Rogers LS7

Rogers LS7 (7K)Back in 1996, I made the mistake of borrowing a pair of LS3/5As from work. Of course, it meant my old Musical Fidelity MC1s had to go!

At the time, the second-hand price of LS3/5As was around £400, which I felt to be a bit much. After a bit of investigation, I discovered The Emporium in Diss, Suffolk. They offered me a loan of a pair of Spendor's BC-1, which were going for just £100, and a pair of Rogers LS7s which were priced at £200.

It was an interesting week, as I still had the 3/5As, plus a pair of Spendor SA-1s that a good friend suggested as a cheaper alternative to the LS3/5A... My landlord was starting to seriously worry about me!

Almost from the moment I heard the LS7s, I knew they were exactly what I was looking for. I normally refrain from making quick judgements until after a few different recordings because first impressions are often misleading, but this time, I was right! The LS7s became my main loudspeakers, and remained so for around 5 years, until I switched to the BBC LS5/9.

Technical details

Rogers LS7 bass unit (47K)The enclosure is made using classic BBC "thinwall" construction, but using cheaper MDF rather than birch plywood. The cabinet walls are 12mm and the baffle is 18mm. All walls except the baffle are damped with self-adhesive bitumen pads and lined with foam. The cabinet has a real-wood veneered which is stained gloss-black in my case. I'm not sure if that finish is original - it's possible they've been re-finished at some point.

The bass driver is retained with decent machine screws and captive nuts, and the port opening is flared to reduce port noises. The tweeter and plastic connection plate on the rear panel (holding the crossover PCB) are secured with wood screws. Gaskets are used on every removable component to ensure good air sealing.

Until I bought the ATCs, this was probably the biggest magnet I'd seen on a bass driver! It's nearly about twice the size of the LS2/14 used in the BBC LS5/9s.

As an aside, note the "Swisstone Electronics Ltd" markings on the casting - I was never 100% sure of the exact relationship between Rogers and Swisstone, but thanks to a unique and fascinating article detailing some of the history of Rogers written by Brian Pook (MD of Rogers 1976-1982), I now know for sure what happened. Basically, Rogers went bust, but the decision was made to relaunch the company - even attending the auction to buy back items that the bailiffs had only just taken away! They needed to be an actual company to do this, so bought "Swisstone Electronics" for this purpose. As far as I can tell, Swisstone was just a vehicle, set up previously and left, awaiting a buyer. I don't understand many aspects of business, so as unusual as this might seem to me, it's quite probable that this is a fairly common practice. Feedback welcome!

As mentioned on the LS5/9 page, the two bass drivers share some obvious visual similarities. However, they measure very differently:

  Rogers LS7 BBC LS2/14
Fs (Hz) 29.8Hz 81.5Hz
Qms 2.97 2.8
Qes 0.245 0.78
Qts 0.22 0.61
VAS (ft3) 4.2 0.4 (!)
Re (ohms) 7.1 6.5

The accuracy of these results are not guaranteed! I made these measurements a little while ago while I was playing around with the LS7 driver in an LS5/9 cabinet (results were interesting, but didn't amount to anything - it was just a learning exercise). Still, perhaps they might be useful if you ever need to find a roughly equivalent replacement driver? That said, do bear in mind that the LS5/9 woofer is subject to ageing (the PVC surround hardens), so I wouldn't expect the LS2/14 results to be the same as a new drive unit.

Crossover

The crossover is quite complex for a typical domestic loudspeaker. Indeed, the topology is quite similar in to the LS5/9, but simpler because it lacks the comprehensive tweeter level adjustment. However, the description given on the page is equally applicable here. The only thing to add is the series inductor in the treble section (L3) - this will help to roll-off higher and ultrasonic frequencies, which might offer the tweeter some small degree of protection from HF oscillation or clipping in the power amplifier.

LS7 crossover
     schematic (9K)

As you can see from the photo below, some components aren't fitted. The crossover PCB, labelled "ROGERS LSX MODULE 1", will have been applicable to several Rogers models at the time, and different components were fitted as required. In the Hi-Fi Choice review below, they mention the "13-element 3kHz crossover" - I can only count 13 components if I include the omitted ones. Perhaps the design was simplified after some time in production to save a few pennies...

LS7 crossover (37K)

I've not bothered to include any details of the Celestion HF1000 tweeter at this stage as it's the least interesting component in the design. It's arguably the weakest part, in my opinion. The criticisms in the review below mostly point to the tweeter, and I certainly feel that my objections can be attributed to it.

Mods

I quite often receive emails asking about moddifying these speakers (and indeed, others on this site). From direct experience, I would advise caution. I tried changing the two electrolytic capacitors for expensive polypropylene devices, and the results were horrible! The midrange glare mentioned below was made much worse, and the original caps went back in a few weeks later!

Electrolytic capacitors have well-known problems and limitations, and the designers working at Rogers back then were talented and experienced engineers. Quite simply, these limitations were accounted for at the design stage, and substituting "better" components will upset the balance.

As for "upgrading" internal wiring, before doing this try to work out how much standard-quality copper wire is used for each inductor in the crossover, not to mention the voicecoil!

Sound quality

At the time, I found that the '7s had all the qualities that I liked about the LS3/5As, but with a extra octave of bass. The thing against the LS7s was their size, mainly because the room I was renting was only 12 by 8 feet, but I knew I wouldn't be there for the rest of my life...

