Hi JAG,
Post #2359: "...These few inches of extra path length will amount to maybe 1 hz lower tuning, if that. As the measurement above shows, these two designs are already quite similar."
I agree, the main difference is in the "cone correction", and the quantity and quality of the bracing, even the mouth segment has bracing through the side rails, and the grill mounting frame.
Regards,
Post #2359: "...These few inches of extra path length will amount to maybe 1 hz lower tuning, if that. As the measurement above shows, these two designs are already quite similar."
I agree, the main difference is in the "cone correction", and the quantity and quality of the bracing, even the mouth segment has bracing through the side rails, and the grill mounting frame.
Regards,
Hi Djim,
Post #2364: "...technically speaking the horn-path starts at S2 and not at S1."
It looks like the driver is pressurizing in both directions equally, towards S1 and towards S3. So could one say the horn path starts in the middle of the driver? That would help w/ the upper frequency response.
Regards,
Post #2364: "...technically speaking the horn-path starts at S2 and not at S1."
It looks like the driver is pressurizing in both directions equally, towards S1 and towards S3. So could one say the horn path starts in the middle of the driver? That would help w/ the upper frequency response.
Regards,
Hi Oliver,
I'm not sure the pressure is really equal (a small difference doesn't matter that much for a driver like the 18SW118), but you are right, S2 as starting point will help w/ the upper frequency. But there is still that volume between S1 and S2 and its effect on the response... ;-)
Regards,
Djim
I'm not sure the pressure is really equal (a small difference doesn't matter that much for a driver like the 18SW118), but you are right, S2 as starting point will help w/ the upper frequency. But there is still that volume between S1 and S2 and its effect on the response... ;-)
Regards,
Djim
The great "mystery" of the TH118 is illustrated in its published impedance curve. It shows a lower resonance point that is below 30 Hz. The TH18's resonance point in a similar-sized box is at or above 35 Hz. The tweaks that have been discussed here are not going to cause the almost 25% decrease in the resonance frequency that would be required for the impedance curve of the TH18 to be similar to that of the TH118.
The low impedance peaks in the TH118's impedance curve suggested to me that perhaps the horn's path is damped at some point (this would reduce the resonance frequency and drop the height of the impedance peaks). However, any damping required to cause a 20~25% drop in the resonance frequency should also cause a noticeable and measureable change in the TH's efficiency and upper frequency response, and that does not seem to be the case, going by the published FR for the TH118.
I'd really love to see a measured impedance curve for the TH118, to see if it really matches the published curve. Marketing may be tempted to fudge an FR curve, but there are few reasons that I can think of to fudge an impedance curve for a subwoofer....
Hi Brian,
There is a clear reference for the response, "outdoors 28.3V@10m ½ space".
However, "Anywhere on earth" is only a reference from IEEE 802.16 and is called 'Howland Island', some dot in the middle of the pacific ocean
Somehow it is hard to believe DSL is referring to that place, or even outdoors....
Regards,
Djim
There is a clear reference for the response, "outdoors 28.3V@10m ½ space".
However, "Anywhere on earth" is only a reference from IEEE 802.16 and is called 'Howland Island', some dot in the middle of the pacific ocean
Somehow it is hard to believe DSL is referring to that place, or even outdoors....
Regards,
Djim
One impedance curve is just one impedance curve. I don't understand the craziness about how accurately the xoc1 design 'should' sim the Danley TH118. IMHO the Xoc1 Th18 deserves his own rightful place in the TH universe.
If you want to be a purist, you can say that somebody took the design of Robert.G. Pruden and flipped the driver... Who knows!
The point I am trying to make is at some time the evolution of the TH designs come to a level where a certain design flow makes the most sense.
If you want to be a purist, you can say that somebody took the design of Robert.G. Pruden and flipped the driver... Who knows!
The point I am trying to make is at some time the evolution of the TH designs come to a level where a certain design flow makes the most sense.
fwiw
cone area+18mm+18mm=366cm2(am i correct seeing 2 sheets wood?)
looking at the measurements between the 2,they look pretty simular.
to me there is no magic thing happening in the th118.
one has a path lengt few inches longer,the other a troath chamber, wich results in simular low end.
is there an impedance curve from th18 some where?
