[jimbones]

I'm thinking of building a 2 way OB. Since I have a subwoofer I only need the OB speaker to go down as low as 90or 100hz. What do you think is the smallest accptable bass/mid driver i would need to get reasonable output. I play mostly jazz and not at ear splitting volume.

[matevana]

Approximate size of the baffle you will be building?

[jimbones]

wouldn't the size depend on the driver and cutoff frequency? I would like to keep it 36 high by 14 wide if possible (really what ever width is necessary). I have a 7 inch driver (dynaudio 17W75) but I suspect that may not have enough Omph!
If that doesn't do it I'll have to get another driver.

[JeffB]

There is a dipole peak at
1135*12/(baffle_width_in_inches) frequency

The peak is 6db of above nominal.
From the peak there is a 6db per octave roll-off.

eg. an 18" wide baffle has a peak at 756Hz that is 6db above nominal.
378Hz is nominal
189Hz -6db
94Hz -12db

If you get to the driver's fs then there is an additional 12db rolloff.

More about this here: 
http://www.audiocircle.com/index.php?topic=115255.msg1204299#msg1204299

You will need a corrective circuit for this to keep the upper frequencies from being too peaky and this will kill your drivers efficiency.
So you are either going to need a very wide baffle like 36" or more, or a very high efficiency midrange driver, or perhaps a 3 way design.

I will note that I have a 15" driver on an 18" baffle and I love the bass that I get for music.  Its probably not deep enough for movies.  I haven't yet worked out how to deal with the frequencies from 150Hz on up.  I have a single 3" driver with no correction for the dipole roll-off.  The basic sound shows promise, but it is too peaky and needs correction.

[matevana]

If you plan to meet the sub at 100Hz, you should probably aim for a wider baffle and/or larger mid driver. The driver's total Q and excursion come into play as well, as these parameters contribute to the amount of compensation required and SPL capability. Alternatively you could experiment with crossing to the sub at 120Hz or 150Hz which may yield a flatter response overall.

You might want to play around with Edge baffle simulation software to predict the roll-off characteristics of your driver/baffle combination. You will discover that variables such as driver location (on the baffle), the drivers height, floor bounce, etc. contribute about as much to roll-off characteristics as baffle width. 

[jimbones]

I am aware of the dipole peak and Edge. OK so this is helpful, it seems I will need a larger driver AND wider baffle. I'll start looking at some 12 inch drivers with Q in range of 0.5 (I know the higher Q is better for OB)

[jimbones]

Can anyone recommend an Eminence driver for a 2 way OB? I've read that they are good for OB but nor sure which ones to consider.

[matevana]

I like the hemp cone guitar drivers in OB very much. Look at the 'Lil Buddy in a 10" driver and the 820H in an 8" driver. Both have adequate Qts for OB but you should use a high pass filter as they have minimal excursion and can be damaged by low frequencies. They are voiced very nicely in the midrange.

[sfdoddsy]

It's worth remembering that the Linkwitz Orion runs an 8 inch mid (Seas W22) down to 90Hz on a 14 inch wide baffle.

[AJinFLA]

It's worth remembering that the Linkwitz Orion runs an 8 inch mid (Seas W22) down to 90Hz on a 14 inch wide baffle.

I thought it was around 120?

In any case, a 2 way that goes down to 90-100hz will require a woofer(s) with some displacement, while at the same time, in all likelihood, have to have good enough MF-HF performance to cross to a tweeter. What that tweeter is (and overall budget), would go a long way to determining the choice for woofer....IMHO.

cheers,

AJ

[jimbones]

Ah,yes the trade offs is driver choices, F3, efficiency etc 

[sfdoddsy]

I thought it was around 120?



cheers,

AJ

120 in the original, 90 in the latest ones.

[Juhazi]

So your plan is a 2-way plus sub. Low driver choice depend very much of your high-driver choice. If you are planning to use a 3-4" fr , then 10-12 woofer is ok, xo around 500Hz. With high effeciency, a PA driver? If you must make xo higher, you must use 8" or two 6½" woofers, and you will anyway be in trouble with eq and distortion in the low range.

Remember that in jazz we listen to wondeful sound of upright bass, drums played (not hit), tenor saxophone etc. instruments and voice with fundamental notes in the woofer region. You will want low distortion there!

My personal choice would definitely be a 12-15" high-eff driver and a fullrange, for a 2-way OB (+sub) You should reconsider to make it 3-way with sub - much more freedom of driver choices!
-
Ladysmith Black Mambazo was listned to while writing this. 12" woofers rule!