Building from leftovers, advice on mixing impedances

djfoundation · 9th February 2010, 06:58 PM

I want to build myself a nice, mono, self powered monitor for taking to (DJ) gigs where there isn't a nice house system -mostly because I've been sitting on a handful of speakers and I want to build something.

I have:

(1) 1" TB tweeter - 4 Ω
(2) 6" Pyle sealed midranges - 16 Ω each (these suckers have been in their box for 16 years!)
(1) 12" Lanzar 12SE - 4 Ω

Obviously nothing is high grade here, but I really want to use those mids before they turn to dust. I'm planning to wire them in parallel to bring 'em down to 8 Ω and figure the rest out with the crossover. Hopefully I can find a plate amp that will be suitable.

Is it reasonable to run the mids as one channel and bandpass it, and the sub and tweet in series as the other? If so, how could I filter that? Or should I just stuff three smaller amps in the enclosure?

Anyone have any suggestions for my Frankenspeaker?

djfoundation · 9th February 2010, 07:43 PM

oh, heh. thanks for the move.

chris661 · 9th February 2010, 08:47 PM

It's fair enough that you want to build something.
Does it have to be a DJ system? I expect those pro drivers would do nicely on an open baffle.
For the crossover - there shouldn't be any problem as long as you remember which driver you're dealing with at the time. Make sure you design an 8ohm XO for the mids, and a 4ohm XO for the bass and tweeter.
Chris

djfoundation · 11th February 2010, 10:07 PM

there's a difference between a 4 and 8 ohm crossover?

Moondog55 · 11th February 2010, 11:25 PM

Yes, reactance needs different values .

For inductors halve the impedance halve the coil value but the DCR of the coil has more effect on SPL

For capacitors it is the opposite; halve the impedance double the cap value needed.

Most tables set out a nominal 8R value, better tables give values for 4 / 8 / 16

if your impedance isn't one of the nominal values you have to calculate using the actual impedance at the crossover frequency chosen, which is seldom the nominal value

djfoundation · 12th February 2010, 06:28 PM

Ah, this must be the vague memory of rectangular and polar number equations from back in school. Time to dig out some old papers!

9th February 2010, 06:58 PM	#1
djfoundation diyAudio Member Join Date: Jul 2009	Building from leftovers, advice on mixing impedances I want to build myself a nice, mono, self powered monitor for taking to (DJ) gigs where there isn't a nice house system -mostly because I've been sitting on a handful of speakers and I want to build something. I have: (1) 1" TB tweeter - 4 Ω (2) 6" Pyle sealed midranges - 16 Ω each (these suckers have been in their box for 16 years!) (1) 12" Lanzar 12SE - 4 Ω Obviously nothing is high grade here, but I really want to use those mids before they turn to dust. I'm planning to wire them in parallel to bring 'em down to 8 Ω and figure the rest out with the crossover. Hopefully I can find a plate amp that will be suitable. Is it reasonable to run the mids as one channel and bandpass it, and the sub and tweet in series as the other? If so, how could I filter that? Or should I just stuff three smaller amps in the enclosure? Anyone have any suggestions for my Frankenspeaker?

9th February 2010, 08:47 PM	#3
chris661 diyAudio Member Join Date: Feb 2008 Location: Lancashire Blog Entries: 7	It's fair enough that you want to build something. Does it have to be a DJ system? I expect those pro drivers would do nicely on an open baffle. For the crossover - there shouldn't be any problem as long as you remember which driver you're dealing with at the time. Make sure you design an 8ohm XO for the mids, and a 4ohm XO for the bass and tweeter. Chris __________________ "Throwing parts at a failure is like throwing sponges at a rainstorm." - Enzo My setup: http://www.diyaudio.com/forums/multi...tang-band.html

11th February 2010, 11:25 PM	#5
Moondog55 diyAudio Member Join Date: Jun 2007 Location: Norlane; Geelong: Victoria: Australia	Yes, reactance needs different values . For inductors halve the impedance halve the coil value but the DCR of the coil has more effect on SPL For capacitors it is the opposite; halve the impedance double the cap value needed. Most tables set out a nominal 8R value, better tables give values for 4 / 8 / 16 if your impedance isn't one of the nominal values you have to calculate using the actual impedance at the crossover frequency chosen, which is seldom the nominal value __________________ QUOTE" The more I know, the more I know, I know (insert maniacal laugh >here<) NOTHING"

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9th February 2010, 07:43 PM	#2
djfoundation diyAudio Member Join Date: Jul 2009	oh, heh. thanks for the move.

11th February 2010, 10:07 PM	#4
djfoundation diyAudio Member Join Date: Jul 2009	there's a difference between a 4 and 8 ohm crossover?

12th February 2010, 06:28 PM	#6
djfoundation diyAudio Member Join Date: Jul 2009	Ah, this must be the vague memory of rectangular and polar number equations from back in school. Time to dig out some old papers!

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