Hello,
I have two questions one that is about subwoofers and another is about amplifiers. Let's get in to the detail about subwoofers and crossovers. I want to make sure that I'm thinking right. Here is two scenarios:
1) Subwoofer has a "Low Pass" filter at 150Hz;
2) Subwoofer has a "High Pass" filter at 30Hz;
I have statements that i want to make sure they are correct. First scenario with a "Low Pass" filter keeps the subwoofers voice coil from overheating. And second scenario with "High Pass" filter keeps subwoofer out of uncontrolled (depends on the enclosure) Xmax. Are they true if the power of amplifiers is constant in both cases and it's not higher than the recommended?
Another question that I'm concerned is about amplifier power and how it powers subwoofer. Let's say I have a way to measure amplifier power at 50Hz. I measure it and for example I choose to power my subwoofer @ 150wRms (in this case 20V). Everything that is below 50Hz will get less power and everything that is higher then 50Hz will get move power. Is this statement true?
I have two questions one that is about subwoofers and another is about amplifiers. Let's get in to the detail about subwoofers and crossovers. I want to make sure that I'm thinking right. Here is two scenarios:
1) Subwoofer has a "Low Pass" filter at 150Hz;
2) Subwoofer has a "High Pass" filter at 30Hz;
I have statements that i want to make sure they are correct. First scenario with a "Low Pass" filter keeps the subwoofers voice coil from overheating. And second scenario with "High Pass" filter keeps subwoofer out of uncontrolled (depends on the enclosure) Xmax. Are they true if the power of amplifiers is constant in both cases and it's not higher than the recommended?
Another question that I'm concerned is about amplifier power and how it powers subwoofer. Let's say I have a way to measure amplifier power at 50Hz. I measure it and for example I choose to power my subwoofer @ 150wRms (in this case 20V). Everything that is below 50Hz will get less power and everything that is higher then 50Hz will get move power. Is this statement true?
Your question is a bit confusing. High pass is for the woofer or sub being filtered from the very low frequencies say below 20 Hz as an example, (could be 15, 30 or other) because they can damage the driver in Xmax excursion and power handling (you may have less power than that @specs because of the excursion). Both are limited for each driver. It also depends on the alignment of the enclosure (Vb, Fb).
As a pratical example a novel 6.5" driver* is 100W from specs but at 15Hz it as a max. excursion of 14.5mm@87W is the mechanical (and electrical 100W@4ohm) limit for that driver ~Vb=20liters, Fb=20Hz of course a bass reflex type, Xmax is 10mm by the way.
*Purifi PTT6.5W04
As a pratical example a novel 6.5" driver* is 100W from specs but at 15Hz it as a max. excursion of 14.5mm@87W is the mechanical (and electrical 100W@4ohm) limit for that driver ~Vb=20liters, Fb=20Hz of course a bass reflex type, Xmax is 10mm by the way.
*Purifi PTT6.5W04
No, the amplifier will deliver to the woofer exactly the same 150Wrms in the frequency range 30Hz - 150Hz.
From my understanding of these things; by putting a 30hz high-pass filter on a sub-woofer. you are effectively turning it into a woofer. The filter it not a switch. It reduces output on a slope (roll off). Spurious figures: a 30hz filter will cause you to lose 5dB @ 35hz and 2db @ 40hz.
If you want to hear the effect of your filter use audio software (Audacity is free). Load an Mp3. Select high-pass filter. Select frequency and roll-off. and listen to the results.
If you want to hear the effect of your filter use audio software (Audacity is free). Load an Mp3. Select high-pass filter. Select frequency and roll-off. and listen to the results.
Not true. The relatively large wire used in a subwoofers voice coil behaves like a inductor with a rising impedance with rising frequency so there is literally no way to overpower the voice coil at high frequencies.
Yes, below box tuning excursions rises to extreme levels and damage can occur at power levels well below the drivers rated power handling capacity.
NO. Again we have to go back to the drivers impedance curve, it is a curve it is not flat as the rated impedance spec would suggest and it will have peaks related to the driver and enclosure resonance frequencies... the null between the peaks is usually the box resonant frequency. Audio amplifiers are really voltage amplifiers so the power delivered will vary a lot over a subwoofers designed operating range, at impedance peaks power delivered is low, at the nulls it is very high. The picture below is just a random example of the dual peak impedance of a bass reflex woofer or subwoofer.
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The low pass filter reduces upper frequency content from the woofer, allowing the low frequencies to be reproduced without increasing (or interfering with) the level of the upper frequencies that are covered better by the upper devices.
Why would you think that? I don't get it. Also, how does 20V yield 150W? P=V^2/R --> 150 = 400/R --> R=2.666. Is that the DC resistance of your voice coil or something?
- First of all, as @conanski pointed out, the ACTUAL power is complicated. So let's adopt the typical convention that you mean "the power that the amp would put out into a resistor" even though speakers are not resistors at all.
- The lowpass filter is so that you don't hear the singer coming out of your subwoofer and so on.
- The highpass filter yes is to reduce excursion below the port frequency.
- Neither can prevent disaster, because you could overdrive the amp input more than the filters are filtering, even clipping the input of the amp.
"Head_Unit’s Rules Of Protection":
1) If when things start to sound distorted or odd you TURN IT DOWN, you are unlikely to ever break anything.
2) If you constantly "turn it up to 11" you will break something.
NOTE: size and power ratings of speakers and amp do not affect rules 1 and 2. Speaker specifications are 92% meaningless (and I say that as a loudspeaker engineer). Specs for amps are not thorough since they are measured into resistors for pragmatic reasons and speakers are not resistors at all. Amps' 4 ohm or even 2 ohm rating is the most meaningful even if your speakers are 8 ohms.