I am looking into adding a 2 ohm resistance to a driver (Monacor sph-130). According to my maths this would change the Qt from .32 to .40
The effect this has on a sealed box with a Q of 0.8 is as follows:
Without series resistance Volume 4.1 litres, Fbox 95Hz, F3 85 Hz
With 2ohm series resistance Volume 7.3 litres, Fbox 76 Hz, F3 68Hz
My question is, is the pay off as simple as that (apart from the sensitivity going down) or are there complications and other considerations?
The effect this has on a sealed box with a Q of 0.8 is as follows:
Without series resistance Volume 4.1 litres, Fbox 95Hz, F3 85 Hz
With 2ohm series resistance Volume 7.3 litres, Fbox 76 Hz, F3 68Hz
My question is, is the pay off as simple as that (apart from the sensitivity going down) or are there complications and other considerations?
When you think that you could go as far as passively bringing down the top end until f3 is 20Hz, losing a lot of sensitivity in the process, it may put into perspective what this simple tradeoff will and won't do. I think it's worth remembering that the region of benefit in this case is wholly within the room controlled region and can or will be manipulated in other ways.
You are quite right that this is a valid way of doing things, albeit a bit of power is wasted in the woofer series resistor.
An equivalent process is considering those exotic SET amplifiers that have significant output impedance:
Arpeggio Loudspeaker - diyAudio
An equivalent process is considering those exotic SET amplifiers that have significant output impedance:
Arpeggio Loudspeaker - diyAudio
In usual home usage, average power applied to loudspeakers is less much than 1 W, so the wasted power is not a problem.
This has also been considered elsewhere:
@Gegentakt & all: Widerstand vor low-Q-Chassis - Visaton Diskussionsforum
Note especially the statements of the user "gegentakt".
As a translation tool I can recommend the page DeepL Translator.
With kind regards
Azrael
@Gegentakt & all: Widerstand vor low-Q-Chassis - Visaton Diskussionsforum
Note especially the statements of the user "gegentakt".
As a translation tool I can recommend the page DeepL Translator.
With kind regards
Azrael
Adding a series resistance is creating a voltage divider between the resistor and the impedance of the driver. For simplicity, think of the driver's impedance as pure resistance that is frequency dependent - the familiar "impedance curve" that you see for the driver.
Because of the voltage divider effect, you will also get changes to the frequency response at high(er) frequencies, where the driver has a rising impedance. In essence, by adding a resistor you are implementing some degree of equalization of the input power that roughly follows the contour of the driver impedance magnitude (the impedance curve). The degree of EQ is related to how much series resistance you add.
So make sure to take the effect at higher frequencies into account when you are considering this change. Just like with high impedance amplifiers, many uninformed tweakers think that using it does "wonders" to the sound of e.g. their single-driver loudspeakers, as if the amp itself is the culprit. Instead it is only the "EQ" effect that is responsible for the tonal changes that they hear.
Because of the voltage divider effect, you will also get changes to the frequency response at high(er) frequencies, where the driver has a rising impedance. In essence, by adding a resistor you are implementing some degree of equalization of the input power that roughly follows the contour of the driver impedance magnitude (the impedance curve). The degree of EQ is related to how much series resistance you add.
So make sure to take the effect at higher frequencies into account when you are considering this change. Just like with high impedance amplifiers, many uninformed tweakers think that using it does "wonders" to the sound of e.g. their single-driver loudspeakers, as if the amp itself is the culprit. Instead it is only the "EQ" effect that is responsible for the tonal changes that they hear.
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Ah. I was thinking of running the main driver quite high, and I see on the manufacturer's impedance curve that the impedance is about 15ohm at 5k. What you point out will be significant. Thank you.
Any competent simulator will take care of the changed frequency response. The resistor just becomes a circuit component.
Software | Visaton
Boxsim has an item in extras menu for box volume calculations. You can load the T/S parameters and add a 2 ohm presristor to the 6 ohm coil resistance.
I just had a go with a Qts = 0.33 Visaton W200S Reflex Woofer.
The critically damped (0.7) closed box went up from 19L to 44L. And the Fs went down. Which is what you want, I think.
Software | Visaton
Boxsim has an item in extras menu for box volume calculations. You can load the T/S parameters and add a 2 ohm presristor to the 6 ohm coil resistance.
I just had a go with a Qts = 0.33 Visaton W200S Reflex Woofer.
The critically damped (0.7) closed box went up from 19L to 44L. And the Fs went down. Which is what you want, I think.
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