I've been reading a ton about sealed subs, but the one thing that is never, EVER discussed, nor shown in the software (at least that I can find) is te efficiency of the final, resultant subwoofer. I guess this is because sealed subs are almost always used in home theater / music rooms and studio control rooms, so no one worries about having enough amperage.
I'm trying to figure out if I can make sealed 18"subs work in a live band / DJ situation, where efficiency is critical.
Note: I have actually already done this, for over ten years. The sound was lovely, but but the subs' inefficiency was a constant headache /nightmare:
I had been using four Bag End single 18's, with a single Lab Gruppen fp6400 driving them. With two subs on each side of the stage, I could do a medium sized wedding or rock club, but JUST barely. A high school dance was basically out of the question.
And I would constantly have to worry about tripping breakers. Those Labs were 1600 watts rms per side into each "two cabinet" 4 ohm load, and I owned THREE of these amps because I was constantly, literally, melting them & sending them off for repair.
Needless to say, I also got very good at reconing speakers. Literally several times per year, in-between gluing the surrounds.
-------------
So a few years ago I retired this system, and got a pair of QSC KW181's. I can't stand the bloody things. No definition, and no "integration" with the tops. This year I decided to try something else, but that's not working either. The problem is, anything small enough to carry by myself is a trade-off.
Before I go any further looking at custom ported builds, I thought maybe I'd revisit the sealed sub idea, which brings me to my actual question:
==========================================
I only need maybe 3 more dB than I had originally with the Bag Ends.
Could a larger cabinet get me there?
I have a pretty good grasp now on the pluses & minuses of a larger sealed cabinet. For me, not needing lots of bass extension, it's all gravy.
I can estimate that the Bag Ends, stock, have a Qtc in the neighborhood of 7.0. That means I have quiet a bit of leeway in enclosure size, assuming I will like the sound of a lower Qtc. I calculated enclosure size for a fairly similar 18" driver, with known T/S numbers, and got this:
Qtc 0.707 ~ 3 ft/3 F3 51.7 Hz. (Max flat amplitude)
Qtc 0.577 ~ 5.69 ft/3 F3 51.9 Hz. (Max flat delay)
Qtc 0.5 ~ 9.6 ft/3 F3 55 Hz (Critically damped)
The Bag End cabs are about 3.5 ft/3
A 5.69 ft/3 cabinet would work great, ergonomically, so I'd certainly consider trying this. (Using the old drivers, at least to start.)
EXCEPT: I can't figure out HOW TO CALCULATE THE EFFICIENCY OF THE FINAL, FINISHED SUBWOOFER!
For my application, I obviously need this critical number. The stock Bag Ends are 96 dB SPL @ 80 Hz (1W @ 1m)
If I doubled the enclosure size but only gained 1 dB at useful frequencies, then the experiment is a bust. - But an extra 3 dB at around 60 Hz would be incredible.
Is there a way to calculate this, if you know the efficiency of the raw driver?
And note: I'm only concerned with efficiency above 40 Hz.
I'm trying to figure out if I can make sealed 18"subs work in a live band / DJ situation, where efficiency is critical.
Note: I have actually already done this, for over ten years. The sound was lovely, but but the subs' inefficiency was a constant headache /nightmare:
I had been using four Bag End single 18's, with a single Lab Gruppen fp6400 driving them. With two subs on each side of the stage, I could do a medium sized wedding or rock club, but JUST barely. A high school dance was basically out of the question.
And I would constantly have to worry about tripping breakers. Those Labs were 1600 watts rms per side into each "two cabinet" 4 ohm load, and I owned THREE of these amps because I was constantly, literally, melting them & sending them off for repair.
Needless to say, I also got very good at reconing speakers. Literally several times per year, in-between gluing the surrounds.
-------------
So a few years ago I retired this system, and got a pair of QSC KW181's. I can't stand the bloody things. No definition, and no "integration" with the tops. This year I decided to try something else, but that's not working either. The problem is, anything small enough to carry by myself is a trade-off.
