Doc modding Marantz imperial 7

[Ithilstone]

Hello Peter, thanks for your comments.

I am over the moon with how this crude little tweeter pod is working. It seems I can have my cake and eat it The imaging was never going to be pin point razor sharp but it is the best I have managed so far even beating a simple one up firing 5" and forward firing tweeter. I know I have said in the past I was willing to sacrifice imaging for lower intermodulation distortion but with this tweeter pod I can have both.

I now realise how important it is to get the tweeter(s) behind an up firing mid bass. I can mess about with it's exact position until I find the best subjective place to mount it. It can be toed in independent of the mid bass cab. The only fly in the ointment I think is reflections off the top baffle. If I get it at the right height the reflections will go above my head when seated i.e I can't see the top of the upward facing baffle. Different story when you stand up I suppose but you can't have everything.

With my next experiment of putting two mid bass right next to each other I have moved them forward a bit so they are closer to front panel. That will give me more room behind them so I can play about with having the tweeters further behind the mid bass.

I have never mounted two 5" mid bass right next to each other before so this will be a learning experience. I need to get them as close to each other as possible - I have the first two actually touching so can't get any closer. Having two next to each other will modify the directivity a little but I am not entirely sure how much yet and if it will be a problem subjectively. Line array's limit the dispersion in the vertical so having my two from side to side rather than front to back might reduce the dispersion to each side of the speaker.

We will see (in the not too distant future).

[karatestu]

Got two of the new baffles made and everything wired up.



This top one has both 5" drivers firing up .I decided to put them on top of the cube with up and down firing mid bass . So there is a gap between the two cabs but only a mid bass firing up in to it. There is of course a mid bass firing down in to the gap just above the floor. Like this.....



This works but wasn't my intention. I was intending to put one cab directly on top of the other and put both drivers in the bottom cab firing down. I didn't get time to convert the other two so this will have to do for now.

I have just proved that it was the two mid bass firing at each other in the gap between the cabs that was the problem with my first attempt. This arrangement has a big sound like I remember the first time but the music still has it's clarity. Bass is not overblown so far but I need to play all my torture tracks before I sign this attempt off.

The increased detail is there that I experienced first time around - my guess is decreased intermodulation distortion from doubling the amount of mid bass. Very promising and spurs me on to get the other two cabs converted.

[karatestu]

Well, I have finished converting the other two 30 cm3 cabs to twin mid bass down firing. One cab sat on the top of the other one.



Looks fab doesn't it Tomasz will love it.

Whilst beavering away on the two cabs I listened to the other two with twin up firing mid bass. Where had the bass gone ? No BSC from the bipolar opposing drivers. It was good apart from that.

The two 5.25 inchers will only just fit inside these cabs with maybe 1 mm to spare. You can see where my hole saw was rubbing up against the side walls when i was cutting the 133 mm holes through the wood.



The holes in the aluminum are of course 114 mm and it was handy to use the hole left by the larger hole saw to get the smaller hole dead centre. Here it is with the drivers installed. They are touching in the middle, talk about tight fit or what.

[karatestu]

So what does it sound like ?

Well, I have the baffle step correction back from the bipolar opposing drivers. Hello bass The drivers are held in place by pressure from four lengths of plastic down pipe which couple each driver to the dividing wall between each cube (no screws or glue required ). The gap between the two down firing mid bass and the floor is 10 cm. I need to increase that to 15 cm to get the tweeters at the right height.

All the detail is there from having four mid bass and four tweeters. It is much louder than with two mid bass. I have them wired in parallel series for an eight ohm load and that in parallel with the 22 ohm load of the four tweeters. As I don't have a way of changing volume without changing a resistor I can't really do a good comparison because this set up is louder than the single cube bipolar jobbie.

What is evident is that I will have to live with this for a while. I suspect the tweeter wiring arrangement may need changing to parallel series for a bit of extra volume.

In the coming weeks I have to decide which I like best. Single 30 cm cube with bipolar opposing mid bass and tweeter pod on top or the two 30cm cubes joined together with dual bipolar opposing mid bass and tweeter pod on top.

Once that is settled then the I have to finalise all the little details and build a final version which will be going home to my living room. I bet Tomasz can't wait

[Ithilstone]

My first impression was. Is that Stu's take on Xmas tree?

[Daniel Quinn]

What do multiple tweeters bring to the party?

[karatestu]

What do multiple tweeters bring to the party?

Lower distortion as the work is shared out. Spaciousness and better high frequency information off axis and stood up. The closer they are together the better. Putting them behind the up firing mid bass was important too.

[Fretless]

[Latteman]

[karatestu]

How rude