Some Rti12 mods (pics)

[mardelgo]

Hi. First I would like to start saying that I am not an expert, so I do not encourage any of this mods to anyone. I do it just for fun, I like to make little mods to my gear (personal touch) and in the process I spend some quality time with my dad. So, this is some mods I did to my RTi12. My Original plan was to use an active crossover instead of the passive one (thanks TLC guy for the information), so I decide to take out the crossover to see what components I need to remove, but to do so I have to disconnect the drivers (cables are to short so I couldn't remove only the crossover). So in the process I decide to do other mods: change the cables, added vertical bracing and some damping material. I take some pictures, I know many of us like to see what is "inside". I am still not very sure about the active crossover (because I do not have the means or knowledge to test the result, but maybe I do it some day just for fun (now I can access just the crossover with the new cables so it can be done easily), and give my impression. Another tweak maybe is to change the mids capacitors (and maybe bass capacitor too?) for a better ones (same value).Any recommendations are welcome.
I did one speaker at the time so I can compare them. The results: well all I can say is that the sound of the mod speaker is a little smoother, a little less “in your face” sound, (sorry no golden ears here). Pics:

 

[mardelgo]

What I find out about the crossover:

The bass drivers are wire in series, and also the two mids, and the tweeter is wire out of phase from the rest of the drivers.

 

[j_garcia]

The bass drivers are probably out of phase because their natural state has a phase shift from the other drivers used and in-phase resulted in a dip in response around the crossover point.

Damping material changes the size of the cabinet - the drivers "think" they are in a larger enclosure. You have to be careful about how much you add because you can overdamp them and that could hurt your midrage. If there was no damping material, I would imaging the amount added would help not hurt though. The bracing may help, but it depends on whether or not it was an issue before.

Changing out the wire should have had little or no effect aside from making them easier to remove, IMO. Changing the caps for the mids I am going to say will make a difference larger than the things that have already been done, though still not going to make a night and day difference.

Keep up the tweaking and let us know how it goes. Looks like a good project

 

[Rickster71]

What did you use for damping material?

 

[jamie2112]

How do they sound to you? Do you like the smoother sound or not? I agree with J GARCIA on this one...

 

[WmAx]

Sadly, in order to actually improve performance by a substantial degree, much more modification is required. Here is an example of a recent modification project I did for someone, and this modification has a significant effect on the resolution and timbre accuracy of the speaker.

Here is some 'added' bracing/dampening....

After gutting this Ascend CBM-170SE cabinet, I added 1/4" worth of Dynamat type material to the MDF, then a attached 1/2" re-enforced concrete slabs to the Dynamat, then a Adhered in generous amounts of steel as a subframe and bracing system, and solid oak re-enforcements on the front baffle followed by steel angle adhered to that for further re-enforcement.

Now, let's add in some high density acoustic dampening...

The white cloth is to isolate the section that the port goes into, to prevent insulation fibers from exiting the port.

-Chris

 

[Haoleb]

Looks like you need a little Mig welder.

 

[Warpdrv]

Looks like you need a little Mig welder.

Or even a simple wire welder...

 

[WmAx]

While I don't have a welder(yet), I can assure you the results of using high quality epoxies and adhesives are more than adequate for this application, and the result here is a speaker cabinet that has less resonances than 99.9 percent of high end speaker systems.

-Chris

 

[Warpdrv]

I have a small question...

doesn't adding all that bracing... not that they don't need it, but doesn't it change the performance of the drivers modeled for a specific size enclosure?

Are you changing the crossover in addition to those modifications as well?

Or changing to a driver that is better modeled for a smaller cabinet..?

 

[WmAx]

I have a small question...

doesn't adding all that bracing... not that they don't need it, but doesn't it change the performance of the drivers modeled for a specific size enclosure?

Are you changing the crossover in addition to those modifications as well?

Or changing to a driver that is better modeled for a smaller cabinet..?

