Upgrade for pin/blade SDA's

ben62670

I upgraded my large inductor for the SDA in my speakers today. It made a big difference. Before the sound was very good. The stereo drivers had a lot of kick to them, but the dim drivers had little punch. I replaced the large inductor(you guys have 1 in each cabinet) with a low resistance Iron core inductor. Usually I would recommend staying away from iron cores, but this is just to the amps ground not in the signal path. The mod helped clean up the mids even better than they were before. The sound stage was more defined. All in all it is definitely worth the coin to change them out.

Ben

schwarcw

Interesting Ben. What were the values of the inductors that you replaced? A side by side picture of the old and the new would be nice.

Not to many on the Forum have tried this tweak. I've often wondered about upgrading the inductors.

Have you ugraded you pin/blade cable as DarqueKnight has documented. I'd be interested in your materials and results. Thanks!

dorokusai

I also found improvements when upgrading inductors, as its standard business when doing Xover upgrades for me. I've never understood why you wouldn't since your tearing down the rest of the assembly anyways. Oh well, to each his own.

treitz3

Everything affects everything. Good for you, Ben.

schwarcw

dorokusai wrote: »

I also found improvements when upgrading inductors, as its standard business when doing Xover upgrades for me. I've never understood why you wouldn't since your tearing down the rest of the assembly anyways. Oh well, to each his own.

Mark, did you go with a different wire size for the same mH value?

ben62670

schwarcw wrote: »

Interesting Ben. What were the values of the inductors that you replaced? A side by side picture of the old and the new would be nice.

Not to many on the Forum have tried this tweak. I've often wondered about upgrading the inductors.

Have you ugraded you pin/blade cable as DarqueKnight has documented. I'd be interested in your materials and results. Thanks!

The large inductors used by Polk were very high in resistance. What model SDA do you have?
My set is totally different than yours because of tri amping, and electronic crossover. I don't even need a crossover cable for my design because I don't need a ground for the other arrays(tweeters, and stereo). The originals usually used 16mh coils in each cabinet. My speaker doesn't require that because of my design. 2 16's in parallel = 8mh just like resistors.
The 18ga 16mh inductors have almost 3ohms of resistance.
The Erse 16G Super Q Inductors are around .5 ohms at 15mh, and 17mh
They do not have a 16mh
http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=312
Resistance is a waste of power on the ground side of the signal. The HF will still pass to the dimensional drivers as before, and the LF will travel to the amps ground easier.

Cheapest best improvement so far to be made to the Pin Blade SDA's. $60 dollars to really tighten up the bass, and mids from residual bass that doesn't make it through the inductors resistive path.

dorokusai

schwarcw wrote: »

Mark, did you go with a different wire size for the same mH value?

Larger gauge, but same mH.

Face

Goertz also has a decent selection of inductors.
http://www.goertzaudio.com/catalog.html

ben62670

Face wrote: »

Goertz also has a decent selection of inductors.
http://www.goertzaudio.com/catalog.html

You will want an iron core for this project. Also make sure the DC resistance is low. I would go with the 15mh from parts express.

http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=312

nspindel

So you've only replace the large inductor that the XO board mounts to, correct? What about the coils that are mounted on the XO board? Any value in mucking about with them?

Also, at least on my 2B's, the XO is mounted to that large coil, and the hex nut that holds the assembly in place connects to this coil. So did you disconnect the stock coil but leave it intact to only have it serve as a mounting to the speaker cabinet? Where did you mount the new inductor?

Also noting that the schematic shows a 16mH inductor, you've used a 15mH. What's the impact of doing this? Also, that partsexpress link is broken, I think this would be the new one, correct?

Thanks....

schwarcw

Nspindel,

I can't answer your question, but I'm impressed with the research that you are doing here with the "Search" feature. Good job and good luck with the project.

With new tweeters, crossover mods and an interconnect upgrade your SDA's will sound wonderful.:D

P.S. I've always thought that the best way to go about the crossover mods on some of these SDA's would be to build a board from scratch, do point to point wiring, use better components throughout including upgrade the inductors.

nspindel

One of these years...

nspindel

If you haven't seen my new thread:

http://www.polkaudio.com/forums/showthread.php?t=62106

Conradicles

Can we verify this upgrade using the Erse 16G Super Q Inductors 15mh is OK for the SDA-1C's and maybe what Ohm the speakers will be afterward? Thanks!

F1nut

Some thoughts on SDA inductors from Stu Lumsden, head of engineering:

Resistance is not always futile. The DCR of our inductors is accounted for in the crossover design. Changing it / lowering it will affect a different balance than the design intent. We typically use large enough wire that the DCR of the woofer inductors is in tenths of an ohm range. As to switching inductor for reasons of other qualities, there can be benefits if the designer has not done his homework. We’ve used air-core inductors for many designs and steel or iron cores for others. We base our decisions on the perceived use of the product, cost and size. Iron or steel cores increase the value of a given inductor by focusing the magnetic field created by the windings. This has the advantage of reducing the size and number of winds needed to achieve an inductance value. This also means that larger wire or fewer turns can be used to achieve a lower DCR. The concern is that the core (iron, steel laminate, ferrite) wil saturate a some maximum field intensity and pushing current above that level into the inductor will make it become non-linear. The inductor is actually reverting to acting like an air-core as it is over-driven – but only for the overdriven portion of the signal. So the signal becomes distorted, bad noises, scratchy, etc.. We have to choose the wire gauge and core material so as to provide head-room for the largest signals (including transients) that we expect the speaker to reproduce linearly. Air-core inductors do not saturate as more current is passed through them unless the current is so great that the wire begins to heat. It is not necessary, however, for the inductors to have such high limits because there are plenty of other practical limitations on loudspeaker output. Many of these are simply physical, like the maximum possible cone excursion of the drive units. Go beyond this and once again – distortion. Typically we can design our speakers with steel-laminate inductors and easily reach undistorted levels well in excess of 100 dB in the case of appropriately sized units. The down side of air-core inductors is as mentioned earlier that they will require more wire and hence have higher DCR. So more power from the amp will go into heating up this inductor and less into making sound. In this case, resistance is indeed futile.

