I long ago thought of using grille cloth over the 12" drivers to slightly reduce high frequency output that is not required from these trouser flappers. Thanks to Stevetheshadow for his recent dabblings for reminding me .
In Richard Dunn inspired diy land we are relying on mechanical attenuation of unwanted frequencies via doping of the cone and the drivers not pointing directly at you (high frequency being directional). Grille cloth seems to be a natural extension of this mechanical attenuation. Oh what lengths we go to avoid electrical filters
Another mechanical attenuation method i have been thinking of lately is already built in to the bass drivers. All it takes is to mount each of the drivers with the magnet facing out. The magnet and basket in the centre of the driver are known to attenuate the highest frequencies from a particular driver as these unwanted frequencies are produced from the middle of the cone and dust cap. These are hidden behind the magnet and spider so some attenuation must be available.
This is all theoretical or second hand information. I think it is an avenue i will have to pursue and try for myself. Only draw back i can think of is thinking of a clever and aesthetically pleasing way of hiding the ugly backside of the final speaker driver in the chain. It would have to include the use of cloth and so use that method of HF attenuation as well. Could this approach be widened to use with the mid range driver as well ? Who knows.
The point of isobarik configuration is to increase the lower frequency beyond the driver and cab size.
With a mid range you just want a nice clear tone. It deosnt need isobarik configuration to reproduce it designated frequency span.
But all that is theoretical and empiricism trumps
The bass will still be isobaric just the drivers will be mounted differently.
I wouldn't be making the mid range isobaric. It's just (imo) free attenuation of high frequencies so maybe less doping required on bass and mid drivers.
Explore all possibilities. That's my motto and probably why my speakers never get finished
I am extremely happy with what i have got now , sound wise. Appearance is another matter mind you
Today i thought about down firing my bass cube but couldn't be bothered. So put some ikea lapp style table tops about 6 inches in front of the bass drivers. Drivers totally obscured. It sounded ok but the sound stage seemed to move back and up. It was weird and not as involving. Laid the table tops back down and normality was resumed. I seem to like the bass drivers pointing at me. The soundstage becomes more 3D and room filling. Mid up firing is a must though.
If i continue to prefer the bass forward firing then my isobaric bass drivers are going to have to be arranged at 90 degrees to each other - inner one down firing and final bass driver at floor level and forward firing.
When will it end. Looking forward to seeing your nailed together speakers Simon
Although the bass is more prominent with the bass cubes than without them it seems like when using them down firing compared to front firing the bass player has turned his amp's volume down a notch. It is not unpleasant but something is missing. Mid range and top seem more prominent now and the balance has been lost.
I will keep them like this for a while and play more music and then switch back.
To make a conventional speaker shape of manageable proportions which is pleasing to the eye means if i want front firing bass and isobaric cubes then the two bass drivers are going to have to at 90 degrees (inner one's firing down and outer one firing forward at floor level. Don't know how successful that will be. There does not seem to be a problem having the bass and tweeter on the front panel. Their overlapping frequencies are probably very well attenuated /rolled off by the point they meet.
The other option of course is to have the 12 inchers up firing and the mid's side firing like the doc did with the bbcubes. I did not really want to copy them as i like to go my own way but if it turns out best then so be it.
My down firing bass idea with up firing mid is only workable when using two bass drivers as with three, a mid enclosure on top and some legs to get the bass out the bottom the height becomes too much for me. Three up firing 12 inchers and side firing mid's works height wise but then you have to put a mid in with every bass driver to keep things the same for the isobaricness?? Gets expensive and complicated but it might have to be done.
It takes a lot of chin stroking to work out all the possibilities and what problems they have either musically, structurally, aesthetically or monetary. The ideal for me would be three isobaric drivers, one mid and one tweeter per channel but i can't seem to make it work ideally.
This is a good thing especially with the down firing bass cubes - the nva boards obviously have more gain than the Avondale's. When i finally get my other NVA amps built then the relative levels will change again. I am now reminded of how inferior the Avondale boards are compared to the NVA (sorry Les). It don't show up as much when the avondale's are on bass duties.
Gets me thinking of four mono volume controls , two for bass cube and two for mid and tweeter. Hell when i have all six nva mono blocs built up i could have six volume controls. Could be the ultimate in level setting Could get rid of the padding resistor before the tweeter. Only problem may be impedance issues with 3 attenuator's in parallel after the sources......and getting pissed off with having to use all them knobs .
Not sure what i make of it to be honest. It is not sounding obviously wrong but things have changed. The sound stage does seem to be more centralised but this could just be my imagination as that is what i thought would happen. Bloody expectation bias at work again.
How to get rid of the padding resistor on the tweeter. It costs money, well two more mid drivers. Double the internal volume of the mid enclosure and fit two 5" drivers close to each other.
I believe that one 8 Ohm, 84 dB driver supplied with 2.83V of signal will give 84 dB SPL. If a second is wired in parallel then both see 2.83V and both produce 84 dB. So the SPL of the two together is 87 dB + 6dB = 90 dB.
This gets the two mid driver's SPL about the same as the Visaton tweeter. Does not account for doping though or the mid and tweeter firing in opposite directions.
What is the point i hear you ask. Well i am not too sure really. Is a 12 ohm resistor that bad between an amplifier and tweeter ?