This long open back seems an hybrid U-Framed variovent, though with less resistive than a variovent (aperiodic) if I sucess to follow ScottG.
Should result in a sligthy lower Fs and damped as shown but also less efficienty, rigth ? -18 dB slope. I assume we are talking of woofer-midrange driver first and if the Fs is lowered back under the Schroder frequency of the room : success reached ?
Assuming the first role is to reduce the residual box sound of the midrange (illustration: Statement Monitor and Statement 2 from Campbell/Holtz) by reducing the back bouncing that migth color the cone output, then assuming iso pression is the goal (?) , I wonder the difference between the variovent and the back damped tunel that furiously looks near a resistive aperiodic ? What is the Qtc of that ? Better dynamic and group delay behavior than a sealed box with final Qtc of 0.5 to 0.6 (midrange discussion in mind) ?
Should result in a sligthy lower Fs and damped as shown but also less efficienty, rigth ? -18 dB slope. I assume we are talking of woofer-midrange driver first and if the Fs is lowered back under the Schroder frequency of the room : success reached ?
Assuming the first role is to reduce the residual box sound of the midrange (illustration: Statement Monitor and Statement 2 from Campbell/Holtz) by reducing the back bouncing that migth color the cone output, then assuming iso pression is the goal (?) , I wonder the difference between the variovent and the back damped tunel that furiously looks near a resistive aperiodic ? What is the Qtc of that ? Better dynamic and group delay behavior than a sealed box with final Qtc of 0.5 to 0.6 (midrange discussion in mind) ?
why ? A tube that is open at the back looks like a U-Frame, no ? If you make it resistive at the back, it looks like a variovent, no ?
What is making little sense here, please explain ?
No one is talking about group delay behavior and Qtc equivalent : it makes sense for me !
I was also wondering if the resistive of the middle of the tube from ScottG has also an open circle at the output or has this resistive in the whole diameter at 1" of the tube output only ?
What is making little sense here, please explain ?
No one is talking about group delay behavior and Qtc equivalent : it makes sense for me !
I was also wondering if the resistive of the middle of the tube from ScottG has also an open circle at the output or has this resistive in the whole diameter at 1" of the tube output only ?
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Like an ML-TL resembles a BR cosmetically. They may look similar topologically but are quite different functionally.
And a Variovent is a crude way to try to make a loudspeaker aperiodic.
In a U-Frame you are balancing the resonance from the tunnel with the size of the box. The deeper the box the smaller the bandwidth.
If youadd a whack of damping to the back of a U-Frame you now have a Boffle. An aperiodic midTL is relatively longer (in relation to the loudspeaker system’s bandwidth) and damped even more. The idea is to remove the entire back wave.
dave
And a Variovent is a crude way to try to make a loudspeaker aperiodic.
In a U-Frame you are balancing the resonance from the tunnel with the size of the box. The deeper the box the smaller the bandwidth.
If youadd a whack of damping to the back of a U-Frame you now have a Boffle. An aperiodic midTL is relatively longer (in relation to the loudspeaker system’s bandwidth) and damped even more. The idea is to remove the entire back wave.
dave
Where stand those "vented" (i.e.: non sealed) designs about equivalent Qtc (sealed wording) ?
classic TL are said to give a bump (wanted or not) in the low end of the driver. Is it because they are bad designed ?
Is the spl magnitude a lot affected ? Or maybe of any or some help because to figth the scary baffle step area ?
At reading the thread, it almost looks like the sealed mid is the evil choice ?! Is there a loss of magnitude in the low end of the driver with that open back designs ?
classic TL are said to give a bump (wanted or not) in the low end of the driver. Is it because they are bad designed ?
Is the spl magnitude a lot affected ? Or maybe of any or some help because to figth the scary baffle step area ?
At reading the thread, it almost looks like the sealed mid is the evil choice ?! Is there a loss of magnitude in the low end of the driver with that open back designs ?
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To get a decent TL in the old days meant a lot of guessing and many prototypes, and still they are less likely to be optimum than modern designs.
dave
Software to develop proper TLs first showed up in 1999. Took a while to catch. Still a lot of “by guess” quarter-wave designs still happening.
dave
dave
I bump, please, my question about the "timing" behavior of the different midrange load discussed in that thread asked by @SoZo ... hoping it makes sense.
If it is relativly easy with a sealed to rule the Qtc when having the acurate T&S for choosing the Qtc -0.5 being transcient perfect and up to 0.6 giving excelent subjective result in that area according the litterature- , how about the different solution of the thread there ?
If I understood the first motivations, it is about to reduce the boxy sound behavior first, and at least better trade off checked ssubjectivly by ears.
Ho would you measure the transcient behavior of the different solutions and which would be the closest to a sealed 0.55 Qtc ? Measurement of the step response is the way ? I assume people wondered the same with open baffle designs and the beginning of an answer is the cone travels 4 times more with an open baffle than a critically damped sealed, rigth ? How that translates ? more IM, less transcients, all of that details not important VS the gain of less boxy sound ?