Before I go any further looking at custom ported builds, I thought maybe I'd revisit the sealed sub idea, which brings me to my actual question:
==========================================
I only need maybe 3 more dB than I had originally with the Bag Ends.
Could a larger cabinet get me there?
I have a pretty good grasp now on the pluses & minuses of a larger sealed cabinet. For me, not needing lots of bass extension, it's all gravy.
I can estimate that the Bag Ends, stock, have a Qtc in the neighborhood of 7.0. That means I have quiet a bit of leeway in enclosure size, assuming I will like the sound of a lower Qtc. I calculated enclosure size for a fairly similar 18" driver, with known T/S numbers, and got this:
Qtc 0.707 ~ 3 ft/3 F3 51.7 Hz. (Max flat amplitude)
Qtc 0.577 ~ 5.69 ft/3 F3 51.9 Hz. (Max flat delay)
Qtc 0.5 ~ 9.6 ft/3 F3 55 Hz (Critically damped)
The Bag End cabs are about 3.5 ft/3
A 5.69 ft/3 cabinet would work great, ergonomically, so I'd certainly consider trying this. (Using the old drivers, at least to start.)
EXCEPT: I can't figure out HOW TO CALCULATE THE EFFICIENCY OF THE FINAL, FINISHED SUBWOOFER!
For my application, I obviously need this critical number. The stock Bag Ends are 96 dB SPL @ 80 Hz (1W @ 1m)
If I doubled the enclosure size but only gained 1 dB at useful frequencies, then the experiment is a bust. - But an extra 3 dB at around 60 Hz would be incredible.
Is there a way to calculate this, if you know the efficiency of the raw driver?
And note: I'm only concerned with efficiency above 40 Hz.
Last edited:
Larger sealed cabinets are more efficient at low frequencies, since the air spring isn't holding the cone so tightly. Simulation programs like Hornresp and WinISD can show you this easily.
However, an important note on sealed boxes: the mechanically-limited maximum SPL for a given driver is the same, regardless of the size of the box. A bigger box gives you more efficiency (more excursion per watt), but that just means it's easier to bottom out the drivers.
The infinite baffle guys (a really large sealed enclosure) often use a couple of hundred watts to drive their subs, while the guys using small sealed boxes use thousands of watts. They can both move the same amount of air.
You were hitting those Bag End subs with their recommended "peak" power, so I'd expect them to be at the end of their tether. ie, they're not going to give you any more output as you'll already be running out of excursion. The fact that the amplifiers were having thermal troubles tells me you might've been running them hard into clipping for most/all of the night.
Since you were running them hard, you might also find that you were experiencing power compression, where the heat build-up in the driver's voice coil means the impedance rises, and you're drawing less power from the amplifier, reducing SPL. Given the sort of drivers used in there and the sealed box, that might've been up to 6dB, to put a number on it.
The way to increase efficiency and maximum SPL is to use a different cabinet. A ported box can gain around 10dB over a sealed box around port tuning, and uses less excursion there. That's like going from one cabinet to three.
A tapped horn can usually get another 6dB over a ported box, at the expense of a larger cabinet. The +16dB total is like going from one cabinet to six, give or take.
Chris
However, an important note on sealed boxes: the mechanically-limited maximum SPL for a given driver is the same, regardless of the size of the box. A bigger box gives you more efficiency (more excursion per watt), but that just means it's easier to bottom out the drivers.
The infinite baffle guys (a really large sealed enclosure) often use a couple of hundred watts to drive their subs, while the guys using small sealed boxes use thousands of watts. They can both move the same amount of air.
You were hitting those Bag End subs with their recommended "peak" power, so I'd expect them to be at the end of their tether. ie, they're not going to give you any more output as you'll already be running out of excursion. The fact that the amplifiers were having thermal troubles tells me you might've been running them hard into clipping for most/all of the night.
