Discussion in 'DIY' started by SirReal63, Jul 5, 2018.
I'm stunned by the beautiful look of that veneer! Wow!
My phone camera does not do it justice.
A couple more shots of the veneer, this was after the second coat, the flash really shows contrast between light and dark that the eye does not. My phone still does not do it justice, it almost glows.
The seams and grain continuity really turned out better than I hoped. This was my first "real" veneer project.
Your enclosures look simply stunning with that Teak veneer. Your supplier did a good selection for you, and your work applying it is spot on. I'm loving this process. Thanks for keeping us in the loop on your project.
I have a couple of questions on the passive crossovers you are employing until you go to your biamp setup. I'm confused about your description of running the tweeters and mids in parallel to yield a 4 ohm combined impedance. I'm not a whiz kid when it comes to crossovers or electronics in general, but in a traditional crossover configuration the impedance "seen" by the amplifiers is reflective of the drivers individually, not combined. For example, a three-way network with three 8 ohm drivers "in parallel" will present an 8 ohm impedance to the amplifier. Am I missing something?
Second question is in regards to your choice of low/mid crossover points - 100Hz for the mid, and 500Hz for the woofer. I'm sure you know that convention has always been common crossover points, ie, 500Hz for the mid and 500Hz for the woofer, otherwise both the mid and the woofer will be reproducing the same frequencies between 100 and 500Hz, which will result in a 3-6dB accentuation of those frequencies.
Please pardon me if I've completely misinterpreted your plans. I'm a relative amatuer at crossover design and thus relegated to regurgitating what I've read by the real experts. So my inquiry is purely elemental and generated by an understanding that is just deep enough to be dangerous.
I will never claim to have everything figured out, but I have researched this to death and have a game plan. That game plan will work until I get hit in the face, then I will adapt.
The reasoning behind separating the low from the mid and highs, each with 4 ohm loads is so that the speakers can either be run off a single 8 ohm amp or split into two 4 ohm loads for two amps is so that down the road whomever ends up with these speakers has the option to run it with a single amp or multiple amps. Two 8 ohm speakers in parallel will present 4 ohms to the amp. The 4 ohm low and 4 ohm mid/high in series will present 8 ohms to the amp, thus enabling a conventional 8 ohm amp to play the speaker without fear of damage to the amp. I have to change the binding posts so that when the bridges are in place it runs the speakers in series instead of parallel.
Three 8 ohm speakers in parallel will present 2.7 ohms to the amp, dangerous to most amps.
I chose the crossover points based on the frequency chart of each speaker (with exception to the sub, none was found, hence the need to experiment a little) to take advantage of the optimum frequencies of each driver. For the 6" mid it has a relatively flat response from 100 hz to 3500 hz, there is a large peak at about 3500 hz and I will roll it off at 3500 hz to avoid that peak, this should work well because the tweeter begins at 3500hz. I fully expect to have to play with the crossover points but this should be a good starting point. I expect to have to lower the crossover point for the sub, I suspect it will be too muddy above 100 hz, but I won't know that until I burn in the sub and see how it actually performs, it has a frequency response of 29-800 hz, but without seeing an actual frequency response, I do not know how it performs. It is entirely possible I will need to raise the low point of the mid driver, if the sub performs better than I expect. The beautiful thing is the crossovers are cheap which lends beautifully to experimentation. If I have it correct right off the bat I will be slightly disappointed, the fun here is in the learning and tinkering.
For me, the crossovers will be temporary, I plan on an active crossover, but I want to leave the passive ones in the box for the future.
Another source that helped greatly with the box design...
Trying to figure out the cubic feet of the box was a challenge to my old brain, the calculators here made it a snap and allowed me to design the box based on the needs of the woofer as well as tell me the optimum size of the box for the mid.
Oh, and I am not even an amateur at crossover design, this is my first attempt, it will work or it will fail.
Thanks for replying. I understand your thinking on the crossover points you've chosen. It will be interesting to see how they work out (and, as you say, fun and educational - let's not overlook the point of a personal build.).
