Thanks for the continued replies and suggestions - I do appreciate that and replied to the new responses below.
One comment first:
I mentioned that I have 3 of these SS-M7A speakers - two I picked up last week and an orphan I've had for awhile. When I did my frequency sweep, they appeared to have similar characteristics, but I now doubt my meter, so I'm not putting a lot of stock into those measurements.
I played around with putting the orphan along with one of the new ones and using them as a pair. I felt some bass did come back, so I subjectively believe that my orphan has proper bass and the two I picked up last week are light on bass.
I opened up both and the bass driver has the same part number. Subjectively, the rubber surrounds don't seem significantly different in softness.
In doing some detective work on the serial #'s and searching previous sales of these units, it was said these were sitting in a warehouse for several years inactive, but that was also several years ago and my understanding is they've been used fairly regularly since then.
There is a lot of stuffing in the box - it's packed quite tight. I can remove some of it, but what am I trading off by removing some of the stuffing?
I'm not holding my breath on new caps being the solution either. I do have a cheap capacitance meter and will measure the old ones after I desolder.
I do believe the bass crossover is 24dB/octave already though as I thought I read that somewhere and it does use two caps and two inductors.
Yours is the second mention of trying less stuffing, so that seems like a potentially promising simple thing to attempt improvement.
I will do the caps and will try less stuffing, so there won't be inaction on those items, but I very much doubt I will try and create a port as I feel that would be potentially destructive and lower the value of the speakers should I decide to sell them down the road.
And believing that the orphan has more bass (and enough for my needs) gives me hope that if I can just identify the difference between the orphan and the new ones, I can get the new pair working with enough bass output to make me satisfied.
Regarding the bass driver and it's a close relative to the Peerless 21WO - I don't know for sure, but I did see that someone had a unit with the aforementioned Sony branded bass driver with part # P21WO-06, so it seems likely they're related in some way.
I notice that the Peerless 21WO is also a 8ohm driver. Do they make them in lower impedance versions and would using a lower impedance driver (4 or 6 ohms) result in more bass than the original 8 ohm?
So if I could get an inductance meter to verify the value and measure DC resistance, my goal would be to find another indicator with the same inductance value but as low resistance as possible, tight? And do it for both inductors in the crossover.
Stay with air core options or would iron core options have less resistance? If so, am I giving up anything significant by going air to iron core?
One comment first:
I mentioned that I have 3 of these SS-M7A speakers - two I picked up last week and an orphan I've had for awhile. When I did my frequency sweep, they appeared to have similar characteristics, but I now doubt my meter, so I'm not putting a lot of stock into those measurements.
I played around with putting the orphan along with one of the new ones and using them as a pair. I felt some bass did come back, so I subjectively believe that my orphan has proper bass and the two I picked up last week are light on bass.
I opened up both and the bass driver has the same part number. Subjectively, the rubber surrounds don't seem significantly different in softness.
In doing some detective work on the serial #'s and searching previous sales of these units, it was said these were sitting in a warehouse for several years inactive, but that was also several years ago and my understanding is they've been used fairly regularly since then.
There is a lot of stuffing in the box - it's packed quite tight. I can remove some of it, but what am I trading off by removing some of the stuffing?
I'm not holding my breath on the capacitor fix. Old electrolytics hold their act together even after 30 years in my experience.
Whatever Sony currently call that bass, it's either a Vifa P21WO or it isn't. "A rose by any other name would smell as sweet..." as the Bard of Stratford put it.
Let's summarise. Closed box has a rolloff that is very characteristic in sound. I quite like it. Reflex at 24dB/octave works for most people these days. It can get more deep bass performance out of a smaller box.
Tone controls might be good, but it's still closed box at 12dB/octave. Really, the only game in town here, the main chance, for more bass is the reflex conversion. Everything I have seen so far suggests the bass is suitable.
These sort of threads often descend into Fear, Uncertainty and Doubt. The perfect being the enemy of the good because it never arrives. In fact 90% of the threads here disappear into inaction. We should mention that reflex works better with less box stuffing. The air has to be able to move.
I'm not holding my breath on new caps being the solution either. I do have a cheap capacitance meter and will measure the old ones after I desolder.
