Frankenstein from Japan: Sansui SP-X7700


I thought long and hard how to name this one. And in a nutshell – current title is accurate. This is a story of one unfortunate purchase from a friend of mine with a somewhat happy ending. It unfolded somewhere around year 2014 and took a while to come to a conclusion.

So I got an excited call from an owner telling me that he had a good deal on some Sansui speakers to match his same brand amp. There are couple problems though and he want’s me to look at it. Unsuspectingly I said sure, I will take a look – send them in. If I only knew back then what I was getting into I wouldn’t be so light-minded.

I didn’t had any previous experience with Sansui speakers. So I was totally free of any predispositions. Almost.  I did had a Japanese speakers once, Technics SB-L95, and they were nothing to write home about. Despite of their good sensitivity, they could do one thing – play loud. That’s more or less it. Oh yeah, and the box was made from paper. Ok, it might be 8mm MDF, but you get the idea. And I totally get it – it’s shipping. You can’t send speaker box, weighting some 60kg, half around the globe and hope it will be competitive price wise. It’s just not a feasible business model. At least not in a Hi-Fi segment.

Is this a joke?

And so they arrive. I’m taking these boxes from a courier and bringing them to a second floor. When suddenly a strong feeling of dejavu strikes me! I’m not carrying any weight at all. It’s just air in my hands it seems. This isn’t a good start already.

Yeah, so it’s 8mm MDF again. Oh well… Lets see what other goods this bad boy is packing! And it’s electrolytic caps for a 3-cap-cross-over. Darn. This is getting better and better by a minute.

By then I was too afraid to hook any of my equipment to these marvels, so I just played some pink noise through my test rig. And what do you know! One of the mid-range drivers is dead and horn tweeter is not tweeting at all. I checked and mid-range was busted for good. Showing confident Open Line on a multi-meter. Tweeter on the other hand seemed to be fine. I traced it to be oxidized front panel switch. Just look at those black terminals, ouch. After some de-ox it was tweeting again just fine.

New “experience”

Quick search through usual places didn’t yield any results. It seems Sansui S-147 mid-range drivers are not popular among vintage aficionados. This leaves only one option… Let’s repair the poor thing. I mean, how hard can it be? ©Jeremy Clarkson.

Some paint thinner and 10 minutes later dust cap is off. This went better then expected. Cone paper is so fragile and soft that it’s not even funny.

More paint thinner and maybe 15 minutes later – cone is off. This time it made me sweat a little bit more. This concertina suspension is press-formed on the cone. So it’s the same material just impregnated. It was already broken maybe 50% of perimeter. I was lucky to take it of without destroying completely. Next goes the coil with former and it’s suspension. Nice blue glow! It must’ve got quite hot at some point. Good party it was.

I counted old coil to have 49 turns of 0.12mm enameled wire. That’s total in two layers. Winding new coil with 0.12mm wire was really fun (not). But after couple failed attempts it was finally looking good. Cone suspension got some bracing with small amount of glue. Nothing I can do about that damage near coil wires though.

Most important part is a proper alignment of coil within a magnetic gap. It took some time for me to find the right thickness paper for a shim. After suspension glue is cured it’s time for cone and dust cap. And voila! Just like new (yeah,right).

It seems I can also do driver repairs. Good. Now I know what to do with my life if I chose to be high all day long from all these toxic materials.

It’s alive!

I was very eager to find out how this repaired mid-driver performs. I felt like I made it my self. Proud constructor so to speak.

dBSPL@1Meter, no smoothing, 4ms gate window (left), Impedance (right). Repaired driver (blue), original driver (red).

This is really not bad! I thought it will look much worse. It seems we gained some sensitivity which doesn’t make much sense. Maybe other driver is also a little bit cooked? Also there are some impedance wrinkles that point to mechanical problems. Most of them related to the (still) busted cone if I must guess.

Having all drivers working and checked against any fire hazards, I decided to listen to these speakers for the first time. I always do that before measuring anything. It’s my way to avoid any confirmation bias. And I didn’t liked what I heard. First the “natural” front panel level switch made my ears bleed. And “soft 2” setting made them sound like an old radio. Also there was no bass to talk about either.

