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Old 4th July 2013, 08:58 PM   #1
jacozz is offline jacozz  Sweden
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Default Crossover point from listening position?

Me was thinking, would'nt it be better to determine crossover calculations from listening position rather than near field?
Since treble energy diminish with distance, and therefor should be accounted for in the crossover design, which should make a considerable different approach to the calculations?

For example, My listening position is some 3.5-4 meters away from the speakers and I feel that treble energy is lacking with the traditional crossover approach.
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Old 5th July 2013, 01:22 PM   #2
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Crossover points are not determined by listening distance. Voicing a speaker should be done in the far field =>2m distant. What speaker are we refering to? Do you have measurements?
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Old 5th July 2013, 04:57 PM   #3
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Tweeter padding would change for listening distance, but not the XO frequency.

As Greebster said, final voicing from listening position. You should be able to take that into account w/ the XO design software.
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Old 5th July 2013, 06:50 PM   #4
JMB is offline JMB  United States
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Just to clarify, the response of the drivers may change based upon where are on off axis. In general, people either model based upon on axis measurements or averaging a few off axis measurements with on axis (a rough estimation of power response) but generally they do not average in measurements that are well off axis. The drop off in frequency response off axis is associated with a beaming effect and this occurs towards the top of the drivers passband and is related to its diameter.

As you get further away from the speaker, the relative amplitude of the drivers will not change in most environments (there may be some exceptions in very large venues) unless you are off axis. Part of setting up where you want to cross over is taking this into account but in general, you are trying to cross the tweeter or mid low enough to mitigate this effect with the woofer. The beaming effect of the Tweeter cannot really be dealt with in setting a crossover point but is addressed using shaping circuitry.

Jay
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Old 5th July 2013, 08:44 PM   #5
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You have to ask if you are creating a specific purpose speaker or a general purpose speaker?

If you custom tailor a speaker to youself personally, then it only fits you and your circumstances. Move to a new house, re-arrange the furniture, and the speaker is no longer suited.

Plus, have you worked it out?

You sit about 12 feet (3.66 meters) from the speakers, the frequency associated with 12 feet is 93.833hz.

How are you going to apply that knowledge to your crossover design?

If the bass driver and the tweeter are balanced at 86dB each 1 meter away, as you move back, they are both going to fall equally with distance (more or less).

Just as an experiment, I took a different approach. I started stepping through frequency tones asking myself at what frequency, to my ears, does the increasing tone lose any sense of bass. For me, with my equipment, that was about 300hz, bass became midrange.

I kept stepping upward then searching for where does a midrange tone lose it sense of midrange-ness and start to sound like Treble. That turned out to be around 3000hz.

So, given that those seem to be the transition points, would it make sense to place the crossovers at those frequencies? Maybe ... maybe not.

Or does it make more sense to cross the drivers over based on their best operating range? If you have a driver that starts to drop or break up above 2khz, it doesn't make much sense to crossover at 3khz?

As to treble energy, are you on axis (the center line) or off axis?

Where are the tweeters relative to your ears? Above, in-line, or below?

Next, are these DIY speakers or commercial? If DIY how much have you padded (attenuated) the tweeters to bring them in line with the bass drivers? Simply attenuate them less.

What are your room acoustics like? Perhaps sound absorbing panels in the mid/high range would soften echoes/reflections that are interfering with your enjoyment?

Also keep in mind that at equal measure loudness, treble will sound louder. Take that into your calculations.

Treble tends to beam, to radiate in a narrow beam of sound as the frequency goes up. That has to be considered.

In the end, to some extent you do custom tune the speakers. You place them in your room and tweak the design until it sounds right. Though it would help if it reasonably measure right too.

So, back to the main question, how does knowing that you are at a 93.833hz wavelength from the speaker, aid you in tweaking the speaker?

Steve/bluewizard

Last edited by BlueWizard; 5th July 2013 at 08:51 PM.
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Old 5th July 2013, 11:15 PM   #6
jacozz is offline jacozz  Sweden
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Thank you guys for your thoughts on the matter.
For me, coming from the single driver world, it's a real challenge try to mix the midrange with tweeter without, or at least minimize the crossover evil i the vocal range Apart from vocal presence, it sound really good.

