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Ok....Another newbie question. 4ohm vs 8ohm driver choice

H

homeby5

Guest
Aug 21, 2013
33
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Key Largo
#1
Yes.....I have searched and read through some old threads so I have gained some insight, but I still believe I have some valid questions that require some more technical clarification :)

I posted before that plan on building a 15/6" cab. I currently have a GB Shuttle 6.2. I am now ready to order my drivers and I need some advice. I'm deciding on which 15" driver to use. One choice is a BASSLITE™ C2515 which has a 4ohm magnet. My other choice is the KAPPALITE™ 3015LF which has an 8ohm magnet and weighs a few ounces more.

My questions are such:
1- Since my Shuttle puts out about 600W when loaded to a4 ohm driver and about 350W when loaded to a 8 ohms driver, which speaker would move the most air and be louder? Or would neither. Does power equate to SPL?

2- Are there any other issues that I need to factor when making the choice between the two drivers? The Basslite definitely save me some bucks but I really am not concerned too much about this because I want this cab to be a keeper for a while :bassist: I will say that I realize that if I go with the 4 ohm driver than adding another cab will not be an option.

3- Anybody have any opinions on the sound quality difference of these two drivers?

Thanks a bunch guy. My head is spinning as I'm doing the research for my new cab and I need to lean on ya'lls strong shoulders:D
 
#2
If you are building a Fearful 15/6 (including the crossover), then you need to get the specified drivers. You cannot sub different drivers of the same size (different 15's or 6's) because they are not the same. Of course, any 15 or 6 will 'work' (make sound), but the sound will be 'off' (quite probably WAY off). The cab was designed for a specific 15 inch driver, and the crossover was designed specifically for the specified drivers.

If you are 'rolling your own' cab design and crossover, get the 3015LF. It will take all the power your GB 6.2 can dish out (unlike the C2515). Given the small difference in price, the 3015LF is a steal (for 2 or 3-way cabs).

FYI, the impedance (4 or 8 ohms) is the nominal impedance of the voice coil. Speaker magnets have no impedance, but are often specified as to weight (in ounces) and type (neo, ceramic, alnico).

Strongly suggest that you stick with the Greenboy plans - you will be very pleased.

Good luck.
 
#5
Oh no...I was not even thinking about substituting the driver on the fearful 15/6. No way, no how. I'm in no position to play with someone's design, given my ignorance on the subject. But since it was brought up, let's stay with that logic for a second. Forget about the crappy sound, efficiency, etc...If one was to put a BASSLITE™ C2515 into a fearful 15/6 design and leaving everything else the same, would it have the ability to produce more volume with my Shuttle 6.2? Again, forget about the sound quality.

I ask this because I am mainly interested in the difference between the volume possibilities between a 4 ohm coil vs an 8ohm coil and which would produce the most volume with my Shuttle 6.2 amp given everything else equal. I guess I'm trying to understand basic amp power in respect to volume.

What got me thinking was that I was surfing the web for light speakers to be used in other enclosures. I came across (can't remember the site) a dude putting the 4 ohm BASSLITE™ C2515 in a DIY cab and mentioned the volume aspect. Got me thinking.

Also, what are the disadvantages or advantages between a 4 ohm coil and an 8 ohm coil? Sonic, efficiency, etc...?

Thanks for the school guys :)
 
#6
Let's boil this down to the essence. For an increase from 350 watts to be noticeably louder into the same number of speakers all things being equal with speaker efficiency you need to multiply the wattage by 3 (350 X 3 or 1050 watts). The 250 watt increase from 350 will make little difference.
Watts don't make any sound, speakers do and at 5% efficiency at best.
 
#7
B-string said:
Let's boil this down to the essence. For an increase from 350 watts to be noticeably louder into the same number of speakers all things being equal with speaker efficiency you need to multiply the wattage by 3 (350 X 3 or 1050 watts). The 250 watt increase from 350 will make little difference.
Watts don't make any sound, speakers do and at 5% efficiency at best.
Click to expand...
Thank you. That's great info.
 
#9
B-string said:
Let's boil this down to the essence. For an increase from 350 watts to be noticeably louder into the same number of speakers all things being equal with speaker efficiency you need to multiply the wattage by 3 (350 X 3 or 1050 watts). The 250 watt increase from 350 will make little difference.
Watts don't make any sound, speakers do and at 5% efficiency at best.
Click to expand...

+1

Another way to look at it is that a 3db increase in spl is a small but obvious change, that requires a doubling of amplifier power. Thermal compression reduces the spl gain even further, so that a 3db increase requires 4+ times as much power. In a practical sense, once you have around 300+w of amplifier power, spl gains are most easily obtained by adding cabs with high quality drivers (having minimal thermal compression). For super-loud outdoor gigs without PA support (getting rare these days), multiple KW+ power amps and multiple (high quality) cabs are required (just rent).

Don't worry, your GB 6.2 and 15/6 will be a formidable rig.
 
#10
if this is a proper 15/6 cab, then the amp is "seeing" the cab's crossover, not the speakers; as such, the only course of action is to use the drivers that the crossover needs to "see" to work right. as i understand it, going with the wrong impedance drivers just throws the crossover frequencies off.
 
#11
walterw said:
if this is a proper 15/6 cab, then the amp is "seeing" the cab's crossover, not the speakers; ...
Click to expand...

