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View Full Version : Is 75w rms too much for 40w rms speakers?



RebelExtrm02
12-02-2009, 01:24 AM
I have an amp that puts out 75w rms per channel and I wanted to use it to power my door speakers which are 40w rms 6.5" coaxial speakers. Will this be too much for the speakers to handle? The amp is an Infinity 475a.

pieper88
12-02-2009, 01:31 AM
It depends more on the type of speaker not the amp. Some speakers might be able to handle it others not. You really need to give more information.

SicAudio
12-02-2009, 01:33 AM
yeah more info. i run 90 rms to my 40 rms mbquarts but they are quarts they can take it a 40 rms polk, pioneer ect would cook.

RebelExtrm02
12-02-2009, 01:37 AM
They are sonys so I'm assuming they will cook lol.

pieper88
12-02-2009, 01:39 AM
Yeah I don't see sonys handling that much.

kraudio12
12-02-2009, 01:51 AM
sorry for post dumping but same question but what about a set of eclipses think they can handle 80 lol sorry again

pieper88
12-02-2009, 01:53 AM
again need for info model number, ratings, etc

SicAudio
12-02-2009, 01:59 AM
yeah sonys cook at rms power with true wattage lolz

DNick454
12-02-2009, 01:13 PM
yeah sonys cook at rms power with true wattage lolz

Troof ^^^


Sony rates their **** in "theoretical watts" assuming a bunch of bullshit variables that most people would never consider.

When TRUE actual power is given to those things they go :banghead:

RebelExtrm02
12-02-2009, 01:21 PM
Couldn't I just set the gains on the amp low to limit the current available to them? Each channel on the amp (front/rear) has its own input level control. Is input level even the same thing as a gain control? The amp is this amp Infinity 475a (http://www.sonicelectronix.com/item_9712_Infinity+Reference+475a.html)

Idealrealist
12-02-2009, 01:26 PM
After inpendance rise you'll be closer to 40w.
Just take it easy on the gain, you'll be fine.

eharri3
12-02-2009, 10:45 PM
Power doesn't kill speakers, people do.

RebelExtrm02
12-03-2009, 03:33 PM
Power doesn't kill speakers, people do.

I've kinda always pondered that. I know sony's are pretty much the low end of low but I'd still be interested in knowing if the ones that died at rated rms wattages also had all the other settings such as gain and whatnot set right to keep them from distorting to pieces. :/

I'm still debating hooking this amp up to them or just leaving them run off the head unit and selling the amp for a mono block and only amping the sub... I'm getting pretty mixed opinions here.

joeybutts
12-03-2009, 03:59 PM
remember. Your speakers will only see the wattage that you allow them, no matter what you set the amp to. AKA, your volume knob is a voltage control, so if you set your volume knob to send enough voltage for your amp to produce 75 watts it will make 75 watts.

Speakers will let you know when they have reached their power handling given the alignment they are in. 95% of people have NO idea how much power they are ACTUALLY sending. Of course a lot of people don't own a clamp meter.....

and headroom is always a good thing....

stocker08
12-04-2009, 02:05 AM
They would probably take it as long as you dont crank the volume. I have my rear stock speakers taking about 90 watts.

supermaxx123
12-04-2009, 02:52 AM
yeah more info. i run 90 rms to my 40 rms mbquarts but they are quarts they can take it a 40 rms polk, pioneer ect would cook.

so is your amp stuck on 90rms output?

joeybutts
12-04-2009, 11:47 AM
so is your amp stuck on 90rms output?

He must run the same volume constantly.....:laugh: It amazes me that people don't understand the basics of electronics.....

RebelExtrm02
12-04-2009, 12:43 PM
He must run the same volume constantly.....:laugh: It amazes me that people don't understand the basics of electronics.....

