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Multi-Way Conventional loudspeakers with crossovers

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Old 9th December 2011, 05:08 AM   #1
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Default 2-Way Sanity Check

I have a set of 2-way speakers that have been with me in one form or the other since 1979. They are (more or less ) closed box 2-ways with (currently) 16 pieces of a Vifa/JBL 4.5" 4 ohm mid-woof speakers offered by Parts Express a few tears ago. There are 3 pieces per side of a Vifa 6 ohm dome tweeter that's so old I doubt I could find the part number.
Anyway, here's the plan - first off , I want to bore two more holes in the back so Ican add two more drivers, so I can string them as series parallel arras of three parallel strings of six drivers per side, bringing the impedance up to 8 ohms from the original 4 (4 parallel strings of 4 series drivers).

I'm thinking of boring an extra hole and replacing the Vifa tweeters with four pieces of the Fountek FE85 full range drivers connected in series-parallel for 8 ohms impedance. I'd give each driver it's own damped chamber cup and cross over somewhere between 250 and 500 Hz. What I'm mostly asking for comments about is my choice of crossover frequency. I want to avoid the 6k suckout that is a characteristic of the Vifa drivers. At the same time, I want to avoid treating 32 drivers to fix mid/high frequency problems. Does this sound sane, or is there a better choice for crossover frequency? I have a wide range of choice, as I'll be doing biamplfication with a discrete jfet electronic crossover.
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Old 9th December 2011, 07:14 AM   #2
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There are some incongruences ..but the thread title said it all !! I haven't tried myself , but putting 2 speakers in series is risky . I see you are an 'electronic' guy : would you put deribelately many transistors in parallel ( like in output stage of an amp , or in input differential..) without selecting them by their curve characteristic ? There will be the sucker ones and the performer ones , and the consequences would be catastrophic , at least from the point of view of efficiency .
Maybe nowadays with quality check at the end of the factory chain you can end in having well matched components , but think : when two coils are in series ,they act like a voltage partition , but there are also self-inductance and more , back-EMF !!
If the electrical side is ( theoretically ,and it may be sufficient only with little drivers ) ok , let's see the effects of combing filter with an array of drivers ,where there is no equalization nor partition between them . The ones that are at ear level would emit the treble band on axis , the others would be attenuated ,etc etc ..
Latest technology would bring to this
Audio Artistry
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Old 9th December 2011, 07:32 AM   #3
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That's not what I meant at all - I've been living with the speakers in their present state, series-parallel drivers and all, for a good few years. It's not about stringing together the speakers - that's all done and settled. My main question is the choice of crossover point, which is a good bit lower than most people seem to put their mid-tweeters.

The speakers were originally inspired by an article in Audio magazine in the late 70's regarding doppler distortion.The multiple drivers limit cone excursion, and reduce said distortion (the author used 32 drivers/side). They sound smoother than most anything else I've come up with so far, but could use some improvement. I have some alternate speakers in place now, so it's time to drag the old warhorses down to the basement to see what I can do.
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Old 9th December 2011, 07:44 AM   #4
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Yes I see , just making the point . Every day there's a new inspiration .
I also listen to late '70 speakers ( found in the trash ...and refoamed ).
I try to make my best to conjugate type of music , source type and eveything
to only one type of speaker ( BTW I saved on my HD your Xover schematic )
but the discrimination I exposed retains me to try serial arrangement .
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Old 9th December 2011, 11:36 AM   #5
AllenB is offline AllenB  Australia
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I'd be happier with a lower frequency. Is there maybe something you could do with the floor ceiling bounce in setting your point?
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Old 9th December 2011, 05:41 PM   #6
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If I set the crossover frequency on the Founteks any lower than 250Hz, what's the point of having the other 32 drivers around? I'm not trying to do a full-range with the Founteks, after all.
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Old 9th December 2011, 07:05 PM   #7
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Quote:
Originally Posted by wrenchone View Post
If I set the crossover frequency on the Founteks any lower than 250Hz, what's the point of having the other 32 drivers around? I'm not trying to do a full-range with the Founteks, after all.
In your first post you said "I want to avoid the 6k suckout that is a characteristic of the Vifa drivers."

That suckout may simply be a result of the center to center distance in the tweeter array.

Four 3" drivers in array will have HF suckout problems too, due to the diameter being quite large compared to the wavelength of high frequencies.

As far as crossover frequency, with a ratio of 16 to four, I'd suggest that 500 Hz would be a better choice than 250 Hz from an IM standpoint.
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Old 9th December 2011, 07:49 PM   #8
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The suckout is a charateristic of each individual driver, and shows up quite plainly in the individual response curve.
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Old 9th December 2011, 07:54 PM   #9
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Originally Posted by wrenchone View Post
The suckout is a charateristic of each individual driver, and shows up quite plainly in the individual response curve.
What does the response of the array of drivers look like?
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