Which Inductor for (First Order) woofer low pass??

[Wikkid]

Hello..

This is for a low pass 70-75hz for the woofer in an OB project.
I'm looking at 2 inductors.
The Audio 18mH 14 AWG C-Coil Toroidal Inductor
Here:Jantzen Audio 18mH 14 AWG C-Coil Toroidal Inductor Crossover Coil
And the ERSE Super Q 17mH 16 AWG 500W Inductor
Here: ERSE Super Q 17mH 16 AWG 500W Inductor Crossover Coil

The Jantzen would yield (theoretically) a 70hz crossing point, while the Erse a 75hz point.
Upon listening to the woofer alone with an electronic crossover into the amp (18db slope)
I found the 70hz point to sound better (surprising with so small a freq difference).

The Jantzen is a good deal more expensive (wouldn't stop me but it's a consideration)
and has a good deal lower DCR.
DC resistance: 0.174 Ohms, Wire gauge: 14 AWG. VS. the Erse @ DC resistance 0.515 Ohms, Wire gauge: 16 AWG.

Power handling is not an issue as it's for use with low powered tube amps.

So I'm wondering which would be preferable?

The Jantzen uses an "epoxy coated iron core".
The core type of the Erse can't be determined but the poop-sheet says this:
"The Super Q line features a specially shaped core that allows for optimal magnetic performance and increases the coil's effective permeability. The result is extremely low DC resistance, reduced distortion and very high saturation levels. The coils are encapsulated in a plastic housing, which eliminates any magneto striction distortion".

I would prefer the lower 70hz crossing point of the Jantzen, but the Erse might be the better choice? (though I'm not sure of that)
I guess the lowest possible DCR is preferable?
Also, I wouldn't mind if the coil caused the woofer QTS to be bumped up a smidge.....

Advice most welcome!
TIA

Greg

 

[ICG]

The Jantzen would yield (theoretically) a 70hz crossing point, while the Erse a 75hz point.
Upon listening to the woofer alone with an electronic crossover into the amp (18db slope)
I found the 70hz point to sound better (surprising with so small a freq difference).

Well, the slope is so slow and the level of the driver rises above that a lot. So a bigger coil will not change the xo point much, because it's very close to the drivers resonance but it will have impact on the slope. The difference there isn't very big. You likely have to go for a steeper slope than 6dB though because the response will likely not drop fast enough.

The Jantzen is a good deal more expensive (wouldn't stop me but it's a consideration)
and has a good deal lower DCR.
DC resistance: 0.174 Ohms, Wire gauge: 14 AWG. VS. the Erse @ DC resistance 0.515 Ohms, Wire gauge: 16 AWG.

[...]

So I'm wondering which would be preferable?

[...]

Also, I wouldn't mind if the coil caused the woofer QTS to be bumped up a smidge.....

See, the difference in the DC resistance changes things a LOT. The coil will increase the Qt and reduce the spl a bit. For an OB a higher Qt is often better but that depends on the drivers parameters. You didn't post which driver it is. If the driver got a Qts of >0,6-0,7, a smaller increase is likely better. For Qts 0,4-0,6 a DC resistance of 0,5 Ohm seems pretty reasonable. With a Qts of <0,4, you will want a higher DC resistance than that, aim for ~1 Ohm (and it's a ton cheaper too).

With you saying you wouldn't mind the Qt going up, then that should be an easy choice.

 

[Wikkid]

Thanks for the reply ICG!

The driver is a custom woofer.
I didn't mention it to avoid a lot of details, and there are a lot.
The testing system is having some issues, but they will be remedied soon.
Meanwhile, I have some crude numbers.
FS is ~37hz, Qts is ~.35 to .45.... SPL ~87db.

So the added resistance increases Q?

I'm still not clear on the choice...

Thanks again..

 

[Lojzek]

Before making a mistake(?) by purchasing any of the inductors, try to build one from an fm tuner ferrite rod and 1mm magnet wire. It should be good enough to get a feel if it's heading in the right direction. I suspect not but you never know other people's taste.

 

[Wikkid]

Before making a mistake(?) by purchasing any of the inductors, try to build one from an fm tuner ferrite rod and 1mm magnet wire. It should be good enough to get a feel if it's heading in the right direction. I suspect not but you never know other people's taste.

GREAT idea! Thank you!!

 

[alayn91]

Hello,
And, where do you find this " 1mm magnet wire" ?

