Minimus 77's with Zaph Audio ZA14W08 5" Mid/Woofers

[cachehiker]

A little patience here, my first post.

I built three pair of speakers in the distant past. Two turned out well, one did not. Lately, the 25 year old pair of Minimus 77's I've been setting up on stands in the backyard for barbeques suffered a rather ignominious demise at the hand of a drunken attendee. The cabinet? Fine. The tweeter? Apparently fine. The Woofer? Its foam surround was torn. Upon removal, the foam practically disintegrated in spite of rather gentle handling. At least after 25 years, I can claim to have gotten my money's worth.

These speakers have been such workhorses for so long that I even custom built some aluminum brackets to mount them on the speaker stands. I have therefore decided to rebuild them. I have the technology. I can make them even better than they ever were. (Cue Six Million Dollar Man theme song)

After spending hours shopping for a replacement set of drivers that would fit the 4-1/2" holes, match the tweeter SPL, and be appropriate for the 2.65 liter cabinets. I settled on a pair of Zaph Audio ZA14W08 5" Mid/Woofers, although I'll have to trim a couple of millimeters (3mm at the most) from the side of each frame for them to fit behind the perforated metal grills. Is this a horrible idea that's guaranteed to make them sound ridiculously bad?

I initially assumed the 0.4mH air core inductor and 4.7 uF bipolar electrolytic were simple 6dB/octave high/low pass crossover components. Upon further inspection, I was wrong. The woofer was not crossed over at all and the inductor and capacitor formed a 12dB/octave high pass for the tweeter at 3.5KHz. What perplexed me was the Q which I calculated at 0.867. Why so high? I thought Chebyshev crossovers had no place in higher end audio. Was it to cover up what the woofer was doing above 3.5KHz?

In the end I settled on a proper crossover utilizing 3.0uF capacitors, 0.75mH inductors, and a Q of about 0.5. Any thoughts? I look forward to any forthcoming advice.

[5th element]

The Q of any electrical network is largely unimportant when considered in such an application. The filters job is to mould the natural frequency response of a driver into a desired target goal, say to a fourth order Linkwitz Riley network with a Q of 0.5. Depending on the drivers natural frequency response this could require an electrical filter of anywhere between 2nd and 4th order with a Q varying from say 0.3 to possibly greater then 1.

Running the ZA14 drivers full range is a recipe for disaster, these are not drivers that should be run full range and require taming via an appropriately designed crossover. Zaph has crossovers for single driver implementations that you could use as a starting point.

[cachehiker]

I was looking at this design for a bit while trying to keep things where I could still fit them inside the sealed minimus-77 box. As it is I will have to build the crossover outside the box, screw it to the terminal plate, and then connect it through the woofer opening.

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From what I've read about the SD-60/SD-61 tweeter, I won't need to do any impedance matching for differing SPL's, at least not until I have some objective measurements telling me I need to. I'm also assuming the 10Ω 5µ network is to knock down that little 3KHz peak in the third harmonic of the Zaph driver. Am I wrong?

Until I get a system to analyze their performance, I'm afraid I'll be shooting from the hip at whatever my untrained and subjective ear tells me I need to aim at. My ultimate goal with this project is to pick up what I need to build the surround setup in the basement.

[tomtt]

Originally Posted by cachehiker

Any thoughts?

i'm thinking any cheep plastic capacitor will sound

-Much- better than any electrolytic.

a half dozen of these aren't very expensive -


1UF 250V 10% METALLIZED FILM CAPACITOR | AllElectronics.com





also those little woofers might be a good thing to save.

like this -


Minimus 77/Audiosource LS-TWO/A refoam - AudioKarma.org Home Audio Stereo Discussion Forums

[5th element]

Originally Posted by cachehiker

At least not until I have some objective measurements telling me I need to.

Indeed, until you take some measurements you won't know exactly what's going on.

Originally Posted by cachehiker

I'm also assuming the 10Ω 5µ network is to knock down that little 3KHz peak in the third harmonic of the Zaph driver. Am I wrong?

No, this is incorrect. The C+R is in principle what's known as a zobel network and is used to flatten the impedance rise that is created by the woofers voice coil inductance. There is no way you can remove the distortion peak at 3khz, the only thing you can do is crossover low enough such that it is effectively removed.

