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Amp and Speaker requirements...

I have a jukebox with a 140w amp, and picked up a 750rms / 300w speaker. will it work or ?

thx



Re: Amp and Speaker requirements...

It will probably work just fine. Saying the speaker is a "700w" speaker only talks about it's power handling capacity to some degree, it could be an amazingly efficient, or horribly inefficient speaker for all we know.

Pay attention to the speakers rated impedance and insure it is in the ball park.

You can go the other way too and run a "50w" speaker with your 140 watt amp too. Music is very dynamic and actual average power is FAR under the peak power. As long as the audio sounds good, the speaker won't be damaged.

In general, I pay little attention to speaker power ratings, except perhaps for live sound applications where they are run hard. Also I have seen more speakers damaged by a under sized amp being run into distortion then when using an amp that is far oversized.

Re: Amp and Speaker requirements...

The correct spec's are actually...

140w tube amp, 750rms / 300w speaker.

And to make matters worst the 140w marked on the amp is the power consumption, the actual output is 19w. This if for a juke box that only has this one speaker.

Thoughts?

JB Wright's picture

Re: Amp and Speaker requirements...

I wouldn't recommend using a speaker that requires much more than half of the amplifiers output. A 140w amplifier will be working way too hard to drive said speaker (kind of like putting a underpowered engine in a vehicle and then drive up a mountain using the air conditioner).

Ideally what you want is just the opposite of what you have. You really can't have too much power, the wonder motor we rely on to faithfully reproduce our favorite sounds (the speaker) may well be one of the least efficient electronic devices we can buy. Don't quote me on this, if I'm wrong, someone let me know, to my recollection, the efficiency of a speaker is around 3-4%. Whatever the volume you are accustomed to you will listen to so if you don't turn it 'up' you will probably be okay, but what are the odds of that happening with a Jukebox?

If this is like most Jukeboxes I have seen, it probably has multiple speakers that need to work together. Your safest bet is likely to match your speaker as closely to the original as possible

Re: Amp and Speaker requirements...

Actually the rms is 750, but its only 300watts. I dont understand how a speaker can overload an amp. Speaker can only be fed what the amp outputs? And speakers cant demand more. I would think it would be like a car that can only go up to 60mph. U can floor it but thats as fast as it can go even though the max highway speed is 80

Thoughts?

JB Wright's picture

Re: Amp and Speaker requirements...

Speakers are among (if not) the most inefficient electronic items money can buy, the amplifier has this against it from the start. The speaker does not "overdrive" the amp, it's something closer to 'over-loading' the amp. The amplifier's job is more than just 'driving' the speaker, the amp has to maintain control of the speaker. This means the amplifier must cycle the speaker anywhere from (give or take (in that order) 20hz-20,000hz, that translates to 20-20,000 cycles per second. Not only that, it has to do this with several frequencies at the same time.

Given the inefficient nature of speakers, the more power an amplifier has the more and better control over the speaker it will have. At higher volume an under-powered amplifier can 'lose control' and damage the speaker. Hope this clarifies my initial response

Re: Amp and Speaker requirements...

Thanks for the reply but could you please explain this...

You stated...
At higher volume an under-powered amp can 'lose control' and damage the speaker.

If that is the case then any stereo running at a low volume would damage the speakers, but as a teen I worked at supermarket where the stereo system was run at a very very low volume for background music. Then at the end of the day when the customers were gone they would pump it up while things were stocked and cleaned. No speaker damage.

JB Wright's picture

Re: Amp and Speaker requirements...

A stereo system's speakers working at low volumes does not take a significant amount of power, I routinely listen to music at moderately loud volumes in my wood shop and my VU meters show that I am using not much more than 20 watts peak power and the sound is quite good and clean. This would be operating at about half volume on my Fisher Studio Standard amplifier which is rated at 35w per channel. Playing music as described does not create a significant load on the amplifier.

However as I turn the volume up closer to 3/4 I average 15-20 watts and the peak power consumption easily pegs the 35 watt mark, the sound becomes less clear and is discernibly stressed. This deterioration in sound quality is because I am working the amplifier near or at it's maximum output capacity, the amplifier is using all it has just to push the volume so the sound begins to lose definition. The speakers I use in my shop are KLH 900B with a minimum rating of 5 watts and a maximum rating of 140 watts.

Now if I had these same speakers hooked up to my 600 watt Sony AV Receiver set to two channel stereo, I'd have 300 watts of peak power to work with for each channel. Now here is where I will try to clarify; I will still only need 10-20 watts to listen to them at the same moderately loud volume as indicated I routinely listen to. Listening to them at volumes equivalent to what I can get out of the Fisher at 3/4 still leaves the amplifier with between 230-240 watts of power per channel that is not even being used, this amplifier is clearly (pun intended) not working hard and has good clear sound with excellent definition. Well certainly as good of definition as this mid level AV receiver is capable of with said speakers

Re: Amp and Speaker requirements...

If the impedance is correct it will work, but won't be very efficient. I would look for something in the 150 watt range.