Doc modding Marantz imperial 7

[CycleCoach]

A bit more copy and paste.

"Is combating diffraction a worthy goal?

I am inclined to say "yes." Twenty years ago, when I first started screwing around with audio, I had the same mindset that most beginners do. My goal was to reduce harmonic distortion by using high quality drivers, and I invested a lot of money in expensive amplifiers and crossover parts.

Twenty years later, I've practically done a 180. Everything I've learned tells me that timing problems are more important than amplitude problems.

So I would argue that the reason that guys like Linkwitz and Dickason discount the diffraction problem is that Linkwitz and Dickason are focused on amplitude problems. (IE, frequency response.)

And I would argue that the Geddes and Danley designs attack problems in the time domain, each in their own way. Geddes is a proponent of preserving the acoustic wavefront via low-diffraction cabinets and waveguides. Danley's designs are engineered so that they preserve acoustic phase across the bandwidth of the loudspeaker.

And as any good engineer knows, engineering is all about compromises. The Geddes and Danley designs do not have the best amplitude response on axis, in fact it's fairly ragged. But the key to their designs, IMHO, is that they get the time domain right. And I think that's humongously important.

Here's a real world example of what I mean. Have you ever clapped your hands in a small room? And have you noticed that there's an echo? In a small room, that echo will occur less than ONE HUNDREDTH of a second after you clap your hands. And yet the echo is very easily audible isn't it?

If you grok what I'm saying there, you'll start to understand why I think the time domain is so important. Our ears are very VERY sensitive to timing problems. You can tell when a sound is 'off' by a HUNDREDTH of a second, perhaps much less.

Conversely, it's VERY HARD to measure. Go ahead and try to figure out how to measure this stuff. It's not easy.

On the other hand, there are iPhone apps for a buck that can measure frequency response.

And THAT is why the audio world is obsessed over amplitude problems, but drops the ball when it comes to time domain problems. Problems in the time domain are devilishly difficult to analyze and quantify, while problems in the amplitude domain are trivially easy to analyze

[antonio66]

Surprised to hear you say mounting them on a one legged stand would not be so aesthetically pleasing since I thought this would be the easiest on the eye, large round base, with a good sized pole and and maybe a saucer on top for the speaker to be attached to, alternatively you're back with the three legged stand which would also look good

[karatestu]

I just prefer the three legged idea Dave. Plus a big circular base which is hard and reflective is something I want to avoid if possible. If I went with a one legged stand with base I can't use a saucer to support the sphere because of the down firing mid bass.

Thanks fof your opinion and input, it is all considered and valued If I ever get them finished you must come for a listen

[karatestu]

There is no doubt that timing was the most important aspect of musical reproduction to RD, along with a clean window (natural detail). The author of the quote in my post above seems to agree ( he also wrote the diffraction quotes I posted.) Get the timing right and we can forgive a moderately ragged frequency response. I suppose the ultimate for timing faithfulness are the full range, coaxial and panel drivers. They all have their compromises in other areas however.

Some manufacturers go to great lengths to time align their drivers, others don't and some ruin it with multiple order xover filters, bsc, notches etc. What surprises me is that Doc was content with having the tweeter on the front of the Cubes way in front of the up firing mid bass. Maybe it was the only way to keep the box simple. There is no delay on the tweeter. In fact a single capacitor high pass filter makes the matter even worse. In the case of a low pass filter (series inductor for mid bass) the output of the filter lags the input (negative phase shift), in the high pass filters case ( single series capacitor on tweeter) the output leads the input (positive phase shift). So the high pass filter cap makes the front firing tweeter appear to be even further forward as regards the up firing mid bass than it was before.

I became particularly interested in the Liniwitz Pluto speaker design which is also semi omni with up firing mid bass and front firing 2" tweeter .



Quote "The mounting of these two drivers is extremely clever and at the same time extremely simple. The SEAS unit faces upward in a 31-inch long 4-inch diameter PVC pipe, and the Aura tweeter faces forward at the short end of a 35-inch tall upside-down L pipe of 2-inch diameter. The Γ-shaped pipe is positioned in such a way that the tweeter is lined up with the periphery, rather than the center, of the midrange/woofer to avoid diffraction, and the input to the tweeter is electronically delayed to make it acoustically centered on the upward-facing driver. This is tantamount to a coaxial configuration while retaining all the advantages of separately baffled drivers. (Contrast this solution with the most probable design using a 2-inch tweeter and a 5-inch woofer the average engineer would have come up with: a nearfield monitor in a tiny box!)"

