I have a pair of Alpair 10.2 speakers in small bass-reflex cabs. I had to apply baffle step correction to get them to sound hi-fi, but I think I've arrived at a good set of values. I need to get a pair of 3.0mH or 3.3mH inductors.
The question is, for an extended-range single driver speaker for nearfield desktop listening, would I be better off using air core inductors, or iron core?
My clip-leaded lash-up uses a scrounged (and probably very cheap) pair of 2.1mH iron core inductors in series with a Dayton 1.2mH 18ga 'Perfect Lay' air core inductor to make 3.3mH. The DCR of the two is about 1.5 ohms. After much experimentation, I ended up with a 10 ohm wirewound resistor across (in parallel with) the inductors. I like the sound I'm getting.
Parts Express lists a laminated iron core 3.0H inductor with 0.36 ohm DCR that's very affordable. (US $8.59 ea)
https://www.parts-express.com/Dayton-Audio-IC183-3.0mH-18-AWG-Laminated-Iron-Core-Inductor-257-658
The 20-gauge Jantzen 3.0H air core inductor has 1.38 ohm DCR. ($14 ea)
The 18-gauge Jantzen 3.0H air core inductor has 0.99 ohm DCR. ($20 ea)
(They're out of stock of the Dayton 18ga 3.0H air core.)
I know that adding 1 ohm in series with the driver will elevate the bass response a little and make it a bit looser. Is that a good thing with a single driver? I suppose that's a taste thing, but single-driver systems do suffer from a frequency response that rises as you go up in frequency. I can live with a bit of tubby mid-bass in a high-falutin' PC speaker if the tonal balance is pleasing.
Do I want the lowest possible DCR inductor? Steel core, for best damping, tightest bass?
Or do I want air core for the most freedom from possible saturation and the most stable filtering -- and accept a slight mid-bass boost and a little worse damping?
Anybody go through this before?
The question is, for an extended-range single driver speaker for nearfield desktop listening, would I be better off using air core inductors, or iron core?
My clip-leaded lash-up uses a scrounged (and probably very cheap) pair of 2.1mH iron core inductors in series with a Dayton 1.2mH 18ga 'Perfect Lay' air core inductor to make 3.3mH. The DCR of the two is about 1.5 ohms. After much experimentation, I ended up with a 10 ohm wirewound resistor across (in parallel with) the inductors. I like the sound I'm getting.
Parts Express lists a laminated iron core 3.0H inductor with 0.36 ohm DCR that's very affordable. (US $8.59 ea)
https://www.parts-express.com/Dayton-Audio-IC183-3.0mH-18-AWG-Laminated-Iron-Core-Inductor-257-658
The 20-gauge Jantzen 3.0H air core inductor has 1.38 ohm DCR. ($14 ea)
The 18-gauge Jantzen 3.0H air core inductor has 0.99 ohm DCR. ($20 ea)
(They're out of stock of the Dayton 18ga 3.0H air core.)
I know that adding 1 ohm in series with the driver will elevate the bass response a little and make it a bit looser. Is that a good thing with a single driver? I suppose that's a taste thing, but single-driver systems do suffer from a frequency response that rises as you go up in frequency. I can live with a bit of tubby mid-bass in a high-falutin' PC speaker if the tonal balance is pleasing.
Do I want the lowest possible DCR inductor? Steel core, for best damping, tightest bass?
Or do I want air core for the most freedom from possible saturation and the most stable filtering -- and accept a slight mid-bass boost and a little worse damping?
Anybody go through this before?
Why not to wind your own inductor? Its not a difficult task. You can obtain similar results to expensive units with marvelous (read stupid) trade marks.
Perhaps an iron core wouldn't be my first choice with a fullrange driver. Iron cores sometimes get 'interesting' at higher frequencies.
