difference between sealed cabs and ported cabs

Discussion in 'Amps and Cabs [BG]' started by sidhk817, Jan 6, 2005.

  1. Hawkeye

    Hawkeye Canuck Amateur

    Aug 8, 2002
    North of GTA, ON, Canada
    Long&McQuade Employee
    Angelopb said:

    "Why can't we bass players have a high-tech molded TL cab? My Yorkville PA NX series are a high tech material said to be a hardened foram and not a plastic. Who knows?"

    Hardened foam is still a plastic, it's just a thermoset polymer vs. a thermoplastic.

    The transmission line itself doesn't need to be structural, but it does need to be stiff enough to resist flexing. Flexing or "stretching" would theoretically decrease the air pressure and velocity of the air flow within the pipe and likely smear the timing of the wave.

    The design requirements for transmision lines are pretty specific in terms of length and volume with the requirement that near the end (output) of the pipe, the circumference also decreases so as to increase / maintain air velocity.

    I was at the Tokyo Auto Show in '91 I think, and the Mazda RX-7 had a Bose system with what looked like black plastic dryer vent pipe coming out of the bass drivers that circled around the back of the trunk. It was kind of lightweight and obviously wasn't structural and I guess was supposed to be some kind of quasi transmission line.

    The thing with plastic cabinets (using thermoplastics) is that they often have ugly resonances that a good stiff wood enclosure is pretty effective at damping. They are als very expensive to tool. A complex mold with slides and moving features to accommodate a complex cabinet could easily cost $500K to a $1m dollars.

    This type of capital expense is prohibitive to most manufacturers unless they are able to amortize it over a very large production run.

    Thermoset structures typically have lower tooling costs, but higher labour costs for the additional fabrication and assembly.

    One old-school rule of thumb is:

    Thermoplastic = high investment costs and fast cycle times with lower labour (lower production costs).

    Thermoset = lower investment costs, and lower cycle times with higher labour (higher production costs).

    These truisms are dependent on design, geometry, performance requirements and anticipated production volume.
     
  2. You either work in manufacturing or engineering or

    you have recently stayed at a Holiday Inn Express.

    You seem to know a lot about this stuff. I hope a company builds such an enclosure and amortizes it over the long run, perhaps in a diversified product line like bass cabs, PA cabs, keyboard cabs, etc. Doesn't Canada susbisdize R&D for such things for the various manufacturers. I here there is a really high-tech lab everyone gets to use for things such as loudspeaker research.
     
  3. bmc

    bmc

    Nov 15, 2003
    Switzerland

    That's what I thought. I'll tell ya why I ask. I picked up a brand spanking new 1996 SWR Basic Black 2-way rear ported cab in a small Swiss village over the holidays for USD350, complete with warranty. I bought cuz it was such a good deal. I have gigged with it yet, but strongly suspected it would closer to a Bag end due to the rear port, which is a sound I desire.

    I have to unload my trusty Nemesis and pick up a head for it. Thanks for the response. It's what I figured.

    Brian
     
  4. Hawkeye

    Hawkeye Canuck Amateur

    Aug 8, 2002
    North of GTA, ON, Canada
    Long&McQuade Employee
    The latter. No seriously folks, I've worked with automotive manufacturing firms far longer than I care to admit.

    I don't think Canada subsidizes research any more than other countries do, but we do have a world-class test and measurement center for electronics and audio in Ottawa run by the National Research Council.

    The NRC is the reason that a lot of Canadian home audio speaker manufacturers like Paradigm, Energy, PSB, Mirage, Athena etc. have been quite successful as they have had access to some of the best facilities available like anechoic chambers to measure and test their products.

    You make a good point about composite cabinets though (yes I know, technically wood is a composite). There is a lot of potential with plastics for light weight, molded-in features for drivers, ports and stacking, No need for coverings like tolex or carpet, Just switch out drivers / components and you could have a keyboard cab, bass cab, PA cab and use a modular design approach to produce a wide variety of products from simple, standardized common structures.

    There are a lot of traditionalists out there though who still like the big "Wall-o-Sound" refrigerators. Do you think they're "compensating"... like Corvette owners.

    Anyway, the vast majority of speaker cabinets I've seen appear to violate every known principle of sound transducer design known. Big slabs of unsupported wood structure with no internal bracing that are highly resonant (just rap on any cabinet with your knuckles and more than likely you're going to hear a nice loud THOK), vibration-prone, skinny wiring of dubious heritage, nasty cheap horn tweeters, drivers mounted with wood screws instead of nuts & bolts, cheap capacitors and parts in the cross-over (if there even IS a cross-over), inarticulate, no pitch definition etc. I could go on.

