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RTally

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  1. Your meter is measuring dc resistance. The dc resistance is not the same as impedance. The dc resistance gives a general indication of whether a driver is 4 or 8 ohms nominal impedance. Two 8 ohm drivers in parallel is equivalent to 4 ohms impedance. Speakers are rated by impedance, which is relative to the frequency applied to the driver. You can measure impedance, but you need something different than an ohmmeter. Impedance for drivers are best shown on a graph with the x-axis being frequency and the y-axis being impedance, generally ohms. Such impedance charts can also show the phase shift of the driver. It is not unusual for an 8 ohm nominal impedance driver to have an actual impedance that varies between 5 and 20 ohms over the frequency range. Nominal impedance is not well defined. In some cases, nominal impedance is the average impedance over the operating frequency range of the driver. Most times, it is an arbitrary value that reflects if the driver impedance is more generally 4 ohms, 8 ohms, or even 16 ohms.
  2. I have several EPI speakers, including a pair of M100. I also have several KLH speakers, including Model 6, Model 17, and Model 20 (4 ohm version of the 17). All of them (except the 17) have been fully restored (surrounds taken care of and recapped with new 5-way binding posts as needed). The KLH Model 6 and 20 are in constant rotation in my main office system. I listen abut 8 hours a day. The EPI M100 is in my shop system, but I rarely listen to them. Instead, I listen to my Epicure 20+. That system also has EPI M70 that I prefer over the M100. The M70 is an amazing speaker, but the 20+ just does everything better. I prefer the KLH Model 20 over the M100. If I had to get rid of one speaker, the EPI M100 would be a goner. You make it sound like owning these speakers is an investment. Neither speaker is particularly valuable, in spite of being very popular. In my market, neither of them would bring much over $100 to 150 unless they were in pristine condition. But they are an easy sell considering their popularity. I suggest keeping the speakers that sound best to you. From your description, it seems like the EPI are keepers.
  3. The NP in 2500 uF-60 V NP on the capacitor you took out of the crossover means it is a non-polarized cap. That is, the cap does not have a negative nor a positive lead as does a polarized cap. That crossover cap should be replaced with another non-polarized cap of the same capacitance value.
  4. A polarized capacitor is intended to be used in a direct current (dc) circuit, like a power supply. Most likely, those caps you bought are dc power supply filter caps. They are unsuitable for use in an ac circuit like a crossover. Crossover caps need to be non-polarized. I would not trust a polarized cap in a crossover circuit.
  5. Masonite is not very strong. I've got some broken grills that failed the same way. I am thinking some 1/4" plywood instead of the masonite. The plywood would be a lot stronger.
  6. Roy's goo is not expensive. Most of the cost is for packaging and shipping. And as JKent points out, it is a pittance considering the other costs and labor involved in restoring great vintage speakers. Also, without documented test results over time, I would not trust anything other than Roy's goo. For your goop to be accepted by those of us that know about Roy's goo, you have a lot of hurdles to overcome.
  7. For $250 a pair, they should be in pristine condition, freshly refoamed and recapped, and the veneered, beveled front, not the utility cabinet. I paid $50 for my OLA that needed to be restored. I've seen others for sale between $100 to $200, depending upon condition. Other places to check are Craig's List and Facebook Marketplace. As for what to look for, if you audition, do all the drivers work, or, if no audition, does the woofer move freely and the drivers appear undamaged. Are the speakers recapped and have they been properly refoamed? For a lower, more reasonable price, I would prefer to recap and refoam myself because some cannot do a good job of it. If they have been recapped, I ask questions and ask if they have the original caps (I save the old ones when I recap). The idea is to determine if they knew what they were doing and did it correctly. An audition may provide evidence of a successful recap or a need to recap. If they have been refoamed, check that the foam was properly installed: for the original masonite woofer the outer edge of the foam is under the masonite (on the bottom side) and the inner edge is on top of the cone. For the replacement metal frame, outer edge is on the metal frame and inner edge under the cone. I like my OLA, but I have many others that are their equal or outperform them, such Advent Legacy II, KLH 6, Genesis II, etc. My OLA is stacked with my Legacy II in my garage. They do fine filling the garage, the driveway, and the street. Fortunately, I don't have close neighbors.
  8. Location information would be helpful. Also, please list your asking price when you decide to sell.
  9. RTally