I do believe the bass crossover is 24dB/octave already though as I thought I read that somewhere and it does use two caps and two inductors.
Yours is the second mention of trying less stuffing, so that seems like a potentially promising simple thing to attempt improvement.
I will do the caps and will try less stuffing, so there won't be inaction on those items, but I very much doubt I will try and create a port as I feel that would be potentially destructive and lower the value of the speakers should I decide to sell them down the road.
And believing that the orphan has more bass (and enough for my needs) gives me hope that if I can just identify the difference between the orphan and the new ones, I can get the new pair working with enough bass output to make me satisfied.
Regarding the bass driver and it's a close relative to the Peerless 21WO - I don't know for sure, but I did see that someone had a unit with the aforementioned Sony branded bass driver with part # P21WO-06, so it seems likely they're related in some way.
I notice that the Peerless 21WO is also a 8ohm driver. Do they make them in lower impedance versions and would using a lower impedance driver (4 or 6 ohms) result in more bass than the original 8 ohm?
So if I could get an inductance meter to verify the value and measure DC resistance, my goal would be to find another indicator with the same inductance value but as low resistance as possible, tight? And do it for both inductors in the crossover.
Stay with air core options or would iron core options have less resistance? If so, am I giving up anything significant by going air to iron core?
In all probability Steve is right!
However, it's worth replacing the electrolytics first to eliminate these as a factor. The very act of doing so may increase your confidence in the speaker's ability!
A reflex conversion requires commitment and calculation, but would be something to consider if simpler suggestions fail to satisfy.
Edit: Posted this before seeing Captouch's reply shown above!
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Lowering DCR in a coil is not in and of itself a good thing though.
Sometimes that is part of the baffle step compensation, at least how Troels and I do it. In other words, I carefully slect the DCR, as opposed to going with the lowest.
OP:
I should also mention I've heard good things of using Mundorf bipolar s, certainly a lot cheaper than film.
Best,
E
I'm open to using Mundorf bipolars. Coincidentally, I just used some Mcap Supremes as coupling caps in a phono pre and am happy with the sound.
I already ordered some cheap PartsExpress bipolar electrolytics just to make the sure values were on target though.
It's a case of swings and roundabouts on the air core versus iron core argument!
I would favour air core wherever possible. However, to obtain large inductance with low resistance requires many turns of thick gauge copper wire. This means they're expensive!
An iron core gives the required inductance with fewer turns of wire which can therefore be thinner for a given resistance. So iron cores can work out cheaper. They can also saturate at high current levels, leading to audible distortion.
Unless you want to buy more expensive, lower resistance air cores, I would stick with the ones you have.
I would favour air core wherever possible. However, to obtain large inductance with low resistance requires many turns of thick gauge copper wire. This means they're expensive!
An iron core gives the required inductance with fewer turns of wire which can therefore be thinner for a given resistance. So iron cores can work out cheaper. They can also saturate at high current levels, leading to audible distortion.
Unless you want to buy more expensive, lower resistance air cores, I would stick with the ones you have.
Update:
I removed a bale of stuffing (see pic) from each speaker. It was really packed tight in there. I need to check, but I'd guess there's still about two similar sized bales still packed behind each woofer, so I took about ~1/3 of the stuffing out and the chamber is still filled with stuffing - just not nearly as tight.
There's also a chamber below the bass enclosure filled with this stuffing as well - see pic with the four open areas that allow you to access the chamber. I didn't check to see how tight it was stuffed in there and just left that alone for now.
Also, the midrange driver has its own isolated enclosure behind the driver, but the chamber around that isolated enclosure I believe also has some of this stuffing around that.
In any case, the bass really does seem to have improved significantly! If I had heard them like this when I first tried them, I probably wouldn't have noted any lack of bass.
I'll still recap the bass crossover electrolytics when I get the new caps in, but I would say my fundamental problem has been largely addressed. Thanks guys!
What I took out was just random though. I wanted it to be enough that it was significant in proportion to what was originally in there, but there was no reasoning beyond that.
So it seems that I really should play around more with the optimal amount of stuffing/fill to keep in the enclosure.
