Understanding multiple woofers
Subscribe to Ask Paul Ask a QuestionWhy do some speakers have multiple woofers? What's their purpose?
COMMENTS
Leave a Reply
You must be logged in to post a comment.
Why do some speakers have multiple woofers? What's their purpose?
You must be logged in to post a comment.
Hey Paul, Also, don’t smaller diameter woofers have better dispersion than larger diameter woofers?
Two Comments:
You can design a 6″ woofer to go as low as a 12″ woofer. But it’s not practical. The 6″ won’t play loud enough to hear it a low bass due to our ears’ roll off at low frequencies.
Two 6″ woofers are only about half as big in area as one 12″ since area goes up as the square of the diameter.
Yes:
6×6 = 36, twox = 72
12×12=144
There is a speaker experiment that I want to try.
If every one in our hifi family knows about the Avantone Pro CLA-10 Reference Studio Monitors, the CLA-10 monitors have 7inch woofers in them.
But why do they put 200watt amplifiers on those, if the peak power handling is only 120 watts?
What I would like to do, is order 16 AV10LFM drivers, and 16 AV10HFM drivers, and a pare of AV10XMO crossover networks.
Also, I will build a pare of speaker cabinets to put the crossover networks and drivers in.
If one can handle 60watts RMS, how much power can I put in to 8 woofers and 8 tweeters per channel without blowing them up?
And also, what kind of a sound would I get?
That’s what I hope to find out in my speaker experiment.
With multiple woofers versus one per channel – I wonder if you lose any sound quality or definition in the bass heard in the room? Dont multiple woofers increase the complexity or existence of standing waves etc?
Well DJB-o-b, it all depends on how the woofers are wired up.
All depending on the wiring, that will predict the sound quality.
But to answer your second question, it all depends on how the speakers are positioned in the room.
If the back of the speakers are ported, then you don’t want to put those too close to the wall that’s behind them.
But if the speakers are a considerable destones away from the wall that’s behind them, then standing waves shouldn’t be too much of a problem.
Thanks John. I’m anxious to replace my stand mounts with floor standers – hopefully this year. Planning to finish my new copy of the Audiophiles Guide first.
Hmmm…some math challenges here, but I’m on my 2nd cup of coffee, so I’ll give it a try.
A = π * r^2
The area of a circle varies with the square of the radius, not the diameter. But the relationship ends up being the same in this case: the area of four circles is the same as that of one circle with twice the diameter.
The tricky thing about woofers is that the diameter of the cone is more important than the diameter of the basket. A typical 12 in woofer may have a cone (excluding surround) with a diameter of 9 in while a 6 in woofer’s cone will be closer to 4 in. Comparing these:
(9/2)^2 / (4/2)^2 = 5.0625
Therefore, to achieve the same air coupling as a single 12 in woofer, we’d need at least five 6 in woofers, if my math is correct. As they say in the motoring world, there’s no replacement for displacement. 🙂
Well Dsnyter0CNN, I have a quod of Dayton Audio B652-Air bookshelf speakers.
Each one, has a 6 and a half inch woofer in them.
But when I checked out the size of the cones minus the surrounds, I calculated about 5.25inches in diameter.
So, based on that fact, not all 6.5inch woofers are made alike.
Sure. I never said all woofers are made alike. In fact, I believe I said, “a 6 in woofer’s cone will be closer to 4 in.” 🙂
I would expect the cone on a 6.5 in woofer to be around 4.5 in, but I guess if the woofer has an unusually small basket + surround or the basket is actually larger than 6.5 in, 5.25 in is possible.
Out of curiosity, I just measured the woofer on my JBL 305P monitors (happen to be sitting next to me). The specs from JBL claim that the LF driver is 5 in; however, the basket actually measures 5.75 in (surprising) and the cone diameter is 3.75 in. I think for smaller drivers, the difference between basket and cone diameter tends to be about two inches, while it’s closer to three inches for larger drivers.
I took a brief look at one of the woofers in one of my Dayton Audio B652-airs.
If you forget about the part of the surround that borders the outer edge of the cone, the part of the surround that’s between the cone and the gasket is exactly 1half inch.
But the whole woofer is 6.5inches.
