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New Peerless STW350 subwoofer on the horizon...
New Peerless STW350 subwoofer on the horizon...
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Old 18th July 2017, 08:37 PM   #21
badman is offline badman  United States
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Quote:
Originally Posted by gbullimore View Post
If you just weaken the motor you have low BL and very low sensitivity.
For a 15" driver with such a low FS and VAS you need a very high Mms which means a strong motor is needed to give reasonable sensitivity.
No offense but it's clear you're not aware of how driver parameters are inter-related.

Hoffman's iron law- you can have 2 out of three: Deep bass, Efficiency, Small Box.

Car audio drivers are easy to design to optimize the first and third.
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Old 19th July 2017, 08:51 AM   #22
gbullimore is offline gbullimore  United Kingdom
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no offence taken, i know my way round transducer design quite well...

in general you have to make space/eff/bandwidth compromises. but there are ways to improve over the current performance level available in the market,

and you are indeed making my point for me, many woofers (especially aftermarket Automotive) have low Fs and Low Vas but are woefully inefficient,
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Old 19th July 2017, 03:11 PM   #23
Josh Ricci is offline Josh Ricci  United States
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Quote:
Originally Posted by gbullimore View Post
many woofers (especially aftermarket Automotive) have low Fs and Low Vas but are woefully inefficient,
This driver also falls into that category as well. Look at the sensitivity rating. The N0 is <0.19%.

I'm not saying it isn't a good driver. It's on my short list of drivers I'd like to test. The areas where it looks like it should excel are linear displacement, inductance, deep bass distortion and power handling. Efficiency and output headroom outside of the deep bass range are not its strong suit though.

You may be surprised what a large increase in the motor force can do to a drivers real world performance.
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Old 19th July 2017, 03:50 PM   #24
gbullimore is offline gbullimore  United Kingdom
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you're forgetting that N0 is calculated based on mid band efficiency, and is a product of Fs, Vas and Qe, it has no relation to actual in use efficiency of a subwoofer.

Ideally there needs to be a new standard to define a single figure efficiency of subwoofers,
most people struggle to grasp multiple parameters to describe subwoofer performance.

this driver is a high end subwoofer, the performance above ~100hz is irrelevant, as is the mid band efficiency (N0 or dB/1w etc.)

I understand totally what a large increase in motor force can do for real world performance,
if a stronger motor would benefit the driver, it would have one..
as it is, the only way a stronger motor would be of benefit would be if the cone area was increased (18" driver), or the Moving mass increase to tune better in an even smaller box,
but a 15" driver that works in 60L is small enough, any smaller and you'd struggle to physically fit the driver in the cabinet!
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Old 19th July 2017, 05:15 PM   #25
Josh Ricci is offline Josh Ricci  United States
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Quote:
Originally Posted by gbullimore View Post
you're forgetting that N0 is calculated based on mid band efficiency, and is a product of Fs, Vas and Qe, it has no relation to actual in use efficiency of a subwoofer.

this driver is a high end subwoofer, the performance above ~100hz is irrelevant, as is the mid band efficiency (N0 or dB/1w etc.)
I am not forgetting. That may be but reference efficiency still has some correlation with the overall efficiency in the bass range as well.

What IS relevant is the performance from 40-120Hz which is the lions share of most of the bass content in media. This is the range being discussed on my end. This driver is neither efficient or sensitive over this range. That is my point. It's overall a lower efficiency driver.



Quote:
Originally Posted by gbullimore View Post
I understand totally what a large increase in motor force can do for real world performance,
if a stronger motor would benefit the driver, it would have one..
as it is, the only way a stronger motor would be of benefit would be if the cone area was increased (18" driver), or the Moving mass increase to tune better in an even smaller box,
but a 15" driver that works in 60L is small enough, any smaller and you'd struggle to physically fit the driver in the cabinet!
We will have to disagree here on a number of points. My opinions on transducer & speaker design and optimization are quite different from the long held traditional views based on F3, constant voltage response shape and small signals.