From Matt Polk:

The thread on the forum has correctly identified most of the concerns. Good job!

However, I can add these comments. Usually, in a typical low pass crossover, one would not want to swap out an inductor for another one with much different characteristics because it would alter the voicing of the speaker. However, in this case there could be a performance benefit if the amp being used doesn't mind seeing a lower impedance. The inductor I believe they are talking about is part of the "Full Complement Sub-Bass Drive" circuit. That's a term that Sandy coined to describe the system we used to allow the SDA drivers to work in parallel with the stereo drivers in the bass while producing the SDA signal at higher frequencies.

In this generation of the SDA's the stereo drivers were nominally 6.5 ohms and the SDA drivers were nominally 3.5 ohms. The plus terminals of the SDA drivers on each side were connected to the plus amp terminal on that side via their cross-over network. Then, the negative terminals of the SDA drivers on one side were connected to the negative terminals of the SDA drivers on the other side via the interconnect cable. This causes the SDA drivers on the right to produce an R-L signal and the ones on the left to produce L-R. Since bass is pretty much mono in most recordings, if the SDA drivers both get full-range R and L signals they would cancel at low frequencies and the SDA drivers would just sit there acting like badly tuned passive radiators. So, we added an inductor in each speaker between the SDA driver negative terminal and the amp negative terminal on that side. At low frequencies that diverts the signal back to ground instead of through the interconnect to the SDA drivers in the other speaker. As a result, at very low fequencies the Right SDA drivers produce only right channel bass and vice versa, while still producing the R-L and L-R signals at higher frequencies. The transition occurs between about 50Hz and 150Hz.

However, because of the DC resistance of the inductor, the system isn't perfect. I don't recall the DC resistance of these coils but it was high, at least several ohms depending on the model. This means that the SDA drivers will continue to produce some SDA signal even at very low frequencies. Decreasing the DC resistance will definitely improve the bass response of the system both qualitatively and quantitatively. However, before you rush out to buy those Hi-Q replacement inductors be aware of some concerns.

We chose the higher DC air core coils for a couple of good reasons. First, we were always on the edge of acceptability with the impedance of the SDA's. The DCR of these coils kept the minimum impedance high enough for the amps available in those days. Depending on the model, reducing the DC resistance of these coils may take the minimum impedance down to around 2 ohms. If your amp doesn't mind, you shouldn't either. The other concern is saturation of the inductor core. Air core inductors don't saturate. Given the cost of adequate ferrite or laminated core inductors at the time, plus the need for a higher DCR, the air core choice was obvious. So, when switching to a ferrite or laminated core inductor make sure it will handle at least 5 amps without saturation. That's equivalent to 100 watts of low frequency power through the SDA driver.

hope this helps.

-msp

A final thought from Stu:

As an addition to the thoughts I gave earlier on inductor quality you should advise that only laminated steel is acceptable for most any high quality system. Ferrite saturates at current levels much too low. It’s high permeability allows one to make very high inductance values with less wire (so lower DCR) but the current range is poor at best. For all I know this may be the reason that all quality / high current transformers use laminated steel.

vmaxer

F1nut wrote: »

Some thoughts on SDA inductors from Stu Lumsden, head of engineering:




From Matt Polk:



A final thought from Stu:

F1 - Great information, MANY THANKS!!

Did this come from a thread that is still available to read?? If so, please provide a link as I would love to read it. I am thinking about replacing the inductors in my 1.2TL's.

ben62670

I think it was an email from MP. I also had an email from MP. It depends which SDA's you want to do this mod to. It would be a big no no on 3.1TL's, and depending on amplification 2.3's. IMHO great on tubed 1C's, and 1.2s

vmaxer

I am considering it on my 1.2TL's

ben62670

What happens is the lower bass passes through the inductor easier so you get tighter punchier bass. If you notice the gauge on the 3.1's you will see they use a highly resistant coil. If you used a low resistance coil on them the dim driver would be at risk of over travelling.

vmaxer

ben62670 wrote: »

What happens is the lower bass passes through the inductor easier so you get tighter punchier bass. If you notice the gauge on the 3.1's you will see they use a highly resistant coil. If you used a low resistance coil on them the dim driver would be at risk of over travelling.

Ben, Its good to see you back!! :cool:I hope everything is going much better!!

Thanks for the info, what is the best brand to use??

F1nut

If you're not getting good bass from your 1.2TL's, changing the inductors is not the answer. You need a different amp and maybe some MIT cables.

F1nut

Did this come from a thread that is still available to read?? If so, please provide a link as I would love to read it.

Those were emails to me that I posted here previously, but I have no idea where.

ben62670

Bump