SEAS Thor crossover- why is it like that?

[acebritbiker]

I've recently finished a pair of SEAS Thor TL's (using the current SEAS Thor infos), and have a newbie about the crossovers. The crossover frequency is (I believe) supposed to be about 2500Hz and the tweeter third order circuit components indeed correspond -approximately- to this (and I've even measured it with a sig gen and scope), but the 2 paralleled W18E001 (so nominally 4ohms) are driven through a 1mH choke. A 4600Hz notch filter is also there to remove a driver resonance at that frequency. But no matter which way I look at it, 1mH looks like a first order crossover for 4 ohms at 640Hz, not 2500! I can't imagine that the enclosure design compensates for such a low crossover and although the basic Thor design has its critics at the lower end, I wasn't aware of the mid-range being reported defective. By 2500Hz the output will 12db down. Also, there's the issue of crossover phase shift (90 deg for 1st order, -90 for 3rd). The speakers also sound pretty fine (to me), image well etc. So, what am I missing here? (Apologies if this Q already has an answer in the Thor discussions but I couldn't find it!).

[planet10]

The XO is using the natural (2nd order) acoustic rolloff of the driver to achieve 3rd order.

dave

[acebritbiker]

Dave, thanks. Looking at the SEAS data graph (and ignoring the various resonances), I can indeed see a roll off from about 2kHz onwards. Still, why did they (D'Apollito?) start the xover 3db slope from ~650Hz rather than 2500? Is this something to do with baffle step correction (?!) (or am I just showing even more ignorance!)?

Tim.

[planet10]

Yes. With a 9" baffle that is just about the right start frequency.

Too bad he didn't get the box right. And then to compound the error, a measure mistake that if done right would have shown its shortcomings.

dave

[acebritbiker]

Ah. Very interesting. Even if its a flawed TL design and only my first build effort, I'm learning a lot from these and then discovering diyaudio.com....! So much to learn. I'm very glad I didn't just shell out $2000 for a pair of commercial boxes but went this DIY route instead. Much more satisfying all round! Many thanks Dave.

Tim.

[planet10]

DIY can easily become an addiction (MuHaHaa). Enjoy them. and know that they can be made even better,

Clarity on Seas Thor Kit

dave

[Shaun]

Originally Posted by planet10

DIY can easily become an addiction (MuHaHaa). Enjoy them. and know that they can be made even better,

Clarity on Seas Thor Kit

dave

acebritbiker, do make sure you read the above thread before putting saw to wood.

[acebritbiker]

Hi Shaun, is that "putting saw to wood" of my present Thors or of a new pair ?!
I see that there are 103 pages (so far) in the Clarity on Seas Thor Kit.... thread. Not sure that if I'd read this lot before making my Thor's, I'd have continued, given up, or just gone mad! On balance, I'm probably glad I made them as they are, as they were finished without too much pain or delay. And now I see there are many, many ways to make something more refined, or different, or better.... Probably the best thing is I will never walk into a shop and buy a pair of ready made speakers, as I nearly did late last year! Cheers,

Tim.

[planet10]

Originally Posted by acebritbiker

Probably the best thing is I will never walk into a shop and buy a pair of ready made speakers, as I nearly did late last year!

[Shaun]

Originally Posted by acebritbiker

Hi Shaun, is that "putting saw to wood" of my present Thors or of a new pair ?!

Oops! I somehow missed that you had built them already. planet10's comment about improvements to be had over the original enclosure design relates its bass-shyness. I have built the original Thor box for a friend some years back. Another friend built one of the later Fat Thor enclosures. The friend who built the original Thors was bitterly disappointed and the DIY world has not heard from him since, whereas the other friend is just chuffed with this speakers.