help with first crossover will this work?

[top gnome]

Hi
I built a pair of small thors the woofers have corroded and I purchased some seas 18wnx001 woofers to replace. My original thought was to use the thor cabinets but I am ok with building new speakers using as many of the crossover components and the t25 tweeters. I have laid out possible crossover designs after reading several articles. I have a TM and an MTM crossover design and would like to know if they will work without hurting the tweeter.Will they work in the small thor cabinet with the crossover for the mtm ( removed one resistor) I also would like to build the cabinet with the drivers aligned raising the woofers on a thicker panel and would like to know if the crossover will work for that. If I build a new cabinet I would like to build a tall narrow floor stander. WAF Not sure of the role impedance plays but some of the articles made a point about it and not really sure if high impedance is bad I understand low impedance taxes the amp. I could only load 5 pics but the other impedance if quite similar. Thank You

[isaeagle4031]

1) Never place a resistor in parallel with a woofer like that. It will get incredibly hot
2) Are you sure L3 is 10Mh?
3) You are best using a crossover designed for your driver.

[top gnome]

Hi thank you for your help - I do not want to make smoke I will pitch the tm and focus on the mtm, you are correct the L3 should be .24. I am sure there is a lot more to it. I understand it Is important to get a relatively flat FR keeping the impedance above the amps minimum and try to achieve a 6db roll off? The thank you again for your help. Will the slight rolloff on the highs work as a baffle correction?

[Chris Roemer]

ya, it looks like you just used the XO for the Thor MTM but swapped in new NX woofers for the old "E" ones? ?

Boxwise, not only doesn't the NX drivers freq. OR imp. curves match the old drivers, their T/S parms aren't really that close.
Given identical Qts values (which DO match, at 0.34), your box size would vary proportional to Vas. Your new drivers have a Vas only 2/3rds of the orig.
Also (w/Qts being equal), your F3 will vary by Fs, which your NEW woofer's is 9Hz higher than your old woofer's.

That said, instead of putting your new MTM woofers in a smaller box, that loses 10Hz on the bottom end, you CAN put them in a larger box (like the one you've got) and they WILL play nearly as low, BUT . . . - I think you'll want to raise the tuning of the box approx. 10Hz (by shortening the port).
IS this a ported box, or is it an MLTL?? What are your old box internal dimensions and port specifics?

AFA using the old Thor MTM XO, the new driver is definitely more efficient (although it "rings" at pretty much the same freq.).
The orig. XO doesn't really appear to have much (if any) BSC applied, are you good w/that?
You won't hurt your tweeters by using the same XO, but I think you'll have to change values to get decent results (although the (shunt) LCR notch is still at the proper freq., so it's OK).

BTW, these are Seas W18NX001 drivers, NOT 18WNX - which doesn't help anyone get a good Google search.

[top gnome]

thank you for the help and the information I am sorry about putting incorrect driver number in. The current cabinets are 65 liters. MLTL port is 3" dia 4 " long I can not figure out how to attach a pdf. I also would have responded sooner but I am not getting notified I am subscribed. Overall I was happy with the sound of the small Thors so I am no sure about the BSC, the cabinets are 9" wide.the only change to the xover was removing the 12.5 resistor after c4 on the tweeter attached pics. I have built a couple of kits but have not done anything from scratch but I am willing to invest some time in learning. I would be willing to change the crossover but would like to use as many of the old components as possible they are premium parts. I have some skill in woodworking so raising baffles or trapezoid cabinets are possible I have scoured the net looking for this combination of drivers but outside a tm from Troels I have not been able to find one. I would have stayed with the Thors as is if not for the corrosion.that being said I do not mind building new cabinets I would obviously like them to sound good when done. so if I understand this correctly the Vas means that the drivers are less stiff and would require a larger enclosure. My room is relatively small 12x15 with 7' ceilings. It also looks like because the drivers are more efficient a single driver may be a better match to that tweeter. good sound and soundstage/imaging are more important than playing loud. What are the important parameters when designing a crossover?. thank you again for your help

[top gnome]

I realized the reason I left the resistor in on the tweeter was to kind of get a BSC with a drop in the FR on the high end. removing c4 and r3 also raises the top end a little.Here is cabinet pdf

[Chris Roemer]

A lower Vas (Qts being equal) means the suspension is stiffer - and a smaller box is in order.
You can model this yourself with WinISD from linearteam.org (sorry Craig).
A good book to read about all aspects of speaker design is Speakerbuilding 201 by Ray Alden.

[top gnome]

thank you I will pick up the book.

[top gnome]

just an update - I installed the drivers and removed the 2 resistors and 1 capacitor one at a time after measurements and listening, from the tweeter side of the crossover The listening position response is not terrible. a little choppy but it took me a long time to get the room right with the Thors. I have decent bass down to 37Hz so about the same. There are some room modes below 200hz . from there to 10000 looks pretty good a little choppy but within +/-5 or so . even taking out many parts from the crossover above 10k there is a steady rolloff that I am not sure how to overcome. on some of the measurements it was as high as 10 but on the last measurements looks to be a bout 6 db to 20k the thors were the opposite having a rising slope after 10k. I have not listened a lot but the sound is certainly not bad. different but not bad. would like to figure out how to raise the db from the 10k to 20k region a little.

[Chris Roemer]

Jumper over the last 2ohm resistor, just before the tweeter (to bypass) it. See if that helps.
On a sim, it SEEMs like your system is pretty loud around 1000Hz (which should make them sound pretty "forward", or shouty).
Personally, I'd think the 1mH series coil (to the woofer(s)) should be substantially larger, like up to maybe 3mH (or more).
The orig. XO is not optimized for your new woofers, at all.

[top gnome]

Hi Chris

thank you I have actually removed the 12 ohm resistor and the 2.2 cap and the 2.2 resistor. they are sounding better. it has shifted the xover to 2k Here is the current fr chart. I an not sure about phase I have read about it but I do not understand the impact of it on sound other than when one speaker is wired incorrectly. the tweeters are inverted on these charts. . there are large suck outs between 100 and 200 hz at 1 meter they measure better at the listening position. there is still a 6 db rolloff after 10hz I am thinking about jumpering the 18 cap to bring the tweet up but I may listen for a while it may push the soundstage back. the FR is still choppy and I am not sure what to do about that. When measured at 6 inchs the drivers are within 1db of flat. so I imagine the choppiness is cabinet and room related. thank you again . .