Hi, I was browse through the threads the other day. Not sure if it was here or car audio, but I'm sure I saw a thread mentioning an LT type circuit for a Reflex box?
I reckon I might have been dreaming, and all I can remember was, I had to rush out, and closed the page by mistake. My History gets wiped at midnight every 2 days and it was the second day. So I couldn't tack down what I'd read, when I came to find it.
I'm sure someone posted a circuit too, I've searched and its bugging me, that I can't find it.
I can't afford to built every design there is, obviously, but just reading all the clever ideas out there is interesting, from like Graham Holoman's patent to Collaborative Tapped Horn. It all makes for great reading.
Can you help? Thanks
Mike 😕
I reckon I might have been dreaming, and all I can remember was, I had to rush out, and closed the page by mistake. My History gets wiped at midnight every 2 days and it was the second day. So I couldn't tack down what I'd read, when I came to find it.
I'm sure someone posted a circuit too, I've searched and its bugging me, that I can't find it.
I can't afford to built every design there is, obviously, but just reading all the clever ideas out there is interesting, from like Graham Holoman's patent to Collaborative Tapped Horn. It all makes for great reading.
Can you help? Thanks
Mike 😕
I don't know if there was a thread, but I suppose one could use the exact same circuit for a bass-reflex box. One would have to be careful, though, in the tuning of the vent.
For example, a solution with the vent tuned to 40 Hz, cannot be "transformed" to a 20 Hz lower cutoff by the circuit alone with any decent maximum output level. The tuning will need to be lowered to achieve this.
For example, a solution with the vent tuned to 40 Hz, cannot be "transformed" to a 20 Hz lower cutoff by the circuit alone with any decent maximum output level. The tuning will need to be lowered to achieve this.
Hello Svante
Interesting, so the benefits of reflex loading, could be retuned as well as a sealed box, giving a small reflex cab behaving like a bigger one. This leads to an obvious need, where size of box is important in a car for example. I got a small Hatch, and i use a 10inch driver in a reflex box, 40 litres if I remember, it doesn't leave much room for a pushchair and shopping bags.
I used a reflex, because of the driver's T/S. I tuned for about 27hz, don't know if I achieved that, but it does reach quite low with limited volume.
A Linkwitz Transform type of circuit would be useful, maybe I could get to 27hz with an even smaller box. An added benifit would be weight too.
Cheers, Mike🙂
Interesting, so the benefits of reflex loading, could be retuned as well as a sealed box, giving a small reflex cab behaving like a bigger one. This leads to an obvious need, where size of box is important in a car for example. I got a small Hatch, and i use a 10inch driver in a reflex box, 40 litres if I remember, it doesn't leave much room for a pushchair and shopping bags.
I used a reflex, because of the driver's T/S. I tuned for about 27hz, don't know if I achieved that, but it does reach quite low with limited volume.
A Linkwitz Transform type of circuit would be useful, maybe I could get to 27hz with an even smaller box. An added benifit would be weight too.
Cheers, Mike🙂
Svante said:
Greets!
FWIW, when I brought this subject up many years ago on the old basslist, John Murphy's response was to view the vented box as two cascaded 2nd order systems with each its own LRT wired in series since it didn't change the driver parameters in the way that would be required for it, suggesting using SPICE or similar to work it out.
WRT using a small vented cab, you can't get around the need for a longer vent that could negate a fair portion of the savings plus its harmonics may need damping, further reducing BW output, making you probably wish you'd just went LRT sealed to begin with. That said, it could be worth the effort if the cab is exceptionally large due to its T/S specs, which was why I was interested, but still haven't gotten around to pursuing it.
GM
Hi Mikee55
---Interesting, so the benefits of reflex loading, could be retuned as well as a sealed box, giving a small reflex cab behaving like a bigger one.---
Such schemes have been described by Jeff Macauley in Electronics World and by Bob Cordell.
---Interesting, so the benefits of reflex loading, could be retuned as well as a sealed box, giving a small reflex cab behaving like a bigger one.---
Such schemes have been described by Jeff Macauley in Electronics World and by Bob Cordell.
