Twin Woofers

[stevem]

Has anyone had any experience comparing the subjective performance of one woofer per side verses two woofers per side (placed vertically)? I have recently built new woofer enclosures with two units per side, and they sound a bit boomy compared to the single units I had before. I don't know if its because the second woofer is so close to the floor (3 or 4 inches), or because I used one large enclosure instead of two sub-enclosures. The two ports are front mounted and also next to the floor (about 1.5 inches). Anyone have any comments? Thanks!

[Zilch]

Check the JBL Pro tech notes. You get a 3 dB bass boost from mutual coupling each time you double the number of woofers....

[stevem]

Thanks, I already reduced the gain by 3 db. It's something else. Maybe a different room resonace is being excited now. I'm thinking of going back to a single woofer.

[davp2000]

Check the JBL Pro tech notes. You get a 3 dB bass boost from mutual coupling each time you double the number of woofers....

\
You get a theoretical 3db boost if the power delivered is indentical. You also lower the mechanical low frquency cut off by about 1/2 an octave, but the devices don't work linearly or in perfect sync so the bass is not as clean-crisp,sometimes called attack, but sometimes low is better than clean.

[Guenter]

I don't know if its because the second woofer is so close to the floor (3 or 4 inches), or because I used one large enclosure instead of two sub-enclosures.

Well, alhough I am not an expert, I don't think that a 'single' enclosure with double the volume and two drivers will work. It will not have the same box driver interaction as the single driver with half (but presumably correct) volume.
Are the double woofer JBL monitor cabinets (forget the #'s) not subdivided into individual ~5ft^3 volumes?

cheers

[Guenter]

\
You get a theoretical 3db boost if the power delivered is indentical. You also lower the mechanical low frquency cut off by about 1/2 an octave, but the devices don't work linearly or in perfect sync so the bass is not as clean-crisp,sometimes called attack, but sometimes low is better than clean.

Sorry, didn't clue in to your (and others) exact response. Please let me ask re above to make sure I understand correctly. If a single speaker in a -say- 5 ft^3 box has a -3dB point of 40Hz and flat response, then two drivers in double the volume will have their -3dB point at 30Hz with +3dB peak maybe right around 40 Hz? I find double woofers interesting and am playing around with isobaric designs that reduce cabinet volume...... can't seem to get it work satisfactorily. I'm starting to think that isobarik designs are wishful thinking other that the smaller volum.

cheers

[GordonW]

I've run into this before. The mutual coupling of the woofers will change the response shape a bit, sometimes causing an excess boost in the middle of the bass range.

I'd try lowering the port frequencies... lengthen the ports by like, 15% in each box. I'd bet that might help smooth things out. Also, you will probably get a noticable bass extension increase, compared to the single woofer...

Regards,
Gordon.

[stevem]

Well, alhough I am not an expert, I don't think that a 'single' enclosure with double the volume and two drivers will work. It will not have the same box driver interaction as the single driver with half (but presumably correct) volume.
Are the double woofer JBL monitor cabinets (forget the #'s) not subdivided into individual ~5ft^3 volumes?

cheers

I'm getting the feeling that the single enclosure is what I'm reacting to negatively. I'm going to add a divider to the enclosures, and ports on the back (no room for all the ports on the front). Major surgery.

Anyone have any thoughts on making the two chambers different sizes with different tuning frequencies (ala JBL's M9500)? Has anyone ever combined a sealed woofer with a ported one? Just a thought.