Home dbx User Forum dbx Archive Threads DriverRack PA & DriveRack PA+ PA Front Panel

Removing the passive crossovers

itsonlymeitsonlyme Posts: 3
edited December 2013 in PA Front Panel
Hi to all, I am new to this forum and was looking for some reassurance more than anything else (I think) anyway any information would be appreciated. I have a two way system with two 18 inch subs and two tops, the Mackie 408's that have 4 of 8 inch speakers and a horn driver in each. I was thinking of removing the passive crossovers from the Mackies and running a three way system and setting the crossover for the highs at the point in the Mackie user manual.Apart from the potential for mixing up the highs with the mids on the cabinet rear connectors, I was thinking of using limiters and setting the DRPA to ensure that the horns cant get destroyed. The Mackie manual has no spec on the horn so i was thinking of running the cabs at full tilt and somehow measuring the voltage across the horn terminals with pink noise running. would that be any good? I can then work out the settings hopefully. I am running two HK 2.4k @ 1200 rms @ 4 ohms per side. I want to use each 2.4k rms in bridged mode into 8 Ohms in to each sub eventually and add another amplifier to run the mids on one channel and tops on another. the system sounds great as it is but I cant help myself trying to make it both tighter and clearer. Thanks for any advice. I have emailed Mackie for the speaker specs. Happy new year to all

I have managed to get some information regarding the 408 horns. Mackie give the crossover point at 2500hz and say that the horn handles ALL vocal frequencies. I see that some vocals are below this frequency,up to 1100hz.Is it not the case that the mid drivers in this cab handle up to 2500kz and then the horn comes in after that according to the crossover slope? Perhaps I am missing something or I simply have misunderstood.

I have decided to run an amplifier for the mids in this cab and one for the compression drivers/ horns. Given that the horns are rated at 100 watts RMS does the rule of thumb of headroom with the amps power still apply buy upping the available amplifier power. I assume I can set the high out at the DRPA to limit any potentially damaging frequencies in terms of the voice coils.Any advice would be appreciated.

I have had a response from Mackie as follows:-Thanks for writing in.

We cannot recommend bypassing the internal crossover, since the speaker was not designed to work that way. Having said that, the 8� drivers are 8Ω, frequency range 125Hz-6kHz. The HFD is 8Ω, frequency range 1.8kHz-20kHz.

The actual crossover point is 2.5kHz, but remember that in any analog cross over, it’s not a brick-wall separation at 2.5kHz. The signal sent to the woofer start to taper down around 2.5kHz, and the signal sent to the tweeter starts to reach maximum at the same point.(End)

Ah I see, well actually I don't see anything apart from the literature from Mackie states that all voice frequencies go through the high frequency driver. The information here contradicts that.

I think this is the only forum that I have joined where there has been no reply to questions.From that I think that may be what I am trying to do is a little beyond the tech guys on here or there is a lack of interest. There have been some views though so I guess its worth finishing off by posting what I have found.

In terms of removing the crossovers, I have so far stripped one out and managed to rewire the four bass/mid drivers to provide an 8 Ohm load. I see that the speaker manufacturers state one thing and provide another so I assume that its best in the lack of any real specs for the drivers to go by the loading and nominal wattage when choosing an amp. As there will be no protection for the highs,somehow this will be set within the DR via the hi out and using the crossover,compressor,equalizer etc.

The same will apply to the bass/mids. Initially after running the 408s through the DR (with passive crossovers), I was surprised to find that the only way that I could get any reasonable sound was to run them through the high output.There was a distinct lack of bass sound as compared to running through a straight non DR setup. I tried attenuating the EQ in the high to boost the low end but this resulted in no real improvement and what little there was also had serious clipping.

I found though that if I dropped the crossover frequency to "out" in the high attenuation then this returned a vast improvement in bass in the high output. So lesson learnt, a two way speaker can be run from the high out on a DR if you effectively turn off the crossover.Makes perfect sense as the speaker has its own which I guess is best left in place at the expense of a little wattage.

For anyone reading this post I have found the DRPA that I have to be an excellent piece of kit which is both versatile and intuitive for someone with a small amount of knowledge like myself.

Off to build my custom subs and buy another power amp for the 408s
Sign In or Register to comment.