Small Speaker Kool-Aid
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soundhound
Well-Known Member
Botch said:
If you are referring to the large HF horn, absolutely not. Technically a regular driver mounted at the end of a horn is a waveguide. A traditional horn is loaded with a compression driver, which increases the efficiency and transient response dramatically. Do a google search for compression driver for details.
Low frequency horns use a conventional driver, but it is pressure loaded at its rear.
soundhound
Well-Known Member
Coytee said:
There is a sealed chamber behind the driver which should provide the same loading as the column of air in the horn proper. Compression drivers are limited to frequencies above the bass. The lowest frequency I've seen a compression driver used for is 300Hz.
Coytee
Member
soundhound said:
I'm not an engineer so I'm certainly not an expert on these things...that said... I might be confused here with semantics.
You're right in that (I'll use mine) some bass horn drivers have a sealed compartment behind them. However, my bass horn drivers are ALSO compression "drivers" (or at least compression loaded). They have two twelve inch drivers that are mounted to a board with something like a 3"x6" slot that the entire 12" driver gets forced (compression) through.
These bass bins will play down to the 40's somewhere, I do not know the bottom of them. They aren't subwoofer range at all but they work perfectly for a full range system.
I might add, I'm referring to front loaded horns not rear/back loaded. So compression drivers are clearly NOT limited to use above the bass as I understand it. Perhaps I'm missing something here and if so, my pardon. I'm not trying to argue.
Coytee
Member
I posted that forgetting what my avatar was. I'll use it.
You have a mix of all horn loaded parts there. Starting at the bottom you have two stacked single "MWM" bass bins. Each one has a 15" horn loaded, compression driver in them. As per above, I don't know how low they go...mid 40's perhaps? They'll pelt you pretty hard if you feed some juice to them. Above them is as 3-way all horn loaded LaScala. Bottom section is a 15" woofer, compression loaded. In fact, the same driver in the LaScala COULD be used in the MWM however they put a more heavy duty in the MWM because of the abuse it takes. This heavier woofer is also put into the industrial LaScalas. The LaScala midrage/tweeter are compression horn loaded and the huge K402 horn on top is also compression loaded. The entire stack is compression loaded horn driven.
The MWM's on the bottom and the LaScala cabinet also have this sealed back air chamber. I'm not sure that the back air chamber is what makes them "compression loaded", my understanding is it's the slot that the sound is forced through.
I'll try to attach a picture of the Jubilee bass bin build, showing said slot. If it attaches, then a 12" driver is mounted above it and this slot is where the compression takes place (as I understand the mechanics)
I'm presuming you know this. When I read the posts though, being not too technical myself I read some inferred logic there that I think could mislead someone who knows even less than I do about horns. I'm just trying to expound a bit to clarify the larger picture.
You have a mix of all horn loaded parts there. Starting at the bottom you have two stacked single "MWM" bass bins. Each one has a 15" horn loaded, compression driver in them. As per above, I don't know how low they go...mid 40's perhaps? They'll pelt you pretty hard if you feed some juice to them. Above them is as 3-way all horn loaded LaScala. Bottom section is a 15" woofer, compression loaded. In fact, the same driver in the LaScala COULD be used in the MWM however they put a more heavy duty in the MWM because of the abuse it takes. This heavier woofer is also put into the industrial LaScalas. The LaScala midrage/tweeter are compression horn loaded and the huge K402 horn on top is also compression loaded. The entire stack is compression loaded horn driven.
The MWM's on the bottom and the LaScala cabinet also have this sealed back air chamber. I'm not sure that the back air chamber is what makes them "compression loaded", my understanding is it's the slot that the sound is forced through.
I'll try to attach a picture of the Jubilee bass bin build, showing said slot. If it attaches, then a 12" driver is mounted above it and this slot is where the compression takes place (as I understand the mechanics)
I'm presuming you know this. When I read the posts though, being not too technical myself I read some inferred logic there that I think could mislead someone who knows even less than I do about horns. I'm just trying to expound a bit to clarify the larger picture.
