Skezza Posted January 10, 2012 Share Posted January 10, 2012 (edited) Hi I seem to be developing an unhealthy fascination with Marbass Heads. Anyway I have read somewhere that Marbass heads will not work if the speaker impedance it sees falls below 4 ohms. Now i have an old analogue peavey Tmax which is supposed to work down to two ohms and I have twice used 4 x 8ohm cabs to build a 'rig of doom' more for the visual effect at outdoor festival where there is plenty of stage So I did a quick check with a multimeter and none of my 8 ohm cabs is actually 8ohm One is 6.5 another is 7.2 etc etc so when you do the Maths you come to a total load if less than 2 but the peavey works fine. If i tried this with two of my 8 ohm cabs would the Markbass refuse to work or is there some tolerance??? I remember a couple of years ago borrowing a little ashdown head and trying to run a a 4 and an 8 ohm cab and it kept cutting out and the only way I could make it work was by leaving out one cab skez Edited February 1, 2012 by Skezza Quote Link to comment Share on other sites More sharing options...
icastle Posted January 10, 2012 Share Posted January 10, 2012 You can't accurately measure speaker impedance using a DVM, the best you'll achieve is a 'near enough' sort of figure to give you a clue if the label has fallen off of an otherwise un-identifiable speaker. Quote Link to comment Share on other sites More sharing options...
Skezza Posted January 10, 2012 Author Share Posted January 10, 2012 Ok but how tolerant are Markbass amps to the impedance of the cabs. I do not want to buy a Markbass head to find it will not with my cabs skez Quote Link to comment Share on other sites More sharing options...
icastle Posted January 10, 2012 Share Posted January 10, 2012 There's going to be a certain tolerance there. If you were to measure two 8Ω Markbass cabs the same way that you measured your two 8Ω cabs, they wouldn't read 8Ω either. Quote Link to comment Share on other sites More sharing options...
Skezza Posted January 10, 2012 Author Share Posted January 10, 2012 Ok fine I did not realise that skez Quote Link to comment Share on other sites More sharing options...
icastle Posted January 10, 2012 Share Posted January 10, 2012 Speaker impedance is dependant on several criteria that a DVM can't measure directly. Add to that the fact that DVMs measure DC resistance but the speaker is designed to work with AC signals and you're only ever going to get a vague figure, and it's always going to be a bit on the low side (which is exactly what you've experienced). Quote Link to comment Share on other sites More sharing options...
chris_b Posted January 11, 2012 Share Posted January 11, 2012 [size=4][color=#222222][font=Arial]Markbass specs are pretty clear. Their heads will go to 4 ohm. That's 2 8 ohm cabs. [/font][/color][/size][color=#222222][font=Arial][size=1][/size][/font][/color] Quote Link to comment Share on other sites More sharing options...
Skezza Posted January 11, 2012 Author Share Posted January 11, 2012 Im sure you correct but is it ?? skez Quote Link to comment Share on other sites More sharing options...
mart Posted January 11, 2012 Share Posted January 11, 2012 [quote name='Skezza' timestamp='1326223856' post='1494112'].... I have twice used 4 x 8ohm cabs to build a 'rig of doom' [i]more for the visual effect[/i] at outdoor festival where there is plenty of stage...[/quote] You could probably still achieve the same visual effect if you had the cabs on stage but [b]not plugged in.[/b] You'd also be following a grand music-biz tradition .... Quote Link to comment Share on other sites More sharing options...
LawrenceH Posted January 12, 2012 Share Posted January 12, 2012 [quote name='Skezza' timestamp='1326283018' post='1494828'] Im sure you correct but is it ?? skez [/quote] Yup. Look at the spec sheet from a typical 8 ohm bass guitar driver from Eminence, B&C etc. The nominal impedance will be listed as 8 ohms. Re, which is the DC resistance, will be in the T/S specs and typically somewhere between 5 and 7 ohms. This is what you are measuring with your multimeter. The impedance plot on the driver datasheet will be a complex curve with a peak at resonance, falling to a mimimum slightly below 8 ohms around a few hundred Hz, then rising again. The actual measured impedence in a cab will be different again according to cab size and design. Despite all that, the Markbass will be fine driving a pair of these drivers in parallel in a typical vented box. Quote Link to comment Share on other sites More sharing options...
Skezza Posted January 12, 2012 Author Share Posted January 12, 2012 I never realised it was this complicated Ive been putting speakers in boxes and putting valve heads on the top since the early 70s and I never new any of this skez Quote Link to comment Share on other sites More sharing options...
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