I went along and made some quick simulations in Hornresp to compare two different drivers, one with Qts > 0.4 and another with Qts < 0.4. I selected SEAS CA18RLY as the one > 0.4 and SEAS CA18RNX as the one < 0.4. I did this since they are available, from the same manufacturer (hopefully tested under the same conditions and with the same methods). They are also measured on Zaph Audios homepage if I would like to run measured values instead of the ones stated by the manufacturer.
I used different line length based on the reasoning above:
CA18RLY -> 42Hz-7Hz -> (340/(4*35))*0.6 -> 146cm/2 -> 73cm (folded)
CA18RNX -> 35Hz+7Hz -> (340/(4*42))*0.6 -> 121cm/2 -> 60cm (folded)
Folded line length determined the internal height of the enclosure and I went with an internal width of 30cm and an internal depth of 20cm (this makes the total volume a tad larger for the CA18RLY).
I will attach screenshots of Input Parameters, Schematic Diagram, Acoustical Power and Impulse Spectrogram from Hornresp for each speaker element (and configuration).
First out is CA18RLY in a MLTL like in my picture B.
I used different line length based on the reasoning above:
CA18RLY -> 42Hz-7Hz -> (340/(4*35))*0.6 -> 146cm/2 -> 73cm (folded)
CA18RNX -> 35Hz+7Hz -> (340/(4*42))*0.6 -> 121cm/2 -> 60cm (folded)
Folded line length determined the internal height of the enclosure and I went with an internal width of 30cm and an internal depth of 20cm (this makes the total volume a tad larger for the CA18RLY).
I will attach screenshots of Input Parameters, Schematic Diagram, Acoustical Power and Impulse Spectrogram from Hornresp for each speaker element (and configuration).
First out is CA18RLY in a MLTL like in my picture B.
Attachments
I then simulated the same drivers in a normal vented bass reflex configuration. I used WinISD to come up with a starting point for the tuning and I ended up tuning the box to 35Hz. I kept the box volume (32 liter) and slotted port (30x3 cm) from the original Silent Speaker (note the length of the slotted port I ended up with, 60 cm).
Here are the same set of screenshots for CA18RLY in this configuration (picture F).
Here are the same set of screenshots for CA18RLY in this configuration (picture F).
Attachments
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I also tried a MLTL configuration with a longer port (in this case 19 cm because that is what would fit with a 20 cm internal depth, 17 + 2), like my picture D. Here are screenshots for CA18RLY in this configuration.
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Thanks for your feedback!
I know but reducing the height is pushing the aspect ratio and I am afraid I loose efficiency. It would probably be better to reduce the width but it has to be done without ruining the visual appearance (maybe taper it?). A height of only 2 cm still leaves the length in the 40 cm region. It would be much easier with a circular port but I like the look of the slotted port on the Silent Speaker
Hi,
You won't lose efficiency. 30cm x 1.5cm is equivalent to a 7.5 cm diameter port.
For the P18RNXP (using Zaphs measured numbers, Qts=0.4, Fs=43Hz, Vas=22L) :
22L tuned to 35Hz looks pretty good (-3dB 50Hz, -6dB 35Hz, -10dB 28Hz)
The rounded bass roll-off won't sound like you typical vented flat box.
WinISD gives 30cmx1cmx22cm or 30cmx1.5cmx38cm for the vented port. *
If you go for the latter build it vertically into the front, and add some
spars into the port to give a double layer front baffle.
rgds, sreten.
* WinISD does not model slot ports against walls. The end corrections
are different for a slot near a floor outside and near a wall inside.
How much difference it makes, I'm not sure.
You won't lose efficiency. 30cm x 1.5cm is equivalent to a 7.5 cm diameter port.
For the P18RNXP (using Zaphs measured numbers, Qts=0.4, Fs=43Hz, Vas=22L) :
22L tuned to 35Hz looks pretty good (-3dB 50Hz, -6dB 35Hz, -10dB 28Hz)
The rounded bass roll-off won't sound like you typical vented flat box.
WinISD gives 30cmx1cmx22cm or 30cmx1.5cmx38cm for the vented port. *
If you go for the latter build it vertically into the front, and add some
spars into the port to give a double layer front baffle.
rgds, sreten.
* WinISD does not model slot ports against walls. The end corrections
are different for a slot near a floor outside and near a wall inside.
How much difference it makes, I'm not sure.
