TB Speakers W8 - 740C Reviews
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Originally posted by I Heart Vinyls:
^ And you're the same guy that told me to put it in a 1+ cube box at 40. Now I have port noise.
^ And you're the same guy that told me to put it in a 1+ cube box at 40. Now I have port noise.
The point being what? A larger box will generally have LESS port noise for a given vent area. It is true that a lower tuning will also lower port velocity but there are tradeoffs.
I recall there being concessions based on port area in your design... I have a pair of 1cuft vented cabinets I used as bookshelves for my home stereo and they were nice and quiet. They have enough vent area though...
50 Watt CAFz'r
Joined: Oct 2003
Posts: 113
FWIW...
I've been playing with modeling these up..
I'm surprised at the comments implying a weak motor... per it's specs, it's got a BL of almost 14 (the bigger cone Adire Brahma's BL is about that), and it's Qes is 0.30! Particularly for an eight, those point to a strong motor.
And for a sub who's calculated EBP is so high...93.3 - that definitely simply screams "port me!" (and also doesn't imply a weak motor)
Now, if it's not capable of driving the cone to the limits of the suspension (and by that, I assume you mean Xmech or Xsus, and not Xmax? Assumption being that Xmax is driven by Xmag in this case?)...then possibly this indicates that this driver is close to an equi-hung type of motor, or at least one that wasn't overhung by very much?
Which would imply a very peaky BL curve...
So if it has a very peaky BL curve, maybe listening to it's attributes as a SQ driver aren't really the most appropriate application (certainly in a sealed box, it would make sense that it wouldn't shine).
Possibly, we need to test out an array of these mini-beasts as legitimate SPL drivers?
At any rate, if you wish to re-do your test with the subs in a ported box, I've got a flat, almost EBP-style response curve out of one in a 0.75 cu.ft. box tuned to 33hz. That seems to offer the best compromise, and it extends really low... hardly thinks about rolling off until 30hz.
But if an SPL test was more appropriate, maybe you could throw the little guy in something more like a 2 cu.ft. box tuned to 45hz, and burp away?(two 3" ports, each 7" long)
If the transient response really is as poor as you say.. maybe that's the best application for this little unknown. [img]graemlins/thumb.gif[/img]
I've been playing with modeling these up..
I'm surprised at the comments implying a weak motor... per it's specs, it's got a BL of almost 14 (the bigger cone Adire Brahma's BL is about that), and it's Qes is 0.30! Particularly for an eight, those point to a strong motor.
And for a sub who's calculated EBP is so high...93.3 - that definitely simply screams "port me!" (and also doesn't imply a weak motor)
Now, if it's not capable of driving the cone to the limits of the suspension (and by that, I assume you mean Xmech or Xsus, and not Xmax? Assumption being that Xmax is driven by Xmag in this case?)...then possibly this indicates that this driver is close to an equi-hung type of motor, or at least one that wasn't overhung by very much?
Which would imply a very peaky BL curve...
So if it has a very peaky BL curve, maybe listening to it's attributes as a SQ driver aren't really the most appropriate application (certainly in a sealed box, it would make sense that it wouldn't shine).
Possibly, we need to test out an array of these mini-beasts as legitimate SPL drivers?
At any rate, if you wish to re-do your test with the subs in a ported box, I've got a flat, almost EBP-style response curve out of one in a 0.75 cu.ft. box tuned to 33hz. That seems to offer the best compromise, and it extends really low... hardly thinks about rolling off until 30hz.
But if an SPL test was more appropriate, maybe you could throw the little guy in something more like a 2 cu.ft. box tuned to 45hz, and burp away?(two 3" ports, each 7" long)
If the transient response really is as poor as you say.. maybe that's the best application for this little unknown. [img]graemlins/thumb.gif[/img]
1000 Watt CAFz'r
Joined: Mar 2001
Posts: 1,626
geolemon - it can't be driven to the limits of it's physical suspension due to the fact that the bottom plate is bumped alot (15mm to be exact)
If somebody wants to build and send me a ported box or test it yourself it can be arranged.
Here are pictures I took of the driver:
http://images.cardomain.com/member_i...4_257_full.jpg
http://images.cardomain.com/member_i...4_258_full.jpg
http://images.cardomain.com/member_i...4_259_full.jpg
http://images.cardomain.com/member_i...4_260_full.jpg
http://images.cardomain.com/member_i...4_256_full.jpg
[ December 03, 2003, 11:28 PM: Message edited by: chaos ]
If somebody wants to build and send me a ported box or test it yourself it can be arranged.
Here are pictures I took of the driver:
http://images.cardomain.com/member_i...4_257_full.jpg
http://images.cardomain.com/member_i...4_258_full.jpg
http://images.cardomain.com/member_i...4_259_full.jpg
http://images.cardomain.com/member_i...4_260_full.jpg
http://images.cardomain.com/member_i...4_256_full.jpg
[ December 03, 2003, 11:28 PM: Message edited by: chaos ]
50 Watt CAFz'r
Joined: Oct 2003
Posts: 113
The bumped backplate doesn't have anything to do with the suspension's capabilities.
