Speaker power question

Uriah,

You have to tell us more.

How much power can your amplifier put out into 8ohms? 4ohms? 2ohms? 1ohm?

What is the efficiency of the 150W speaker vs the 300W speaker?

Bob

If you connect 2 150W 8Ohm speakers in series, you get a 300W 16Ohm speaker. Because of the increased resistance, you'll actually get less power from a given voltage. If you want to increase the power, you'll need to increase the voltage.

If you connect 2 150W 8Ohm speakers in parallel, you get a 300W 4Ohm speaker. Because of the reduced resistance, you'll get more power from a given voltage, but you will need an amplifier that can supply the increased current.

You can adjust the effective resistance using a suitable transformer (one designed for audio, not mains), although this will add to the cost.

Or you could connect 4 75W 8Ohm speakers to get a 300W 8Ohm speaker by wiring pairs of speakers in series and the two pairs in parallel:

| | +--+--+ | | - - | | | | | | | | - - | | - - | | | | | | | | - - | | +--+--+ | |

Each "leg" will be 150W 16Ohm, giving 300W 8Ohm overall.

Lower power speakers will tend to be physically smaller, and will tend to be less efficient at low frequencies, so you'll tend to get less bass that way.

Oh, and you need to connect all of the speakers with the same polarity, otherwise they will tend to cancel each other out, reducing the overall volume.

Not really... There is more to a speaker than just its wattage which is just how much electrical power it consumes. You can easily connect your 150 watt speakers to form the 300 watt in the sense of "electrical equivalency" but they won't necessarily be equivalent sound wise.

For example, you can build a wall of tweeters that use the same power as your 300 watt speaker but its surely not going to sound the same.

You need to weigh cost, size, quality, etc... to get a better answer.

"Uriah"

The power rating of a speaker is its INPUT power - which does NOT tell you how much sound it can deliver.

You need to provide a link for the make and model of the speakers and say what YOU intend to use them for to get any useful advice.

....... Phil

As others have noted, the efficiency of the speaker is important here. This is given as the SPL output at 1 meter for 1 watt into the speaker. The specs may just say something like "Sensitivity: 98 dB", or they may put "1w/m" or some such after that. If you look at a lot of speaker specs, you quickly discover that there is a rather wide range in sensitivity values, and that sensitivity is usually directly correlated with magnet weight, and likewise with price.

Also note that each 3 dB increase in sensitivity is the same as doubling the input power, and it comes without additional heating in the amp or the speaker. I'll bet if you check the sensitivity numbers you'll find that you need quite a lot of the cheap speakers to equal the expensive speaker in output, assuming 1 watt into each of them. (Actually, if you are adding speakers with the exact same program input, then two speakers with the same power output will produce a 6 dB increase in sound where they are in phase... see below.)

Again as others have noted, even if all else is equal there can be drawbacks to having multiple speakers. For midrange and high frequencies the image will be smeared out because the sound will not be coming from a point in space. Worse, with two or more sources producing the same frequency, there will be locations where the two sounds add together in phase and others where they cancel, leading to peaks and dips in the frequency response that vary with location.

For low bass (below 100 Hz or so) there is not an imaging problem because we don't localize these low frequencies very well. That's why many systems can have a single subwoofer that combines both left and right channels. (And recorded music rarely has much low-frequency difference between channels anyway.) There probably won't be a phase cancellation problem either, as long as you keep the two drivers close together. (Phase issues arise when the separation is more than a significant fraction of a wavelength. You may find it educational to compute the wavelengths of a few selected audio frequencies, just to get a feel for this. The speed of sound depends upon temperature and humidity, but just for a simple approximation use 1000 ft/sec.)

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis

In the tube amp days, we had big theater speakers because the amps were wimpy. Now we have big powerful amps, speaker size and mass are probably more important than effciency. Especially if you are loading them in and out of a truck with no lift gate. If the only thing you are worried about is blowing speakers, that is almost purely a thermal problem... a 1" voice coil can handle about 100W, a 2" vc about 200, and a JBL 4" vc with square wire might handle 400... so you get an rms reading meter with a very slow time constant, and keep the long time average rms level about 1 or 2 db below what the speakers will handle heat wise. Big 20dB peaks like rim shots should go right through, contribute thier little bit to the rms, and keep on chuggin.

Thank you everyone. I do now think I have enough info to make a decision . I appreciate all of the input, and I am double checking things, especially the sensitivity part that I wasn't aware of how it worked. I haven't even got to the amp part. I wanted to make sure I understood the speaker part first. The speakers are sold through a local liquidation place and I have to go back there to get more details. It seems there is a little bit of conflicting advice but the bottom line is that yes wired correctly and powered correctly I should be able to produce more db from multiple speakers then from just a single speaker given that all things are equal or ideal. Quality of the sound is not at issue in this setup. Thanks again Uriah

If they are cheep enough, buy a couple extras for spares in the future, and a couple to 'test'. Play your favorite cd into the fft analyzer in cooledit and get an idea of the general shape of the spectrum to be reproduced, then play the cooledit pinknoise generator thru a graphic eq with about the same shape. Read the volts with an rms voltmeter and run your test speaker and see if they'll take 50w for 30min or so. Let em cool down for a while and turn it up 3db to

I wouldn't be at all surprised if the liquidators don't have sensitivity specs to provide.

Ahh, but with speakers things are always a lot farther from "equal or ideal" than with any other part of the system. If you are unable to get sensitivity specs, the best you can probably do is go by weight, magnet weight in particular. This is also fraught with problems since

different types of magnets have different strength-to-weight ratios, and because manufacturers often include the magnet "structure" in their weight numbers (if any). But in general a manufacturer who is trying to make a cheapo speaker won't put a lot of metal into it if it can be helped. So if you see a big difference in magnet weight, that might be a good indicator.

Best regards,

Bob Masta DAQARTA v3.50 Data AcQuisition And Real-Time Analysis