Axiom Home Page Forums Multiple Drivers?

Dear Axiom,

I'm planning a 7.1 speaker setup, and have been interested in your products. I'm considering floorstanding speakers to use for the front left and right channels, and a center speaker. My room is mid-sized (haven't done the measurments), but you could put three or four dinner tables in there.

My real question is whether multiple tweeters are necessary? There are floorstanding speakers I've seen such as RBH that have just one tweeter and two woofers with a subwoofer for $5,000 a pair. Since so many people have said excellent things about RBH and of course Axiom's speakers, I was wondering whether multiple tweeters are necessary or not? Some high-end speakers I see on the market may have four woofers and one tweeter (e.g., the RBH 6000), then one step up the speaker may have four aluminum woofers but this time have three tweeters. I am a bit hesitant to spend thousands of dollars on products with just one tweeter if I think to myself I may have lost out.

Why are tweeters considered less important for quality purposes than woofers? I do note that your Axiom VP150 center channel has two tweeters and three woofers, while your M80v2 tower also has dual tweeters. The high-end speakers I see often use VIFA or Scanspeak tweeters that are powerful. What is meant by thermal compression? I often thought that a speaker's driver size would limit its output eventually (although driver size is just one factor) and that is why people use dual subwoofers or multiple woofers.

I also note that one of RBH's subwoofers, the 1212se, has two 12-inch woofers. However, my thought was that spreading out speakers (i.e., using two subwoofers in a large room) is better than focusing on just one speaker. Advice would be appreciated as to what is thermal compression, what is lobing, are multiple tweeters necessary,etc.

Also, is it safe to use a pair of M80's that are 4-ohm impedance with a 6-ohm center (vp150) and 8-ohm bookshelfs with a receiver such as a Denon 3807 costing around $1,000? I currently have a Yamaha RX-V2600 and I know it doesn't drive 4-ohm loads that great but is it safe to test to see if a speaker works using my Yamaha?
-- Peter

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Hello Peter,

Adding more tweeters (and midrange drivers) and/or woofers increases a speaker's power handling and ability to play cleanly in bigger rooms at very high playback volumes without distortion. That is the main design reason for increasing the number of drivers in a speaker. For example, if you go to the page for the Axiom M60 v2 tower speaker and scroll down, http://www.axiomaudio.com/m60ti_main.html , you'll note that the M60 v2 has two woofers, one midrange driver and one tweeter and that its "Maximum Amp Power" (power handling) is rated at 250 watts per channel. Click on "Compare all Floorstanding Speakers" and you'll see that the Axiom M80 v2 tower adds an additional midrange driver and a second tweeter, for a total of six drivers, thereby increasing its power handling to 400 watts per channel. In actuality, the M80 will routinely handle peaks of 700 watts per channel and play at near-deafening levels before dynamic compression kicks in.

All drivers are basically reciprocating electric motors, air pumps if you will, powered by magnets and voice coils of wire that move rapidly back and forth to generate sound waves at appropriate frequencies and loudness. As you increase the power to the speaker, the drivers have to "work" harder (pump more air, producing greater loudness) so the voice coils heat up and move farther back and forth. Eventually, every speaker has a limit both in terms of thermal compression from heat and dynamic compression because the voice coil moves as far as it can from the magnetic gap and can move no further. Thus it can't produce any more volume or output. With the M80 in our test anechoic chamber, that point is reached at about 400 watts of input and 118 dB SPL output. The latter is approaching the threshold of pain in terms of loudness. In a room, it would be significantly higher in output.

Now look at our simpler bookshelf speakers like the M2 v2, which uses a single woofer and tweeter. Its power handling is 150 watts. By adding a second identical woofer/midrange unit, the M22 v2 handles more power (200 watts) and plays louder in bigger rooms, although it doesn't approach the M60 or M80 in bass output or power handling.

Lobing occurs when multiple drivers are used and may result in some cancellation of certain frequencies common to both drivers. It is overrated in terms of audible effects. You can easily hear it with pink noise test signals but its effects with program material are not intrusive.

Yes, it's fine to use different impedances of speakers (4 ohms, 6 ohms, 8 ohms) with an AV receiver because each pair of speakers is driven by a separate individual amplifier inside the receiver. Only 4-ohm speaker present problems for some brands like Yamaha, Sony, and Onkyo. Denon AV receivers will drive our M80s with no difficulty. Yes, it would be safe to try your Yamaha with the 4-ohm M80s.

Send me the dimensions of your room; "mid-sized" has different meanings in Texas, Manhattan and elsewhere. When I know the length, width and height, I'll be able to estimate which speakers will be appropriate for your room. By the way, there is nothing inherently "powerful" about VIFA or Scanspeak tweeters. It depends entirely on their power handling ratings and impedance, as well as how large an amplifier will be used to drive the speakers. Axiom's drivers--all of them--are custom designed by Axiom and made by Axiom in our Axiom-owned and managed driver plant in Shanghai. All the design and remaining assembly, electronics, construction, wood enclosure finishing and testing are done in our Canada plant. RBH speakers, while well designed, strike me as being greatly overpriced, which may reflect the high costs of maintaining a dealer network, wholesalers and other associated costs. As you know, Axiom sells direct on-line, passing the savings on to the consumer. And yes, if a large tower speaker uses only one tweeter, it will have more limited power handling and output capabilities compared to a similar speaker with more drivers.