Introduction to designing crossovers without measurement - Page 13 - diyAudio
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Old 23rd April 2013, 10:00 AM   #121
AndrewT is offline AndrewT  Scotland
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The title states "without measurement".
Judging by the number of graphical plots in the first few posts, it seems that measurement is critical to determining some, or many, of the component values.
Quote:
Furthermore, without phase and delay information available, chasing higher orders can be relatively ineffective.
seems to reinforce my conclusion.
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regards Andrew T.
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Old 23rd April 2013, 06:56 PM   #122
mart.s is offline mart.s  United Kingdom
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Quote:
Originally Posted by AllenB View Post
There are a couple of common reasons that the top end might sound rough or fatiguing. Since you seem to prefer the woofer to play higher in frequency, I'd assume it's due to the off axis sound up high. This can come down to personal preference but I prefer less.

As a woofer goes higher in frequency, it produces less off axis sound. Just to illustrate, imagine taking a small stone and dropping it into a pond. Note the width of the ripples. Now take some sand and drop it over that wider area. The ripples will have trouble forming as the parts do not add properly and they partially cancel one another. Woofers will lose most of this energy off to the sides, more with increasing frequency.

Having been in this situation I understand the temptation to try and run the better driver as wide in frequency as possible to get the best out of it. What you end up with in this case will be reflections that are more loud above the crossover frequency than below due to the tweeter and its wider radiation.

When you listen to speakers in a room, you can expect the lower frequencies to be coming from all around, and you can make a choice to taper this off so that the higher frequencies are mostly coming to you directly. What you want to avoid is reducing the off-axis sound at some frequency and allowing it to be present again at higher frequencies, which is what you have when you cross a woofer quite high to a dome tweeter.

It could be worth exploring some different types of speaker, and there are two common alternatives that can achieve this end. One of them is to use a larger driver for the treble. An example would be using a small full range driver. The advantages of this are that the treble will be more direct (meaning less reflected sound) and therefore more relaxed even when designed for the same level on your listening axis as a dome. You'll also be able to cross lower in the midrange (good), and you'll be able to use a larger woofer. This format has come to be known here as a F.A.S.T.

The other is to use a horn to control the dispersion in the treble. A waveguide is a kind of horn that has been designed primarily for controlling the directivity. It is usually conical or similar. If you know the woofer and the waveguide angle you want to use, you find the frequency where the woofer radiation narrows to that amount and make sure the waveguide and tweeter can be crossed that low.
The drop off is happening with the tweeter not the bass/mid. If I move my head slightly left and right up or down from the normal listening position I lose a considerable amount of treble.
Sorry if I didnt explain myself properly. The speakers did not have this problem when there was the original tweeters in the speaker (which blew) that was using a first order x-over.
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Old 24th April 2013, 12:06 AM   #123
AllenB is online now AllenB  Australia
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OK, there are a few more possibilities but firstly are you familiar with standing waves? I first recall noticing this as I was doing some measurements on a tweeter. I had a tone of maybe 3kHz playing and I was walking around the room trying to find my pencil. The sound would cut in and out as I moved and it seemed to be laid out on a grid of a few inches per square. This is an interaction of room reflections. It can happen as the result of a single reflection, or even dissimilar distance between speakers although it is easier to notice when you play a steady tone like I was.

A loss in treble is a broad statement which could mean any of the kHz range and it is sometimes difficult to tell which driver is actually responsible just by listening.

You say that this happens when you move vertically or horizontally. If it were the tweeter interacting out of phase with the woofer then it would happen vertically, as you move closer/further from each driver, but not horizontally. It is possible that you have more than one outstanding issue but I'll deal with the possibilities separately.

Another concern is the fact that you use the P17 up to 4kHz. This sized driver is beginning to lose its off axis energy down at 2kHz or so. It's normally not too much of a problem to cross there as the tweeter's energy below its crossover may be enough to fill the holes. In your case the odds are stacked against you so to speak...firstly the 17 will have fair losses to the sides by 4kHz. Secondly the tweeter would have to reach more than an octave below its crossover still having enough energy which thirdly, it might have if you were using a first order crossover but you aren't, (Obviously doing so would have its good and bad points).