Sometimes you will see C + R shunt networks and might confuse them with a zobel when in fact they are not. A second order electrical low pass has a series inductor followed by a shunt capacitor. Now you can attenuate how much affect the C will have by adding in a small resistor in series with it. If the resistor value is small, then it is more then likely there to shape the knee of the 2nd order network, rather then be a true zobel, that is there to completely flatten the impedance.

Originally Posted by cachehiker

Until I get a system to analyze their performance, I'm afraid I'll be shooting from the hip at whatever my untrained and subjective ear tells me I need to aim at. My ultimate goal with this project is to pick up what I need to build the surround setup in the basement.

Better get that measurement system together then

Originally Posted by tomtt

i'm thinking any cheep plastic capacitor will sound

-Much- better than any electrolytic.

Good quality electrolytics sound fine to my ears and are more then acceptable in anything other then what you could call your critical listening setup. The only thing to watch out for with lytics is if they are old and the electrolyte as dried up and thus changing its value.

The idea of re-surrounding the woofers is a good one, albeit the new surround will probably affect the drivers mechanical damping in some way, but it's unlikely to be a problem, unless again, you are aiming for perfection.

[sreten]

Hi,

Zaphs driver is not appropriate for 2.65 litre cabinets.
Either refoam the original drivers or start from scratch.

https://sites.google.com/site/undefi...ightsensations

Should work sealed in that cabinet, playing with the tweeter L-pad
should allow you to use the original tweeters, but stick to that
c/o, the result should be far better than they ever were.

rgds, sreten.

[cachehiker]

Originally Posted by sreten

Zaphs driver is not appropriate for 2.65 litre cabinets.
Either refoam the original drivers or start from scratch.

The farther I get into this, the more inclined I am to agree. The sealed enclosure calculator on mh-audio indicated the resulting Q wouldn't be so bad but now that I have them in hand, I can say for certain that getting a decent crossover in there along with the Zaph driver isn't something I'm going to attempt regardless of their suitability or lack thereof. I've never tried to replace the foam surround on a speaker before but there's a 5" repair kit on speakerworks.com that I'm measuring for as I take breaks from typing. I think I'm going to give it a shot.

Originally Posted by 5th element

The only thing to watch out for with lytics is if they are old and the electrolyte as dried up and thus changing its value.

I'm an engineer by trade (mostly motors, controls, and data acquisition) and I'm well aware of the limitations of electrolytics. I ordered film caps but not because the electrolytics won't work. It's because if I get this right, the speakers may well be in use for another 25 years.

Originally Posted by 5th element

The C+R is in principle what's known as a zobel network and is used to flatten the impedance rise that is created by the woofers voice coil inductance. There is no way you can remove the distortion peak at 3khz, the only thing you can do is crossover low enough such that it is effectively removed.

The clarification is appreciated. I think I'm probably going to have to live with it at this point. The Zaphs are currently destined for the same enclosure as that in the earlier link although with an 8 ohm tweeter crossed over at 12dB to start with. It will make for a cool winter project now that I'm out of components to build more computers with.

Originally Posted by 5th element

Better get that measurement system together then.

If I were independently wealthy I would already have something. Care to float me a loan? As things go, it will likely be late January. I'm looking at that OmniMic system at Parts Express. I doubt it's up to the standards of a more experienced builder but it's probably enough to get me started.

[tomtt]

Originally Posted by 5th element

Good quality electrolytics sound fine to my ears and are more then acceptable in anything other then what you could call your critical listening setup.

surplus plastic capacitors are so inexpensive, at least in the usa,

there is no reason not to.

unless one likes the electrolytic sound.


Picking Capacitors - Walter G. Jung and Richard Marsh

[cachehiker]

After careful measurement, I picked up a pair of 4.5" foam surrounds from speakerworks.com and will attempt a replacement on the next weekend when weather prevents me from making a dent in the 3000 lbs. of leaves I have to deal with every year. I will post the complete repair process on instructables.com when I'm finished as well as adding a few pics and a link to this thread.

The Zaph ZA14's will be used to build up a pair of Zaph ZA5.2 clones. I will likewise post a few pics and start a thread with the results when I am done.

[sreten]

Originally Posted by cachehiker

The Zaph ZA14's will be used to build up a pair of Zaph ZA5.2 clones.

Hi, clones ? why clones ? in what way ? what wrong with the real design ? rgds, sreten.