Trying to get a general consensus on how low a center channel speaker needs to go? Is 80 Hz OK?
I'm in the middle of an W-M/T-W design (woofer on either side of mid/tweet with tweet above mid in middle. Woofer to mid crossover point at around 600HZ; mid to tweeter turnover at 2.8K. with what would be superb null response when mid out of phase (showing near perfect in phase at respective crossover points).
I picked some very good/cheap 5" woofers (Peerless 835024 Aluminum cone) for bass that will perform in sealed enclosure(s). They will however only give me -3dB at around 80Hz (9 litre enclosure volume per/driver). I dislike the sound coming from rear port(s) of a vented center channel speaker that resonate within the TV stand cabinet it's placed into. I can set the AV receiver to only deliver sound down to 80 Hz for the center speaker (theoretically remainder goes to sub) for this setup but should I worry about going as low 60 Hz or less for Center Channel?
I'm in the middle of an W-M/T-W design (woofer on either side of mid/tweet with tweet above mid in middle. Woofer to mid crossover point at around 600HZ; mid to tweeter turnover at 2.8K. with what would be superb null response when mid out of phase (showing near perfect in phase at respective crossover points).
I picked some very good/cheap 5" woofers (Peerless 835024 Aluminum cone) for bass that will perform in sealed enclosure(s). They will however only give me -3dB at around 80Hz (9 litre enclosure volume per/driver). I dislike the sound coming from rear port(s) of a vented center channel speaker that resonate within the TV stand cabinet it's placed into. I can set the AV receiver to only deliver sound down to 80 Hz for the center speaker (theoretically remainder goes to sub) for this setup but should I worry about going as low 60 Hz or less for Center Channel?
I hope you find what I write as useful, although my views tend to diverge from conventional wisdom and therefore concensus. In my defence my views are underpinned by a successful career over 5 decades in electroacoustics, spanning live sound, cinema sound, architectural acoustics and electronic architecture, professional and consumer loudspeaker design and manufacture and home theatre system design.
If you perceive "sound coming from rear port(s) of a vented center channel speaker that resonate within the TV stand cabinet it's placed into" there is something fundamentally wrong with the design of the center speaker. The only sound that ideally comes out of a reflex port should be around the tuning frequency, where the wavelength is far too long for whether it is coming out of the front or the back to be an issue. However a lot of speaker designs do exhibit a problem with crap leaking out of the port so I understand why you are worried about it.
In terms of loudspeaker integration in a home theatre system, it is almost always better to send full-range to all loudspeakers, unless they are tiny. In an ideal world, all of the channel loudspeakers would have a DC to blue light frequency response, but they don't. IME the additional phase rotation generated by a high pass filter does more harm to the integration of the sound field than the notion that the particular loudspeaker doesn't have enough low frequency bandwidth. The guys mixing multi-channel audio soundtracks for cinema ensure that everything that needs to be in the LFE channel is there; it doens't need to be added to by setting channels to small. In any case a cinema sub is usually a pretty poor integrator with the center or surrounds, if only because it isn't anywhere near close enough physically! That's my experience borne out by engineering surround systems over the past few decades, both for commercial cinemas and consumer home theatre systems.
It is much more important that your center loudspeaker is properly behaved at low frequencies than whether the bass alignment is 2nd order (sealed) or 4th order (bass reflex). However if you can engineer the required SPL bandwidth in the volume available a sealed system is likely to be better, especially with intelligibility/naturalness of speech, where the ringing that makes a reflex system actually work (AKA port resonance) is not helpful.
If you perceive "sound coming from rear port(s) of a vented center channel speaker that resonate within the TV stand cabinet it's placed into" there is something fundamentally wrong with the design of the center speaker. The only sound that ideally comes out of a reflex port should be around the tuning frequency, where the wavelength is far too long for whether it is coming out of the front or the back to be an issue. However a lot of speaker designs do exhibit a problem with crap leaking out of the port so I understand why you are worried about it.
