Doc modding Marantz imperial 7

[karatestu]

I will be keeping the Marantz cabs for another project, sorry. You would need a fork lift to move the buggers any way

I have completed one isobaric bass cube and I am listening as I speak

Rear baffle was screwed to the wooden strips that are screwed and glued to the cabinet. I used plenty of silicone sealant too so that there are no air leaks between the two chambers.



The hardest part was putting all those wires through the back panel as I put it back on. Plenty of decorator's caulk on the joints there so it is air tight.



I have not finished the other one yet so am listening to a the left bass cube only plus the two small cabs.

It is early days yet but some things I have noticed already with only one bass cube in use. Playing Portishead Dummy at the moment with plenty of very low bass.

1)The bass goes deeper but it so much clearer / cleaner at the very lower frequencies.
2)The room is not being overpowered by too much bass as was my concern. In fact it is tighter and so much more well behaved (not that it wasn't good before). In fact the bass is as tight as a duck's arse in water....... Did I say it was tight ? Fast bass notes stop and start lightening fast.
3)There is extra detail, probably due to this extra tightness
4)Not only is the bass improved. The mid and high frequencies seem tighter and more detailed also. I witnessed a similar thing when adding the original non isobaric bass cubes to the small semi Omni cabs. The tighter / cleaner bass must be letting more of the mid & high through in a more detailed and composed way.
5)The whole thing is much more musical, even with only one bass cube.

This is very, very, very good, frighteningly good, so good in fact that I can't wait to get the other one finished next week. I am going to run out of superlatives at this rate. The music is so so good I am in speaker heaven.

Isobaric done correctly (as the Doc instructed me) is awesome, I really don't think speakers can get any better than this........................

[Dr Bunsen Honeydew]

Yes Linn fecked it up per usual, and everyone if they wanted home build they copied Linn. Stupid choice, lost most of the benefit, all it needed was to go back to the designs of the guy who invented it, Harry F. Olson in the early 1950s.

[karatestu]

I wonder why Linn felt the need to feck it up ?

Not having done it wrong, i don't have anything to compare it to.

Maybe i should try it the wrong way then i will know just how wrong Linn got it - isobarik's and sara's. I believe Linn fecked it up the most with the sara's because they are only a two way and so have isobaric mid range which is not a good thing.

[Dr Bunsen Honeydew]

The whole thing was daft it was just two Kef Kit 2 in one box, but instead of the second tweeter they just put a resistor. The Isobarik was just two Kef Kit 1 in a box.

[_D_S_J_R_]

I wonder why Linn felt the need to feck it up ?

Not having done it wrong, i don't have anything to compare it to.

Maybe i should try it the wrong way then i will know just how wrong Linn got it - isobarik's and sara's. I believe Linn fecked it up the most with the sara's because they are only a two way and so have isobaric mid range which is not a good thing.

Ummm - Cubix have isobaric bass-midrange too.....

The only thing Linn did wrong with 'Briks and Saras was choice of drive units, especially the KEF B200 in the Sara and B110 in the Isobarik, which are inclined to screech if not properly crossovered or PVC doped and depending on the batch used as they varied a heck of a lot! Not sure what other drivers were around back then that they could have bought in quantity.

Saras and 'Briks were TWO KEF-KITs in a box and offered a three ohm load in the midrange to prove it! the tweeters were far more expensive than T27's though but in my opinion, not really better, although going active helped the 'Briks to sound far better depending on the generations of amps used... Falcon made the crossovers but I don't know how different they were from the KEF originals. Good wiring was used inside and the Sara boxes with radiused edges were superbly sealed and finished - copious amounts of a foul tar like substance was used inside and all over the driver chassis too to seal the boxes and drivers up, the 'Briks getting better cabinets as the years went on. I could go on, but it's not worth it here.

[antonio66]

But did they sound any good Dave? I never heard Sara's but did hear Isobariks and did not like them, although this is many, many years ago.

[karatestu]

Oh don't hold back Dave

All points of view welcome......i think......

[Dr Bunsen Honeydew]

I wonder why Linn felt the need to feck it up ?

Not having done it wrong, i don't have anything to compare it to.

Maybe i should try it the wrong way then i will know just how wrong Linn got it - isobarik's and sara's. I believe Linn fecked it up the most with the sara's because they are only a two way and so have isobaric mid range which is not a good thing.

Ummm - Cubix have isobaric bass-midrange too.....

*The only thing Linn did wrong with 'Briks and Saras was choice of drive units*, especially the KEF B200 in the Sara and B110 in the Isobarik, which are inclined to screech if not properly crossovered or PVC doped and depending on the batch used as they varied a heck of a lot! Not sure what other drivers were around back then that they could have bought in quantity.

Saras and 'Briks were TWO KEF-KITs in a box and offered a three ohm load in the midrange to prove it! the tweeters were far more expensive than T27's though but in my opinion, not really better, although going active helped the 'Briks to sound far better depending on the generations of amps used... Falcon made the crossovers but I don't know how different they were from the KEF originals. Good wiring was used inside and the Sara boxes with radiused edges were superbly sealed and finished - copious amounts of a foul tar like substance was used inside and all over the driver chassis too to seal the boxes and drivers up, the 'Briks getting better cabinets as the years went on. I could go on, but it's not worth it here.

* Wrong! - in isobaric terms they got it wrong by putting the drivers only a couple of inches behind each other. And now people say on forums that is the right way to do it WRONG!!! go look at original Larson designs to find out how to do it properly. This is the big problem with Linn bullshit so many people have been brainwashed into thinking they are always right instead of always being wrong.

[_D_S_J_R_]

Not what I read last night - the volume of air between the drivers supposedly doesn't matter - maybe I read it wrong...

By the way, the first Isobariks were also 'ARISTON Isobaric's,' judging by the HiFi yearbook I had and a pic I have, showing similar but not the same styling..

I owned THREE pairs of passive 'Briks in the early to mid 80's. The first, a chipboard pair from late 1979, were a bit rough sounding and bettered when Linn changed to MDF cabs in around March 1983 (90 degree XLR sockets). My second pair in walnut came in August 1984 and I have found some non-flashlit pics of their unboxing my wife dug out recently - terrible pics but the memories are vivid. This pair sounded as smooth as passive briks could ever sound and with a good amp, they were great and I'd have 'em here I think (memory cheats badly though and they may sound vague and veiled today).

In mid '85 Black became the new, well, black, and I wanted a pair to go with my 'Original Glasgow' black Ittok... Jimmy Hughes had got a cheap pair from Linn to write an appreciation of them (aborted 'cos of following - ) and he willingly passed them on to me, my walnut ones going to a friend in South London who long ago sold them and emigrated back to South Africa... This black pair were the absolute PITS! KEF had by this time altered the mid drivers (and bass drivers in the Saras) and they quacked and screeched terribly in a near-field environment - think David Gilmour higher guitar note frequencies really piercing... These were absolutely terrible and even a Linn LK1/LK2 amp with mellower tones than a Naim couldn't save them. They, with my sweet bolt-up Naim 250 amp, went to a mate with a very large room where they didn't sound so bad and I took his NS1000's in part exchange (NS1000's are now worth more than Isobariks, but not then). I also had his Snell E-II's but they lasted two days - ghastly squeak in nearfield...

[karatestu]

My big bass cubes are made of chipboard. If what you say about the improvement with briks going from chipboard to mdf then i am in for a real treat when i do the final build in baltic birch ply. Maybe some steel too.