compression drivers

[biglaz]

Silly question! How does a compression driver work? I have looked on the insides and changed diaphrams but, I just can not understand how these fragile looking diaphrams can make so much sound especialy at the lower frequencies.

Thanks for any info.

Robert

[twistedcrankcammer]

Silly question! How does a compression driver work? I have looked on the insides and changed diaphrams but, I just can not understand how these fragile looking diaphrams can make so much sound especialy at the lower frequencies.

Thanks for any info.

Robert

Robert,

Compression drivers don't make it loud, the horn does. When horn loading the speaker, it is just like taking one of those stupid plastic horns you blow into at a socker match, or blowing the mouth piece of a trumpet or trombone without it being in the instrument/horn, it is not very loud. Now being in a compressed state, the driver sees more resistance then in free air. The 4 Ohm woofer of a K-horn makes the amplifier see a 16 Ohm load because the driver is being restricted in it's movement. This is why the back of the woofer has a closed chamber of a certain amount of air space to compress, and the motor board has a limited sized slot. The tweeters and squakers similarly have an enclosed structure behind the diaphram. I hope this helps you understand it a little better.

Roger

[biglaz]

Thanks Roger.

[WMcD]

Wow, Roger is terrific.

Let me add that if you want more bass out of the same set up, you need a tuba. Basically the same driving system but a bigger horn.

PWK explains that if you have a piston in a lake of water and move the piston, it doesn't pump much water. But if you put a cylinder around the piston, it can pump water. Or at least INTO a pipe.

It is a bit more complicated with air. We should discuss why a direct radiator doesn't work well. When the diaphragm moves, the air in front of it (being pressurized) moves away. Therefore the diaphragm does not have initially pressurized air to bump up in pressure. And, roughly speaking, the slower the piston moves (lower freqs) the more relative time the air has to move away.

This means that only large diaphragms can move air at low freqs.

Let's go back to the pipe issue. We've done well putting pressurized air into the pipe. Being confinded the air can't run away to the sides. But what about at the other end of the pipe? In a pipe we can get a resonance going and pump air out the other end, but that is only at one freq.

What we need is a pipe which increases in area. Now it has a large area at the mouth end of the horn (which is the pipe of increasing area). To some extent, we back to the same issue of diaphragm area. Now the mouth is "seeing" the same issue of air running away. However, the mouth is very large and thus acts somewhat as if it is moving diaphragm. But it is big diaphragm.

By way of example. The K-400 mid horn has a mouth area of about 100 square inches, while the driver is pushing air into a throat (pipe) of about 0.5 square inches. The LaScala has a mouth area of about 4 square feet, while the driver is pushing air into a throat of about 0.5 square feet (leaving out the restrictor plate).

The bottom line is that we have a good pumping system at the throat end, and a good radiating system at the mouth end.

The result is that the piston does not have to move much to pump air. That cuts down on distortion and increases acoustic efficiency.

Wm McD.

[biglaz]

It is getting clearer. Thanks for the addition info.

Robert

[DavidF]

Consider a trumpet compared to a horn and compression driver combination.

A musician blows air through compressed lips to cause a vibrating sound. This high low-displacement but high- pressure sound from the mouth does not amplify well into the air but rather disperses as the well known buzzy raspberry sound effect. The trumpet mouthpiece is cup or cone shaped which acts to further increase the pressure and then channels the sound waves into the horn itself. Blowing into the mouthpiece outside of the horn will produce a higher pressure sound but still very low displacement that does not couple well into the air to produce a louder sound wave. Add the horn and the high pressure wave/low displacement sound wave is gradually transformed into a low pressure but high displacement sound at the horn mouth. That low displacement buzzy vibration at the mouthpiece is now a full bodied growl at the mouth of horn that is capable of moving quite a bit of the air as the sound wave launches from the horn.

So too is a low displacement but high pressure sound wave pushed through the compression driver and phase plug able to move a far greater amount of air as it exits the horn.

[Blvdre]

OK, now do phase plugs.

[twistedcrankcammer]

OK, now do phase plugs.

Phase Plug Technology In any conventional loudspeaker, the highest frequencies of audio emanate from the area around the center of the cone and the lower frequencies are produced by the area of the cone that is farther from the center. In fact, the distance from the center at which a sound wave will come off a loudspeaker cone is directly related to its frequency. This helps explain why larger cone loudspeakers are usually capable of producing more bass. Due to the shape of the conventional loudspeaker cone, the higher frequency sound waves tend to collide at a focal point. This causes phase distortion and a loss in clarity. As a result, accuracy and transparency suffer. This also has detrimental effects on the realism of the sound environments created by today's high fidelity digital audio and surround sound systems. The phase plug pole piece extension improves driver performance and clarity by deflecting delicate midrange audio out into the sound space and minimizing distortion producing collisions.

Roger

[biglaz]

This has become a really educational post.

Robert

[DavidF]

Unfortunately, this little bit of info is the tip of the iceberg. If it seems compression driven horns are the end-all be-all, it ain't necessarily so. Horns have their own faults and inherent problems. Limited bandwidth and diffraction issues are big ones but hardly the limit of pesky design considerations. It takes a real "man" to tackle horns in a domestic environment. So remember that about PWK.

[twistedcrankcammer]

Unfortunately, this little bit of info is the tip of the iceberg. If it seems compression driven horns are the end-all be-all, it ain't necessarily so. Horns have their own faults and inherent problems. Limited bandwidth and diffraction issues are big ones but hardly the limit of pesky design considerations. It takes a real "man" to tackle horns in a domestic environment. So remember that about PWK.

David,

I fail to see what question you are asking or answering at this point, or anything possitive you are offering to the discussion at hand. The orriginal poster asked a question, that we (including yourself) tried to answer, then another question was put forth and addressed. Your current offering serves no useful purpose. Furthermore, if you think limited bandwith of a horn is a problem, I would disagree with you and say to the contrary. Horns in speakers help limit unwanted distortional frequencies in reproduction from a driver (think Cornwall vs Klipschorn Bass here). An even more important benifit of the horn wave guide is the fact that we humans could not differentiate frequencies without it, go brush up on your anatomy and physiology of the human cochlea and how it differentiates frequencies to the human brain.

Roger

[CECAA850]

Roger, I could be wrong but I think David was trying to point out how complex the compression driver/horn set up is and give kudos to PWK for mastering it.

[JL Sargent]

Roger, I could be wrong but I think David was trying to point out how complex the compression driver/horn set up is and give kudos to PWK for mastering it.

Carl, I think your correct, but lets give kudos to Twisted for not including some kinda car analogy up to this point in the thread.[Y]

[DavidF]

Correct, Roger, I seem to have answered a question not yet asked. Guilty. If, down the thread a ways, the question is asked why horns are not more universally used in speaker systems- fully knowing the advantages of lower distortion and greater bandwidth (is that correct?) over a direct radiating driver- I will join in with a more positive contribution. Then I might try to explain that while many, including me, prefer the benefits of compression drivers and horn loading, there are design difficulties involved with horn driver applications.