To have equal displacement, the Sd (surface area of the driver) multiplied by excursion must be equal.
Around half the speaker's surround is "wasted area", not contributing much to Sd.
Regardless of driver diameter, the surround width must be near equal for a given excursion, so the smaller the driver diameter, the higher the ratio of "wasted area" to Sd.
Deep "U" shape surrounds can "cheat" in a bit more Sd, but may require a double spider to keep the coil centered, adding another expense that makes small, high displacement drivers less affordable.
Around half the speaker's surround is "wasted area", not contributing much to Sd.
Regardless of driver diameter, the surround width must be near equal for a given excursion, so the smaller the driver diameter, the higher the ratio of "wasted area" to Sd.
Deep "U" shape surrounds can "cheat" in a bit more Sd, but may require a double spider to keep the coil centered, adding another expense that makes small, high displacement drivers less affordable.
It's about volume displacement. In your example, each 4" driver must be able to match the excursion of the 8" driver.
Since that tends to be difficult to fit into a small chassis, we often see only a few mm of Xmax on a typical 4" driver. So, you'll need even more 4" drivers to make up that difference.
ie, 1x 8" with 9mm of Xmax will be matched by 12x 4" drivers each with 3mm of Xmax.
It's possible to get excellent bass from a couple of 4" drivers, but those drivers have to be carefully chosen, used in well-designed cabinets, and (importantly) given an amplifier capable of delivering quite a lot of power. The ones I've been messing with recently took everything a Cyrus Lyric (200w/ch IIRC) could give, and wanted more. Hoffman's Iron Law strikes again.
Chris
Silly old Iron Law from Wikipedia: Hofmann argued that the designer had "... three parameters that cannot all be had at the same time": good, deep low-frequency sound, a small cabinet size, and high sensitivity
Better Iron Law: .... unless you are clever.
Nobody is arguing about (1) the elementary physics of cone displacement volume or (2) the self-evident cost of 12 drivers at Parts Express compared to one driver. The problem is finding a little driver with a low enough resonance for quality bass and without having to EQ a speaker resonance located higher up in the music band.
Better Iron Law: .... unless you are clever.
Nobody is arguing about (1) the elementary physics of cone displacement volume or (2) the self-evident cost of 12 drivers at Parts Express compared to one driver. The problem is finding a little driver with a low enough resonance for quality bass and without having to EQ a speaker resonance located higher up in the music band.
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Would you mind mentioning which drivers those are? Not doubting, just curious. I am having a hard time picturing what driver that small could absorb that much power and not be bursting into flame...
A quad of these 4" drivers could be fed 200 watts.
W4-2089 - 4" PPM Subwoofer - TB SPEAKER CO., LTD.
Even with a quad, the sensitivity would still be very low - I'm guesstimating 83dB at 50Hz.
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IMO the best use of mini subs, in a "normal" system, would be to distribute the bass.
e.g. you have a single large sub that you wanted to run from 20-100Hz. No matter where you put it in the room, you measure a 20dB hole.
-->In position A, there is a hole around 50Hz.
-->In position B, there is a hole around 80Hz.
With only that one sub to work with, you'd need heroic room treatment or lots of EQ to smooth out that response.
...however, with a second (tiny) sub, you could position the main sub at (B) and the tiny sub at (A). Then you'd use the tiny sub (with a DSP) just to fill in the 80Hz hole.
The main sub, because it'd be running 2 octaves lower, would be doing the vast majority of the work.
W4-2089 - 4" PPM Subwoofer - TB SPEAKER CO., LTD.
Even with a quad, the sensitivity would still be very low - I'm guesstimating 83dB at 50Hz.
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IMO the best use of mini subs, in a "normal" system, would be to distribute the bass.
e.g. you have a single large sub that you wanted to run from 20-100Hz. No matter where you put it in the room, you measure a 20dB hole.
-->In position A, there is a hole around 50Hz.
-->In position B, there is a hole around 80Hz.
With only that one sub to work with, you'd need heroic room treatment or lots of EQ to smooth out that response.
...however, with a second (tiny) sub, you could position the main sub at (B) and the tiny sub at (A). Then you'd use the tiny sub (with a DSP) just to fill in the 80Hz hole.
