Hi,
I am starting to design new 3-way speakers with Scan Speak 26W/8534G00 woofer inside a box of about 76 liters.
I would like to increase the depth of the bass and therefore the simplest solutions that come to mind are two: bass reflex or passive radiator.
I have carried out simulations with the bass box that I have attached.
As you can easily see, opting for a simple bass reflex results in significantly higher performance than a passive radiator such as a Scan Speak 26W/0-00-00.
I also did some tests with the SB Acoustics SB29NRX2-00 and the result is more or less similar.
The best result is with dayton audio passive radiator:
If the simulation is correct from a sonic point of view there should be no reason to opt for a passive radiator also considering the non-negligible additional cost.
The reasons why they made me evaluate a passive radiator instead of the bass reflex are two:
1) The crossover is positioned on the bottom of the speaker, to access it I would have to position the woofer at the bottom and therefore far from the midrange and this is not positive. If I used a passive radiator I could position the woofer near the midrange and the passive radiator at the bottom so that I could access the crossover by removing the passive radiator instead of the woofer.
2) Aesthetic reasons, the front passive radiator is nice to look at.
Now I wonder from a predominantly sonic point of view could the passive radiator have advantages over the bass reflex? It seems to me not.
What do you think?
Update
I have corrected the Scan Speak 26W/8534G00 parameters and compared to Dayton Audio DSA315-PR.
much better now and is close to reflex. What you think ?
I am starting to design new 3-way speakers with Scan Speak 26W/8534G00 woofer inside a box of about 76 liters.
I would like to increase the depth of the bass and therefore the simplest solutions that come to mind are two: bass reflex or passive radiator.
I have carried out simulations with the bass box that I have attached.
As you can easily see, opting for a simple bass reflex results in significantly higher performance than a passive radiator such as a Scan Speak 26W/0-00-00.
I also did some tests with the SB Acoustics SB29NRX2-00 and the result is more or less similar.
The best result is with dayton audio passive radiator:
If the simulation is correct from a sonic point of view there should be no reason to opt for a passive radiator also considering the non-negligible additional cost.
The reasons why they made me evaluate a passive radiator instead of the bass reflex are two:
1) The crossover is positioned on the bottom of the speaker, to access it I would have to position the woofer at the bottom and therefore far from the midrange and this is not positive. If I used a passive radiator I could position the woofer near the midrange and the passive radiator at the bottom so that I could access the crossover by removing the passive radiator instead of the woofer.
2) Aesthetic reasons, the front passive radiator is nice to look at.
Now I wonder from a predominantly sonic point of view could the passive radiator have advantages over the bass reflex? It seems to me not.
What do you think?
Update
I have corrected the Scan Speak 26W/8534G00 parameters and compared to Dayton Audio DSA315-PR.
much better now and is close to reflex. What you think ?
Last edited:
The BR will emit out of band pipe resonance from the port that would not be a problem with a PR.
Depending on the Low/Mid crossover frequency, that may be a non-issue.
The Fb of the passive radiator is much lower than the bass reflex.
The BR is slightly oversized for it's Fb, the PR could use a smaller box for the same Fb.
In such a large box, there is not much of a sonic advantage for a PR.
If the PR does not have at least double the displacement of the driver, a BR has the output advantage.
always wondered if a bigger passive radiator can bring more efficiency like generously dimensioned reflex pipes do
small reflexes have losses when driven hard
small reflexes have losses when driven hard
Er -not sure where to start here, so this may be disjointed. But FWIW:
A passive bass radiator is generally used as an alternative to a regular vent when the latter's dimensions end up problematic -this can be particularly an issue with the modern tendency toward acoustically inefficient drive units, i.e. drivers that can be tuned to a low frequency an an acoustically small volume. Often, you find yourself faced with a situation where to keep the duct cross section reasonable (and the air velocity in it low), it needs to be unreasonably long, with self-harmonics becoming a problem, or you compromise on the vent cross section to avoid the issues with self-harmonics, and then end up with obviously excessive velocity in the duct. Of those, I tend to find the latter to be the lesser of the evils as you can always locate it on the rear of the box, which can help reduce any audible flow-noise. Be that as it may, PBRs can be a good solution in those cases -not exactly the same in alignment terms, & they have their own foibles, but you can usually get something usable, and no issues with self-harmonics or flow noise.
Turning to the above -those are somewhat different parameters to those that Scan publish (sorry, I don't have time to go through both), which I usually find to be accurate as they measure at a voltage similar to real-world usage conditions, rather than the low voltages many DIYers have to measure at. Using the values shown above though -if I'm honest, those don't look like great alignments to me. The closed box is stated as having a Qtc of 0.422 which assuming no external modifications (e.g. from a high output impedance valve amplifier like a SET type) is chronically overdamped: there's no value in a Qtc below 0.5. The vented box has a peaking alignment which with only a few exceptions I'd never recommend as you're likely to get an obvious 'one-note' booming from both that, and potentially from heavily triggered room modes. Lowering Fb to 23Hz or thereabouts with that same Vb should provide something a bit more usable in most situations. Like the sealed box, the PBR also looks to be heavily over-damped, though arguably the best of the three as-is. Try adding a second of the PBRs to your sim & see where you're at from there -most of the time, you need a larger PBR area than that of the main driver. Some exceptions, but it's a good quick 'getting started' ROT.
