| Author | Message | ||
| richbass939
Senior Member Username: richbass939 Post Number: 694 Registered: 11-2004 |
Once again I'll admit I don't know squat and ask a technical question. I hear a lot about amps producing, say, 320 watts into 8 Ohm or 480 watts into 4 Ohm. I know that Ohm represents impedence but that's about all. Is there a performance or sound advantage of using 8 Ohm speakers? Why not use a 4 Ohm system and get more power? Will someone please give me an Ohm 101 lesson? Thanks, Rich | ||
| fc_spoiler
Advanced Member Username: fc_spoiler Post Number: 250 Registered: 5-2006 |
My Ampeg gives 275 watt at 8 ohm and 450 watt at 4 ohm. There should be no difference in sound, only in output. Some amps , for instance the Mesa 400+ have the same output at 2,4 or 8 ohm. With my amp the volume difference between 4 and 8 ohm is minimal, far enough for most situations. Never go below the minimal impedence (4 ohm on my Ampeg) You'll fry your amp if you do! So I can use two 8 ohm cabinets or one 4 ohm cabinet (my mesa is 4 ohm) Following examples are when the cabs are wired parallel, Most connections are wired this way: Two 8 ohm cabs will result in 4 ohm Two 4 ohm cabs will result in 2 ohm Two 16 ohm cabs will result in 8 ohm Four 16 ohm cabs will result in 4 ohm Four 8 ohm cabs will result in 2 ohm Please anyone correct me if I'm wrong or fill the gaps I left This is just basic info, I'm not that technical also... I hope it's a bit usefull for you and I'm sure there are others here who will have a more technical answer... Cheers! F.C. | ||
| olieoliver
Senior Member Username: olieoliver Post Number: 603 Registered: 2-2006 |
I believe you are correct Flip. Cabinets can be rewired to change the impendence too. Two 8 ohm speakers wired parallel should give you an 8 ohm cabinet while the same two 8 ohm speakers wired series should give you a 4 ohm cabinet. (I believe, anyone please correct me if I am wrong). | ||
| bigredbass
Senior Member Username: bigredbass Post Number: 959 Registered: 9-2002 |
There's other more-qualified members who can explain ohm-age properly than myself. In the real world, pay VERY good attention to FC's chart. Make sure at what minimum ohms YOUR amp operates: Virtually all bass amps (Ampeg, Eden, SWR, and on and on) and commercial power amps (the Crests, Crowns, Stewarts, etc.) will operate at a 4 ohm load. A lot of amps will operate at 2, and you occasionally find a very few that will not go below 8 (the old Yamaha P Series power amps from the 80s come to mind, and others). You also find (usually) tube amps that have a selectable output selector, so be sure that control matches your cab(s). If you run a power amp in bridged mode, remember that they often bridge at one ohm value only, even though in stereo they will operate fine at several different values. You want to obey the manufacturer's suggested spec, period. As far as the cabinet side goes, the higher the impedance of the cab, the more of them you can run: You could run 2 8-ohm cabs (equals 4 ohms) instead of one 1 4-ohm cab off the same amp. This is a cheap(er) way to get louder, as you get the same bump in db level (+3db) doubling cabs as you would in doubling the power of your amp (500w to 1000w). This is why a Marshall stack with both cabs sounds so much louder than a half-stack. And why you can move earth with the original SVT setup (300w head and TWO 810 cabs) instead of simply rattling the bottles behind the bar with a single 810. J o e y | ||
| lbpesq
Senior Member Username: lbpesq Post Number: 1551 Registered: 7-2004 |
I believe the formula is two 8 ohm speakers wired in parallel yields 4 ohms of resistance, wired in series yields 16 ohms of resistance. You can usually safely go up - for example an amp putting out a 4 ohm signal can push an 8 ohm speaker, but going down - an 8 ohm amp into a 4 ohm speaker will fry the speaker and/or amp. The folks at Boogie tell me that the 4 ohm out pushing an 8 ohm speaker is often a preferred tone. Bill, tgo | ||