The main sub, because it'd be running 2 octaves lower, would be doing the vast majority of the work.
I was just fooling around this evening with a Ciare HWG130-4 that I want to use for a future mini subwoofer project, beautiful build quality, and even just using it's cardboard package as ridiculous makeshift enclosure, it's got remarkable clarity and slam for a driver of it's size. If the mfg. specs are accurate, it's also way more efficient than similar size Tang Band drivers
A really nice set of specs, with 31 Hz resonance, strong Bl, light weight cone, etc, is Accuton C158-6-851.
You can buy a set of 12 from Madisound for about us$4,000 (10% quantity discount available).
Accuton C158-6-851 6.25" Ceramic Cone Mid/Bass from Madisound
You can buy a set of 12 from Madisound for about us$4,000 (10% quantity discount available).
Accuton C158-6-851 6.25" Ceramic Cone Mid/Bass from Madisound
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Look at the Ciare HSG 160 and 200
nice low Qts, pretty low FS, good sensitivity, good power handling, able to work in pretty small enclosures, not discount-rate priced, but not off the charts expensive, either
Ciare HSG160 - 6.5" Subwoofer
Product – Ciare
Ciare HSG200 - 8" Subwoofer
Product – Ciare
I have no connection with Ciare, I just stumbled across the product/company and bought the HWG-130 for my mini subwoofer project and am very impressed with the HWG130
nice low Qts, pretty low FS, good sensitivity, good power handling, able to work in pretty small enclosures, not discount-rate priced, but not off the charts expensive, either
Ciare HSG160 - 6.5" Subwoofer
Product – Ciare
Ciare HSG200 - 8" Subwoofer
Product – Ciare
I have no connection with Ciare, I just stumbled across the product/company and bought the HWG-130 for my mini subwoofer project and am very impressed with the HWG130
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Low qts means strong motor relative to cone size/mass and often stiffer suspension. Doesn't mean it suits the intended application or even that it's high quality. A cheap PA woofer can have very low QTS. In a subwoofer, low qts means big box and almost always ported. Arguable if that's always the best option for a sub. A higher qts sealed system may produce better results for someone. Low qts is also easier to achieve with a smaller magnetic gap and coil vs an underhung motor.
Using small drivers with low qts will mean a big box for sure with limited low end. Seems pointless for a subwoofer using small drivers, may as well use a larger driver more suited to the purpose.
As a mid bass, it's a different argument.
Using small drivers with low qts will mean a big box for sure with limited low end. Seems pointless for a subwoofer using small drivers, may as well use a larger driver more suited to the purpose.
As a mid bass, it's a different argument.
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It was the Kartesian Sub120 Ferrite. Part of a 2-way speaker with an SB65. Can't remember where the crossover was exactly, but probably in the 4-800Hz octave.
Those speakers (as complete 2-way boxes) were on the receiving end of the Cyrus amp. Remember - the amp ran out of headroom at the peaks, but the long-term average power delivery was within tolerance for these drivers.
I'd estimate the 1w sensitivity of these speakers to be in the region of 77dB@1w. But hey, they're pretty much flat down to the mid-30s and they're each the size of a shoebox.
Going back to Hoffman's Iron law for a moment, these particular drivers represent the biggest compromise to efficiency in the name of small enclosures and extended LF response that I've ever seen. It's interesting to see what's at the edge.
Chris
Thanks- I'd not heard of that driver before, looks very interesting. I searched a bit and saw your mention in other discussions of it having a 'rattle' - did you get that resolved (and if so, was the product revised, or is there some aspect of 'how to use' that avoids the rattle). Thanks
I, er, manually revised the drivers I had on-hand. Made some holes where I thought the air was trapped, and it seemed to help.
I did send a few emails around to the supplier, manufacturer, etc, but was only told to get an RMA number and send them in. Didn't bother - I wanted to play with my new toys!
FWIW, the neodymium version of that subwoofer has extensive ventilation, but isn't available to DIYers for reasons unknown.
Chris
I did send a few emails around to the supplier, manufacturer, etc, but was only told to get an RMA number and send them in. Didn't bother - I wanted to play with my new toys!
FWIW, the neodymium version of that subwoofer has extensive ventilation, but isn't available to DIYers for reasons unknown.
Chris