Maintaining and modifing the Jamo SW 505E subwoofer.

Hello and welcome to whatishifi blog.

Back in late 90's I was working as a salesman at the Hi-Fi department of a big retail chain. I already had my own home (or should I say room) cinema, but without a subwoofer. I believed that since I had really big transmission line floorstanding speakers driven by a big power amp, there was no need for a subwoofer. How little did I know.

At the store I was, we had a home cinema studio. The speakers were not big, the amps were low / medium level so I was always keeping a sub in order to impress customers. And one day, the mighty Jamo SW 505E arrived. I won't say much, just mention that the nice ladies in the cashier one floor below were shaking each time a customer was asking for a demo of the home cinema. This sub was just arrogantly superior compared with any other sub we had back then.

Still, it took me quite some time to start wondering if a sub in my home cinema could be worth. So, I decided to take one 505E at my home for a test drive, just for fun. I remember telling my supervisor that the next day I would either return it or I would bring the money. As you guessed, I gladly brought the money.

Back then my best home cinema source was LaserDisc. The 505E made me wanting to watch all my movies again. What I was lacking before the 505E was the seismic impact of low frequency energy that you feel like it is arising from the ground underneath the floor. This sub is nothing less than amazing, I kept it in two different home cinema studios in the stores I was working and two friends of mine bought it; each and every time in all these different setups and rooms, this sub was a real killer at a very affordable price. I guess the secret was that it was tuned for home cinema use; perfect for the steps of T-Rex but not so perfect for music. Anyway, the sub was so damn good that I bought a second one, not because I needed it but just because I had a free space at the size & shape of the sub and I couldn't think of anything better to fit in.

The 505E is a band pass design with a single 12" driver and a 100 watt amp. The bass it reproduces is the kind of bass that you need in the movies; whether it is about earthquakes, missile attacks, aircraft, ships at a storm or captain Kirk saying "prepare to go into lightning speed". This happens not because this sub is an extreme design, it just happens because this sub is a damn good design making the right compromises in order to sound best in Home Cinema use. The sub is literally moving my sofa, making my plates falling in the sink or reminding me that the bathroom door is open, since I can hear the glass from the shower doors complaining. But it is not only about volume, it does have control and dynamics. In a few words, if you find it, get it! There is only one "but" here and this "but" is the aging of the 12" speaker's surround suspension.


The suspension of the speaker has started to age. What you see like a missing area is the rubber coating of the foam suspension.

One of my subs was made in 1997 and the other in 1998. I was regularly testing the status of the suspension by putting my hand through the port and touching it. Lately I noticed that my finger was becoming black and I could see some particles of the suspension, so I guessed that it was about time to replace it. The speaker suspension, not the sub.

The suspension is made of foam covered with a thin layer of rubber. As it turned out, it was the layer of rubber that had started to deteriorate, meaning I probably still had one year or so before total failure.

After talking with some experts including a speaker designer, I was worried if the sub would sound as good as it was after replacing the suspension. It seems that the suspension affects the damping of the cone movement, so changing it theoretically would affect the sound. More about this later. At that point, I communicated with Jamo (which now belongs to Klipsch Group) asking if there is any spare part like a speaker driver unit (item 20387) or a suspension. Unfortunately I was informed that there wasn't and my attempt to get any specs regarding the suspension (like how stiff it is, Qms) gave no results.

Item 20387 is not available as a spare part anymore.

The only way was to go ahead and attempt a suspension replacement. Before tearing down the subwoofers, I remembered that back when I bought the first sub, I decided to open it. Noticing that it did not had any damping material at the sealed chamber behind the woofer, I was sure that this was due to economic reasons and it would be a good (good? great!) idea to add some. But when I bought the second one (which I didn't treat with damping material) I didn't do any sound comparisons, so I felt that the time has come for a test. Together with Panos we placed the subs near each other, put the volume to the max position in order to get same S.P.L. from both of them and we fed them with the same signal. Turning them on and off, we easily decided that one sub had a deeper and more solid base. As it turned out when we opened them, the one sounding better was the one I didn't mess with. So, if you get tempted to add some damping material at the Jamo SW505E, please don't!

We took the two woofers off and we gave them for suspension replacement. In the meanwhile, we decided to mod the amps just a little bit by doubling the main capacitors (the original were 2x 4700 μF, 50V per sub). In a perfect world I would take the old capacitors off and put new ones, plus the additional ones. But since the subs were already sounding great as they were and the factory capacitors where nicely installed on the boards without any signs of deformation, I decided to just add another two.

