Doc modding Marantz imperial 7

[karatestu]

Fixing all the drunken tipos in that tuck me buddy ages

[antonio66]

Will look something like these when your finished Stu?

[karatestu]

Will look something like these when your finished Stu?

I hope not Dave

[Latteman]

Some tweeter "pod" developments. I have put four tweeters in one of them so far.

Some blurry pics

Quick question- if u run two drivers in isobaric both up firing do they have to be in line or can I offset the upper driver to allow room for tweeter placement as above???

[Latteman]

Some tweeter "pod" developments. I have put four tweeters in one of them so far.

Some blurry pics

Quick question- if u run two drivers in isobaric both up firing do they have to be in line or can I offset the upper driver to allow room for tweeter placement as above???

Hi Peter,

I think it is ok to do that as the isobaric thing works on pressure being constant in the closed enclosure between the two drivers. I haven't tried it however.

[karatestu]

Mucking about in Winisd (freeware speaker designing software) I can achieve a Qtc of 0.494 with bipole 5 inchers in a 24 Litre enclosure. Probably not much bass but it all depends on room gain really because the bipole is baffle step compensated by it's very nature.

In a small almost square room like my living room I will have to really careful with the bass loading otherwise it will be boomy. Oversizing the box will lower the Qtc and the Fsc (frequency at which the bass has rolled off to minus 3dB ) but there is a balancing act to be done here regarding my in room response versus box size (don't want massive cubes) and very low bass output which with a mid bass involves more excursion and inter modulation distortion. Have to find a happy medium here.

But it was only the other day that I realised there is an input for added cone mass in winisd and voice coil temperature and other things. As doping adds mass then I had a play. I knew adding mass lowered resonant frequency and F3, and increased Qts and Vas (box size required) but I never knew by how much. I know this is just a simulator

I wish I knew how much dope I had added in weight but that would mean weighing before and after with accurate scales and it is too late now. Anyway playing around with the added mass was a useful exercise to see just how much the other parameters are influenced by different weights.

With two 5 inchers in 24 L the qtc is 0.494 and the Fsc is 67.79 Hz. Adding mass of 1 gram changes Qtc to 0.552 and Fsc to 60.1Hz. Add another gram and Qtc is 0.603 and Fsc is 54.53 Hz. By the time you have added 4.3 grams the Qtc is 0.707 and Fsc is 46.86 Hz. So with adding 4.3g we have gone from a sub Bessel alignment to bang on a Butterworth with the same 24 Litre enclosure throughout.

So what ? Well adding the 4.5g makes the speaker play lower in frequency (be that good or bad). And the output at 20Hz has increased from -22 dB to -14 dB. Won't be good for the midrange in a 2 way. Need to get a happy subjective balance here between everything.

Amount of dope added is really set by how much you need to attenuate the higher frequencies that are produced from the mid bass that is run fully open. We can't just say lets add 2g to suit bass output box size and room gain if the mid range is too hot and the cone's break up is still audible.

25 Litres is as high as I can go but you have to take off that things like the volume of the driver itself that protrudes into the enclosure and any bracing. But saying that I am currently running the two 5 inchers in about 16 Litres after deductions and the bass performance is very good. With no added weight in 16 Litres that sims at Qtc of 0.53 and Fsc of 73.1 Hz. With 3.25g of added weight that has changed to Qtc 0.707 (Butterworth) and Fsc 53.13 Hz.

So the 24L box will definitely be too big for two 5 inchers. But maybe big enough for two 6 inchers ? Need to do the sims for that. If going with the bipole 5 inchers then the box can be braced to within an inch of it's life to get the volume down for best subjective bass response with my room and range of music which ranges from stuff with hardly and bass to electronic music which can have loads. need tone controls

[karatestu]

So, will 24 Litres be good for two 6.5 inchers ? The room will have a lot to say about that I tried the bipole 6.5 inchers in 19.5 Litres and although excellent on bass light music it was too much with bass heavy material. I pulled the speakers away from the wall and it improved but not enough as I don't have room for speakers in the middle of the room. The box was too small but will an increase from 19.5 to 24 litres be enough ?

Another variable is that the bipole with 6.5 inchers were in crappy chipboard boxes with no steel lining or bracing. After steel lining and bracing the bipole with 5 inchers, I am well aware that with crap chipboard enclosures the whole box is the speaker driver . That will have had some influence on the outcome for sure.

Simulating two 6.5 inchers in a 24 Litre box and no added weight resulted in a Qtc of 0.518 and Fsc of 75Hz. Probably ok depending on room gain and added displacement of the larger drivers (280 cm2 versus 160 cm 2). But we need to add weight due to the doping and I once again have no idea what that will be. All I know is that i didn't need to dope the 6 inchers anywhere as much as the 5 inchers but it can be misleading due to the differences between the two cone profiles.

