Author Topic: Calculating fuse value for fusing speakers.  (Read 2375 times)

TheGuitarist

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Calculating fuse value for fusing speakers.
« on: June 02, 2010, 11:50:11 PM »
Ok so this may be another dumb question from me, but its best to ask first before i blow something up.

I just fused my NS-10mxs (don't wanna know your opinion about the speakers) and i'm not sure what value to put in. I fused the tweeter and woofers seperately.

Most people say get .75A for the tweeter and 1.5 for the woofer, i could only get .8 and 1.6, which i don't think is too much of a problem, but here is my dilemma. My ns-10s have a vastly higher wattage rating than the original ns-10s. 120w avg and 150w peak. I'll be using an adcom 555 to power the speakers which is 200W a side, no attenuation control (using one of igors wonderful CRM kits for that but i'm sure i could add a stepped attenuator onto the unit if i really needed to).

Do those values sound like they'd still be correct? I'm not sure how much voltage a power amp puts out so i'm not sure if i should raise the value if the speakers can handle more, or does wattage have little effect on current?


abbey road d enfer

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Re: Calculating fuse value for fusing speakers.
« Reply #1 on: June 03, 2010, 02:25:11 AM »
You're opening a big can of worms here. There's no simple answer to your question. A loudspeaker can handle many times its rated power for short durations and a fuse does not blow instantly either.
Let's make it simple, if possible: taking 100W for the woofer, using P = R.I², it suggests I = 3.5A.
The problem is that the rating of fuses is such that their nominal value is what they can withstand for an infinite duration. You want the fuse to blow before the speaker, right? So you start with a lower value, let's say half the calculated value, in that case, the nearest value is 1.6A, and you see how it goes; if the fuse blows even when using moderate power you need to increase its value. Or to use a slow-blow version of the same rating.
Yes, there are fast and slow fuses. I would start with fast ones because speakers tend to burn pretty fast too.
By using half the calculated value, you're limiting the long term power to 1/4 of the nominal power, which should be ok if you're listening to reasonably dynamic programme.
I don't know what's the rating of the tweeter, but they generally are between 10 and 20W, which would suggest a max current of 1 to 1.6 A, and the use of a 0.5 to 0.8A fuse. Again, you will ned to experiment. Tweeters are even quicker to blow, so definitely the fuse should be a fast type.
I've spent 20 years designing protection systems for high power loudspeakers (I'm talking about kilowatts here) and there is no system today that can guarantee complete safety and optimum sonic performance.

Finally, an attenuator doesn't change the amplifier's power, it changes its overall sensitivity, so putting a 3dB attenuator in front of a 200W amp expecting it to become a 100W amp doesn't work. It just means you need to crank the level 3 dB more to make it deliver its rated power.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

sodderboy

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Re: Calculating fuse value for fusing speakers.
« Reply #2 on: June 03, 2010, 09:59:11 AM »
Standard for NS-10's is a single 1.5A fastblo on the speaker.  No need to fuse the drivers separately.
1.5 works for most nearfields.
Your separate values are OK.
Mike

bruno2000

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Re: Calculating fuse value for fusing speakers.
« Reply #3 on: June 03, 2010, 10:10:39 AM »
I use fast acting, self resetting circuit breakers on each element of our NS10s, 700mA for the woofers, and 300mA for the tweeters.  If a client plays them too loud, they just stop, and the breaker stays open for about 10 seconds, as the second engineer explains why they stopped working.  This scheme has pretty much eliminated blown speakers.
Best,
Bruno2000

abbey road d enfer

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Re: Calculating fuse value for fusing speakers.
« Reply #4 on: June 03, 2010, 11:23:50 AM »
I use fast acting, self resetting circuit breakers on each element of our NS10s, 700mA for the woofers, and 300mA for the tweeters.  If a client plays them too loud, they just stop, and the breaker stays open for about 10 seconds, as the second engineer explains why they stopped working.  This scheme has pretty much eliminated blown speakers.
Best,
Bruno2000
Can you tell me what brand/model you're using?
We use resettable CB's on most of our speakers but we've found the low-power types (less than 1 amp) to be very inaccurate and fragile. On tweeters we use Polyswitches instead.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

bruno2000

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Re: Calculating fuse value for fusing speakers.
« Reply #5 on: June 03, 2010, 12:33:03 PM »
I use fast acting, self resetting circuit breakers on each element of our NS10s, 700mA for the woofers, and 300mA for the tweeters.  If a client plays them too loud, they just stop, and the breaker stays open for about 10 seconds, as the second engineer explains why they stopped working.  This scheme has pretty much eliminated blown speakers.
Best,
Bruno2000
Can you tell me what brand/model you're using?
We use resettable CB's on most of our speakers but we've found the low-power types (less than 1 amp) to be very inaccurate and fragile. On tweeters we use Polyswitches instead.
The ones at the bottom of the page.
http://www.newark.com/jsp/content/printCatalog.jsp?display=single&cat=c127&page=1406
Best,
Bruno2000

sodderboy

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Re: Calculating fuse value for fusing speakers.
« Reply #6 on: June 03, 2010, 01:13:41 PM »
I had Polyswitches on small Westlakes and the engineers HATED them.  I went back to fuses when I kept finding them wrapped in tinfoil.
Mike

owel

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Re: Calculating fuse value for fusing speakers.
« Reply #7 on: June 03, 2010, 01:23:15 PM »
How about just create a "speaker protection circuit"...  in normal operation, the relays are closed and signal goes to the speakers.