| keavin
Senior Member Username: keavin Post Number: 890 Registered: 12-2002 |
 I'm running two JBL 15's @200watts per chanell via a Carvin ProBassII bass amp which gives me pretty good flexibility for my situitations,but out doors i use my Hartke 350watts for my stage shaking alembic sounds! | ||
| marcky
Intermediate Member Username: marcky Post Number: 119 Registered: 11-2005 |
You are right Bill, two 8 ohm speakers wired parallel gives a 4 ohm cabinet. Use this impedance calculator for more wire options http://colomar.com/Shavano/impedance_proc.php | ||
| richbass939
Senior Member Username: richbass939 Post Number: 696 Registered: 11-2004 |
Thank you, everybody, for the Ohm lesson. Very helpful. Rich | ||
| lbpesq
Senior Member Username: lbpesq Post Number: 1554 Registered: 7-2004 |
Rich: Now go sit cross-legged in a quiet tranquill place, close your eyes, empty your mind of the mundane thoughts of everyday life, visualize your dream Alembic and the appropriate matching dream rig, take a deep breath, and chant: oooohhhhhmmmmmm, oooohhhhhmmmmmm, oooohhhhhmmmmmm! You're welcome, grasshopper. LOL Bill, tgo | ||
| olieoliver
Senior Member Username: olieoliver Post Number: 604 Registered: 2-2006 |
As my daughter would say "...OOHHMMM you bought another bass, mama's gonna' kill you..." | ||
| fc_spoiler
Advanced Member Username: fc_spoiler Post Number: 251 Registered: 5-2006 |
Olie: Maybe your wife is responsible for the 'fraudulent' ebay listings? -LOL- | ||
| richbass939
Senior Member Username: richbass939 Post Number: 697 Registered: 11-2004 |
Oh, is that what Ohm really means? Bill, tgo, does it work if you set something on fire and stick it in your mouth before you do the "deep breath" part? Thank you, Grasshopperbass939 | ||
| bigredbass
Senior Member Username: bigredbass Post Number: 967 Registered: 9-2002 |
Or is this post an ohmage to impedance? J o e y | ||
| gtrguy
Member Username: gtrguy Post Number: 74 Registered: 9-2004 |
OK, Question for the experts: I have a SWR Goliath senior cab 4x10 @8 ohms. I also have a Ampeg BXT115 cab at 4 ohms. I'd love to run both with my SWR 550 amp. I think I need both cabs to be at 8 ohms. Any solutions? Do I just need to sell the BXT115 and get another 8 ohm cab? Bye, Dave | ||
| olieoliver
Senior Member Username: olieoliver Post Number: 609 Registered: 2-2006 |
Dave, I believe you should be able to run both cabs. If you ran them in series it should bring you down to 6 ohms, which the SWR 550 should be able to handle just fine. ALL feel free to correct me if I am wrong though. | ||
| lbpesq
Senior Member Username: lbpesq Post Number: 1562 Registered: 7-2004 |
I think if you run 8 and 4 ohm cabs in series, you wind up with a 12 ohm load. On my boogie I have 3 speaker outs, 8, 4, and 4 ohms. The folks at Mesa tell me I can use any of them, so long as the cab ohm rating is equal to, or greater than the amp outs. Thus, in Dave's situation I would plug the 4 ohm cab into the 4 ohm out, and the 8 ohm cab into either the other 4 ohm out or the 8 ohm out, whichever sounds better. Of course this is for a Boogie Mark amp. Your situation may be different. Bill, tgo | ||
| olieoliver
Senior Member Username: olieoliver Post Number: 610 Registered: 2-2006 |
I stand corrected, Bill is right. I meant to say parrallel would be 6 ohms. | ||
| lbpesq
Senior Member Username: lbpesq Post Number: 1563 Registered: 7-2004 |
Olie: I was also about to opine that parallel would yield a 6 ohm load, but I tried it on the ohm calculator Marcky posted above and an 8 ohm speaker wired in parallel with a 4 ohm speaker yeilds 2.67 ohms. Then when I thought about it, it seemed to make sense. If two 8 ohm speakers wired in parallel yield a 4 ohm load, reducing one of the speakers to 4 ohm wouldn't raise the level to a 6 ohm load. Bill, tgo (Message edited by lbpesq on August 16, 2006) | ||