As for crossover etc. location -you might also want to think about alternate means of access. A detachable oversized plinth / base plate can be a good solution for e.g. if you want to mount the filter on the bottom panel.
A passive bass radiator is generally used as an alternative to a regular vent when the latter's dimensions end up problematic -this can be particularly an issue with the modern tendency toward acoustically inefficient drive units, i.e. drivers that can be tuned to a low frequency an an acoustically small volume. Often, you find yourself faced with a situation where to keep the duct cross section reasonable (and the air velocity in it low), it needs to be unreasonably long, with self-harmonics becoming a problem, or you compromise on the vent cross section to avoid the issues with self-harmonics, and then end up with obviously excessive velocity in the duct. Of those, I tend to find the latter to be the lesser of the evils as you can always locate it on the rear of the box, which can help reduce any audible flow-noise. Be that as it may, PBRs can be a good solution in those cases -not exactly the same in alignment terms, & they have their own foibles, but you can usually get something usable, and no issues with self-harmonics or flow noise.
Turning to the above -those are somewhat different parameters to those that Scan publish (sorry, I don't have time to go through both), which I usually find to be accurate as they measure at a voltage similar to real-world usage conditions, rather than the low voltages many DIYers have to measure at. Using the values shown above though -if I'm honest, those don't look like great alignments to me. The closed box is stated as having a Qtc of 0.422 which assuming no external modifications (e.g. from a high output impedance valve amplifier like a SET type) is chronically overdamped: there's no value in a Qtc below 0.5. The vented box has a peaking alignment which with only a few exceptions I'd never recommend as you're likely to get an obvious 'one-note' booming from both that, and potentially from heavily triggered room modes. Lowering Fb to 23Hz or thereabouts with that same Vb should provide something a bit more usable in most situations. Like the sealed box, the PBR also looks to be heavily over-damped, though arguably the best of the three as-is. Try adding a second of the PBRs to your sim & see where you're at from there -most of the time, you need a larger PBR area than that of the main driver. Some exceptions, but it's a good quick 'getting started' ROT.
As for crossover etc. location -you might also want to think about alternate means of access. A detachable oversized plinth / base plate can be a good solution for e.g. if you want to mount the filter on the bottom panel.
Thank you I have updated the post and corrected the wrong paramters and compared to Dayton Audio DSA315-PR. What you think ?
Quickly eyeballing the above, the sealed is a more usable, near Bessel alignment & with reduced leakage & damping should in practice see Qtc increase to somewhere in the mid 0.6 regions, whichcan be a decent compromise in many cases. The vented and passive radiator boxes are still what I'd personally call a poor alignment though -peaking around tuning can be useful with certain designs (the LS3/5a nearfield TV / radio broadcast monitor is a good example) but not generally in cases like this, with larger speakers -you'll generally get an obvious 'one-note' bass-heavy effect around that frequency, which may also tend to trigger more in the way of room modes.
FWIW, for a sealed alignment, I'd probably be inclined to look toward something with a Qtc in the mid 0.6 region -assuming light - modest damping & relatively minimal box leakage, that should be about 76 litres. Vented really wants a larger box: about 106 litres tuned to Fs would be a reasonable compromise between alignment & power-handling. Assuming the same volume & the same-size Scan passives, you'd need about 4 of the latter for what I'd call a decent alignment -which is a bit excessive, but if you're not cheating, you're not trying hard enough. 😉 With, say, a Dayton DSA270, then you'll be more or less maximally flat in the same volume and damping at the higher end of medium. Since that can end up triggering room modes if you're not careful, adding 20g of mass should damp that a bit.
FWIW, for a sealed alignment, I'd probably be inclined to look toward something with a Qtc in the mid 0.6 region -assuming light - modest damping & relatively minimal box leakage, that should be about 76 litres. Vented really wants a larger box: about 106 litres tuned to Fs would be a reasonable compromise between alignment & power-handling. Assuming the same volume & the same-size Scan passives, you'd need about 4 of the latter for what I'd call a decent alignment -which is a bit excessive, but if you're not cheating, you're not trying hard enough. 😉 With, say, a Dayton DSA270, then you'll be more or less maximally flat in the same volume and damping at the higher end of medium. Since that can end up triggering room modes if you're not careful, adding 20g of mass should damp that a bit.
Hello,
If we may. What does a sonic point of view mean?
Usually in this conversation frequency response comes up first. Most important? May be. Seems the simulation only addresses FR.
Delayed sound out of the port is a consideration. Does the delayed output from the port or passive radiator time smear the primary output from the woofer?
Passive Radiators and Bass Reflex leak out of bass band frequencies.
Which type of enclosure has the lowest measured harmonic distortion and modulation distortion?
My preference is to high pass filter the woofer input and go with a sub-woofer.
Thanks DT