Why no high efficiency bass drivers for sealed bass channel?

This is how it stands: Many, many audiophiles promote the use of sealed enclosures to produce bass sound, and while I am not into arguing the merits of one type of box vs. another type, the sealed enclosure does hold some desireable properties.

HOWEVER - despite of this there are not many options for us who seek high efficiency woofers for the sealed topology! Why is this? Maybe it is because most pro format drivers are made for the PA market and ported boxes. Maybe the hifi home audio manufacturers have withdrawn from the large format woofer market.

What I would like to see are more 12" and 15" woofers made for the sealed topology. Preferably 16 ohm so that they can be paralleled for more efficiency.

Suggestions for 12" or 15" hi-eff. woofers for a sealed 30 - 150 hz channel are much appreaciated.

Sincerely
Kris
 
high efficiency woofers are always efficient above 100 Hz. The only way I know of, to get high eff in low freq, is massive cone area. Like the fostex 30" or multiple 12 to 15". Another way is large horns, but that's no what you asked for.

Try comparing a 15" pro speaker like Beyma and JBL. They could be rated 97 dB, but below 100 Hz. they are only 90 dB and at 30 Hz typical 85 dB.

You should go for low freq woofers designed for large cabinets (high Vas), since they will, in real life, produce deep bass with the highest eff. possible But don't expect anything above 90 dB.
 
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CLS

Member
2005-06-17 6:58 am
Taiwan
Some factors just don't come together.

To get high efficiency, you'd need light cone & big motor, than you end up with a low Q driver with high fs, which is no bass.

To keep the above and make the fs lower and Vas high, you'd need super soft suspension which is not easy to maintain consistence, in both manufacturing and operation of the driver itself. (and even then, the Qts is still low, it's dominated by the motor)

If you manage to get all the above, than at the operation of high excursion at low fs, your light cone and super soft suspension might probably deform too much or even flapping around. (the high pressure of a sealed box is not even added to the picture)

Let's see the new woofers of those mainstream pro sound brands, the cones tend to be heavier and heavier. Because they need to lower the Vas to make the cabinet small. Thick and heavy cones survive the high power (excursion) torture better than light cones, and power is the easy part. So they just go this way.

Unless we have a super light and rigid material (let's say 24" cone of under 100g, for ex.), we can never escape the circle.
 

StigErik

Member
2008-02-21 12:30 pm
You might actually end up with better efficiency using very large and extremely high sensitivity woofers in open baffle (with EQ) instead of typical "hifi" drivers intended for sealed box. As an example my own dual 21" H-baffle sub's are close to 100 dB sensitive (2.83V / 2W into 4 ohms) at 20 Hz. Admittedly, the boxes (or baffles) required are quite large.... :D

In my opinion, open baffle offers a bass quality that cannot be matched.
 
Kjeldsen and CLS -> your replies are well appreaciated.

I was careful not to ask for subwoofer drivers and only for 30 - 150 capable drivers.
The issue with motor strength, mms, Fs and Q is of course a framework we have to work within. And there have been drivers before that were high(ish) sensitivity and would work in a sealed box such as Beyma 15B100R which would give adequate output to 30 Hz with a bit of room gain.

Still, the white elephant would be a 16 ohm woofer with 92+ sensitivity that would be suited to sealed box implementation. In parallel such a beast would be able to take the strain off my actively crossed all tube amplifier playback system.

Kris
 
I bet the Beyma 15B100R will not give more output below 100 Hz., than the Peerless I mentioned. But (there's always a but), the energy needed at real low freq. are not so demanding as from 100-200 Hz., so the Beyma will gain here - but eq. or roomgain are needed to smothend out the freq. response.

Since you're from Denmark, why not just call flex units and have two 15" custom made.
 
Open Baffle

You might actually end up with better efficiency using very large and extremely high sensitivity woofers in open baffle (with EQ) instead of typical "hifi" drivers intended for sealed box. As an example my own dual 21" H-baffle sub's are close to 100 dB sensitive (2.83V / 2W into 4 ohms) at 20 Hz. Admittedly, the boxes (or baffles) required are quite large.... :D

In my opinion, open baffle offers a bass quality that cannot be matched.