In terms of loudspeaker integration in a home theatre system, it is almost always better to send full-range to all loudspeakers, unless they are tiny. In an ideal world, all of the channel loudspeakers would have a DC to blue light frequency response, but they don't. IME the additional phase rotation generated by a high pass filter does more harm to the integration of the sound field than the notion that the particular loudspeaker doesn't have enough low frequency bandwidth. The guys mixing multi-channel audio soundtracks for cinema ensure that everything that needs to be in the LFE channel is there; it doens't need to be added to by setting channels to small. In any case a cinema sub is usually a pretty poor integrator with the center or surrounds, if only because it isn't anywhere near close enough physically! That's my experience borne out by engineering surround systems over the past few decades, both for commercial cinemas and consumer home theatre systems.
It is much more important that your center loudspeaker is properly behaved at low frequencies than whether the bass alignment is 2nd order (sealed) or 4th order (bass reflex). However if you can engineer the required SPL bandwidth in the volume available a sealed system is likely to be better, especially with intelligibility/naturalness of speech, where the ringing that makes a reflex system actually work (AKA port resonance) is not helpful.
It's a rare occasion that I can fully agree with a post as long as the above on this type of forum, and on such a subject as surround sound performance requirements/capabilities, which tends to be mired in inaccuracy and expediency in practice. In this case, I agree fully with "Johnmath" and his advice. If your goal is high fidelity and acoustic performance in a 5.1, etc. array--I find that everything he says is spot on.
I've actually worked fairly diligently over a time period longer than I care to reveal to accomplish what he says above, along with along-the-way learning of those requirements first hand. Each point that he's making is a good one.
It would have saved me a much time and money if I knew those requirements at the beginning rather than later, as I learned them. Of course, then I wouldn't have the pleasure of learning them first hand--which, of course, I will likely never forget.
Chris
I've actually worked fairly diligently over a time period longer than I care to reveal to accomplish what he says above, along with along-the-way learning of those requirements first hand. Each point that he's making is a good one.
It would have saved me a much time and money if I knew those requirements at the beginning rather than later, as I learned them. Of course, then I wouldn't have the pleasure of learning them first hand--which, of course, I will likely never forget.
Chris
Hi there and thank you for the response. I would like to know more about you and who you worked for as you seem to be a wealth of information! At the same time I do respect your privacy.
I believe the low amplitude garble that trickles out the back of the center channel speaker port is also mixed in with what sound propagates around the speaker itself and into the inside of the center channel speaker cavity in the entertainment stand (which is closed up at the back) and thus produces unwanted resonances. What ratio would be difficult to calculate/measure. If I hear you correct, the advantage of a sealed center channel speaker would mitigate these possible effects plus port tuning resonances/harmonics to boot. Granted the theoretical purpose of the vent is to act as a Helmholtz resonator, it certainly cannot stop other midrange frequencies from finding their way out the port tube from inside the speaker enclosure, albeit subtle.
I understand your points of proximity relationships from LFE channel sub speaker and center channel and rear channel speaker placements. Not a perfect world by any means, conventional 5.1 (and beyond) configuration - but we live with it.
I have the option on what I am designing to vent (out the front baffle) the 5" bass drivers to get down to 55 Hz (-3dB) although 4th order rolloff compared to the sealed enclosure yielding 80Hz (-3dB) with a 2nd order rolloff but I think I would at least try to see if I'm satisfied with the 80Hz sealed first.
Could I pick your brain on what is sonically better including dynamic presentation of low end response to have a bass reflex vented to the front or rear of the speaker enclosure? This would be for free standing bookshelf sized speakers (on speaker stands). Knowing wave lengths are very long at the respective port tuning frequency to localize but I'm thinking in terms of better phasing/dynamics of the bass? If I could pitch in another question while "I have you on the line" and what's acceptable for the highest vent air speed in enclosure/venting design? I always maintained mach 0.1 or under but I see people comment that up to mach 0.15 is still OK. Problematic port "chuffing" would be a result of several factors to discuss. Many variables within this question/answer but I was thinking what might be a general rule?
