Tweeter bass blocker - Page 1
Forum section: electronics / beginners

author: symbianas
author_rank: Regular Contributor
timestamp: September 26, 2019, 06:41:47 am
content: Hi, I want to add tweeter speaker to my car, it came with factory 15v 4.7uF inline capacitor crossover capacitor. When connected it seems that I still hear bass "squawking" sometimes.I would like to clarify: will increasing or reducing capacitor size make it speaker to ignore lower frequencies? If I change to 15uF it will get more lower frequencies than with 4.7uF? So it means I should try <4.7uF it would get less lower frequncies?Could it be volts which are bad? or maybe an old capacitor? radio is producing 4x15W so not that much.

author: Whales
author_rank: Super Contributor
timestamp: September 26, 2019, 06:45:24 am
content: If the capacitor is wired in series with the speaker: lower capacitances will give you less bass.You will want to use non-polarised capacitors. Polarised capacitors (such as most electrolytics) can be made non-polarised by using two of them in a certain way, you can find details (including photos) on the web.

author: Zero999
author_rank: Super Contributor
timestamp: September 26, 2019, 09:35:24 am
content: Two electrolytic capacitors of equal value, connected back-to-back will make a non-polarised capacitor of half the value.Yes, the capacitance needs to be reduced to cut the bass more. Don't remove the existing capacitor, just add another capacitor in series with it.The total capacitance of two capacitors in series can be calculated using the following formula:CTOTAL= (C1*C2)/(C1+C2)

author: themadhippy
author_rank: Super Contributor
timestamp: September 26, 2019, 11:05:22 am
content: Assuming its a 8 ohm driver the capacitor is crossing over at around 4.2Khz,instead of moving the crossover point you could try making the cut off rate steeper by wiring an inductor in parallel with the tweeter. The back of a fag pack calculator says a value of around 0.30mH should do the trick.

author: Zero999
author_rank: Super Contributor
timestamp: September 26, 2019, 01:06:50 pm
content: Quote from: themadhippy on September 26, 2019, 11:05:22 amIf there is enough room in the speaker enclosure, then an air core coil will do.I threw in some figures into the calculator linked below.A 40mm former diameter, such as a toilet role tube.Inductance = 300µHWire diameter of 0.63mm which is 22AWG.http://www.circuits.dk/calculator_single_layer_aircore.htmResults:144 turns wound over a coil length of just under 91mmI confirmed the results with this calculator:https://m0ukd.com/calculators/air-cored-inductor-calculator/It gave a wire length of 18.1m. The resistance 22 AWG wire is 52.96mΩ/m, so the ESR of the inductor will be just under an Ohm. The self-resonant frequency is 1.85MHz, which is nearly 100 times the audio bandwidth.https://en.wikipedia.org/wiki/American_wire_gaugeSpace can be saved with a multilayer coil. I just chose a single layer because it made the calculations easier.

author: symbianas
author_rank: Regular Contributor
timestamp: September 26, 2019, 01:55:01 pm
content: Forgot to mention its 4ohm driver. I will try 3.3uF 100V bipolar capacitor.

author: Audioguru again
author_rank: Regular Contributor
timestamp: September 26, 2019, 04:46:53 pm
content: The 4.7uF capacitor in series with the 4 ohms tweeter cuts 8500Hz to half power and cuts 132Hz bass to 3.3% of full power. If full power is 15W then 3.3% is only 0.5W.If the 4 ohms tweeter with the capacitor it came with produces bass "squawking" sounds then your input signal level is too high for it. Is it a cheap tweeter?EDIT: Maybe the amplifier is clipping with loud bass and the tweeter is simply producing the high frequency harmonics of the clipping distortion? It might become damaged by playing the high frequency distortion.

author: symbianas
author_rank: Regular Contributor
timestamp: September 26, 2019, 06:46:19 pm
content: Quote from: Audioguru again on September 26, 2019, 04:46:53 pmTweeter is high quality "logic7", but used and from 2007 year car. Power comes not from dedicated amplifier but from radio itself, so maybe it could be that radio is producing not clear signal?Quote from: Audioguru again on September 26, 2019, 04:46:53 pmDoes this mean that the issue might be in radio, and there is no way to fix it without buying dedicated amplifier and upgrading all system?

author: symbianas
author_rank: Regular Contributor
timestamp: September 28, 2019, 11:01:16 am
content: Is this radio problem and I need amplifier or the issue is that I connected tweeter and its capacitor is impacting the system?Would such thing solve my "squawking" issue once and for all? Is it much different from only capacitor?

author: Audioguru again
author_rank: Regular Contributor
timestamp: September 28, 2019, 03:20:00 pm
content: Since we do not know if the tweeter makes "squawking" that is caused by the radio clipping during bass sounds or caused by the tweeter being driven by clear bass that is too powerful for it then try another radio or another tweeter.Any amplifier or radio can produce clipping if its volume control is set too high. Without the tweeter, can't you hear the radio clipping?A 2007 car radio produces a maximum of about 15W into each 4 ohms speaker when the engine is running and the battery is near a full charge. An ordinary speaker is an inductance at high frequencies then it draws less power so adding a tweeter with a capacitor does not overload the amplifier. Maybe you have the volume control turned up higher than the 15W clipping power so turn down the volume until below 15W there is no clipping, or get an amplifier that produces much more power. 10 times the power (150 real Watts) sounds twice as loud.Why did you show a photo of a 3-way crossover network?