Since you were running them hard, you might also find that you were experiencing power compression, where the heat build-up in the driver's voice coil means the impedance rises, and you're drawing less power from the amplifier, reducing SPL. Given the sort of drivers used in there and the sealed box, that might've been up to 6dB, to put a number on it.
The way to increase efficiency and maximum SPL is to use a different cabinet. A ported box can gain around 10dB over a sealed box around port tuning, and uses less excursion there. That's like going from one cabinet to three.
A tapped horn can usually get another 6dB over a ported box, at the expense of a larger cabinet. The +16dB total is like going from one cabinet to six, give or take.
Chris
There is no difference in overall efficiency for a driver in a small or large sealed box or even a vented box. Half space efficiency=k*Fs^3*Vas/Qes
Your question actually appears to be "how can I get louder". Your answer is arrays. You can get some gain using a bandpass arrangement, or horn-loading (making the speaker more directional)
Since you have a prosound question, why not ask your (how can I get louder) question on a prosound forum?
Have you ever measured how loud you are? My guess is not. Perhaps you could have amps made that go to 11....
Very loosely speaking, if you seek for energy efficient sealed sub try to accommodate the following points :
1. Find excessively strong driver among 18" drivers (highest possible BxL squared divided per Re) with excess amount of linear stroke.
2. Use them twin connected in series.
3. Use too large box for it which results in Q below 0.5
4. Observe impedance peak frequency
5. Tune the DSP response and box size such way that peak voltage gain, peak SPL and peak impedance will overlap
6. Tune the system to have that peaks centered inside of the passband (ideally between low-cut off and low pass filter)
I might suggest using IPAL drivers.
With cheap power from energy-efficient class-D amplifier using Proper driver and DSP shaped response is everything in this regard.
1. Find excessively strong driver among 18" drivers (highest possible BxL squared divided per Re) with excess amount of linear stroke.
2. Use them twin connected in series.
3. Use too large box for it which results in Q below 0.5
4. Observe impedance peak frequency
5. Tune the DSP response and box size such way that peak voltage gain, peak SPL and peak impedance will overlap
6. Tune the system to have that peaks centered inside of the passband (ideally between low-cut off and low pass filter)
I might suggest using IPAL drivers.
With cheap power from energy-efficient class-D amplifier using Proper driver and DSP shaped response is everything in this regard.
Last edited:
Not surprised you didn't like the QSC, they get loud but don't go particularly low. So why not just build your own reflex subs with a current state of the art driver like the B&C 18sw115. Bassboss uses these in powered boxes they sell and have compared them to various contenders and posted the FR graphs on their forum. The link below shows them against the QSC KW181 at something below full output but have a look at some of the other threads to see the response at full output.
Forum | BASSBOSS Powered Loudspeakers
And of course the same driver in a tapped horn would exceed these results by a good margin again, there is an extensive thread on this forum for the TH18.
Forum | BASSBOSS Powered Loudspeakers
And of course the same driver in a tapped horn would exceed these results by a good margin again, there is an extensive thread on this forum for the TH18.
Below its box-resonance frequency, B&C IPAL driver will consume up to 2-3 times less power than 18SW115 when placed in 60 liter enclosure (roughly 2x Qts box align for both drivers). IPAL driver impedance will be higher than 2.3 Ohm in 20-150Hz band with resonance peak occuring at 60 Hz. After filtering-away bands with too-low impedances this will be casual load for 2-Ohm capable amplifiers. It will require more than 2 times less voltage than 18SW115 model to produce the same SPL curve after DSP applied Linkwitz transforms with Qp = 0.71 and fp = 30 Hz. Despite having silly low nominal impedance which is counter-logic from current draw point of view, IPAL driver placed in the same enclosure will behave much more power-efficiently than typical subwoofer driver witch less strong (normal) motor. And 18SW115 is one of the best overally 18-inch pro-sub-driver ever produced.