I invite you to comment on another thread I started a few days ago titled "TMT or MTM Center Channel Speaker" and would also love to hear your feedback. Its about the Angstrom Six/C center channel speaker I have.
Thanks and cheers from Calgary, Canada!
Hi Chris,
(Cask05)
Thank you for your input!
I have to ask you on your profile picture is that an American Eskimo dog you have? I have one as well and he his the king of our hearts and household here in Canada!
Gordon
Actually, a Samoyed named Tex. He was given his name by my daughter (who lives in Seattle). He's grown a bit. He likes to yodel--and has many vocalizations. He keeps us laughing.
Chris
He must have been a pup in your avatar photo. Looked like an Eskie at the time as they do until the Sammies get bigger and fuller. I love Sammies too! Our (Osito) is loving our winter now - loves his walks in the snow. Your Tex is at least away from the Texas heat living up in the Pacific NW. I used to live in Houston for a year many many moons ago. All my siblings are there still (had migrated Canada). I attach a shot of mine, done up for X-mas a few years ago. Shall stop boring others about our beloved dogs...!
Attachments
The electrical circuit equivalent of the air mass in a port tube or vent is a series inductance, AKA low pass filter, so with a bit of care of the internal design of a loudspeaker cabinet the sound coming out of a port should not have a lot of midrange frequency energy in it. Despite that, the benefit of a rear facing port is that it will attenuate and delay the crap that is heard at the listening position, thus ameliorating any deleterious port leakage. The rule of thumb is to keep the opening of the port at least one port diameter from any reflecting surface so as not to detune the port.
When you put a loudspeaker into a cavity, like on a shelf in a home theater stand, the the cavity's resonances will be excited. To simulate the effect, put a bucket over your head while listening to music. I think you'll soon get the picture, or sound, of what I am talking about. I always stuff the enclosed space with polyester sound absorption in those circumstances.
Limiting the mach of airflow in the port is to prevent compression, however the problem of chuffing caused by turbulence usually manifests long before the airspeed approaches compression. Turbulence in the airflow is caused by sudden impedance changes and bends. No tuning port should ever have a bend in it, period. Sudden impedance changes can occur at the ends of the port tube. Flared ports ameliorate the sudden impedance change. Historically a lot of loudspeaker manufacturers have used PVC tube ports with radial arm saw cut ends. The sharp edges at the port ends cause premature delamination of airflow, and consequently turbulence and chuffing. Even a 1mm radius cut with a deburring tool will substantially reduce the chuffing of a butt ended port.
I can't say I have ever played with a horizontal T-M-T arrangement, and I probably wouldn't. Such an arrangement may result in severely comb-filtered high frequency responses either side of the horizontal axis of the center speaker, which is where most of the time everyone will be listening. I expect that comb-filtering will add a distinctive 'caste' to the sound of natural acoustic sources, although without the natural reference handy to listen to and compare with most listeners would not know.
