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Subject: Blowing Speakers
Ya'll have a great site, I thought I knew a lot before, but not until I visited y'all I have 2, 3-way speakers that I am afraid I blew or popped. They are 10". I have never popped any speakers before, so I don't know how I did it, or if I really did, but they are very distorted and don't hit as hard as they used to.
I am running a Pioneer receiver that is 180Watts I think. I need to know if I can put the Mobile Authority 10" sub in place of mine if they really did blow. If not the Mobile Authority would anything else work. Can you also tell me what wattage to look for so they will still hit pretty hard and not need a lot of power. Also, tell me how not to blow me speakers in the future.

Thank You A lot,
Patrick

Dear Patrick,
Thanks for the compliment!

DISCONTINUE using the speakers immediately until you can ascertain whether they are in fact, defective. Shorted voice coils, or scraping of the form against the magnet structure, will short circuit and damage your receiver/amplifier.

The important specification in your Pioneer receiver is the power output per channel rated in RMS. It is probable that the figure of 180 watts is the peak output, which means the actual output in RMS is more like 90 watts. Divide this into 4 channels (I assume it is a 4 channel unit) and the actual power output is 22.5 watts per channel RMS. This is still pretty respectable however, if you are using regular 4" to 6.5" car speakers, or even 6 x 9's.

But, if you have these 10's in a box, and you are trying to make the big bass sound, you will definitely need a power amp to go with the speakers. The receiver alone is simply inadequate for that purpose. For most 10 inch speakers an amp rated at 100 to 200 watts peak ( or 50 to 100 watts RMS) should do the trick. They should be compatible with the requirements of the woofer to within 65 to 110 percent of its rated handling power.

Good Luck with your system!

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Subject: Eliminating Unwanted Noise
I just bought an amp, but I have alternator whining. I put the RCA and remote turn on down the driver's side of my car and the power cable direct from the battery down the other side. Would a filter fix the problem or did I do something else wrong?

Thank You,
Jason

Dear Jason,
Yes, a power line filter may solve the problem. But before you go to that expense, check a few other things first.

After you have determined that there is noise in the system, determine if the amplifier is causing the noise. To do this, mute the signal at the inputs to the amp by disconnecting the input cable and turning down the gain (volume) controls. If there is no noise, then the amp is fine. However, if there is noise, then use a test speaker at the amp's output. If this stops the noise, then the problem is originating in the speaker wiring, or the passive crossovers. Check to make sure that none of these are shorting with the body of the car, and try it again. If noise is still present when using the test speaker, then there may be a problem with the power supply on the amp.

Try isolating the power supply by turning off the engine - if this does not get rid of the noise, then there is something seriously wrong with the amp, and it should be replaced. If the noise goes away, then there may be a problem with power supply filtering or isolation. This can be fixed by changing the amp's ground point or by adding external supply filtering.

1. Make sure your amp is properly grounded to a heavy frame part with adequate gauge wire.

2. If the noise is present in the system's other speakers connected to your receiver, then the car's power system is definitely involved.

There are many popular noise suppression systems on the market ranging from a simple capacitor to an elaborate filtering circuit. Since the noise source is seldom known with precision, try the simplest and least expensive solution first. A non-polarized 50 mfd. 50 volt electrolytic capacitor costing about $1.50 may do it. Try installing this directly on the alternator output terminal. Since its non polarized, either end may be used.

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Subject: What Is Gained By Adding Subwoofers
How can I figure out how much increase in SPL will my system gain by adding a second subwoofer?

Example: If I have a subwoofer that will put out 120db with the power that I feed to it, What will the db gain be by adding the second identical subwoofer with the same amount of power?

Thank you.
Eric

Dear Eric,
I would like to offer you a simple mathematical formula in which all you have to do is enter in the specifications for your system and then hit "compute." I'd like to, but I can't. Because, what we are dealing with here is an acoustical question. And unfortunately the science of acoustics is a lot like economics. There are so many variables to consider that any sort of prediction of even a very general outcome is fraught with uncertainty.

It would seem that merely adding another woofer to a system would simply double the sound pressure level in the listening space. However there is a peculiar quality to the production of low level bass effects that is called phase cancellation. It can be produced by the action of the woofer directly, or as the consequence of an improper enclosure, or as a result of room (interior) reflections. Anytime that frequencies below 100 Hz are produced, even by just one woofer, cancellation can become a factor. So when you have 2 or more subwoofers, a situation can easily arise wherein you can have effectively less, rather than more, bass energy produced. How to proceed...

In a word, EXPERIMENT! There are many methods of dealing with phase cancellation. If you do not use the services of a good professional installer, you will need an audio generator, and a sound level meter at a minimum. Two controllable variables are: the electrical polarities (the + and - on the input terminals) and the position of the enclosure in the listening area.

In fact, before you buy that next sub (unless you're buying it from us, of course) I recommend that you experiment with those two factors in your existing sub, if you believe the bass to be inadequate. Good Luck! If you have additional questions, please let us know.

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Subject: Elevated Woofer Cone
I have a question about an audio Situation. Here is my problem. I just recently bought a Pyramid 1800 watt amp and 2 Rockford Fosgate 12" hx2. I've got them all hooked up. I checked and double checked my connections and they are right. I turn on my radio and one subwoofer's cone sticks up ½" higher than the other. Naturally I checked to see if its the sub. So I switch the subs channels. The opposite sub is now ½" higher. Now I know the amp is causing the problem. My question is why this is happening and how do I stop it? If you are confused about what I'm telling you just tell me and I'll try to explain myself better. Please email me back.

Thank you.
Stephen

Dear Stephen,
Your analytical approach cannot be faulted. You just need to take the additional step to see if the same symptom recurs if you first reverse, then unplug, the Line inputs to the amplifier. What you are seeing is either an extremely high ultra sonic frequency played extremely loud, or (more likely) the presence of DC in the output, indicating a shorted amp. The presence of a DC component in the input signal could cause this, as could a failure in the amplifier. Frankly, that is the more likely problem, however.

Possible causes of failure apart from internal faults, may be any or some combination of the following:

1. Connection to speaker with an improper impedance. 4 ohm is usually optimal.

2. Playing low frequency high volume program with the gain and loudness set too high.

3. Power feed cable too small for amp demand.

If the damage is confirmed to be in the amplifier, you will need to have it repaired.

DO NOT USE THIS UNIT! It will damage your speaker.

Good Luck!

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