Like I said, the cone is 5.25inches.
I understand what you said about your JBL monitors.
But take a very close look at a Jensen P6V 6inch speaker.
The surrounds are in deed smaller then that.
I’d say, about 3 quarters of an inch.
But the cone itself, is exactly 5.75inches.
And this is a guitar amp speaker!
I had a look at the PV6 (here: https://www.jensentone.com/vintage-alnico/p6v). Of course, I don’t have one on-hand to measure, but according to the product specs, the basket diameter (including flange) is 165.8 mm (6.528 in). They don’t publish the cone diameter, so I pasted the photograph of the driver into Photoshop and used guides to arrive at an estimated cone diameter of 129 mm (~5.1 in). This leaves a difference of 1.43 in between basket and cone diameter, but as you said, this guitar amp speaker has a smaller surround than what you’ll typically find in a driver that is designed to reproduce low frequencies.
Carrying out the same exercise for the Dayton Audio B652-AIR, published cabinet width is 7 1/16 in. According to my Photoshop guides, diameter of the woofer basket, including flange, is 6.50 in and diameter of the cone is 4.71 in, which is about what I’d expect. I’m not sure how you came up with 5.25 in without including part of the surround in your measurements.
Since we’re attempting to be precise, I’ll admit that I’m completely ignoring the fact that most woofer drivers are not flat circular pistons; they are usually 3-dimensional with a bit of depth to them. This depth gives them somewhat greater surface area than the simple diameter-based measurements we’ve been discussing. Not sure how significant this is when comparing 6 in to 12 in woofers, but I thought I should call this out. 🙂
Dsnyter0CNN, sense you asked, I took a brail tape measurer to it.
I measured it that way.
But however, you’re correct about the size of the cabinets that my B652-airs are in.
And as for the Jensen P6V guitar speaker, you’re some what correct about that one too as well.
But a little more then 15 years ago, I both designed and built a pare of 2-way bookshelf speakers around those drivers.
Yae thoe they can handle 20wattts RMS, I drove them with an 8watt per channel tube amp.
The lowest they’ll go, is about 40HZ.
And the highest they’ll go, is about 40KHZ.
But when I added a pare of 1half inch tweeters to them, I was able to raze the top end of them to about 90KHZ.
They don’t work too well for a serious hifi application, but they do work very well on a computer as apart of a decent sounding desktop sound system.
Those specs (40 Hz to 40 kHz from the P6V) are rather difficult to believe. From the response plot on the Jensen website, it looks like they are -10 dB 10.6 kHz. The 90 kHz extension from the pair of 1/2 in tweeters you added is equally difficult to believe. My hearing stops rather abruptly at 14 kHz, so I would not benefit from such extension anyway. LOL.
It sounds like you had fun with the P6V, and that’s all that matters in this hobby as far as I’m concerned. 🙂
I think Jensen measured it by playing many deferent types of electric guitars throo it.
All of them except the electric bass.
I don’t remember the name of the software I used 15 years ago, but all you needed, was a microphone plugged in to your computer.
And if you had it close enough to the speaker, it would measure the frenclicy response.
And that’s how I took the measurements.
But I also used a pop music CD to do that for me.
A musical ensterment like an electric guitar, is one thing.
But a full blown musical Pease, is another way deferent thing.
If you really want to know the truth about what a speaker can do, then you have to put a whole entire band throo it.
And so, that’s what I did.
But also at the same time, I learned that the P6V makes either a grate mid range, or a grate mid bass driver.
And I’ve used it all three ways.
Woofer, mid bass, and mid range.
Don’t let any one tell you that you can’t use guitar speakers that way, because you sure can if you know exactly what you’re doing.
Moreover with multiple woofers there’s less distortion because each woofer is asked to do less and the result is effortless bass.
one more thing,
we have one 6″(for instance), 3watt speaker
it’s powered with 1WATT
assume that
at its fs loudness is -12 dB and at 200hz is -6 dB
next, we put 2WATT so it becomes
at its fs loudness is -8 dB and at 200hz is -3 dB
in the second case actually -6 dB was expected, but loudness increasing at the deep base a bit slower, than it supposed to be
so we put the second speaker power each of it with 1watt and we have the total sum as
-6 bd at fs and -3db at 200hz
“Don’t buy bookshelf speakers, buy foorstanders!”