Don’t forget you will probably use some kind of highpass for the mid. So where does that leave Qtc (this is rhetoric of course).
That's basically just a long enclosure (with potential resonant behavior mostly depending on length and interior fill) with a resistive vent that when properly damped will be aperiodic.
Really, it's just another sealed (line) enclosure with an aperiodic vent.
Note: you can improve on that with layers of resistance at different intervals within the enclosure's line's length (not just having a single resistive vent on the end of the line/enclosure's rear). In fact you can "tune" a line-enclosure like this (with a LOT of effort of trial & error) to get a perfectly flat Impedance.
Gary Pimm did one of these for a woofer/sub once that was in a long'ish "rear-open" box with various resistive sections near the rear-opening. It was a great result below about 80 Hz.
Thanks Scott. I remember the longer a u-frame shape the more the chance of resonances when talking of bass subs. Curt Campbell also has given a formula for such open back tunels on P-E forum.
@markbakk : yep... I assume the high pass has to mimic that and that also the open resistive tunel is nearer from a big sealed with its low end 12 dB slope acoustical ? (rethoric I mean as I dunno)... that not give too much liberty for the electrical high pass filter: max 6db ? Well feasible with some midwoofers. Also purely theoric as I will try with two 5.25" NE-149W-08 in MTM layout (each driver with its own pipe so).
Ideally I would like not to have higher high pass for them than a 12 dB Bessel. But I am a noob, I am just at the beginning of that design, sorta of Statement II on steroids but only one bass driver (12PR320) : WMTM, with separated cabinets à la Andromeda Mezzo from HumbleHomeMadeHifi to give freedom to play with Z delay and driver changes (wood is expensive today) ! Ideally again passive, but I know wuld have to design with active to find the cut offs that works...
@markbakk : yep... I assume the high pass has to mimic that and that also the open resistive tunel is nearer from a big sealed with its low end 12 dB slope acoustical ? (rethoric I mean as I dunno)... that not give too much liberty for the electrical high pass filter: max 6db ? Well feasible with some midwoofers. Also purely theoric as I will try with two 5.25" NE-149W-08 in MTM layout (each driver with its own pipe so).
Ideally I would like not to have higher high pass for them than a 12 dB Bessel. But I am a noob, I am just at the beginning of that design, sorta of Statement II on steroids but only one bass driver (12PR320) : WMTM, with separated cabinets à la Andromeda Mezzo from HumbleHomeMadeHifi to give freedom to play with Z delay and driver changes (wood is expensive today) ! Ideally again passive, but I know wuld have to design with active to find the cut offs that works...
Port on a mid? You know that the acoustic phase is off kilter around port tuning?
I would only use ports on a large box where Fs is very loooowww.
there are indeed woofer drivers with low Fs enough used for midrange purpose with the high pass cut-off two or three octave above.
MJK’s article on teh H-frame does a really good job at the math. the deeper the tunnel the lower th eunwanted resonances and the more limited teh bandwidth becomes.
Scott’s comment on the sealed with an aperiodic vent neglects that the actual performance of these 2 styles of enclosure sis kinda different. ie look at the impedance response.
dave
Hello,
Let me say it again.
Sealed or vented the (mid-range) crossover will likely be above the resonance. There will normally be little or no difference.
maybe that helps for open back tunels : https://techtalk.parts-express.com/...n-back-midrange-speaker?p=1431394#post1431394
I have been reading through this thread with interest. I am a relative newcomer to speaker design but was under the impression that sealed was best for transient response and dynamics, at the expense of low freq extension.
Reading some of the above posts (particularly Dave's) it seems that MLTL might be better for transients/dynamics and also for clarity with the rear wave being neutralised? Have I interpreted this correctly?
I ask this because I am in the middle of a 3 way build where I am using a 15W4531G00 as a mid (250hz to 3Khz) in a sealed enclosure calculated for QTC of 0.707
As these are still in development cabs I can still try different things and was wondering if trying a MLTL enclosure for the mid would give a cleaner more dynamic sound?
Reading some of the above posts (particularly Dave's) it seems that MLTL might be better for transients/dynamics and also for clarity with the rear wave being neutralised? Have I interpreted this correctly?
I ask this because I am in the middle of a 3 way build where I am using a 15W4531G00 as a mid (250hz to 3Khz) in a sealed enclosure calculated for QTC of 0.707
As these are still in development cabs I can still try different things and was wondering if trying a MLTL enclosure for the mid would give a cleaner more dynamic sound?
For transcient perfect (if talking dynamic) in sealed you have to use 0.5 Qtc (critically damped) ; 0.6 Qtc is often chosen as good enough and so less big enclosure. 0.707 is maximum extended response you perhaps doesn't need for a mid and that particular driver if you have a bass driver below.