Erse Inductors

[dcmeigs]

Has anyone who has replaced their stock inductor with the Erse Super Q done so as a second step, after their crossover mod has had adequate time to burn-in?

Or alternately, has anyone with a burned-in cap and inductor mod gone back in and unplugged the Erse and plugged the stock inductor back in for a comparative listen?

It would be a useful test, isolating the inductor, to see how much improvement can be attributed to the inductor as opposed to that attributed to the balance of the mod.

[billbillw]

Erse SuperQ are about the best iron core inductors, but most still feel that air cores are better. Polk uses air core, so there is probably no need to replace them.

I used a set of SuperQ to replace the inductors in my Mirage M3 and I liked the improvement, but the Mirage originally had a plain old laminated iron core.

[Marty913]

Has anyone who has replaced their stock inductor with the Erse Super Q done so as a second step, after their crossover mod has had adequate time to burn-in?

Or alternately, has anyone with a burned-in cap and inductor mod gone back in and unplugged the Erse and plugged the stock inductor back in for a comparative listen?

It would be a useful test, isolating the inductor, to see how much improvement can be attributed to the inductor as opposed to that attributed to the balance of the mod.

The only recent Polk upgrade (inductor) I'm aware of was nspindel's a couple of months ago. It's pretty welll documented in here somewhere. I believe his was to his 2B's and was done at the same time as his XO's. He replaced the stock 3.5 ohm one with a .5 ohm iron core from Parts Express. He mentioned it gave him more "bass slam". I'm considering it for my 2's (XO's are done) but haven't gotten around to it yet. I'd be interested in any thoughts on the relative merits. Maybe he'll chime in.

[GV#27]

. He replaced the stock 3.5 ohm one with a .5 ohm iron core from Parts Express. He mentioned it gave him more "bass slam".

If the coil he replaced was in series with the woofer (or woofers)and the DC resistance was reduced from 3.5 to .5 ohm's then yes he should hear a big difference.

[dcmeigs]

If the coil he replaced was in series with the woofer (or woofers)and the DC resistance was reduced from 3.5 to .5 ohm's then yes he should hear a big difference.

I am concerned how this mod affects the impedence of the speaker. It's beyond my expertise but it seems that it might drop the impedence to the point that it would be a problem for the amp.

[GV#27]

I am concerned how this mod affects the impedence of the speaker. It's beyond my expertise but it seems that it might drop the impedence to the point that it would be a problem for the amp.

If the 3.5 ohms figure is correct then that is a lot resistance for a coil to have,if so it must be a big air core type using small guage wire.If this coil is in series with the woofer then yes removing 3 ohms of resistance will affect a number or things like ,the impedance load seen by the amp,the damping or Q of the woofer will be changed so bass response and tuning will be altered.

Also the woofer section may be louder with the resistance removed so the frequency balance of the system of the will possibly change. If you are planning to change inductors try to keep the DC resistances values close to the same as the originals.

[jaysmackie]

I thought it was the inductor on the circuit to the interconnect pin, 16mH 18ga according to the schematics . However the resistance calculators I have estimate that at just over 2 ohms.

edit : up to about 2.5-2.6 depending on the diameter and height

[dcmeigs]

Yes, I see your points. It sets in series between the (-) speaker terminal and the (-) lead of dimensional speakers which are tied by the interconnect cable. I am inclined to think that reducing resistance here would not affect the speakers impedence too much. But, it seems to me that the dimensional driver would be louder with out affecting the stereo driver in any meaningful way. I expect that the SDA affect would be altered in ways I can't begin to predict.

[F1nut]

Yeah, you don't want the SDA drivers to be as loud as the stereo drivers.

[GV#27]

But, it seems to me that the dimensional driver would be louder with out affecting the stereo driver in any meaningful way.

This may be the result.Normally designers would try to keep DC resistance as low as possible.However if the coil in question is for the DA then Polk might be cleverly using it to add some attenuation to that section?

[ben62670]

I did this a while ago with great success. This is probably one of the best SDA mods you can do for the buck. The lower resistance has no effect on the mids, or highs, only the low bass. The fact that it is iron-core has no impact on SQ. The inductor on the Pin Blades is between the ground, and the IC cable.No signal passes through it, and to a driver.



http://www.polkaudio.com/forums/showthread.php?t=54561

[GV#27]

No signal passes through it, and to a driver.

So it is not in series with a driver(s)?hummm very interesting.I wonder why Polk didn't opt for a Iron or laminated core coil in the first place ?

[ben62670]

So it is not in series with a driver(s)?hummm very interesting.I wonder why Polk didn't opt for a Iron or laminated core coil in the first place ?

Probably using up old stock? Copper was much cheaper then too.

[MillerLiteScott]

I am wondering if I should try this in my 2b's also. Seems like a simple plug and play upgrade.

Scott

[F1nut]

Go for it Scott. I'm thinking about it for my 4.1TL's as they could use a bit more low end. My 2.3TL's have thunderous bass, so I'm not so sure any change is needed for them.

[MillerLiteScott]

I agree with you on the 2B's. Which inductor would you recommend Jesse? The same one nspindel used?

