Audio Systems: Car Amp and Sub, watts rms, inch subs

Question
QUESTION: Im thinking about getting an amp,(http://www.allaudioexpo.com/nav/details.asp?itemid=2025&catid=68) but im not sure how big of subs(watt rating wise)i should get? i do know that i want 12's. also i want to be able to crank up the volume without distortion, should i get 1 or 2 subs? would (http://www.allaudioexpo.com/nav/details.asp?itemid=120&catid=175) those subs be a perfect match for the amp above? if not, how many watts RMS do i need to look for in the subs? im most likely going to be getting that amp, im just having trouble determineing how big of sub i should get (watt rating wise).

ANSWER: I don't like to give equipment recommendations because there are so many subjective factors involved.   Further, in order to give recommendations it would be necessary to know the vehicle you are installing them in.

The performance of subs can make a very great difference in the overall acoustic and music quality of the system.  The performance of the sub system is greatly effected by the internal acoustic space of the vehicle and the loading (enclosure) of the sub speakers.  These two factors are much more important than raw amplifier power.

The 12 inch subs you refer to are fine drivers, but they will not do much without being mounted in the right enclosure and acoustic loading.  You can tell me about that and I can give you my judgment as to their efficacy.

Amplifier power, by the way, is not in rms watts.  There is no such thing as rms watts even though amplifier and speaker manufacturers improperly use the term.  The proper term is continuous average power.  In any event, you will need a big power amplifier to drive the speakers because they are only 89db sensitive, which is not too high. The one you have selected is sufficient if the speaker loading is optimum.

But the amp and speakers you have chosen are able to produce good, chest vibrating and heart thumping bass if they are properly mated and loaded.  Will they produce exactly what you are expecting?  Only if the loading on the woofers are optimized and the acoustic space of the automobile are all properly matched up.

Please check with the driver manufacturer for proper enclosure or loading ideas.  If they don't have any help for you try www.crutchfield.com who lists many types of enclosures. They also have technical assistance that may be able to give you some recommendations for your system.

All the best,
C


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QUESTION: Ill be putting this in a !987 Ford Ranger XLT Single Cab. And Could You PLease Explain The 89dB Sensitive thing? Also How Big of a Box Shhould I Make. I was thinkin a Trapazoid type box with a height of 18" width at the bottom of 8" and a width at the top of 6" and a length of 36", and i was gonna make it a sealed box. Woudlt that be sufficeint? Also how many dB Sensitive should i go?
ANSWER: Sensitivity figure is how much output does the speaker give with 1 watt of power input to it.  Each 3db is two times power.  So, if you had, for example, a sensitivity of 3 db more or 92db it would take half as much electrical power to obtain that.  Nothing wrong with an 89db sub. It is pretty good, actually, but there are ones with higher and ones with lower ratings.  It just means you will need to put in a little more power to get out what you would get with a higher sensitivity figure.

I could not find the technical parameters on the woofer you have in mind.  The free air resonance, Qas and a few other technical details are necessary for plugging into box design computer programs.  I called the company ( Phone: 718-534-1811) to get the technical information but there was no answer;  I left a message but they have not returned my call.

However, your box is a little over 2 cubic feet which would be sufficient for most 12 inch sealed subs.  If you are planning on putting both 12 inch subs in that box it is a little over 1 cubic foot per each - which is a little small.  My opinion is you would get better performance in that box with just one woofer than with two.

Finally, the pickup truck is a rather small total acoustic space, so don't expect miracles.  It should be okey, especially since the driver and passenger are with in the pressure field of the woofer.

If I get more information back from AllAudio I will let you know.

Hope this helps further.
C

PS:  By the way, here is a box design for a pair of 10" units for use in pickup trucks.  I have not tested this design but it looks good.  A good pair of 10s in a box this size will usually give better performance at the low end than 12s.

http://www.decware.com/tbk10.htm

Here is a good primer:

http://www.termpro.com/articles/buildbox.html

Another tutorial:

http://www.caraudiohelp.com/custom_car_audio_boxes/custom_car_audio_boxes.htm

Crutchfield primer:

http://www.crutchfieldadvisor.com/ISEO-rgbtcspd/reviews/20030701/custom_or_prefa

Design software (advanced):

http://www.ajdesigner.com/speaker/index.php

End


---------- FOLLOW-UP ----------

QUESTION: i determined that its approx 2.3 CU.FT which i read that it was just a little to small for 2 12's? should i just get two 10's? wih that same amp? (http://www.allaudioexpo.com/nav/details.asp?itemid=2277&catid=174) or (http://www.allaudioexpo.com/nav/details.asp?itemid=1993&catid=174) or (http://www.allaudioexpo.com/nav/details.asp?itemid=628&catid=174) would either of those work with the amp im planning on getting? which ones would you recomend? also i was looking at capacitors, and i found one thats 1.5 farads (http://www.allaudioexpo.com/nav/details.asp?itemid=2001&catid=105) would that be suffiecient enough to keep my headlights from dimming? also im gonna buy a pair of 6x9's to put in place of the two rear speakers that are hooked up to just the head unit (http://www.allaudioexpo.com/nav/details.asp?itemid=1188&catid=93) or (http://www.allaudioexpo.com/nav/details.asp?itemid=170&catid=93) which would you recomend? also 4AWG wire for my amp should be big enough right? and how big of a inline fuse should i get?

Answer
Too many questions for me right now. I have so many other questions waiting for me from other correspondence and  a couple of big projects to work on. So, please forgive me. I will try to get back to you tomorrow or the next day.

Don't hesitate to try one of the other audio experts if you are in a hurry.

Thanks for your patience.
C