Is there an improvement potential, or are these trash?

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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 :cool:

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 :D

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.

An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.


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
 
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 :D
 
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
 
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!
 
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
 
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).
 
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.
 
I always thought they had something good to them... just those exalted high freqs...

This is great advice, guys, thank you!

I am putting together an order at Allied to do some opamp mods on an old mono compressor... I'll be sure to include some new caps...

ay this means I have to read up on how this crossover frequency is determined and manipulated... :xeye:

Can you recommend some tutor page or faq to get me started on this?
I have some rudimentary electronics knowlegde and think I should be able to get on my feet... just need a nugde in the right direction!

as for a new amp, I think I will have to build one or buy one......

especially since I am in the business of changing the drivers on my beovox 1000 that recently took off for kingdom come...
any suggestion for a driver would be great
I live close to Denmark so Vifa is readily attainable at fair prices... I have heard these drivers are good..
I am looking for clarity in the midrange(listen to lots of music in the style of 70s folk, and 70s folk of course!) and I hope to attain good imaging so that listening to live recordings will be even more interesting =)

The beovox cabs are good even though the drivers they came with managed to meet the DIN standard for hi-fi back in the days...
Also my current amp doesnt really manage to give them enough juice since they're 4 ohms...still sounded great though...

salutations wise diyers

-canakas
 
ay this means I have to read up on how this crossover frequency is determined and manipulated...

don't bother..............I would just change the caps.



I am looking for clarity in the midrange(listen to lots of music in the style of 70s folk, and 70s folk of course!) and I hope to attain good imaging so that listening to live recordings will be even more interesting =)

well I guess everybody want this, and it's not that easy to achieve.
I choose active crossover everyday. :D
 
Im back from exams

Dear all,

Thanks for your interest. I am reading your suggestions and agreeing that for reasons concerning both sound improvement and learning about crossovers, I will try to change the capacitor, with an equally specified one...

I have been looking at two caps, both of metallized polypropylen, and I would like to ask you to recommend one based on the specs if that is possible:

An externally hosted image should be here but it was not working when we last tested it.

Mfr. SCR, type MKP
An axial capacitor with metallised poly-propylene dielectric. Polypropylene has several excellent properties such as high stability, low losses, low di-electric absorption and high withstand voltage. The capacitor is self-healing and has low impedance. Particularly suited to audio applications.
Technical data:
Tolerance: ±5 %
Temp. range: −40 to +85 °C
Dissipation factor tan δ
(at 1 kHz, +20 °C)
≤4.7 μF: ≤5×10-4
≤50 μF: ≤10×10-4
≤100 μF: ≤15×10-4
≤200 μF: ≤20×10-4

PRICE of 4.7uF at 250 Vdc/110 Vac: ~ 5USD

or this one


An externally hosted image should be here but it was not working when we last tested it.

Mfr. Icel, type MPL
Metallised polypropylene precision capacitor. Self-healing with low induction. Suitable for frequency setting applications due to its close capacitance tolerance, low temperature coefficient and excellent long term stability.
Manufactured acc. to IEC 68, 384/1.2, CECC 30000, 31200.
Technical data:
Tolerance: ±1 %
Temp. range: −55 to +105 °C (above 85 °C, Umax is reduced by 1.25 % of Un/°C)
Dissipation factor tan δ: ≤6×10-4 at 1 kHz and +25 °C
Insulation resistance R: ≥1×1011 Ω at C≤0.33 μF,
(at +25 °C) R×C≥30000 s at C>0.33 μF
Long term stability: ≤±1 % at 40 °C, 2 years,
≤±1 % at 85 °C, 1.25×Un, 1000 h

PRICE of 4.7uF at 160 Vdc/90 Vac: ~ 8 USD

thanks people
 
Hi

given this application, I would pick the cheap one, but others may not agree. make sure you break in the caps after you put it in, some might need around 50 hours to sound best. before that the sound might seems "constained" and sharp. also check using multimeter to see if the caps have "shorts" , this sometimes happen with metallized caps.


Hartono
 
Hi Canakas ,

'shorts' are shortcircuits?

yes , sometime this happens.


using the multimeter, just check the resistance of the capacitor. you should get very high value, if it's close to zero it's a short circuit

PS: If you're lucky, some caps didn't need long break in or break in at all.


Cheers,
Hartono
 
Well I learned a lot at least =)

Thanks Hartono, both caps showed very high resistances.


My problems in the first place was:
- a tireing, distorted peak somewhere in the high mids/low highs
- lack of integrity in bass reproduction

The following interventions were performed:
-Change caps in cross-over to better quality caps of equal capacitance
-Fill the cabinet with reticulated foam

The results can be described as follows (subjective impressions):
- increased overall clarity, and better integrity in bass reproduction
- somewhat less tireing sound, but there are still peaks, so these elements probably need to have their crossover reworked.

Conclusions:
- I am surprised to hear the positive difference made by new caps
- cabinet filling is a must!

-Cheap computer speakers like these have an improvement potential, and can be made usable.

- Still my ears get tired and numb, indicating a frequency peak(or two) and probably some distortion.

Thanks to everyone who has contributed in this thread.

Now I am thrilled to start looking for elements for the BeoVox cabinets, and the challenge of choosing a cross-over model...

Time to read some webpages!!
 
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