Multiple Drivers to Increase Efficiency

[markkanof]

I have asked this question myself before as I am sure others have but never gotten a conclusive answer. Many people on this forum and other places when asked increasing efficiency of a speaker say something like "don't worry, just add more drivers".

So my question is does this really work? Lets say to a given amplifier I connect one driver. It has an impedence of 8 ohms and a rated sensetivity of 87 db 1w/1m. Now lets say I take four of these same drivers and use them in two diffrent ways. One is to wire them in a series parallel combination so that they still present an 8ohm load. The other is to connect them in parallel so they present I beleive a 2 ohm load. Would either of these combinations be more efficient than the single driver?

I think the problem with this question is that it is somewhat ambiguous. What I am trying to get at is how loud will the speakers be in my room. I have a relatively low powered amp, so would adding more drivers give me more volume or just a less strained sound cause each driver is doing less work?

Mark

[AudioFreak]

So my question is does this really work?

For low frequencies, say below about 300Hz, it works really well.

Lets say to a given amplifier I connect one driver. It has an impedence of 8 ohms and a rated sensetivity of 87 db 1w/1m. Now lets say I take four of these same drivers and use them in two diffrent ways. One is to wire them in a series parallel combination so that they still present an 8ohm load.

This will result in a little under 6dB increase in On-Axis efficiency for the same amount of total power.

The other is to connect them in parallel so they present I beleive a 2 ohm load.

This will also result in 6dB increase in efficiency but because of the lower impedance, assuming the amplifier is not current limitted, you'll get another 6dB raise in SPL because the extra power being supplied to the speakers.

Would either of these combinations be more efficient than the single driver?

Yes, both.

[markkanof]

Okay, well that is obviously the answer that I wanted to hear. Does anyone else have anything to say about this? AudioFreak I thank you for your guidance and I am not trying to insult you in any way by asking others advice. I am really just looking for some confirmation because of the conflicting answers I got in the past.

Mark

[AudioFreak]

No, problem. No offence taken. You will find the above information to be factual so long as we consider low frequency on axis measurement. Alter either of those conditions and things are not as favourable.

[pinkmouse]

Hi Markkanof,

yes it will give you more effenciency, but you may run into comb filtering problems if you are not very careful with driver positioning, you may be better off just using a single high sensitivity driver.

Cheers

Al

[markkanof]

Thanks guys. Is there anywhere I can get more information about these issues. I honestly have no idea what comb filtering is. I know what on axis means, but would like to no more about the off axis performance of a multiple driver speaker.

Thanks
Mark

[AudioFreak]

Comb filtering is where certain frequecies or more commonly most frequencies above a certain point develop peaks and nulls within the listening area so that you might be sitting in a particular area in the room that is a null at say 1kHz this is to say that in that exact spot in the room because of the effects of comb filtering related to the particular speaker setup, any 1kHz tones are acoustically cancelled out and you will not hear them or they will be very quiet and partially or fully out of phase. If you mount the drivers physically very close to each and keep the array to low frequencies (I suggested below 300Hz earlier in this thread) then you shouldnt have trouble with comb filtering. Off axis, some degree of comb filtering is inevitable and most of the acoustical efficiency gain is lost getting worse the further off axis you move.

[markkanof]

AudioFreak,

Thanks that clears up comb filtering for me. Would the loss of efficiency as you move off axis apply in a single driver speaker as well? If not could you possibly explain why there is a diffrence.

I feel this need to build a high efficiency speaker and have been going back and forth between using a pro driver and gaining efficiency but losing bass extension, or using hifi drivers and getting the bass extension and possibly getting the efficiency by using multple drivers. Then sometimes I just start thinking about wheather I even need a high efficiency speaker or if 90 db sensetivity might be good enough.

Mark

[AudioFreak]

Originally posted by markkanof
Thanks that clears up comb filtering for me. Would the loss of efficiency as you move off axis apply in a single driver speaker as well? If not could you possibly explain why there is a diffrence.

It does also apply to single drivers but to a lesser extent. The difference is that with an array you are dealing with the effects of comb filtering and the addition of multiple acoustic waves.

[Bill Fitzpatrick]

markkanof:

I do this all the time. How you handle situation will differ depending on the frequency range the particular driver array is meant to reproduce. Are you talking woofers only for your application?

Is this for home or sound reinforcement and are you looking for quality or just loud?