Hi all
I have a simple question that I haven’t been able to quickly google up a reply to, I hope that someone here can help:
If I build a pair of subs (passive, 4 ohm), each containing a low pass filter (to tackle the introduced noise from the amp at the severe breakup frequency of the woofer at 2 kHz, I´m using active X-overs); what would happen to the low pass frequency if I later decide to add two more subs (same design) and connect them in series (for a total load of 8 ohms per side) and still with one low pass filter in each sub? Will the two coils act as one (but 8 ohm load) and provide the same low pass frequency as before for each woofer, or will something else happened and if so; what?
Thanks in advance!
I have a simple question that I haven’t been able to quickly google up a reply to, I hope that someone here can help:
If I build a pair of subs (passive, 4 ohm), each containing a low pass filter (to tackle the introduced noise from the amp at the severe breakup frequency of the woofer at 2 kHz, I´m using active X-overs); what would happen to the low pass frequency if I later decide to add two more subs (same design) and connect them in series (for a total load of 8 ohms per side) and still with one low pass filter in each sub? Will the two coils act as one (but 8 ohm load) and provide the same low pass frequency as before for each woofer, or will something else happened and if so; what?
Thanks in advance!
Jens,
1) The frequency response of the series subs with LP filters will be the same as the single.
2) The sensitivity of the two series subs will increase by 3 dB, the power used will be reduced by 3 dB. At low power levels, the SPL will be the same, at high power levels, the series voice coils will heat less, so will have 1/4 the power compression as the single driver.
Art
Hang on..do you mean that you're going to add a second woofer that's also attached to the output of a passive crossover?
The crossover frequency should go up, if I'm imagining your situation properly.
The crossover frequency should go up, if I'm imagining your situation properly.
Correct Me if I,m Wrong But...
I don't see why you would want a low pass filter in each sub if you are running the speakers on an active sub output.
I think that the passive low pass filters in each sub in series might change the frequency of the passive filter.
If you imagine a simple first order hi pass filter consisting of a single capacitor and the speaker load then linking the 2 speakers and 2 capacitors in series would result in double the speaker impedance and half the capacitance - IE the frequency response would be unchanged.
When you look at a first order low pass filter with an inductor, then connecting the 2 speakers and inductors in series would result in double the speaker impedance and double the inductance. IE the frequency response would be lowered by 2 octaves.
The change from 2K to 500hz might be irelevant if the active crossover filter is at a low enough frequency.
I don't see why you would want a low pass filter in each sub if you are running the speakers on an active sub output.
I think that the passive low pass filters in each sub in series might change the frequency of the passive filter.
If you imagine a simple first order hi pass filter consisting of a single capacitor and the speaker load then linking the 2 speakers and 2 capacitors in series would result in double the speaker impedance and half the capacitance - IE the frequency response would be unchanged.
When you look at a first order low pass filter with an inductor, then connecting the 2 speakers and inductors in series would result in double the speaker impedance and double the inductance. IE the frequency response would be lowered by 2 octaves.
The change from 2K to 500hz might be irelevant if the active crossover filter is at a low enough frequency.
I kinda asked myself that question too, I think we need a bit more info about the whole setup.
Isn't it better to wire woofers in parallel rather than series when ever possible? Something about the EMF from the voice coils having more interference with one another when wired in series? I can't for the life of me remember where I saw that explained.
2khz? What happens way up there at that frequency is irrelevant when it comes to subwoofers, and you're gonna have the active lowpass filter set more than a decade below that so there is no need whatsoever for a passive filter. Unless of course you're actually building a fullrange speaker system and have mistakenly identified the woofer?
1) No, series connections can be better in situations where the amp will not operate well in to a lower impedance, and for long speaker cord runs, the additional damping factor of a higher impedance load can be an improvement.
2) Not true.
You can see in the measurements of single vs. multiple cabinets each with two series woofers using a second order passive crossover, and a tweeter also using a second order crossover, that the response barely changes at all from a single, and the sensitivity of the two series loudspeakers increased by 3 dB, while the power used was reduced by 3 dB.
http://www.diyaudio.com/forums/subwoofers/204472-multiple-cabinet-combined-response.html
Art
Let´s settle the confusion:
What I´m trying to do is to build a couple of subs that can be used alone or in pairs (in series for 8 ohm load, or ever four per side; in series/parallel configuration to get back to 4 ohm). Always in stereo configuration.
I´m using active (DSP) X-overs and the woofer is a 4 ohm 15” aluminum cone driver with an approximate 15 dB sensitivity increase at about 2 kHz due to the breakup, and even if there will naturally not be any program material playing in this range; the noise floor of the X-over and amp will still be present and a 15 dB boost in this range is audible, especially in critical listening rooms (yes; I know since I´ve tried it) so a passive low pass filer is needed to filter out the noise and this is what I´ve done in the past and know that it works well (why shouldn’t it). A simple first order is sufficient.
Again; the passive LP filter is only used to get rid of the noise from amp and X-over that is boosted by the increased sensitivity due to one break up; not as the actual X-over filter which operates much lower in frequency and taken care of by the DSP based X-over.
