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Old 1st September 2013, 05:16 PM   #1
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Default Crossover advice needed

I found this speaker at a recyclers and Ive replaced the tweeter diaphragm but there are no markings whatsoever on the woofer so I cant find any specs for it. I have no idea what I'm doing with this now, I don't know if its a P.A. speaker or a guitar speaker box or what? Can anyone suggest a crossover for it or how I could use it?
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File Type: jpg Guitar amp 002.jpg (1,000.4 KB, 99 views)
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Old 1st September 2013, 05:29 PM   #2
system7 is offline system7  United Kingdom
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It LOOKS like a practise guitar speaker to me. The corrugated bass seems to say that.

How big is the bass and does it have a cloth or rubber surround? you usually measure the diameter of the frame in inches.

You'll probably end up with an LC filter and some attenuation on the horn unit. The bass might get a coil or nothing at all.
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Old 1st September 2013, 05:58 PM   #3
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The bass measures 12 inches across,the surround isn't rubber it looks like paper/cardboard? It is 6.9 ohms and the tweeter is 6.2 ohms. What do you think Steve?
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Old 1st September 2013, 08:36 PM   #4
system7 is offline system7  United Kingdom
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I really can't claim to know a lot about a 12" bass plus Horn tweeter, but can do a rough sim using another tweeter and a conventional 12" hifi bass.

What makes the combination good, is the time alignment you get by setting the tweeter back in a horn. Here I set the acoustic centre of the tweeter a mere 2 cms in front of the bass' acoustic centre. You can see how big basses rolloff steeply. People like Klipsch use 2nd order filters on both drivers, so I've gone with that. I can't comment on whether the horn needs equalising. A lot do.

This particular speaker is more of a wallmounter than a stand alone. We have no idea of efficiencies here, so I can't really guess the attenuator values beyond being about 8 ohms load overall to the LC. Impedance dips lower than I would like, but not bad.

You wouldn't get away with this circuit with a regular tweeter on a flat baffle. Phase would be horrid.

Whether you want to try this is up to you. It'll take a bit of fiddling to get right.
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File Type: png 12inchbass_HornTweeter.PNG (7.3 KB, 79 views)
File Type: png 12inchbass_hornTweeter_FR.PNG (19.4 KB, 74 views)
File Type: png 12inchbass_HornTweeter_Phase.PNG (23.8 KB, 70 views)
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Old 2nd September 2013, 02:17 AM   #5
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If I try your setup how would I know that I could make it better by fiddling with it? I have an oscilloscope and a signal generator.The thing is though,guitar speakers are built to handle distortion,not like a Hi Fi speaker? I might have a look around on some pro gear sites and get back.
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Old 2nd September 2013, 03:33 AM   #6
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Pa drivers require different crossovers, impossible to guess with mystery drivers. Look at the crossovers for PA drivers like Eminence, others. Study the work from Wayne Parham (with SPICE) and give a go to the Econowave. Any xover might work mediocre without the driver parameters, sorry. Regards.
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Econowave(ish) design - 12" woofer and 12" waveguide
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Old 2nd September 2013, 06:44 AM   #7
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Isn't there some way that I could run some frequencies through this woofer and get the parameters on my oscilloscope? Thats all the info I need for the crossover isn't it?
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Old 2nd September 2013, 10:21 AM   #8
AllenB is offline AllenB  Australia
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An oscilloscope is a good thing but isn't of much help in this aspect of crossover design. Before computers were used in this way, I used to use my CRO to plot impedances and other things, now I save it mostly for making amplifiers.

The primary choice here will be in matching the dispersion of the two drivers. Look at the angle of the tweeter. the woofer will be narrowing to this angle somewhere above 1kHz, possibly 2kHz.

Next, can the tweeter do this frequency well? It looks a little small for this. You'll be compromising by crossing higher but sometimes this is a better option.
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Old 2nd September 2013, 11:19 AM   #9
ODougbo is offline ODougbo  United States
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Generator - voltmeter - load resistor: all the basics tools for tuning BR boxes.
Did you measure the Fs of the woofer?
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Old 2nd September 2013, 01:10 PM   #10
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Quote:
Originally Posted by ODougbo View Post
Generator - voltmeter - load resistor: all the basics tools for tuning BR boxes.
Did you measure the Fs of the woofer?
I have absolutely no idea of what a BR box is,I take it that Fs is frequency? If it is, that is basically what I'm asking about here? How do I find the crossover frequency? What do people do if they are in my position when they cant get the specs for a perfectly good driver,throw it in the bin? Maybe someone can recognize what type or model of driver the woofer is and I can go from there?
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