Page 1 of 1 [ 2 posts ] 

lowfreq50
Veteran
Veteran

User avatar

Joined: 1 May 2005
Gender: Male
Posts: 1,536
Location: Gainesville, Florida

30 Jul 2006, 1:09 pm

I wasn't sure if this should be in the tech forum, or music forum, or entertainment forum. I'll start here and see what responses I get.


Recently I took the Alpine CDM-9801 head unit out of my car and installed it in my truck. IT sounds very much better than the factory stereo but now I need new speakers.

My 2-door Ford Ranger uses four 6"x8" speakers. I was looking at Crutchfield.com and it seems that most 6"x8"s are smaller speakers (e.g. 5"x7") that have an adapter to fit in a 6"x8" speaker mount. Pioneer and a smaller number of others make true 6"x8"s, and I believe it is best to get the true size instead of a smaller speaker.

I am looking at the Pioneer TS-A6871R speakers, but I really am unsure of what speakers will get the most volume+quality from my head unit. These particular speakers are a 3-way coaxial design, have a power range of 2-50 watts RMS, and a sensitivity of 90 dB.

My head unit is only 45W x 4, and i'm not amping it. So at peak it is sending ~10 watts per channel, which falls within the power range of the aforementioned speakers. A sensitivity of 90 dB is on the higher end of that range, so I think that should be sensitive enough to get good volume from a 45W x 4 head unit.

I'd like to get some second opinions, some personal experiences, etc. to help me decide if I am making the right speaker choice.



AV-geek
Veteran
Veteran

User avatar

Joined: 14 Feb 2006
Age: 49
Gender: Male
Posts: 614

02 Aug 2006, 11:21 pm

Don't look at the wattage handling number as much if you are concerned about loudness!

This number ONLY tells you what the speakers can take. The number you want to look at is the efficiency number, that 90 db number is not a bad rating. The second number to look at is the frequency response. A good speaker design has a wide frequency response, and a high db number in watts. Frequency response however is highly subjective. One thing that is not frequently published in frequency response measurements is how much it deviates between those numbers. An accurate frequency response spec would say 45 hz to 23Khz +- 3db. The important part is the +-3 db part. Frequency response is also highly dependant upon the installation method recommended by the manufacturer...highly important in an automotive application. Trunk shelves make lots of bass because the trunk acts as a gianta speaker cabinet. Doors and interior side panels are not so good becasue there's not much air back there to absorb the back wave off the speaker. ...Your truck's doors may not give quite the frequency response that the spec's indicate, but they are at least a good method to compare the speakers.

Unfortunatley, there are some tradeoffs in the speaker design. A more efficient speaker, typically does not handle as much power as a lesser efficient speaker of the same size. This is because a speaker is a mechanical device. In order to produce sound, a speaker has a moveable cone in it. That cone is moved by an electromagnet. A more efficient speaker has more windings, but with smaller wire, and will move more distance than a higher wattage one. In order to make a speaker tolerate higher power ratings, larger wire is necessary in this electromagnet...called a voice coil. Because the wire is larger, fewer windings can be placed in the coil...fewer windings means less magnetic flux...less magnetic flux, means the speaker moves less. The other factor is what's called the speaker "excursion" and it doesn't have anything to do with big Ford SUV's. When that magnetic flux moves the speaker, it can only move but so much. If you want the speaker to tolerate higher power levels, you design it with a tighter surround so it takes more power to move it. BUT the less the speaker moves, the less sound it makes! Sometimes you will see woofers advertised as "high excursion" speakers. Increasing the excursion increases the efficiency, but also decreases the surface area of the speaker's cone. In small speakers (6inches and smaller), increasing excursion ends up reducing the surface area so much the efficiency actually goes down.

Your thinking is correct in what you are trying to achieve....go with the largest speaker possible to make the most sound. Contrary to popular belief, a larger speaker does NOT require more power to drive it...although it CAN take more power, and thus make more sound, doesn't mean you NEED to drive it with more power. Typically, the larger the speaker, the more efficient it is, and the better frequency response it will have, and also the more power it can handle! A larger speaker simply has more room for a larger electromagnetic voice coil with bigger wire. A larger speaker obviously also has more surface area to radiate the sound, and like mentioned above, also can have more excursion. All these factors combine to give you more sound, with less power needed, and the capability of making even more sound, with more wattage!

..just like the hot-rodders say, there' s no replacement for displacement...and this applies in speakers just as much as it does in engines!! !!

You can easily calculate how much sound a speaker is going to make. Every 3db increase in sound level will require a doubling of power. 3db's however is not a significant difference in volume level...it's just barely percieptable. So if the speakers you mention produce 90 db at 1 watt, they will produce 105db at about 24 watts RMS, which is about what as best as you'll get straight out the deck. At their maximum rating, you'll get an addional 108db (48 watts)...so don't even worry about installing an amp...it won't get you all that much more!

.