I have a pair of decent loudspeakers—Braun LS200. I discovered these speakers have Qtc of 0.5 on their closed boxes bass system. I’ve read that the low Qtc suits to classical music or any kinds of music that require bass’s precision and accuracy. Regrettably, I rarely listen to classical or jazz; but pop, soft rock, and sometimes disco. The LS200 performs well, however, I felt I wasn’t totally satisfied with their bass response. I think it’s too TIGHT and a bit too LOW efficiency. As a result, it led me to add an active equalizer to the system at present. To date, I no longer want to use the EQ. So I’d like fix the problem at its cause, that is the speakers. As mentioned earlier, the bass system has Qtc of 0.5 which should be the root cause. I know one method to increase the Qtc is to decrease the cabinet volume. But, I’m just curious is there any method to create a variable Qtc? So I could return to the factory design whenever I want.
Make an amplifier with adjustable output resistance using both series and shunt feedback, or connect a power resistor between amplifier and speaker, or use a long and thin loudspeaker cable.
You would need an extra resistance of about half the loudspeaker's DC resistance to increase the Q from 1/2 to (1/2) √2.
You would need an extra resistance of about half the loudspeaker's DC resistance to increase the Q from 1/2 to (1/2) √2.
I don't believe you can directly do what you want.
- Reducing the cabinet volume will indeed raise the Q but it will also raise the resonance frequency. The lowest bass will reduce. I'm guessing that is not what you want however you can easily test it by putting some bricks inside the enclosure.
- Those are tower speakers? Those are the pictures I see on the internet.
- I would not put a resistor in series. It would have to be super powerful as it would waste a lot of heat. I have to confess as a loudspeaker engineer I never measured this effect, but I don't know any engineers that would do that. I'm feeling offhand that while yes the system Q goes up maybe the response from the speaker itself doesn't do what you want...I could be wrong.
- Negative output impedance amplifier as @MarcelvdG says, if you can make one.
I'd be more interested in trying to add a low tuned port, to bring up the lower bass and make the bass more full sounding. Do you feel comfortable mounting one? You are in Costa Rica? If so you can access some kind of port tube kit? Ideally you would measure the enclosure size and all the driver parameters. More pragmatically you probably can't get the driver parameters, and if you don't want to spend maybe $100 for a Dayton Audio DATS V3 (https://www.daytonaudio.com/topic/wheretobuy) you could just accurately measure the enclosure and use an online calculator to put in a port tuned to 30 Hz.
I'd go some steps further:
- Put in cross-bracing inside (I cut 1x1" slightly too long, force them in under a bit of pressure, wood glue sit to dry, rotate to the next side wood glue sit to dry, repeat
- Coat inside with anti vibration goop, or maybe sheets, depending what you can get.
- Stuff with maybe 1.3 pounds per cubic foot of fiberglass, not touching the woofer cones or electric leads. And not within a hemisphere maybe 3X them port diameter of the inside port opening. This will make the enclosure act at least 20% larger, and absorb internal acoustic energy from reflecting back out through the enclosure panels.
I found that some speaker manufacturers in the 80s used 4th-order or vented enclosures, whose design was over-damped characterictic, was aided by a second-order Chevbyshev ‘active’ filter. The result yields 6th-order Butterworth alignment. I’m curious whether this trick is also valid for the over-damped (Qtc = 0.5) closed/ second-order enclosures. And which alignment will be created?
Actually, I thought the same. But, my audiophile friends wouldn’t definitely accept it and will laugh at me for sure. Lol
Anyway, I found there’s a trick to add a capacitor in series with the woofer. It will produce a boost at the low-end but also change the slope from 12 to 18dB/oct. Has anybody ever heard about this? What do you think about it, please?
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Just embed the EQ into a golden box and say it's the magic box, price tag it with big number and laugh back 🙂
It must be the early phase of audiophileness where everyone seems to know everything.
You need a positive output impedance to increase Q.
I say negative, you say positive, I say tomato you say tomatoh, let's call the whole thing off! (Even though yeah I think you are correct, I mindlessly typed negative output impedance as a phrase from the past).
So a tube amp could do this most likely.
Actually, how do you know it is not the ROOM (and positioning within)?
- How did you make the response curve you showed? Is that a nearfield measurement (i.e. microphone almost touching the woofer)? Because if so that bump is not necessarily a response bump related to Q, it can be the upper midbass rolloff is just the power response. I measured curves like that all the time, and was amazed LEAP actually predicted such.
- What are the frequency responses around the listening position?
This is an established trick, in German it's called GHP (Geschlossen mit HochPass -- closed box with high-pass). It gives DC Protection and Subsonic Filter function "for free".
The capacitor will be of large value, thus only non-polarized electrolytic types qualify. It also needs to be high voltage (so as to block DC in case of catastrophic amp failure) and of excellent quality (smooth plates, preferably) and low tolerance --> rather costly.
Distortion around resonance may render slightly different compared to an equivalent line-level (or DSP) EQ before the amp but usually that's totally insignificant if even measurable at all.
Well, there's your problem right there. Who gives a crap what your audiophile friends would accept, or not accept?
Dave.
Try placement close to back wall or near a corner.
Small R in line helps already: 0.15 to 0.47 ohms also reduce distortion slightly. And helps the bass if it sounds too tight.
Maybe you have a preamp/amp which is not linear and reduces the bass? Due to maybe small coupling C's
Small R in line helps already: 0.15 to 0.47 ohms also reduce distortion slightly. And helps the bass if it sounds too tight.
Maybe you have a preamp/amp which is not linear and reduces the bass? Due to maybe small coupling C's
Actually, Qes is highly temperatur depended. So, the more Qes is part of the total Q, the more Qtc will will change with temperature.
Low level Qtc 0.5 easely becomes 0.6 or higher.
If you really want to make a boombox, one way to rise the Q would be increasing the mass of the resonant system.
Result would be, higher Q, lower resonant frequency, lower efficiancy.
Low level Qtc 0.5 easely becomes 0.6 or higher.
If you really want to make a boombox, one way to rise the Q would be increasing the mass of the resonant system.
Result would be, higher Q, lower resonant frequency, lower efficiancy.