Attachments
Yeah, I'm not terribly clear on what really distinguishes a compression driver from a regular dynamic driver. Even Wikipedia's article isn't much help there, for me. Does a compression driver use the same basic technology (e.g. voice coil inside a magnet), but is just contained within a (small) enclosed space, open only to the front throat? Or maybe the throat is smaller than the actual moving internal surface that's generating the sound? I'm not sure...
SH (or someone), do you have a good definition of what constitutes a compression driver?
SH (or someone), do you have a good definition of what constitutes a compression driver?
Coytee
Member
I'm not sure that you can make a rule that "this" is a compression driver and "that" one isn't.
I'll stick with the brand I know. Take the woofer in the Klipsch Khorn, LaScala or Belle. They use the K33 inside their bass horns. This driver is mounted to a board with a sealed back chamber. They ALSO are forced through a slot that is 3x12 or something in size. THIS is what makes it a compression application. They put this SAME K33 driver inside their Cornwall and here it is operating as a normal ported box dynamic driver. There is no slot for compression.
To make a stupid analogy.... blow as hard you can out of your mouth. You can exhale the air pretty quickly. Now, stick a straw in your mouth and exhale as hard as you can. NO WAY will you be able to exhale as freely now because you are now in a compression situation. Same "driver" (mouth/lungs) but setup with a different format. With the straw in mouth, under compression you now build up a lot more pressure as you try to blow through the straw. This would be the compression. As you step down in oriface size (open mouth to straw) you create this back pressure, up the sensativity.
For the sensativity, you can now take very small movements of your lungs and feel a lot of air movement out of the straw. You might not get the volume but you can get a lot of pressure (sound) out of minor lung movements.
The construct of these drivers are essentially the same as all other drivers but I'm sure there are different specs when you get into that Xmax, Z, and other things (that I don't know much about). All that Theil-Small stuff.
Different drivers might be better suited for compression application than others and vice versa.
I'll stick with the brand I know. Take the woofer in the Klipsch Khorn, LaScala or Belle. They use the K33 inside their bass horns. This driver is mounted to a board with a sealed back chamber. They ALSO are forced through a slot that is 3x12 or something in size. THIS is what makes it a compression application. They put this SAME K33 driver inside their Cornwall and here it is operating as a normal ported box dynamic driver. There is no slot for compression.
To make a stupid analogy.... blow as hard you can out of your mouth. You can exhale the air pretty quickly. Now, stick a straw in your mouth and exhale as hard as you can. NO WAY will you be able to exhale as freely now because you are now in a compression situation. Same "driver" (mouth/lungs) but setup with a different format. With the straw in mouth, under compression you now build up a lot more pressure as you try to blow through the straw. This would be the compression. As you step down in oriface size (open mouth to straw) you create this back pressure, up the sensativity.
For the sensativity, you can now take very small movements of your lungs and feel a lot of air movement out of the straw. You might not get the volume but you can get a lot of pressure (sound) out of minor lung movements.
The construct of these drivers are essentially the same as all other drivers but I'm sure there are different specs when you get into that Xmax, Z, and other things (that I don't know much about). All that Theil-Small stuff.
Different drivers might be better suited for compression application than others and vice versa.
soundhound
Well-Known Member
Here is a cross section of an Altec Lansing compression driver: http://www.lansingheritage.org/images/altec/specs/components/802d-804a/page1.jpg
The feature which distinguishes a traditional compression driver is the presence of a phase plug in front of the diaphram. The Klipsch legacy drivers are similar to this one.
A bass horn does, depending on the design of the throat of the horn, provide some degree of compression, but its not a "compression driver" in the sense that most people associate the device with. Really, I've been talking about the traditional compression driver as used in mid-frequency and high frequency applications anyway - the one in the original picture did NOT provide any compression and did NOT have a phase plug: it was simply a speaker mounted at the end of a horn structure as so many "horns" do these days.
