Basic design Q

[Sitka]

I think this is a basic speaker design question.

When selecting components for a two way speaker; woofer and driver/horn; is there any advantage/disadvantage to selecting 8 ohm vs 16 ohm?

I’m contemplating a new project- 8 v 16 ohm?

 

[swechsler]

Unless your amplifier has 16Ω taps (pretty rare these days), you'll get half the output power (-3dB) into the 16Ω speaker vs the 8Ω speaker.

 

[homebrew]

If your speaker is going to be MTM for example, using an 8 ohm high frequency driver and two woofers, then if you use 16 ohm woofers connected in parallel, that would yield a net of 8 ohms. So in that instance you'd have compatibility with your tweeter and a better load for a solid state amplifier. For a single woofer, a 4 or 8 ohm nominal impedance would be the preferred way to go.

 

[Nat]

I think you would find that the selection of 16 ohm drivers is smaller than that of 8 and 4 ohm drivers.

 

[Sitka]

hmm...here's my thinking, please correct me if I am wrong. The impedance (resistance) is double w the 16 v 8 ohm speaker, so all other things being equal, the 8 ohm speaker should be 3 dB louder. However, since sensitivity ultimately determines max SPL, the 3 dB difference between the two seems relatively unimportant.

When I review the sales catalogs of the various manufactures, they offer16 ohm versions of many different compression drivers and 15" woofer models. People must buy them. Why? What is the advantage?

I have two pair of large main front speakers: EV's @ 16 ohm, and Altec's @ 8 ohm. Both pair are fairly sensitive at about 98, but that number is not precise. When I A/B test the speakers on my system, the volume difference at a given amp volume setting is negligible. Of corse they have different tonal qualities, but volume difference is minor.

I have never used any speaker at less than 6 ohm. Have always avoided 4 ohm due to the current load they present.

My next project will be two way speakers; 15" woofers w compression/horn driver. My current amplifier power is more than needed (110 -150) but I plan to select high sensitivity components, any suggestions?

 

[Nat]

Hmmm - didn't realize you were looking at compression drivers and large woofers perhaps oriented to PA applications, rather than standard domestic audio drivers.
No idea why higher impedances are more common for sound reinforcement applications, but it might be that they offer a margin of safety for solid state amps, or that less efficiency makes it easier to achieve low volume, when it is wanted. Or it may simply be habit - how its always been done.

 

[GordonW]

In most cases- the compression driver will be significantly higher efficiency than the woofer in a system- it will play significantly louder at the same input power. However- a higher impedance driver, with the same efficiency, will have a lower voltage sensitivity than a lower impedance driver all else equal (it will produce less sound at the same drive voltage, due to the higher impedance causing it to draw less power).

So, sometimes, by using a 4 or 8 ohm woofer/mid driver, and a 16 ohm tweeter/ compression driver- it's possible to closer-match the voltage sensitivity of the driver (at any reference voltage, usually 2.83V is the standard), so that less padding is required. Less padding can equal better sound- putting resistance in series with a driver can change its parameters, sometimes to the worse...

Regards,
Gordon.