Realistic Minimus 2.5 mods

[audiozaz]

So I picked these up at goodwill earlier this week, 3$ for the pair, could not pass that up. I got a thing for small speakers, especially Realistic... 5.75" high, 4" large, 2.75" deep (internal dimensions) 1/2" particle board, veneered, acoustic suspension design. Plastic faceplate with fullrange 4" driver in the center. A little wad of fiberglass wool in the box. 10W max, 8ohm. Cannot find any info on the internet on them except on TAC, which stated manufacture date from 1993-????

It's not like I was expecting these to sound great, but I was quite disapointed when I plugged them in and gave them a go... They sound like music through a telephone. I EQ'ed them to check, and 64Hz is barely usable, as in the ±12dB slider's absolute difference of 24dB is barely heard. I know the limitations of a single 4" driver, but I've heard them do better.

I would like to do some cheap mods to help them sound just slightly more decent if possible. Here is what I had in mind, feel free to improve or comment on that.

1. Find driver's Fs and put in a low-cut filter something like 1 octave below it to avoid uncontrolled cone motions for frequencies at which it cannot respond properly. The amp is still trying to pump them to it.

2. Better acoustic isolation of the driver and wiring terminals. The speaker is screwed-on metal to plastic, while the terminal pad is plastic to wood. A little dense foam cut-out would help making the cab more airtight.

3. Dampening material. Not sure which way to go on this one, remove or add. But that's an easy one to test and re-test and re-re-test until best compromise is found.

4. I would like to do something to help high-frequencies, but I'm afraid nothing can be done for that.

All of this can be done withing a couple of hours and practically for free, so I don't stand to lose anything, which is kinda what I aim for, since they are not great speakers to begin with.

So is all of it pure madness or am I making some sense?

az

 

[cfranz]

I don't even remember the 2.5s There were early 90s I think...

Deaden the box (asphalt roofing), seal the speakers (caulk), new/better parts for the crossover. As an experiment it may be worth the trouble... As a listening esperience, perhaps not.

OTOH a friend was playing with one of the Rat Shack speaker with the linneum ribbon tweeter on the top. When he was done, I was astonished. Through his 300B-SE amp they absolutely vanished in the room and the stereo imaging was dead solid. I guess you never know.

 

[mhardy6647]

The 4" FR is probably an 40-1107/FE-103 clone of some sort. I think the best thing you could do is put it in a big (1 to 2 ft^3) sealed box and you might be suprised. The driver cone itself might benefit from one or two thin coats of Dammar varnish (if it sounds 'tizzy' to you -- the R/S 40-1197 does to me!). Damping the speaker basket with some rope caulk, putty, or what have you couldn't hurt, either. You can consider adding baffle step correction and/or a Zobel filter, too.

www.fullrangedriver.com
www.zillaspeak.com
http://www.planet10-hifi.com/
www.t-linespeakers.org

 

[mario58]

From page 24 1990 RS Catalog:

Part# 40-1999-10 watt extension speaker for TV. $19.95

 

[audiozaz]

The 4" FR is probably an 40-1107/FE-103 clone of some sort. I think the best thing you could do is put it in a big (1 to 2 ft^3) sealed box and you might be suprised. The driver cone itself might benefit from one or two thin coats of Dammar varnish (if it sounds 'tizzy' to you -- the R/S 40-1197 does to me!). Damping the speaker basket with some rope caulk, putty, or what have you couldn't hurt, either. You can consider adding baffle step correction and/or a Zobel filter, too.

Thanks for the info.

Might be such a clone but I don't know. Dustcap is wider and more hemishperical, suspension roll is "inward". It has those dual magnets too. Only info on it is "8ohm Made in Malaysia".

What would that varnish coating do? Added rigidity to cone? Added mass? (however little it may seem)

az

 

[thefragger]

I think my thrift has three of what you're describing, but wanted $10/ea. so I passed. Let's see what you can do with 'em!

 

[mhardy6647]

The Dammar varnish damps the cone. Definitely helps the 1197,. IMNHSO.
The FE-103/40-1197 photos I linked to have Dave Dlugos' phase plugs.
The dual magnets mean they're shielded (the back magnet is a 'bucking' magnet to counteract the external field of the speaker's magnet).