Try moving your ears horizontally so that the problem happens, and move further to the side and see if the treble returns. This might indicate that you have a reflection/standing wave issue (try this as well with only one speaker playing). Also try using a second order filter on the tweeter. If this helps it could indicate one of three things either the 2-4kHz region needed filling, or the third order filter was producing a lumpy response (as these can be more difficult to get smooth using standard formulas on a real driver), or that you have crossover phasing issues. If this last one is the case, then simply flipping the polarity of the tweeter will change the locations where you can hear the treble going in and out.

Last edited by AllenB; 24th April 2013 at 12:10 AM.
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Old 24th April 2013, 03:58 AM   #124
mart.s is offline mart.s  United Kingdom
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Quote:
Originally Posted by AllenB View Post
OK, there are a few more possibilities but firstly are you familiar with standing waves? I first recall noticing this as I was doing some measurements on a tweeter. I had a tone of maybe 3kHz playing and I was walking around the room trying to find my pencil. The sound would cut in and out as I moved and it seemed to be laid out on a grid of a few inches per square. This is an interaction of room reflections. It can happen as the result of a single reflection, or even dissimilar distance between speakers although it is easier to notice when you play a steady tone like I was.

A loss in treble is a broad statement which could mean any of the kHz range and it is sometimes difficult to tell which driver is actually responsible just by listening.

You say that this happens when you move vertically or horizontally. If it were the tweeter interacting out of phase with the woofer then it would happen vertically, as you move closer/further from each driver, but not horizontally. It is possible that you have more than one outstanding issue but I'll deal with the possibilities separately.

Another concern is the fact that you use the P17 up to 4kHz. This sized driver is beginning to lose its off axis energy down at 2kHz or so. It's normally not too much of a problem to cross there as the tweeter's energy below its crossover may be enough to fill the holes. In your case the odds are stacked against you so to speak...firstly the 17 will have fair losses to the sides by 4kHz. Secondly the tweeter would have to reach more than an octave below its crossover still having enough energy which thirdly, it might have if you were using a first order crossover but you aren't, (Obviously doing so would have its good and bad points).

Try moving your ears horizontally so that the problem happens, and move further to the side and see if the treble returns. This might indicate that you have a reflection/standing wave issue (try this as well with only one speaker playing). Also try using a second order filter on the tweeter. If this helps it could indicate one of three things either the 2-4kHz region needed filling, or the third order filter was producing a lumpy response (as these can be more difficult to get smooth using standard formulas on a real driver), or that you have crossover phasing issues. If this last one is the case, then simply flipping the polarity of the tweeter will change the locations where you can hear the treble going in and out.
OK Thanks, I'm going to try a 2nd order linkwitz-riley again and drop the
x-over to 2400Hz with polarity reversed on the tweeter. I did try this a few weeks ago but the top end was a bit splashy for me so maybe I need a notch filter in there also. Tried it with Pink and white noise and there was definitely an audible rise at the top and it didn't blend well.
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Old 24th April 2013, 04:44 AM   #125
mart.s is offline mart.s  United Kingdom
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[QUOTE=mart.s;3466218]OK Thanks, I'm going to try a 2nd order linkwitz-riley again and drop the
x-over to 2400Hz with polarity reversed on the tweeter. I did try this a few weeks ago but the top end was a bit splashy for me so maybe I need a notch filter in there also. Tried it with Pink and white noise and there was definitely an audible rise at the top and it didn't blend well.

This was the circuit I used for 2nd order a few weeks ago.
Attached Images
File Type: jpg 2order xover_LR.jpg (79.6 KB, 310 views)
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Old 24th April 2013, 07:50 AM   #126
AllenB is online now AllenB  Australia
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It's worth a try, and at the least will give you the chance to cross some possibilities off the list. Don't lock yourself in to one polarity, there are a number of factors that will detract from what the texts will say, as true as they might be in an ideal world.