It can be a good means of pushing the Xmech out beyond Xsus - but that's only if the VC-former to back-plate clearance was the limiting Xmech factor.
Consider a subwoofer like Adire's Brahma...
You can't physically bottom the former out on the backplate... it's just too far away.
The hard-stop (Xmech) point rather is where the cone touches down on the spider landing (or rather, the outer roll of the tall spider).
And Xsus is reached really just before that happens (Xsus being a 400% increase in CMS, from it's "at rest" position... you can drive the sub past Xsus, but it gets dramatically more difficult with every additional mm...).
The need for a bumped backplate is also dependent on the voice coil geometry, along with the rear clearance. If this driver were underhung, it wouldn't need a bumped backplate, even with the same Xmag excursion numbers.
Based on Dave's observations, I would have guessed this overhung motor to be a bit closer to an "equihung" design, than to one that was exceptionally overhung (although his observations could be caused by other factors too).
You'd think though, that with the big bumped back-plate, that maybe it would actually be more overhung... but that's really taking a leap, these are probably all "stock parts".
I think my primary confusion might be in how I'm interpreting where he said "couldn't get it to reach it's suspension limits"...
Because that suspension doesn't look like it would be stretched (at least the half-roll.. can't see the spider too well) until it reached way more than 12mm...
Was it that he couldn't get the half-roll to the point where it looked stretched, or he couldn't get it to 12mm?
Big difference there, too.
I'm also responding partially in surprise..
There's a reputable professional audio engineer on CAF who is well experienced (and seems to have a good ear), who actually does have six of these little subwoofers, in a 4.5 cu.ft. box tuned to 34hz [which is more ideally suited to the subs] and he has basically completely different things to say in regard to the subwoofer's sound quality, and it's output levels.
So there's also the bit of sorting out as far as 'which of two very reputable, unbiased people do you trust, or is it a wash?'
It's no offense toward Dave M - but I'm leaning heavier on the other review simply due to the fact that Dave didn't evaluate it in an enclosure that was ideally suited to it's needs (even though I agree with his statement that the TR wouldn't be improved in a ported box).
It can be a good means of pushing the Xmech out beyond Xsus - but that's only if the VC-former to back-plate clearance was the limiting Xmech factor.
Consider a subwoofer like Adire's Brahma...
You can't physically bottom the former out on the backplate... it's just too far away.
The hard-stop (Xmech) point rather is where the cone touches down on the spider landing (or rather, the outer roll of the tall spider).
And Xsus is reached really just before that happens (Xsus being a 400% increase in CMS, from it's "at rest" position... you can drive the sub past Xsus, but it gets dramatically more difficult with every additional mm...).
The need for a bumped backplate is also dependent on the voice coil geometry, along with the rear clearance. If this driver were underhung, it wouldn't need a bumped backplate, even with the same Xmag excursion numbers.
Based on Dave's observations, I would have guessed this overhung motor to be a bit closer to an "equihung" design, than to one that was exceptionally overhung (although his observations could be caused by other factors too).
You'd think though, that with the big bumped back-plate, that maybe it would actually be more overhung... but that's really taking a leap, these are probably all "stock parts".
I think my primary confusion might be in how I'm interpreting where he said "couldn't get it to reach it's suspension limits"...
Because that suspension doesn't look like it would be stretched (at least the half-roll.. can't see the spider too well) until it reached way more than 12mm...
Was it that he couldn't get the half-roll to the point where it looked stretched, or he couldn't get it to 12mm?
Big difference there, too.
I'm also responding partially in surprise..
There's a reputable professional audio engineer on CAF who is well experienced (and seems to have a good ear), who actually does have six of these little subwoofers, in a 4.5 cu.ft. box tuned to 34hz [which is more ideally suited to the subs] and he has basically completely different things to say in regard to the subwoofer's sound quality, and it's output levels.
So there's also the bit of sorting out as far as 'which of two very reputable, unbiased people do you trust, or is it a wash?'
It's no offense toward Dave M - but I'm leaning heavier on the other review simply due to the fact that Dave didn't evaluate it in an enclosure that was ideally suited to it's needs (even though I agree with his statement that the TR wouldn't be improved in a ported box).
1000 Watt CAFz'r
Joined: Mar 2001
Posts: 1,626
Originally posted by geolemon:
Was it that he couldn't get the half-roll to the point where it looked stretched, or he couldn't get it to 12mm?
Big difference there, too.
Was it that he couldn't get the half-roll to the point where it looked stretched, or he couldn't get it to 12mm?
Big difference there, too.
http://images.cardomain.com/member_i...4_308_full.jpg
http://images.cardomain.com/member_i...4_309_full.jpg
http://images.cardomain.com/member_i...4_310_full.jpg
(Dustcap dented due to cat incident)
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