Are there any guidelines or rules of thumb to help me zero in on an optimal amount of fill, or is it just a matter of trial and error?
And should the various areas (the main area behind the bass driver, the chamber below the bass enclosure, and the area behind the midrange driver) all be roughly equal as far as density of stuffing, or are certain areas generally more tightly packed than others?
Finally, here's a link to multiple pictures of the speaker. To be clear, this isn't mine, but the same model speaker. Just to give you an idea of how it's all put together:
Album Archive - Sony SS-M7A Speakers
I removed a bale of stuffing (see pic) from each speaker. It was really packed tight in there. I need to check, but I'd guess there's still about two similar sized bales still packed behind each woofer, so I took about ~1/3 of the stuffing out and the chamber is still filled with stuffing - just not nearly as tight.
There's also a chamber below the bass enclosure filled with this stuffing as well - see pic with the four open areas that allow you to access the chamber. I didn't check to see how tight it was stuffed in there and just left that alone for now.
Also, the midrange driver has its own isolated enclosure behind the driver, but the chamber around that isolated enclosure I believe also has some of this stuffing around that.
In any case, the bass really does seem to have improved significantly! If I had heard them like this when I first tried them, I probably wouldn't have noted any lack of bass.
I'll still recap the bass crossover electrolytics when I get the new caps in, but I would say my fundamental problem has been largely addressed. Thanks guys!
What I took out was just random though. I wanted it to be enough that it was significant in proportion to what was originally in there, but there was no reasoning beyond that.
So it seems that I really should play around more with the optimal amount of stuffing/fill to keep in the enclosure.
Are there any guidelines or rules of thumb to help me zero in on an optimal amount of fill, or is it just a matter of trial and error?
And should the various areas (the main area behind the bass driver, the chamber below the bass enclosure, and the area behind the midrange driver) all be roughly equal as far as density of stuffing, or are certain areas generally more tightly packed than others?
Finally, here's a link to multiple pictures of the speaker. To be clear, this isn't mine, but the same model speaker. Just to give you an idea of how it's all put together:
Album Archive - Sony SS-M7A Speakers
Attachments
If you have stuffing near the driver It lowers q more (reduces bass thump basically) than when It's further away, so best to try and keep It as far away from the driver as possible. Some say It's best to have some on the opposite wall to the driver to try and stop reflections from coming back through the cone but this obviously depends on the crossover frequency and slope (how much midrange Information the bass driver Is producing)
Stuffing should never be tightly packed IMO. I like to make sure there Is some at the top and bottom of the enclosure but It really Is best to experiment.
Once you're happy with the amount of stuffing you can weigh It to make sure you have equal amounts In each enclosure.
Back in the day of Edgar Vilchur's Acoustic Research speakers, the stuffing used in closed box acoustic suspension (which uses a heavy cone with a powerful motor, almost a reflex driver, and the air spring controls displacement in a very linear way) was hugely heavy and nasty glass fibre.
The theory says enough stuffing effectively makes the box 25% bigger. But there is a limit to how much you can add before it makes things worse. In my experience, stuffing near the driver makes it sound congested.
Nobody fits heavy stuffing any more with closed box. A bit of foam lining the walls and a bit of BAF fluff in the middle. It does more for the midrange really.
Reflex has totally different requirements, of course.
The theory says enough stuffing effectively makes the box 25% bigger. But there is a limit to how much you can add before it makes things worse. In my experience, stuffing near the driver makes it sound congested.
Nobody fits heavy stuffing any more with closed box. A bit of foam lining the walls and a bit of BAF fluff in the middle. It does more for the midrange really.
Reflex has totally different requirements, of course.
I took out another 1/3 of the stuffing, so now there's only 1/3 of what was originally in there, packed near the walls and away from the driver. I can't say that it's obvious w.r.t. the difference between having 1/3 and 2/3 of the original stuffing in there - only that both are far superior to having all the stuffing in there.
When the caps come in, I'll recap the crossovers and add some stuffing back in. I'm not confident I'll be able to tell when I've reached the optimal point, but I'm pretty pleased with how they sound now compared to when I first got them, so it's all good.
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