Well, the theory behind the closed box is that it behaves like a second order highpass filter. Such a filter has one "pole pair" which results in a f0 and a Q, and these two determine its behaviour. The Linkwitz transform adds "anti-poles" (zeroes) on top of the poles, which effectively cancels them, and adds a new pole pair at a lower frequency. The net result is that the original poles are replaced by a pair that is freely selectable.
The cost is that the amplifier has to deleiver extra power at the lower frequencies.
The bass-reflex box, on the other hand behaves like a fourth order highpass filter. A fourth order filter can be divided ito two second order filters. The Linkwitz transform can be used to modify one of these sections. In theory, two Linkwitz transforms could be cascaded to get full control of the response of the bass-reflex box, but I suppose that the limitations below the vent tuning will make this unnecessary. I guess that lowering the vent tuning and applying an ordinary Linkwitz transform will do the trick.
The cost is that the amplifier has to deleiver extra power at the lower frequencies.
The bass-reflex box, on the other hand behaves like a fourth order highpass filter. A fourth order filter can be divided ito two second order filters. The Linkwitz transform can be used to modify one of these sections. In theory, two Linkwitz transforms could be cascaded to get full control of the response of the bass-reflex box, but I suppose that the limitations below the vent tuning will make this unnecessary. I guess that lowering the vent tuning and applying an ordinary Linkwitz transform will do the trick.
The future is now
So, can todays Guru's come up with a workaround for the port length, or is this getting into T-Line territory/ big boxes? Is todays PC upto the simulations?
Another minus, the harmonics, could be electronicaly removed but could be complex, way out of my league. But there sure are a lot of clever guy's on this site. Just need to strike up interest, perhaps.
Any takers?, is it worth it?, even her indoors would approve WAF on the reduced size!
What do you think?🙂 😕
So, can todays Guru's come up with a workaround for the port length, or is this getting into T-Line territory/ big boxes? Is todays PC upto the simulations?
Another minus, the harmonics, could be electronicaly removed but could be complex, way out of my league. But there sure are a lot of clever guy's on this site. Just need to strike up interest, perhaps.
Any takers?, is it worth it?, even her indoors would approve WAF on the reduced size!
What do you think?🙂 😕
Hi Svante,
---The cost is that the amplifier has to deleiver extra power at the lower frequencies.---
I think there are some subtleties here.
Suppose a closed box of fc = 50 Hz and Qtc = 1.4 which is LR transformed to an apparent fc of 25 Hz with a Qtc = 0.7.
The initial response at 50 Hz with a Qtc = 1.4 was +3 dB. It is made almost flat with the LR transform. The required power at 50 Hz is then halved .
The initial response at 25 Hz with a Qtc = 1.4 was about -10 dB. It is made -3 dB with the LR transform. This required power for this new response will theorically need about 5 times more power.
However, statistically, the spectral distribution of has 12 dB less energy at 50 Hz than at 25 Hz. I think even peak levels at 25 Hz are very rarely as loud as at those at 50 hz.
This implies that the mean power required from the amplifier can often be curiously less with an LR transform than without.
---The cost is that the amplifier has to deleiver extra power at the lower frequencies.---
I think there are some subtleties here.
Suppose a closed box of fc = 50 Hz and Qtc = 1.4 which is LR transformed to an apparent fc of 25 Hz with a Qtc = 0.7.
The initial response at 50 Hz with a Qtc = 1.4 was +3 dB. It is made almost flat with the LR transform. The required power at 50 Hz is then halved .
The initial response at 25 Hz with a Qtc = 1.4 was about -10 dB. It is made -3 dB with the LR transform. This required power for this new response will theorically need about 5 times more power.
However, statistically, the spectral distribution of has 12 dB less energy at 50 Hz than at 25 Hz. I think even peak levels at 25 Hz are very rarely as loud as at those at 50 hz.
This implies that the mean power required from the amplifier can often be curiously less with an LR transform than without.
forr said:
Ah, yes for such a high Qtc there will be a peak that will have to be lowered, yes. Also, the since the maximum output level is typically limited by Xmax and not Pmax at low frequencies, it is perfectly ok to have some bass boost.
