Are my Sanyo M9994 speakers bad?

[ScottSpeed]

Hello good folks! Had a simple question here, I have a few Sanyo boxes here that I have recently been listening to. Models such as the MX-720, M9994, M9996, MX-920, and then some Sharp's such as the GF9696 and the GF9494. These are not my only boxes either just for reference.

Anyhow I have noticed that the 9994 has almost the worst sound out of all of those. Gets plenty loud, louder than most of the others but if you try to add any amount of bass and I mean just barely turning the knob up from being buried on the -5 side the speakers distort horribly. It's like the surrounds are so loose and floppy that the speaker gets to flopping way more than they should.

Now I know that one of the keys to the Sanyo's making their bass was for them to have flexible speaker surrounds but this seems excessive.

For all the folks and reviews I have seen of folks praising the M9994 I feel this box should sound so much better than this one does, as all of the other models listed above seemed to sound better than my 9994 with only the 9996 having less ability to produce low notes which is expected with its 12cm speakers.

I mean at low volumes you can have the bass setting at 0 or slightly above and it sounds fine but add any volume or extra bass and it starts to sound very muddy and distorted. Playing the same music at the same volumes on the 720, 920, or the sharps produce a much cleaner sound at even higher volumes with the ability to produce even more bass without getting muddy.

Could it be that my 9994 speakers have become too loose? I was considering putting a layer of paper speaker glue on the surrounds to possibly "stiffen" them up some but I wasn't sure what the best route here was.

There not "blown" or anything and still produce the rest of the frequency range fine, they just don't play well with low notes at all.

Like it seems this box has a LOT of power for what it is and plenty of bass to add if you want it. Just the speakers can't handle what the amp is trying to give them it seems. I would like to keep the original speakers as I feel replacing them with something new would really kill the look of the box.. I do however have a local speaker company that could put new cones and surround on if needed?

Plus I have heard that they will not sound correct as Sanyo designed everything for the "flexible" speakers..

Please give any advice you may have as I was wanting to find another 9994K model but I just expected a better sound with all the praise I have seen the 9994 get.

(I know these boxes are not made to play bass heavy music and I understand that completely. However if the majority of my other boxes can play that same amount of bass and do it well, I feel the 9994 should be able to as well or even come close but this one can't for some reason. It's like the speakers move way more than they should.)

Thanks everyone!

 

[Reli]

Open it up and see if the speakers are original. Mine has good bass, better than the MX920 in fact. And better than the GF9494 too. Of all those boxes you listed, the GF9696 is the best, with the most power. Here is how I would rank those boxes:

1) GF9696
2) MX720
3) M9994
4) MX920 (disappointing for its size, weak bass)
5) GF9494/M9996 (tie)

 

[Superduper]

I’m not sure what or where you’ve heard about “flexible” speakers, most all 1-pc classic boomboxes use speakers that are just paper cones without a conventional “surround” that is a separate material that interfaces the cone to the basket with glue. These true surrounds can be foam or rubber or cloth. On these boomboxes, it’s just corrugated ribs molded into the outside edge of the paper cone. They can tear and then if subject to bass, can buzz or fart.

I would suggest you remove the speakers to see if there are any tears. If none, then you’d need to check and see if the voltage is sagging. What I mean is “is the voltage dropping under load”? If so, you’ll get distortion. If you ever operated a boombox with batteries that are partially discharged, you’ll know what I’m talking about. At low volumes, sound will be ok but if you crank it, demand for current surges and if unavailable, sound quality just crashes. Also by chance is this a multi-voltage unit? If so, make sure that the voltage is set properly. A box set to 220v but operated at 110v will still function believe it or not but it would not sound good.

Lastly, you do know that of the list of boomboxes you mentioned, the M9994 is the only 12V boombox there, right? All the rest are 15V boomboxes so you shouldn’t expect the same power output from the M9994 compared to the rest, as those have more power available to their amplifier.

 

[BoomboxLover48]

Open it up and see if the speakers are original. Mine has good bass, better than the MX920 in fact. And better than the GF9494 too. Of all those boxes you listed, the GF9696 is the best, with the most power. Here is how I would rank those boxes:

1) GF9696
2) MX720
3) M9994
4) MX920 (disappointing for its size, weak bass)
5) GF9494/M9996 (tie)

What of M9998? That one always surprised me!

