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Multi-Way Conventional loudspeakers with crossovers

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Old 11th May 2007, 07:30 AM   #1
canakas is offline canakas  Norway
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Join Date: Nov 2006
Default Is there an improvement potential, or are these trash?

I am on the verge of my first loudspeaker diy, so when I found these old IBM speakers sitting around, I gave them a listen. They look like 07H1627-V-01 10W, but they draw around 2amps...

When turning the treble and bass up a bit the they produce a level of detail that will be sufficient for my use, which is learning about speaker diy, and possibly ending up with speakers to use in the boat

There is a problem though:
After a while, my ears got tired and for short period afterwards everything sounded kinda dull...
The only time this has happened before was mixing with a couple of genelecs that had a less than pleasing treble...

So now I wonder if they are anything worth saving at all... if this strange effect is caused by the elements themselves or by the pcbs...

I thought I'd take my question to you, as I am not the guy to throw anything out before the its potential is revealed.
Let me just state that my economy is thin... but I am not cheap, so dont be afraid to say that making new cabinets for these speakers is a waste of time

See, I got to looking the speakers over and they have a sub out, so I am figuring the signal is being split/filtered somewhere.
Also the amplifier built onto the pcb is probably not the best, to say the least.
The crossover if I am not mistaken, is simply a cap between the tweeter and the driver(correct me if I am wrong)
This x-over is a potential source of problems, as I understand from my readings on the forum, but I dear not change it as there are no markings at all on the speakers and thus their specs are unknown to me.

Click the image to open in full size. Click the image to open in full size.

Click the image to open in full size. Click the image to open in full size.

My question is thus; If I take out the drivers and tweeters, keep the x-over and use another amplifier and build them into a new cabinet, do you think I will be able to get some decent, non ear-wrecking sound from them? Maybe get some more integrity in the lower frequencies...

or does the "if it sounded bad once, it'll never sound good" apply?
were computer speakers from the nineties really that bad?
or
should I save for better drivers, and take it from there... and forget about this ol' junk?

I will appreciate any take on this!

-canakas
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Old 11th May 2007, 10:13 AM   #2
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It's entirely up to you, I wouldn't bother personally.

The amp is probably at 10% thd at 10 watts, the woofer is running full range by the looks of it (so you'll probably be listening to some nice cone breakup) and the tweeter looks to be on a first order slope. Depending on the crossover frequency, first order + small tweeter will give lots of lower treble colouration from the dome bouncing around trying to go lower than it really can. I imagine you will end up replacing pretty much all of it improving it.

On the flip side it might be a good project to play with and learn from, depends on how you look at it really
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Old 11th May 2007, 11:31 AM   #3
owen is offline owen  United Kingdom
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I have a set of those...

Not worth taking to extreme measures, but:

1/ use self adhesive roof flashing to damp the cabinet.

2/ use some reticulated foam to add some absorbtion to the void at the tweeters edge

3/ remove the 'woofers' (it really is a full ranger in disguise) dust cap

4/ apply a small amount of silicon type adhesive at the edge of the cone/voicecoil interface on the woofer, and in the deep groove around the tweeter

5/ add some BAF in the box


6/ paint an irregular pattern on the woofer cone with PVA glue

Overall they will then sound quite smooth, and reasonably detailed, although the top end does drop a bit (15k or so), but thats better than a cheap-o metal tweeter twittering.

The tone controls should be flat, and require very little equalisation on the PC.

I'll try and add some screen grabs/photos later..


Have fun


Owen
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Old 12th May 2007, 09:25 AM   #4
canakas is offline canakas  Norway
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Join Date: Nov 2006
elo folks

Thanks to both of you for sound advice.
I will perform the upgrades described and I think it'll be a good first time around speaker diy.

I have a few questions which I think some pics would answer easily...

- I remove the dust cap, never to put in on again? I mean, am I supposed to cut it off or use some solvent, to keep it whole...? I have found some guides on how to do this here and a movie here

-what will the PVA glue in the woofers do? wouldn pva glue soak up in the paper and harden, leaving the cone less flexible? what kinda polyvinyl glue do you use, wood glue or paper glue?

Your advices are brilliant though, Owen!

some semi-OT just for conversation:

I have been looking for monitors for my home studio for a long time, and after reading quite a bit on the forum I see that with my knowledge of electronics and such, the fun/work/cost/bang ratio indicates that with the little time I have outside school and work I should buy a couple of monitors... which is sad as I like to learn how to build a pair...
especially to control such nasty treble issues... a bit like the speakers we are talking about modding... maybe it was an eq thing with those 1031a, because I have heard some expensive genelecs in a big studio(dunno which model) and they were all one could wish for in mixing acoustic instruments and voice... ay ay

Many thanks again!
-
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Old 12th May 2007, 11:12 AM   #5
owen is offline owen  United Kingdom
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Join Date: Mar 2004
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The PVA will harden the fibers, and stiffen the cone in your irregular pattern.

That will kill some resonances, and heavily damp others on the cone.

My dust cap is gone forever. Just be very careful to not sever the voice coil leads.

I've just taken a few pix, so I'll find somewhere to display them, and post a link here


Owen
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Old 13th May 2007, 02:29 AM   #6
canakas is offline canakas  Norway
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I see. Resonance minimization will definitely help the sound of this woofer.

Id love to see some pictures. Thanks for all your help, mate.

I'll post back to when I've undertaken the mods.

-
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Old 24th May 2007, 03:44 PM   #7
canakas is offline canakas  Norway
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Default next week: exams...

Did you find a site to host your pics, Owen?
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Old 24th May 2007, 04:14 PM   #8
Hartono is offline Hartono  Indonesia
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if you can stretch you budget a bit, you can change the tweeter capacitor to generic metalized polypropylene, might only cost a couple bucks each, I did try change on cheap speaker before, also using mylar tweeter (looking from your picture), and exactly same value (4.7uF).

It still bring significant improvement.

change your amplifier feedback caps and input coupling caps to nonpolar , find electrolytics(cheap) 50V or 63V caps, Panasonic caps is quite good(for the price).
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Old 24th May 2007, 04:26 PM   #9
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I am in agreement with FullThrottleRic. Manufacturers of this type of speaker almost always cut corners just to save a few cents. Rather than doing a bunch of cabinet and cone tweaks, I think you'd be much better off giving the drivers a better amp, and reworking the crossover. Fatiguing sound is generally caused by big peaks in the high frequencies, and mega distortion.

Building a real crossover for this driver is a reversible thing to try before cutting it apart and painting it with things.

I agree that a polypropylene capacitor would be a big help, but I would also re-evaluate the crossover frequency to see if maybe you want to cross it over second order, or higher. Cheap tweeters are not renowned for their low frequency performance, and if it's crossed too low and shallow it's going to hurt the sound a lot.
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Old 24th May 2007, 04:32 PM   #10
Hartono is offline Hartono  Indonesia
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Some cheap product sometimes is surprisingly listenable,I guess this have something to do with absence of meeting "specs"

they just tweak it to get "okay" sound.
many times this approach produce quite listen able product.
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