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Multi-Way Conventional loudspeakers with crossovers

Infiniti Reference Three --> Summer Project
Infiniti Reference Three --> Summer Project
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Old 16th July 2017, 06:56 PM   #1
fastandlight is offline fastandlight  United States
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Default Infiniti Reference Three --> Summer Project

For the past 27 years (or so, no one can really remember when we got the Infiniti's), my family has been passing around a pair of Infiniti Reference Threes for whomever needed a decent set of speakers. Now they've come back to me with the foam surrounds completely gone. Despite all the years, please don't assume I have any nostalgia for these things...I'm not a nostalgia kind of guy.

However.

After building a few pairs of speakers I need to confess that I am terrible at building cabinets. My dad was an electrical engineer, not a woodworker, and my strengths are in the same areas. Electronics, soldering, circuit design, etc. don't scare me one bit. Varnish? Sanding? Joints? No thank you.

That brings me back to the current situation. The sound of these speakers was never amazing, but the black cabinets still feel really solid. I'd like to re-use the cabinets and put in some modern drivers and crossover(s).

Here are the original specs:
Frequency Response: 47Hz - 25kHz
Crossover Frequency(ies): 400Hz and 3.5kHz
Sensitivity: 90dB (1 watt/1 meter)
Nominal Impedance: 6 ohms
Power Rating: 20 - 125 watts
Woofer: 8" (20.3cm) IMG
Midrange Driver: 5" (12.7cm) IMG
Tweeter: 1" polycell

The outer dimensions of the cabinets are:
Height: 21 5/8"
Width:10 1/2"
Depth: 9 1/2" (a little tough to measure, as the baffle is beveled)
Sealed cabinet.

I've always used kits and the cabinets they were designed for in my previous projects, so I'm not sure where to start with this one.

Basically, given this cabinet, what is a good pairing of drivers (1", 5", 8") and crossover design?

I was thinking of bi-amping the new speaker (I have plenty of amps that deliver lots of clean power) to make the replacement design easier. Most of the places I would use these I don't have a sub, so a setup that providers for a good bit of strength down low would be appreciated.

Thanks for any help (or suggestions that I just toss the things into the trash if that's the right answer).
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Old 16th July 2017, 07:26 PM   #2
Lojzek is offline Lojzek  Croatia
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Hi F&L, and how do you feel about repairing those shot foam surrounds, midrange too? I think a challenge of this kind is good for one's own intelect. If it were me, I'd certainly try that and then completely design a modern XO filter from scratch, reusing the coils and modifying these if necessary. I am a recycling kind of a DIYer. The potential for good SQ is there.

The procedure to start with would be first to make sure the units are electrically sound, voice coils measuring normal dc resistance values, and the tweeter not being stuck because of old ferrofluid, assuming it was there in the first place.


Have you got a service manual?
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Last edited by Lojzek; 16th July 2017 at 07:30 PM.
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Old 16th July 2017, 09:40 PM   #3
fastandlight is offline fastandlight  United States
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No service manual. I'm inclined to put my refoaming skills in there with my cabinet making skills....weak. These were always OK, not great, so the effort to just restore that level of sound quality is not quite worth it in my mind. Playing the matching game with a design and components that are 30 years old seems like it would leave a lot on the table. I have to imagine drivers have improved a great deal in the last 3 decades.
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Old 16th July 2017, 10:39 PM   #4
Lojzek is offline Lojzek  Croatia
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There is all kinds of good quality brand name drivers to choose from. Is there a specific limit to the budget?
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Old 17th July 2017, 02:24 AM   #5
fastandlight is offline fastandlight  United States
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Great question. I can probably spend $200 or $300 before my wife starts asking tough questions. I might be able to make some room for something I haven't had a chance to play with before like a minidsp for active crossover .
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Old 17th July 2017, 02:30 AM   #6
fastandlight is offline fastandlight  United States
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I was just thinking, given that I need to get 3 drivers per speaker instead of 2, I should find some more money for this project. If there is a big improvement by spending more on a recommended driver hit me with it. That said, this isn't a thousand dollar project. Right now the speakers don't work, so any improvement over that would be good.
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Old 17th July 2017, 05:55 AM   #7
picowallspeaker is offline picowallspeaker  Italy
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Infinity used to use 4 Ω woofers to obtain more punch in the bass ( see the 6 Ω label : ( 4+8)/2=6 ) and that makes things easier ( for sensitivity, and for the smaller coil for lowpass... lower R for correct alignement in sealed box) but it's not so good
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Old 17th July 2017, 08:02 AM   #8
Lojzek is offline Lojzek  Croatia
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Dayton Audio RS range of drivers are very good value for the budget of yours, also Scan Speak Discovery Series, Peerless Nomex woofer and PPB midwoofer, Peerless fabric tweeters. SB Acoustics has alternatives and the list of brands goes on! Mini dsp and accompanying 6 channels of amps, measurement microphone will add to the costs. Maybe a hybrid solution, passive XO on mid and tweeter combo, mini dsp for woofer LP and MidTw HP.
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Old 17th July 2017, 01:00 PM   #9
fastandlight is offline fastandlight  United States
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Quote:
Originally Posted by Lojzek View Post
Dayton Audio RS range of drivers are very good value for the budget of yours, also Scan Speak Discovery Series, Peerless Nomex woofer and PPB midwoofer, Peerless fabric tweeters. SB Acoustics has alternatives and the list of brands goes on! Mini dsp and accompanying 6 channels of amps, measurement microphone will add to the costs. Maybe a hybrid solution, passive XO on mid and tweeter combo, mini dsp for woofer LP and MidTw HP.
Lojzek,
Thank you for all of the help and suggestions. I really appreciate your time. I think we are thinking along the same lines. I have a measurement microphone already, though my skills and experience in using it are limited so far. I was thinking a relatively simple tweeter and mid with their own crossover, then using a minidsp to do the crossover to the woofer.

Is there some open source software (or something) I could use to start modeling out the driver combinations and seeing what might make sense?

I think I also need to take apart one of the speakers and see what the internal bracing looks like, etc. and get a good idea of the internal volume of the box.
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Old 17th July 2017, 01:35 PM   #10
Lojzek is offline Lojzek  Croatia
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Sure, there is free software and powerful too.

Jeff Bagby's Software Page
http://libinst.com/Xsim/XSimSetup.exe
FPGraphTracer : fprawn labs
Tolvan Data

I think that's all you might need, even more.
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