 

[hopey]

op it reads like you have coil damage on the woofers, try different speakers to confirm.

 

[ScottSpeed]

Okay so I opened her up to see what I could find and it appears to be stock speakers inside? I have noticed that some models come with speakers that have "dimpled metal baskets" and others that do not.

They do appear to be factory though without tearing it further apart. However upon looking further it seems that on one speaker the cone has what appears to be fiber breakdown or something similar as you can see what almost looks like cracks in the paper where the cone has the "creases or ribs" that are close to the edge. I think these "creases / ribs" act as surround in a way and mine appear to be not in the best shape. At least on that one speaker.

I have not noticed the same issues on the other speaker but I am guessing if one of them is starting to breakdown then the other can't be far behind it.

Oh I guess it would help too if I stated that this is actually an MR9600 instead of the M9994 as it was imported from Japan to me. It has the white cone speakers with black dust caps. Love the way the speakers look but I'm afraid they will have to be re-coned to perform as they should.

I did hook up external speakers and they sounded just fine so i believe it's just a speaker issue here.

I’m not sure what or where you’ve heard about “flexible” speakers, most all 1-pc classic boomboxes use speakers that are just paper cones without a conventional “surround” that is a separate material that interfaces the cone to the basket with glue. These true surrounds can be foam or rubber or cloth. On these boomboxes, it’s just corrugated ribs molded into the outside edge of the paper cone. They can tear and then if subject to bass, can buzz or fart.

I would suggest you remove the speakers to see if there are any tears. If none, then you’d need to check and see if the voltage is sagging. What I mean is “is the voltage dropping under load”? If so, you’ll get distortion. If you ever operated a boombox with batteries that are partially discharged, you’ll know what I’m talking about. At low volumes, sound will be ok but if you crank it, demand for current surges and if unavailable, sound quality just crashes. Also by chance is this a multi-voltage unit? If so, make sure that the voltage is set properly. A box set to 220v but operated at 110v will still function believe it or not but it would not sound good.

Lastly, you do know that of the list of boomboxes you mentioned, the M9994 is the only 12V boombox there, right? All the rest are 15V boomboxes so you shouldn’t expect the same power output from the M9994 compared to the rest, as those have more power available to their amplifier.

So on to the sagging issue would this be apparent in the dial light? When it is on and the bass hits the lights dim. This isn't cranked either on the volume. This was at 1/2 volume listening to songs that have bass (hip hop) and the bass knob is not cranked either (seems to have plenty of reserve power when you turn the bass knob up or the volume it really cranks the speakers and distorts them quite bad with heavy bass songs. Yes, I know that is not what is intended to be played on these speakers. Just doing some testing here)

I am using a voltage reducer that takes my 120 volts and reduces it to 100V but it's rated for 200W so I would think its not causing the issues here??

So could the speakers have coil damage if they are capable of sounding wonderful until they reach the point where bass is too much and they start "flapping"?

Yes I do know that it is only 12 volts. I am not measuring total output and volume but more sound quality at room listening levels.

THANK YOU ALL SO VERY MUCH FOR THE INPUT!!! I am somewhat new here so it's so nice to see people are still willing to help out folks.

(PS if I did want to re-cone these speakers what would be the best way to make sure there good or would I be better off taking them to my local speaker repair shop and having them give them a once-over? As it may require testing tools that I do not own?)

Kind regards!

 

[Superduper]

You don't need to re-cone your speakers. If the fiber breakdown is at the ribs, then you can probably install new surrounds and this would likely fix the flapping/farting issue. I would use a stiff surround as opposed to a loose surround because frankly these drivers are not designed for high x-max (cone excursions) so using something loose like foam or rubber can cause unexpected consequences and perhaps damage the voice coil from excessive movement. If that's too complicated of a fix, you can try to just replace those speakers with some off the shelf speakers. Keep in mind that it's hard to find replacement drivers that are shallow enough for this application as deeper speakers won't fit. Many boomboxes have space behind the drivers but on this model, the drivers back up to the chassis so deeper drivers just isn't an option.

These pioneer speaker will probably fit and based on your description, I think the looks might be similar to what the factory drivers look like. I installed a pair in a Sanyo M9990 which is a similar model and they do fit. You may want to consider trying them.