Last edited:
Keruskerfuerst,
Doubling drivers in double the box size increases efficiency by 3 dB. Doubling the power available to double the drivers adds another 3 dB for a total of 6 dB increase.
The OP does not want the expense of doubling either, yet does not want to change from sealed cabinets, so is stuck with the limited output available from them regardless of the cabinet size.
A bigger box will produce the same output with less power, but other than energy lost from power compression (voice coil heating) there will be no difference in output.
Art
that is power hunger amp.
replace stock fans to stronger ones and put couple of pressurising fans to front of amp rack.
using sealed subs does not help you not to melt your amps again
OK, so I think I get this now.
A bigger box won't increase output above 40Hz, but it WILL let the amps run at lower power, thus at least solving the blown-breaker problem.
That would certainly help.
So what I'd need is a super-efficient 18", that can take at least 400w rms, and has the correct parameters to work in a sealed box. - Then maybe just use my existing boxes, with a little luck.
(I'd still have to worry about blowing them up, but maybe later I could build new cabs with high quality plate amps, and dial-in the needed limiting.)
If this makes sense, then how do I go about finding such drivers?
A bigger box won't increase output above 40Hz, but it WILL let the amps run at lower power, thus at least solving the blown-breaker problem.
That would certainly help.
So what I'd need is a super-efficient 18", that can take at least 400w rms, and has the correct parameters to work in a sealed box. - Then maybe just use my existing boxes, with a little luck.
(I'd still have to worry about blowing them up, but maybe later I could build new cabs with high quality plate amps, and dial-in the needed limiting.)
If this makes sense, then how do I go about finding such drivers?
Find one you like the looks of, and put it through a simulation program. Hornresp is my go-to, but WinISD can let you have many different curves on the same screen.
Chris
Read the seminal papers by people like Small and Thiele on the subject.
Anyway, I believe the answer to your question is max efficiency in a sealed box is achieved when Q of the sealed box system is 1.1
Edit: Here is the paper I was thinking of:
Closed-Box Loudspeaker Systems Part I: Analysis
The efficiency constant is shown in figure 7.
Last edited:
However, that lab gruppen has input current limiter. It allows only 20Amps @ 230V continuously (we have bench tested that amp, 2700W max cont. rms output power / bridged).
Surely, 20A still is quite a bit of current for standard "house hold" fuses.. more so if multiple amps is used.
Sealed box is very efficient, if there is horn in front of the driver
Last edited:
From power compression instead point, the sealed box is one of the worst design related, mainly at long use. If you really must use this specific design, try to implement some heat transfer in the box, when you reduce power compression you improve efficiency. That means you can achieve more SPL with the same amp.
Many T/S parameters will change when the temperature rise, of one them is the Re, increasing Re will increase the impedance as consequence the current will reduce as well resulting in less magnetic flux on the voice coil and less cone displacement (less SPL).
It's true that power compression will occur with any driver when lots of power is sent to it. Even a high-SPL "pro" driver is only on the order of a couple of percent efficient in converting the input power to acoustic output. The remaining power (e.g. 95% of it or more) is lost as heat in the motor. This heat will cause the TS parameters to change, as "hot" and "cold" parameters can be quite different, e.g. Fs increases, Qts increases, etc.
A sealed box is probably one of the most "forgiving" cases for response drift versus VC temperature. I believe that a vented box will be worse in this case.
Perhaps you were thinking that the vent will conduct some heat out of the box? Probably not any significant amount. The plug of air in the port is just moving back and forth - there is no net "flow" to exchange cool outside air with hot inside air!
One advantage a vented enclosure has over a sealed one is that it will inherently be (or can be) a couple of dB more efficient than a closed box for the same input power. You can discover this by reading some of the early papers on the vented boxes. It's one of the main reasons why pro audio sound uses vented boxes, since every dB more that you can get out of a Watt of input power is useful.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.