Firstly, I'm aware of the even order distortion cancellation and vibration cancellation benefits of the push pull driver arrangement .
I'm pondering a "wide" bandwidth hybrid bass horn (such as a DJK ported la scala bass bin) to cover midbass down to at least the 2nd octave.
This type of horn typically has a single 12 or 15" pro bass driver firing into a split throat.
What if the single driver were substituted by a push pull manifold employing a pair of smaller but otherwise suitable drivers in order to derive the benefits mentioned above?
In this situation, I've heard anecdotal evidence of the drivers see-sawing and working against each other ( not sure if this is due to back emf or air pressure effects)? A single bass driver would obviously not exhibit these issues.
Thoughts, experiences? Would a series (vs parallel) connection help?
Thanks
I'm pondering a "wide" bandwidth hybrid bass horn (such as a DJK ported la scala bass bin) to cover midbass down to at least the 2nd octave.
This type of horn typically has a single 12 or 15" pro bass driver firing into a split throat.
What if the single driver were substituted by a push pull manifold employing a pair of smaller but otherwise suitable drivers in order to derive the benefits mentioned above?
In this situation, I've heard anecdotal evidence of the drivers see-sawing and working against each other ( not sure if this is due to back emf or air pressure effects)? A single bass driver would obviously not exhibit these issues.
Thoughts, experiences? Would a series (vs parallel) connection help?
Thanks
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"Firstly, I'm aware of the odd order distortion cancellation and vibration cancellation benefits of the push pull driver arrangement ."
Even order, not odd.
"What if the single driver were substituted by a push pull manifold employing a pair of smaller but otherwise suitable drivers in order to derive the benefits mentioned above?"
It sounds much better than the single driver.
"In this situation, I've heard anecdotal evidence of the drivers see-sawing and working against each other ( not sure if this is due to back emf or air pressure effects)? A single bass driver would obviously not exhibit these issues."
Sounds like made-up BS.
"Would a series (vs parallel) connection help?"
Shouldn't make much, if any difference. My LaScala, and the Bull-nosed horn use series-parallel conected quad 8's.
Even order, not odd.
"What if the single driver were substituted by a push pull manifold employing a pair of smaller but otherwise suitable drivers in order to derive the benefits mentioned above?"
It sounds much better than the single driver.
"In this situation, I've heard anecdotal evidence of the drivers see-sawing and working against each other ( not sure if this is due to back emf or air pressure effects)? A single bass driver would obviously not exhibit these issues."
Sounds like made-up BS.
"Would a series (vs parallel) connection help?"
Shouldn't make much, if any difference. My LaScala, and the Bull-nosed horn use series-parallel conected quad 8's.
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Ok, I have to ask - why is the midrange horn in that picture vented?
I'd wager that the vent is actually for the woofer rear chamber that happens to be connected to the midrange horn outer enclosure
@djk ,
Do you have a hornresp model for the hybrid lascala (or bullnose), or is there another method you use to derive the optimal port tuning?
Thx
Do you have a hornresp model for the hybrid lascala (or bullnose), or is there another method you use to derive the optimal port tuning?
Thx
1) That may work well, depending on the drivers used.
2) Drivers that have non symmetrical drive systems get the most benefit in even order distortion reduction from push pull mounting, but also are the type of driver most likely to "work against each other" when one is reversed. Many driver's suspensions and cones are not up to the tasks imposed in high compression horn loading, or even when used in a very small plenum (slot) volume.
3) No, drivers in series perform exactly like in parallel other than the impedance difference. The higher impedance does improve damping factor, which can have a very positive result, and make an audible improvement when very long (like over 100 feet) cable runs are used.
Many arenas now have such high ceilings that speaker cable runs for portable systems may have to be as much as 150 feet, and multi core speaker wire over 12 gauge starts getting so heavy that the chain motor lifts could be overloaded, or need a separate (expensive) motor just for a cable pick.
Decades ago Harry Witz of dB Sound (now with Clair Global) told me that the difference in sound when they changed their EV MTL4 (a quad slot load 18" bass reflex cabinet) cabinets with long cable runs from parallel 2 ohms operation to series parallel 8 ohms was quite significant. Even though the drivers were getting a lot less power at 8 ohms rather than 2 ohms, they sounded a lot punchier, so seemed louder than they did before rewiring. Being loud was quite important with most of dB's clients 😉.
Having already experienced the difference in "punch" with my own two ohm L4 quad manifold subs going from 15' of 12 gauge to 100' of the same, Harry's rewiring made perfect sense to me, though since I was in the process of selling off my company at the time he mentioned it, I never did rewire my system's 28 L4 cabinets.
http://www.diyaudio.com/forums/subwoofers/228342-please-critique-my-idea-3.html
http://www.diyaudio.com/forums/subwoofers/250032-old-school-horn-vs-modern-vented-box-8.html
I presently am using a pair of dual 15" Dayton PA385S-8 loaded PPSL bass reflex cabinets, although I am fairly pleased with their performance and small size, they have far more distortion than the single BC18SW115-4 loaded Keystone tapped horn subs recently sold as part of my "downsizing" campaign.
http://www.diyaudio.com/forums/subwoofers/255010-compact-2x15-ppsl-using-dayton-pa385-8-drivers.html
http://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers.html
Other than their much greater odd (and even) order distortion, and the fact that it takes four drivers and more power to get just a little louder than a single 18" Keystone, and that a pair of the compact subs weigh about 50 pounds more than the Keystone, and the Keystone goes a little lower, I am not too disappointed in their response. That said, I'll be sticking with B&C for my driver choice from now on.
Anyone interested in a pair of compact dual 15" PPSL Dayton PA385S-8 cabinets 🙂 ?
