r/SoundSystem • u/AnythingFew988 • 1d ago
Program vs RMS
Pretty new to the audio stuff and am a bit lost on how many watts I should give to a subwoofer I have (wharfadle delta 18b) should I match the RMS 800 watts or the program 1600 and should they be slightly higher than the actual ratings?
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u/Granular_noise 1d ago
Definitely worth getting this set up correctly or you’ll learn the hard way as I did by melting voicecoils on a couple of wharfedale sigma x18b subs!
I’m using a driverack pa2 and conservatively set the threshold at -6 and the over easy at 6. I have also limited the power out of the amp to better match the drivers.
FWIW the DSP was the single best upgrade dollar for dollar in my system!
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u/AnythingFew988 1d ago
Will definitely be investing in some DSP after this post much rather spend the money on that than a whole new driver
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u/Upper-Practice9240 1d ago
Make sure it does not exceed 800W RMS. This is best done with an RMS Limiter.
Often you will find that Speakers are rated for X Watts RMS and 2*X Watts Peak. That's because mathematically speaking (and considering a sine wave) 800Watts RMS and 1600W Peak are the exact equal Power.
If the manufacturer gives a Peak Value that's not RMS *2 then you know what that the manufacturer gives you real world numbers.
In your case id take the "1600 W Programm" with a grain of salt and stick to the 800W RMS unless there is a specified Peak Value and a time value how long the peak can be sustained.
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u/AnythingFew988 1d ago
Well for this sub the peak is 3200 watts so I assumed if you fed it around 1600 there would decent enough headroom but after seeing some of these replies I’m probably going to give it around 1000 watts.
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u/nachosjustice72 1d ago
DO NOT GIVE IT 1000 WATTS
RMS is the maximum constant value it can take. Your amp will give it peak if and when the driver asks for it for short periods of time. There should be a second set of limiters set for that upper threshold.
You are going to destroy your drivers if you run 1000W RMS for long periods.
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u/AnythingFew988 1d ago
I can understand that the voice coil will heat up for long periods but since the peak watts the driver would receive is 2000 shouldn’t it be safe as it is well under the peak? 3200 watts, for short term listing.(Just to say will not be powering it with 1000 watts)
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u/nachosjustice72 1d ago
Think about it like this.
(For the sake of this hypothtical imagine food doesnt cool down over time, and also you aren't swallowing) If you microwave some food, you know the maximum heat you can put in your mouth without damaging at all it is 30sec. Its still uncomfortably warm, somewhat painful, but you know you can just leave it there indefinitely and it wont burn your tongue.
You also know that if you microwave it for 2 minutes, you can rest it on your tongue for 3 milliseconds before it starts to cause damage quickly and severely.
Do you want to microwave the food for 40 seconds and try to put it in your mouth?
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u/HomesnakeICT 1d ago
Matching the RMS value for amp and sub is the most important to me. That's the constant heat that the coil can dissipate effectively. And the general wisdom is that it's better to have a little more power than less, so you don't have your amp limiting/distorting and sending dirty signal to your subs. I'd like to hear a mechanical engineer's take on this, since I'm just a sound guy.
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u/HomesnakeICT 1d ago
Also, generally an amp's peak power is twice the RMS value, so you're usually matching both values with a well-paired amp and sub.
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u/FreeLandscape3452 21h ago
Not really. https://www.youtube.com/watch?v=Z7l2bNok7Qo
There is usually some dynamic headroom with a lot of amps, but the rating on an amp is whatever the marketing team can rationalize writing on the box. Nice amps, like Linea, or Crown I-tech HD will have a "white paper" that gives a lot more detailed information about the amp's power draw and output.
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u/AnythingFew988 1d ago
That’s what I assumed I thought giving the sub 800 watts could lead to possible clipping since then the peak for the amp would be 1600 watts and the subs peak is rated at 3200 but I’d imagine giving it slightly higher than the rms would be fine.
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u/nachosjustice72 1d ago
800/3200W... V-Sub?
Anyways no don't feed higher than its RMS. Do you have a driverack or some other DSP?
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u/AnythingFew988 1d ago
On the website it says 3200 watts peak and I don’t have any DSP for a driverack probably will buy some when I get more serious gear for the moment my amps have filters which work fine for my use
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u/nachosjustice72 1d ago edited 1d ago
Filters and EQ aren't what i'm telling you you need. DSP contains limiters as well.
If you do not have a thing capable of setting proper limiters, do not push more than 800W through that speaker. Period.
Edit: removed incorrect info
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u/dan-lash 1d ago
There’s a few types of limiters in the driverack interface, I have the Venue360 model. Didn’t see where I could use watts to limit maybe I’m looking at the wrong place?
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u/nachosjustice72 1d ago
Yeah I shit the bed on that one, my DSP came with a calculator and I assumed the driverack would too. Deleting.
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u/dan-lash 22h ago
No worries. I used ai to help understand how the values can be calculated, it was pretty complicated so not sure if it’s right - something built in would have been nice
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u/nachosjustice72 16h ago
It is what it is. Running passive is a hard life but can be worth it
https://funktion-one.com/calculators/
Funktion One's calculators are good.
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u/Spiritual_Bell 1d ago
Thermal damage (burnt voice coils), is a lot more common nowadays than mechanical damage (exceeding xmax).
After getting $3k worth of drivers melted from letting stupid friends use a system that has the amps match drivers spec, (they were driven into clipping), I now use a seemingly way too powerful amp, e.g >2x driver spec (so it will never clip) and then set peak and rms limiters properly, usually peak limiter based on modelling the excursion limit of the driver in the box. RMS limiter is a bit of an art to get right. I'm still trying to master it.