I could easily imagine them in a year 1973, playing light jazz somewhere at a corner of a bar in one of the Haruki Murakami novels. Just casually filling an already cigarette smoke thick air with some unpretentious light music from a worn out vinyl record. Perfect match.

“Kinda lonesome without music, huh?” said J, throwing the Rat the keys to the jukebox.

Haruki Murakami, Pinbal, 1973

And it’s dead…

After no more then 15 minutes I was already bored. At “soft 1” setting they were bearable, but the sound quality left to wish for so much more. OK, time to blow dust from a measuring mic and see what’s going on.

Measured dBSPL@1Meter, tweeter axis, no smoothing, 4ms gate window, “natural” front panel setting.

So it must be reversed polarity on one of the drivers – I thought to my self when looking at this graph. And why it’s never ending story with used speakers? I quickly checked all drivers and to my surprise they were connected correctly. But what is this?

And why there is a Pioneer logo on horn tweeters from a Sansui speaker? After quick google search it was obvious that these belong to a Pioneer SC-903. Another paper-weight wonder from the same era. And then it struck me – it’s over! It’s all lost…

These were very mediocre speakers to begin with. All the value they hold was for their authenticity and vintage looks. More like a interior decoration or collectible then anything else. And now it’s lost. Good luck finding these T-149B horn tweeters…

Resurrection attempts

Sansui SP-X7700 original cross-over and resulting SPL from a service manual.

Looking at the original cross-over I was wondering how much different the original T-149B was. Actually these are compression drivers with a wave-guide. Factory SPL graph doesn’t have that massive hole @2-3kHz, so there is some differences for sure. Or is there? Let’s try to recreate original cross-over.

dBSPL@1meter (left) and phasing (right). Woofer (blue), mid-range (red), tweeter (green), super tweeters (magenta).

This matches previously measured SPL pretty good all around. Those super-tweeter nonsenses are doing whatever and are only for a show. They can be safely forgotten. But it’s quite remarkable how good this alien tweeter phase matches the woofer. And what is even more staggering is how bad original mid-range does this! It’s almost 130° out-of-phase. Are you thinking what I’m thinking?

dBSPL@1meter (left) and phasing (right). Woofer (blue), mid-range (red), tweeter (green). Mid-range not inverted.

Yes. It’s much better when not inverted. Lowering mid-range cap to 4.7uF and with a proper attenuation they look really good. These vintage speakers are driving me nuts sometimes! How the hell they were designing things back then? By ear? It must’ve been tough. And yes. I checked. Dozen of times probably. They’ve come out of factory with mid’s and tweeter inverted!

All soldering looked like factory one and nothing was suspicious enough to call it a diversion. This is also confirmed by a service manual. So I don’t know. Maybe the right tweeter was filling this cancellation? But I highly doubt that. Maybe their design axis was totally different and it all falls into place at some magic distance? Who knows.

More dilemma

I quickly mocked up new cross-overs and this is what I got.

Measured dBSPL@1Meter, tweeter axis, no smoothing, 4ms gate window. Updated cross-over.

Much better. At least tonal balance was there and it stopped sounding like old AM radio. But do they suddenly started to sound decent? No. Not even close. And this is were measurements fail. Everything technically is more or less right, but something just didn’t work.

The culprit was these Pioneer compression drivers. Sound was just harsh and dull. With a bad taste of metal. They didn’t played ball with other drivers no matter what I’ve did.

It’s not my prejudice against compression drivers. I love them. Well, some of them. Something like TAD TD-2002 with a beryllium membrane can blow your mind away. Even cheaper options from 18Sound or BMS can be really good when paired with a proper wave-guide or horn. This cheap piece of plastic was not from the same planet I’m afraid.

The BASS problem

When listening to these speakers I noticed one more thing. There was no lowest octave. Like at all. So I started investigating it further.

Sansui SP-X7700 speaker box simulation.