The materials chosen were also due to minimum volume displacement. Normally, I would use primarily oak. Before the particular modifications were performed, the mid-bass driver was measured in order to determine actual effect of the modifications of LF performance. The end effect here was minimal, with barely any degradation of F3. In fact, the biggest negative effect on original response is the extreme acoustical dampening I use, not the volume displacement. This type of dampening is so effective that it even reduces the ability of the cabinet volume to act as a resonator at the tuned frequency, thus causing a slight gradual roll off starting at about 300hz and increasing in depression as you go lower in frequency, as if the speaker was in an infinite baffle. But these speakers are going to be used by the owner on a system using a Behringer DCX2496, and the DCX can apply a subtle filter to counter-act the depression effect of the dampening in this situation. Otherwise, I would have used less dampening, but this would be detrimental to lower mid-range transparency by a small degree, so the owner agreed that he would rather use the DCX to compensate instead of using less dampening. Obviously, if no DCX was being used, I would only used about 1/2 the level of dampening currently installed.

I have not modified the xover; I was not commissioned to do that.

-Chris

 

[mardelgo]

For the damping material I use something call "Pelero" in my country (Costa Rica). I use it because I have others speakers that have this material (2 speakers and a sub), is like a carpet material form of fibers of what appears to be cotton or some kind of cloth. Is 5 millimeters thick, I glue it to the walls, around 70 % of the internal walls of the woofers case, and around 90 % of the mid-tw case. What I like of this material is that is not very thick, and did not alter the airflow o between the speakers and the port.And then I reinsert around 80 % of the original damping material.(Polyfill?).
I also use this material to cover the walls of a klipsch subwoofer that have NO damping material with good results.(A little less boominess)
As for the smooth sound, yes I like how it sounds, but keep in mind that the change is small, so it is more like a tweak than a modification. The reason why I add bracing and damping was because after I removed the drivers and when I put my mouth inside the lower half of the cabinet and speak, I felt the vibrations in the side of the cabinet,(and I do not have a Luciano Pavarotti voice) and after I add the bracing and the damping material, I can not longer felt the vibration.
I do not have the knowledge to do a heavy modification like WmAx, so that's why I try to keep it simple, and like I said, , I was just for fun, and did not expecting a night/day . I fact my next tweak will be to fabricate a bass tramps for my room with mineral wood or rigid fiberglass and I expecting (hopping) a bigger difference that this speaker mod. I also think ( j garcia) that a better capacitors in the mids can make a difference, after all the initial idea was to change the crossover. Here is a closser look of the damping material:

 

[j_garcia]

My front speakers all use Sonicaps in the crossovers. My surrounds are basically identical to them with the exception of the caps and when compared side by side, I can hear a subtle difference - there is an even smoother nature to mids, most notable on vocals and there is just a touch more detail in the mids, though the highs are actually a bit softer. I do like the difference, however I am not in any way disappointed with the sound of the pair that don't use the higher grade caps.

 

[WmAx]

There is no credible evidence that exotic capacitors make any difference in the capacity of a crossover circuit, so long as the actual relevant measured values of the compared units are identical. A cheap polyester/mylar capacitor is every bit as good as a SoniCap. Even electrolytic will sound identical if it has the right values - but I never recommend using electrolytic in value sensitive circuits such as xovers, as they will drift in value and fail much sooner as compared to plastic film capacitors.

-Chris

 

[TLS Guy]

What I find out about the crossover:

The bass drivers are wire in series, and also the two mids, and the tweeter is wire out of phase from the rest of the drivers.

Thanks for the pictures! Wow! Those speakers are a bigger mess than I predicted. We had a member recently having trouble getting any mid bass out of them. That is quite the nastiest misbegotten cobble of a speaker I've seen in many a year! It can't fail to sound awful.

For a start the speakers are wired in series to keep the impedance high so it can be driven by cheap receiver amps. It would be much better to have higher impedance drivers in parallel, with a total impedance around 4 ohms.

The chokes are small iron cored ones, so small that with the power at the 120 Hz crossover they have to be driven to core saturation.