I thought the top-end of the frequency response was radiated pretty much entirely by the magnet-side of the driver in a tapped horn. If that's the case, a couple of dB's worth of damping at ~100Hz at the cone side is unlikely to do much to the frequency response of the TH in its useful bandwidth, but I'd expect it to absorb some of the top-end mush bouncing around inside the horn.
That'd lower distortion and smooth the out-of-band peaks, too.
Chris
I thought so too, but apparently adding enough stuffing to shift the resonance frequency noticeably downwards also impacts the performance in the passband as well, at least in the HornResp sims. Which, when you think about it again, does make sense, seeing that a TH is basically a 1/4 wave resonator that's sized in such a way to obtain a good passband performance.
Oh, I agree, the TH18 design stands on its own merit. It's just curious when you have to boxes the same size, the same type of alignment (TH), the same basic layout, very similar low frequency performance in terms of bandwidth and efficiency, but one demonstrates a lower resonance frequency that's 20~25% lower than the other. Curious people like me would like to know why
.
I have no issues with the published FR and the process specified to obtain it as indicated in the brochure. It's an industry-standard method of obtaining the FR of a bass horn at a drive level that's slightly more reflective of real-world use than a 1W (or 2.83V) test. Of course, if the response graph is subjected to 1/3 octave or less smoothing...
No, at all frequencies the dominant output is coming from the throat side tap.
In a tapped horn the mouth side tap is only there to fill in a natural harmonic dip in response.
Here's a random tapped horn.
An externally hosted image should be here but it was not working when we last tested it.
Now here's that same enclosure but the driver is mounted on the outside, making it an offset driver transmission line. Nothing has changed except the driver mounting location. See the harmonic dip that is natural in transmission lines? That's what the tapped horn aims to fix.
An externally hosted image should be here but it was not working when we last tested it.
Now here's the response of the same tl with different driver locations - this is showing the horn output only, not looking at the driver side output.
An externally hosted image should be here but it was not working when we last tested it.
You can see that a driver mounted near the end of a transmission line does not do much of anything except some harmonic spikes of energy. These random spikes are sufficient to fill in the naturally occurring harmonic dip in response that tls have but it doesn't do much more than that. At all frequencies the throat side tap is dominant in a tapped horn, the mouth side tap is just there to fill in a hole in response.
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In addition of the drivers analysis I was checking the sketches available with the cone correction and the major parts was not detailed or they changed other dimension like the cab width and so on. Due to that I decided to keep the dimensions closest as possible to the original Xoc1 proposal and just add the cone correction, but my skills still not aligned with your. Do you guys think it worth a try?
Gray = original dimensions
Blue = changes to add cone correction
Gray = original dimensions
Blue = changes to add cone correction
An externally hosted image should be here but it was not working when we last tested it.
Hi Brian,
Sorry Brian if I wasn't clear enough but I was referring to the so called 'reference' of the Impedance that says, "Anywhere on Earth", what can mean anything.
Since it can mean anything, while the graph doesn't seem to correspond with the Frequency response, you can exclude a 'normal' 1/2 space situation.
Regards,
Djim
Sorry Brian if I wasn't clear enough but I was referring to the so called 'reference' of the Impedance that says, "Anywhere on Earth", what can mean anything.
Since it can mean anything, while the graph doesn't seem to correspond with the Frequency response, you can exclude a 'normal' 1/2 space situation.
Regards,
Djim
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1) Have you compared simulations of various drivers in the XOC1 TH18, and do all have identical impedance curve lower resonance point?
2) Although Tom has used damping in some DSL TH, he does not in the TH118.
3)The published DSL TH118 curves are from a measurement using an 18Sound driver that was used for just a short period of time before DSL transitioned to the B&C18SW115-4. DSL has still not published measurements with the B&C18SW115-4, but according to Ivan, the differences in FR were minimal, though I never asked him about impedance differences.
Art
The lower resonance point is a function of the horn's geometry, not the driver used in it.
Using a different driver will impact the magnitude of the impedance peaks. However the driver would have to have a pretty low Qms (or the box would have to be pretty lossy) to achieve the results shown in the TH118's impedance curve.