    OLAs again

    I use a similar technique except I glue one side and then clamp it while I work on the opposite side. I clamp the opposite side when I get it glued. I have some aluminum bars (about 1/8" x 1/2" x 20") that I place against the glued section. I use paper spring clips as clamps. It is compact and works well for me. I can usually get the cloth tight enough using this method without resorting to spritzing. The Aileene's glue has enough working time to let me stretch the fabric to align the fibers with the edge.
  10. Schematic from AR is doing some fancy crossover work with the upper midrange. The 40 uF cap, 6 ohm resistor, and the 1.37 mh inductor are in parallel with the VC. A capacitor and resistor alone would form a Zobel network, which is used to smooth the impedance curve for that driver. The resistor in the Zobel network defines the upper limit for the impedance over the frequency range in which the capacitor presents minimal impedance. See https://speakermakersjourney.blogspot.com/2016/12/crossover-basics-zobel_8.html Generally, a driver will be attenuated by a Zobel network depending upon frequency. At the lower frequencies where the impedance of the cap is high, there will be little attenuation. As the frequency increases to where the capacitor's impedance becomes low, the resistor will decrease the power delivered to the driver based on the relative impedance, considering that the driver's impedance varies based on frequency. With the traditional Zobel network, the frequency above the point where the capacitor has a very low impedance defines the lower end of the frequency range where the impedance correction is applied. If a Zobel network has an inductor instead of a capacitor, the frequency below the point where the inductor has a very low impedance defines the upper end of the frequency range where the impedance correction is applied. But the AR crossover has an inductor in series with the cap and resistor. Not being familiar with the specific circuit in the AR, I would guess that the cap, resistor, inductor are used to shape the impedance curve in a specific manner over both low and high frequency ranges. I would be interested to see the curves XSim generates for SPL and impedance (assuming you have the response measurements for the drivers).
  11. I had a pair of Advents that had dark colored open-celled foam inside. That foam is speaker fill and does not degrade over time. It is very similar to the foam often found in seat cushions. It is safe. Put the foam back in the speakers in the same relative position that you found it.
  12. RTally

    Baby II crossover

    Generally, I find the best source of crossover information is what is installed in the speaker. Manufacturers often make changes during production. And not all the changes are documented. Sometimes the part changes are due to component availability. Sometimes it is a design change. I suggest waiting until you have the speakers in-hand and then inspecting them to see what is installed.
  13. RTally

    CB-10 crossovers

    The tweeter is wired out of phase to the woofer. Why? The designer determined that the speaker sounded better at the crossover point by shifting the tweeter phase. It may be that the the phase angle between the two drivers was sufficient at the crossover point that wiring the tweeter out of phase made for a flatter response at the crossover. The 7.5 ohm resistor forms a portion of a voltage divider circuit with the other resistors. With the switch in the illustrated "Decrease" position, the voltage divider is a 3 ohm equivalent resistance and a 7.5 ohm resistance. Moving the switch to Flat or Increase reduces the 3 ohm equivalent resistance and increases the resistance of the lower portion of the voltage divider, resulting in a higher voltage applied to the tweeter and less attenuation.
  14. Please do not ruin any speakers by trying that unless you plan on testing some sacrificial speakers over time. it is hairbrained ideas like this that caused people to think latex, Permatex, white glue, and other crap was a good idea for surrounds. The proper butyl compound is readily available and has been proven to not damage speakers.
  15. With current camera technology, large-format scanners are not necessarily needed for scanning drawings. I am finding that using a camera to capture documents is more convenient and typically as good a quality as using a scanner. Line drawings, in particular, do not require high resolution scanning. A good option to scan large drawings is to mount them on a wall and position the camera on a tripod with the lens centered on the drawing. If a smartphone camera is used, depth of field can be increased by using very bright lighting. It is important to ensure that the drawing is flat. I am used to large-format drawings (D to F sized) being stored flat, not folded.
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