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-   -   tell me where I'm wrong. (http://www.diyaudio.com/forums/multi-way/136929-tell-me-where-im-wrong.html)

raypalmer 20th January 2009 02:39 AM

tell me where I'm wrong.
 
2 Attachment(s)
Okay so my Mk.1 speaker was a bit of a bust. But that's why pencils have erasers right?


I've decided on a bookshelf for Mk.2, my original notion was to clone the Totem Model One but have decided to try something else.

I'm going to extricate my drivers from the Mk.1 attempt as I feel they're pretty good kit. I'm dealing with:

1 Peerless 830657 mid-woofer per speaker
1 Peerless 812978 textile tweeter per speaker

So a 2-way. For xover. I'll probably go with a first order butterworth straight, no chaser. Adhering to my "lite is rite" design ethic. Although I'm wide open to any and all opinions on xo design as well.


Here's my preliminary design. A more concise draft to follow...

http://img135.imageshack.us/img135/4612/mk2ro7.th.jpg

I admit it's a pretty ambitious little TL but I have high hopes. Let me know why it won't work!

fwater 20th January 2009 02:48 AM

It will certainly work, to what level of performance is to be seen. How did the geometry of the TL come to life?

leadbelly 20th January 2009 02:50 AM

1) IMHO 1st order crossovers are a bad choice for those drivers. 1st is really only appropriate for extended range drivers. I think you will be hard pressed to find a spot where either the tweeter isn't over excursion or the woofer isn't beaming under power.

2) The cross section on the TL looks wrong. Are the sides flat? How did you calculate?

raypalmer 20th January 2009 02:53 AM

It's mostly the product of a creative eye. I'm lacking the software and/or formulae necessary to work it out proper. Although I think I may need to narrow the channel more, at the ratios shown I don't think there'll be enough resistance. Only problem is that I will definitely need a baffle-step if I do that, and I hate to(am unable to) work those out.

raypalmer 20th January 2009 02:54 AM

Quote:

Originally posted by leadbelly
1) IMHO 1st order crossovers are a bad choice for those drivers. 1st is really only appropriate for extended range drivers. I think you will be hard pressed to find a spot where either the tweeter isn't over excursion or the woofer isn't beaming under power.

2) The cross section on the TL looks wrong. Are the sides flat? How did you calculate?


Good! I need xover ideas.

The sides are flat, and the geometry needs a tweak. Like I say, it was worked out rather ad hoc.

Cloth Ears 20th January 2009 03:01 AM

Re: tell me where I'm wrong.
 
2 Attachment(s)
Quote:

Originally posted by raypalmer
I admit it's a pretty ambitious little TL but I have high hopes. Let me know why it won't work!
I'll have a go, but I won't tell you why it won't work, just why it may not work.

I'm assuming that you were looking at a TL tuning of around 70-80Hz, as it appears that is the length of your quarter wave (ie. about 1.15 metres).

Generally, TLs are tapered pipes - either expanding (in the case of TQWT) or contracting (in the case of a more 'normal' TL). Yours has a large (expanding) driver enclosure followed by a 65cm(?) constant area tube. I would suspect that this might act more like a bass reflex enclosure than a transmission line. How did you model the design?

The design is also wasteful of space. All that sand is not going to really have much effect except after a few weeks of use. It will have settled by then and will start to 'rattle' a bit unless you keep it topped up. If you want it heavier, why not try thicker pieces of wood in the cabinet sides?

Without working out the measurements, have you thought of something more like the attached picture?

raypalmer 20th January 2009 03:05 AM

Well I must say I like the look of that. Would I have to increase the length of the transmission path to tune closer to 60-55Hz?

fwater 20th January 2009 03:07 AM

One place I can give advice is the XO. 1st order won't cut it. Crossed high enough to prevent distortion or damage, the tweeter will never be able to mate up with the woofer. Crossed low enough to avoid beaming and any breakup modes, likewise for the low end. A carefully planned out 2nd order for the woofer can build in impedance compensation and BSC. A 2nd order for the tweeter will be easier. If you can get me the .frd files (SPL trace, or if somone already has them), I'll take a shot at the XO and let the more experienced guys critique it...


planet10 20th January 2009 03:07 AM

cloth ears TL makes more sense.... to do a proper TL you need to at least plug the driver parameters into Martin's design tables.

dave

raypalmer 20th January 2009 03:11 AM

Fair enough... Where are the tables?



fwater; The TS Parameters are:
http://www.solen.ca/pdf/peerless/830657.pdf

and

http://www.solen.ca/pdf/peerless/811978.pdf

Your input is greatly appreciated mate.


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