 

[caution]

These pioneer speaker will probably fit and based on your description, I think the looks might be similar to what the factory drivers look like. I installed a pair in a Sanyo M9990 which is a similar model and they do fit. You may want to consider trying them.

Those TS-164P speakers are 4 ohms, but the M9990 uses 6-ohms. Is that close enough that you didn't worry about over-driving the amp?
The M9994 uses 2.5-ohm speakers. Would 4 ohms cause any noticeable loss in performance?

 

[hopey]

Those TS-164P speakers are 4 ohms, but the M9990 uses 6-ohms. Is that close enough that you didn't worry about over-driving the amp?
The M9994 uses 2.5-ohm speakers. Would 4 ohms cause any noticeable loss in performance?

You can go up in resistance = less volume. If you go down = more volume and overdrive the amp chip due to poor voltage regulation. It's ohms law.

 

[Reli]

Sometimes boombox manufacturers used speakers with more impedance than they really needed to. Some have 8 ohm speakers, which is dumb because they could have gotten more output with 6 or 4 ohm speakers.

If you google the datasheet for the amplifier, it will provide test results at 2 or 3 different impedance levels. They wouldn't have done that if it was unsafe to do so. So if 4 ohms is one of the levels they tested at, then it's safe to use with 4 ohm speakers. Some are safe down to 2.5.

 

[floyd]

It also has to do with the signal to noise ratio aka sensitivity rating.
A more efficient speaker may have a higher ohm rating because it makes the most use of the available power.
A lower ohm speaker will put more of a load on the amp but it's usually built for higher power handling but the drawback is less sensitivity which means it makes less use out of the available power. I think the reason for a specific impedance speaker means they probably trying to either get more power out of the amp or longer battery life depending on what the design specifications are. Most boomboxes are basically designed to be portable which means they're probably being used on batteries which also means they're probably trying to stretch the batteries out or they just want them to go full out all the time so they can put out a boatload of power and don't give a damn how long the long the batteries last.

 

[Superduper]

Those TS-164P speakers are 4 ohms, but the M9990 uses 6-ohms. Is that close enough that you didn't worry about over-driving the amp?
The M9994 uses 2.5-ohm speakers. Would 4 ohms cause any noticeable loss in performance?

The Sanyo M9994 and M9990 basically shares the same amps. The M9994 uses BA521 (early ones) and the M9990 uses BA532 but I believe there may have been a service bulletin to update the BA521 rohm chips to the BA532 on the M9994. Regardless, both chips appear to be 100% pin compatible. As for power, as most people know, distortion ratings are based on power output. If you throttled one of these small amps down a bit by using higher impedance drivers which have otherwise similar SPL sensitivity, I suspect that the observable volume probably wouldn't be significantly different. At some point in the volume control range, the distortion usually takes over to the point where people automatically self-throttle the control to where you get a good balance of volume to distortion. Unless of course if you are deaf or can't discern good music from bad. If you had installed 4 ohm drivers instead of the 2.5 ohm drivers, I suspect you can probably just crank it higher before the onset of distortion but the volume at that point probably would be about the same with 2.5 ohm drivers, only at a slightly lower point on the volume dial. Honestly, 20 years ago, I had worked on many M9990 and M9994 boomboxes for customers and had gotten very familiar with them. I will say that I have changed power amp chips on the M9994 more times than I can remember and the 2.5 ohm drivers probably had something to do with it. I also had to change the power transformer on one, and on a third, the rectifier diodes blew out. Therefore, for reliability reasons, I think that 4 ohm drivers would probably be a better choice, certainly with regards to the M9994. Now the M9990 is a different animal. This model I've never had the occasion to replace the amp chip, which is probably because of the 6 ohm drivers. On the other hand, I have had to replace the power transistors which turns the boombox on and off. All of the power that goes through the boombox goes through those transistors. This is because of the clock/timer feature which could turn the boombox on and off and therefore needed a solid state way to switch the boombox power. If this boombox were to substitute lower impedance drivers, the amp chips obviously can handle the power (it clearly does so on the M9994) but the additional load might be too much for the power transistors if cranked too high for too long. Regardless, 2.5 ohm drivers that are full range, thin profile are difficult to find and 4 ohm drivers are probably better suited anyhow for the M9994.