Out of curiosity are you affiliated with Tymphany? Do you work in the industry?
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Old 20th July 2017, 07:39 AM   #26
gbullimore is offline gbullimore  United Kingdom
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I do indeed work in the transducer design industry,

it seems you're confident on the performance of this driver having never tested it or simulated in cabinet,

during real life testing we found that this driver beat competing drivers by 12dB at 30Hz, for the same power,
SPL in cabinet, at subwoofer frequencies are significantly higher than similar sized subwoofers (or larger), that is higher than usual efficiency in my book.
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Old 20th July 2017, 02:27 PM   #27
Josh Ricci is offline Josh Ricci  United States
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Quote:
Originally Posted by gbullimore View Post
I do indeed work in the transducer design industry,

it seems you're confident on the performance of this driver having never tested it or simulated in cabinet,
I thought you might.

Why do you make this assumption? Why would I not have run some sims with this driver? On top of the factory information there is 3rd party data on systems using this driver and other data that is not public.


Quote:
Originally Posted by gbullimore View Post
during real life testing we found that this driver beat competing drivers by 12dB at 30Hz, for the same power,
SPL in cabinet, at subwoofer frequencies are significantly higher than similar sized subwoofers (or larger), that is higher than usual efficiency in my book.
Did they have comparable SD and Xmax? A 12dB efficiency difference is big. The most obvious explanation for such a difference is that one system was near it's impedance maximum at 30Hz and the other had a much different impedance curve with the peak well away from 30Hz placing the efficiency maximum in a different range. This is why I never try to look at efficiency at a single frequency. It always favors one system over another.

The STW-350 has a maximum efficiency of around 1.3% in a very small sealed enclosure. In a larger sealed cab for maximum 30Hz efficiency it should be <1%. 12dB less than 1% is about 0.06%.

Let me reiterate I'm in no way saying this is not a good driver. I'm not bashing on it. All I said is I would be more interested in it with a stronger NdFeb based motor.
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Old 21st July 2017, 05:37 AM   #28
Tranquility Bass is offline Tranquility Bass  Australia
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New Peerless STW350 subwoofer on the horizon...
Xmax=10.5 mm ??

Is that a misprint or design failure ?

cheers
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Old 21st July 2017, 05:41 AM   #29
Quard is offline Quard  United States
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what's wrong with is what it is?

I don't know enough to answer, just asking,
mebbe someone who comes this way knows;

Quard
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Old 21st July 2017, 08:08 AM   #30
gbullimore is offline gbullimore  United Kingdom
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Quote:
Originally Posted by Tranquility Bass View Post
Xmax=10.5 mm ??

Is that a misprint or design failure ?

cheers
it's Neither,
remember that Xmax is not the limit of linear excursion, it is unrelated to the ability or performance of a driver at that excursion,

it's merely the length that the VC winding width overhangs the to plate of the driver, i wish we could replace this parameter!

be very aware many manufacturers 'interpret' the measurement of xmax in different ways,
for some reason the pro manufacturers use VC overhang + 1/2 or 1/3 of the gap height, there is no justifiable reason for that!
some other companies use Peak to peak values for the bigger numbers,
some use arbitrary calculation methods, i've even seen maximum peak to peak mechanical excursion limit published as Xmax!

you can only get an idea of the performance by considering the Xmax (VC overhang) and gap height,

a) imagine a VC 20mm long and a 1mm gap height, the maximum excursion must be limited to 9.5mm, and published Xmax is 9.5mm
b) for the same 20mm VC and a 18mm gap height the maximum excursion is 18mm, yes the published Xmax is only 1mm
the subject is much more complex than this basic calculation, but typically for a subwoofer a long gap is very advantageous even though it reduces the published xmax.

the driver being discussed has a very long gap, hence the low published Xmax,
it will however have very low distortion and very large excursion capability,

a good rule of thumb is to look at the VC overhang, and also look at the displacement where 1mm of VC ramains int he gap,
using the example above this gives,
a) 9.5 and 9.5
b) 1.0 and 18.0

just fyi, i'd choose driver (a) as a midrange (less than 5mm excursion)
and i'd choose driver (b) as a woofer or subwoofer (as it would have higher excursion)
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