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Old 16th February 2012, 08:19 PM   #11
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Since the OP was dome tweeters:

Most cheap dome tweeters don't go much higher than a good 3-4" wide-range driver, at least on axis. However, putting a 1" dome on top of a 6-8" wide-ranger can screw up the power response off-axis. The off-axis response of the large driver is collapsing to a very narrow angle, then all of a sudden the little dome starts producing at near 180*. For this reason, I always go for a horn loaded tweeter. The down side, and everything has a down side, is that horn loaded tweeters are hugely more efficient than most wide-rangers.

A thought: If you insist on using a dome tweeter, mount in from the rear of the baffle and quisi-horn load it by contouring the baffle cutout.

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Old 16th February 2012, 10:37 PM   #12
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How about rearmounting the tweeter? That way the cab would approximately cast a sonic shadow where the FR driver casts its HF lobe. The same thing would maybe go for two sidemounted tweeters?
I know this is not kosher with phase and early reflection purists, but you kind of gave that up the second you said you wanted a tweeter.

Last edited by Squeak; 16th February 2012 at 10:43 PM.
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Old 16th February 2012, 10:54 PM   #13
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The best is to match directivity and stay away from early reflections. You're multi-way the second you add a tweeter, and this is how a multi-way system should be designed. Most aren't, which is part of why FR is so enjoyable.

To match directivity, most FR enthusiests tend to cross over very high where both the tweeter and FR driver are directional. I think this is mostly because they want to push the xo up away from the sensitive hearing regions, but as a side result, they're matching directivity better (probably without knowing it most of the time).

As bob pointed out, you could use a horn loaded tweeter that has a similar directivity.

I'm not familiar with rear firing, but if it can do it, then go for it. I don't see how it would, but haven't looked at it closely.

Twin side firing tweeters has to many issues. That approach should probably not be pursued, but this is DIY. Knock yourself out
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Old 16th February 2012, 11:03 PM   #14
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Side note. This is something I've been learning more about recently. It's old news, but I think it's something often left on the table. Since being introduced to FR about a year ago now, I was forced to ask myself the question. How come these things work so good? Being a multi-way guy, it was exciting to ponder, but a bit of a struggle. I started to ask, is it because there are no electrical hinderinces. Possibly, but I'm to sciencey for that. So there's got to be a better explanation I thought.

Well, that's lead me down this path. Seamless integration of drivers at the cross over. A cross over will NEVER be as seamless as a FRer. But I can try

OT, but perhaps someone out there is wondering what I had been and that'll shed some light on why FRs have some kind of edge on multi-ways.
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Old 16th February 2012, 11:11 PM   #15
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Quote:
Originally Posted by Godzilla View Post
Am I alone in simply not wanting to use these things? I have a bunch at home sitting unused in boxes. The better sounding and most expensive ones seem to roll off around 10k (smoothly)
Zilla
I don't believe I am familiar with this phenomenon.
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Old 16th February 2012, 11:15 PM   #16
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The only reason I can see for adding a tweeter to a "real" FR (that is a driver that goes low enough and at least up to 15-16Khz, a FR with shelved or rapidly sloping response is another matter) is to get better off-axis response. Using a horn/waveguide to add directionality to the tweeter geddes style will only dublicate the problem of the highs falling off sooner than the mids AFAICS.
Again AFAICS, what you really want is a tweeter with a hole in the polar response, or the exact opposite of normal driver behaviour. That could be accomplished in the two ways I described above.

Last edited by Squeak; 16th February 2012 at 11:18 PM.
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Old 16th February 2012, 11:24 PM   #17
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If there is not enough off axis power, because the driver is to large and beaming, then a tweeter that has 180d directivity can be used. Fine. But it should be crossed in where appropriate. In this case, that might be down around 2.5khz. Which is usually out of the question for FR guys. What is not a good idea, is what I suspect turned the OP off of domes, and that is to cross in a flaring tweeter at 5khz to a woofer that was beaming as low as 1khz. Doing this takes you from a directivity controlled midrange to an intense power response treble region that will splash all over the room and ultimately turn you off of dome tweeters.

Again, I'm not seeing how rear mounting would help. Lots of energy would reflect off the rear wall and not match the frontal power afaics. Possibly there's something I'm missing? Please point that out.

Side firing has to many phase issues in my mind. It may "fill" in that off axis power you're missing, but at the expense of comb filtering. You're fixing the off axis problem with an off axis problem. You still have an off axis problem.
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Old 16th February 2012, 11:31 PM   #18
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Quote:
Originally Posted by Squeak View Post
Using a horn/waveguide to add directionality to the tweeter geddes style will only dublicate the problem of the highs falling off sooner than the mids AFAICS.
I somewhat missed what you're saying here until I re-read it. But I disagree that a waveguide tweeter having controlled off axis attenuation is a problem. It needs to be matched to the FR driver. Out around 8khz, many FRers have a steeply falling off axis behaviour. A proper waveguide tweeter won't do this. And if matched to the FR driver at the appropriate frequency, the results SHOULD be good. (I haven't done it, except in a multi-way system using dedicated midwoofers).

Here is an example of the type of tweeter response that should be used.

Click the image to open in full size.

Click the image to open in full size.

That tweeter/waveguide has not been adjusted for flat response, so just consider the off axis trend to see what I mean.
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Old 16th February 2012, 11:32 PM   #19
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Quote:
Originally Posted by tuxedocivic View Post
Side note. This is something I've been learning more about recently. It's old news, but I think it's something often left on the table. Since being introduced to FR about a year ago now, I was forced to ask myself the question. How come these things work so good? Being a multi-way guy, it was exciting to ponder, but a bit of a struggle. I started to ask, is it because there are no electrical hinderinces. Possibly, but I'm to sciencey for that. So there's got to be a better explanation I thought.

Well, that's lead me down this path. Seamless integration of drivers at the cross over. A cross over will NEVER be as seamless as a FRer. But I can try

OT, but perhaps someone out there is wondering what I had been and that'll shed some light on why FRs have some kind of edge on multi-ways.
I think it's a number of things. The old phase coherency thing is probably true to some degree. While FR driver also have phase problems they generally happen more gradually and higher up than with a multi-way system.
But I don't think that is the one, or even most important reason for FR drivers allure.
Having two drivers with very different sonic characteristics overlapping and interacting, and in general covering the same material, in the most sensitive band of hearing to boot, can't be beneficial.
Also with regards to the topic at hand, the falloff of highs is probably better psychoacoustically accepted than the weird off-axis response of multiway speakers, often with a dip in the middle and reflections of a different kind than what would happen with a natural sound source.

Last edited by Squeak; 16th February 2012 at 11:36 PM.
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Old 16th February 2012, 11:57 PM   #20
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Quote:
Originally Posted by tuxedocivic View Post
I somewhat missed what you're saying here until I re-read it. But I disagree that a waveguide tweeter having controlled off axis attenuation is a problem. It needs to be matched to the FR driver. Out around 8khz, many FRers have a steeply falling off axis behaviour. A proper waveguide tweeter won't do this. And if matched to the FR driver at the appropriate frequency, the results SHOULD be good. (I haven't done it, except in a multi-way system using dedicated midwoofers).

Here is an example of the type of tweeter response that should be used.
Unless your driver takes a nosedive from 8Khz I can't see how integration would be successful *on* axis. You would get a very bright sounding speaker. Unless of course you are talking about putting a filter on the FR to force it down, but then many would probably argue that you are loosing a lot of the purity of the FR idea, even though you are crossing over higher than usual.

Last edited by Squeak; 17th February 2012 at 12:10 AM.
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