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Compression Drivers -- Diaphragm Materials, Magnet Materials, and Throat Dimensions

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  • Compression Drivers -- Diaphragm Materials, Magnet Materials, and Throat Dimensions

    For starters I am only putting this in the "tech talk forum" because people use these style of drivers in home audio applications and I also figured it wouldn't get much attention in the pro sound forum.

    I recently built a set of line array style powered cabinets in two (2) different sizes/configurations. The top picture uses an Eminence Kappalite 3012HO 12" driver while the bottom uses an Eminence Kappalite 3015 15" driver. The high frequency of the 12's cabinet uses two (2) 16ohm Eminence NSD20015:16 compression drivers in parallel with an L-Pad controller. The system is powered by a Dayton full range plate amplifier with a built in crossover of 1.5KHz. I used that amplifier because the 1" thoat drivers in the P-Audio horns had a minimum crossover frequency of 1.5KHz. To my ears the 12" models sound good. The mid range is a little hollow, but I haven't had the time to mess with my DSP unit and really tweak things.

    Here is where things get interesting. I hooked up the 15" model with the same horns, drivers, and wave guides. It sounded like mud. Tons of beaming and the vocals sounded like they were coming through a pillow. P audio makes an identical horn with a 1.4" throat that is safe down to 1KHz and dayton also has an identical amp, but with a crossover frequency of 1KHz. My question is, will I fix the issue I am having by going to a larger diaphragm and throat diameter compression driver (FaitalPro HF140) or is the design just inherintly bad because I chose a 15"? It was an experiment so don't hate. I had eight (8) of those Kappalite 3015's lying around and decided to build a 'bigger' model for grins. The outcome was not what I expected though.

    To add to the complexity, I see where the average person can purchase a compression driver from a couple dollars all the way up to 800 dollars or more. They have different throat and voice coil diameters as well as diaphragm materials (titanium, aluminum, Keytone Polymer, etc). Different magnets are also used on some of them. I'll come out and say it that I am an Eminence guy as they are American made and I have had decent success with them so far. Can anyone shed any light on the price differences, materials, magnets, etc?

    My other question lies in 2 way formats where a single woofer is used with a compression driver and wave guide. If I built a cabinet with a 3012HO and crossed it at 800Hz with an Eminence N320T-8, am I going to get good results or is a 3 way set up always in order? I have read many articles on compression drivers and most of them contradict the next one. Although Eminence says that the recommended crossover frequency for that compression driver is 800Hz, would the end user have issues in doing so?
    "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

  • #2
    Ignoring for the moment some difference in frequency response and sensitivity as being the cause, did the difference in acoustic centers between CD & woofer differ between the two designs? What you describe sounds like going from one design with relatively in-phase summation, to one where they were cancelling.
    ~Brandon

    Soma Sonus
    DriverVault

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    • #3
      Originally posted by augerpro View Post
      Ignoring for the moment some difference in frequency response and sensitivity as being the cause, did the difference in acoustic centers between CD & woofer differ between the two designs? What you describe sounds like going from one design with relatively in-phase summation, to one where they were cancelling.
      excellent question. They are definitely different as can be seen in the picture. I'd have to pull open CAD to get you exact dims.

      12-3/16" from 15" center to CD center
      11-13/16" from 12" center to CD center

      I didn't even think of that.
      "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

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      • #4
        Also consider the front to back axis. A 15" acoustic center is probably 2-3" further back then a 12". Try flipping the polarity on the tweeter and see how it sounds.
        ~Brandon

        Soma Sonus
        DriverVault

        Comment


        • #5
          For what you are investing in drivers you should consider measurement gear.
          John H

          Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

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          • #6
            Originally posted by STIchris722 View Post
            ...To add to the complexity, I see where the average person can purchase a compression driver from a couple dollars all the way up to 800 dollars or more. They have different throat and voice coil diameters as well as diaphragm materials (titanium, aluminum, Keytone Polymer, etc). Different magnets are also used on some of them. I'll come out and say it that I am an Eminence guy as they are American made and I have had decent success with them so far. Can anyone shed any light on the price differences, materials, magnets, etc?...
            Since Compression Drivers are used near exclusively in Live Sound, I have heard a huge difference in the quality and performance from the low cost ( OEM etc ) and the upper end, particularly in large sound systems.
            The upper end devices offer outstanding performance and durability, the constant goal is to find quality at lower prices.
            "Not a Speaker Designer - Not even on the Internet"
            “Pride is your greatest enemy, humility is your greatest friend.”
            "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

            Comment


            • #7
              Originally posted by jhollander View Post
              For what you are investing in drivers you should consider measurement gear.
              I have an OmniMic and DATs analyzer. Is that what you are referring to?
              "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

              Comment


              • #8
                Yes. So, I'm surprised you have not measured to get a definitive answer to the differences.
                John H

                Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower

                Comment


                • #9
                  Originally posted by jhollander View Post
                  Yes. So, I'm surprised you have not measured to get a definitive answer to the differences.
                  I have measured a N320T-8, but they all should be measured in their appropriate wave guide. measuring free air doesn't tell you much about a compression driver. I don't have an abundance of money to purchase drivers and horns.

