I have a '95 F150 with the basic stock FM radio/cassette player, not the fancier version. I get a lot of buzzing/static in the speakers. These are the stock speakers in the rear pillars. The measure 8 x 5.75 OD, but I suspect the actual speaker is probably 5 x 7. I have been cranking them up to about 12 out of a total 15 bars on the volume and on some songs boost the bass nearly as much. Probably over powering them. Anyway, I pulled the speakers from the back of the motorhome, which are nearly identical and are Ford speakers, just from a year 2000 and differnet connector clip. Still buzzing.

So the big question is can I pick up a new set of speakers, say 50 watt each or something and drive them with the stock head unit? Will it have enough power? What is the likelyhood that my stock speakers are okay and its the head unit that is bad? Some music plays pretty clear (usually well engineered studio stuff) other makes the buzz/static like live performances or studio where the bass is too heavy and I have to back it off.

Finally, I am running a MP3 player through a radio transmitter into my FM. If I had speakers that included their own amps and had a headphone jack (like computer speakers, though I believe those would not work in a car very well), I could just skip the head unit and run the MP3 direct into the speakers. Do they make speakers like that?

Simplest seems to just pop a new set of speakers in, but if my running the headunit too high of volume is going to trash them then it's not worth it.

Thanks for any input. Again I want to keep it simple and minimize cost.

 

5x7's are mid and high range (supposedly) speakers. They should not be forced to produce much bass (the 20-80Hz range), this is probably where you're running into the noise, the speaker just isn't designed to clearly reproduce those freqs. Popping in another set of full range speakers will not help out much since they are usually capped at 80-200hz on the bottom end. My suggestion would be to get a subwoofer to handle the 20-80hz bass and to take the strain off the mid range speakers.

I haven't seen integrated speaker/amps for mid-range. MTX and I'm sure others make bass packages with fitted boxes, speakers and internal amp. You can always use an amp to power your speakers, then use your MP3 player as the input source. It would take a little work to get the gains and volume just right every time, but it works.

 

I've got a 100 watt amp but the fuse holder is partly melted. I got it second hand, so don't know if it is okay or not. Guess I could try it. I am currently running the stock front speakers and a single 8 ohm (stock were 4 ohm) cabinet speaker with a 5.5" woofer and that gets much better base than the 5x7s probably because of the box, but not enough power. Also, the 5x7 is running with both channels into one speaker--was hoping for higher output, but doesn't seem to work. All I know is that with the stereo turned on I get just under 6 volts at the speaker output, regardless of moving the balance or F-R adjustments.

Saw somewhere that I could get a powered equalizer and run the MP3 direct into that instead of a head unit.

 

Two channels into one speaker? That's not likely to work, and could damage something in the radio or amp.

Powered equalizer, or an amp, and run the MP3 directly? That's what I've mostly done. $20 ought to get you a good used amp if you shop at the right yard sale.

Or, stop messing around and get a 4 channel amp and power a sub (bridged) and two speakers. That should satisfy your need for bass.

 

Tried the two channels into one speaker. Did not increase volume.

I have to give the 100 watt amp a try. See what it sounds like, then maybe get some better speakers.

I can get a nice looking amp for around $15 off ebay, just not sure if it's any good. Here it is:

http://http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260439914827&ssPageNam e=STRK:MEWAX:IT

Should be better picture of it here:
http://http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=120451302827&ssPageNam e=ADME:X:AAQ:US:1123

I emailed the seller for this second one and was told 20 watts per channel.

"Thank you for your enquiry!
its output is 2*20W and its RMS is 4 Ohm
The input power supply is 12V/5A"

This would simply replace my head unit. I like that it has three big *****, bass, volume, and treble. These are all I really need to mess with and ***** make it easy while driving.

Look at the listed specs and if you think this would be a decent improvement over the stock radio, I'll go for it. I don't need deck rattling bass, just decent sound quality at highway speed with good volume, not to destroy my ears, but I do like it relatively loud.

 

20watts isn't going to be much improvement over the OE headunit and that's assuming it can reach that figure. It's only taking in 60watts, and a good class D amp would be capable of 30watts total rms output. A cheap amp will be closer 10watts per channel which the factory headunit should be able to do.

 

Now I am thinking if I can open it up and hook leads into the Amp imputs for the MP3, or better yet, hook in before the volume control, but finding those connections could be impossible on a digital radio wo wire diagram. Of course would need a switch or else eliminate the radio connection.

 

There is trying to get away cheap and there is asking for headaches. For now it sounds like your FM modulator will provide better sound than the speakers can produce. Fix one problem at a time and life will be simplier, put in an amp and sub to handle the low freq, and half decent mid range speakers for the rest.

Once you have the ability to produce the dynamic range your looking for, then start on the input sources. The FM modulator you have will give you the same dynamic range as FM radio, CD's have a little more range, but it's not full 20Hz-20kHz. I think the CD's that created your mp3s had a range of 25Hz-16kHz and radio is something like 80Hz to 12kHz. You're going 2 octaves lower and 1/3 octave higher with CD mastered audio. Now it was analog mastered Lossless audio that's a different matter, but that is kind of rare.

