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Step 10: Notes and Disclaimers

Picture of Notes and Disclaimers
Notes:

This system is very heavy and will probably require two people to move it. I will probably mount handles on the front to make it easier to handle and create some kind of removable cover to protect the drivers while in transit or storage.

The room does not actually act as an enclosure for the woofers as much as it just keeps the front wave separated from the back wave, which is known as an infinite baffle arrangement. If there is some way for the rear wave to reach the front wave (e.g. mounting in the doorway of a room with multiple entrances), this system will not be very effective. The two waves will be 180 degrees out of phase and at least partially cancel each other.

This is effectively a 4 ohm system. Make sure the amplifier used is compatible with this impedance.


Disclaimers:

I have not yet fully tested the capabilities (or potential dangers) of this system. The heating and cold air return ducts in most rooms in a house should be enough to relieve the pressure induced by large woofer excursions. However, if there are no ducts in a room for some reason and there are windows, be aware of the effect of the pressure on the window(s).

Very low frequencies travel well and are not easily absorbed, so if you are using this system at full or nearly full capacity and have immediate neighbors, they will hear it and probably call the police. Use good judgement .
 
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amclaussen4 years ago
Just a couple of reflections (thoughs)... If Efficiency is a primordial objective, then the use of a Passive Crossover network is not the best selection. The simple first-order (6 dB/octave) crossover used, theoretically produces a 3 dB loss. They call it "Insertion Loss".-<br/><br/>For many good reasons, the absolutely best way to go is to go with an ACTIVE crossover and arrive to a BIAMPED system. In such system the woofers are connected directly to the bass amplifier, which avoids the loss caused by the unavoidable resistance of the coil. An additional benefit is that the amp is now able to better control the heavy woofer cone (specially when the magnet size is somewhat small, like the ones in inexpensive drivers like those selected for this project).<br/>As the efficiency using an active crossover rises, the headroom becomes more ample, and the need to use a sufficiently large power amplifier is greatly reduced (a 3dB increase in efficiency means that instead of a (say)100 watt amp, we now need a 50 watt amp. Since today small car audio stereo amps are good sounding enough and relatively inexpensive, by using a, say 50 W amplifier for the low frecuency channel plus a 20 W amp for the mid+high is more than enough (I AM refering to REAL, so called RMS watts). The differences of efficiency and sound level between the low and midrange drivers are easily corrected with the input level controls at each amp.<br/><br/>2.- The Piezo tweeters can be connected directly to the mid+high amplifier WITHOUT any crossover components, since the capacitive nature of the transducer works exactly like a capacitor, then you don't need the high frecuency capacitor network and the load resistor; it is shown in the schematic only because this crossover network was designed for a Dynamic cone or dome tweeter, which has a typical impedance around 8 to 10 ohms at the typical crossover frecuency.<br/><br/>The false impression that a Biamped or Tri-amped or Multiamped systems have to be costly, or complex or only for professional use is nonsense! Even a low budget system benefits a lot from at least biamping...<br/>The passive crossover is surely going to produce a widely varying impedance curve that only has the nominal 4 ohm value at two or three frecuency points, varying hugely across the full frecuency range, Phase response will certainly vary tremendously also, because the driver's impedance does vary inmensely (between lower than 4 ohm to higher than 80 ohm or more at the resonance point, and 20 or so ohms at crossover frecuencies because of driver interactions, remember, passive crossovers require resistive terminations of equal impedance to be able to produce a smooth impedance curve. Some amplifiers DO NOT like such impedance excursions.<br/>3.-Why mount all drivers in the same panel??? Stereo image and coverage is destroyed when the speakers pair is not properly arranged to create a Stereo image, usually left and right speakers should form an equilateral triangle between them and the listener... May I humbly suggest that ONLY the woofers are mounted to the panel, creating an effective Sub-Woofer taking advantage of the nice and clever concept of putting those in a panel like you did, but installing the midranges and tweeters in much smaller panels/enclosures mounted in small pedestal bases that rise them to ear level and permit to locate them for a proper Stereo image and be very portable and lightweight. That is called a "subwoofer-satellite system" and is capable of very good results without the need for enormous tower speakers for a nice and balanced system. But for a good result, the crossover frecuency must be below 150 Hz, preferably 100 Hz, since lower frecuencies are not directionally perceived, which allows us to place the subwoofer almost anywhere in the room, and to place the left and right satellite speakers where acoustics, Stereo image and room decoration best fit together. Since now the midrange speaker will have to work from 100 Hz up, a 6" to 8" unit will be required per side (or a pair of good 5" per side) , with its necessary enclosure, which won't need to be large since only below 100 Hz a huge volume is needed (which is already solved by your woofers mounted in the large panel at the room door).<br/>Finally, where do we get a good Active crossover? May I suggest to go to "Elliott Sound Products" website and look for an excellent fourth order (24 dB/octave!) crossover network PCB (printed circuit board) which is a good way to obtain a tryed and tested solution! The owner, Mr. Rod Elliott from Australia sells these PCB's bare and ready to be populated with some really inexpensive IC's, small capacitors and resistors. ANY self respected Instructables reader should be fully capable of assembling and setting an excellent two way, stereo Linkwitz-Riley electronic (active) crossover with an outstanding frecuency and phase response, which combined with a couple of nice sounding inexpensive Alpine (or similar) brand car audio small power amps (a 2X50W RMS unit costs only 50 bucks new, the woofers 2X100 W RMS unit another 70 USD or so), The Active Crossover circuit board is 24 USD plus around 10 dls in IC's and small parts, plus a small aluminum extrusion box for a chassis. If you already have a good small stereo amp, then you can replace one of the car audio amps to save some bucks...<br/>You will also need a 12V DC power supply to feed the car amp(s), but Instructables has a few computer power supplies articles that use old PC's power supplies being rescued at no-cost, and capable of giving more than enough current Amperes to run the amps to full power!<br/>Make no mistake, the system I am describing is not a mediocre sounding pile of pieces, the results of using a Biamped system is so "sound" (no intended pun!) that it rivals ANYTHING costing several times as much. Mine has put to shame some extremely expensive (read over a couple of thousands) big amplifier plus passive large size speakers. (the reason, obviously, is that it is plainly stupid to put A LOT of cash in a large very expensive amplifier that will waste half its power just in teh passive crossover, and that a lot of famous speakers present an horrible load to the amplifier. I cannot make an Instructable of my system or design approach at the moment, because I don't have a decent digital camera and I'm in the middle of moving from an apartment to an old house and my wife is waiting our first baby... maybe next year (I hope..)<br/>Good Luck, I may suggest fully reading Rod Elliott's excellent articles (parts one and two) on Active vs Passive Crossovers, and also on the almost unsurmountable difficulties of making a properly behaving passive crossover (yes, it can be done, with a lot of effort, electronic lab equipment and some years of available time to test, retest, and test again a miriad components and crossover parts values... believe me, been there done that. The Active crossover IS the WAY to GO. A webpage reporting on the relative quality of popular car audio amps is at: <a rel="nofollow" href="http://slumz.boxden.com/f359/worst-best-car-audio-brands-419293/">http://slumz.boxden.com/f359/worst-best-car-audio-brands-419293/</a><br/>Good Luck<br/>Alfredo Marquez Claussen, Mexico City. amarquez (aT) i m p dot m x<br/>
Just a couple thoughts?
amclaussen4 years ago
Just a couple of reflections (thoughs)... If Efficiency is a primordial objective, then the use of a Passive Crossover network is not the best selection. The simple first-order (6 dB/octave) crossover used, theoretically produces a 3 dB loss. They call it "Insertion Loss".-

For many good reasons, the absolutely best way to go is to go with an ACTIVE crossover and arrive to a BIAMPED system. In such system the woofers are connected directly to the bass amplifier, which avoids the loss caused by the unavoidable resistance of the coil. An additional benefit is that the amp is now able to better control the heavy woofer cone (specially when the magnet size is somewhat small, like the ones in inexpensive drivers like those selected for this project).
As the efficiency using an active crossover rises, the headroom becomes more ample, and the need to use a sufficiently large power amplifier is greatly reduced (a 3dB increase in efficiency means that instead of a (say)100 watt amp, we now need a 50 watt amp. Since today small car audio stereo amps are good sounding enough and relatively inexpensive, by using a, say 50 W amplifier for the low frecuency channel plus a 20 W amp for the mid+high is more than enough (I AM refering to REAL, so called RMS watts). The differences of efficiency and sound level between the low and midrange drivers are easily corrected with the input level controls at each amp.

2.- The Piezo tweeters can be connected directly to the mid+high amplifier WITHOUT any crossover components, since the capacitive nature of the transducer works exactly like a capacitor, then you don't need the high frecuency capacitor network and the load resistor; it is shown in the schematic only because this crossover network was designed for a Dynamic cone or dome tweeter, which has a typical impedance around 8 to 10 ohms at the typical crossover frecuency.

The false impression that a Biamped or Tri-amped or Multiamped systems have to be costly, or complex or only for professional use is nonsense! Even a low budget system benefits a lot from at least biamping...
The passive crossover is surely going to produce a widely varying impedance curve that only has the nominal 4 ohm value at two or three frecuency points, varying hugely across the full frecuency range, Phase response will certainly vary tremendously also, because the driver's impedance does vary inmensely (between lower than 4 ohm to higher than 80 ohm or more at the resonance point, and 20 or so ohms at crossover frecuencies because of driver interactions, remember, passive crossovers require resistive terminations of equal impedance to be able to produce a smooth impedance curve. Some amplifiers DO NOT like such impedance excursions.
3.-Why mount all drivers in the same panel??? Stereo image and coverage is destroyed when the speakers pair is not properly arranged to create a Stereo image, usually left and right speakers should form an equilateral triangle between them and the listener... May I humbly suggest that ONLY the woofers are mounted to the panel, creating an effective Sub-Woofer taking advantage of the nice and clever concept of putting those in a panel like you did, but installing the midranges and tweeters in much smaller panels/enclosures mounted in small pedestal bases that rise them to ear level and permit to locate them for a proper Stereo image and be very portable and lightweight. That is called a "subwoofer-satellite system" and is capable of very good results without the need for enormous tower speakers for a nice and balanced system. But for a good result, the crossover frecuency must be below 150 Hz, preferably 100 Hz, since lower frecuencies are not directionally perceived, which allows us to place the subwoofer almost anywhere in the room, and to place the left and right satellite speakers where acoustics, Stereo image and room decoration best fit together. Since now the midrange speaker will have to work from 100 Hz up, a 6" to 8" unit will be required per side (or a pair of good 5" per side) , with its necessary enclosure, which won't need to be large since only below 100 Hz a huge volume is needed (which is already solved by your woofers mounted in the large panel at the room door).
Finally, where do we get a good Active crossover? May I suggest to go to "Elliott Sound Products" website and look for an excellent fourth order (24 dB/octave!) crossover network PCB (printed circuit board) which is a good way to obtain a tryed and tested solution! The owner, Mr. Rod Elliott from Australia sells these PCB's bare and ready to be populated with some really inexpensive IC's, small capacitors and resistors. ANY self respected Instructables reader should be fully capable of assembling and setting an excellent two way, stereo Linkwitz-Riley electronic (active) crossover with an outstanding frecuency and phase response, which combined with a couple of nice sounding inexpensive Alpine (or similar) brand car audio small power amps (a 2X50W RMS unit costs only 50 bucks new, the woofers 2X100 W RMS unit another 70 USD or so), The Active Crossover circuit board is 24 USD plus around 10 dls in IC's and small parts, plus a small aluminum extrusion box for a chassis. If you already have a good small stereo amp, then you can replace one of the car audio amps to save some bucks...
You will also need a 12V DC power supply to feed the car amp(s), but Instructables has a few computer power supplies articles that use old PC's power supplies being rescued at no-cost, and capable of giving more than enough current Amperes to run the amps to full power!
Make no mistake, the system I am describing is not a mediocre sounding pile of pieces, the results of using a Biamped system is so "sound" (no intended pun!) that it rivals ANYTHING costing several times as much. Mine has put to shame some extremely expensive (read over a couple of thousands) big amplifier plus passive large size speakers. (the reason, obviously, is that it is plainly stupid to put A LOT of cash in a large very expensive amplifier that will waste half its power just in teh passive crossover, and that a lot of famous speakers present an horrible load to the amplifier. I cannot make an Instructable of my system or design approach at the moment, because I don't have a decent digital camera and I'm in the middle of moving from an apartment to an old house and my wife is waiting our first baby... maybe next year (I hope..)
Good Luck, I may suggest fully reading Rod Elliott's excellent articles (parts one and two) on Active vs Passive Crossovers, and also on the almost unsurmountable difficulties of making a properly behaving passive crossover (yes, it can be done, with a lot of effort, electronic lab equipment and some years of available time to test, retest, and test again a miriad components and crossover parts values... believe me, been there done that. The Active crossover IS the WAY to GO. A webpage reporting on the relative quality of popular car audio amps is at: http://slumz.boxden.com/f359/worst-best-car-audio-brands-419293/
Good Luck
Alfredo Marquez Claussen, Mexico City. amarquez (aT) i m p dot m x
lpoiy4 years ago
how do you power the subs if its a "homewrecker"?
codongolev5 years ago
put them facing inward in a multi-entrance room and bam, you have a torture chamber.
Gonazar5 years ago
Haha, very clever, turning a room into an enclosure (sorta). What effects would there be if you put multiple homewreckers in a multiple-entrance room, given that the other rooms are closed off?
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