 

[Brett]

Hello,
And, where do you find this " 1mm magnet wire" ?

Search for enameled wire. It's not rare.

 

[Lojzek]

You can use an existing air core inductor, salvage magnet wire from a transformer secondary, electric motor, buy new magnet wire...etc

 

[Scottmoose]

Type it into Google or your choice of search engine e.g.:
1mm magnet wire - Google Search

You should find a wide selection of suppliers.

 

[ICG]

I have to admit, I've never heard the term 'magnet wire' either. It's not logical either, the wire itself isn't magnetic, it's not used directly with a magnet and yet it is a thing. Well, I guess that's where the huge gaps in my vocabulary are 'shining'. (Not a native speaker).

 

[phivates]

It is used to make an electromagnet.

You won't get anything like the results from an active 3rd order crossover with a single coil. You might like what you do get.

 

[ICG]

Yes, I understood what it was (and verified it with LEO and Wiki), it doesn't make it any more logical since it's used for a lot more different stuff. Anyway..

Lojzek's suggestion to use a ferrite bar and wind the coil yourself is a good way of approach. The driver doesn't seem to be fit well for an open baffle project though. Low Qts (typical BR driver) is generally a bad indicator for OB and the low spl of just 87dB hints it doesn't have much cone surface either, likely <18cm and that's bad for the spl, dynamics and deep lower frequency. It will likely result in a spl of only ~75-78dB and it needs to make high excursions. TBH, I wouldn't use such a driver for that range at all. There are really cheap, good drivers with reasonable cone surface (12"+ since the membrane surface is very important for OB bass) with perfect parameters for OB that will result in a much more satisfying speaker. To be able to tell any more about that requires informations about the concept and other drivers.

 

[YSDR]

Agree with ICG above. I don't see any advantage of using this driver as a bass driver in open baffle. For midrange duty might be ok, but that's another story i think.

 

[Wikkid]

Firstly, my error.. a typo.. it's *97* db and it's a 15" driver.

You won't get anything like the results from an active 3rd order crossover with a single coil. You might like what you do get.

I wondered about that.... that is, the degree of difference (between the first order and the current 3rd order).
So are you suggesting I might like the (slightly) higher 75hz rather than the 70hz?
I'm curious to know.

Agree with ICG above. I don't see any advantage of using this driver as a bass driver in open baffle. For midrange duty might be ok, but that's another story i think.

Not at all for midrange! It sounds awful much above 100hz.

The driver doesn't seem to be fit well for an open baffle project though. Low Qts (typical BR driver) is generally a bad indicator for OB TBH, I wouldn't use such a driver for that range at all. There are really cheap, good drivers with reasonable cone surface (12"+ since the membrane surface is very important for OB bass) with perfect parameters for OB that will result in a much more satisfying speaker. To be able to tell any more about that requires informations about the concept and other drivers.

As mentioned earlier, it's a 15" woofer... above it is a vintage Supravox T-215 RTF 64.
It is being custom designed to my preferences (to the degree that there are a wide range of choices in parts).

The concept:
It may surprise some here that the high-Q approach to OB isn't for everyone.
There is a school of thought (mostly elsewhere) that bass-reflex range Q is more desirable, but add cone area (a second... or more... woofer usually) *IF* powerful/loud bass is the goal.
Personally, I hate the bonky indistinct "juke box bass" that the high Q woofers provide.
I have played around with many of the usual alternatives, and am very unsatisfied with the results.
In short... I gladly trade off loud bass, for well defined articulate (and reasonably low) bass.
I have downsized into a very small apartment with thin walls/ceilings.....
Much prefer bass lower than the "midrange" can provide, but There... and defined.... so that I don't have to constantly worry if the muddy bass is actually the neighbor stomping on the floor!

The supravox rolls off slowly and smoothly from ~100hz down to it's 55hz FS.
I will cut it at ~100hz first order.
Cutting the woofer's (slightly rising response above 75hz) first order around 75hz with a single high Q coil will flatten the response between ~40-45hz and 100hz.
That is the goal. To fill in below where the mid goes away. Not to fill it in with massive autosound subwoofer bass.
I'm content with that area of the bass being of lower amplitude than the midrange.
This is essentially a full range (wide range/mid range) with (slight) augmentation.