It is fairly easy to take the power amps out of the subwoofer cabins, just note at which lead does the + and the - of the speaker wires goes. Also, you have to unplug a small plug that ignites the red LED at the front of the sub when you turn it on and that's all. Have a look at the photos and text below for what we actually did.

We putted a red mark below the board where the + speaker cable was connected. You can see it almost at the center of the board.



It is a good idea to put some contact lubrication spray at the three potentiometers of the amp.



Can you spot the difference? At the top amp (manufactured in 1997) the spark suppression capacitor was missing from the on / off switch. At the bottom amp (manufactured 1998) Jamo solved the problem; without this capacitor, when you turn off the subwoofer there is a boom noise.

As you probably guess, the logical thing to do is to add a spark suppression capacitor (0.033uf 275VAC X2 metallized polypropylene film cap) on the back of the on / off switch. For 20 years I was wondering why this particular sub was making a noise when I was turning it off.

The two amps before the modification.

Two extra capacitors added. We putted some soft rubber tape between them. We are not very proud of the looks but the space available was limited - also the additional capacitors had to be installed in a way that would allow the amp boards to be re-inserted at the subwoofer cabins.

Good thing is that we kept the cables very very short.



I choose these capacitors - no need to be 63V, they could be 50V.

I covered the leads at the back of the fuse box with some plastic tape, just in case. However please note that the leads are not so much close to the capacitor as it looks in the photos.

In the meanwhile, the speakers were ready with a new suspension. Since the foam of the new suspension was a little thicker than the original, I was advised and decided not to treat it with a rubber coating like the originals. The stiffness of the new suspension without the rubber coating was similar to the stiffness of the original suspension with the rubber coating and that was what I wanted - I also understand that the rubber coating might increase the life of the foam suspension by protecting it, but I choose as I said not to apply it. I didn't install a 100% rubber suspension because I was told that foam sounds better than rubber, the only reason not to prefer foam is that it doesn't last forever.



The speakers with new suspension.

Another mod we did was the sealing of the box. I bought one side self-adhesive soft rubber tape which was used in order to perfectly seal the chambers as well as the speaker's frame with the cabinet. From the factory, the chambers were sealed with a kind of black glue and the speaker driver had nothing like of a flange. This is not something bad - but if over time the screws that hold the driver unit get a bit untighten, you might start hearing some noises, so we decided to add the rubber sealant also there.

We installed soft rubber tape around the back of the speaker's frame.

We removed the old sealant in order to have a flat surface for the new soft rubber tape.

Cabinet ready to accept new sealant, mod amp and repaired woofer. The sound absorbing material you see is the factory installed material.

The soft rubber tape in position - the white strap you see is a protective one and will be removed before closing the box.



Everything back in place, starting to remove the white protective strip from the soft rubber tape. Remember, this side is not self - adhesive so we can open the box again if we want to.

The most important part that benefits from perfect sealing, is the chamber at the back of the subwoofer driver. As I explained earlier, please don't be tempted to put any damping material to this chamber!

After everything was put back together, I left the subs on, playing in low volume some low frequencies in order for the new suspensions to brake in. Then I feed them both with the same low frequency signal and by an SPL meter I adjusted each volume control on each sub in a way that both subs produce equal sound output levels, so both subs share an equal amount of the work load. The position of the volume control I choose on the subs is a position that will not force the amp to go to extreme +/- dΒs during calibration.

I will put the volume on the subs at a position that will allow the amp to be near 0 dB during auto calibration and not force him to go for example at + 8 dB (meaning I have placed the volume control at the subwoofer too low) or vise versa.

I re-calibrated my Yamaha home cinema amp and started the first movie. An antiaircraft weapon was fired, the sofa jumped, I almost had a heart attack - yes, the subs are still sounding great! Of course it would be nice if I had measured the subs before and after suspension repair, but I am afraid I didn't take care of that. However, the base is strong again (I understand it from the room vibrations) and the joy they offer is more than what you or the house structure can handle.

Another question is if the capacitor and sealing mods added something, while the new suspension took something away. I am afraid I don't have a direct and objective answer to that. The subs were always capable of providing more than what is required, they still do and I am not sure if now they can provide more "more" or less "more". For sure, it is more than I could wish for and exceeds the structural integrity of many objects in the house. So, I am 100% satisfied with the repair and the mod.

Some general thoughts about subwoofers.

As I confessed, back in the 90's I thought that if you have big speakers and power amp you won't benefit form a sub at your home cinema but I was wrong. Thing is that the .1 LFE channel in a movie soundtrack has different requirements compared to bass in music. As I found out, a sub offered more enjoyment in movies and I still believe that my speakers have enormous low end. Something that helps subs perform better is the fact that they are placed on the floor - the closer on the floor the source of low frequencies is, the more efficient & impressive it becomes.

