Doc modding Marantz imperial 7

[Latteman]

For God's sake I need to get something finished. Something that meets my expectations in regard to sound and appearance. I have got the sound bit done (just about) but the aesthetics are a whole new project which I have to combine with material selection to get the best outcome possible.

When I have something I'm pleased with and it is in my living room playing music then I might have a play with bipolar 8 inchers (just for you Tomasz)

[karatestu]

Currently listening to Dinosaur - Wonder Trail (modern jazz). Trying to relax after this mornings events, do a bit of paper work and do some critical speaker observations.

These bipolar up and down firing 6.5 inchers are a clear step up in the bass and presence areas. Although I suspect the cabinets are slightly undersized for my taste, I cannot detect an obvious bass hump like what you get in an undersized cab (trust me when I say I know what it sounds like).

I am testing them with my usual bass torture music of Portishead, Jamiroquai, Air, Gorillaz, Beck, The Comet is Coming and Morcheeba. Doing alright so far although I have yet to try Portishead Dummy. My isobaric 12 inchers used to have things rattling and falling off shelves when I played that album. Even four 5.25 inchers per channel were too much although positional aspects might have contributed to the that.

What I can say is that I don't like mid bass drivers down firing when they are any less than 30 cm (1ft for the old timers ) from the floor.I have my down firing 6.5 " mid bass at 45 cm (1.5 ft) from the floor and that is about right thankfully. Any more than that and the tweeters will be getting too high. The whole speaker up the top of the tweeter pod is 90 cm (3 ft). I can't go any higher but don't need to - I could actually go 5 cm (2") lower and still be good. That would be 40 cm between the down firing mid bass and the floor.

I have pulled the latest bipole out a little from the wall and found the best spot. That is 12 cm from the back panel to the wall. With the 2x 5.25" mid bass bipole (single cab) the back of the cabinet was 1 cm from the wall. I was yearning a little more bass from that - meaning the smallest amount, I could happily live with that configuration.

As I have pulled out the 6.25 " driver bipole 11 cm further out to get best bass response, I may end up trying the 6.5" down firing and a 5.25 " up firing to see how far back to the wall I can get them. Out of curiosity more than anything. I did think that having identical drivers up and down firing was essential to get the most of the baffle step compensation and the force cancellation. It will still work with different drivers i think so worth a shot. Not for a while yet though as I need to do much more listening with these until they have run in (the suspension - surround and spider).

Maybe a position where the cabinets are nearly touching the wall is not that essential. It is just that I remember the destructive boundary cancellation from the wall subjectively disappearing when right back to the wall.

[karatestu]

Yeah, I know that was all about bass No mention of the music My attention always goes to the bass region first when assessing a new speaker, probably because that is where most of my dissatisfaction has been in the past. Once I have a handle on that I can move to other parts of the music and then the performance as a whole.

Sounding good to me although I have been known to change my mind and do a Boris style U turn.

You might not believe this when I tell you, especially after some of the Heath Robinson, aesthetically challenged monstrosities (thanks Tomasz) I have churned out, but i am actually very much a perfectionist . Nothing is good enough and if one little thing about something niggles me then i can't forget it. Toys out of pram sometimes.

All those crap chipboard enclosures I have made cost me zero. I still have them all in the corner of an outbuilding, saved for a time when they might be useful But the point is I wouldn't have done all this if I hadn't access to all these materials for free. All I have bought so far are the drivers - yes lots of them , good job the mid bass' aren't expensive. I consider myself very lucky to have materials and a multitude of tools at hand not to mention agricultural buildings to store and build things and generally make a mess.

Not sure where I get the time except to say that I could be a lot richer if all my diy audio energy was directed at paid work This experience at the moment is worth more than riches to me though.

[Toontrev]

Things seem louder than with the bipole 5.25" version. Looking at the TS parameters of these drivers and the reason is apparent. The 5.25" mid bass have a sensitivity of 84.8 dB. The 8" has a little more at 85.5 dB. The star of the show as regards SPL is the 6.5" model at 88 dB. I know sensitivity isn't everything but it is useful non the less.

What I did notice when comparing this 6.5 incher to the 6.5 incher in my B&W P4 speakers is the magnet is much larger, the suspension seems stiffer (but still needs to break in) and judging by the size of the dust caps, this one has a much bigger diameter voice coil which I presume will effect Le (inductance).

They are both kevlar coned but one is a PA driver and the other a hifi driver (B&W). I presume (not exactly sure) that the magnet strength and BL parameter will be what determines whether a driver is suitable for doping or not (plus the cone weight possibly). The magnet on the B&W driver looks very feeble in comparison but then it probably has a lighter cone and other differences to even things out. I don't fancy doping the B&W driver although I have thought about it many times

[Ithilstone]

The magnet on the B&W driver looks very feeble in comparison but then it probably has a lighter cone and other differences to even things out.

This or B&W magnets are made from different material ;]
like regular magnets and N52 ones
Is there a large weight difference?
OFC you might be right that B&W has much "weaker" magnets as cone is lighter etc ;]

[karatestu]

I have been listening to my speakers most of the day and played all sorts of different stuff. Bass heavy music, jazz, funk, classic rock, electro, country, pop, blues, reggae and one classical CD

I'm in love They haven't put a foot wrong all day. It's such a relief to know that I can now stop faffing about with speakers.

Well, apart from building a final pair that look as good as they sound. I am sure there are some improvements to come. Some good performing materials instead of this crap crumbly chipboard. I think the idea is to push any panel resonances as high as possible as there is less energy as you go up in frequency. Not that there will be much in the way of resonance due to the force cancelling nature of the bipolar design with mid bass on opposing panels and wired in phase

If this is anything to go by https://www.audioholics.com/loudspeak ... abinets and this https://www.audioholics.com/loudspeaker ... speakers I want to be choosing very dense materials that are also very stiff. Or a mixture. So steel, quartz, concrete, granite etc etc.

In one of those link's it does go on about weight being good to stop the speaker moving which loses output, colours the sound and affects imaging. Doc more or less always said the same thing. But we have drivers that are firing up and down and largely cancelling each other out, so there won't be much movement to start with. Plus the drivers are in mechanical phase with the earth so they can't wobble as such.

Still, it won't hurt to make them a healthy weight if for no other reason than my kids will bounce off them if they run in to them I went to pick up one of the old Marantz Imperial 7 cabs that I lined with 6 mm steel the other day. Bloody hell, hernia time I have been using them as a jig for my LP12 so I can lay on the floor and fiddle about inside

I still have loads of things to work out like what to do for grille's, how to finish off the tweeter pod's and connect them to the main cab. Need to plan carefully so everything is perfect. I was going to try and make it so the pods could be rotated for toeing in but I am not sure I can be arsed with the complexity of that. We will see.

Then there is still the decision about making the stands integral to the speaker or making separate stands. I like the idea of just having four integral legs. one in each corner (obs) which run from the top of the main cab to the floor. That way they could be a bit of a feature especially if they were round and the panels go in to slots cut in to them. One quarter of the round would then be inside the speaker eating up internal volume but I think it would look ace if I could actually pull it off. May need to draw a picture to convey that idea.

[Latteman]

Here is a rough sketch of what I was thinking. Plan view.



I don't know if this idea will fly or not.

[Latteman]

azad oommen

External fixator

[Latteman]

You've gone and got me thinking now Peter. I don't particularly like the look of those but they might give me a light bulb moment

[karatestu]

By the way Peter, it's about time you sorted a new avatar out