What I have not tried yet, is to add another coil + woofer in series (or parallel either for that matter).
Now, suppose I choose to use a 1,6 mh coil for a 400 Hz 1st order low pass (assuming a single 4 ohm woofer) for an approximate 14 dB down at 2 kHz:
From what I understand, adding an additional coil (1,6 mh) and woofer in series simply doubles the inductance (and naturally the impedance of the system) so the end result should be the same (3,2 mh and 8 ohm = 400 Hz low pass) and since it´s an AC current, it doesn’t really matter where the coils (or woofers) are in the chain.
All clear or am I missing something?
Thanks all for your interest in my question, much appreciated.
What I´m trying to do is to build a couple of subs that can be used alone or in pairs (in series for 8 ohm load, or ever four per side; in series/parallel configuration to get back to 4 ohm). Always in stereo configuration.
I´m using active (DSP) X-overs and the woofer is a 4 ohm 15” aluminum cone driver with an approximate 15 dB sensitivity increase at about 2 kHz due to the breakup, and even if there will naturally not be any program material playing in this range; the noise floor of the X-over and amp will still be present and a 15 dB boost in this range is audible, especially in critical listening rooms (yes; I know since I´ve tried it) so a passive low pass filer is needed to filter out the noise and this is what I´ve done in the past and know that it works well (why shouldn’t it). A simple first order is sufficient.
Again; the passive LP filter is only used to get rid of the noise from amp and X-over that is boosted by the increased sensitivity due to one break up; not as the actual X-over filter which operates much lower in frequency and taken care of by the DSP based X-over.
What I have not tried yet, is to add another coil + woofer in series (or parallel either for that matter).
Now, suppose I choose to use a 1,6 mh coil for a 400 Hz 1st order low pass (assuming a single 4 ohm woofer) for an approximate 14 dB down at 2 kHz:
From what I understand, adding an additional coil (1,6 mh) and woofer in series simply doubles the inductance (and naturally the impedance of the system) so the end result should be the same (3,2 mh and 8 ohm = 400 Hz low pass) and since it´s an AC current, it doesn’t really matter where the coils (or woofers) are in the chain.
All clear or am I missing something?
Thanks all for your interest in my question, much appreciated.
I've never, ever in my life heard a subwoofer breakup mode when crossed over electronically.
Not only that, but I'd imagine there's not anything you can do with a passive component that you couldn't replicate with the DSP, even notching out frequencies that are probably 30 or 40 db down.
Lastly, if your noise floor is high enough that a driver's breakup mode makes it audible, then you've got wayyyy wayyyy worse problems than what might happen with additional drivers.
Not only that, but I'd imagine there's not anything you can do with a passive component that you couldn't replicate with the DSP, even notching out frequencies that are probably 30 or 40 db down.
Lastly, if your noise floor is high enough that a driver's breakup mode makes it audible, then you've got wayyyy wayyyy worse problems than what might happen with additional drivers.
Regarding not being able to fix it in the DSP:
The issue is related to the noise floor of the DA stage of the DSP and the amp following it: This cannot be addressed by the DSP since it is ahead in the signal chain. The noise floor of the following stages will still be added. The only solution is a passive filter after the amp. Do you see what I mean?
Question:
Have you ever used a woofer with a 15 dB or more, breakup boost (above average) in the critical midrange (where the ear is most sensitive) in a professional installation where you need to have enough headroom to handle the transients of uncompressed material but still need to be able to produce a high RMS SPL and using active DSP based (AD/DA conversion stages) for the woofers?
If not; I completely understand your doubts, but you simply have to believe me when I say that I have tried to do this without the passive LP filter, and the noise (even if not severe) is too loud to be acceptable for me (… but yes, guilty; I am known to be a bit picky …). A simple first order filter is an easy fix that completely solves the situation.
Oh, and yes: I have designed other subs (other woofers without breakup issues) that did not require this filter simply due to the lack of severe break up, so I know that most woofers (that are using active X-overs) will not need this passive filter treatment, but even if a breakup related boost due to stiff cone woofer is used; in a normal consumer situation, you still might not have a problem.
YES I got it wrong 😱
The response is very similar with 2 speakers in series!
Must try to resist those hasty lunch time posts.....
Yeah, I get what you're saying, I just think there's got to be a way to reduce the noise to solve the problem.
I'd tape a pillow in front of my subs before I'd add passive components to an already actively crossed over driver.
Hornresp definitely shows an increased rolloff effect with 2 speakers in series
Might be worth checking out a few sims🙂
Might be worth checking out a few sims🙂
Are the interconnects between the DSP and amplifiers digital? Balanced? Unbalanced? Are we talking about professional equipment here or DIY?
I still don't see this being audible, with 24db low pass at 100hz or less the signal would be over 120db down at 2khz, so if you got noise it's not subwoofer cone breakup.
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Balanced.
Again:
The level is only 14 dB down at 2 kHz using a first order filter at 400 Hz. This is however sufficient to solve the issue of the around 15 dB gain at 2 kHz caused by the woofer at the breakup frequency.
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