Next the caps except one are non polarizing electrolytic types. Just look at the value. As I predicted previously, very high values, 220 MFD!

Now you won't find polypropylene caps that value. You would have to use multiples in parallel, and it would be expensive.

The tweeter is out of phase because it is a second order crossover, and it is out of phase with the mid at crossover. However I suspect it is the mids that should be reverse polarity. It isn't as that would put the speakers out of phase with other speakers in the mid band and bass. I would wager the mids and woofers are out of phase at crossover.

Those speakers are worth no time and effort. A design like that just needs a decent burial.

You are a young man and want to learn. Bond with your father and start a design from scratch. With those speakers you will be stating from a low bar, and that should give you confidence.

 

[mardelgo]

Hi TLS Guy. I never had the opportunity to thank you for the PDF document. Thanks. There are a lot of aspects of the speakers that I just beginning to understand. (What still can not understand is how a company like Polk Audio can design a crossover with so many flaws….) First when I use the bass management t in my receiver (Yamaha DSP-A1) I have to change the subwoofers to out of phase (Rev) to get more output (in-phase?), and the subs are near the speakers (see pic). I get greater output this way (I confirm this playing a test tone at the crossover frequency.) But in the crossover the polarity of the woofers and mid appears to be normal and is the tweeter that looks that is connected in reverse polarity, (same as the center channel, so when I check the phase between speakers they sound correct.) This is one of the reasons why I set the speakers to Large and no sub, then I connect the pre-out of the receiver to an external amp (I use a Y-adapter so the signal goes to the subs too), and use (before the amp) an in-line crossover (see pic) (70hz high pass filter), and this way the subwoofers appears in phase in the normal position(greater output) Then I set the subwoofer crossover (70hz). I guess this is not the optimal configuration but this is the best way the speakers sound to me. Also, in effect, I have a dip in the 120hz area in my room of around 6-8db(also confirmed with test tones) no matter how I set the bass management, I always thought that was the room, but now I starting to believe that in fact is the speaker-crossover. But even with all the technical problems that this speakers have,they IMO, sound good enough for home theater applications (after all this is what this line is design to, I believe) because they go low (good output between 30-60 Hz), are detail and can play pretty loud. But I agree that for stereo or music listening you can do a lot better in this price range. And the bright side is that know I have a better knowledge and can improve in my next speaker upgrade (although not very soon)

Sub position:
http://i289.photobucket.com/albums/ll234/mardelgo2001/100_3821.jpg

 

[mardelgo]

High Pass filter (70hz):
http://i289.photobucket.com/albums/ll234/mardelgo2001/100_3829.jpg

 

[TLS Guy]

High Pass filter (70hz):
http://i289.photobucket.com/albums/ll234/mardelgo2001/100_3829.jpg

You have confirmed what I predicted, that those speakers have to have a null at 120 Hz, and as you have shown it is not correctable, as the drivers still cancel as you increase power. Did you see the thread, "How to I get my six woofers moving?"

A lot of the problems have to do with the unsatisfactory situation regarding receivers, which I have little to no time for. They refuse to design the output stages so they can drive 4 ohm loads with good current output. It is pretty much nigh on impossible to design a narrow fronted speaker with, decent upper and low bass performance without blowing up those receivers.

The ghastly receivers, as I call them are a big root cause of a lot of the difficulties with speakers talked about on these forums. In the price ranges talked about, the designers are trying not to blow those receivers up. Actually most of them need blowing up. It is highly limiting to speaker design.

I'm just about to go off line until next week. We are moving our town home from Grand Forks ND to Eagan MN this weekend.

 

[CGilson]

I know this is an old thread, so I hope some of you people are still around!

I am looking to bi-amp my RTi12s. I read this whole thread, and noted the 120hz issue.

Would it be wise to run an active crossover above 120hz, removing the crossover from the three 7inch subs? Leaving the high pass crossover in place for the mids and tweeter?