The woofer has a heavier than original (hemp) cone & loose suspension, to lower FS, and
a Big azz 15lb alnico magnet.
(the original was 101db and 60hz FS.... a very light 'n tight cone)
It will never see more than 10 watts... and curently about 3 tube watts.
Everything in the system I'm building is geared towards good sound at low volumes.
To understand this concept, a paradigm shift (for most) is required.

I'm listening to them right now and they sound fantastic! I just need to fine tune the crossover to the mid and eliminate the 3rd order electronic crossover. Plenty of great sounding bass.
That returns us to the original question.... which of 2 inductors... the Erse, or the Jantzen.
5hz difference (in the wrong direction) but a slight Q bump up and .5ohm resistance, VS. .1ohm but I don't know which type of core is preferable.

 

[Wikkid]

Practical tips loudspeaker DIY
This might provide some insights...

I'm not slavishly trying to replicate it.. but many of the concepts are ones that experience has taught me are valid.

 

[ICG]

Firstly, my error.. a typo.. it's *97* db and it's a 15" driver.

Okay, that changes a lot. However, the problem with the quick slope to the low frequencies is still an issue, it will look pretty much like this (15", Qts 0,38, fs 47Hz):

You see the low spl in the sub-bass? Well, that driver got a ~3dB higher sensitivity, so the response plot of yours will run parallel below that, any driver with a comparable fs and Qts will behave exactly the same there, even smaller or bigger drivers do, just with different spl, smaller drivers only got a lower rise towards the mids. That's actually not good. And, as you can see, the response rises much faster than your 6dB, it's actually ~9+ dB. That means, a first order crossover will never work, it still rises +3dB/octave with it!

I wondered about that.... that is, the degree of difference (between the first order and the current 3rd order).
So are you suggesting I might like the (slightly) higher 75hz rather than the 70hz?
I'm curious to know.

Well, I doubt you'll be any happy with either of them.

Not at all for midrange! It sounds awful much above 100hz.

That can ofcourse be the case, but in denibenis defense, there are a lot of 15" drivers which do, in PA that's often even midrange territory and tons of PA tops are 15"+tweeter two-ways which makes it actually pretty likely.

As mentioned earlier, it's a 15" woofer... above it is a vintage Supravox T-215 RTF 64.
It is being custom designed to my preferences (to the degree that there are a wide range of choices in parts).

Supravox claims it got a Qts of 0,58 (which would be a lot better) but 60Hz fs. I found a huge range of variing measured parameters which show they got a huge range of tolerances. With a Mms of just 8,5g the voice coil is not only small in diameter, it has to be extremely short too, otherwise a that low cone weight is simply impossible. A 15" PA bass-mid driver has usually 70-80g Mms, a sub 100-200g. Expect the driver to have an Xmax of <2mm.
With a that small voice coil, so low excursion, just 35W power rating and no ventilation behind the spider or the dustcap it's a terrible choice for a subwoofer. That driver is built like a fullrange, to use it as a sub is the worst ever you can do with that driver.

215 RTF 64 Full range driver unit 35W / 97dB / 8 Ohms - Supravox

The concept:
It may surprise some here that the high-Q approach to OB isn't for everyone.
There is a school of thought (mostly elsewhere) that bass-reflex range Q is more desirable, but add cone area (a second... or more... woofer usually) *IF* powerful/loud bass is the goal.
Personally, I hate the bonky indistinct "juke box bass" that the high Q woofers provide.

I have played around with many of the usual alternatives, and am very unsatisfied with the results.
In short... I gladly trade off loud bass, for well defined articulate (and reasonably low) bass.

Have you been listening to high Qts woofers in an OB? My suspicion is, you probably haven't. But well, if that's your taste, fine by me. The Supravox doesn't fit to that concept at all though. If you're not using it in the midrange, there's no single argument left to use it at all. According to Supravox's parameters, it does not even fulfill your lower-Q philosophy. It's expensive, it's exotic but it's the completely wrong choice for that use.

The woofer has a heavier than original (hemp) cone & loose suspension, to lower FS, and
a Big azz 15lb alnico magnet.

Uhm, how do I tell you..? Both weaker suspension and heavier cone increase the Qts. The weight of the magnet doesn't say much, it depends on how it was magnetized and how strong the magnet field is in the air gap. The quoted driver above got a Bl of 16,6 - the unmodified Supravox just 5,8 (!!).

To understand this concept, a paradigm shift (for most) is required.

