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Multi-Way Conventional loudspeakers with crossovers

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Old 30th October 2012, 03:40 PM   #621
puppet is offline puppet  United States
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Originally Posted by krivium View Post
Let's go back to original subject: does anyone use FIR in active config? What are advantages of Brickwall filters compared to classic configuration?
Are they really worth the money and which method to parameter filters like this?
The advantage of a brickwall filter is the attenuation slope. Phase problems can arise when IIR/analog slopes are steep.

... but a brickwall filter also cuts the fourier components of the signal. Those parts of the signal get removed above and below the target frequency. Because of this, a ripple appears in the impulse response. This can't be avoided. You could get the on axis to sum correctly seeing as the ripples would appear on both sides of the target (and if identical they will cancel) but off axis they will/can be audible. How audible depends on the target frequency. Lower targets might be masked by the wavelength ... higher targets not so much. The steeper the slope, the longer the ringing lasts.
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Old 30th October 2012, 04:15 PM   #622
krivium is offline krivium  France
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Originally Posted by puppet View Post
You could get the on axis to sum correctly seeing as the ripples would appear on both sides of the target (and if identical they will cancel) but off axis they will/can be audible. How audible depends on the target frequency. Lower targets might be masked by the wavelength ... higher targets not so much. The steeper the slope, the longer the ringing lasts.
Thank you Puppet, so as i understand it except in certain particular cases (higher efficiency needed - P.A./ live act- or problematic's driver behavior - for eliminate breakup e.g.) no real and definitive advantage upon a 'classic' filter case (LR or JMLC kind) if drivers are good upon the bands they're dedicated to.
I suppose the audibility of the ringing off axis could be 'nasty' as narrow band, and audibly modify the radiated power pattern of loudspeakers.

Still a pick your poison situation if i understand correctly...

Is there an advantage of brickwall considering lobing in a three way with aligned drivers versus a classical filter configuration like say a LR?

Last edited by krivium; 30th October 2012 at 04:19 PM. Reason: precision added.
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Old 30th October 2012, 05:32 PM   #623
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Originally Posted by AndrewT View Post
Rooms can easily achieve 70dB of dynamic range
Easily? I guess you live out in the highlands... 60 to 65dB is more like it.

Last edited by flavio81; 30th October 2012 at 05:34 PM.
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Old 30th October 2012, 05:40 PM   #624
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Lobing occurs as a direct result of two things, the first is the interference pattern created when two or more drivers cover the same band of frequencies and the second is due to any off axis characteristics that would modify this and or be responsible for any lobing in it entirety.

Lets say you take a standard two way loudspeaker with a 4" mid/bass, a 1" dome tweeter, place them 30" apart and now cross it at 1500Hz with a 4th order filter. At and around the xover frequency the 4" will not be beaming but both it and the tweeter will be reproducing the same band of frequencies. If you go vertically off axis, due to the large driver separation you will get an interference pattern created by the two drivers going in and out of phase with one another, this is standard lobing. If you were to cross these two drivers to one another with brick wall filters, then theoretically only one driver would reproduce a given frequency at any one time, so all lobing around the xover frequency would disappear.

If you keep going up in frequency, until the tweeter starts to beam, then the primary listening lobe would start to narrow. If you were using a driver of a suitably large diameter, or were crossing the two drivers over at say 6kHz, where the 4" will have already started to beam, then the lobing pattern will be modified due to its response starting to droop. In this instance if you were to use a brick wall filter then you'd still get the primary lobe narrowing as the mid/bass starts to beam and then widen as you crossover to the tweeter, before it narrows again.
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Old 30th October 2012, 06:22 PM   #625
krivium is offline krivium  France
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5th Element, Thank you for your answer about lobing, it clarify certains things i had not entirely understood.

In fact now i understand why taking measurement about directivity behavior of each drivers in box are important to determine for optimal results.

For what i understand from the second part of your answer one of the main concern in choosing the cutoff point of Xover is the 'continuity' of directivity pattern between adjacent drivers.

So it raise another question for me: for best results which general directivity pattern must be choosen ( in case of drivers without horn)? I would say a natural narrowing of directivity dicted by medium/tweeter transition (e.g. if at 6khz medium as directivity of 60 -6db, tweet should be the same).
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Old 30th October 2012, 07:24 PM   #626
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I think it's a mistake to look at the dispersion pattern of any driver @xxxx frequency without examination of off-axis response too. Choosing where, in the frequency range to cross over, would have to include those aspects as well.
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Old 30th October 2012, 07:42 PM   #627
Pano is offline Pano  United States
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Just how different is the off axis response of cone drivers of the same diameter?
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Old 30th October 2012, 07:50 PM   #628
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Could be large indeed.
Some cones are flatish efforts while others are of geometric section.
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Old 30th October 2012, 08:08 PM   #629
Pano is offline Pano  United States
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That makes perfect sense of course, except - I remember reading an old Altec technical bulletin in which they actually measured cones of different sizes and profiles. IIRC, they found only the diameter have have a significant effect. There was a graph with the tech note showing beaming vs cone size. I'll see if I can dig it up.
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Old 30th October 2012, 08:58 PM   #630
krivium is offline krivium  France
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Quote:
Originally Posted by puppet View Post
I think it's a mistake to look at the dispersion pattern of any driver @xxxx frequency without examination of off-axis response too. Choosing where, in the frequency range to cross over, would have to include those aspects as well.
Could you be more precise Puppet please? I don't understand the difference between dispersion pattern and off-axis response, in fact the way i see it (and what i've got in mind in my precedent comment) is to take measurement of frequency response using a sine sweep of usable area of driver (plus/minus one octave) at different angle to define dispersion pattern.

E.g.: one measurement on axis then at 15 off axis, then 30, then 45, etc,etc.

And repeat this same process for each driver in Loudspeaker.

This should give all nescessary informations no?

Bare, interesting though about section geometry. In my case drivers are 'flat': honeycomb disk aluminium drivers from Technics. A 'big' Three way with 15" woofer 3" medium and 1" tweeter, and by nature all drivers are time aligned.

Pano i'm curious to see this document if you can find it.
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