Career wise from highschool I studied electrical and electronic engineering whilst employed to design studio mixing consoles and lighting dimmer controllers for an educational television studio, and then in the next job whilst still studying I designed electronic security and access control systems for hospitals, and installed tape recorder based language laboratories for schools. Then I worked as a live sound engineer, until promoted to Technical Manager - Sound for a large organisation responsible for ~15+ performance spaces, 25+ audio engineering staff, plus the audio engineering for cinemas, outdoor venues, and designing the sound for outdoor rock and opera concerts and national touring musicals. Then after a stint as Asset Manager for the same organisation, I was sent on a world tour of concert venues to investigate acoustics, and then project managed the electronic architecture installation for a multi-function 2000 seat auditorium to create variable acoustics to suit everything from conferences to rock concerts, opera and symphony orchestras. This system is basically a 3D surround system with ~205 distinct and different audio channels and 340 loudspeakers concealed around the auditorium. Then I was head-hunted by a national firm of consulting engineers and acousticians to represent them as their national electro-acoustic engineer, doing stadium designs and acoustic simulations using CATT acoustic software, the (very expensive) bee's knees at the time. Next I worked for a loudspeaker manufacturer designing professional and consumer loudspeaker systems, and designing and setting in place quality assurance procedures to minimise warranty claims, and while there designed a futuristic booth based entertainment and sound system for a space-ship concept restaurant in Sydney for the 2000 Olympics. Then I owned a hifi store and sold only the premium equipment that I would be prepared to buy and take home myself, which precludes an awful lot of what was (and still is) sold as hifi. During this period I designed the crew audio systems for a navy submarine during its refit, which became "type-cast" i.e. the standard for all submarines of that class, which resulted in a lucrative supply contract and a national award by the CES for best commercial installation in Australia that year. After that exercise I was again head-hunted by a consulting engineering company, this time focussing on virtual reality meeting room video conferencing systems, sound reinforcement in historic auditoria (concealed elements), and sports stadia and airport sound systems design, etc. When I'd had enough of that (a lot of which was due to the infiltration of professional audio with IP based technology), I retired, moved to an off-grid wilderness property on an island and, aside from lurking on DIYaudio, amuse myself with restoring and upgrading (mostly) pre-digital professional and consumer audio equipment for clients who care to find me and, of course, for myself. Thanks for asking.
When you put a loudspeaker into a cavity, like on a shelf in a home theater stand, the the cavity's resonances will be excited. To simulate the effect, put a bucket over your head while listening to music. I think you'll soon get the picture, or sound, of what I am talking about. I always stuff the enclosed space with polyester sound absorption in those circumstances.
Limiting the mach of airflow in the port is to prevent compression, however the problem of chuffing caused by turbulence usually manifests long before the airspeed approaches compression. Turbulence in the airflow is caused by sudden impedance changes and bends. No tuning port should ever have a bend in it, period. Sudden impedance changes can occur at the ends of the port tube. Flared ports ameliorate the sudden impedance change. Historically a lot of loudspeaker manufacturers have used PVC tube ports with radial arm saw cut ends. The sharp edges at the port ends cause premature delamination of airflow, and consequently turbulence and chuffing. Even a 1mm radius cut with a deburring tool will substantially reduce the chuffing of a butt ended port.
I can't say I have ever played with a horizontal T-M-T arrangement, and I probably wouldn't. Such an arrangement may result in severely comb-filtered high frequency responses either side of the horizontal axis of the center speaker, which is where most of the time everyone will be listening. I expect that comb-filtering will add a distinctive 'caste' to the sound of natural acoustic sources, although without the natural reference handy to listen to and compare with most listeners would not know.
Career wise from highschool I studied electrical and electronic engineering whilst employed to design studio mixing consoles and lighting dimmer controllers for an educational television studio, and then in the next job whilst still studying I designed electronic security and access control systems for hospitals, and installed tape recorder based language laboratories for schools. Then I worked as a live sound engineer, until promoted to Technical Manager - Sound for a large organisation responsible for ~15+ performance spaces, 25+ audio engineering staff, plus the audio engineering for cinemas, outdoor venues, and designing the sound for outdoor rock and opera concerts and national touring musicals. Then after a stint as Asset Manager for the same organisation, I was sent on a world tour of concert venues to investigate acoustics, and then project managed the electronic architecture installation for a multi-function 2000 seat auditorium to create variable acoustics to suit everything from conferences to rock concerts, opera and symphony orchestras. This system is basically a 3D surround system with ~205 distinct and different audio channels and 340 loudspeakers concealed around the auditorium. Then I was head-hunted by a national firm of consulting engineers and acousticians to represent them as their national electro-acoustic engineer, doing stadium designs and acoustic simulations using CATT acoustic software, the (very expensive) bee's knees at the time. Next I worked for a loudspeaker manufacturer designing professional and consumer loudspeaker systems, and designing and setting in place quality assurance procedures to minimise warranty claims, and while there designed a futuristic booth based entertainment and sound system for a space-ship concept restaurant in Sydney for the 2000 Olympics. Then I owned a hifi store and sold only the premium equipment that I would be prepared to buy and take home myself, which precludes an awful lot of what was (and still is) sold as hifi. During this period I designed the crew audio systems for a navy submarine during its refit, which became "type-cast" i.e. the standard for all submarines of that class, which resulted in a lucrative supply contract and a national award by the CES for best commercial installation in Australia that year. After that exercise I was again head-hunted by a consulting engineering company, this time focussing on virtual reality meeting room video conferencing systems, sound reinforcement in historic auditoria (concealed elements), and sports stadia and airport sound systems design, etc. When I'd had enough of that (a lot of which was due to the infiltration of professional audio with IP based technology), I retired, moved to an off-grid wilderness property on an island and, aside from lurking on DIYaudio, amuse myself with restoring and upgrading (mostly) pre-digital professional and consumer audio equipment for clients who care to find me and, of course, for myself. Thanks for asking.
