. And that being the case there's very little difference between them in how they function where performance is dictated by the specs. Dispersion is the exception, as dispersion isn't dictated by specs, it's dictated by the dimension of the radiating plane.

[quote name='alexclaber' post='1120399' date='Feb 8 2011, 01:35 PM']Except that I've heard plenty of Peavey 2x10"s and 4x10"s with more bottom and less midrange than many Peavey 1x15"s and 2x15"s. And so on and so forth... It's still bollocks. The old rule of thumb only holds up if you ignore the numerous exceptions - but they really are too numerous to ignore.[/quote] +1. When the exceptions are the rule there is no rule.