need stereo aplifier for 4 2" 5Watt 8Ohm driver speakers.

[johnathon007]

I know you are probably tired of answering my questions but what would a good sensitivity be for a 4" woofer to run fairly loud at 20 feet or more if possible ? And what kind of amp am i looking at [if its huge ill probably just buy one]? power isnt really a problem becuase i have over 100 rechargable batteries laying around here [im going to need a charging circuit for them but ill worry about that when i get to that part]

Edit > i found a calculator but i think it might be having problems it said i would need 1000 watt apm to run a single 25 watt speaker 1 foot from me with a 89DB SPL, i think something has to be wrong with that calculator becuase my car system has a 5k watt amp and you can hear it for over a 1/4 mile when i turn it up.

 

[transistor495]

You're complicating the things up! 5kilowatt amp means 5000watts PMPO? Nowadays 1000W desktop speakers can be suspected of using a crap TDA2822 inside.

First describe elaborately about your application( What you are going to do?) and scenarios. Second buy the speakers immediately(!!) so that we can start of discussing about the required driver circuit.

 

[johnathon007]

Im just looking for an all around OK sounding stereo to use boombox style with a left and right 4" speaker and 1" tweeter, this is more about building it and it working then really using it much i have an old stereo i was going to use for testing my speakers before i worried about a driver circuit and to get my crossover designed and working and im also working with a budget of as little as possible up to $40 [i know its asking a lot to do this for that but i do have everything but the speakers and some driver components already] The speakers im looking at are out of stock on the website im using and wont be back for a week. And i think im having trouble with the watts not all being the same unit of measurement or something between the speaker ratings and amp ratings, but i still have trouble understanding how 5000 watts in my car is so loud but the sound calculator i found says i need to be within 1 foot of a 4" speaker to hear it at 5000 watts. I hope this helped clear things up.

 

[Nigel Goodwin]

And i think im having trouble with the watts not all being the same unit of measurement or something between the speaker ratings and amp ratings, but i still have trouble understanding how 5000 watts in my car is so loud but the sound calculator i found says i need to be within 1 foot of a 4" speaker to hear it at 5000 watts. I hope this helped clear things up.

Well it's unlikely your car amp is 5000W, they are generally highly imaginary specifications.

I've no idea what this 'calculator' is?, or why you would be playing with it? - but the speaker has a certain RMS power specification, just build an amp of that RMS power (or slightly less). Power is directly related to the power supply, off of a car battery (13.8V) you can only get 4W to a 4 ohm speaker from a single ended amplifier.

 

[johnathon007]

here is the wattage calculator i was talking about **broken link removed**

 

[audioguru]

Most little 4" woofers have a sensitivity of only 86dB/W at a distance of 1m.
Fostex have a pretty good one FW108N (it is fairly expensive) $117.70US each that has a max allowed continuous power of 17W.
It needs a fairly large enclosure for bass down to 55Hz.

You want it to play fairly loud at a distance of 20 feet which is 6m.
For an amplifier to produce 17W into 8 ohms it could be bridged then it will need a supply of about 20V (sixteen AA Ni-MH cells in series).
So 86dB at 1W and 1m.
Then 98dB at 17W and 1m.
Then 82dB at 17W and 6m. Not fairly loud. Two woofers produce 85dB which is slightly louder. This is the sound level of the peaks of music. Average levels are much lower.

 

[Nigel Goodwin]

here is the wattage calculator i was talking about **broken link removed**

And it's completely rubbish!.

 

[transistor495]

Well, stick on to the RMS specifications of audio.

Your budget is fairly low however the key is to get the best one at that price.

 

[audioguru]

Years ago I bought a pair of RadioShack Minimus 7 speakers on sale. They were in small cast aluminum sealed enclosures with a 4" long-throw woofer and a dome tweeter.
Their response was flat down to 100Hz with some output as low as 50Hz. They were rated at 40W (40 Whats).

I used them for years with a low power amplifier then I connected them to my home stereo which had an output of 70W per channel. One woofer burned out and when I looked inside the woofer was stamped "Korea, nominal 5W". The replacement woofer was inexpensive and was also stamped "Korea, nominal 5W".

 

[transistor495]

It is a question that why you connected it to your 70W hi-fi? But I can understand that everybody do it at times. You connected 40W PMPO to 70WRMS ?

 

[audioguru]

It is a question that why you connected it to your 70W hi-fi? But I can understand that everybody do it at times. You connected 40W PMPO to 70WRMS ?

I hardly ever play my stereo at full blast. I know that 40W is only slightly less loudness than 70W so I thought the "40W" speakers would survive.
I didn't know that RadioShack lied about their power rating that was actually only 5W.