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The reflex resonance and port resonance are actually two different things, and they are helpful in some situations otherwise people wouldn't build reflex boxes. Ringing (aka resonance) is something that closed boxes do too.
OMG John, I'm blown away by your knowledge/experience!! Aus. (and beyond) is certainly a better place for having you!
I though about lining the center channel speaker cavity to lower the resonance - not sure how it will look but a person has to decide on aesthetics or increased sound quality.
I could become an absolute nuisance to you picking your brain on so many things but I will post my queries as time goes on and hope you might input sometimes. Haven't been on this forum since I reached out for assistance on a crossover design for some Dynaudio drivers a few years back.
One more question if I could though about injecting a baffle step correction circuit to a 2-way speaker I designed for Vifa D27TG35-06 and P17WJ008 drivers (units made by ScanSpeak). Speaker baffle width would only be around 8 to 9 inches. Not sure if I want to loose so much speaker efficiency with the compensating coil/resistor in front of everything. I wonder if ultimate speaker placement near a wall would compensate to some degree to retrieve enough lost low frequency output due to boundary effects. Could be a long discussion...
I though about lining the center channel speaker cavity to lower the resonance - not sure how it will look but a person has to decide on aesthetics or increased sound quality.
I could become an absolute nuisance to you picking your brain on so many things but I will post my queries as time goes on and hope you might input sometimes. Haven't been on this forum since I reached out for assistance on a crossover design for some Dynaudio drivers a few years back.
One more question if I could though about injecting a baffle step correction circuit to a 2-way speaker I designed for Vifa D27TG35-06 and P17WJ008 drivers (units made by ScanSpeak). Speaker baffle width would only be around 8 to 9 inches. Not sure if I want to loose so much speaker efficiency with the compensating coil/resistor in front of everything. I wonder if ultimate speaker placement near a wall would compensate to some degree to retrieve enough lost low frequency output due to boundary effects. Could be a long discussion...
Baffle step compensation is probably best left to be discussed by others. FWIW if a loudspeaker is designed to meet what I consider desirable power response performance, the baffle step issue is irrelevant. This is because the human auditory system integrates sound energy over a few tens of milliseconds, and the total radiated power and how the room responds is what we hear, not merely the loudspeaker on-axis response. At the frequencies where baffle step anomalies occur, they are typically anomalies in directivity not power response, and therefore the room performance combined with human auditory processes will remove any perceived issues. Conversely if they don't, there is likely a system design problem. JMHO.
Re-read your response and see your daughter lives in Seattle but Tex has to put up with the Texas heat after all!
Thanks AllanB, I should have said "port determined system resonance" or something similar, but I think most people would understand the point I was making. Sure closed boxes have a system resonance too, but look at impulse responses to see where a reflex alignment differs from a sealed one, which explains why the former smears speech to a greater degree if the system resonance is high enough.
Tex has a good life in the company of two border collies and a cat in air conditioned comfort--and large back yard. He's certainly the sweetest dog I've known...except with squirrels, which he enjoys herding with the BCs.
Chris