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#1 2006-04-19 10:50:59

Zero One
Registered: 2006-03-27

Redback Update

Some of you may have noticed my el-cheapo redback driver posts.

Well I now have the system up and running and tuned in and the results are brilliant, these will be a gift for my daughters home office so I now have to finish the paint etc but I thought some of you might be interested in what I have found out in the process.

First up the drivers are very efficient, probably about 94db, they are supposed to be 92db but seem louder than some others I have that are 95db, anyhow they run on the smell of an oily watt.

I had trouble with bass- not enough of it, so I modded some old boxes I had, basically work like fostex double bass boxes for the FE127 drivers, these are only 4 inch not 4.5s but it works well. 

I found through experimentation that adding a port at the rear of the top and one at the bottom front actually gave very tight balanced bass when the box is placed 30cm or so from the wall.  The top port is tuned to about 120hz and the bottom somewhere in the 50hz range, the internal bypass port also works at about 120Hz.

The speaker is used in conjunction with an active bass boost module that altronics in OZ sell for about $13.00, this works amazingly well and sounds nothing like using a tone control or even an equalizer.

I found a post somewhere that suggested stiffening the cone with PVA at the point where the cones meets the surround worked well to improve bass with small drivers, I did this but added a twist by adding thin circular tissue paper cutouts plus the PVA, I used two layers of paper and four coats of glue on the front and on on the back, the glue in the centre of the cone was much less as I wanted to maintain some flexibility there, I also put 2 coats on the centre cap.  THis mod more than anything else made the biggest difference, bass was substantially increased and you could easily tell the cone had gone from flexible at the join to very rigid. The bass was also much tighter and lower mids better too.

The next issue was a bit of roughness in the highs, this was greatly reduced by adding a circular ring of little foam pads to the junction between the cone and the centre cap, the dots are used as pads under ornaments etc.

There was still a small roughness left and this was fixed today by changing the Zobel network on the gainclone, after much head scratching!

Ringing of the baskets was fixed by adding some non slip runbber matting to all the exposed surfaces.

One thing that made a difference to bass/mid that was out of all proportion was the actual mounting, these speakers only have smallish openings behind the driver, now when mounted on an 18mm MDF baffle it occurred to me that the baffle may actually be limiting sound transfer from the back and causing a bit of compression there, so I ran the router around the rear opening with a curved bit to introduce a scollop.  I did only one speaker first, the difference was quite amazing, the bass went lower and louder at the bottom end. Such a simple thing!

The drivers are very responsive to port length changes and I am still experimenting here.

The cabinets were then beefed up with bracing and some damping on the walls with felt underlay material, but no stuffing, once again a tightening of bass with very little colouration from the cabs.

Now the last two mods are interesting, one is a keeper and the other I'm not sure about yet.  The surrounds are cloth with some sort of rubber compound on them, I wondered if there is some sound transfer from the rear of the drivers through the surrounds, anyhow I made some shields very roughly with some padding on the back of them (actually the same rubber matting material used above). There is a hole in the middle the size of the cone itself but the sheild covers the area above the surround.  Now I didn't expect this to work but it did, the whole mid range became clearer, sibbilance was reduced also, when you flip the shields on and off the difference is really obvious,  The volume is very slightly reduced but not enough to worry about.  I think it may help to add some matting to the inside scollaped edge behind the driver too.  This mod does not change bass or highs at all.

The final mod is placing a circular ring of 30mm semi hard foam on wire at the front of the driver, this foam ring has a centre cutout and is used to buffer the CDs when stacked onto spindles.  The foam sits level with the front of the driver and centred over the centre cap, it does smooth the sound in the highs and removes a bit of directionality.  I quite like the result but my son reckons trumpets and similar intruments don't have the same punch, I know what he is saying but then I like the smoother less focused feel, so the jurys out on that one.

At this stage I have not done much with shelving, I wanted to get everthing as good as possible by other means, something in my mind niggles me that shelving will reduce overall efficiency and therfore possible dynamics,  I will however try it to see.

And now a final mod that falls outside the realm of the box.  I took a CD and copied it into audacity on my MAC as  32 bit floating files.  I then made very precise equalization adjustments guided by some testing I did using an old equalizer patched into the system.  The equalized files were then re-burnt to CD, though in the final set-up all my records and cds will be burnt to DVDs as 24bit DVD-A files.  This was then played on the system, now I must say there is still some fine tuning of settings to do here but the results in a back to back comparison with the original discs are pretty mind blowing, if there are deficits in this I can't hear them.

Why go to this trouble, well normal equalizers introduce distortion (at least mine does) and lack ultra fine control that audacity has, and second I feel that adjusting the music after it has been through the DAC is just adding extra problems with dynamic ranges, clipping etc.
Once I have a bunch of settings nailed for my system them re-recording the modded files is just a few minutes work.

Overall this project has cost me about $40.00 Oz dollars ($30.00 US) and the sound is out of all proportion to that, could I be happy with these speakers, YES, they actually eat my B and W 602S 3s and sound better that the the other two better systems I have except for low bass, which could be fixed with a nice tight musical sub (does such a beast exist).  But overall it has been an experiment, I really want to build Rons Fostex 166 horns, but I reckon my daughter will be grateful for her new gainclone and speakers and I am in a much better position to really make those horns of Rons rock.

Now one last thing, how the heck do you post pics on this forum, I have them to show but no buttons anywhere?


#2 2006-04-19 11:47:05

From: Sacramento, Ca.
Registered: 2005-08-06

Re: Redback Update

Zero One wrote:

Now one last thing, how the heck do you post pics on this forum, I have them to show but no buttons anywhere?

give them a url (uploadthem someplace) then use [img]url[/img]


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