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Multi-Way Conventional loudspeakers with crossovers

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Old 25th February 2016, 12:18 AM   #1
Seaco is offline Seaco  United Kingdom
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Default Just gone for it!

Hi All

First post okay so I'll admit it I don't really know what I'm doing but my Mission 702e's don't really do it for me I find them to bright so I thought so you like woodwork make some!

So on looking I see some "Transmission Line" speakers and they seem to have a good write-up so that was it into the shed and the Frankenstein Speakers grew no formulas, I used the Mission 6" mids and I had some reed type Infinity tweeters so I tried them after putting them together and clamping the last side on for trial it appears one of the tweeters doesn't work, (note to self TEST FIRST").

So I will put 2 more holes in and fit the original tweeters but do you think that the brightness will come back or will the new cabinet take some of that away, or should I buy some new tweeters and lastly if that is the case what would be a good tweeter to buy?

Buy the way the speaker does sound better that the 702e thank heavens...
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Old 25th February 2016, 08:27 AM   #2
system7 is offline system7  United Kingdom
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A friend of mine has these missions and doesn't think much of them either.

It's a 100mm tweeter and 150mm woofer IIRC. If it's too bright, you need to attenuate the tweeter probably. But I'd draw the crossover schematic to know what I am doing there. I'd also measure the DC resistance of the bass and tweeter with a multimeter to avoid mistakes.

Changing tweeter is easy enough. Especially since you are not tied to a monacor-like 100mm or less. The world is your oyster.
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Old 25th February 2016, 12:15 PM   #3
system7 is offline system7  United Kingdom
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With the crossover, can you tell me the capacitor values and whether the resistor is wired to the big capacitor in the bass shunt or the small one in the tweeter filter. This looks like second order on both.
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Old 25th February 2016, 03:40 PM   #4
pkitt is offline pkitt  United States
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Default Why this TL?

Your wood-working skills look to be quite good, but I can't imagine the results you'll get from the TL will be at all good, in addition to the crossover and brightness issues. A TL must be designed for the specific driver in it if you want an optimum result, but it looks like you simply chose an existing TL design to build, which likely is not at all appropriate. That particular line configuration is also fraught with a major deficiency; the driver's placement in the line will likely result in really big dip in the output between 100 and 200 Hz, and because the line is probably way too long for the driver's Fs and Qts, its 1/4-wavelength resonant frequency will be much too low. Also, a line that is neither tapered nor mass-loaded will have other large dips in its response at higher frequencies that cannot be smoothed out adequately without stuffing the life out of the line and causing a larger detriment to the bass response. Finally those angled and rounded corner reflectors provide no improvement whatsoever to the TL's performance and are really a waste of time and effort to use. Why, you ask? Their original intent was to "steer" the sound waves, but the wavelengths of importance are so long that those reflectors and curves aren't even "seen".

I know what I've said is highly negative, but it's not meant to be personal. Many people have made similar mistakes when first getting into TL "design", believing and adhering to really old information that seemed valid or at least logical when it was first created, but which has subsequently been dis-proven. I bought into some of the TL myths, too, when I first started. If you really want to design a proper TL, you need to use design software created for that purpose, plus design the TL for the driver to be used in it.
Paul
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Old 25th February 2016, 08:10 PM   #5
system7 is offline system7  United Kingdom
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Oh I don't know, pkitt. I'm more in the "have a bash" camp...

Lovely joinery!

Worst comes to the worst, you can just overrstuff the line and leave the side panel unglued while you fiddle with stuffing. I agree it's long, but the reflex SS 15W-8530-K00 is a FS 30Hz driver so might vaguely fit a quarter wave length which, IIRC, at 30Hz is 2.5m.

Troels gives you a nice filter here:
Ellam-XT

It fixes the narrow baffle midrange shout problems that affect small drivers.
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Old 25th February 2016, 11:39 PM   #6
pkitt is offline pkitt  United States
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Well, the OP was planning on using the midwoofer from the original speaker, and that's what I was addressing, not the SS 15W/8530 you're mentioning here. I would never try use an existing TL design with a random driver I happened to have on hand unless I knew beforehand the line's design was at least reasonably appropriate for that driver's T/S values (not just vaguely possible). And, I certainly would not waste my time in building a line unless I had a strong belief it would be appropriate.
Paul
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Old 26th February 2016, 12:04 AM   #7
Seaco is offline Seaco  United Kingdom
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Thank you Steve and Paul for all the information, Paul you lost me in the first line I'm not a Physicist, I now realise that my speakers are probably all wrong so is there a program that i could use to tell me where to go with my next attempt because working it out on a piece of paper just ain't going to work?

Steve I need to learn alot more about this and I do understand that now reading this forum has opened my eyes to how complicated this is but at least I know I can build speakers now the hard bit starts!

Tonight I opened the speaker up and I've included a quick image of the crossover I could remove it tomorrow if you need a better image but as for changing parts on them I can solder but I have no idea what to change if someone said buy part A and replace part B then I could, I have also added a couple of pics of the speakers I'm going to use...

Thanks again

Lee
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Old 26th February 2016, 02:58 PM   #8
pkitt is offline pkitt  United States
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I use Martin King's modeling software [http://www.quarter-wave.com/] for all of my TL work, but it's no longer available from Martin. You can at least go to Martin's site and read up on his work in order to gain a better understanding of TL design, and Martin also has a Yahoo group that you can join and learn from. OTOH Leonard Audio out of the UK has developed some TL design software which you could try, and there are other software programs which aren't specific to TLs that have been mentioned on this forum and can be used (up to a point).

If you really want to get into TLs quickly, I and others on this forum can model a design for you once you've chosen a driver and can provide its T/S values (published T/S values can be used instead but may not truly reflect your actual driver).
Paul
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Old 26th February 2016, 09:03 PM   #9
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As Paul has stated, your chances of success are very low with this approach. Paul has designed more transmission line speakers (for DIY users and commercial users) than anyone I know. I'm sure that Paul would be able to generate an awesome design if you have T/S specs of a driver of your choosing.

Last edited by Jim Griffin; 26th February 2016 at 09:08 PM.
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Old 26th February 2016, 09:24 PM   #10
Seaco is offline Seaco  United Kingdom
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Quote:
Originally Posted by Jim Griffin View Post
As Paul has stated, your chances of success are very low with this approach. Paul has designed more transmission line speakers (for DIY users and commercial users) than anyone I know. I'm sure that Paul would be able to generate an awesome design if you have T/S specs of a driver of your choosing.
As you can see I'm totally new to all this and as such I now realise my speakers are not really going to work, as for someone else designing for me I think that would be a great idea if Paul had the inclination and or time firstly though I'd like to get some better speakers to make it all worthwhile, I have been reading and it seems three way speakers are a better way to go. If anyone has any recommendations on what size/make speaker cones to buy then I'd be very grateful?

Lee
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