Thanks,

Scott

[decato]

I used a Madisound Sledgehammer 16.0 mH custom-wound inductor in my 1.2tls. It has ever so slightly more resistance than the Erse inductor, but still somewhere in the neighborhood of 0.5 ohms. I did notice an increase in bass response. My original writeup is found here:

http://www.polkaudio.com/forums/showthread.php?t=35433

If you have the 2.3tl or 3.1tl, I don't think you want to make this upgrade. There are less dimensional drivers than stereo drivers, so they already take on a greater bass load, and lowering resistance for that array would cause the dimensional drivers to have even larger excursions at the lowest frequencies. This restricts the system as a whole, since the dimensional drivers will reach their limits before the stereo drivers. It is no surprise that Polk used a 20 or 22 gauge wire in the large inductor of the 3.1tl.

As for models with an equal number of drivers in the stereo and dimensional arrays, give it a try...

[F1nut]

Interesting point Brian. Thanks for your input.

[dcmeigs]

It's simple and inexpensive. I think I'd be remiss if I didn't order a pair and give them a listen.

I'm still sub 100 hrs on my Sonicap upgrade and horns do sound a lot like a guy stepping on one of those mouse-like squeeze toys cats play with. By the time the inductors arrive, I should be past that.

[zingo]

So I take it I would be replacing the large inductor that the x-over sits on if I decided to mod my 4.1TLs?

And I think THIS GUY looks right.

[F1nut]

Ok, I wanted to get the opinions of those who designed and built the SDA's. Here are their responses, which I have permission to post.


From Stu,

"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,

"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"



And again 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."


I would like to thank Ken for all his help in getting the above responses.




I do believe I will leave my inductors stock.

[GV#27]

Thats some go info right there.;)

[nspindel]

Wow, I can't believe I didn't catch this thread until now! Great conversation you've got going here.

I'm definitely the least knowledgeable one here from an electrical engineering standpoint, so all I can say is that yes, the stock air-core inductor did measure out at 3.5 ohms and the Erse metered at 0.5.

It sounds like the saturation issue could be a problem if pushed very hard. However, I've got my 2B's in a relatively small room, so I don't really need to pump them very hard. My NAD 2200 seems to have no problems whatsoever with the decreased impedance, so maybe in my case I'm able to reap all the benefits of the lower impedance without reaching the saturation points of the iron-core inductor. All I know is that it sounds great.

Jesse, remember that Parts Express has got a great return policy. You can always try them out, they're easy enough to connect. If you don't like them, return 'em...

I'm quite pleased with them.

[dcmeigs]

Well, it looks like we have THE definitive answer. Thanks F1nut for your interest and please pass along my thanks to Stu and Matt. It's great of them to take the time to share so much detail.

The inductor issue aside, this is interesting stuff for the noob. It's one thing to take something apart, see how it works and speculate on the why. It quite again another thing to gain some real insight to the method behind the design.

Cheers

[jaysmackie]

yep, great answers, that's why we keep coming back here.
Looks like I will need to stick with a higher resistance air core when I build my SDAs. Yes, you all convinced me to give it a try, stay tuned over the next few months. I think Ben has sold me on the idea of single tweeter 1Cs instead of 2Bs.

My amp is only happy down to 6 ohms and I can't afford to upgrade that as well as building an SDA clone. So I'll need to match the inductors as close as possible otherwise I'll need to run with the volume well down. A Marantz SR7300, it has got 105W in to 8 and 130 in to 6 ohms, so I have a little volume to play with.

cheers

[F1nut]

Jesse, remember that Parts Express has got a great return policy. You can always try them out, they're easy enough to connect. If you don't like them, return 'em...

Yeah, I push my modded 2.3TL's pretty hard at times and even though my amp wouldn't have a problem with 2 ohms, the bass is already clean, deep and powerful. For them, I don't see the point. I was thinking of trying the inductors in my 4.1TL's, but I hardly ever use them and when I do it's with a relatively low powered tube amp, which isn't going to like a 2 ohm load one bit. So, there you have it.

[F1nut]

Jay, the 1C's use two tweeters.

[nspindel]

Yeah, I push my modded 2.3TL's pretty hard at times and even though my amp wouldn't have a problem with 2 ohms, the bass is already clean, deep and powerful. For them, I don't see the point. I was thinking of trying the inductors in my 4.1TL's, but I hardly ever use them and when I do it's with a relatively low powered tube amp, which isn't going to like a 2 ohm load one bit. So, there you have it.

Fair enough, then. First rule of thumb - if it ain't broke, don't fix it!

[MillerLiteScott]

Very interesting read, Even though I started getting lost after (From Stu).

I guess moral to the speaker is that it was done right the first time.

Thanks Jesse for your efforts.

Scott

[heiney9]

Ok, I wanted to get the opinions of those who designed and built the SDA's. Here are their responses, which I have permission to post.


I do believe I will leave my inductors stock.

Absolutely excellent post from Stu and Matt. I'm book marking this page just because this gives us (me) some more great insight on the design side of SDA's. I'm still very curious why all the different MW drivers were used across the entire SDA line up. That's the only issue not covered in the compendium and as I understand it the info was proprietary and would have been quite involved.

Thanks Jesse for taking the time to get it from the horses mouth (so to speak). These types of posts are as interesting to read as Nelson Pass' posts are when they start talking about the how's and whys of design philosophy.

Great stuff and I have always intended to leave my inductors stock too.

H9