I'm doing a Open Baffle arrangement with a 2.5-way active design.
Bass drivers are: Eminence 15 KappaLite LF (Running with Hypex sub amp with a 12db Lp-filter around 130 Hz), they are great!
Midrange: Visaton B200 (running without HP-filter, but a in line lowpass filter-fmod around 1k) and with a separate class T amp
Treble: HiVi RT2H-A (running with a 18 uf coil + a 2,5 khz Hp inline f-mod and with a separate class T amp.

Real world acoustical crossover points between mid and tweeter:
about 2500 Hz with a true 6 db slope one the midrange driver, but the planar tweeter measure more like 12 db slope from 2k downwards...

It's sounds really great and they measure pretty flat., except, compared to my fullrange drivers, the vocal is somewhat confused, and somewhat distant. Maybe that is the trade of with multiple drivers in the critical frequency range, or it's take some woodoo work to get that coherence that I hear with my full range drivers work in a 2-way?
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Old 6th July 2013, 10:55 AM   #7
AllenB is offline AllenB  Australia
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The dome tweeter will have a wider coverage and more presence in the room for a given on axis response, some of which will not be positive unless your baffling and positioning are good.

If these suit your preference and they match the mid, you still need to choose the best angle to listen to each of them. If this is good you should be able to design a crossover from the listening axis, but it means you will have taken a number of measurements already to demonstrate this. Unless you use good judgement regarding all these things and just do it.

As was suggested, I find a small number of measurements around the listening position helps to average some of the reflections, and it is sometimes better not to equalise reflections in the crossover but deal with them separately.
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Old 6th July 2013, 06:37 PM   #8
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I'm curious why a 1,000hz low pass on the Midrange/Mid-Bass?

You said -

Bass = 12dB 130hz Low Pass (Sub plate amp)

Midrange = 12dB, 1khz, Low Pass only (FMOD)

Treble = 2.5khz High Pass (FMOD) followed by a 1100hz (coil) High Pass

But from what I understand, the FMOD is on the amp and the 18uF is on the tweeter.

The FMOD passes everything above 2.5khz from the amp to the tweeter, which mean nothing between 1100hz and 2.5khz reaches the coil on the tweeter. You seem to have a gap in your frequency response.

Perhaps I misunderstand something, but the 18uF coil, if we assume it is on the tweeter, is doing nothing.

WAIT! - I just realized something, you said 18uF COIL. Is that a Typo? Is that 18uF Capacitor or a 18mH coil? Now I'm even more confused?

Steve/bluewizard

Last edited by BlueWizard; 6th July 2013 at 06:45 PM.
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Old 7th July 2013, 02:45 AM   #9
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jacozz,

There are two things I see that stand out is your choice of crossover point. The B200 should be lower, say 1700-1800Hz based on the polar plots I've seen.

The cross at 1K is to reduce the rise peaking around 2.5k but doubt this will be enough due to the rising response to 10K. Off the top would do nothing but make it flat. Try a second order with a shelf filter as a min.
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Old 7th July 2013, 03:38 AM   #10
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Repeating my point -

----[FMOD 1.0khz]----[T-Amp]----[6 ohms B200 Mid]
----[FMOD 2.5Khz]----[T-Amp]----[18uF (1100hz]----[8 ohm tweeter]

You have a gap between 1.1khz and 2.5khz.

Am I lost here? Do other people see this?

If I am wrong, please explain HOW I am wrong?


I could be wrong, as I indicated, but I suspect this is what you really wanted -

----[FMOD 1.0khz]---[T-Amp]-----[7.95uF (2.5khz)]-----[8 ohms tweeter]

First cross at 1khz, then at 2.5khz add a sharper slope to the crossover.

Though in all honesty, I'm not sure that makes perfect sense either.

Further, the HiVi RT2H-A has a low end of 1,700hz, why are you crossing it at 1khz, at least theoretically?

If you want to cross at 2.5khz, then you have to move the Mid cross up to 2.5khz.

Again, I'm happy to have anyone tell me I'm wrong and why?

Either the Mid has to go up, or the high as to come down to fill that gap.

Steve/bluewizard

Last edited by BlueWizard; 7th July 2013 at 03:55 AM.
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