Construction Workbook BR-1 2-Way Reference Monitor System Congratulations on your purchase of the BR-1 2-Way Monitor System. The BR-1 was designed by lifelong audio enthusiast and speaker builder Paul Holsopple. Paul has many years experience designing and building high end systems. Paul was commissioned by Parts Express to design a relatively low cost system that could rival the high end name brands in sound quality.
Parts Inventory Carefully unpack the kit, take inventory of all parts and make sure that nothing was damaged during shipping. Your BR-1 Reference Monitor System should include the following: Part # 300-645 295-305 275-070 999-200 027-352 027-452 004-8 027-418 266-832 027-427 015-4 015-6.
The Drivers Included in your kit are two each of the #295-305 6.5" Dayton mid-woofer and the #275-070 Dayton 1-1/8" silk dome tweeter. Both units have been a hot bed of discussion on the Parts Express Tech Talk board and are good candidates for this project. The woofer incorporates a treated paper cone, coupled to a rubber surround. The response is generally well behaved, but does exhibit a peak centered around 3.3KHz.
About Zobels This simple circuit consists of a single resistor and capacitor. It is commonly referred to as a Zobel network, named for the Bell Laboratories engineer whom invented it. An excellent starting point can be calculated by using this formula. R = 1.25 x Re C = Le / R squared Re is measured voice coil DC resistance in ohms.
1-1/8" Dome On Axis Frequency Response and Impedance Sweep The Crossover Network and Description Here is the BR-1 crossover schematic. The low pass filter is a four element filter. L2 and C2 form an electrical 2nd order filter and yields a 2nd order acoustic response. The impedance compensation circuit consists of C3 and R1 which effectively flattens the woofer’s inductive rise, yielding a smooth impedance curve. C3 is actually two capacitors, one a 47uf non-polarized electrolytic, with a .
Most loudspeakers including the BR-1 use drivers mounted on a flat baffle. One problem encountered here is the fact that the tweeter’s relative acoustic center is set ahead of the woofer’s relative acoustic center. In general, a flush mounted tweeter’s acoustic center is aligned with the front baffle. A typical 6.5” woofer’s relative acoustic center is set about 1-1/2” behind the tweeter.
Individual Driver and Summed System Response The above graph was produced with the microphone at a distance of 45", on the tweeter’s axis. I prefer to use the slightly farther then 1 meter (39.37") distance to be more in the far field, to get a better representation of how the drivers will blend. The response is within the +/- 2.0 dB window to 12KHz. In fact, the response is commendably flat from 300 Hz to 3.5KHz. It can be seen that the acoustic crossover occurs at 2.1KHz.
So the values for our proposed parallel notch filter is a 9.4uF capacitor, .26mH inductor, and a 14 ohm resistor. Unlike the impedance compensation filter discussed earlier, this filter is harder to generate from just design formulas. It is best to use some means of measurement to validate the result. Please note that adding this notch filter to the existing BR-1 crossover will change the filter roll off and will necessitate a low pass filter redesign.
The system impedance and electrical phase is quite smooth, with a nominal 8 ohm impedance. This loudspeaker will be an easy load to drive for most any amplifier. However due to the 82.5 dB sensitivity, a minimum of 75 watts per channel is recommended. The center to center driver spacing is 5.75", with the tweeter being offset 1" in a mirror image pair. The tweeter is flush mounted to the baffle, while the woofer is recessed only to the top of the basket.
BR-1 Assembly Instructions 1) Installation Tools Needed • • • • Phillips Screwdriver Hot glue/gun or RTV Sealant Soldering iron Silver or Electronic grade solder • • • • Wire Cutter / Stripper Small pliers Crimp tool Utility knife Crossover Assembly Note Warning!! The correct assembly and wiring of the crossovers is critical to the proper operation of this speaker system.
3. To help reduce the risk of components rattling on the p.c. board, (especially the inductors) use RTV sealant or hot glue to mount the components to the p.c. board. We recommend using hot glue due to its faster setup time. If you use RTV sealant, you may need to let it setup over night, before proceeding with the assembly. 4. Solder all component connections on the p.c. board using silver or electronics grade (60/40) solder. At this time, you should also solder the riveted .205 terminal connections.
7. The locations where the input and driver output wires connect are clearly marked on the p.c. board. While observing proper polarity attach all input and driver wires to their respective mounting terminals. Example: To attach the input wire, take the positive (+) input wire and connect it to the “IN+” terminal. Next, take the negative (-) input wire and connect it to the “In-” terminal. Repeat this step for the woofer, tweeter and other crossover.
3. Pull the “labeled” input wire through the terminal cup hole and while observing proper polarity connect the wire to the terminal cup. The positive (+) input wire should be connected to the “red” binding post. 4. Orient the terminal cup with the binding posts toward the bottom and install using the small #6 screws and a phillips screwdriver. 5. Repeat these steps for the other speaker cabinet. B. Install Acoustic Damping Foam We’ve included two (2) sheets of acoustic foam, one sheet for each speaker.
1. The foam must be cut to fit internally on the right/left side walls, rear, top and bottom panels. Do not apply it to the front baffle. Cut the foam to the dimensions shown in Fig. 1 FIGURE 1: Foam Cutting 2. Install the foam on the back of the cabinet first and trim around the port tube. Make sure it does not obstruct the airflow to the port tube, as this will alter the tuning of the box. 3. Next install both sides and then top and bottom.
C. Installing Drivers Put sealing caulk around the woofers prior to mounting. When applying caulk it is a good idea to first roll the caulk between your fingers to “thin out” the caulk bead. The tweeter is supplied with a gasket so it does not need sealing caulk. Putting sealing caulk on the tweeters mounting flange may not allow the faceplate to mount flush with the baffle. 1. Attach each wire to the appropriate driver terminals while observing proper polarity (positive to positive, negative to negative).
Speaker Placement Many loudspeakers are designed without regard to baffle step loss. If a woofer has a midband sensitivity of 88 dB for example, and is mounted on a large infinite baffle (like your living room wall), it will maintain the 88 db sensitivity right down to it’s rated f3. All frequencies, even the large low frequency wavelengths are supported by the large wall. But speakers are usually mounted in boxes with varying degrees of baffle width.
