Transmission line cabinets? c'est quoi ca? And now in english: what does it mean
There's a very nice explanation here.
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Double Bass Amps, Speakers, Volume...
- Thread starter charmicarmicat
- Start date
There's a very nice explanation here.
As I understand it, transmission line cabinets are a sophisticated version of a ported cabinet. Euphonic Audio has some more detail on their website, and I THINK they are the only ones doing these kind of cabs.
No, actually, the two are completely independent. Ideally you want as high an SPL rating as possible to wring every bit of sound out of each watt.
"speaker spl" is (if accurately measured) a number that tells you how much sound output (SPL = Sound Pressure Level) you get for a given amount of power- typically expressed as the average output in dB measured at 1 meter from the speaker with 1 watt of power at (typically) 1KHz. A fairly insensitive cabinet might produce around 93 dB SPL per watt; a very sensitive cabinet would product 103dB. That doesn't sound like a huge difference, but dB is a logarithmic scale, so 103dB SPL is 10x as loud as 93dB SPL.
Sort of. All cabinets are designed to a common purpose- to get rid of the out-of-phase backwave from the speaker so that it doesn't interfere with the wave coming off the front of the speaker. Sealed boxes can simply block the back wave, or in more sophisticated versions, use the air in the box as part of the "spring" that restores the cone after excursions.
Ported cabinets take the sealed box design, and add an out-of-phase resonance at (typically) the point where the sealed-box response of the speaker is down by 6dB. This resonance reinforces the falling output of the speaker. This resonance is created by using a short Helmholz resonator- the port.
A true transmission line design delays the backwave through a long tube filled with some absorbant material. The tube is long enough so that the backwave at the lowest frequency of interest will have its energy dissipated before being reflected back. The idea is to allow the speaker to operate as though it were in free air yet still get rid of the backwave.
Many "transmission line" speakers are really a sort of ported/transmission hybrid that uses a delay line to allow the backwave to exit the cabnet in phase with the front wave at some low frequency, much as a ported cabinet does.
Forgive me if I am way off base here - but is a transmission line anything like what the Bose Wave music systems use to get such a (reportedly) "big" sound out of a small box? They give it a special name and refer to it as their "proprietary Waveguide Speaker Technology." There is a pop up w/ a colorful pic in the third paragraph on this page.
Sure seems somewhat similar to a non-techie like me.
Sure seems somewhat similar to a non-techie like me.
A speaker in a simple sealed box has a resonant frequency where the speaker's impedance goes up dramatically. This impedance peak can be very high, and 60 to 80 ohms or higher is not uncommon. This is important because, at this resonant frequency, an amplifier cannot supply the same amount of power as it can at the speaker's nominal impedance (such as 8 ohms). The higher the impedance, the less power can be delivered to the load. There's an old saying "as the impedance grows, the wattage goes," and this is very true.
A typical ported enclosure trades one large impedance peak for two smaller peaks. A properly designed transmission line has the flattest impedance curve of any type of speaker enclosure, and therefore an amplifier can deliver more power to the speaker throughout the transmission line's design bandwidth.
(See the Transmission Line article on EA's web site: [Invalid or Expired Link Removed])
Re: Bose Waveguide -- Bose has always done a good job of marketing.
A typical ported enclosure trades one large impedance peak for two smaller peaks. A properly designed transmission line has the flattest impedance curve of any type of speaker enclosure, and therefore an amplifier can deliver more power to the speaker throughout the transmission line's design bandwidth.
(See the Transmission Line article on EA's web site: [Invalid or Expired Link Removed])
Re: Bose Waveguide -- Bose has always done a good job of marketing.
...but because the impedance peak coincides with a resonance, then the response is exaggerated there and not as much power is not needed. No? As a practical matter, one worries most about the frequencies at which the impedance drops very low because when it does, it presents a difficult load that can exceed the current capability of the amp.
Thanks for the link to the EA article. I take issue, however, with the tuba analogy. That is quintessential horn loading! Never done better than here.
Ah, pronoun trouble! ;-)
The purpose of an enclosure is to prevent the backwave from interfering with the main wave; delaying it and using it to reinforce the main wave at the 6dB down point is one way of accomplishing that, but it's not the reason you need an enclosure in the first place.
What he said. The tuba, like the Klipshorn, is designed to provide a good impedance match between a relatively massive diaphragm (speaker or lips) and the relatively light surrounding air. A true transmission line is designed to convey energy in a lossless manner with a constant impedance.
Yes. Bose is very clever at patenting prior art and pretending they have something new; transmission line speakers have been around since the 1950s. The Bose patent simply makes claims about a particular alignment- essentially, a particular choice of how long to make the waveguide for a particular speaker cutoff frequency. What they do have is a team of very expensive lawyers who will make it extremely difficult for anyone to challenge their patent.
So... last night was time to practice with the band and I tried what Fingers suggested below and lo and behold, it worked. What I may try now, just to make sure I squeeze as much as I can from the amp, is an extension cabinet. Any suggestions? What has worked for you? Again, thank you for taking the time!