We cannot even begin to discuss open baffle and its limitations pertaining to sound. Suffice it to say that I am familiar with open baffle and I use it in very specific manner in the midrange.

I do run my speakers actively but with pure tube amplification only. In a sense I do use EQ since I cross well below target XO point in order to raise sub 100 Hz output. In a way this is a nonconformist setup since I think bass sounds more real with tube amps than with solid state. Most audiophiles disagree - their loss.

Best
Kris
 

StigErik

Member
2008-02-21 12:30 pm
Why rule out open baffles? The only disadvantage I can see is that they must be large to provide much low bass.

The EQ required is very simple, in fact a passive 1st or 2nd order network before the power amps should do it all.

Power requirements can also be very low. I rarely exceed 1W with my own open baffles, even if I do like to play rather loud.
 
There is this relationship for sealed boxes-

(maximum efficiency)= (2E-6)*(F3)*(F3)*(F3)*Vb

Where efficiency is in acoustic watts, F3 in Hertz, and Vb in cubic meters. Believe this is the formula for a sealed box but it could be the formula for a vented box. The only difference between the sealed box and vented box formula is the constant in front. The key point is one can see there is a relationship between box size, F3 cutoff frequency, and efficiency. This is why there are no small woofers with loud bass. Please notice there is no mention of woofer cone area because cone size does not affect the outcome of the relationship. Cone area does affect the maximum SPL and so on. As example, I have a little woofer that in a quater cubic foot sealed is -3dB at 40Hz but is very low efficiency and will only play like 85dB max.

With this relationship in mind I look for woofers which come close to the maximum efficiency in a given box size with a given cutoff frequency.

Here is a 10 and a 12 that come moderately close to the max if no error was made in calculation:
Peerless 830500 12" XLS Subwoofer | Parts-Express.com
Peerless 835016 10" Aluminum Cone XXLS Subwoofer | Parts-Express.com
 
>>> In my opinion, open baffle offers a bass quality that cannot be matched.

I love my H-frames and think they sound better than plain open baffle speakers without sides... in my room anyway. My sealed powered sub sits unused in the laundry room. It could not match the H-frames in any way. I believe they get down into the mid 30hz range and spoil me daily with rich, full, effortless sounding bass. Imo, the best sounding home setups would include H-frames... perhaps stacked H-frames... they sound amazing!
 
High efficiency driver for closed box.

The eminence kilomax 18"
 

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http://www.parts-express.com/pdf/290-427s.pdf has the IEC baffle response showing nominal efficiency at 97.5dB which is the right size box should come out about -3dB at 65Hz not 40Hz- oops. A little EQ will bring out the rest of the bass and might still qualify for high efficiency. Everyone makes errors- sorry for this one. The 10" and 12" are good though but not so efficient.
 

CLS

Member
2005-06-17 6:58 am
Taiwan
Please don't let those numbers spoil the fun. In reality, these woofers are not that bad.

I remember, years ago, before I built the cabinets, I tried using the woofers just in their own cardboad boxes:D

I just opened the four lids of the box and let the woofer show its cone upward, done! How quick! (that's really a 'fast' bass, LOL) The cardboard 'frame' inside the box for supporting the woofer forms a small baffle, and the box itself is a very leaky sealed box, so the small volume is not bothering.

Later I took another woofer, faced it down and covered the one in the box, an isobarik box was done:D I used them this way for a while. Pushed the box into the corner, and they played quite loud and not boomy at all - they were actually better than the 'real' cabinets I built later (with 24mm thick MDF and heavily braced) in this regard. What a ooxx....

With large enough cone area and decent motor, the sensitivity, or the acoustic power eventually, is not a major problem, if we step back a little and see the whole picture. There are many ways to tune them to get what you need.

With the size of ordinary woofers, they tend to be omni in their operation range if enclosed. So the in room response is largely supported and increased by boundaries. Since I used 18" pro woofers, my major problem is always too much energy, instead of the opposite. They are just easily overflowing the house. So now I use them on OB.

With 2 12~15" per side, in ordinary home environment and under sane SPL, I don't think there'd be any lacking. (15" would be my choice if I start over.) Active xover helps a lot, too.

Have fun!