Anyway, continuing to watch and enjoy. Can't wait to see your further progress.
If I had no concern about anyone else, I would just do an active crossover from the start. These speakers will outlive me, I have already died once and I know I will again. I need to do the right thing and make them idiot proof for the future, our idiots will inherit them.
It keeps me busy and out of the heat, I cannot take the heat any longer. I would be finished with them if I could stand to be in the shop for more than an hour at a time.
The speakers are almost finished, the Left is assembled, crossed over and breaking in. I will definitely have to change the sub crossover down to 100 hz, it is muddy and did not drop enough in the upper frequencies to blend in with the mid. It is ordered and will be here today. I am glad I chose to L-Pad the mid and High, their higher sensitivity overpowers the bass, so they are padded down.
The sound is actually better than I hoped, the mids and highs are very clear and detailed, the bass may actually be hitting 30hz which I had doubts about while building. The bass hits with enough authority to be felt 30' away. All in all, I am very happy with the sound and it should improve with the crossover change for the sub. I had it playing off my old JVC RX-709V for a couple of days to break in the sub, yesterday I moved it upstairs to it's final place and hooked it up to the Sonance amps, it should be more than I ever need for sound.
Great looking build. And, if I may brag a bit, I did say they would sound great in my first post.
I was wondering when we would hear from you again. The speakers look great. Thanks for the update. Keep us informed as you dial in the crossover frequencies.
Sure would be nice to have an active crossover to use to immediately dial in the correct xover frequencies, then all you'd need to do is build the appropriate passive to match those on the active.
Yes it would, but there are budget constraints, the house build comes first and doors are next on the list. SWMBO wants nice doors, amd there are a lot of them.
I want a really nice active crossover, and they are not cheap. I am leaning away from the miniDSP.
You know, it just dawned on me that you could rent an active xover and any other gear you need from a music store or prosound rental. You'd need the gear for only a day or two, so the cost would be piddling. The active xover would allow you to dial in the exact xover points you want, then you'd know which passive to build.
Hmm. I might do just that to fine tune my Altecs.
After a month of listening to and tweaking these speakers I can rate them as excellent. I have had several other people listen and all have commented on how full and crisp the sound is. Limiting the woofer to 100hz and below cleaned it up nicely. I made a pair of isolation stands from some 1-1/2" full round and they helped immensely. I wanted to use spikes but these speakers weigh over 100 lbs each. They play from 25 hz to 20k hz and make my little Genesis speakers seem like Fisher Price toys. The only real issue I have is around 3500 hz which is a bit shrill. This is the crossover point for the mid to tweeter. I will use the active crossover to fine tune where that frequency hand off should be before ordering a passive crossover for it.
I have decided to use the Dayton Audio DSP-408 for an active crossover. It is cheap enough and has more features than I will need.
The finished product...
The rack system powering them...
Top to bottom
JVC QL-F61 TT, Nagaoka MP-110 cartridge
Outlaw 950 Preamp
Tube(ish) based preamp for BT streaming, though I have the DVD player running through this, it sounds better than through the Outlaw for CD play.
Little Bear phono preamp. I took a gamble on these ChiFi items, so far they have done the job.
Sonance 260MK3 amp, not hooked up but will be used for the tweeters when DSP arrives to provide 60 watts into 8 ohms
Sonance 275x3 SE providing 125 watts into 4 ohms split for the mids and highs. With DSP it will provide 75 watts into 8 ohms for the mids only.
Sonance 2120T providing 160 watts into 4 ohms for the woofers.
I am impressed with the Sonamps, for not being a "HiFi" item they sound clean and powerful and barely get warm. I used the 260x3 with the Genesis and the sound was vastly improved over the 100wpc JVC I had been using. I expected these amps to be temporary but I am keeping them.
gdmoore28 raised a good point about determining speaker impedance.
Speaker impedance is not a single, fixed value. Speaker impedance will vary over the speaker's frequency range. The impedance of three drivers, each operating over a different frequency band, are not combined as described in your link when determining the total speaker impedance. Calculating impedance for a speaker of multiple drivers is much more complicated and depends upon the specific frequency of interest and how the crossover is wired.