Let's also see some facts - or how some facts can be misleading. At my current listening position, my main speakers start rolling off at around 32 Hz, my center speaker at around 29 Hz @ 3 meters (!!!) and my surround speakers (which they are identical to my front speakers) at around 30 Hz. My subwoofers start rolling off at around 32 Hz. In some cases, the SPL meter at C weight insists that the roll off happens at a lower frequency than the one I hear, indicating that it is not that the speaker is running out of steam but that my room will not allow some frequencies to be heard. So, by just examining these figures someone would say that I don't need a sub at all or that these subs are worthless and should be replaced by some center speakers because of this unimpressive 32 Hz. But this is in no way true; the subs add to the pleasure of watching an action movie and this is not just because they increase low frequency SPL. As I said, plates are falling in the sink and the house (made of bricks) trembles like there is an earthquake going on.

The easy thing to do is to say that a good sub is the one that will go lower, however like many things in Hi-Fi this chase (or obsession) of a single parameter can be misleading. Of course, if there was unlimited budget and enough room space, I would also love to get subs that go down to 15 Hz at -3dβ. But in real life you have to make the right compromises and the right compromises are the ones that give a better experience. Here is a nice article about what are the trade offs for a sub in order to go some Hz lower. Also, here is a very interesting youtube video, but I have to warn you: it is one hour long and you should not fast forward it, since it has many interesting points hidden inside.

Another question that bothers me is how low a sub is really meaningful to go. Or to state it in a different way, is it worth considering upgrading my subs with something that at least on paper goes -3dβ at 20Hz or even at 15Hz? Again, the easy answer is yes. If you search this subject, everybody claims that there is content at the LFE channel at 15Hz so you should get such a sub. But as usual, things are not so straight forward. First issue is that this sub should also be able to reproduce high SPL at these frequencies and at the same time be good at reproducing high SPL at higher frequencies. By simply looking at a graph that indicates that a sub will go 20Hz -3dβ but at 90dβ SPL doesn't really help to make a decision. Let me put it in a different way; if you look at the graphs of a well known American subwoofer brand, you will note that an older non-ported 13" sub (1,600$ retail) the specs state +/- 3dβ at 20-460Hz. If you look at the graph, you see around -8dβ at 20Hz compared to 30Hz. A current non-ported 13" sub (1,000$ retail) states +/- 3dβ at 18-270Hz. If you look at the graph, this seems more or less accurate. Let's now suppose that you find the old model at a stock clearance at 1,000$ so you have to choose; the older or the new model? Taking a decision by simply looking at these specs can be misleading. Anyway, to make a long story short; my opinion in regards to answering the question "how low a sub is really meaningful to go" is this: I would love to get a reference sub at my living room and connect it through a high pass filter. This way I will be able to see from which frequency and up it is really crucial and worth paying for the enjoyment of watching a movie.

However, I am not much of a fan for using a sub for 2ch music. It is not that I don't like base, it is that I prefer to have big floorstanding speakers with at least 2x 8" woofers instead of smaller speakers plus a sub. Reason for this is that I always feel that I can hear two different things playing their own way, except if you lower the sub volume so much that it becomes pointless. One exception to this is if you are listening to dance music, then yes, a sub can easily do the job. Another exception is when you listen to 5.1 music; in this case, even my not-so-perfect-for-music subs with the help of my multi channel AV sound great and disappear in my room.

Of course, the hard question is when you have to stick with small speakers for music listening, then what do you do, will you go for a sub? Well, I guess it is a matter of taste and appropriate compromises. I have to admit that there are quite a few sealed subwoofers out there designed primarily for music use, the 505 E however is not one of them.

There are also some pretty expensive designs that will equally do in music use and home cinema use but the bill will grow and as I said, apart from the economics, I prefer big speakers for music and a sub designed for home cinema use. But hey, this is just me.

(2023 update: There is a new argument regarding subs for music, saying that the position of the main speakers for best soundstage imaging is almost never the same for optimal low end performance, so you can position your speakers for best imaging and augment the speakers with a sub positioned for best bass performance. Not a bad argument but still, I have no experience.)

Anyway, regarding music listening and subs, here is a short video on how to connect a subwoofer and here is another one on how to set it up.

Happy listening as always!

Christos

P.S. Do you want to do some subwoofer / low frequency testing? Here you go but hey - be cautious not to blow any woofers!
- Low Frequency Range Test (10 - 200 Hz)
- Low Frequency Harmonic Distortion Test
- Low Frequency Sound Localization Test 

Also, in case you are searching for the Jamo SW 505E manual, here you go: