Building Compact Subwoofer with 8 inch speakers

[armandoeramos]

Hi guys,

I'm new to building speakers. My church, sits 100 - 150 people, needs a compact subwoofer that will be placed under stage (in an 24 in. x 13 in. opening) in the center. The stage is not very large and has no room for a 15 - 18 inch subwoofer. I have attached a photo of the stage.

After doing some research and talking to technical support at parts-express.com, looking into building a very compact subwoofer using two 8 inch BC 8FG64 woofers (600 watt 8 ohm each) using two 12 in. x 12 in. x 12 in. cabinets from Parts-Express.

Will I get enough bass from these speakers? If so, what other parts (crossovers, high pass filters, etc) would I need?

 

[Jensen567]

How low of a frequency do you need to hit? That driver seems to be more of a midbass driver, with an f3 near 80Hz by my calculations. They certainly have the power handling though.

 

[chris661]

What does the main PA look like? - Those look like some serious wedge monitors for vocal use, so I'd expect a fairly hefty main system to reflect this.

IMO, a pair of 8"s in a room that big won't help much. Put them in a fairly big TH tuned quite high, and you might hear them from the back. Those small sealed boxes won't help the drivers.
You'll need an amplifier, and (presumably) a feed from the mixing desk. Something like an NU3000DSP will do nicely - a few hundred watts per side, and all the crossovers etc built-in.

Chris

 

[billshurv]

Is the stage hollow all the way back. Can't help wondering if you view the slot you have as the port you could fit something meaty in there.Either that or behind the plants and in front of the drummer isolation unit. (I really want to photoshop animal from the muppets in there).

 

[BP1Fanatic]

Exactly billshurv! If there is more depth than 12", then a BP4 is possible with a 15" or more.

 

[armandoeramos]

How low of a frequency do you need to hit? That driver seems to be more of a midbass driver, with an f3 near 80Hz by my calculations. They certainly have the power handling though.

Thanks for the info! I was hoping for 50Hz. I thought these speakers would work as a subwoofers based solely on it's frequency range.

 

[armandoeramos]

What does the main PA look like? - Those look like some serious wedge monitors for vocal use, so I'd expect a fairly hefty main system to reflect this.

IMO, a pair of 8"s in a room that big won't help much. Put them in a fairly big TH tuned quite high, and you might hear them from the back. Those small sealed boxes won't help the drivers.
You'll need an amplifier, and (presumably) a feed from the mixing desk. Something like an NU3000DSP will do nicely - a few hundred watts per side, and all the crossovers etc built-in.

Chris

Hi Chris,
The mains are two EAW FR129z speakers. Each box has 12 inch woofers and a 1 inch HF driver. Speaker is 500 watts each.

 

[armandoeramos]

Is the stage hollow all the way back. Can't help wondering if you view the slot you have as the port you could fit something meaty in there.Either that or behind the plants and in front of the drummer isolation unit. (I really want to photoshop animal from the muppets in there).

Hi,

That area of the stage is at least 2 feet deep.

 

[Brian Steele]

1. 8" drivers are likely not going to produce enough bass to keep up with those stage monitors

2. You're likely to get a nice notch in the response due to the subwoofer being located that far from the back wall. Measure that distance, then the "notch" frequency is going to be 345/4*d.

3. I suggest trying out (maybe renting) a small sub and placing in that location first to see how it sounds, before committing to a design.

4. Consider locating the sub (or subs) high on the wall near the ceiling if you don't have space for it on or in front of the stage.

 

[armandoeramos]

How low of a frequency do you need to hit? That driver seems to be more of a midbass driver, with an f3 near 80Hz by my calculations. They certainly have the power handling though.

I forgot to mention that I was planning to add a 2 inch in diameter, 7 inch long port to each cabinet. I don't know if that changes anything though but thought to share the missing information.

 

[armandoeramos]

1. 8" drivers are likely not going to produce enough bass to keep up with those stage monitors

2. You're likely to get a nice notch in the response due to the subwoofer being located that far from the back wall. Measure that distance, then the "notch" frequency is going to be 345/4*d.

3. I suggest trying out (maybe renting) a small sub and placing in that location first to see how it sounds, before committing to a design.

4. Consider locating the sub (or subs) high on the wall near the ceiling if you don't have space for it on or in front of the stage.

Thanks for the advice, Brian!

 

[chris661]

If your EAW speakers (and amps) and some headroom left, try turning up the bass on those. They're fairly nice speakers, so if your amplifiers have the power to spare, you could probably get away with +6dB boost at 60Hz and see how you like it.

I'd expect those 12"s to run rings around almost any 8" driver you can name.

Chris

 

[Jensen567]

About the only 8 inch driver I have found that I consider a true subwoofer is the Polk DB840, preferably DVC model.* You can hit a sub 30Hz f3 using ~2 ft3 of volume.* You may have enough room in that space for 2 of them, but they do not handle a ton of power (compared to the drivers you posted anyway, 180W continuous is pretty decent for most things)

*http://www.polkaudio.com/Media/POLK/Product Manuals/dbSub_MN.pdf

You can use this tool as a quick calculator to give you an idea of performance.* Not the best but it certainly gets you in the ballpark.

*Subwoofer Box Enclosure Design Calculator - Sealed Ported Bandpass Closed Vented

 

[armandoeramos]

If your EAW speakers (and amps) and some headroom left, try turning up the bass on those. They're fairly nice speakers, so if your amplifiers have the power to spare, you could probably get away with +6dB boost at 60Hz and see how you like it.

I'd expect those 12"s to run rings around almost any 8" driver you can name.

Chris

Hi Chris,
Thanks for the advice! I'm going to try what you suggested.

 

[armandoeramos]

About the only 8 inch driver I have found that I consider a true subwoofer is the Polk DB840, preferably DVC model.* You can hit a sub 30Hz f3 using ~2 ft3 of volume.* You may have enough room in that space for 2 of them, but they do not handle a ton of power (compared to the drivers you posted anyway, 180W continuous is pretty decent for most things)

*http://www.polkaudio.com/Media/POLK/Product Manuals/dbSub_MN.pdf

You can use this tool as a quick calculator to give you an idea of performance.* Not the best but it certainly gets you in the ballpark.

*Subwoofer Box Enclosure Design Calculator - Sealed Ported Bandpass Closed Vented

Thanks for the info!