The link you provided is for speakers, not for individual drivers that are connected to a crossover where only one driver operates at a time depending upon the frequency. That is, only the woofer is being driven at bass frequencies. At higher frequencies, the woofer can be considered to have a very high impedance. But that is when the mid-range driver kicks in. For the frequency range of the mid, the amp only sees the impedance for the mid-range driver and its portion of the crossover circuit. And a simple first order filter for a tweeter has a capacitor in series with the tweeter. Below the crossover frequency of the impedance of the tweeter circuit increases to infinity at dc (a capacitor blocks dc). As the frequency increases to the crossover frequency for the tweeter, the impedance seen by the amp for the tweeter will decrease to somewhere around the nominal impedance for the tweeter driver.
Also, depending upon how you wired in the L-pads, that will also affect the impedance. So, too, will any attenuating resistors in the crossover circuit.
See https://www.avforums.com/threads/ohms-problem-diy-speakers.1578046/#post-16226293 for another explanation of how an amp sees only one driver at a time for a 3-way speaker with passive crossover.
Thank You! The entire purpose with this project is to learn. Responses are in body of quote.
Do you have any idea how to do what I am trying to do, make the speaker safe for most amplifiers that expect to see an 8 ohm nominal load, or will it be a 4 ohm nominal load no matter what because the woofer is a 4 ohm? It won't matter with the active crossover but the goal was to have it so it could be used safely by any normal amplifier.
I pulled out my multi-meter and the woofer with the 100 hz LPF is giving 4.3 ohms on both the left and right, the mid/tweeter gives no ohm reading, no short but no actual measurement on any of the Ohms settings. The meter is not really meant for this, it is a Klein MM100 that I got when I was doing the electrical on the house and it has issues.
Learning is good, but only so much knowledge can be conveyed on a forum by asking questions. The best way to gain knowledge about impedance and crossovers is to study electrical theory. This is not a subject where someone can gain a full understanding in 5 minutes or less or by reading a paragraph or two. If you look at speaker wiring diagrams, you will see that crossovers range from simple, first order circuits to very complex, multiple order circuits with things like Zobel networks. A first step to building a speaker from scratch is to have a full understanding of such circuits. Otherwise you are depending upon luck to get it right.
If you want a speaker with 8 ohm impedance, you should use 8 ohm drivers, unless you are using pairs of drivers, then you can use 4 ohm drivers in series. That is, find an 8 ohm woofer or use a pair of GRS 12SW-4 drivers in series.
You can add impedance to a 4 ohm driver so that the amp sees 8 ohms, but that means you will be dissipating one-half of your power in the added impedance. For example, use an inductor with 4 ohm DCR or use a 4 ohm series resistor. This is not a good option for a woofer because that is a lot of wasted power. It is best to select drivers that meet your design requirements. Many mid and tweeter circuits use attenuation resisters in the crossover to match sensitivity. The power dissipation is designed in the crossover and is typically acceptable because less power is need to drive most HF drivers compared to woofers.
An ohm meter measures dc resistance. It will tell you nothing about the impedance of a driver at audio frequencies. If you are measuring the tweeter resistance through the crossover, you will get an infinity reading because there is a series cap in the crossover.
Some vendors publish impedance vs. frequency graphs for their drivers. If you want to measure impedance, you will need an audio signal generator and a scope to measure current (or voltage drop) and phase.
I knew I could add impedance and also why I did not want to do that. It makes sense that the meter cannot read the mid/tweeter, thanks for that.
The mid and tweeter are both 8 ohm, wired in parallel and when binding post is bridged the mid/tweeter combination is in series with the 4 ohm woofer. Do you think this will present too low of a resistance that would be damaging to amps expecting an 8 ohm nominal load from the speaker?
It is not my desire to become a speaker manufacturer, the constraints on my time are too great but I would like for these to safe to play after I am gone.
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