That depends on the size of your H-frame. If it's too shallow to be of any use, of course you can say so; but if the H-frame is deep enough, it will give more output than dual baffle-less woofer.
The maths is easy: Dual baffle-less woofer means a 6dB hike in efficiency (assuming you're connecting the woofers in parallel) when compared to a single baffle-less woofer. If your H-frame is deep, the roll off occurs lower than a baffle-less woofer. Try to come back with some workable figures before anyone can give you a more definite answer, I would say.
Olle,
let's pretend we have a 12" driver and a 18" driver, both with the same Xmax excursion. The 12" driver in a tight H frame with an upper limit of 300 Hz should be no deeper than 20 cm (per frame side). This combination would have roughly the same max output as the naked 18".
Ah.
How many % larger (same Xmax of course) would a naked driver to have roughly twice the max output as the smaller one?
I don't understand why people use expensive low Q drivers on open baffle. you paid BIG $$ for the strong motor, which needs to be horn or at least bass reflex loaed.
If I needed full range driver for free air use, I'd look no further than this one 8" Full-Range Ceiling Speaker.
If I needed full range driver for free air use, I'd look no further than this one 8" Full-Range Ceiling Speaker.
"Thinking out of the box" is a universal theme to be applied here 😀
It is a common misconception that low Qts pro drivers are wasted on OB / SB (sans baffle) because of the low Qts.
The problems are to find one which has the right compliance, stroke and resonance, because those you cannot change and they are more critical, while Qes and thus Qts only affect damping and can be changed by the user -- in rare cases you might want to increase the LF output impedance to get less damping with some tricks, but high damping works in favor of linearity when the motor is linear because the non-linear effects of the compliance etc are overrun more by the stronger damping (which is local feedback from the voice coil induced voltage), and this is the main asset of low Q vs high Q.
By changing Qes one can effectively fine tune linearity, drift/offset behaviour and overload recovery, but using straight voltage drive from normal amps is not changing things significantly... at higher freqs some series impedance in front of the driver is more important and needed/useful anyway for EQ.
Then you simply use line level EQ to get the response on target, that's it. Especially with Class-D this will be the most green, most efficient system you can think of (within the limit of OB). Money-efficient it is not, that's to admit.
I'm using big high eff pro drivers, woofers and coax, with Qts of 0.3 and below and a good mix of other params, the precision sound transcription and impact is stunning every time, even after 10 months of constant usage.
how do you equalize them? by boosting low frequencies? that is terribly inefficient, pumping huge amount of watts into a speaker, making it work really hard just to match output of a cheap woofer with puny motor. As I remember we've already had a long thread here with high vs low Q drivers on open baffle.
I assume that OP wants a full range baffleless speaker.
I'd look for a biggest driver I can find, with weakest motor 🙂 maybe buy pair of 18in goldwoods and glue whizzer cones on top of their dustcups 😀
I assume that OP wants a full range baffleless speaker.
I'd look for a biggest driver I can find, with weakest motor 🙂 maybe buy pair of 18in goldwoods and glue whizzer cones on top of their dustcups 😀
There are a lot of other factors here.
High Qts drivers do not start and stop moving as quickly as lower Qts counterparts. It's not always the higher the Qts the better.
Adding whizzers to woofers may not always work. Watch the inductance of the drivers.
High Qts drivers do not start and stop moving as quickly as lower Qts counterparts. It's not always the higher the Qts the better.
Adding whizzers to woofers may not always work. Watch the inductance of the drivers.
Again a misconception here. Drivers with very high BL for a strongest motor and hence low Qes are an almost completely reactive and/or high impedance load for frequencies of interest, in a broad area around resonance. While you need to eq to get enough voltage at the driver, current is remains low, much lower than with the nominal 8ohms or the DC resistance. Low-Q driver just have their optimum load-line vs frequency tilted, so to say. That is one option.
The other option is to use an amp with a simulated high output impedance (a few ohms), which you must built yourself or modify an existing one. Then you effectivly raise Qes until eventually Qms remains the dominating factor for the now very little damping left. Qts 0.7, or 1.0 or whatever, is just dialed in by the right output impedance. Even when EQ'd to the identical response of option 1 it will sound different, that's the fine-print (with any driver, btw).
With standard linear Amplifiers (Class-B/AB) either way may lead to an efficiency penalty in the amplifier from the out of phase currents vs voltages, but with Class-D the efficiency of the amp and the driver is as good as it gets, because they don't care much about output voltage when it comes to dissipation. Because of the occasional high peak currents it should be beefy stuff, still.
No question there are many pro woofers completely unsuited to the task in OB, especially the latest monsters in the multi-kilowatt camp, but more moderate designs can work very well when the rest of parameters is not too far off for OB usage. Also, the net benefit of a driver costing 5x as much as another will probably never be a subjective 5x improvement, so when you are one a budget it's all a no-brainer...
