Doc modding Marantz imperial 7

[Latteman]

How have u found different tweeter brands compared to all same brand
I have been using different and can’t find anything wrong with it
I’ve just joined to ‘isobaric club‘- I have the equivalent of 2 x cube2 size cabinets joined to create the effect- lower cube has 5” doped driver from Royd Minstrel and a Trio/Kenwood horn tweeter with the top cube supporting Only a ‘doc modded’ 8” driver
The lessons I learn today are stand height and type of support matter for focus- low n stable.
Just got to decide if I want another tweeter in

[karatestu]

Hello Peter

I have to say that I am like you and can't find anything wrong with using different tweeters but then I am not as anal as most. I do tend to think things will tighten up with the same tweeters. Some I am using now are real cheap crap and I don't like metal domes since I discovered fabric domes.

Even so, it sounds awesome. Maybe there is an advantage to using different tweeters. It is said when designing line arrays that you must choose your driver wisely as the end result will be like that driver on steroids. Maybe having different drivers with different resonant frequencies, frequency response etc would smooth things out ? I don't know, perhaps that is all bollox.

I do intend to eventually use mostly visaton g20sc except for the in firing tweeters which will be visaton g25ffl. That is because they are 2 dB more efficient and should help equalising volume when you are sat nearer one speaker than the other.

Glad to see you are trying isobairic. I have never heard of anyone trying it with different drivers though. Don't let that put you off though. As I said up thread many things that so called internet guru's go on about as being totally wrong (theoretically) ends up imo not sounding wrong at all. You just have to find what sounds right and wrong for you be trying everything, even things that may seem ridiculous and that brings scorn from internet "know it all's".

After saying all that, the Doc used the same drivers in the cubix but I doubt he matched them and there could be slight differences between samples. Plus Doc used to dope the drivers progessively less from inner to outer driver. So they will all have had different moving mass (mms), resonant frequency (Fs) , frequency response and Qts. I have read nothing but praise about the cubix so it obviously makes feck all difference.

Doc used to say that isobaric was only done properly when each driver has the same box volume behind it. I have never read that anywhere else. Not saying he was wrong but in the end I couldn't live with the size the enclosure was going to have to be so went for the clamshell isobaric instead. Doesn't sound inferior to me but that might be my cloth ears.

You can read much about Linn Sara's and how they do it all wrong. Because they are only a two way the isobaric pair has to handle the mid range as well. It is said that isobaric only works well when handling bass and distortion is introduced when the mid range is included. Many people like the Sara even though they do it all "wrong". When I asked The Doc if he thought there was a problem with isobaric and midrange his reply was essentially "what problem?". Some would say he was bound to say that considering the cubix isobaric handles mid range as well but I tend to think he was speaking the truth from his own experiences.

Wow, that quick reply turned in to this long mind numbing bollox. Believe the bits you want to

[Latteman]

Just got to decide if I want another tweeter in

Of course you do Peter, of course you do Be warned this tweeter worship can become an unhealthy obsession if you are not careful.

[karatestu]

One of the advantages with diy is that we can design and fine tune our speakers to specifically suit our room and our taste. It should (if we know what we are doing) result in the perfect speaker FOR US. Feck what anyone else thinks. If you are the bake off type and / or need the praise and patting on the back from fellow enthusiasts then you may never be totally happy. Trust your own ears more than anything. It took me ages to realise that last bit. There are people who would rather trust the ears of others

Manufacturers can't do this, they have to please the magazines, the internet know it alls and the anechoic chamber. Is it wrong to like a speaker that most think is rubbish ? I don't think so, I would respect them much more than the average sheep (baa you know who you are ) who just goes along with the willy waving pack.

It may seem like I have blundered my way through this speaker discovery experiment. Well that's because I have but it has been a voyage of discovery and the journey is just as important as the destination. Is it really an experiment ? Some would say it can't be an experiment without measurements and a hypothesis What have I learned along the way ? There is no chance to learn anything when you are too busy learning nothing. At least I have had a go and if the end result is rubbish why should it bother anybody but me ?

[karatestu]

Listening to my speakers today and one of the full rangers used as a tweeter on the back of the upper enclosure fell off whilst I wasn't in the room Well it was only blu tack and gaffer tape holding it on Lucky nothing shorted out but it was still playing when I came back in and I didn't notice at first

That was the excuse I needed for a bit of a dabble with a down firing tweeter. So I have used the four G20sc I bought off zebbo and put one of them on the back panel and one down firing to mirror the up firing . All six now wired in series. Listening as I type These new ones won't fall off No hint of the sibilance that was reported by zebbo

[karatestu]

I think when I get my six channel inegrated built the bass amps are defo gonna get their own volume contol. Late night listening can bring problems with too little bass as the ear is less sensitive to it at low volumes (Fletcher Munson curve) . We need a loudness button which essentially bòosts low frequency for this very reason.

But we don't need one if we can just turn a knob and get the level just right. Ever listened to Rumours or Led zep 4 and thought where's the bloody bass gone ? Not anymore

[Latteman]

I thought about separating the bas and tweeters to their own volume pot - it was a thought that I thought would remove the padding resistor

[karatestu]

I thought about separating the bas and tweeters to their own volume pot - it was a thought that I thought would remove the padding resistor

Hey Peter. Yes it does enable the removal of any padding resistor Every little helps

I would try it with two cheapish pots to see that everything works out. I am going to do it with another potential divider (two resistors) at first. In a three way it would be kind of cool to have one on each. Gets expensive though.

[Latteman]

Expensive but totally tuneable
I do fancy this though
https://www.ebay.co.uk/itm/123938059635

[karatestu]

I removed the down firing tweeter as it wasn't bringing anything to the party, I actually think it sounds better without it. I am going to disconnect the rear firing tweeter sometime soon and see if I notice. I don't mind if it stays or goes. The high pass filter knee frequency will change with reduced impedance but that can't be helped - don't have the right value of cap to keep it where it is.

I am nearing the end of this journey now I am fixed on the concept of four or five tweeters firing in separate directions, up firing isobaric bass with magnet out and the upper enclosure with up and down firing five inch mid bass (down firing one with magnet out).

Just my new concrete cabs to finish now and probably more bass drivers to further lower the cabinet volume required. Not knowing the specs of these bass drivers has been a huge pain in the arse. Doping complicates things even further - as cone mass increases so does Qts and therefore cabinet volume required. Yes, doping also lowers Fs (resonant frequency) which is nice as the speaker can theoretically go a bit lower.

I did contemplate adding another five incher as the upper enclosure has enough internal volume to handle it (I intentionally over sized it) and I may still try two up firing and one down firing but I am wary of upsetting things too much. I do not know what the effect will have on the baffle step correction that drivers on opposite sides of an enclosure provide (bipole). Suck it and see seems to be the way.

I am really enjoying listening to these speakers at the moment on the end of just two channels of amplification. I managed to wire things as to provide an acceptable load and surprisingly even frequency response to my ears.

The end is in sight