## 4 Ohms or 8 ohms electricity word search printable

As you can imagine, cranking more power out of the same amp stresses the amp a bit more (i.e., produces more heat, which is bad). As a general rule, for example, I generally run my amps at about twice the minimum impedance they are rated for; so if an amp will handle a 4-ohm load, I usually run it with 8 ohms. If it can handle a 2-ohm load, I usually limit it to 4 ohms. I’ve never had a problem with amplifiers running this configuration. OTOH, I have had some low-end amps (Crown XLS 602) overheat and shut off when running them at 4 ohms (their minimum impedance). Some might think I’m foolish to waste the power, but again, I’d point out that I’ve never had a problem with amps except when running them at their minimum impedance.

Now as to why you would buy 8 ohm cabinets rather than 4 ohms, well, you can always stick *two* 8-ohm cabs on an amp that will handle 4 ohms (assuming you’re wiring them in parallel, which is the standard way to do it). This lets you hook up twice as many speakers (or use half the number of amps), all other things being equal. When you learn about power compression, you’ll find out that it’s better to run two speakers at half power than one speaker at full power. Once the voice coils heat up (which they will if you start shoveling full power into them), their efficiency decreases dramatically.

If loudest volume is your concern, I’d be far more interested in the sensitivity of the speakers than their impedance. If one speaker has a 96 dB SPL (1w/1m) rating and another has a 99 dB SPL (1w/1m) rating, then it will take *twice* the power for the first speaker to reach the *same volume* level as the second (i.e., 2w/1m).

The sensitivity is an area that baffles me too to be perfectly honest. I have been looking at some celestion SR1 speakers with spl 99dB rated at 4 ohms and then I noticed an 8 ohm SR1 also with a spl 99dB I would have thought the sensitivity ie being the amount of volume would have been greater on the 4 ohm speaker.

I need to get a handle on sensitivity because as far as I can tell dB is logarithmic multiplier but what is the starting figure that it is multiplying from? If you knew you started off with a signal that had an amplitude of lets say 1 v peak to peak then you could use your dB figure to calculate it’s final amplitude coming from an amplifier. The sensitivity of a speaker is spl measured in decibels too but 99dB is obviously a lot quieter than 120dB so given the same amp delivering the same settings to identical impedance speakers but one being 99dB and the other being 120dB would the 120 dB speaker be a lot louder? So if that is the case then a high sensitivy rating throughout the range of speakers no matter what impedance or power rating will always be better. So What is the professional desired spl figure?

I run mostly portable setups. In that realm, maximum SPL per pound (and related, maximum sensitivity per pound) is important to me. Efficient (sensitive) speakers are important so that you don’t have to carry around dozens of **huge amps** (not to mention, trying to find power for those *huge amps* — I already have to take a 60 KVA genie with me and I’m getting to the point where that might not be enough).

Personally, I get scared as the sensitivity drops to 96 dB or below (e.g., the JBL SRX 712m monitor wedges have a 96 dB rating). I once was looking at some JBL VLA932 cabinets until I noticed they had a 90 dB sensitivity rating. That means that the SRX 725 cabs I have (99 dB SPL @ 1w/1m) produce almost twice the volume at the same power level; another way of looking at it is that it takes *ten times* the power to a VLA932 to achieve the __same volume__ as it does to an SRX 725. When I can put the cash together, I’d like to get some Danley SH46 cabs (106 dB SPL @1w/1m); those puppies require less than 1/4 the power to achieve the *same volume* as the SRX 725 cabs (albeit with a slightly smaller coverage pattern).

Generally it’s manageable at 4 ohms assuming relatively short cable lengths (50′ or less) and 12 Ga or better (e.g., 10ga) speaker cable. If you’re running 100′ speaker cables, I’d be careful about running 4 ohms. If you’re down to 2 ohms, I’d worry about anything more than a couple of feet.

More often than not, if you see two LF drivers, it’s 4 ohms. If you see one LF driver, it’s likely to be 8 ohms. Not a perfect rule, but works more often than not (e.g., my Mpro 418 subs are 4 ohms, but only have a single 18" driver; the other 4 ohm speakers I own all have two 15" or 18" LF drivers)

8 ohms is a convention that goes *way* back. As I pointed out, the advantage of 8 ohm speakers is that you can stick two of them in parallel on the same amp channel (or four of them if you can go down to 2 ohms). If the amp can handle it (in my case, if it can handle 1 ohm or 2 ohm impedances), then by all means go for it. That’s less weight and less space in your rack.

I certainly wouldn’t make that claim. What I would claim is that using two 8-ohm speaker cabinets in parallel is arguably better than running that same amount of power into a 4-ohm cabinet because you’re splitting the power across two voice coils. HOWEVER, if your 4-ohm cabinet is something like a JBL SRX 725 (dual 15" LF drivers) then you’re already splitting the power across two voice coils, so replacing the 725 by a pair of SRX 715 cabinets (single 15" LF driver) won’t really buy you much.

I run mostly portable setups. In that realm, maximum SPL per pound (and related, maximum sensitivity per pound) is important to me. Efficient (sensitive) speakers are important so that you don’t have to carry around dozens of **huge amps** (not to mention, trying to find power for those huge amps — I already have to take a 60 KVA genie with me and I’m getting to the point where that might not be enough).

Personally, I get scared as the sensitivity drops to 96 dB or below (e.g., the JBL SRX 712m monitor wedges have a 96 dB rating). I once was looking at some JBL VLA932 cabinets until I noticed they had a 90 dB sensitivity rating. That means that the SRX 725 cabs I have (99 dB SPL @ 1w/1m) produce almost twice the volume at the same power level; another way of looking at it is that it takes *ten times* the power to a VLA932 to achieve the same volume as it does to an SRX 725. When I can put the cash together, I’d like to get some Danley SH46 cabs (106 dB SPL @1w/1m); those puppies require less than 1/4 the power to achieve the **same volume** as the SRX 725 cabs (albeit with a slightly smaller coverage pattern).