[thirdeye]

Hi,

Many of the driver designs these days such as something like a good 7" mid/bass driver can come in a variety normally from around 86 db to 89 db 1/w-1/m and everything between with an 8 ohm impedance.

Now I understand that putting two of these in "Parallel" such as in an MTM should net you around a 6 db increase generally on the acoustic side of things in efficiency?

Example if you used an 88 db driver, and put another in parallel you end up with about 94 db or not? Or is it just a 3 db increase getting up to only 91 db?

**So if you have dual 88 db woofers in parallel should you shoot for a 91 db TWEETER, or a 94 db TWEETER?**

What is the actual output difference you would get doing a dual woofer in any cases above?

Is it a 6 db from the two woofers in parallel?

Or will you get a 3 db parallel woofer increase?

I have read up on many topics behind this, and seems most end up at + 6db with these drivers in parallel, however do you base your tweeter on the + 6 db, or is it based on the electical efficiency side of it in fact being just 3 db higher with 2 drivers in parallel?

Thanks

[Danny Richie]

Technically the pair in parallel will give you 6db increase.

But then there is baffle step loss and how much compensation is needed for that....

[thirdeye]

Thank you for your response.

Basically if I am assuming what your saying is correct technically the electrical match should be tilted toward looking for a 91 - 92 db tweeter in order to not end up padding it way down?

So more or less look for a tweeter that's around 3 db higher than the single woofer.... in this example above an 88 db woofer is better matched with the 91 db tweeter as once in parallel those 2 woofers will compensate closer to that "Technically" vs. the higher 6 db output?

While we are at it... One more question :

What are your thoughts on the woofer specs. for example if it takes a 0.5 cuFt cabinet for one woofer with a 2" x 7" port currently to get down to 55 hz, and you are of course multiplying that woofer x 2 roughly you will now need a 1 cuFt cabinet with QTY.2 - 2" x 7" ports? Simply double the volume and double the amount of ports in the same diameter and length?

I have seen this normally done with 2 ports, but should they be mounted Vertically behind the woofers, or Horizontally for better performance?

Thanks again

[Danny Richie]

What are your thoughts on the woofer specs. for example if it takes a 0.5 cuFt cabinet for one woofer with a 2" x 7" port currently to get down to 55 hz, and you are of course multiplying that woofer x 2 roughly you will now need a 1 cuFt cabinet with QTY.2 - 2" x 7" ports? Simply double the volume and double the amount of ports in the same diameter and length?

Yep, that works.

If you are using one woofer though I recommend the 8 ohm version. If using two woofers than I recommend paralleling the 16 ohm version. The specs on the woofers are different though. The 16 ohm woofers needs a little more air space. 

I have seen this normally done with 2 ports, but should they be mounted Vertically behind the woofers, or Horizontally for better performance?

You can put the ports anywhere and the tuning of the box will be the same.

[thirdeye]

Thanks for the info again

[Danny Richie]

Is there any negatives to running 4 ohm drivers in "series" instead of "paralleling" dual 8 ohm drivers?

Sensitivity is the same as for one driver.

Mainly there are more choices for good efficient 4 ohm drivers and keeping the "Re" in series above 4 ohm as well vs. paralleled.

Or is there more advantage keeping drivers in parallel for any reason?

Running them in parallel doubles your output.

You say in your first response that "technically" putting 2 drivers in parallel will give a + 6 db, what would be the difference in using them in series then? In other words I read that putting the drivers in series actually will not be as efficient?

Correct. The series drivers will be down 6db.

Or to make it simpler if you have 2 - 4 ohm drivers with 90 db 1/w-1/m in series what is the final sensitivity, and in this case what should the tweeter sensitivity be in order to match it? 90 db? 93 db? 96 db? None of the above!

You will also have baffle step loss to deal with. If the driver together only hit 90db and you have 5 to 6db of baffle step losss compensation then you'll be in the 85db range.