The feature which distinguishes a traditional compression driver is the presence of a phase plug in front of the diaphram. The Klipsch legacy drivers are similar to this one.
A bass horn does, depending on the design of the throat of the horn, provide some degree of compression, but its not a "compression driver" in the sense that most people associate the device with. Really, I've been talking about the traditional compression driver as used in mid-frequency and high frequency applications anyway - the one in the original picture did NOT provide any compression and did NOT have a phase plug: it was simply a speaker mounted at the end of a horn structure as so many "horns" do these days.
soundhound
Well-Known Member
Coytee said:
Please look at this diagram of a conventional compression driver - the key defining feature of this type of driver is the presence of a phase plug:
http://www.lansingheritage.org/images/altec/specs/components/802d-804a/page1.jpg
There's no sense getting worked up about all of this: your horns qualify as "real" horns anyway. Many of the "horns" that are being marketed today are merely drivers at the end of a waveguide device, like the device I was originally referring to. There are many ways to make a bass horn: some have compression in the throat of the horn and some do not - one is not inherently better than the other - they are simply different design choices.
You're blowing this whole thing up far more than it deserves to be............
SH, in that Altec cross section, it looks like the voice coil is not actually around (or inside) the stationary magnet? And it's hard to tell what actually moves in that diagram - looks like the whole voice coil+diaphragm are bolted to the "plate"...? Must be some freedom of movement somewhere - does the diaphragm move left/right in that picture? What is "tangential compliance"?
Sorry, just curious how this technology works, I've never really examined such a driver in detail.
Sorry, just curious how this technology works, I've never really examined such a driver in detail.
soundhound
Well-Known Member
PaulyT said:
The voice coil is in a pretty conventional magnetic gap. If you try to visualize the dome and voice coil as facing to the rear, facing away from the throat of the driver, then it more clear. Here is a page with the picture of an Altec 34647 diaphram, viewed from the part which is facing toward the rear of the compression driver (the voice coil is around the edge of the dome part, on the opposite side of the view).
The key part about the compression aspect is that the actual moving diaphram is larger than the mouth of the horn, so the wavefront is compressed at the throat of the horn. Compression ratios of 10:1 and more are common. Of course, the higher the compression, the more efficiency in the driver/horn combination. In the original picture I was referring to with the speaker at the end of a horn structure, there is NO compression because the speaker is the same size as the throat of the horn.
The importance of the phase plug is that it assures that sound wavefronts coming from all parts of the diaphram dome arrive at the throat in perfect phase. If there were no phase plug, the sound from the edges of the diaphram would arrive at the throat of the horn later than sound from the middle of the diaphram, and thus there would be phase cancellation at different frequencies. In low frequency horns, phase plugs are not needed because of the great length of the wave at bass frequencies means there is little phase difference between sound reaching the throat from the edge of the driver verses the center. Also, in horns where the driver is the same size as the throat of the horn there is no potential for phase cancellation so no phase plug is required.
But the presence of compression and horn structure is key to the vast advantage these devices have sonically over conventional speakers. In a proper compression driver / horn arrangement, the virtual "size" of the diaphram is multiplied, and the virtual "mass" of the diaphram is divided - plus on top of all this, distortion is drastically reduced. The net mass of the diaphram at the mouth of the horn can be less than the mass of the diaphram in electrostatic speakers, which are known for their fantastic transient response because of the low mass of their diaphram. A compression driver / horn combination can have less mass than even an electrostatic speaker, and thus even better transient response. It is this lighting fast transient response which gives these horns their realistic quality in reproducing sound, all the while having a vast dynamics advantage (because of their efficiency) which no other type of speaker can touch.
soundhound
Well-Known Member
PaulyT said:
It doesn't matter: DIYer posted better pictures.
TitaniumTroy
Well-Known Member
SH, just wondering what you thought of these modern versions of the Western Electric, Mirrorphonics? http://www.stereophile.com/content/now- ... e-speakers Or what ever your thoughts are on the originals, as they look similar to the VOTT.