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Found some LOMO 4A28 drivers. What do I do with them?
Found some LOMO 4A28 drivers. What do I do with them?
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Old 24th June 2015, 03:34 PM   #1
djduck is offline djduck  Estonia
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Default Found some LOMO 4A28 drivers. What do I do with them?

We were cleaning out the storage room at my high school a few days ago and I came across a soviet-era speaker cab ( I live in Estonia so this is common here). The box was a suitcase type deal that opened up in the middle to give you two speakers. The box was moldy and smelled like sh!t but after opening it up, to my surprise it was fairly clear inside. Neat. After a bit of digging, out came another smaller speaker box. All drivers were inside this cloth bag. After finding a screwdriver and a bit of elbow grease, out came the drivers and into the bin with the boxes.

Got them home and cut the bag, and inside were Lomo 4A.28 full range drivers!
As far as I know, they should be decent enough.
Looked up the price and they seem to go for quite a bit on ebay, but not so much here. So now I'm looking for ideas what to do with them. OB would be the easiest but I want to see if there is something else out there worth trying.
Looking for something not overly complex that would sound good.
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Old 24th June 2015, 05:07 PM   #2
IRONHAND54 is offline IRONHAND54  United States
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http://www.diyaudio.com/forums/full-...en-baffle.html This is an old thread, but it may serve to give you some ideas for a build to do these drivers justice!

Hope this helps,
Mac
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Old 24th June 2015, 05:34 PM   #3
djduck is offline djduck  Estonia
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Quote:
Originally Posted by IRONHAND54 View Post
http://www.diyaudio.com/forums/full-...en-baffle.html This is an old thread, but it may serve to give you some ideas for a build to do these drivers justice!

Hope this helps,
Mac
Thanks. I take from this that I should have these panel things on the sides? As in, attach the 4A28 to a wooden panel and them put a long, thin panel onto the sides?
Other than that, I can't take much from that link. He uses 4A28's bigger sibling, the 4A32. Mine is either a 10" or actually 11", since the "28" stands for the size, 28cm which is 11". Also, he uses six drivers in total. I only have three and will be using two.
Any ideas how big the baffle panel be?

Here are some specs I found online, can't confirm if accurate:
Impedance 15ohm
Free-air resonance 70Hz
Freq. response 70Hz-14KHz
Sensitivity 93.5 db
Power handling RMS 6W
Power Handling max 12W
Maximum sound pressure 104.2 db

Last edited by djduck; 24th June 2015 at 05:54 PM.
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Old 24th June 2015, 06:30 PM   #4
IRONHAND54 is offline IRONHAND54  United States
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Sorry I don't have any experience with this driver or design. I just happened to remember this thread from my forum browsing, and thought it might help? There are some OB enthusiast that should chime in, that will have the wealth of knowledge to point you in the right direction though.

Mac
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Old 24th June 2015, 07:35 PM   #5
djduck is offline djduck  Estonia
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I'm still grateful for the link, tho, because I know know what I want the speakers to look like when they're done

Before we go any further, I want to make sure that OB would actually work for my taste of music. I know it's great for classical and jazz, and while I do enjoy that occasionally, I mostly listen to Pink Floyd, Radiohead, Metallica, etc...
Mostly heavier music.

Is OB even any good for that? If not, what should I use?

Would be good if someone gave me some plans for OB just in case I can't find another design
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Old 24th June 2015, 09:18 PM   #6
IRONHAND54 is offline IRONHAND54  United States
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www.youtube.com/watch?v=lw6NU_OzY5I Found this You Tube Video, have a listen and see what you think? I think they sound fine, but need some bass support, but most guys with OB systems always augment the FR driver with a larger bass driver.


Mac
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Old 24th June 2015, 10:30 PM   #7
djduck is offline djduck  Estonia
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Mine actually cam with very similar boxes. Except mine were moldy. Kept the grills, tho, those were alright. They seem very good in the mids but can't tell if any bass at all because this isn't my type of music so I don't know how bassy it should be.

I don't have much for LF laying around. I have two RFT L3060PB FR drivers, both 12". One of them has been repaired and painted. Light aerosol spray paint, only on cone not surround. Seems like it didn't change the sensitivity because they still sound the same IMHO. Screw it, might paint the other one as well. I didn't paint the first one BTW, I got them like that. I got a third one as well, has had some repair done to it but I think it's a bit scratchy. Don't really know, haven't used it in a while. My friend used it as a bass amp speaker so it saw quite a bit of torture having to outplay a drum kit.
I could cut the cones on the RFT and use them for LF. should I keep that in FR as well or would it need a XO?
I also have four 8" woofers. 10GD30B or something was the model. They're also soviet.
then there's a Pioneer 1.4KW car subwoofer sitting somewhere around here, I doubt that'd be of much use for this I guess it would sound decent with a good box but I ain't got time for that.

So what about the RFT?
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Old 24th June 2015, 10:48 PM   #8
Greg B is offline Greg B  United States
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To state the obvious, you will get a lot more help if you take the time to measure T/S parameters for this driver. Any suggestions without specs are basically guesses, and optimization is impossible. That said, we can probably assume this is a moderately high qts OB friendly driver. So OB is a solid suggestion, but you may not have much bass.

A Voigt pipe or metronome would also be a good choice.

Strangely enough, the only design I have seen specifically for that driver is this one:

Click the image to open in full size.

By a strange coincidence of convergent evolution, it is pretty similar to a Karlsonator. Actually, I would suggest modifying the folding by extending the stub up to the port like a karlsonator to offset the driver properly. (or make a karlsonator of similar dimensions instead)
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Old 25th June 2015, 12:49 PM   #9
djduck is offline djduck  Estonia
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Thanks for the cabinet plans, Greg B! If nothing else comes up, I might just try that!

I have no way to measure the TS parameters of the drivers, but I know a bit of Russian so I can try to scavenge for parameters.

EDIT: And I found specs. No idea how accurate, tho.

Re 12.04
Qms 8.06
Qes 1.31
Qts 1.93
Vas 39
Le 0.216
L 1.79
R 8.08
Fs 74.2
dF 82-14000
Cms 0.208
Mms 22.19
Rms 1.28
Bl 9.72

Last edited by djduck; 25th June 2015 at 01:14 PM.
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Old 25th June 2015, 01:47 PM   #10
GM is offline GM  United States
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OK, Qts this high are normally limited to OB or TL alignment, so based on this, I have to wonder how accurate they are if the Karlson concept cab worked well for whoever designed it.

Based on the specs, a stuffed to 'taste' TL would be tuned to Fs/Qts = ~38.44 Hz or ~56"/142.24 cm long and ~18"/45.72 cm in diameter or its = area = ~254.47"^2/1641.73 cm^2, so probably too big for most folks.

GM
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