Doc modding Marantz imperial 7

[karatestu]

Glad you are feeling better Steve. I have my own problems but a light box has been a revelation.

I remember your room flooders. Wasn't the problem that they couldn't fill a large room ? As you know semi omni's work perfectly in the average UK living room. You do right keeping them to yourself. The only people you have to please is yourself and the wife. Sod everybody else

[SteveTheShadow]

....I remember your room flooders. Wasn't the problem that they couldn't fill a large room ? As you know semi omni's work perfectly in the average UK living room. You do right keeping them to yourself. The only people you have to please is yourself and the wife. Sod everybody else

Yep the flooders didn’t work. Richard was spot on with the reason, ie high ceilings are certain death to omnis. Like my flooders, his cubes didn’t work at either Owston or Huddersfield.

[karatestu]

Quote from diyaudio.com


'So by covering the 90Hz though 4,000Hz with one driver we completely eliminate all crossovers in the critical hearing, vocal and fundamental range of most instruments. I am completely annoyed with beaming that goes with most larger wide-range drivers,

I incorporate that technique into my projects. It works well. I will not crossover lower than 3.5k, preferably 4Khz or over. Though THEIR IS signficant audio information still in this range, I find it to be of minimal consequence. Also remember that IM distortion rises significantly when trying to cover too wide of a range with a single transducer.

I do find that their are some drivers that are suited for that range that are not so small as you seek. A 4" driver will have to be crossed signifcantly higher than 90 Hz. You can use a few 5" units that low, but will then have to use a ported enclosure tuned close to that range which IMO compromises that frequency range. Realisticly, you will need to cross with a steep slope at 150-175 with any 4" driver, while allowing for acceptable output levels. I do not see any way to use a driver 5" or smaller under 100 Hz, with excellent results. You will deal with either non linear distortions or poor transient performance.

Focal makes a very coherent W cone woofer and an Audiom midrgane, 6.5" and 7" respectively, thatoffer outstanding off axis performance a little over 4 Khz. Suprisingly, many of the 'full range' drivers have poor off axis response over 3 Khz, even though on axis in flat to around 20 Khz. Pay attention to this little fact when viewing their data sheets.This will result in poor power response, very undesirable IMHO as this will seriously damage imaging"

I found this particularly interesting as I use the doped 5.25" mid bass units full range. Well their output rolls off due to the dope from around 6KHz so the crossover with the tweeter is well out of the most important range

But it is not all good news Beaming is happening and there is increased intermodulation distortion. I don't know what IM distortion sounds like and don't know how to reduce it without going three or four way and using electrical filters. Filters are not happening so I must accept that everything is a compromise. I don't know if having four mid bass drivers per channel will reduce IM distortion as the work is shared out and the cones hardly moving.

[karatestu]

I read further in to the diyaudio thread and found this. Don't know if it is true.

"My take on it is this: Use a very small 3-4" drivers for the mid, and use a bunch of them spaced as close together as possible... this should cause the IM distortion to decrease as a result of the shared power handling and lower excursion among the drivers.'

Maybe IM distortion is the one I have been banging on about for ages. If so I know exactly what it sounds like.

[karatestu]

High on Bison kit fumes at the moment. Headache coming

[karatestu]

My bison kit supply is getting quite old now and has become noticeably thicker and so does not pour as well as it used to. There is a thinner made by Bison but you can't find it anywhere. Found some in Holland but I got to checkout and the buggers won't post it to UK

Ordered some industrial acetone (nail polish remover ) instead as that is said to be a good thing to thin down contact adhesive. See what that does apart from give me a headache.

[karatestu]

My thoughts have turned to grills. I don't know if I will be mounting the 5.25" mid bass from the outside or the inside of the cabinet, That affects my choice of grill. If mounting from the inside (which is what these drivers were designed for) then I could route a rebate to fit a nice little circular grille which sits flush with the outside face of the cabinet. This is only for the mid bass on the top. The others will be hidden by L shaped grills to cover the open ends of my two "slots".

Looked at this grille for the top mid bass



I am seriously thinking of putting the four tweeters in a rounded edge dice shaped pod above the top, up firing mid bass. The grills for those can't be bigger than the tweeter face plate so was looking at these which are 99 mm wide and should hide the four screw hole in the face plates.



Just realised they look exactly the same. They are different sizes though. Both made by Monacor. There are some made by Visaton but they have their logo on and that doesn't seem right as these speakers are going to be called The Doc or FFS - haven't decided yet.

[karatestu]

An interesting idea that I had not thought of. Quote from diyaudio

"Quote:
Originally posted by Variac
Also this brings to mind my idea of having a dome tweeter facing up, with another one facing down on top of it, separated with spacers so the domes almost touch at full excursion. The sound is sqeezed out the side 36o deg-maybe more effortlessly and faster a la heil tweeeter? Maybe the faceplates need to be changed a bit to create a horn'

This is the type of thinking I like

[karatestu]

None of the pictures throughout this thread can be seen anymore. I have tried various search engines and it's the same.

In light of that, this thread will have to continue without pics because I don't know what the problem is. Even the few I put on imgur aren't showing

[Latteman]

I can see pics