                  I do not have the 1.4" drivers and horns yet, so that's why I asked the question. What is the microphone going to tell me? I asked a lot of questions and a microphone isn't going to answer them John. I understand where you are coming from, but I didn't come to a forum for a figure it out yourself response. I was hoping someone had some experience with this stuff and could shed some light on my confusion.

                  to be honest I don't really know how to use that OmniMic anyways.
                  "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

                  Comment


                  • #10
                    IMO it's not possible to build a pro audio speaker without custom DSP processing, on very rare occasions you might get lucky and get something that sounds half decent but given that the cabs are often more complex than most home audio designs and the drivers less well behaved processing just isn't optional.

                    Now WRT your speakers, you said the 12" version sounds decent but the 15" is muddy, no surprise there IMO as 15's often produce more low mid and because of cone breakup they really should not be used beyond about 800-1khz. The horns and drivers are the same as the 12" version so they aren't at fault for this part of the sound but that's not to say they shouldn't get some EQ. Larger comps and a lower crossover frequency would be a good move for this box for the same reason it is for a regular 15" PA box but I don't think you should go there until you have had a stab at taming them as they are.

                    What will a test mic tell you? It will show you what the systems response looks like and with a little time and experimentation you can DIY some custom processing that will make a big difference in the way these boxes sound. Do a driver time alignment and tame the worst of the response anomalies and you'll be well on your way to a useful product.
                    Paul O

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                    • #11
                      when you get those things sorted out you can consider the match between the exit angle of the CD with the entry angle of the horn.
                      Mongo only pawn in game of life
                      ____
                      Ed

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                      • #12
                        Originally posted by Paul O View Post
                        IMO it's not possible to build a pro audio speaker without custom DSP processing, on very rare occasions you might get lucky and get something that sounds half decent but given that the cabs are often more complex than most home audio designs and the drivers less well behaved processing just isn't optional.

                        Now WRT your speakers, you said the 12" version sounds decent but the 15" is muddy, no surprise there IMO as 15's often produce more low mid and because of cone breakup they really should not be used beyond about 800-1khz. The horns and drivers are the same as the 12" version so they aren't at fault for this part of the sound but that's not to say they shouldn't get some EQ. Larger comps and a lower crossover frequency would be a good move for this box for the same reason it is for a regular 15" PA box but I don't think you should go there until you have had a stab at taming them as they are.

                        What will a test mic tell you? It will show you what the systems response looks like and with a little time and experimentation you can DIY some custom processing that will make a big difference in the way these boxes sound. Do a driver time alignment and tame the worst of the response anomalies and you'll be well on your way to a useful product.
                        Paul -- Thank you for the response. This is what I'm looking for. My only problem with this particular setup is that these speakers were a stab at a powered PA setup. I have no control except for and L-Pad on the compression drivers to balance the the woofer and tweets. Normally all of my projects are bi-amplified or tri-amplified and ran through an Ashly Protea DSP. From there I have endless control really.

                        For now I was looking for some insight on these 15" boat anchors that I already have built, but am waiting on the finishing parts. My question was whether they were worth finishing and if so, were the larger compression drivers and lower crossover frequency the ticket.

                        I was also looking for some help on all the different compression driver choices out there.

                        "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

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                        • #13
                          Originally posted by edlafontaine View Post
                          when you get those things sorted out you can consider the match between the exit angle of the CD with the entry angle of the horn.
                          Could you elaborate on this? I thought the exit angle of the CD was fixed (i.e. straight).
                          "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

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                          • #14
                            Could someone elaborate on the throat diameters? Is it always better to use a 1" and go 3-way on the speaker, or 1.4"/2" and crossover lower and go 2-way on the speaker? I am trying to understand when to use which size CD....
                            "I don't know everything and do not claim to. I continue to learn and that is what makes me human."

                            Comment


                            • #15
                              Originally posted by STIchris722 View Post
                              Could someone elaborate on the throat diameters? Is it always better to use a 1" and go 3-way on the speaker, or 1.4"/2" and crossover lower and go 2-way on the speaker? I am trying to understand when to use which size CD....
                              Like the Ka relationship with cone speakers, the 2" driver is better suited for a lower passband, at the expense of the highest frequency.
                              Note that performance of these drivers and appropriate horn lenses reflect that, ie larger driver, bigger lens and lower crossover.
                              "Not a Speaker Designer - Not even on the Internet"
                              “Pride is your greatest enemy, humility is your greatest friend.”
                              "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

                              Comment

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