Not exactly. The amp is "seeing" the speaker(s) that is not "masked" off by the crossover and that depends on the frequency(s) that is being output.

If the amp were seeing only the crossover that would mean that nothing is coming out of the cabinet because the entire signal is being masked.

Crossovers work by acting as a variable impedance in series with each of the drivers. When a frequency is being output that should not go to a driver that leg of the crossover presents a high impedance so the signal goes to the other drivers. For frequencies that are supposed to go to a driver it presents a minimal impedance so all of the power will pass through to the driver.

walterw said:
... as such, the only course of action is to use the drivers that the crossover needs to "see" to work right. as i understand it, going with the wrong impedance drivers just throws the crossover frequencies off.
Click to expand...

Yes, this is true. It is the reason that when you buy a crossover you will see them listed for specific speaker impedances. [Invalid or Expired Link Removed]. There are different models for 4 and 8Ω drivers.
 
#12
If the crossover leg absorbs all the power sent to that driver wouldn't the rest of the frequencies be just turned into heat and not passed on to other drivers? I get that you were probably simplifying things. But don"t they really just not allow frequencies that are not supposed to go to that driver to just pass by that leg?

Not attempting to start anything or challenge anyone's knowledge on this. Just asking so I understand better myself.
 
#13
Nighttrain1127 said:
If the crossover leg absorbs all the power sent to that driver wouldn't the rest of the frequencies be just turned into heat and not passed on to other drivers? I get that you were probably simplifying things. But don"t they really just not allow frequencies that are not supposed to go to that driver to just pass by that leg?

Not attempting to start anything or challenge anyone's knowledge on this. Just asking so I understand better myself.
Click to expand...

Depends on the crossover.

Active crossovers are very efficient and do more "splitting" of frequencies while passives "filter." Filtering involves more heat.
 
#16
Vince Klortho said:
The difference is the level of signal they operate on. An active crossover works after a pre-amp and before a power amp so the signal level is low - typically less than 1V. A passive crossover operates after the power amp so the signal level is as high as it gets.
Click to expand...
All of that is true, but it is not the only difference.

As I said in my previous post, an active crossover "splits" the signal. That is, it (a two channel crossover) sends the highs on one path and the lows on another. A passive "filters" the signal, filtering out the highs on one path, and filtering out the lows on the other.

So, there is virtually no signal "lost" in the active crossover, while the passive one only functions by removing some signal from each path.


As a sort of analogy, imagine you have a quart that is 1/2 water and 1/2 oil. The active crossover sends the pint of oil on one path, and the pint of water on the other. The passive crossover divides the quart into two paths, each a pint that is 1/2 water and 1/2 oil. Then it filters out the oil on one path, and the water on the other, so one path gets a cup of water, and one gets a cup of oil.

That's a simplified description of the difference in how they work. In reality they don't absorb 1/2 the signal, but, as I said, this is a simplified description.
 
#17
Nighttrain1127 said:
If the crossover leg absorbs all the power sent to that driver wouldn't the rest of the frequencies be just turned into heat and not passed on to other drivers? I get that you were probably simplifying things. But don"t they really just not allow frequencies that are not supposed to go to that driver to just pass by that leg?
Click to expand...

You are right. I completely spazzed on that part. What I wrote was :

When a frequency is being output that should not go to a driver that leg of the crossover presents a high impedance that absorbs all of the power sent to that driver.
Click to expand...

I will edit my post to correct this but what I should have written was it presents a high impedence load to unwanted frequencies so they are sent to the other drivers which are of lower impedance.

As an analogy, say you have an amp putting out 30W and you have an 8Ω speaker and a 4Ω speaker. The 4Ω speaker will get 20W and the 8Ω speaker will get 10W. The higher impedance load will get less power and that's what happens in a crossover - it presents a high impedance to unwanted frequencies so the driver will not receive them.
 
#18
Major Softie said:
All of that is true, but it is not the only difference.

As I said in my previous post, an active crossover "splits" the signal. That is, it (a two channel crossover) sends the highs on one path and the lows on another. A passive "filters" the signal, filtering out the highs on one path, and filtering out the lows on the other.

So, there is virtually no signal "lost" in the active crossover, while the passive one only functions by removing some signal from each path.
Click to expand...

Actually that's not exactly true. The two crossovers work very similarly in that they split the signal into different paths and unwanted frequencies are filtered out from each path. Because of the difference in signal level, active crossovers usually use op-amps so the gain level is maintained and there are no losses. That's why they are called active. It is possible to design a passive crossover that operates at a low level, prior to the power amp, with no op-amps and it will still have losses similar to a post-power amp crossover. No one does that though because op-amps are cheap and clean so there is no point to it. Prior to the presence of good op-amps, discrete transistors were used in active crossovers as miniature gain stages to maintain the level. Op-amps are easier to use though and they are essentially just a circuit of around ten or twenty transistors in an IC package.

FWIW, when I was in engineering school I had a computer-aided circuit design class and we had a project to design an op-amp with no more than ten transistors and a given frequency response and minimum gain level. It became a contest among the class to get the highest gain level. This was before PCs were available and we had to use one of the campus mainframes to run our SPICE models. We ended up going WAY over our time budget for the class because of the contest. The next year we got some minicomputers (PDPs and VAXes) for the EE department and we didn't have to deal with the mainframe any more. I have a ton of stories about the old, pre-PC computer age. :)
 

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