Well if it were that easy
If we assume that the two loudspeakers have exactly the same loudspeaker chassis, then the floor stand would still be considerably more expensive because the cabinet contributes a lot to the sales price.
So what to do?
Buying a bookshelf speaker with a better chassis, or a floorstander with an inferior chassis?
And yes – you can buy good speakerstands for much less than the difference in cabinet prices.
I was thinking about this along similar lines. It’s much more difficult (expensive) to achieve the same cabinet rigidity in a tower speaker vs a bookshelf enclosure of similar width and depth. What’s more, because cabinet resonance levels vary with the area of the enclosure, we actually need even greater rigidity in a tower design to match the naturally lower resonance levels in a bookshelf design.
I think this is why the PSB Alpha P5 bookshelf speaker outperformed the Alpha T20 tower in my evaluation. Yes, the T20 made more bass, but the bass was comparatively loose and lacked the pitch definition of the P5. The P5 also had better top to bottom integration and imaging.
It probably would have been possible for Paul Barton to design a tower that matched the P5’s performance, but not within the cost constraints of the given product line and T20 tower specifications.
We’re confusing peak output and frequency (bass) response.
Peak output as SPL relates to the maximum volume of air displaced by the speaker cone. Volume displaced is area multiplied by excursion. As people correctly noted, we have to disregard the surround, so the effective area of a 12 inch driver is less than 144 square inches. Suppose we lose an inch in each case; we need five 6 inch drivers to match the area of a 12 inch driver. Even then, it’s almost certain that the excursion of the 6 inch drivers is maybe half. So, the larger driver still wins as far as peak output is concerned. Against that we have to consider that we might not actually have any need for the extra SPL.
Multiple small drivers definitely wins for dispersion.
Then consider bass response. In general, a larger diameter speaker will have a lower resonance than a smaller one. That’s not guaranteed, because a 5 inch HiFi speaker will go lower than a 12 inch guitar speaker, but if we compare like with like, the larger driver wins.
Then think about the cabinet. If we take a bookshelf speaker with a single woofer and increase the internal volume, we might expect to get lower bass. However, if instead we add multiple drivers and increase cabinet volume in equal proportion to the additional drivers, we’re not getting any lower bass, just a bigger peak output. It could still be a good compromise.
Hi Paul
Thanks’ for explaining the meaning of surface area in woofers. Regarding that I have made another observation, but I can’t quite understand the reasons: I have been listening to Bowers & Wilkins Speakers for many years. For some time there always were two models at the top of their 800 Series line. Model 801 with a single huge woofer and Model 800 with two smaller woofers. The total surface area of the woofers was about equal in both models and so were the technical specs for bass-extension and frequency response. However, to my ears, the model with one woofer always had a different sonic character than the one with two woofers. Eventough, with regard to measurements, bass response was very similar in both models, I always had the impression that model 801 produced a sound with more “weight” to the bass. It also sounded more harmonious to my ears. Model 801 being discontinued I am now listening to the newest version of model 800 (because of great over-all improvements in the latest version of the 800 series). However, even with the addition of a subwoofer (B&W DB1D) to my stereo system I do not get the feeling of sufficient “weight” of the bass reproduction. For example, with a great Symphony Orchestra playing live you will get the feeling of immense inherent power of the bass section, even if they are playing at whispering-soft levels. Also the over-all sound will always be present and never thin out, even in the faintest ppp. For me the greatest master with regard to such sound was Herbert von Karajan. I haven’t heard equal pianissimi from an orchestra ever since. I am however currently missing this property in my system, even in recordings of his. What could the reasons be, what could I do to get more weight to the bass reproduction of my system?
Thanks’ for your advice and kind regards
Max
Can I disagree? I disagree. Simply, sats on a stand can be placed at or close to ear height which in many cases are the best location. We can take a pair of specialized subs, say JL Audio cross them in at below 100Hz and remove the size /weight and limitation of a single combined box. I have two great older sats by Krell, the Resolution 2s and the Lat-2s and the combo is really a hard to beat setup in a smaller space or mostly any space.