So the Pluto has the tweeter dome at the front edge (nearest to the listener) of the up firing mid bass. This is to minimise diffraction caused by the mid bass driver and it's enclosure. Linkwitz gets round this by using electronic delay before the speaker to delay the tweeter signal so it appears to be coming from the centre of the mid bass dust cap.

Obviously in my purist, less is more, tiny brain the prospect of adding active electronics to provide delay for the tweeter makes me feel sick. So I put the tweeter on the back periphery of the up firing mid bass furthest away from the listener and the passive line level high pass filter in the input stage of my nva amp boards moves the tweeter forward in time a little. Having a separate pod for the tweeters means I can play with positioning quite easily. The side and up firing tweeters obviously complicates this and screws up the concept a little. Have to live with that compromise.

I will have to live with the diffraction off the mid bass driver and cabinet. I hope to minimise this particular source of tweeter source diffraction by making the mid bass enclosure a sphere. I can't get rid of the up firing mid bass but a least there isn't a deep concave cone as the 5 inchers are filled with dope nearly up to the surround

Onward. I go further down this rabbit hole like a ferret in search of rabbits.

[antonio66]

What was I thinking of, of course you've got downward firing units, gotta be the three legged design then
You'll get them rabbits in the end

[karatestu]

The three legged idea is winning at the moment. The wall mount comes second only because of how limiting with positioning it is. If it wasn't for that it would be ideal. Takes the suspended floor out of the equation and could hide the three sets of speaker cables. Luckily these speakers are best close to the wall especially when placed across a room corner like they are now (and will continue to be.)

I haven't stopped thinking about the wall mount option and maybe I can come up with something that works and is slightly adjustable.

I am leaning towards having the down firing mid bass fixed to circular ply or aluminum adaptor which either has three tabs sticking out to screw the legs into or extends out at the back to attach to the wall. Much like the wooden part in the Linkwitz Pluto pic below.



I even thought about chasing out a mortar joint in the brick walls and have the wall mount go into the space between two courses of bricks. That will be very sturdy as long as I go deep enough into the wall. If these speakers are made out of 5mm acrylic they won't be very heavy. If I am very clever I could even chase the speaker cables into the wall and be totally invisible from amp to speaker

That should please Jammy

[CycleCoach]

If you're a Daddy you can do whatever you like today eh ? It's cost me money going out to the local wildlife park and the purchase of a couple of teddies and four ice creams. I have to pay for the Indian take away anorl

I got to spend some time listening to some music earlier with my new tweeter arrangement Goddammit, the level of detail now on offer has snuck up on me. The sound is now so smooth and easy to listen to I have been in a trance dribbling from one corner of my mouth (as drummers do when the drum riser isn't level ) or with a stupid grin on my face. Not smooth and boring like a BBC style speaker, there is still all the life it had before. The system sounds slightly quieter and there is no way it can be as my volume is set by a pair of two resistor potential dividers that are soldered in. Loudness comes with distortion as Doc used to say.

Listening to The Blackbyrds - City Life (1970's jazz funk produced by Donald Byrd) I was blown away by how well each instrument could be picked out from the mix. Things like the way singers tailed off into the background for longer reverb tails reducing in volume into silence, echo or reverb on vocals and instruments. Details uncovered. The soundstage is more ordered and certain instruments can now be heard further back in the stage compared to others.

A real result in my book from removing eight tweeter face plates, removing plastidip from four of the tweeters and the application of some gaffa tape. The spherical tweeter and mid bass enclosures are just going to blow my mind at this rate. I just have to make them a reality as I will never rest until I have.

[Latteman]

In the spirit of suck it n see I removed the tweeter faceplates earlier today. I was sat listening and thought this sounds smooth and quieter???- logged on and read the above post. Thanks Stu

[karatestu]

In the spirit of suck it n see I removed the tweeter faceplates earlier today. I was sat listening and thought this sounds smooth and quieter???- logged on and read the above post. Thanks Stu

Do you like it Peter ? Give it time.

[Latteman]

In the spirit of suck it n see I removed the tweeter faceplates earlier today. I was sat listening and thought this sounds smooth and quieter???- logged on and read the above post. Thanks Stu

Do you like it Peter ? Give it time.

I thought I would lose projection but there is better integration of mid/bass & tweeters- I don’t have to listen for details etc- it’s just there with greater quality/quantity. The sound stage is more open and invites you in- very engaging