Prototyping a 4- way open- baffle speaker with the mini. DSP 2. In the first tutorial, I introduced the mini. Best Full Range Driver For Open Baffle LoudspeakerThe 3" FE87 full range may be small, but it delivers everything you have come to expect from Fountek. The extremely light aluminum cone and voice coil are driven by a. Type: Open baffle loudspeakers SPL: 94-96db measured in a typical room Frequency Response: 32Hz – 20,000Hz (all Trio15 models) Impedance: 3.5 to 8 ohms. Technical documentation. 2006-02-19 © Tolvan Data 2004-2006. The Edge program is a baffle diffraction simulator. Typically it is intended to use for. I measured the 16 gauge Megacable from Radio Shack (278-1270) that I use. A 10 foot length has 0.07 ohm resistance, 714 pF of capacitance and 1.9 uH of inductance. Fullrange speakers. DIY speakers. DIY Speaker kits. Open Baffle Speakers. Fullrange drivers, Audio Nirvana, Lowther, Fostex. Vacuum Tube Amplifiers For Sale. Full range speakers single driver extended range bamboo. Glow speakers full range speakers single driver orb shaped loudspeakers recycled scrap wood enclosures hemp. This is the second in a series of tutorials on the miniDSP. In the first tutorial, I introduced the miniDSP 2×4 standalone unit and showed how it could be used for. DSP 2. For this tutorial, I decided to use the mini. DSP 2. The speaker is an open- baffle loudspeaker, a configuration that has been gaining popularity in DIY circles in recent years. After (re) introducing the mini. DSP 2. The emphasis in the tutorial is intended to be on the use of the mini. DSP, and not so much on the speaker itself. Best Full Range Driver For Open Baffle DiyThe Slot Loaded Open Baffle Project by Nelson Pass Intro: ESS and the Heil Years In 1972 I had the good fortune to begin working for ESS, arriving a few weeks before. So I hope that you will find the tutorial useful even if you are using the mini. DSP for a more conventional (boxed) 3- way or 4- way loudspeaker. This article is Part 1 of the full tutorial. In this part, I will get as far as getting the crossover running and some basic measurements and equalization. In Part 2, I’ll present more sophisticated measurement and processing techniques for integrating the drivers. In Part 3, I’ll complete the four- way system with an open- baffle subwoofer. The mini. DSPHere is a quick recap of the mini. DSP 2. Physically, it’s a small metal case, about 1. RCA input connectors and four RCA output connectors. In addition, there is a USB Mini- B connector to use for configuring the mini. DSP from your computer, and a DC plug with screw terminals if you wish to use an independent power supply. The signal processing functionality that the unit performs is determined by the specific software “plugin” that you load into it. There are quite a number of these available from the mini. DSP online store. For this tutorial, we will be using the 4- way PEQ plugin. This plugin turns the mini. DSP into a mono 4- way crossover with a raft of parametric equalizers that we will use to correct driver, baffle, and room responses. Thus, for this project, we will need two mini. DSP 2. The mini. DSP circuit board provides 2- in 4- out processing, and additional boards can be added for S/PDIF I/O, USB input, and even a Class D amplifier module with digital (I2. S) connection to the mini. DSP. This tutorial is, however, focusing on the crossover and equalization capabilities of the mini. DSP, and not the hardware – perhaps future tutorials will demonstrate the integration of the various boards in the mini. DSP system. A little open- baffle speaker theory. In its simplest form, an open- baffle speaker can be constructed by cutting a hole in a sheet of wood (or other material) and mounting a driver in it. Unlike conventional speakers, there is no box enclosing the driver. This has a number of consequences, which largely revolve around the fact that the acoustic energy from the back of the driver’s cone is radiated into the room, as well as the energy from the front of the driver: Figure 1. Acoustic radiation from an open baffle speaker. The acoustic radiation from the rear of the cone will interfere (cancel or reinforce, depending on frequency and location in space) with the radiation from the front of the cone. The most notable effect of this interference is that there is a null to the sides of the baffle – that is, the front radiation and the rear radiation cancel each other out along an imaginary line drawn out to either side of the baffle. The result is a “figure of eight” radiation pattern, as shown in Figure 2a. The grey line on this diagram represents the locations around the speaker where a constant acoustic power is produced. The diagram illustrates that the highest output power is to the front and rear of the speaker, and the lowest to the sides. Theoretically speaking, this shape is caused by two oscillating point sources of opposite polarity – a dipole. So, open- baffle speakers are often also referred to as dipole speakers. Now, this is an idealised curve, which really applies only at low frequencies. At higher frequencies, the interference between the front and rear waves produces more complex “lobing” patterns, such as in Figure 2b. Figure 2. Radiation patterns of an open- baffle speaker. The interference between the front and rear waves has another effect: below a certain point, as frequencies get lower, the total amount of acoustic energy produced gets lower. An open- baffle speaker thus typically needs more volume displacement (cone area . See this page at Linkwitz Lab for the calculations and explanation of the theory. For the less gifted, we can see the same effects by running a simulation program such as the Edge. Here, for