I have measured  W-192 woofers TS parameters using added mass method (10g). This is how it looks in an original 67L box. Basically it has too high Qts of 0.57 to be used in a vented box. So that port on the cabinet is again – just for looks. It’s doing absolutely nothing. Another marketing miracle. And just look at those +4dB@90Hz! That’s a boom-box material right there.

W-192 driver in a 120L closed box.

If we would want to extract anything meaningful from these drivers we would need at least 120L of box volume. That’s a lot of space. And there are thousands of better drivers to put into new 120L boxes. So it’s out of question for this project. I think they would do well on open-baffle also. But it’s not for everyone. And certainly not for every interior.

So what now? These speakers are worth no more then their equivalent weight of a firewood now. They sound so-so even with “improved” cross-over and bass doesn’t go deep at all. I don’t really know what to do with them. Maybe… let’s make a boom-box out of them?

Let the party begin!

At least they will be good party speakers. Or so I thought. But there is no way I’m leaving that Pioneer horn tweeter. And these barely-alive mid-ranges do not like to party. That was very obvious.  So new drivers it must be. To the hunt!

Monacor MS-130 mid-range and DT-99 tweeter SPL and Impedance graphs by manufacturer.

I was already familiar with Monacor drivers. Mostly from a Pro Audio segment. I always thought that they were decent products. And if we take price into consideration – they are real bargain. Perfect for repairs in these kind of situations. I had a sensitivity target of ~94dB and was choosing from 5″ mid-ranges and 1″ tweeters. Only these two candidates were up to the task: MS-130 and DT-99. Few weeks and just 150€ later these drivers were on my desk.

dBSPL@1Meter, 1/24 octave smoothing, 4ms gate window. Monacor MS-130 (right), DT-99 (left).

Above are measured SPL response with drivers already mounted in cabinets. So take all these measurements with a grain of salt. On a baffle it would look much better. Both drivers doesn’t quite reach their declared sensitivity numbers and MS-130 pays a hefty price for such a high efficiency in this price range. DT-99 is very well behaved and just shy of 93dB/W/m.

Distortion@1Vrms, 1/24 octave smoothing. Monacor MS-130 (right), DT-99 (left).

Distortion graph has a good clue about up-coming cross-over design. MS-130 has a nasty break-up @4kHz and DT-99 distortion starts to rise below 3kHz. So it seems to be good idea to cross them @3-4kHz range. Although MS-130 distortion looks bad, it’s only 2nd and 3rd harmonics. Still very usable.

CSD waterfall, 4ms gate window, 1ms rise time, 25dB range. Monacor MS-130 (right), DT-99 (left).

Despite its shenanigans in SPL domain, MS-130 resonances are well controlled. That was later confirmed by actually good sonic performance. DT-99 on the other hand, has some decay problems, but again – that’s in a cabinet, so I will retain from any further interpretations. As a whole – I have nothing much to complaint about. Very usable drivers given the price.

The face lift

Cabinets needed some work. Old mid-range drivers were sealed-basket so they didn’t needed separate compartment. New ones on the other hand are open-basket. Here comes PVC tubing to the rescue.

New mid-range compartment ended being about 2L of volume. With a right amount of damping I measured no change in resulting SPL. Then front panel got a new face-plate and the cut-out was used as bracing for the back wall. So it would act less like a passive radiator.

I then glued final decorative face-plate layer of a black mat PVC sheet. After some considerations I decided to leave the port just for aesthetics. Finally almost 100% stuffing with sound damping material. It should help to virtually increase box volume and extract just a little bit more of that bottom end.

New cross-over

A lot of hair-splitting went into taming MS-130 mid-range. It’s not a very easy driver to work with. And it’s not difficult to see why when looking at SPL graph.

dBSPL@1meter (left) and phasing (right). Woofer (blue), mid-range (red), tweeter (green).

So this is the best I could manage without going nuts. Not quite ideal LR3 slopes at mid-tweeter cross, but phasing is good and that shelf @4-7kHz helps to bump up total treble level. Well worth compromise. After few listening iterations I made overall tonal balance slightly tilted downwards higher frequencies. And this worked like a charm here. Lower end suddenly has much more authority and overall picture has quite improved.

