Hi everyone I am going to be building MTM LR speakers. My aim is 4 Ohms for for each speaker. I will be paralleling to 8 ohm 10" woofers for 4 ohms but how do i wire in a 8 ohm compression driver and restrict its power to 80-100 watts? I will be using 200-300 watt 10" drivers. I welcome any suggestions.
The 'Ohm' value in speaker impedance is not a fixed number, it varies across the entire audible range and a '4 ohm' speaker may go from 2 or 3 to 50 ohms depending on where you're measuring it.
For the HF driver we normally don't pick the impedance, a 16 ohm CD works fine in a '4 ohm' speaker. Get your crossover right and neither the impedance or FR will be an issue. I can guess with two 10" drivers your CD will still need some padding, albeit only a little bit.
As Allen said, when you cross correctly the CD will not see as much power as the woofers.
For the HF driver we normally don't pick the impedance, a 16 ohm CD works fine in a '4 ohm' speaker. Get your crossover right and neither the impedance or FR will be an issue. I can guess with two 10" drivers your CD will still need some padding, albeit only a little bit.
As Allen said, when you cross correctly the CD will not see as much power as the woofers.
Think of the inductors and capacitors as also providing resistance (if you are thinking in DC terms). The filter network reduces the power (really, voltage) seen by the driver. Because SPL is based on the piston volume, you don't want a tweeter trying to produce low frequencies -- not enough displacement. This is why the prior posts have said that if you cross at the right frequency, this isn't an issue. Depending upon the realized sensitivity of your dual woofers (e.g., after baffle step and other contouring), you will likely need to pad the CD a bit, as well.
If you are planning to dump a lot of power into your speakers, then make sure the wattage/VDC rating of your components is consistent to the task. A 10W resistor that's fed a too much power will turn into slag or even become a fire hazard outright.
Most musical energy resides in the lower octaves.
Typically 50% of the power of a total system is below 300Hz, and roughly 50% of energy in pink noise - most representative of music - resides below 800Hz.
Thus most amplifiers tend to need produce most of their energy in the lower octaves, and this is where impedance has a major part to play. For higher frequencies this is not as important as the amount of energy an amplifier will produce/supply in real music is much less.
However your question is different: do the woofer and tweeter sections have to have equal impedance?
No they do not.
This is why off-the-shelf crossovers rarely work well, if at all - they are designed for drivers with a theoretically flat impedance in mind. You should read Allen's excellent tutorial on designing crossovers without measurements. It is written for those who are probably looking for basic instruction and knowledge. I'm sure it would help you out.
Introduction to designing crossovers without measurement
Typically 50% of the power of a total system is below 300Hz, and roughly 50% of energy in pink noise - most representative of music - resides below 800Hz.
Thus most amplifiers tend to need produce most of their energy in the lower octaves, and this is where impedance has a major part to play. For higher frequencies this is not as important as the amount of energy an amplifier will produce/supply in real music is much less.
However your question is different: do the woofer and tweeter sections have to have equal impedance?
No they do not.
This is why off-the-shelf crossovers rarely work well, if at all - they are designed for drivers with a theoretically flat impedance in mind. You should read Allen's excellent tutorial on designing crossovers without measurements. It is written for those who are probably looking for basic instruction and knowledge. I'm sure it would help you out.
Introduction to designing crossovers without measurement
The impedance of the high frequency driver shouldn't matter, as long as it isn't too low to upset the amplifier.
What you're interested in is the sensitivity (dB/2.83Vrms @ 1metre) of the high frequency driver. This should be equal or higher than the sensitivity of one of the woofers. The reason for this is that you have two woofers (+6dB) but then loose 3-6dB due to baffle step, bringing you back to around the anechoic sensitivity of a single woofer.
If the tweeter/HF driver is at least this sensitive, you have head room to attenuate (pad down) the tweeter to the appropriate level in the crossover to match the woofers. It is a lot easier to attenuate a tweeter than a woofer, due to the low frequency resonances of the woofers.
What you're interested in is the sensitivity (dB/2.83Vrms @ 1metre) of the high frequency driver. This should be equal or higher than the sensitivity of one of the woofers. The reason for this is that you have two woofers (+6dB) but then loose 3-6dB due to baffle step, bringing you back to around the anechoic sensitivity of a single woofer.
If the tweeter/HF driver is at least this sensitive, you have head room to attenuate (pad down) the tweeter to the appropriate level in the crossover to match the woofers. It is a lot easier to attenuate a tweeter than a woofer, due to the low frequency resonances of the woofers.
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