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Multi-Way Conventional loudspeakers with crossovers

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Old 17th January 2018, 08:43 AM   #11
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Old'n'Cranky View Post
To me those butchered words are like someone asking how much milkerage can be squeezed out of a cow.
This is not what you wanted to hear, but I really like the ridiculousness of "milkerage". I might have to start using it!

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Old 17th January 2018, 09:54 AM   #12
TNT is offline TNT  Sweden
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Originally Posted by Old'n'Cranky View Post
Amperes (or Amps) is the unit of measurement.
Another measurement of Power.
Current (ampere, I) is not ("another measurement of") power.

Power is produced when a certain current flows in presence of a voltage (volt, U) difference (over a resistance, R). Power is calculated by multiplying the current with the voltage: P=I*U.

As U=I*R => P=U*U/R

For AC (a tone), if U is peak, RMS = U/1,4. (RMS is not "exactly half"...)

P=(12/1,4*12/1,4)/8=9,2 watt RMS.

And yes - it's the voltage and current on the speaker terminals that creates output power, not the power supply. Indeed one can get higher voltage on speaker terminals than what the supply (e.g. a battery) provides but never more power (but if you do - Nobel Prize for U!)

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Old 17th January 2018, 10:00 AM   #13
TNT is offline TNT  Sweden
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Originally Posted by Gnobuddy View Post
...
It is possible that the amp you have does not in fact operate in bridge mode. If that is the case, then the peak-to-peak (not peak) maximum output voltage will be about 9 volts.

That means the peak voltage is now only 4.5 volts. Half the voltage translates to one quarter of the power. That is about 1.25 watts RMS, instead of the 5 watts you'd get in bridge mode....
This became a bit confusing...

Peak and p-p.... for a real word voltage, be it from a half bridge or a bridge, there is only peak-to-peak, p-p. Nothing is just "peak". Bridge gives you double the voltage swing compared to half-bridge (this is amplifier configuration technology). So in one case you have 9 V p-p and the other, 4,5 V p-p.

p-p/1,4 => RMS.

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Old 17th January 2018, 05:22 PM   #14
Lojzek is offline Lojzek  Croatia
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Hi sdbarnold, what kind of enclosures did you put these units into? I was contemplating on simulating your current speaker setup with premade amazon crossovers, and then maybe try suggesting mods to improve on it, if possible. The trouble is I can't possibly know the inductor value, only suspect it to be around 1.5 mH.
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Old 17th January 2018, 05:31 PM   #15
picowallspeaker is offline picowallspeaker  Italy
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That Dayton Audio PC105-8 isn't a tweeter !
Why is it supposed to be crossed at > 1 kHz ?
Leave it for future projects...hmmm nice midrange ! Or it could be used as a mid woofer
for something smaller.
Try a cheapish cone tweeter if you don't like dome tweeters.
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Old 17th January 2018, 07:13 PM   #16
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by TNT View Post
Peak and p-p.... for a real word voltage, be it from a half bridge or a bridge, there is only peak-to-peak, p-p. Nothing is just "peak".
I disagree. All three measurements (peak to peak, peak, and RMS) have their uses, and all can be converted back and forth as needed.

Peak-to-peak is easiest to read off an oscilloscope screen.

Peak value is used to determine, for example, the necessary current rating for the output transistors, or when setting recording levels in your DAW.

RMS is the best description of actual power delivered to a load, particularly when the load is not purely resistive, but also has a reactive component.

Quote:
Originally Posted by TNT View Post
Bridge gives you double the voltage swing compared to half-bridge (this is amplifier configuration technology).
Agreed!

Quote:
Originally Posted by TNT View Post
So in one case you have 9 V p-p and the other, 4,5 V p-p.
You are off by a factor of two - in one case you have 9 V peak to peak, in the other case, 18 volts peak to peak.

This happens because, in bridge mode, each half of the bridge swings by 4.5 volts peak, in opposite directions, so the total peak voltage is 9 volts. The total peak-to-peak voltage is double that, or 18 volts.

Power can be calculated using either peak or peak to peak voltage (both will give the same answer if the proper formula is used):

P(RMS) = Vp*Vp/(2 R)

P(RMS) = Vpp*Vpp/(8 R)

And the answer is, about 5 watts RMS power into an 8 ohm load if in bridge mode; about 1.25 watts RMS power into 8 ohms if NOT in bridge mode.

These very low power levels are one of the reasons why automotive speakers are almost always 4 ohms rather than 8 ohms (doubles the power for the same 12V supply). It's also the reason many automotive amps are spec'd at a somewhat unrealistic 14.4 volts supply voltage, rather than at 12V.

That doubled power from using 4 ohms speakers still wasn't enough for many people, so car audio amps also sometimes use switching power supplies to raise the supply voltage internally, and/or bridge mode power amps to quadruple the output power for a given supply voltage and speaker impedance.

There are a few weird Bose car audio systems that use very low speaker impedances (around 1 or 2 ohms) in order to deliver more power with the same 12V supply rail, but that is an oddball that, thankfully, was not followed by anyone else in the automotive audio industry.

-Gnobuddy
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Old 17th January 2018, 07:19 PM   #17
picowallspeaker is offline picowallspeaker  Italy
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Quote:
Originally Posted by picowallspeaker View Post
That Dayton Audio PC105-8 isn't a tweeter !
Why is it supposed to be crossed at > 1 kHz ?
Leave it for future projects...hmmm nice midrange ! Or it could be used as a mid woofer
for something smaller.
Try a cheapish cone tweeter if you don't like dome tweeters.
and the Peerless PLS 75F25AL04 isn't a tweeter either !

What shall we do ?

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Old 17th January 2018, 08:28 PM   #18
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by picowallspeaker View Post
What shall we do ?

As my speaker-designer former co-worker used to say, "They all make a sound. That's all that most people care about."

-Gnobuddy
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Old 17th January 2018, 09:59 PM   #19
Borus is offline Borus  United States
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"milkerage" +1!
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Old 18th January 2018, 01:59 AM   #20
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by TNT View Post
For AC (a tone), if U is peak, RMS = U/1,4. (RMS is not "exactly half"...)
This is worth clarifying. Yes, RMS voltage is peak voltage divided by 1.4142... (the square root of two). So RMS voltage works out to be about 71% of the peak voltage, for a sine wave.

But RMS power is in fact exactly half of peak power (again, for a sine wave). This is because, if you square the square root of two, you get...two!

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