The treble region is very difficult to get just right, even when great lengths are taken. You should be aware of the following things.... Small problems here will sound like large problems. Most speakers seem to be set with the treble too high for reality and when people such as ourselves try to build a speaker we may find it hard to trade realism for what we are used to. Also you shouldn't assume that a dome tweeter is what you're looking for, although it may be. They have a specific nature about them (dispersion pattern, and the way in which they produce distortions), but they have advantages as well. I stopped using them some time ago.
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Old 24th April 2013, 02:29 PM   #127
mart.s is offline mart.s  United Kingdom
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Yes it is the treble region I'm having the most difficulty with, I am Confident the bass/mid seems right now but I am trying to get the tweeter to blend in and not stand out. I want it to be natural sounding, and yes I have fallen into the trap of having too much treble before and leaned from that. I always swap the polarity on the tweeter between every new configuration test so as not to miss anything.
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Old 26th April 2013, 12:17 AM   #128
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AllenB, your posts #116 and #117,

To a certain extent I agree with you. The acoustic response can be a great deal different from the applied voltage versus frequency.

If a first order cross-over network is constructed with electrolytic capacitors, and off-the-shelf inductors that are of a value that is only as close as possible to the calculated value, then yes, there is no point in quibbling about a few Ohms of difference between nominal and what the impedance actually is.

But if the order is 2nd or higher and capacitors with tolerance of 5% or even 1% are used, and the values of the inductors are within a few percent of the calculated values, then I think the designer would also want to base the values of inductance and capacitance on a load impedance that is at least a good deal closer to the actual impedance than nominal.

In the above situation where greater accuracy is sought for, and perhaps would result in improvement from the start, why would anyone say, "Well, I know that the impedance of this driver is about 1,2 times Re at the crossover frequency, but I'm going to base my values of capacitance and inductance on the nominal impedance"?

Regards,
Pete

Last edited by cT equals piD; 26th April 2013 at 12:19 AM. Reason: typo
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Old 26th April 2013, 01:40 AM   #129
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by mart.s View Post
I always swap the polarity on the tweeter between every new configuration test so as not to miss anything.
What do you mean here, do you design the speaker by ears or by software? (Software will tell you sufficient information)

Quote:
Originally Posted by mart.s View Post
Yes it is the treble region I'm having the most difficulty with
Is that acoustically 2nd order too? (It looks so to me). Acoustically LR2 is difficult. First issue is to get the overlapping phase at Fx is not always possible with normal measures. When you get it right (the phase, the response) the sound may still not right, especially at high spl where the slope may not be steep enough to avoid the driver resonance (Fs).

I don't recognize the tweeter, but the values are a bit strange to me. For the woofer, 0.9mH/4u7/5R6 is relatively very high, but for the tweeter 6u8/0.6mH is relatively low. Are you sure there is no extra dB at midrange frequency?

From my experience, no tweeter will sound good with 6u8/0.6. This of course depends on the tweeter parameters, what I mean here is from tweeters that I have ever used. Honestly, by intuition I think the crossover won't work, but you know better.
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Old 26th April 2013, 02:37 AM   #130
Jay is offline Jay  Indonesia
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mart.s, sorry I just read your previous posts regarding your crossover. I think you should post the original crossover before the original tweeter blew.

If you're familiar with designing speaker with these FRD/ZMA files, even without measuring the new drivers, you can still do it using similar drivers. Yes, there is little effort to find this similar drivers, but doable.

So the original is at 4kHz? And you don't have issues with breakup? Then there is no problem with the woofer. We don't need additional filter and we can cross the woofer anywhere we want.

Now the original tweeter. First order you said? I think we can forget the tweeter. Your crossover posted above definitely is too low.

But you still can show the original crossover at 4kHz, to understand the "properties" of the woofer. It is also difficult if both woofer and tweeter has different impedance (e.g 4R versus 8R). What is the impedance of this Audax tweeter?
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