I’m planning to build a Pure Audio Project inspired OB tower. Two 15” and a single fullrange. Trouble is, all the speakers I’m looking at are 8ohm. So using a pair of 15’s is going to give me either 4 or 16 ohms. The Re on one set of subs I’m considering is 5 ohms so maybe actually closer to 10 ohms for the woofers. I’ve seen many use a pair of Alpha 15a’s with TB W8-1808.
What is the work around for the mismatched impedance?
What is the work around for the mismatched impedance?
It's not something you need to worry about, as long as the amp has no problem with you going too low or too high for it, which this shouldn't be.
It is no problem to mix woofers and tweeters/fullrange with different impedance.
As mentioned above just be sure that the amp can handle the total impedance of the speaker.
To use 2x Eminence Alpha 15a in paralell is OK. To use 3x could be a problem due to very low impedance.
When you use 2 woofers in parallell then the crossover values changes. Capasitor x2 and inductor /2.
2 woofers in paralell are also 6 dB more efficient than one.
I made this clone and it sound very good. You should consider to try a quality 3 or 4 inch fullrange instead of a 8 inch. A smaller driver sounds cleaner, more coherent and have more brilliant top end. (I have used a lot of expensive 8 inch drivere before Fostex ltd edtion, Tang-Band, Seas Alnico, Lowther Alnico)
You maybee ask: what about the capasity? No problem, the dipole peak from the bafle gives extra power acousticalily to the small 3 inch driver and then you can cross over (electrically) much higher. Just test it 🙂
DIY apen baffel - Pure Audio Project Duet 15 Prelude klone | Hifisentralen
As mentioned above just be sure that the amp can handle the total impedance of the speaker.
To use 2x Eminence Alpha 15a in paralell is OK. To use 3x could be a problem due to very low impedance.
When you use 2 woofers in parallell then the crossover values changes. Capasitor x2 and inductor /2.
2 woofers in paralell are also 6 dB more efficient than one.
I made this clone and it sound very good. You should consider to try a quality 3 or 4 inch fullrange instead of a 8 inch. A smaller driver sounds cleaner, more coherent and have more brilliant top end. (I have used a lot of expensive 8 inch drivere before Fostex ltd edtion, Tang-Band, Seas Alnico, Lowther Alnico)
You maybee ask: what about the capasity? No problem, the dipole peak from the bafle gives extra power acousticalily to the small 3 inch driver and then you can cross over (electrically) much higher. Just test it 🙂
DIY apen baffel - Pure Audio Project Duet 15 Prelude klone | Hifisentralen
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Thanks for the reply’s. I have considered some smaller fullrange drivers. I’ve used Mark Audio in the past and may again. Efficiency seemed low compared to a pair of 15” woofers however.
So, if I used a pair of high efficiency 15” woofers wired them to 4ohms and used an 8 ohm fullrange that was less efficient it won’t cause issues? I’m thinking the lower impedance will allow the amplifier to provide more power to speakers that are already more efficient. Is this just fixed with an L-pad?
So, if I used a pair of high efficiency 15” woofers wired them to 4ohms and used an 8 ohm fullrange that was less efficient it won’t cause issues? I’m thinking the lower impedance will allow the amplifier to provide more power to speakers that are already more efficient. Is this just fixed with an L-pad?
L-pad, yes. Some 4 ohm drivers list their sensitivity by Watts and some by Volts, so some are like you say and some are not.
In any case you also have the open baffle which has a significant effect on sensitivity. After all this it's good to have the higher driver more loud so you don't have to put an L-pad on the woofer, because that would soak up more power and could affect your bass alignment if you're not expecting it.
In any case you also have the open baffle which has a significant effect on sensitivity. After all this it's good to have the higher driver more loud so you don't have to put an L-pad on the woofer, because that would soak up more power and could affect your bass alignment if you're not expecting it.
Just a quick FWIW that an L-pad on the LF drivers is typically not a good idea, unless you alter your cabinet design to account for the increased series resistance, which will change the effective Qes, Qts, of the driver(s).
Chris
Chris
So if you find yourself in a position where you woofers are outpacing your fullrange, what is the workaround? I’ve seen these types speakers built by many DIYers so I don’t expect any serious issue, but I’d like to understand what I might be up against.
Thanks,
Thanks,