With and added weight of 1g the Qtc has gone up to 0.558 and the Fsc down to 68 Hz. Add 5.5g and the Qtc goes up to 0.707 and the Fsc down to 53Hz.

These last two posts would have been removed by Doc if he was still with us. Actually I wouldn't have dared to post them It's all just simulation at the end of the day. It is the doing and listening that counts. Bipole 5 inchers heavily doped in approx 16 Litre boxes is about right in my room with my range of moosic. Bipole 6.5 inchers lightly doped in approx 19.5 litres is too bass heavy in my room with electronic music but fine with bas light material.

It could well be that bipole 6.5 inchers will be ok in 24 Litres in my room with all music. But I won't really know until I try and I always have the bipole 5 incher design to fall back on if it fails the bass test. What complicates matters with comparing the two drivers is the different TS parameters with the bigger driver having a lower Qts (0.35) than the little one (0.41). Published VAS of the 6.5 inch is twice as much as the 5 inch (10 litres versus 5.8). Saying that manufacturer figures are rarely 100% accurate (marketing )

[karatestu]

Oh bugger, the need to faff about with things got the better of me again I clapped eyes on my 12" drivers today and it got me thinking about trying them open baffle with the bipole 5 inchers. Bipole and dipole in the same speaker

Attached some bits of wood between the back legs of the speakers to screw the 12 inchers to. All very rushed and untidy of course.



I wasn't expecting much from this as the bass driver is right against the wall and with no filters apart from the dope there is mid range coming out but attenuated and beaming along the floor. Plus the support for the driver is not optimal and they are not quite time aligned with the forward firing tweeter.

Well a pleasant surprise for me. Last time I tried dipole bass driver I just took the back off the big 50cm cubes. Then filled it with open cell foam. There were good things about it and bad things. This effort is much much better. At first I thought there was no bass but it is much tighter than closed box. Notes stop and start a lot faster. This has unearthed some previously masked information in the mid band.

It is strange listening to bass which doesn't pressurise the room. It takes a little getting used to. With the cancellation from the front and back of the cone being out of phase, I was expecting this to be a complete failure but it's not. Everything was good (if not perfect) until I put Air Moon Safari on. One of my torture albums for closed box. The bass is very well behaved with this dipole 12 incher added on but there is a resonance in the mid band which is a bit annoying.

Probably due to the driver being right up against the wall and running full range but I'm not sure, dipole theory is not my strongest. Earlier I pulled the speakers out away from the wall by about 3ft and the bass reduced to unacceptable levels making the sound mid and top heavy . Quickly returned them to as close to the wall as I could. That's better.

Not sure where this little adventure will go as I don't want to be adding dsp to pull the mid range down and even if I wanted to pull the speakers right out from the wall I can't as the bass disappears. I thought of adding more dope to the 12 inchers to raise their Qts which might give a touch more bass. A baffle that covers between the legs might help a little too. Independent amp and volume control for the 12 inchers ? And maybe bipole 6.5 inchers will help lift the bottom end a bit. The mid range problem on Air Moon Safari has now disappeared and seems to be on one song only

It makes you wonder if this dipole bass driver and the new sound is actually how it is on the recording ie more faithful ? Or is this just shit ? I don't know. It is different and it is not only the bass which is more stop start and detailed. Not as "fruity" though.

This has given me a huge problem because I don't know what to do now

[Ithilstone]

This has given me a huge problem because I don't know what to do now

have a beer or 6 - sleep on it ;] then come back to it again
I need to admit there is something intriguing in this set up of 4 tweeters 2 bipole mid range and OB 12 incher
well it looks shit but I know it is not a final product - but concept is very interesting
is like you will get most of the benefits of 3 different concepts.

[karatestu]

This has given me a huge problem because I don't know what to do now

have a beer or 6 - sleep on it ;] then come back to it again
I need to admit there is something intriguing in this set up of 4 tweeters 2 bipole mid range and OB 12 incher
well it looks shit but I know it is not a final product - but concept is very interesting
is like you will get most of the benefits of 3 different concepts.

Yes, I too think it is interesting. But prone to failure like anything else if care is not taken. "Most of the benefits of three different concepts" and all their flaws

Dopole is said to work best at least a metre from any wall. Doesn't work in my case as the bass is too lean. DSP and some monster amplification would maybe sort that out but I refuse to go there. The driver is not particularly high qts either at about 0.5 in stock form. Adding mass through doping will raise that figure which will be beneficial but there us only so far you can go without sensitivity falling off a cliff edge.

There must be a balance to be achieved here. There are many good things about the dipole 12" added to a pair of bipole mid bass. The three drivers are overlapping and playing much of the same frequencies including the bass. That maybe where the answer lies - making a bipole with a pair of 6.5 inch mid bass to go with the open baffle 12".

I will continue experimenting with it and see if I can improve it. Don't really want to have to resort to putting an inductor on the 12".