So would a clamp meter be the only way to tell at what volume the rated/max rms of the amp is being sent (or received by the speakers)? Or is it like max volume? I'm assuming it's the former as the latter seems too simple :p

A clamp meter looks fun. I like gadgets. :D

joeybutts
12-04-2009, 01:23 PM
I think that is the only RELIABLE way since different frequencies will cause the speaker to have different impedances and the source could ask of the equipment to produce different volumes, so the impedance and wattage is constantly changing. Also, who knows what type of enclosure the speaker is being set into so that can change the amount of power handling capability a speaker has as well.

LOTS of variables. :)

you can use a DMM to estimate the power being sent which will put you in the ballpark but can still be off by 100's of watts at worst, 10's of watts at best. Some people will use a dmm with a tone to set a certain wattage. I've done this before, but find doing it by ear easier, quicker, and usually allows you a better sense of what you are capable of running without actually knowing the number.

http://en.wikipedia.org/wiki/Current_clamp

Some good quick reading.

eharri3
12-05-2009, 11:23 AM
I've kinda always pondered that. I know sony's are pretty much the low end of low but I'd still be interested in knowing if the ones that died at rated rms wattages also had all the other settings such as gain and whatnot set right to keep them from distorting to pieces. :/

I'm still debating hooking this amp up to them or just leaving them run off the head unit and selling the amp for a mono block and only amping the sub... I'm getting pretty mixed opinions here.


Common practice in many car audio shops and chain stores is to try to get people focused on closely matching wattage ratings on amps and speakers. This is very likely because staff is afraid that if they enlighten the masses about the benefits of lots of overhead and explain how meaningless rms ratings can be if you know what you're doing, there will be less room for error when people go home and start doing silly things with the controls. As a result, they'll have more blown speakers coming back.

Understand, if a given amp is rated for 75 watts rms it does not mean that it is putting 75 watts to a speaker 100% of the time. These amps are usually rated with input voltages that most stock electrical systems won't deliver,
using test tones that don't represent what the amp will do when it's playing music. Depending on gain, the music, and the volume level, at times, your amp may be delivering as few as 1-15 watts or as much as 50-60. It will reach 75 watts if you have an upgraded electrical system capable of pushing it to its full capabilities, the volume dial is at the maximum undistorted level, and you've reached a musical peak that matches the volume level of an unattenuated test tone. About how often do do you think all of these stars will align while you're driving around listening to your system?

I'll tell you: All the time if you set the gain to high, regularly go above that with the volume dial, and boost signal, which alot of people do. This is why most shops will strongly discourage a package deal involving an amp making too much more rms wattage than the speaker is rated for and will incorrectly tell you this is always a no-no. This misinformation gets around, and now everybody thinks it's better to match watts exactly down to a fraction of a watt then turn gains up and boost signal when it's not loud enough, rather than to safely exceed the speaker's ratings and give yourself more loudness without sacrificing clear volume.

You may never see all of that amp's power if you set your gains properly and avoid over-boosting at the head unit, which is why it's not uncommon for people on here to run 2-3 times a speaker's rms rating with no problems. Meanwhile many who match rms ratings end up disappointed with their system's loudness.

It is possible that your amp could be rated at 75 watts rms but never, ever actually deliver that to a speaker for as long as you run it. Even if your amp can do an honest 75 watts rms and your speaker is rated for 40, most of the time that speaker may see an average wattage that doesn't exceed its rating by much. If it does exceed it, it probably only does for a brief instant before going back down because as the loudness of the music changes the wattage being delivered changes. Where you get into trouble is when a combination of bad adjustments causes you to deliver more 'dirty' power to the speaker than it's rms rating for extended amounts of time. Even a little bit of a clipped signal is extremely powerful and can put you way above the speaker's rating more quickly than running clean power at or above the speaker's rating at moderate volumes.

Dial back the gain if you hear something wrong and make further adjustments at the volume dial as needed when playing a louder recording and you will be fine. You may also have to run your high pass filter a bit higher than the standard 75-80 hertz.

Sir-Lancelot
12-05-2009, 11:59 AM
Set your gains, crank them up and listen. Listen to them. if they sound bad they didnt like your settings. Easy.