 

My weekend project is to set up the 100 watt amp. Got a new fuse holder. Will back down to a 10 amp fuse and see if it works. Had a 15 amp fuse in it when I bought it.

 

WOW! I have great sound now. I hooked up the 100 watt Radio Shack amp with two cabinet speakers on the back floor. Running the MP3 direct into the amp with RCA plugs on an adapter out the headphone jack. Sound is phemonenal, even sounds clear with the MP3 volume nearly all the way up.

I guess I was scared to use the amp because of the partly melted fuse holder but I replaced that and noticed the old fuse holder did not hold the fuse tightly, which may have been the reason it was partly melted.

I am debating whether to hook the rear pillar mound speakers to the amp instead of the cabinets. Not sure I will get all the base of the cabinets, but I do recall the pillar mount was much louder under the old setup, so worth a try. Else I have to decide on the Scotts or the motorhome speakers rigged into the Scott cabinets--I have one of each right now, a 4 ohm on right and an 8 ohm on left.

 

Stock pillar mound speakers are hooked up and sound great. I am wondering if I have to limit to 2/3 volume on the MP3 player, or since it does not have a pre-amp (can't with nothing but a AAA battery), then it is not putting in a huge signal, so likely the amp is nowhere near full power at 2/3 MP3 volume. I think I can test it by measuring volts and ohms at the speaker terminal and the equation Amps = Volts / Ohms and then Watts = amps * volts to determine the output wattage of a particular setting. Would guess have to do it with the speakers disconnected.

 

Depends on the gain in the amp. I usually find 3/4 volume on the source then control the amplifier to produce the volume I like. It tends to keep the clipping to a minimum.

How do you have the MP3 wired in? Is it direct to the amp inputs? If so, I would set the Amp's gain to not clip at your max listening volume. Then you're pretty well set for partial volume sound.

 

MP3 is wired in with an adapter that one end plugs into the headphone jack of the MP3 and the other end is RCA plugs. The RCA plugs are connected to the Low Input terminals of the amp. Amp also has High Imput for speaker wires to connect as input. So I guess the low input is prior to the head units amp, but a head unit may have a pre-amp of some sort.

Not sure what gain is in an amp. There is a level control for adjusting the level of the input signal. The amp gets somewhat louder when I turn Level up. If that is gain, I could set it to lowest setting, then run MP3 up to say 3/4 volume or so. OTOH, I could treat the Level control as a sort of pre-amp, turn it all the way up, then not turn up the MP3 as much. Probalby 6 of one and half dozen the other

Well I probably wouldn't know clipping if I heard it. What does it sound like? Also I guess I don't care if it clips so long as I don't notice a degadation in the music quality, but what I don't want is to burn out the amp or blow the speakers.

Probably best keeping it at 21 out of 31 (about 2/3) and jacking it to 25 for songs recorded at lower volume, and dropping it to about 18 for songs recorded too loudly. Seems that would even out the input signal and any higher volume is not going to be good for my ears. Not sure these volumes are that good for my ears.

Well, what am I worried for, the amp cost me $2, so what if I blow it. Also I have a spare set of similar speakers. Still, to replace the amp is not cheap, saw same amp on internet listing used for $75!

 

Gain is a simple term for how much the voltage gets amplified, and it's the same thing as the level. Kind of like you were saying about testing it with a voltmeter, the amp mutliplies the voltage up to a certain level. Once it reaches that level it's done all it can, but the sound gets flattened out rather than staying a wave.

Say your 100watt amp is running 4ohm speakers, then p=e*e/r for 100=e*e/4 or 400=e*e so square root of 400 is 20. This makes the max voltage the amp can produce 20Vac. If your input is 1.5v, then the amp has to have a gain of 13.3x to reach the 20v. If you go above 13.3x it will clip as the amp can't produce 21vac. The amp will probably survive clipping, but it will damage the speakers.

If any of this makes sense to you, you're doing pretty good.

 

ReAX,

With LEVEL set at 2/3, I put a 2 amp fuse in the amplifier and raised the volume. The fuse blew at 81 percent of full volume. With a 3 amp fuse it blew at 91 percent of full volume. Since the engine was off, it was battery voltage measured as 12.65. Therefore,

81% volume was approx 25 watts or 12.5 per channel.

87% volume was approx 38 watts or 19 per channel.

This was done with one of the loudest albums I have, so the actual speaker output was much higher than I would listen to (ear preservation, not dislike of high volume).

Anyway, I put a 5 amp fuse in the amplifier and figure that will protect me:

Using alternator voltage estimated 14.4, the 5 amp fuse should blow around 72 watts (36 per channel), but again, I am unlikely to listen to anything that loud for very long (maybe for a guitar solo).

Seems I am all set, but I'd love to hear your comments on this unorthodox method of evaluating amplifier output wattage.

I don't fully understand your message, but am running 4 ohm speakers. I can measure output with the AC voltage setting on the tester and see if it jumps past 20 volts, or would that be 10 volts on one channel? Do I measure the voltage with the speaker hooked up or unhooked?

Thanks much.