I didn’t go full cheapskate on cross-over parts. Standard Jantzen Z-Caps and air coils were it matters. Remember – things will always sound as good, as a weakest component of a whole chain will allow.

The modern Prometheus

Here goes the final measurements of both finished speakers.

Left – dBSPL@1Meter, 1/24 octave smoothing, 3ms gate window. Right – impedance. Blue (right speaker). Red (left speaker).

That’s why I love to work with new drivers – consistency. That hole @2kHz is not audible and impedance is very smooth with a minimum of 5.6Ω. Together with a healthy 92dB sensitivity – that’s a very tube friendly speakers I must say.

Step response (left) and distortion profile @1Vrms (right).

More or less typical step response of  a three-way. That massive 15″ woofer with a tinny magnetic sistem is having trouble mooving all that air. Distortion spectrum is dominated by a mid-range with a non-intrusive 2nd harmonic. I wonder, how many of those electronic engineers that is constantly beating their head against the wall for the last 0.0001% of THD has actually saw or measured a real speaker distortion?

And this is how they finally look. Not bad for a quick face-lift. Veneer on cabinets was in a reasonable shape, so it got a proper bee-wax treatment and I called it a day. Sorry for no more decent photos. I was in a hurry to give them back to the rightful owner. And finally free-up some storage space in my lab.

Closing chapter

But before giving them away, I had managed one last good listening session. I put them on a 50cm stands above the ground and at least 80cm from my back wall. At my usual 3 meters listening position, overall tonal balance was just fine. I have a substantial room-mode @34Hz, so after some acclimatization, low end didn’t seemed to be lacking much.

I had really forgotten over the years how a bass from sealed box sounds like. It’s really different. I hate term “fast bass” because it’s an oxymoron. I mean, just look at that step response and  witness how fast this 15″ woofer is.  Nevertheless it sounds tight and precise. You suddenly start to realize that this one-note over-hanged interpretation from a vented box is hiding whole world of sounds. Different parts of drum kit starts to emerge more clearly and bass-guitar is more defined. And even though drums still doesn’t sound like drums – it’s a closer rendition of reality I feel.

This el cheapo mid-range was surprisingly transparent. No problems with vocals or any noticeable sibalance. Although it took a lot of filtering to achieve that. Tweeter was nothing special. It was just doing it’s job without any claims to be something unique. Overall picture was very precise and clean. More then I like it to be. But from my experience it’s always the case with LR3 and higher order crossovers. It’s a price to pay for a good power handling.

Unforeseen consequences

We had a second listening session at an owners place. And it was a disaster. Problem is – people often don’t realize the room requirements when buying speakers. Room is an integral part of any speaker system and it’s treatment, together with a speaker placement, plays a decisive role on our sound perception. His dining room was just 2×4 meters large. Bare walls, wooden floor and a couch with a TV table in front of it. Despite my concerns I was told that speakers will be standing sideways TV table, on the floor and basically pushed against the wall. Because of reasons… (insert a random wife joke here).

We sat on the couch and speakers were some 1.8 meters in front of us. Sound was (as expected) terrible. This 3-way had a very good dispersion and was just flooding room with reflections. These early reflections, having nothing to damp them, were just destroying the sound image. From this short distance – there was no stereo separation to speak of and that boominess. My gosh. It was just gut-wrenching with this combined full ground and wall gain. Some improvised stands and a little bit of distance from back wall was a small positive improvement but changed nothing ultimately. These speakers not gonna work in this room position! Period. And not even like a party speakers. Not much of a party with everybody vomiting from tinnitus. This environment calls for a small 2-way monitors having proper directivity control. And not these 15″ fire spitting gargantuas!

Post scriptum

I was left with a little bitter-sweet feeling there. Having spend so much time and effort on breathing in a second life to these speakers and eventually failing to bring the “proof in the pudding”. Through no fault of mine of course, but nevertheless. I know that these speakers eventually found their new and (I hope) acoustically more appropiate home. They really deserve it.

Thanks for reading!

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