Hi,
I wonder if the original text was referring to a 5th or 6th order reflex box, but using a different name for it?
These higher order alignments can allow slightly lower bass to be played. However there main purpose is to allow higher SPL without overextending the Xmax limitation.
I wonder if this could be optimised to forego the higher SPL potential and substitute lower frequency bass?
I cheated and mass loaded the cones and retuned the box half an octave lower to get a similar effect without needing any extra power and it was able to play louder (at the very low frequencies) using the same Xmax limit.
I wonder if the original text was referring to a 5th or 6th order reflex box, but using a different name for it?
These higher order alignments can allow slightly lower bass to be played. However there main purpose is to allow higher SPL without overextending the Xmax limitation.
I wonder if this could be optimised to forego the higher SPL potential and substitute lower frequency bass?
I cheated and mass loaded the cones and retuned the box half an octave lower to get a similar effect without needing any extra power and it was able to play louder (at the very low frequencies) using the same Xmax limit.
Re: Hello again
Do I have to build it? 😀
Here is the default system in Basta! (black) with a lowered fh (blue) and a Linkwitz transform applied to it (red).
The green curve is an attempt at a 6th order system. See post below.
mikee55 said:
Do I have to build it? 😀
Here is the default system in Basta! (black) with a lowered fh (blue) and a Linkwitz transform applied to it (red).
The green curve is an attempt at a 6th order system. See post below.
An externally hosted image should be here but it was not working when we last tested it.
Mike the problem with making a small vented box and transforming it, is that it becomes extremely difficult to fit the vent into the box. It has to be very long because it has to be tuned low, but the box is small so often the longest dimension of the box is shorter than the vent length needed.
If you want a smaller sub in your car I would go sealed and maybe add a Transform.
If you want a smaller sub in your car I would go sealed and maybe add a Transform.
AndrewT said:
No. Or... Yes. My idea of a 6th order bass-reflex is to add a second order high-pass filter to an ordinary 4th order bass-reflex. A second order highpass filter has a pole pair at the cutoff frequency, and a pair of zeroes at 0 Hz. The Linkwitz transform has a pole pair at the lower frequency, but the 0 Hz zeroes are moved up to ~fc. This results in a sloping response (a bass lift) that is rather different from that of a highpass filter with a high Q.
Edit: I added the green curve in my picture above to show the difference.
richie00boy said:
Yes, indeed. I suppose that is why we don't see more of it. One could go for a passive radiator, though.
What is the objective here? To increase bass output in a small reflex loaded box?
The LT circuit spreadsheet needs input from a sealed enclosure design: Qtc and Fb. Qtc is a sealed box parameter - does it apply to a reflex box?
One of the biggest advantages of using the Linkwitz transform is that it allows you to use the driver below it's resonant peak (Fs). This is done by pushing the resonant peak up wards by using a sealed box of the correct volume for the driver.
Example: The driver has a Fs of 30Hz. Put it into a sealed box 50 litres. The resulting Fb is 60Hz. The system has a relatively flat impedance up to 60Hz, making it an easier load to drive.
Using an LT on a reflex enclosure is asking for excursion problems, as reflex boxes should not be driven below their Fb.
The LT circuit spreadsheet needs input from a sealed enclosure design: Qtc and Fb. Qtc is a sealed box parameter - does it apply to a reflex box?
One of the biggest advantages of using the Linkwitz transform is that it allows you to use the driver below it's resonant peak (Fs). This is done by pushing the resonant peak up wards by using a sealed box of the correct volume for the driver.
Example: The driver has a Fs of 30Hz. Put it into a sealed box 50 litres. The resulting Fb is 60Hz. The system has a relatively flat impedance up to 60Hz, making it an easier load to drive.
Using an LT on a reflex enclosure is asking for excursion problems, as reflex boxes should not be driven below their Fb.
Nice link, it's almost identical to what I've been doing for over 10 years and kept a bit of a secret 😀
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