 

[audiozaz]

The Dammar varnish damps the cone. Definitely helps the 1197,. IMNHSO.
The FE-103/40-1197 photos I linked to have Dave Dlugos' phase plugs.
The dual magnets mean they're shielded (the back magnet is a 'bucking' magnet to counteract the external field of the speaker's magnet).

Should the dust cap be varnished as well, or better to leave it alone?

I never knew that was a bucking magnet, thanks for the info!

I have two other 4" drivers salvaged from JVC ported boxes on a mini-system. They look rather nice and played decently well in the bass-reflex boxes they were in. I swaped them in the Minimus 2.5 boxes and had it slightly better bass (Fs of 115Hz measured in free air for those drivers alone), but had some problems in upper midrange and a bit clearer highs.

I might give these a try in an acoustic suspension design as you suggested, as I want to keep the Minimus 2.5 "original", nothing removed or swaped, only additions or mods.

az

 

[mhardy6647]

I think they might work really well in a mass loaded TQWT (straight or folded, as you prefer)... but that might be 'polishing a turd', as it were.

I've never done anything to dustcaps on a 40-1194... phase plugs might be a great idea though (I like them on the 40-1354 twincone FR driver that R/S sold for many years).

 

[audiozaz]

Looking at some online resources and at what some of you have instructed in this thread, I'll go with the following:

1. Try to "deaden" the plastic fascia and driver frame with Ductseal mastic;

2. Coat the driver cones with varnish for added dampening and rigidity;

3. Seal the driver and terminal pad better using some dense foam/rubber cut-out or Ductseal;

4. Add a baffle step compensation circuit, as I believe the box size helps give it that "telephone" sound;

5. Experiment with padding/stuffing inside until I get decent results.

On a side note, has anybody ever tried adding whizzer cones to drivers? I'll search the web and see what comes up on that.

I might do the above during the coming weekend, I'll post update once I have results. Thanks for the tips everyone!

az

 

[matt_s78mn]

I have some Minimus 2.5's currently that I threw in as rears in my 5.1 setup to see how they'd sound, not at all satisfied with their performance. (very tinny sounding, and lacking a lot of lows) So i'll be interested to see where this thread takes us and maybe try some of these mods.

 

[audiozaz]

Yours differ a bit from mine, as mine have the stamped metal grill.

Yeah, they don't sound that great... I don't have great expectations for this project of mine, I mostly do it because it will be cheap, fun and potentially, if only very slightly so, sonically rewarding!

But where would we be if we only took on projects with not-so-dim outlooks?

Well it would be cool to find a solution to salvage both my and your set of 2.5's.

az

 

[audiozaz]

Results...

Ok, here I am reporting back on the results of my modifications to Realistic Minimus 2.5’s.

The below list is what I had set out to do:

1. Try to "deaden" the plastic fascia and driver frame with Ductseal mastic;

2. Coat the driver cones with varnish for added dampening and rigidity;

3. Seal the driver and terminal pad better using some dense foam/rubber cut-out or Ductseal;

4. Add a baffle step compensation circuit, as I believe the box size helps give it that "telephone" sound;

5. Experiment with padding/stuffing inside until I get decent results

I did all of the above except for the baffle step compensation. I did not have inductors handy, nor did I wish to get any and I was able to experiment with an EQ to get similar compensation response.

First thing I did was measure the driver’s impedance curve in the following way. Output of my signal generator is connected to a 1000 ohm resistor in series with a 10 ohm resistor. I adjusted the generator’s output so I would get 10mV around the 10 ohm, which will give me accurately enough 1mV reading for 1ohm of impedance. I used a True-RMS Fluke 787 processmeter to take the readings. The graph below shows the impedance response for the unvarnished cone, and with 3 thin coats of varnish afterwards.



As we can see, the Q got sharper.

I was able to calculate some T/S parameters with formulas I got online, I assume they are correct since I checked them with drivers with known parameters, but it yielded these very high Q’s for this specific driver:

Without varnish: With varnish:
Fs 175 ohm 175 ohm
Zfs 28.7 ohm 26.9 ohm
Re 6.4 ohm 6.4 ohm
Qms 6.86 8.54
Qes 1.97 2.67
Qts 1.53 2.03

Also, it had been suggested that this driver might be a FE103 clone. Although it physically looks like it, the above parameters GREATLY differ from that of the FE103, with an Fs over an octave higher.

Below are pictures of the modification process.

 

[audiozaz]

cont'd...

