Have 18Sound ND1030 + XT120 and want to get Faitalpro 8PR200 - diyAudio
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Old 15th June 2017, 02:56 PM   #1
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Default Have 18Sound ND1030 + XT120 and want to get Faitalpro 8PR200

I got the first 2 objects for a good price. So I went off and found an 18Sound application note that has a 2 way with an 8 inch driver. Except....This project is meant to be a gift and since I have seen a deal for the 8pr200...I want to shoe in the Faitalpro 8PR200 instead of the 8MB400 by 18sound.

The application is for a single ended amp (5-7Watts) in a smallish room.

Will the cab and crossover be reasonable for the 8PR200 instead of the 8MB400/8MB500?

I also don't like the pro look for my friend's home. And for ease of build I'd like to have the sides parallel to each other. Problems? Suggestions? Changes to betters suit a home music listening situation instead of a pro environment?

Link to the application note
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Last edited by Bas Horneman; 15th June 2017 at 02:59 PM.
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Old 15th June 2017, 06:34 PM   #2
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You should be able to get excellent 2-way sound from these speakers.

The T/S parameters of the 18Sound 8MB500 (Re=5.1, fs=74, Qtc=0.43) are "close" but not a "close enough" match to the Faital 8PR200 (Re=5.1, fs=58, Qtc=0.35) to allow a simple switch without both some changes to the cabinet volume or at least the ports, and also changes to the 8MB500 midbass crossover. You also may need additional attenuation (higher value >0.5 ohm input resistor) to the ND1030 compression driver.

Parallel flat sides are typically not a SPL/freq flatness issue, the curved sides on the 18Sound cabinet typically reduce cabinet resonances with simple bracing. The round radius edges on the front baffle are important in reducing diffraction. So, flat sides are fine. So, round baffle edges are worth the effort.

Faital 8PR200 cabinet ideas:
Qtc ~ 0.7, box volume ~0.3cuft, two 2" ports ~ 10.3" long

EBS3(-3db bass-shelf), box volume ~0.72cuft, two 2" ports ~7.5" long
============
Locating the speaker near a rear wall enhances the bass, and typically complements the droop of the EBS3. Discuss this alignment & near-wall placement with your friend, as it can produce improved bass without boom.
==
So, a cabinet with internal woofer volume between 0.3 and 0.7cuft can be used with the correct port size selection.
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File Type: jpg 8PR200 Ported Options.JPG (238.5 KB, 129 views)
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Old 15th June 2017, 07:02 PM   #3
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Quote:
You should be able to get excellent 2-way sound from these speakers.
I was hoping you would chip in. I was afraid that you were going to say without two 18 inch drivers to do the bass... this design would be severely flawed.

Quote:
EBS3(-3db bass-shelf), box volume ~0.72cuft, two 2" ports ~7.5" long
So this last figure is what I should aim for?

Thanks for helping.
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Old 16th June 2017, 12:39 AM   #4
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It seems smart to copy the proven 250mm x 435mm front baffle, including the cutouts for the drivers.

A cabinet depth of about 250-260mm should create about 0.7cuft open volume after the speakers+bracing volume. The owner can experiment with EBS3 bass shelf for extended&balanced bass with near wall placement. The internal box volume can be reduced by adding wood blocks internally to reach ~0.3-0.4cuft for a Qtc ~0.7 Butterworth alignment with improved reduced delay and phase shift with deeper in-room placement.

Even with similar Re=5.1ohms, the 8PR200 SPL/freq slope around 2kHz is different from that of the 8MB400, and I suspect a different BW3 crossover circuit for the 8PR200 will be necessary for perfection.

TIME ALIGNMENT. Some designers use different crossover frequencies for the midrange and tweeter in order to get a phase shift which mimics the physical time difference of a long horn from a short midrange. You will need to measure(square wave delay) the time delay between the horn+tweet vs. Mid.
example:
3rd order Butterworth Low Pass, -3dB @ Fx*0.87 (+)
3rd order Butterworth High Pass, -3dB @ Fx*1.15 (-)
Offset = 0.22*c/Fx
= 1.5" physical difference at Fx=2000Hz.

www.diyspeakers.net/Projects/Tools/offset.xls
https://www.google.com/search?sclien...=Google+Search
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Old 16th June 2017, 07:28 AM   #5
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Quote:
It seems smart to copy the proven 250mm x 435mm front baffle, including the cutouts for the drivers.
It does.
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Old 16th June 2017, 11:02 PM   #6
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Before you cut wood...

1) Box alignment plots can help discussion with your friend on the "bass shelf" alignment and how it complements a near-wall placement for deeper, more even in-room bass.
b) If friend wants to locate speakers several feet into the room for a "wider more 3D" soundstage, the traditional BW3 alignment will have less deep bass, but more even in-room sound with slightly less shift in time and phase. Adjust internal box volume. Now we can sell him on dual 18" woofers.

Faital 8PR200
EBS3 = extended bass shelf -3db
19822cm^3 volume (0.7 cuft volume) tuned to 50Hz with
two ports with internal diameter = 48mm (1.9"), length 183mm (7.2")

2) I can recalc ports if you post the internal pipe diameter available in your area... plastic, cardboard, steel, etc....

Crossover.
3) You can physically(ruler) or electronically(square wave pulse) measure the on-baffle time offset difference between the dome of the compression driver and the voice coil of the 8PR200. Maybe do some research before you decide on crossover options. Maybe check your passive Xover parts box for early experiments.

a) Steep BW3 and LR4 slopes often hide modest time offset listening artifacts. Build 2kHz Xover circuits on both tweet + midbass just like the professional 18Sound design.
b) Use the attached Excel crossover delay spreadsheet for time offset compensation from different frequency BW3 circuits on the midbass and on the reverse polarity tweeter.

Fx= 2Khz example for 1.5" physical(time) offset:
3rd order Butterworth Low Pass, -3dB @ Fx*0.87 (+)
3rd order Butterworth High Pass, -3dB @ Fx*1.15 (-)
Offset = 0.22*c/Fx
= 1.5" physical difference compensation at Fx=2000Hz goal.

1740Hz BW3 Xover circuit on midbass
2300Hz BW3 Xover circuit on tweeter with reverse polarity connection
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Old 18th June 2017, 10:02 PM   #7
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Quote:
Before you cut wood...
The thing is my friend lives in South Africa. And I live in the Netherlands. So the plan was to take the drivers, a pair of frontpanels, a crossover and some pipes over in the airplane...suprise him and say I'm going to build you a speaker (If you know someone that can cut us some plywood....) that will fit the amp I built you... he does not listen often...and is not very critical. (But I still want the speakers to be awesome sounding ofcourse)
Quote:
I can recalc ports if you post the internal pipe diameter available in your area.
I checked and the 50mm pipes here have a wall thickness of 2.4mm. Wich makes the inner diameter of the pipes that are readily available 45.2mm.
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Old 19th June 2017, 08:27 AM   #8
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The next size up in tubing is 70.2mm.
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