So the question remains, does the resistance matter? It seems to come down to the response, which is arbitrary enough so more resitance isn't necessarily a bad thing. In fact by manipulating the three values in this circuit I was able to produce a sort of EQ in either the treble, midrange, upper bass or bass region.. and it's all relative.
I decided to simulate your example. I started with a flat response but used an Alpair impedance plot, so this shows the filter effects. Here is the difference between the two inductor examples..
So the question remains, does the resistance matter? It seems to come down to the response, which is arbitrary enough so more resitance isn't necessarily a bad thing. In fact by manipulating the three values in this circuit I was able to produce a sort of EQ in either the treble, midrange, upper bass or bass region.. and it's all relative.
I decided to simulate your example. I started with a flat response but used an Alpair impedance plot, so this shows the filter effects. Here is the difference between the two inductor examples..
Typo or 1000 times too high inductance?
As you like the sound with the inductors you have now, why not use the inductors you have now?
Usually, an 8ohm driver does not need more than 1mH inductor. 3mH is too high and you will attenuate down too low.
I have used iron core for full range with good success. But low resistance is usually not a big issue on full range drivers so an air coil would be the highest sound quality. However, the distortion caused by the iron core is almost inaudible unless you drive it hard and get hysteresis effects.
The biggest advantage of iron core is the significantly lower cost.
I have used iron core for full range with good success. But low resistance is usually not a big issue on full range drivers so an air coil would be the highest sound quality. However, the distortion caused by the iron core is almost inaudible unless you drive it hard and get hysteresis effects.
The biggest advantage of iron core is the significantly lower cost.
TYPO!
Good catch.
Yes, that was supposed to be 3.0mH, as in 3 millihenries.
1) I could wind my own, I guess. I would have to buy the magnet wire, though.
2) Maybe I should just use the 1.2mH and 2.1mH inductors I already have.
Good catch.
Yes, that was supposed to be 3.0mH, as in 3 millihenries.
1) I could wind my own, I guess. I would have to buy the magnet wire, though.
2) Maybe I should just use the 1.2mH and 2.1mH inductors I already have.
With no BSC the Alpairs sounded extremely bright, harsh and too shouty/forward in the midrange.
I tried the 1.2mH inductors first. Better, but the midrange was still too harsh and forward.
I then tried the 2.1mH inductors. Better yet, and maybe that's the 'correct' value I need.
Then I tried the 1.2mH and 2.1mH inductors in series. That sounds best to my ears. I actually like them this way.
Not trusting my ears, I put the Alpairs with the radical BSC into my main system, comparing them to a pair of JBL Studio 530 (small 2-ways).
The tonal balance was different between the two, with the Alpairs still a bit more 'forward' in the mids, but just a different flavor, not obviously wrong.
I listened to the Alpairs for a while that way. I didn't hate them after a couple of days. I figured they're good enough this way.
The speaker cabinets are very small. The baffle is only 22cm (8.5 inches) across. 36cm (14.5 inches) tall.
Using the BSC formula to solve for the center frequency that would need to be attenuated:
The Baffle Step Correction circuit consists of the components denoted by Lbsc and Rparallel. To calculate the values of these two components, the following equations are provided.
f3 = 4560 / WB Hz
Rparallel = Re x (10dB/20 -1) Ohms
Lbsc = Rparallel / (2 x π x f3) Henries
where
WB = width of the baffle in inches
Re = driver’s DC resistance in ohms
π = 3.141592……
dB = amount of attenuation required
f3 = 4560/8.5 = 536.5 Hz
Lbsc = Rparallel / (2 x π x f3) Henries, so 10/2 * pi * 536.5
6.283*536.5 = 3370.65
I used Rparallel = 10 ohms
10/3370.65 = 2.9668 mH
I think I did that right.
I put these numbers into VC for a baffle simulation. (Ignore the high frequency rolloff as I chose to use 30 degrees off-axis to represent power.) Your choice of 3.3mH(1.5Ω) seems reasonable in this case.