More pictures of process:









Here they are being listened to in my bedroom system.



Subjective listening results:

Ok, so it was pretty awful sounding when I first tried them, how are they now?

Still awful. Ok – as I mentioned in another post, I was aware this could not turn 20$ speakers into hi-fi big-league performers. There IS an improvement though. When un-EQ’ed, they retain their telephon-esque sound characteristic. When applying –3dB EQ for all frequencies at and above 500Hz, thus imitating a BSC circuit, they sound is a bit more natural and pleasent.

The biggest improvement was in bass response. The 64Hz slider on the EQ now could be used and heard. Room wasn’t quite shaking yet…. but bass is kinda usable now. I’m aware such speakers are highly sensitive to room placement and backwall loading and I didn’t experiment much with that either, but same placement conditions were reproduced before and after.

They need to be heavily equalized to sound decent still. My scheme ended up looking something like this:

32Hz : 0dB ( unusable of course…)
64Hz : +6dB
125Hz : +3dB
250Hz : 0dB
500Hz : -3dB
1000Hz : -5dB
2000Hz : -3dB
4000Hz : 0dB
8000Hz : +3dB
16000Hz : +3dB

Add Loudness compensation for low-volume listening and it's decent enough.

All in all, this took up an entire weekend afternoon and cost very little, around 10$. If you have similar speakers and whish to “save” them, the above mods won’t do miracles. You will get a slight improvement with the usual YMMV disclaimer .

It was a fun and educational project for me and far from a waste of time.

Hope you enjoyed this,

az

 

[mhardy6647]

It actually reminds me of the semi-legendary 269-469 "69 cent wonder" from PartsExpress. That big dustcap is a coax "tweeter", you know?

I am a big fan of the 269-469, a really fine sounding little 4" driver.

Stay tuned for more irrelevant tangents from yours truly... ;-)

 

[audiozaz]

It actually reminds me of the semi-legendary 269-469 "69 cent wonder" from PartsExpress. That big dustcap is a coax "tweeter", you know?

This driver's Fs is more what you would expect, being around 110Hz. For some reason mine measured much higher ~175Hz. My JVC's are more typical at 115Hz too.

I'll build some ~1.4 cubic feet sealed boxes to test my 4" JVC's and try the Realistic 4" as well in it. I think this box volume should provide big enough compliance to hear the speakers "as they should be heard".

az

 

[mashaffer]

Here is an experiment for you. Get a pair of high Q helper woofers and put them and the RS drivers on an open baffle of about 1 1/2 to 2 feet wide. Now biamp them with a crossover of around 200Hz. If you don't have a line level crossover just use your eq to simulate a 200Hz LP for the woofer channel. Might surprise you.

mike

 

[audiozaz]

I realize I did not mention this earlier now, but the Radio Shack drivers in my Minimus 2.5 definitely have not the best high-end and I don't think any enclosure would help that. Anything ~12KHz and up sound like a shodilly sampled MP3.

Your suggestion might go better with my JVC 4", whose high-end spectrum performance is much better. I don't have any woofer to play around with now, but if I can get my hands on something cheap, I might give that a try.

BTW, I gotta get me some testing gear, I found out I like playing around with speakers lately....

az

 

[C.Hencke]

I know this a pretty old thread, but these speakers do seem to show up on the cheap frequently, so I thought I'd weigh in with my experience.

I found these at a junk shop for the (I thought exhorbitant) price of 4 bucks per. I recently picked up an MCS receiver with the faux-quad "matrixing" channel and was looking for suitable small speakers that I could use in that role. Long story short, I ended up duct sealing all of the various joins and putting them into service with my EV 1122 in the bedroom setup. They are on a built in bookshelf near ceiling level and actually sound pretty great for the jazz/classical/NPR news that gets played through them. For kicks I also played young marble giants "colossal youth" this morning, and it was surprisingly good as well...

I dunno if it's room placement or some witchcraft with the little EV, but I haven't experienced any of the tinny telephone quality mentioned by others. They sound pretty fair with a t-amp as well, but not nearly as nice as with the (in sore need of a recap) EV.

Anyway, they've been worth 8 bucks and 25 cents worth of putty...

 

[audiozaz]

Looking back at these, they might have had stiff surround syndrome, with such a high Fs. A version of this driver with suspension elements in more compliant shape might sound better.

az