Help me decide on a sub& combo!
July-18th-2003, 02:17 PM
#197
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Location: Fremont, CA
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UNDERSTANDING DAMPING FACTOR
Loudspeakers have a mind of their own. You send them a signal and they add their own twist to it. They keep on vibrating after the signal has stopped, due to inertia. That's called "ringing" or "time smearing."
In other words, the speaker produces sound waves that are not part of the original signal.
Suppose the incoming signal is a "tight" kick drum with a short attack and decay in its signal envelope. When the kick-drum signal stops, the speaker continues to vibrate. The cone bounces back and forth in its suspension. So that nice, snappy kick drum turns into a boomy throb.
Fortunately, a power amplifier can exert control over the loudspeaker and prevent ringing. Damping is the ability of a power amplifier to control loudspeaker motion. It's measured in Damping Factor, which is load impedance divided by amplifier output impedance. Let's explain.
If the speaker impedance is 8 ohms, and the amplifier output impedance is 0.01 ohms, the damping factor is 800. That's a simplication. Since the speaker impedance and amplifier output impedance vary with fre-quency, so does the damping factor. Also, the impedance of the speaker cable affects damping. Thick cables (with low AWG) allow more damping than thin cables with (high AWG).
The lower the amplifier's output impedance, the higher the damping factor, and the tighter the sound is. A damping factor of 1000 or greater is considered high. High damping factor equals tight bass.
How It Works
How does an amplifier control speaker motion? When the loudspeaker cone vibrates, it acts like a micro-phone, generating a signal from its voice coil. This signal generated by the speaker is called back EMF (back Electro Motive Force). It travels through the speaker cable back into the amplifier output, then returns to the speaker. Since back EMF is in opposite polarity with the speaker's motion, back EMF impedes or damps the speaker's ringing.
The smaller the amp's output impedance, the greater is the effect of back EMF on the speaker's motion. An amplifier with low output impedance does not impede the back EMF, so the back EMF drives the loud-speaker with a relatively strong signal that works against the speaker's motion. When the speaker cone moves out, the back EMF pulls the speaker in, and vice versa.
In short, the loudspeaker damps itself through the amplifier output circuitry. The lower the impedance of that output circuitry, the more the back EMF can control the speaker's ringing.
To prove it to yourself, take a woofer that is not connected to anything. Put your ear next to the cone and tap on it. You might hear a low-pitched "bongggg" if the speaker itself is poorly damped. Now short the speaker terminals and tap again. You should hear a tighter thump.
Damping factor varies with frequency. As you might suspect, damping factor is most important at low fre-quencies, say 10 Hz to 400 Hz. The chart on the next page shows typical damping factor vs. frequency of a Crown CTs 600/1200 power amplifier. It's well over 3000 from 10 Hz to 1 kHz.
All Crown amplifiers are designed to have high damping factor. That's why you can count on Crown amps to deliver clean, tight kick drum and bass.
Typical damping factor vs. frequency of a Crown CTs 600/1200 power amplifier.
Loudspeakers have a mind of their own. You send them a signal and they add their own twist to it. They keep on vibrating after the signal has stopped, due to inertia. That's called "ringing" or "time smearing."
In other words, the speaker produces sound waves that are not part of the original signal.
Suppose the incoming signal is a "tight" kick drum with a short attack and decay in its signal envelope. When the kick-drum signal stops, the speaker continues to vibrate. The cone bounces back and forth in its suspension. So that nice, snappy kick drum turns into a boomy throb.
Fortunately, a power amplifier can exert control over the loudspeaker and prevent ringing. Damping is the ability of a power amplifier to control loudspeaker motion. It's measured in Damping Factor, which is load impedance divided by amplifier output impedance. Let's explain.
If the speaker impedance is 8 ohms, and the amplifier output impedance is 0.01 ohms, the damping factor is 800. That's a simplication. Since the speaker impedance and amplifier output impedance vary with fre-quency, so does the damping factor. Also, the impedance of the speaker cable affects damping. Thick cables (with low AWG) allow more damping than thin cables with (high AWG).
The lower the amplifier's output impedance, the higher the damping factor, and the tighter the sound is. A damping factor of 1000 or greater is considered high. High damping factor equals tight bass.
How It Works
How does an amplifier control speaker motion? When the loudspeaker cone vibrates, it acts like a micro-phone, generating a signal from its voice coil. This signal generated by the speaker is called back EMF (back Electro Motive Force). It travels through the speaker cable back into the amplifier output, then returns to the speaker. Since back EMF is in opposite polarity with the speaker's motion, back EMF impedes or damps the speaker's ringing.
The smaller the amp's output impedance, the greater is the effect of back EMF on the speaker's motion. An amplifier with low output impedance does not impede the back EMF, so the back EMF drives the loud-speaker with a relatively strong signal that works against the speaker's motion. When the speaker cone moves out, the back EMF pulls the speaker in, and vice versa.
In short, the loudspeaker damps itself through the amplifier output circuitry. The lower the impedance of that output circuitry, the more the back EMF can control the speaker's ringing.