I have made loads of assumptions on my way to figure out the Silent Speaker. What I was most uncertain about was the line length and the "magical" 0.6 factor I used so far, so I started to browse for some facts. I think I found the last piece of the puzzle at the Brines Acoustics Quarter Wave Resonators page and in the paper Classic Transmission Line Enclosure Alignment Tables.
Working my way backwards from the 50Hz used (compared to a 1/4 wave length) I get the following factors per pipe geometry:
I now got enough (I think) to actually start and reverse engineer my way into a fused Silent Speaker & Heed Enigma design. I will probably use CA18RLY and a Negative Tapered Transmission Line as the basis for my calculations. I am still a bit uncertain of what tuning frequency to use though, 50, 42, 35?
Note: plug in the values based on the Silent Speaker in the Pipe Geometry Summary table and they pretty much correspond to a MLTL with a 50Hz tuning frequency. Only problem is the slot port that makes it look more like a -ve TL. It would be a tad taller according to the table if it was a -ve TL.
Working my way backwards from the 50Hz used (compared to a 1/4 wave length) I get the following factors per pipe geometry:
- Classic TL = 0.97
- Negative Tapered Transmission Line (-ve TL) = 0.71
- Tapered Quarter Wave Tube (TQWT) = 1.38
- Mass Loaded Tapered Quarter Wave Tube (ML-TQWT) = 0.89
- Mass Loaded Transmission Line (MLTL) = 0.57
I now got enough (I think) to actually start and reverse engineer my way into a fused Silent Speaker & Heed Enigma design. I will probably use CA18RLY and a Negative Tapered Transmission Line as the basis for my calculations. I am still a bit uncertain of what tuning frequency to use though, 50, 42, 35?
Note: plug in the values based on the Silent Speaker in the Pipe Geometry Summary table and they pretty much correspond to a MLTL with a 50Hz tuning frequency. Only problem is the slot port that makes it look more like a -ve TL. It would be a tad taller according to the table if it was a -ve TL.
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You are probably right but I just started to play with the idea of a full range instead of something like the CA18RLY and a tweeter. Extended bass response by the -ve TL and no XO. Experimenting is half the fun right? I could otherwise just by a pair of great sounding vintage speakers
Naaa, mid-range is just as overrated as tone controls and Loudness are underrated! Next stop a big fat Graphic Equalizer from the 80th...
Tapered TL model for CA18RLY
Just for kicks, I modeled a 12:1 tapered TL for the CA18RLY. The line is 60" long, has a starting area of 7.5"W x 15"D and an ending area of 7.5"W x 1.25"D, ending with a terminus also 7.5" x 1.25". The first 40" of the line is stuffed with polyester fiber at a density of 0.75 lb/ft3 (about 22 ounces of fiber total). The woofer's center is located 12" from the beginning of the line. I modeled with Zaph's T/S measurements and with 0.5 ohms added in series with the driver to replicate the effects of the resistance of a series crossover inductor (which raises Qts to 0.596). I've attached the predicted anechoic system bass response (red line) for an input of 2.83v/1m. The likely maximum safe output will be ~95 dB SPL from a 12-watt input. The system's tuning is 28-29 Hz.
Paul
Just for kicks, I modeled a 12:1 tapered TL for the CA18RLY. The line is 60" long, has a starting area of 7.5"W x 15"D and an ending area of 7.5"W x 1.25"D, ending with a terminus also 7.5" x 1.25". The first 40" of the line is stuffed with polyester fiber at a density of 0.75 lb/ft3 (about 22 ounces of fiber total). The woofer's center is located 12" from the beginning of the line. I modeled with Zaph's T/S measurements and with 0.5 ohms added in series with the driver to replicate the effects of the resistance of a series crossover inductor (which raises Qts to 0.596). I've attached the predicted anechoic system bass response (red line) for an input of 2.83v/1m. The likely maximum safe output will be ~95 dB SPL from a 12-watt input. The system's tuning is 28-29 Hz.
Paul
Attachments
Thanks a lot Paul! May I ask what you modeled it with and how you came up with the length, S0 and SL? I only got Hornresp for modelling and simulation of T-Line. I started to make some drawings today but my line was shorter, 140cm (55"). I used an S0=506cm2 (yours 722cm2) and SL=92cm2 (yours 57cm2). I just wanted to keep the enclosure as compact as possible (total volume 39liter) and I ended up around 43Hz in Hornresp (using the manufactures spec. not Zaphs).
Ps. I had my woofer almost centered on the line (because I imagined a folded line with an up-firing speaker), I used no stuffing or XO resistance...
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