| olieoliver
Senior Member Username: olieoliver Post Number: 611 Registered: 2-2006 |
I checked with SWR's web site and they show minimum load at 4 ohms. I believe the 2 spkr outputs on the rear are wired parrallel. And looks like Bill is right about the 2.67 ohms. So I probably wouldn't run these cabs at the same time through your 550. | ||
| dadabass2001
Senior Member Username: dadabass2001 Post Number: 653 Registered: 6-2002 |
Okay guys, The straight formulae from physics class (jeez, I still remember taking physics class!) are: For Series: R1+R2+R3 ... = R total so 4+4=8; 4+8=12, etc For Parallel: 1/R1+1/R2 ...=1/R total so 1/4+1/4=2/4=1/2 total impedance= 2ohms; but you must find the common denominator (ouch... math too!) 1/4+1/8=2/8+1/8=3/8=1/2.67 total impedance=2.67 "I don't FEEL tardy... class dismissed!" Sorry Mike | ||
| marcky
Intermediate Member Username: marcky Post Number: 120 Registered: 11-2005 |
You are right again Bill, one 4ohm cab + one 8ohm cab = 2.67ohm. I've just finished building two cab's like this for a customer of mine. His Aguilar power amp is set on 2ohm when he runs both cabinets. Please everyone when you are not sure about connecting your cabinets use the ohm calculator posted above or send me an email to prevent any amp damage!! Marcky Vanderkley | ||
| gtrguy
Member Username: gtrguy Post Number: 75 Registered: 9-2004 |
Thanks, it's not a good match for the SWR. anyone want to buy a mint Ampeg 1x15 BXT115-HL4 cab designed to Vic Wooten specs? It's got amazing tone. You can feel the air move right through you on the lows! | ||
| davehouck
Moderator Username: davehouck Post Number: 4277 Registered: 5-2002 |
Rich; when I bought my Eden 210 cabs, I went with 4 ohm, and here's why. Two channel power amps put out more power per channel into 4 ohms than into 8 ohms. If I don't plan to carry more than two cabs to any gig, then I will make more efficient use of my amp if I get the 4 ohm version of the Eden 210 cabs rather than the 8 ohm version. Of course if I play a gig where I want to use four cabs, then I'm going to be wishing they were 8 ohms cabs. (This of course ignores the fact that some power amps will operate with a 2 ohm load, but generally 2 ohm loads are to be avoided.) Thus the decision whether to go with 4 ohm or 8 ohm cabs is difficult and involves anticipating your needs in addition to matching power amp output with cab power ratings. As a generalization, the power amp output rating should be equal to or higher than the speaker cab rating. | ||
| richbass939
Senior Member Username: richbass939 Post Number: 700 Registered: 11-2004 |
Thanks again, everyone. I now have a basic understanding of impedence. I have a 115 combo and 210 cab (both 8 Ohm). That is plenty for the gigs I do. Dave, I don't see myself playing any gigs that would require a boatload of cabs. My rig is just fine right now. I don't need anything else. My wife is starting to seriously ask me, "Don't you have enough stuff, already?" The marital bliss could start to show some wear marks pretty soon. I think I'll stop the abrasive action. Rich | ||
| davehouck
Moderator Username: davehouck Post Number: 4284 Registered: 5-2002 |
Yes, two cabs is all I've needed for the gigs that we play too. | ||
| elwoodblue
Member Username: elwoodblue Post Number: 68 Registered: 6-2002 |
thanks rich for the thread, I needed a reminder to check what impedence my custom cab is. ...when I was using a old 2 ohm peavey PA head the only worries I had was how to get rid of the honkiness . Now I have a Stewart world 2.1 and I want to keep it working good for a long time. The impedence calc will come in handy. thanks all |
