Istoc 3-way XO rework

[Istoc]

I am happily posting these images of my first ever custom speaker build. Simple yet effective....Sadly a prebuilt crossover...I just don't understand the mechanics well enough....Until I build my new set of mains and use these as my rears. I am hoping to get insight and help from the experienced DIY'ers here.

[planet10]

Originally Posted by Istoc

I am happily posting these images of my first ever custom speaker build. Simple yet effective....Sadly a prebuilt crossover...I just don't understand the mechanics well enough....Until I build my new set of mains and use these as my rears. I am hoping to get insight and help from the experienced DIY'ers here.

Istok,

I's suggest getting the FF125 & the FT17 as close together as you can. You should be able to XO that combo with a single cap. I prefer the cross very high & let the roll-off bring the tweeter down to the right level (at 12-15k with the FF125), but some people use an L-Pad + larger cap.

Getting the woofer integrated given the large values needed when XOed low can be problematic, i've found series XOs to work well here, but active would clean things up a lot.

dave

[Istoc]

Problem with active in my situation is my front AV area is already rather crowded and not much room for an amp. I actually only run them off of my AVR, sad and a little unclean I know, but for now its the best I've got.

Also really you would cross it over that high? I've found the FT17 to sound tiny myself I plan on using a different style of tweeter in my next build, more than likely a Soft Dome.

The Crossover currently inside the speakers are Dayton Crossovers from Parts-Express set at 5.6k High Pass and 700 Low Pass.

No Ohm differentiation with resistors or anything like that....they are extremely basic Cap/Inductor 3 way Xovers. What would the Cap inductor setup be for a crossover at 375(This is an odd low pass but I had a LEAP done at Madisound and this was the recommended Low Pass to get linearity. I also would like to cut out some of the low male vocals from the Scan-Speak 8" woofer, its a weird sound when it happens ya know?) and a 10k High pass?

I have some Xover stuff laying around from when I was planning on building my own...Which this next loudspeaker project will actually use.

[planet10]

That XO is too low for the FT17 which would explain its sound. What you should try is to disconnect the tweeter completely and bypass the low pass on its part of the XO.

The FF125 will reach up to at least 12-15k.

To do the simple XO with no low pass on the FF125 we consider the relative efficiencies. FT17 is rated at 98.5 dB. FF125 is rated at 92 (althou i find the Fostex FRs usually rated a bit high). To get a starting point lets say the difference is 6 dB. So if we XO the FT17 at 30k, then it has dropped 6 dB by 15k. So you'd start with a 0.75 uF cap.

On the bottom end a small sealed box (i'd use 2-3 litre) will get you down to ~200 Hz with a natural 2nd order roll-off.

On the bottom you could get a couple plate amps and fit them in the back of the enclosures. Jack Hidley is selling Surplus NHT/Foster plate amps for $35 each. They come packed 2 to a master carton. You'd have to tweak some Rs to get the built-in XO up to 200 Hz.

I'd also put a cap in front of the HF amp to add another order of roll-off to the FF125. This would increase its dynamic capability and give an acoustic 3rd order XO that matches the 3rd order XO in the Foster.

I guarantee you won't recognize it as the same speaker (in a good way).

dave

[Istoc]

I can't even find a .75 mfd cap. Its either .82 or .68

Tweak some R's?

[planet10]

It isn't overly critical... you want some room to play. I'd get the smaller one (or even the next size down) and some 0.1 uF caps. Start with the main cap, and then add 0.1s until you find the tweeter a bit hot, then back off one of the 0.1s.

dave

[Istoc]

Also do you believe it necessary to use a plate amp? At the time being the SS Woofer I have in the bottom of the speakers handles bass really well independent of amplification, without an external sub its well defined and tight without being overbearing.

[planet10]

I'm not talking about an external sub.

I'm just suggesting the plate amps as a way to biamp and not use up more space for amps. And the NHT/Foster amps i mentioned are actually less expensive than (quality) 200 Hz XO parts. And the bass should get better with a direct connection to the amp amp.

A plate amp to drive each SS woofer, and your current amp to drive the rest.

dave

[Istoc]

Would it be possible to give a link to the amps? Thanks for the assist here btw.

Also how would I do the tweaking to the amps? Never dealt with the innerds, of this kind of stuff.

[planet10]

Foster WF-100K plate amps

For Sale: NHT Loudspeaker drivers and amps-Discussion Thread

For Sale: NHT Loudspeaker drivers and amplifiers

dave