author: drussell
author_rank: Super Contributor
timestamp: September 28, 2019, 03:37:19 pm
content: I think the OP is trying to understand some basic filtering concepts.What they probably don't realize is that not only can you change where the crossover point is (for example, using a smaller value capacitor in series with the tweeter will raise the frequency at which the filter is effective) but you can also change theslopeby creating multi-order filters.A single capacitor in series with a tweeter, or a single coil in series with a woofer will provide a 6 dB per octave roll-off.A second order (12 dB / octave) high-pass filter for a tweeter would be built with a slightly different capacitor value in series and then the appropriate coil in shunt across the tweeter. (You can think of that coil as helping to bleed off the lower frequencies by shunting them around the tweeter voice coil, decreasing the amount of those lower frequencies that actually getintothe tweeter voice coil. This increases the roll-off rate, or slope...)A second order low-pass would be a coil in series with the woofer and a capacitor across the voice coil to "shunt" some of the higher frequencies that make it through the crossover coil. etc. etc.You can keep adding more stages for steeper slopes with the appropriate values. For example, an 18 dB / octave (thirdorder) tweeter crossover you would go series capacitor to "shunt" coil, to another capacitor, to the tweeter.It gets a little more interesting when you start to look at the phase relationship at crossover if you don't use "matched" crossover sections with the same slope. ie. sometimes you will need to reverse the polarity of the tweeter terminals to maintain correct phase at the crossover point if you have an uneven number of orders to orders.Good ol' Parts Express has these simple calculators especially to help beginners:https://www.parts-express.com/crossover-calculators

author: drussell
author_rank: Super Contributor
timestamp: September 28, 2019, 03:45:21 pm
content: Quote from: symbianas on September 26, 2019, 06:46:19 pmYes, this is a fundamentally good concept to understand. As stated above by others, if you are reaching the clipping point, (inanyamplifier,) distortion increasesDRAMATICALLYas soon as you try to go beyond that. The sound quality will suffer greatly and the splatter of the harmonics caused by the clipping will be very pronounced, especially in a reasonably good quality tweeter, even with a very steep crossover slope. (A steeper slope will help protect the tweeter itself under these kinds of conditions, though.)

author: Kasper
author_rank: Frequent Contributor
timestamp: September 28, 2019, 05:27:19 pm
content: Might want to measure resistance of the capacitor just to check its not shorted.

author: symbianas
author_rank: Regular Contributor
timestamp: September 28, 2019, 06:29:29 pm
content: So this is video of my test rig:At start bass is set at -6 so tweeter is ok. As I increase bass to +6 it starts playing bass from tweeter. So I guess the sound gets distorted correct?The same with increasing sound at some point it starts doing it even if bass is 0.So there is no way around correct? Radio signal is horrible and I need dedicated amp and better setup?

author: drussell
author_rank: Super Contributor
timestamp: September 28, 2019, 06:53:33 pm
content: Quote from: symbianas on September 28, 2019, 06:29:29 pmWhat you are hearing is the higher frequency harmonic components of the bass distorting due to the amplifier clipping.QuoteIf you want to listen at a level greater than that amplifier will provide at a reasonable level of distortion (ie.beforeit clips) then you need a more powerful amplifier. No amount of "filtering the lows" from a distorted signal will remove those high frequency components. You're not really hearing the bass per se, you're hearingharmonicsof the clipping caused by the bass, occurring at the beat of the bassline.My preferred way of doing this kind of thing is typically with at least two amplifiers and an active crossover, which has many benefits, although cost or simplicity are not one of them.QuoteThe radio signal isn't your main problem, running out of amplifier power is.Ideally you want an amplifier that is powerful enough to drive your loudspeaker drivers to levels higher than you would ever want to go so that you never get any clipping distortion. While this may be fine in a large PA system with 3000 watt RMS amplifiers feeding speakers that will burn up on more than 1000 watts continuous, letting you still have peak excursions well above what the speakers can handle continuously, that is not always practical in a car.That's why I tend to use an active crossover on the line level signal, feeding to two separate amplifiers. That way your mids and highs are still always undistorted as long as you have sufficient amplifier headroom, and the less noticeable bass distortion can run well into clipping, generating 10%, 20%, or even higher levels of distortion before really sounding messy, distorted and smeared.If you use the same amplifier to drive your bass as your highs, youwillnotice the distortion as soon as it begins, as you have discovered.You can imagine how bad itlookson an oscilloscope when you canhearit...(Although, if you're listening to a sine wave, you canhearas soon as it touches clipping....)Welcome to the deep rabbit hole of audio electronics! Happy learning!