best crossover point for Dayton Audio ST385-8 15"

[metalman]

Hi everyone, i am looking to replace the junk crossovers in my Optimus floor standers equipped with the venerable Dayton Audio ST385-8 15" that replaced the factory 15"s. It is going to be crossed over to a closed back 6 1/2". Most closed backs dont seem to go much lower than 400-500hz. I am thinking 375-500, but any thoughts on the "better" choice? (2.7cft box, 3" port tuned to 24hz) the speakers in question are out at the ends, thanks!!

[Chris Roemer]

Are you an XO designer?

[metalman]

no, i wish to purchase premade crossovers, and was not sure what would be an appropriate crossover point to my mid with the st385-8. i am looking for suggestions.

[billfitzmaurice]

no, i wish to purchase premade crossovers, and was not sure what would be an appropriate crossover point to my mid with the st385-8.

That depends on the response and impedance chart of the mids and the response and dispersion of the woofers. Perhaps 800Hz, but you won't get a great result with a pre-made crossover in any event. And it will have to be a 3-way in any event.

[mdocod]

Hello metalman,

Closed back mids are tricky to cross because their impedance peak is often within an octave of where you want to cross them over. No "pre-made" crossover will come even close to properly dealing with the issue. Horns are tricky to cross because of their physical offset, which effects the time alignment, no "pre-made" crossover can hope to address the issue.

I can help you design a crossover for them, if you can provide response, impedance, electrical/mechanical data for all 3 drivers, box dimensions, driver locations, side-view schematic of drivers, and intended speaker placement relative to listening position.

Regards,
Eric

[Paul O]

The optimal low-mid crossover freq is gonna be somewhere in the 500-800hz range but like the others have already said that's just the starting point, you then have to combine the correct passband slopes for each section, add zobels and L-pads and likely some filters if you don't have outboard DSP processing. You can use a pre-made crossover as the starting point but you will have changed most of it and added another board about the same size by the time you're done.

[metalman]

well, i think if i was going all out and was trying to exact the best possible performance i would do as Eric and Paul suggest. I guess i should have worded my thread somewhat differently. I wish to replace the "stock", (ie-junk) compromised crossover with a better crossover that is pre-made that i can easily wire and mount into my cab's that will offer me as much of a substantial increase in sound quality as i can get, prior to custom designing and building a crossover. I am looking at a Dayton, Eminence, RADIAN etc. I need some advise as to the best crossover frequency and slope for the ST385-8 15 to the closed back mid i have

[mdocod]

You have just as good a chance of making them sound worse with a "textbook" pre-made crossover. In a way, the act of selling those "premade" crossovers, is actually highly deceptive, because it creates an illusion about speaker design being far more straight forward than it actually is.

[Paul O]

You have just as good a chance of making them sound worse with a "textbook" pre-made crossover. In a way, the act of selling those "premade" crossovers, is actually highly deceptive, because it creates an illusion about speaker design being far more straight forward than it actually is.

+1 on the above... and by the sounds of it you(the OP) understand this so we'll get on with it. To protect the mid/high drivers you will need a crossover with roughly 800/3000hz crossover frequencies though you could probably get away with 500/1600hz. I thought Eminence made a wider range of these but I don't see them now and that's where it becomes necessary to be able to modify what you can get. To balance the output levels from each driver you will also have pad them down with an L-pad which is just a voltage divider consisting of a couple power resistors. With that and the crossover the box will make noise and not blow up but like we said it's still far from optimized but that's something you can study up on and implement once you ahve the knowledge and tools necessary.