example, is the simulated on- axis response of a very small (1mm diameter) driver in the centre of a 4. Figure 3. Frequency response of an ideal point source driver in a circular baffle(Click on this or any of the graphs in this article for a larger version.)At around 7. Hz, we see what is known as the “dipole peak,” which occurs at the frequency at which the rear wave acts to reinforce the front wave. Below that frequency, the front and rear waves progressively cancel each other out, with the slope of the curve tending towards a drop of 6 d. B/octave. Above that frequency, the front and rear waves alternately cancel and reinforce, leading to the “comb” pattern that you see in the plot. Now, in practice, we don’t put a teensy driver in the centre of a round baffle. As it happens, a realistically- sized driver acts to spread the locations of the cancellation notches, evening out the response to some degree. A non- circular baffle adds to the effect. Here is the simulated on- axis response of a driver with a cone of 1. Figure 4. Frequency response of 1. As you can see, the frequency response is still not exactly flat, and there is a fairly significant notch in the frequency response at around 1. Hz. But it is better than the point- source driver in the circular baffle. To summarise: the front and rear waves of an open baffle speaker interfere in a complex way to create patterns of reinforcement and cancellation in frequency and space. One might then be tempted to ask: why bother? Well, because, in practice, it can be made to work remarkably well. Here are some possible advantages of the open- baffle approach: Higher direct- to- reverberant energy. As Siegfried Linkwitz explains, the total radiated power from a dipole is 4. B less than from a monopole (equal radiation in all directions), given the same on- axis level. Less excitation of room modes. An open- baffle speaker tends to excite room modes less in the direction to the sides of the speaker, where the radiation null occurs. No “box sound.” This is controversial, but since there is no box, pressurization caused in that box by the loudspeaker driver can’t excite resonances in the box material. A conventional box speaker tends to radiate in all directions at low frequencies, and only to the front at high frequencies. An open- baffle speaker, which radiates to the rear over a greater range of frequencies, can result in a more “spacious” sound. Loudspeaker design is a complex set of trade- offs and the above list is intended to indicate the kinds of things that could be taken into consideration – they are not absolutes. The prototype speaker. The fact that a box is not required is one of the fun aspects of making a DIY open- baffle speaker – it’s relatively quick to knock up a prototype to experiment with. This is my second prototype of this particular speaker – I made some mistakes and learned some things with the first prototype, and I will no doubt make more mistakes and learn a few more things with the second prototype! The overall configuration is a three- way loudspeaker mounted on an open baffle, with the fourth “way” being a separate subwoofer on each channel. One channel is illustrated in Figure 5 (click to enlarge): Figure 5. The anticipated crossover points are around 4. Hz and 4 k. Hz, with the subs reinforcing the woofers underneath around 5. Hz. Each channel uses a single mini. DSP 2. A total of six channels of amplification are needed for the main open- baffle panel, and an additional two channels for the subwoofers. I am using the “Rev A” version of the mini. DSP 2. This has a maximum input voltage of 0. Vrms, and a maximum output voltage on each channel of 0. Vrms. At the input, we must not exceed that limit, or we will get clipping of the input signal. At the outputs, the maximum output level together with the amplifier sensitivity and the driver sensitivity determines the maximum acoustic signal level that can be obtained from each driver. In general, the topic of matching signal levels with the gain/sensitivity parameters of various units is referred to as gain structure. We don’t want to have signal levels too high anywhere in the chain, or we will get clipping distortion. Nor do we want to have signals levels too low anywhere in the chain, or we may introduce noise. In a typical domestic system, the configuration shown above with the “Rev A” mini. DSP 2. There may be cases where the “Rev B” version, with a 2. Vrms maximum input level, should be used instead. And, amplifiers with an unusually low or high input sensitivity may not be best suited for this application. Choosing drivers. Using a mini. DSP (or other digital crossover/EQ) is quite liberating for a DIYer, as you have less to worry about in terms of selecting drivers: With steep crossover slopes available, you can set a crossover point for a given driver lower than you would if using a passive crossover. With powerful and flexible EQ on tap, you can use drivers that you might otherwise avoid because of the need to implement a notch filter or other response shaping. With an active system, there is less concern about matching driver sensitivities. This opens up opportunities to use drivers that you might not otherwise. I am using the Bohlender Graebener Neo. PDR, in “dipole mode” (that is, with the back cup removed). This tweeter is relatively inexpensive, and flexible enough to be used in a lot of different ways. Although I would have liked to use the more sensitive non- PDR version of this tweeter, I already had the PDR version, so I’m using those for now. Midrange. This is a hard one, as there are so many possible choices! For this prototype, I’ve gone with the B& C 6.
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