To prove it to yourself, take a woofer that is not connected to anything. Put your ear next to the cone and tap on it. You might hear a low-pitched "bongggg" if the speaker itself is poorly damped. Now short the speaker terminals and tap again. You should hear a tighter thump.
Damping factor varies with frequency. As you might suspect, damping factor is most important at low fre-quencies, say 10 Hz to 400 Hz. The chart on the next page shows typical damping factor vs. frequency of a Crown CTs 600/1200 power amplifier. It's well over 3000 from 10 Hz to 1 kHz.
All Crown amplifiers are designed to have high damping factor. That's why you can count on Crown amps to deliver clean, tight kick drum and bass.
Typical damping factor vs. frequency of a Crown CTs 600/1200 power amplifier.
Last edited by Intruder; July-18th-2003 at 04:54 PM.
July-18th-2003, 05:30 PM
#198
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I just came back home and my sub is finally here.
I also received the terminal plate. I'll resume work on the box now. I have all I need to finalize it. I wish I could test it as well.
I also received the terminal plate. I'll resume work on the box now. I have all I need to finalize it. I wish I could test it as well.
July-18th-2003, 05:37 PM
#199
get orvillized! WTF?
Join Date: Mar 2003
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Now you can put the sticker on the car and say I got screwed by EDesigns! Is ED going to give you free shipping to help with your feelings of resentment towards them? They should not only do that, but do more for you like throw in something to make it more worth while. It's a nice sub. From a distance, it almost looks like carbon fiber on the flat cone. Now you can put your box with sub on a high shelf and admire it every time you go to sleep. Sucks about your amp dude.
MisterT
MisterT
July-18th-2003, 05:41 PM
#200
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eD won't give me ****! I could really use their sticker but add a "Screwed by..." on it...
the "sales rep." insists on "helping" me, but all he does is ask me if I want to cancel my order or go for another amp. he sort of mentioned that he could give me a better amp for the same amount of money, but that's IT! but what is a better amp??? I don't want a multi-channel amp. All I need is a GOOD MONO AMP.
I don't know...
I don't want a different amp. I don't want to wait till "early August" (this could mean Aug 15th!!!). *sigh*
the "sales rep." insists on "helping" me, but all he does is ask me if I want to cancel my order or go for another amp. he sort of mentioned that he could give me a better amp for the same amount of money, but that's IT! but what is a better amp??? I don't want a multi-channel amp. All I need is a GOOD MONO AMP.
I don't know...
I don't want a different amp. I don't want to wait till "early August" (this could mean Aug 15th!!!). *sigh*
July-18th-2003, 06:18 PM
#202
get orvillized! WTF?
Join Date: Mar 2003
Location: I am here --> x
Posts: 948
Use wood screws. You can buy a box at a hardware store or at lowes or similar store. Be careful not to poke a hole in the rubber surround. Not to insult your intelligence or abilities, but I have seen it happen. Luckily not with me.
MisterT
MisterT
July-18th-2003, 06:23 PM
#203
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Originally posted by MisterT
Not to insult your intelligence or abilities, but I have seen it happen. Luckily not with me.
Not to insult your intelligence or abilities, but I have seen it happen. Luckily not with me.
The screws shouldn't come out from the other end, right? i.e very short wood screws
July-18th-2003, 06:33 PM
#205
get orvillized! WTF?
Join Date: Mar 2003
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Originally posted by Intruder
The screws shouldn't come out from the other end, right? i.e very short wood screws
The screws shouldn't come out from the other end, right? i.e very short wood screws
MiStErT
July-18th-2003, 06:36 PM
#206
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Originally posted by MisterT
No, you want them to. Mine are about 2" screws but I have seen people use 4 inch on up. 2" is all you need though, but you want them to go all the way through. Don't worry about the inside of the box. No one sees that.
MiStErT
No, you want them to. Mine are about 2" screws but I have seen people use 4 inch on up. 2" is all you need though, but you want them to go all the way through. Don't worry about the inside of the box. No one sees that.
MiStErT
okay
2" screws then... I'm leaving in about 10 minutes.
July-18th-2003, 08:24 PM
#208
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Originally posted by MisterT
No, you want them to. Mine are about 2" screws but I have seen people use 4 inch on up. 2" is all you need though, but you want them to go all the way through. Don't worry about the inside of the box. No one sees that.
MiStErT
No, you want them to. Mine are about 2" screws but I have seen people use 4 inch on up. 2" is all you need though, but you want them to go all the way through. Don't worry about the inside of the box. No one sees that.
MiStErT
July-19th-2003, 09:58 AM
#209
get orvillized! WTF?
Join Date: Mar 2003
Location: I am here --> x
Posts: 948
You mean six - 1 1/2" screws? That will work if they are wood screws. Wood screws go in easier than any other ordinary screw. I just bought a box because I can always use wood screws not just for car, but any other projects around the house or in my case, apartment.
MiStErT
MiStErT