References :
www.extra.research.philips.com/hera/people/aarts/RMA_papers/aar03c4.pdf
www.xlrtechs.com/dbkeele.com/PDF/Keele (2003-10 AES Preprint) - Nom vs True Eff High BL.pdf
- Klaus
Need never be baffled again
Hi, this is a refinement of a simple idea I tried first about a week ago.
The tweeter is a non dipole AMT from Taiwan.
The woofers are 3.5 dcr vintage Seas TV21 NOS, they have a Qts. Of 0.707 before being wired in series. The array is actively crossed at 3000, and 250 hz to a 15" Celestion with a Qts. of 0.50.
I had no idea baffleless could be this good.
With 8 watts to the tweeters, 10 watts to the woofers, and 500 to the open baffle bass driver ( I'm currently awaiting an 18" subwoofer driver better suited for deeper bass), this weird little system is as enjoyable as any I've heard, and I completely expected the opposite!
Sounds better with 2 8"ers per channel, but could get by with one , and a little eq.
The only problem is that equalizing them to sound flat removes the long term enjoyment, for some reason.i suspected boxes do mean things to midrange and treble; but had NO idea an open baffle contributed to a kind of smearing to clarity.
I'm not going to worry about basket resonances, the trade offs here seem completely worthwhile .
Built with scraps, I will redo them soon, but am tired of builds.
Only regret is the two pair of TV21's don't match cosmetically .
Maybe some sort of stretch grill around the woofers?
All wood surfaces will be round radiused,but I like the minimalist frame.
The sound is refined , spacious, almost completely natural, and fast fast fast start and settle time.
Sadly , I can't take credit for the results, it was a fortuitous accident to assemble parts I've had around for a while . I tried other drivers from peerless, Swan, Aucharm 4" full rangers, Dynavox 6 1/2"ers, and even a Neo 10/Neo 3 pairing, couldn't get acceptable results.It's good to be lucky.
Hi, this is a refinement of a simple idea I tried first about a week ago.
The tweeter is a non dipole AMT from Taiwan.
The woofers are 3.5 dcr vintage Seas TV21 NOS, they have a Qts. Of 0.707 before being wired in series. The array is actively crossed at 3000, and 250 hz to a 15" Celestion with a Qts. of 0.50.
I had no idea baffleless could be this good.
With 8 watts to the tweeters, 10 watts to the woofers, and 500 to the open baffle bass driver ( I'm currently awaiting an 18" subwoofer driver better suited for deeper bass), this weird little system is as enjoyable as any I've heard, and I completely expected the opposite!
Sounds better with 2 8"ers per channel, but could get by with one , and a little eq.
The only problem is that equalizing them to sound flat removes the long term enjoyment, for some reason.i suspected boxes do mean things to midrange and treble; but had NO idea an open baffle contributed to a kind of smearing to clarity.
I'm not going to worry about basket resonances, the trade offs here seem completely worthwhile .
Built with scraps, I will redo them soon, but am tired of builds.
Only regret is the two pair of TV21's don't match cosmetically .
Maybe some sort of stretch grill around the woofers?
All wood surfaces will be round radiused,but I like the minimalist frame.
The sound is refined , spacious, almost completely natural, and fast fast fast start and settle time.
Sadly , I can't take credit for the results, it was a fortuitous accident to assemble parts I've had around for a while . I tried other drivers from peerless, Swan, Aucharm 4" full rangers, Dynavox 6 1/2"ers, and even a Neo 10/Neo 3 pairing, couldn't get acceptable results.It's good to be lucky.
Attachments
Use what's there
I'm finding no back up tv21's for sale, and was uncomfortable with their fragile 6watt power rating.
Didn't want to resort to paralleling them to a resistor to get better power handling.
Doh!
I've had some old NOS M&K/Peerless 5 1/4" woofers laying about for a while ...
These measure at 6.97 Re each on a multimeter, so the paralleled Seas in series with the M&K's yields 8.72 Re for my mid amp, adds a little inductance which smooth things enough for me to bump the tweeters roll in up to 3000 hertz, much better for their longevity, I bet.
On solo voice that last bit of nasality is gone, no longer need any eq from the BBE Maximizer processor, so that's on bypass, also a good thing.
I figure if I'm going to use an inductor, why not get some output from it too?
Unorthodox, and it works great!
I'm finding no back up tv21's for sale, and was uncomfortable with their fragile 6watt power rating.
Didn't want to resort to paralleling them to a resistor to get better power handling.
Doh!
I've had some old NOS M&K/Peerless 5 1/4" woofers laying about for a while ...
These measure at 6.97 Re each on a multimeter, so the paralleled Seas in series with the M&K's yields 8.72 Re for my mid amp, adds a little inductance which smooth things enough for me to bump the tweeters roll in up to 3000 hertz, much better for their longevity, I bet.
On solo voice that last bit of nasality is gone, no longer need any eq from the BBE Maximizer processor, so that's on bypass, also a good thing.
I figure if I'm going to use an inductor, why not get some output from it too?
Unorthodox, and it works great!
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