Marantz Imperial-9 resurection

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peplepew

Audiophyte
I'm going to pick up a pair of hammered imp-9's and all I know at this point is that they are "not working." I think it's going to be a given that the 10's will need to be replaced so I looked at some of the drivers at Parts Express and wasn't all that impressed with the specs of the drivers, most of them are are for small volume boxes. I think the 9's have a volume of about 5.5-6.0 cu ft. for the two 10's. From what i've read the tweeters aren't up to par with modern technology either so I'll probably end up replacing those as well. If I have a blown mid or two is it possible to get them reconed properly anywhere? If not I do have eight JBL 2105's I could load in there but the response on those isn't exactly flat. I do have a stereo 1/3 oct tdm eq I could use to help out. Anyways my experience is in the pro-audio (live sound) field and was hoping some of you fellas could get me going in the right direction. I plan on using the factory passive x-overs to start with but I would like to eventually bi or tri-amp these. Any help would be much appreciated.
 
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stiletto pat

Audioholic
Marantz Imperial 9s

Peplepew,

Wow, your post sure brings back memories. I bought a set of new Imperial 9s back in the mid 70s, and for the money, and the competitively available product in their price range, they sounded great. Of course, you're absolutely right about many of your assessments - the woofers were weak and bounced all over the place, the tweeters seemed to roll off early, but the mids were sweet.

I don't envy the project you're about to undertake, having built one set of speakers myself with only semi-good results, but there are a lot of people that have the DIY fever on this site. Get these members to comment.

Good luck, and keep us informed on your progress.

Pat
 
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peplepew

Audiophyte
Thanks Pat. I will keep all of you up to date with my progress. These speakers bring back memories for me too, in fact these particular ones belonged to my friend's dad. I remember being about fifteen listening to Michael Jackson's beat it on them and thinking they were the greatest sounding speakers in the world, which they were from my perspective at that time. I'm not expecting magic from these boxes, but I should be able to get them sounding pretty decent. I'm not super picky when it comes to stuff for myself anyways. I have access to measuring equiptment so I should be able to fine tune and share the results.
Brent
 

plhart

Audioholic
I was the designer of the Imperial 9's. They unfortunately were changed quite a bit from my original design because I left Marantz to start my car stereo speaker company at that time in 1973. Maybe some of this info will be helpful>

The 9's cabinet is closer to 4 cubic feet. The original woofers were doped cloth surrounds which actually survived much longer than the first foam surrounds which came out at the time. Original Thiele-Small parameters were something like> free air resonance = 26Hz, Qts = .4, Vas= (I'm guessing here)10, DCR = 3.5 ohms (to be wired in series).

As mentioned, this passive version of the 9 speaker could sound pretty "loose" so one needed a powerful transistor amp, like 250 watts minimum, with a high damping factor. All drivers were made by CTS of Padukah, KY, long out of the speaker business. I would suggest someone like speakercity.com to possibly rebuild the original drivers using a very stiff new- formulation foam surround. Or they might be able to match the T-Ss with one of the drivers from the numerous manufacturers they carry.

The mids are quite a bit harder. Also made by CTS you'll have to really search to find a driver with a similar basket and similar driver Thiele-Smalls. From memory (32 years!)>> FAR ~150Hz (crossovers were 600Hz and 2800Hz). DCR ~5.6 ohms. Not sure about any other parameters. The four mids are hooked up in series-parallel configuration.

The tweeters were the ubiquitous-at-the-time CTS phenolic ring tweeter. It became widely copied in Taiwan way before China was even in the game. This tweeter was very, very flat out to 17KHz after which it dropped like a stone. At the time there were no good and inexpensive dome tweeters with this tweeter's 92-93dB sensitivity. Today there are many alternatives.

Major changes (cheapening) were made to the 9's crossover once it went into production (I had left Marantz by that time). Originally it was a constant impedance design with zobel components. The production version threw out all the zobels and got rid of the individual and critically damped midrange enclosures in favor of a single enclosure.

Hope all this is helpful. Good luck with the rebuild...
 
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peplepew

Audiophyte
Wow! How lucky can a guy be to stumble onto the man who designed the speaker!!!! Small world-this is great. I'm looking at a service manual I bought on ebay and everything you are telling me checks out. Even the parameters for the 10's look about right when punched into the bass box program for a four cu.ft. box. Yeah, the x-over is bare bones alright, however the manual says "early versions of the I-9 employ a different crossover assembly." Maybe the first ones off the line had the real x-overs?
I wonder if it would be worth it to construct a new mid-tweeter array assembly and put those mids back in individual enclosures? I have access to a hell of a wood shop but without the ts's I couldn't be quite sure about the specs.
As far as the 10's go, I'll have to replace I think. When I looked at the speakers two of them had been replaced with "other" drivers from a quick glance. I'm sure if they were, the old baskets are looooong gone.

Thanks for the help! ;) I'll let you know how they turn out.
 
3

3beanlimit

Junior Audioholic
What a cool project!


I just finished doing a pair of Marantz HD88's. I rebuilt the crossovers and refinished the wood.

I bought these brand new around 1975? I finally decided to upgrade my speaker system.

I have them stored in the original boxes...(no kidding) untill my daughter has a place big enough for them.
 

plhart

Audioholic
peplepew said:
the manual says "early versions of the I-9 employ a different crossover assembly."
Really! I've never did see a manual for the 9's as I'd left Marantz by that time. I did hear a story what confirms what the manual says though. I knew that the parts for my constant impedance crossover network had already been ordered and I knew that many of the Marantz employees had heard my original design passive Imperial 9's.

A huge first order of the correct crossovers had come into Marantz so rather than junk the expensive constant impedence networks it appears that Marantz did indeed make a batch of the first systems almost as designed (save for the non-critically damped, separate midrange enclosures).

I had heard a $ figure of $25,000 in first production crossovers was used with most of the these Imperial 9 systems going to employees. Thanks for clearing up a 30+ year old mystery!
 
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Hornitos

Audiophyte
I had (4) Imperial 9’s since the 1970’s connected to my Marantz 4300 . . . We used to blow the Mid-Range speakers several times, but they were under warranty and kept replacing them. After the warranty expired. . . We didn’t blast them like we used too. A friend of mine worked at a bar about a quarter mile away from our house, he said he could hear them all the way on his walk to his job.

I just sold all (4) of them this year to a friend for $1000 - I also still had all the original boxes.

I replaced the (4) Marantz Imperial 9’s with (4) Bose 901’s hanging from the ceiling . . . I just didn’t have room for those monster Imperial 9’s anymore.
 
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