Art
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"Do you have a hornresp model for the hybrid lascala (or bullnose), or is there another method you use to derive the optimal port tuning?"
The Hornresp model did not give any idea as to what sounded the best.
On the LaScala I started out with a 31hz tuning, as it looked best in the computer models. Various listeners around the world noted that a 35hz tuning had better PRAT. There was virtually no difference in response, so the ear wins.
I have tried two different 8's. The SEAS have better bass (but is un-available now), the Silver Flute have better midrange (but the Qts is a too low for best bass). I may have to have a driver custom built for this purpose.
The Hornresp model did not give any idea as to what sounded the best.
On the LaScala I started out with a 31hz tuning, as it looked best in the computer models. Various listeners around the world noted that a 35hz tuning had better PRAT. There was virtually no difference in response, so the ear wins.
I have tried two different 8's. The SEAS have better bass (but is un-available now), the Silver Flute have better midrange (but the Qts is a too low for best bass). I may have to have a driver custom built for this purpose.
This stuff makes my head hurt...
So the increased damping factor improves the rising waveform at transients, in the same way that lower QTS means cone control (and therefore accurate waveform reproduction) is better?
If that makes any sense to anyone rather than just me in my head?? 😕
Adding half an ohm of series resistance to a 2 ohm cabinet is just going to detune the hell out of the alignment. A lot less effect with 8 ohms. And the amplifiers are probably better behaved and clip more cleanly at low frequency driving 8.5 ohms instead of 2.5.
You are correct in that a high damping factor improves transient response and more accurate waveform reproduction. A damping factor of over 20 is generally accepted as "high fidelity". With typical home stereo cable lengths and amps with high damping factors, the DF is usually much higher than 20, but with low impedance loads and long cable lengths, the DF can be well below 20 unless very large gauge cable is used.
The trend now is to locate amplifiers within speaker cabinets, eliminating DF issues, but trading them for voltage drop on peaks (unless very large gauge cable is used), the peak "brownouts" can result in premature clipping, probably even more objectionable than reduced DF.
The value of Qts is proportional to the energy stored, divided by the energy dissipated, and is defined at resonance (Fs).
Q is the inverse of the damping ratio.
Art
Fb (box tuning) remains exactly the same regardless of the speaker impedance, but a 25% series resistance will certainly lower the effective damping factor an amplifier can impart on the loudspeaker.
Thanks for the replies, all, on the damping factor questions 🙂
I seriously need to read up on it as it's still pretty unclear in my head and I can't visualise the mechanisms involved, which usually helps my understanding 🙁 lol
I am guessing that the "Damping Factor (400 Hz) >300 at 8Ω" stated within my CV5000's manual:
CV-5000 CERWIN VEGA HIGH PERFORMANCE PROFESSIONAL POWER AMPLIFIER (right hand side)
varies with frequency and resistance, as indicated above, but I am also guessing that it will pretty much be an unknown quantity unless I somehow measure it?!
I am such a noob 🙁 LoL
I seriously need to read up on it as it's still pretty unclear in my head and I can't visualise the mechanisms involved, which usually helps my understanding 🙁 lol
I am guessing that the "Damping Factor (400 Hz) >300 at 8Ω" stated within my CV5000's manual:
CV-5000 CERWIN VEGA HIGH PERFORMANCE PROFESSIONAL POWER AMPLIFIER (right hand side)
varies with frequency and resistance, as indicated above, but I am also guessing that it will pretty much be an unknown quantity unless I somehow measure it?!
I am such a noob 🙁 LoL
You can calculate damping factor for any frequency if you know the impedance of the loudspeaker, the resistance of the speaker cable and the DF of the amp.
This will sort you out:
http://www.bennettprescott.com/downloads/dampingfactor.pdf
sameness of mind
I've been pondering the same thing. I did actually have my ppsl midbass slot firing into a short "stub" horn for a while. It was not an ideal horn, had very thin walled flares, but it did some amazing things. I have re-built my ppsl enclosures to where the two drivers now share a common volume (which should have been done in the first place, but long story). The sad truth is I do not know how to use the "Horn response" program, but I do believe the ppsl common drivers can be termed "offset", but I admit to knowing very little.
In it's existing form, the ppsl is quite dynamic, but I have a feeling that being loaded in to a mid-bass sized horn would provide even more dynamics.
I don't need sub bass, as I have an infinite baffle sub woofer.
I've been pondering the same thing. I did actually have my ppsl midbass slot firing into a short "stub" horn for a while. It was not an ideal horn, had very thin walled flares, but it did some amazing things. I have re-built my ppsl enclosures to where the two drivers now share a common volume (which should have been done in the first place, but long story). The sad truth is I do not know how to use the "Horn response" program, but I do believe the ppsl common drivers can be termed "offset", but I admit to knowing very little.
In it's existing form, the ppsl is quite dynamic, but I have a feeling that being loaded in to a mid-bass sized horn would provide even more dynamics.
I don't need sub bass, as I have an infinite baffle sub woofer.
Attachments
Somewhat off-topic, but this thread reminds me of one of the "cleanest-sounding" builds I've ever done, which was a 4th order BP alignment driven by a pair of drivers in a clamshell isobaric arrangement. I'm guessing that the isobaric arrangement minimized the even order distortion and the odd-order distortion was filtered out by the vent as it would start somewhere above the system's passband. I'm guessing that a push-pull 4th order BP alignment might have the same advantages too....
Awesome, thank you very much 😎
I will print that out to take it home and digest it properly! 🙂
Thanks for all the info. Seems like PP (mid)bass horns are viable if the drivers can handle the abuse (should'nt be an issue for home SPL levels)
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