Use a comparator circuit, adjustable "trip levels" using a trimmer. When the signal exceeds the trip level, comparator activates an SCR which powers up the relay coil, and automatically opens the relay, cutting off signal to the speakers.

Press a RESET switch to reset the SCR/Relay.

bruno2000

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Re: Calculating fuse value for fusing speakers.
« Reply #8 on: June 03, 2010, 01:52:11 PM »
I had Polyswitches on small Westlakes and the engineers HATED them.  I went back to fuses when I kept finding them wrapped in tinfoil.
Mike

Mine are on the INSIDE of the cabinets.  So far, with the NS10s anyway, no one has complained, and these have been installed for over 3 years.
Best,
Bruno2000

abbey road d enfer

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Re: Calculating fuse value for fusing speakers.
« Reply #9 on: June 03, 2010, 04:14:03 PM »
I use fast acting, self resetting circuit breakers on each element of our NS10s, 700mA for the woofers, and 300mA for the tweeters.  If a client plays them too loud, they just stop, and the breaker stays open for about 10 seconds, as the second engineer explains why they stopped working.  This scheme has pretty much eliminated blown speakers.
Best,
Bruno2000
Can you tell me what brand/model you're using?
We use resettable CB's on most of our speakers but we've found the low-power types (less than 1 amp) to be very inaccurate and fragile. On tweeters we use Polyswitches instead.
The ones at the bottom of the page.
http://www.newark.com/jsp/content/printCatalog.jsp?display=single&cat=c127&page=1406
Best,
Bruno2000
OK. These are Polyswitches. For larger speakers we use magneto-thermal CB's, but as I said lower values are not accurate enough.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


bruno2000

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Re: Calculating fuse value for fusing speakers.
« Reply #10 on: June 03, 2010, 04:44:25 PM »
I use fast acting, self resetting circuit breakers on each element of our NS10s, 700mA for the woofers, and 300mA for the tweeters.  If a client plays them too loud, they just stop, and the breaker stays open for about 10 seconds, as the second engineer explains why they stopped working.  This scheme has pretty much eliminated blown speakers.
Best,
Bruno2000
Can you tell me what brand/model you're using?
We use resettable CB's on most of our speakers but we've found the low-power types (less than 1 amp) to be very inaccurate and fragile. On tweeters we use Polyswitches instead.
The ones at the bottom of the page.
http://www.newark.com/jsp/content/printCatalog.jsp?display=single&cat=c127&page=1406
Best,
Bruno2000
OK. These are Polyswitches. For larger speakers we use magneto-thermal CB's, but as I said lower values are not accurate enough.

Yea, I guess I just made this up.

Conductor

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Re: Calculating fuse value for fusing speakers.
« Reply #11 on: June 04, 2010, 12:34:56 AM »
"...Two different types of fuses are required for thermal protection and voltage protection.
Slow-blow fuses are usually selected to protect loudspeakers from thermal damage because they are similar to loudspeakers in the way they respond to thermal conditions over time.
In contrast, high-speed instrument fuses like the Littlefuse 361000 series are used to protect loudspeakers from large transient voltages.
The nomograph can be used to select the properly rated fuse for either type of loudspeaker protection.
In general, low-frequency drivers (woofers) are most susceptible to thermal damage and high-frequency drivers (tweeters) are usually damaged by large transient voltages.
This means that your loudspeakers will tend to have better protection when the woofers are protected by slow-blow fuses and high-frequency drivers are protected by high-speed instrument fuses..."

(http://crownaudio.com/pdf/133472.pdf)

JUSTICE FOR HUNGARY

abbey road d enfer

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Re: Calculating fuse value for fusing speakers.
« Reply #12 on: June 04, 2010, 07:56:23 AM »
Electrodynamic loudspeakers, even tweeters, cannot be desproyed by overvoltage. It's the thermal or mechanical effects that destroy speakers. Sine the thermal capacity of a tweeter voice-coil is much smaller than that of a woofer, they can be destroyed much more rapidly, but it's still the thermal effect that damages it (or the diaphragm crashing with the pole pieces).
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

lernith

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Re: Calculating fuse value for fusing speakers.
« Reply #13 on: June 05, 2010, 02:32:33 PM »
Has anyone tried either of Rod Elliot's DC protection schemes?
http://sound.westhost.com/project33.htm
http://sound.westhost.com/project111.htm

abbey road d enfer

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Re: Calculating fuse value for fusing speakers.
« Reply #14 on: June 05, 2010, 02:59:05 PM »
This is just the standard DC and turn-on/turn-off click protection. It certainly works, but it's no good at protecting speakers from overpower.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


 

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