    It seems like the majority of manufacturers just go for high SPL's and rely on heavy-handed active EQ to right all the wrongs.

    I for one, would like to see manufacturers focus on clean reproduction of bass pitches without distortion. Distortion should be something that you choose to add when you need it, not an ever-pervasive "tone" that colours the signal IMO.

    Here's where the audio and pro design philosophies start to diverge. In audio circles, manufacturers are always trying to get better bass response with smaller and smaller cabinets.

    Those cabinets are acoustically inert, the wiring and parts are increasingly high-spec and high-performance and the sound is coming closer to the real thing. It's remarkable what you can get for $300 in home audio speakers these days.

    With bass and guitar speakers, it's all about "tone" and each manufacturer adding or reinforcing certain sonic colorations which are not necessarily accurate in order to achieve their signature sound or "tone".

    This is why many bassists are on a never-ending gear-quest to get their tone, because there is no normative approach, just a lot of highly individualist design approaches which result in a lot of products that have their own unique sonic character. Maybe not a bad thing, but it sure requires a lot of experimentation to find what you want.

    Just an opinion, maybe not even an informed opinion, as I've only been playing for 2.5 yrs.
     
  5. My entire quote is: "I've done a large amount of reading on TL designs. They are quirky at best, and design consists of many iterations of trial by build, test, refine, repeat." My intended meaning is, the design process is quirky at best. I should have been more clear on this and apologize for my lack of clarity on this.

    Up until recently, there did not exist any computer assisted TL design tools. This makes a TL a difficult build because it is all trial and error. Despite this, the Euphonic Audio designs are particularly effective and work well. I think EA is the only commercial venture making TL designs. My correspondence with the design engineer confirmed the difficulty involved in arriving at the final design. The EA designs were done the hard way: build, test, refine, repeat.

    George Augspurger did a lot of pioneering work on TL when he was at JBL. I read his published works where he documents the difficulty of the design process. He currently has a software offering for TL design. Martin King is another who is on the leading edge of TL design.

    IMO bass horns vs. TL is not speculation at all. There is larger interest in horns than in TL and brilliant minds are certainly not confined to a single audio discipline. The pro sound crowd has both the resources and desire to produce the best possible product. If TL was superior to bass horns, then TL would be wide spread, and horns would not. This is not the case.

    I concede this may be an unfair comparison of apples vs. oranges. The TL is more an audiophile product, where the bass horn is for pro sound. A single TL will reach far lower than a bass horn of the same size. However, an array of bass horns will smother a TL array in low frequency response, harmonic distortion, directiveness, and loudness.

    I have never disputed the sonic qualities of TL. I gave my reasons for preferring horns to TL because I look at them from the engineer/builder point of view. It is much less work to get a usable bass horn than a TL on the first build. As a player, you don't have that problem because you plug into the end result of somebody's genius. The TL sound you love is the direct result of a long and difficult design process.
     
  6. +1
     
  7. Mike Dimin

    Mike Dimin Inactive

    Dec 11, 1999

    Then for the most part, we agree

    Mike
     
  8. The TL EA cabs are awesome, my low B has never sounded bigger. I agree that the sound is more "hi-fi" than most of the ported cabs I've tried, more flat sounding. I've used them at a party for music, and was surprised that they sound great for that, and I'm very picky about my stereo speakers.

    There could be many reasons companies don't produce TL cabinets that have nothing to do with their advantages. Complexity of construction, difficulty getting a good design (lots of trial and error). Its not like plugging THiele parameters into a program and cranking out the type of response you want. You can easily try a bunch of designs, find none that work well, and get your funding pulled by the bean counters. Until the mathematics gets worked out so the output is more predictable, its too risky for big companies to try. That may just be that people really don't understand what's going on in them. Maybe EA only thinks they understand them, and simply got lucky.

    But the results of the EA cabs are nothing short of spectacular, the amount of clean low end sound you get out of simply 2 10" drivers is remarkable, without being boomy like a ported box tuned for max bass output tends to be. I replaced a 1-18" + 4x10 stack with a pair of 2 2x10 cabs and get way better sound.

    Sometimes it takes someone to realize that "it can't be done" means "you can't do it, but I can" and the EA guy is that person.

    People said the same thing about fuel injection in the 60's. Too complicated, unreliable, not worth the effort. It took the computer technology of later years to really take advantage of the concept economically.

    I don't think you can make generalizations about horns being better then TL cabs yet, the TL technology hasn't been explored fully and horns have. You're comparing NASA to the Russian space agency in 1960, when NASA was just getting started.

    Randy