4 ohm tweeter design question - AVS Forum
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post #1 of 10 Old 07-26-2014, 11:57 AM - Thread Starter
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4 ohm tweeter design question

So I'm wanting a simple two way design, basically a tweeter that can be crossed over relatively low, then two larger woofers, basically 8 ohm for everything. What I'm running in to is that many of the tweeters I've been looking at is 4 ohm, sometimes less. Dayton Reference and Esoteric for example is 4 ohms I believe.


Problem is, most all of the receivers I've been looking at is designed for 8 ohms. A Marantz rep said if I want to run 4 ohms they wouldn't recommend any of their current receivers, to wait for a new one that is coming out soon. All the pre-built crossovers are designs for 8 ohm as well, which yeah I can build my own in the future but really didn't want to get into that right now.


So, is there something I'm missing or am I going to be forced into finding a different 8 ohm tweeter? Their classic line is 8 ohm but anything nicer is lower, I don't understand it.

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post #2 of 10 Old 07-26-2014, 12:48 PM
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I don't know anything about the pre-built crossovers - I wouldn't recommend them on general principle. Still, I would expect that the tweeter will be significantly more sentitive then the woofer, even if doubled. When that's the case, a series resister is usually required to bring down the level of the tweeter to match the other section(s). The impedance of the series resister is simply added to the impedance of the tweeter, and the load presented to the amp is much better.

So that's not specific advice, I guess, but I think it's what you were missing.
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post #3 of 10 Old 07-26-2014, 12:58 PM
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The maranta rep is an idiot in terms of understanding the problem. An 8ohm woofer section and 4ohm tweeter section would never present a problem to a receiver.

Having said that, careful with what you're getting into. If using something prebuilt of some online XO calculator, you better use woofers with a naturally full lower end, smooth response, break up way up above the XO point, a tweeter with a very low Fs, and equal sensitivity. I did this once about 8 years ago to try it even though I knew it was wrong. I had the same feelings as you. I figured I'll try the right way later. But I knew enough to pick drivers with those properties. Later I measured it when I could afford the equipment and it was actually ok but far from good. So expect mediocre results if you do this. I'd generally not waste my time again if I were you, but I understand.
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post #4 of 10 Old 07-26-2014, 04:24 PM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post
a tweeter with a very low Fs
Actually my first choice is the Dayton air motion pro, with an Fs of 800 hz. Is that low enough? I had about given up on it but the more I look at other alternatives it seems like it would be pretty easy to work with, as even an Ultimax 10 will go to almost an octave above that.
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post #5 of 10 Old 07-26-2014, 05:17 PM
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Depends. To cross over at 400hz to a pair of ultimax 10s? No. To cross over at 2khz to a well behaved 5.25" paper cone woofer? Barely. Those cross overs don't do much to compensate for Fs and other problems.
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post #6 of 10 Old 07-31-2014, 02:33 PM - Thread Starter
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Quote:
Originally Posted by tuxedocivic View Post
Depends. To cross over at 400hz to a pair of ultimax 10s? No. To cross over at 2khz to a well behaved 5.25" paper cone woofer? Barely. Those cross overs don't do much to compensate for Fs and other problems.
I keep looking at combos such as two Dayton Reference 7" paper woofers, 4 ohm wired in series to 8, sensitivity at 88.2 db, double the drivers should get it close to 94. Frequency response up to 5,500 hz but starts acting weird past 3,000. Couple that with an 8 ohm planar tweeter at 94 db sensitivity, nearly a perfect theoretical match, which is supposed to be crossed over at 3,000 hz. Put a simple two way 3,000 hz 12 db/octave simple crossover on it and call it good.

Probably not audiophile quality but I mean would it really sound like total ass? We're talking $179.43 plus wood/wire/terminals/paint for front towers and centers, and I can probably subtract a woofer and get an 8 ohm for the surrounds, probably having to attenuate the tweeter or get a different one. Basically $869.58 plus small parts and wood for all 7 channels if I use that tweeter everywhere.

If you can't easily put together simple projects like this on the cheap, then why does this company seemingly promote such things? You call their tech support and they're like yeah that'll be awesome, ask you guys and you get the feeling that it would sound like total ass. It's aggravating. I come from a car audio background and we didn't overthink crap there, we built it and rocked it and had big smiles.


http://www.daytonaudio.com/index.php...fer-4-ohm.html

http://www.daytonaudio.com/index.php...r-tweeter.html

http://www.parts-express.com/dayton-...00-hz--260-144
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post #7 of 10 Old 07-31-2014, 02:41 PM
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post #8 of 10 Old 07-31-2014, 02:44 PM - Thread Starter
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Originally Posted by Manic1! View Post
I'm going to have to do something like that I guess due to the crossover situation. I got stuck on an air motion type of tweeter after hearing some Martin Logans with the same type, sounded totally different than usual and I liked it.
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post #9 of 10 Old 07-31-2014, 02:47 PM
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Ha, ya, the tech support probably does tell you that. Don't listen to them.

Will it sound like *ss. Yes, IMO it would. But our standards might be different. Here's why. First, you made a huge mistake. Two of those woofers in series don't give you 94db sensitivity. They give you 88. Then in the low frequencies they'll actually only be 82 because of baffle step losses. With that tweeter you'll have more than 10db from low to high. That sounds like total *ss if you ask me.

On top of that those woofers are useless above 3khz due to cone break up, which will sound ugly and mess up the response. Those need a 2khz XO if you ask me. The XO doesn't account for phase, so you don't know what you're gonna get for a full 2 octaves width at the XO. They don't consider any baffle diffraction effects. They don't consider the inductance of the woofers (or the tweeter but planars usually have flat impedance, so you're actually ok there ). they don't equalize any response anomolies. And they don't offer good value (you can make your own for much less).

Your $180 doesn't sound like a lot, but after all the bits and pieces and woofer you'll probably have close to $400 into them. So why not just build something that actually works. Like this: http://www.diysoundgroup.com/speaker...enham-kit.html

In your price range and will be a heck of a lot better. There's many many more speaker designs out there as well.
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post #10 of 10 Old 07-31-2014, 03:32 PM - Thread Starter
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Here's what I need right here.

http://www.divine-audio.com/canaiolo/3/
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