They were my main speakers for about 5 years. Happily my first impressions were largely confirmed. They have a very neutral midrange that make vocals sound worryingly natural. The imaging is very good and easily up to the standard of modern loudspeakers. What impresses most is the bass - modern speakers just don't sound the same unless you're able to spend a large amount of money. It's very clear and natural, and doesn't sound boxy or boomy like some modern designs I've directly compared them to.

I know this is a slightly strange thing to say, but if there's bass in the music, then you hear it. If there isn't, then you don't. I say that because there are too many loudspeakers that have higher and less well damped system resonances that always seem to sound the same, whatever the programme material, almost like the bass is failing to move up and down the scale like it should.

If I had to find a minor complaint, it would relate to the midrange. At low listening levels it's fine, but when you listen at higher levels some 'glare' is apparent. It may be a peak in the response, or perhaps the tweeter is unhappy at the lower end of its frequency range above a certain power level. Unfortunately, the acoustics of my lounge contribute to the effect, with the net result that some CDs are uncomfortable to listen to at moderate levels. A recent CD player change helped slightly, but having tried a variety of alternative models, I know that the speakers are at least partly responsible. A colleague has a pair of LS7s and I'm considering asking him for a loan, which would help me decide if it is a 'characteristic' or a fault...

They are quite efficient (88dB/W), which means that my Musical Fidelity A1 can drive them to reasonably high levels. They are well-suited components, and I was happy with the combination for many years...

Click here to read some interesting comments from visitors.

For details of what eventually replaced them, first check out the BBC LS5/9 page, and then the ATC SCM20SL page...

LS7 Hi-Fi Choice review

Click here for a review of the LS7. On the whole, I like this review, for fairly obvious reasons. One thing I'd comment on is the "slightly 'edgy' and 'sibilant' treble" they observed: having heard CD players from the time, I wonder how much of that is a function of the source?

I use mine without the grilles for the reasons given. And I've found that the 'rich' bass can be tuned by careful positioning. In the test room they were positioned a metre from each of the side walls and 0.8 metres from the back wall, firing down the length of their 13'9" by 18' listening room, whereas I listened to them across the width of my lounge, which puts them at least 1.5 metres from a sidewall.

Update - October 2013

A few years back, I was offered another pair of LS7s, completely FOC - I simply had to pick them up. I am indebted to Lionel Smith for this very generous offer; simply, the LS7s were too large for him, and because he'd found the information on this website of interest, he wanted to offer them to me first of all.

They are finished in walnut, and apart from some water marks on the top panels, they are in excellent condition. I'm optimistic that I'll be able to restore them at some point in the future. However, in the meantime, I'm pleased to offer the following update on the sound quality:

At this point in time, I'd been using ATC SCM20SLs for a long time. Going back to the LS7s after some 8 or so years was fascinating. The first thing I noticed was that the midrange actually sounded fine - even at higher levels. Now, is this a fault with my original black pair, or is it because I'm using a much more powerful amplifier? Time pressures prevented further investigation, but I still have my original black pair, and I still have the Musical Fidelity A1 that I used back in the day. One day, I will get back to this...

The next observation was the bass; well extended and tuneful as it was, there was definitely a hint of "slowness" to it. The Hi-Fi Choice review alludes to this. The issue is transient response, and the symptom is confined to kick drums - and mostly the electronic type in practice. So, this is probably not a problem for most listeners, but playing some '70s disco might show it up. I noticed it with "Tragedy" from the Bee Gees. Not that I'm a massive fan, you understand, but the kids enjoy a good bop to that sort of thing!

I will return to this at some point in the future...

The LS7t

The later version of this speaker, the LS7t, used a different tweeter, but kept the rest of the design largely unchanged. A titanium dome unit was selected, hence the "t" suffix. I've only ever heard an example very briefly, and to my ears the treble was much crisper and more detailed, but I wonder if this could become tiring after extended listening. Critics didn't seem to receive the model quite as warmly as the predecessor, but there are plenty of happy owners out there who love them...

Thanks are due to Andrey Tiurpenko for sending me these pictures and allowing me to publish them here.

Front view of the LS7t's (11K)
Close-up of metal-dome tweeter (16K)

Note how the front edges of the sides, top and bottom panels are square - my older LS7s have a 45 degree machined edges that makes the panels seem thinner and lighter, but also leaves it slightly more vulnerable to knocks. The grill cloth appears to be a conventional material, as opposed to the heavy Tygan used on the original LS7s.

The tweeter is clearly very different to the original Celestion model. Many thanks to Danko Suvar for identifying it as an MB Quart model, apparently a well-regarded model.

As you can see, the port has been moved off the centre line and the chassis of the bass driver has been painted black. I wonder if any other changes were made to it?

View with grill
       removed (15K)
Connection plate (21K)

These models can be buy-wired, as the market demanded at the time. This is something that is easily done with conventional parallel crossover networks, so the tempation must have been overwhelming for manufacturers to do this - an extra "tick" on the reviewers check-list.

Many thanks to Chris Hardy for supplying me with the crossover schematic, sketched from the crossover PCB in his examples:

LS7t crossover
     schematic (8K)

As you can see, it's slightly simplified compared to the LS7. The bass section is almost identical, but lacks the impedance correcting network R3 and C2. The treble section is, not surprisingly, quite different. The inductor is used as an auto-transformer as well as a frequency-dependant component - the 15 ohm LS3/5A and LS5/9 use this trick.