I do understand your concept, that doesn't change the fact the driver doesn't fit your concept.

E: fixed quote

 

[Wikkid]

I think there's a bit of a misunderstanding....
The Supravox is being used as the "midrange".

High and low are relative terms...
"high Qts vs. low Qts in this case.
The 15" woofer... as it now IS.. has a Qts of ~ .37. (due to measurement related issues it might be .45)
SO: To bump it up a bit with a big coil is part of the goal.
Would this then be a "high Q woofer"?
Considering that some are as much as 1.5 plus QTS... it's all relative.
I tend to like a QTS of .45 to .5 in OB. Gives me the right balance.
This brings me closer to what you're suggesting.

First order low pass should also help fill in the region below where the Supravox slowly goes away.
Software shows only a 1.5db dip around 85hz.
There is also floor reinforcement, and (small) room reinforcement to consider as well.

Also, the FS for the 15 is 37hz, not 47... hope I didn't do another typo.

Regardless of the rest, the 15" woofer will fill in (at least somewhat) below where the midrange cuts off.

The Q peak at the low end, plus the high cut @ 70-75hz should flatten the overall bass response, and keep it flat to ~100hz or a bit more (rather than rising)..

Once again... I'm listening to it and and it's fine!
It's just a matter of fine tuning the crossover...
So again... which of the 2 coils would be better.
I'm beginning to think the Earse @ 75hz and .5 ohms...

 

[Moondog55]

In the context of your original post I don't think it really matters all that much so pick the cheapest. Although I personally prefer a lower DCR for your driver the larger resistance may be better.
I have to say tho that I have never had that "One note boomy bass " from my own OB woofers but perhaps I lucked out.

 

[ICG]

I think there's a bit of a misunderstanding....
The Supravox is being used as the "midrange".

Obviously.

High and low are relative terms...
"high Qts vs. low Qts in this case.
The 15" woofer... as it now IS.. has a Qts of ~ .37. (due to measurement related issues it might be .45)
SO: To bump it up a bit with a big coil is part of the goal.
Would this then be a "high Q woofer"?
Considering that some are as much as 1.5 plus QTS... it's all relative.
I tend to like a QTS of .45 to .5 in OB. Gives me the right balance.
This brings me closer to what you're suggesting.

You don't give 80% of the information and half of the rest is wrong. How do you expect to get correct answers to your questions?

A DCR of the coil of 1 Ohm would bump up the Qts from 0,37 to ~0,42. That's not relevant though, as you need a much steeper xo anyway.

First order low pass should also help fill in the region below where the Supravox slowly goes away.
Software shows only a 1.5db dip around 85hz.

You'll get a bump at 100-150Hz of about 3-4dB. That makes the dip below 4,5-5,5dB deep.

There is also floor reinforcement, and (small) room reinforcement to consider as well.

That doesn't work that way with an OB. Try it and place your OB directly in the corner. The bass gets quieter, not louder. That's why you need ~1,5m distance from the back wall.

Regardless of the rest, the 15" woofer will fill in (at least somewhat) below where the midrange cuts off.

It will only do that if you cross it over at 18dB, which will result in an acoustical slope of ~9-10dB. The serial resistance of the coils will push the Qt additionally. No, it doesn't become a 'high Q' driver because of that.

The Q peak at the low end, plus the high cut @ 70-75hz should flatten the overall bass response, and keep it flat to ~100hz or a bit more (rather than rising)..

Uhm, no. With a Qts of 0,37 or 0,42 you won't get any bump, you only get that bump in an enclosure with a (relatively) small enclosure. In OB you'll get almost exactly the curve of the datasheet.

Once again... I'm listening to it and and it's fine!
It's just a matter of fine tuning the crossover...
So again... which of the 2 coils would be better.
I'm beginning to think the Earse @ 75hz and .5 ohms...

*sigh* With two different tries of each 2 coils you'd be out of 170 bucks? Why don't you buy a cheap, used active crossover and try the xo frequency and filter order to try it first? That's around 30 bucks for a used active PA crossover.

 

[Wikkid]

In the context of your original post I don't think it really matters all that much so pick the cheapest. Although I personally prefer a lower DCR for your driver the larger resistance may be better.

Thanks!
That helps..

I have to say tho that I have never had that "One note boomy bass " from my own OB woofers but perhaps I lucked out.

Then let me ask... what sort of Q did the woofers you used have?