Small OB in a FAST setup

[adason]

"There's a huge chasm at 300Hz."

Have you tried switching the polarity?

 

[perceval]

"There's a huge chasm at 300Hz."

Have you tried switching the polarity?

Yes, That's the first thing I tried. Didn't change much.

 

[wesayso]

Floor bounce?

 

[perceval]

Hmm.. wouldn't floor bounce be universal?

I don't have that chasm with the sealed boxes doing up to 500Hz. Didn't have it either when the 1772 were in ported boxes.

Anyway, I have a 3-week vacation that started yesterday, so I moved all the gear to a room that has bass traps in all corners, and I'm adding some panels at the first reflections... can't wait to start measuring in there!

 

[BYRTT]

Sounds nice you have 3 weeks vacation, enjoy and have best time also thanks sharings so far and please continue keep us updated : )

 

[perceval]

Been busy camping, as the weather was cooperating. Now, we're hiding in the house for the next couple of days because the roads are invaded with tourists.

I'm about to cut my beautiful hinoki boards to make the baffles.

Quick question: Since this is OB, do I need to put a speaker gasket to isolate the driver from the baffle, or should I couple the driver to the baffle directly? The baffles are 5cm (2") thick and hinoki (camphor wood) is not resonant with the resin in the wood, acting as an organic dampener.

 

[perceval]

Thanks for the folks from the line array build, I got introduced to Fusion360...

My days of doing 3D work were about 25 years ago... and I was using FormZ at the time.

I never caught the SketchUp bug, hated it actually.

I'm far from anywhere with Fusion, having a few hours of practice, bu I like it so far... just a little sluggish at times.

Ronald will be happy I'm going back to marble, and wood design.

This file has some mistakes, and not finished design wise. It's a U Frame sub (didn't have a cad file so it's just a 2D picture pasted there), and an OB fullrange (here with wesayso's TC9 cad design... thank you!)

I think I like where this is going...

 

[scottjoplin]

Hello all. Hope you don't mind me asking this question as you are discussing similar at the moment. I have open baffle Jordans xd over at 125Hz to 4 12in in U frames. I measure a large dip at xover yet only hear a small one. It's probably obvious but what's that about?

 

[perceval]

Not sure what you mean... besides saying your ears are not as accurate as your microphone.

Have you tried inverting the polarity (phase) of the Jordans?

 

[scottjoplin]

That could be all it is. No haven't tried inversion because all should be in phase using 24dB/oct LR xover

 

[perceval]

Also, low end has a lot of room resonance, nulls and peaks.

Just try moving the subs around a bit, or even your listening position, if possible.

 

[scottjoplin]

Active crossover then LF EQ managed to correct quite well. The subs and fullrange are equidistant and well away from walls. Seems more than a coincidence that the only problem is at crossover. The dip is very narrow, about 10Hz at most, is that to be expected? I'm measuring using amplified panasonic wm61a and oscilloscope

 

[BYRTT]

Active crossover then LF EQ managed to correct quite well. The subs and fullrange are equidistant and well away from walls. Seems more than a coincidence that the only problem is at crossover. The dip is very narrow, about 10Hz at most, is that to be expected? I'm measuring using amplified panasonic wm61a and oscilloscope

Be aware drivers by themself have a natural acoustic stop-bands roll off so if active electric XO is textbook LR 4th order at 125Hz then final slope sum (LR4 x acoustic roll off) can end with some error. Below black curves show LR4 at 125Hz that will sum flat in amplitude and be in phase although a rotating phase, where orange curve show the error from ideal if one add textbook active electric LR4 at 125Hz to a driver that has say 80-20kHz acoustic band width. So target is to hit those black curves in acoustic domain then they sum in amplitude and be in phase in XO region with some added group delay coused by the minimum phase rotating XO point.

Think 125Hz area is overall hard to measure right and probably especially when using oscilloscope method, because XO point is so low in frq suggest as a test scenario do near field low level measurement with ~1cm microphone distance in center of cone and then try to get subs and OB fullranger hit ideal LR4 curves in acoustic domain with whatever means of electric EQ plus strange XO slopes it takes to hit those acoustic target curves. Then if acoustic center for subs and OB fullranger have same distance to listening position and polarity is right system should be tuned in theory correct and if further errors show up its probably room boundery modes as pointed by perceval. Regarding polarity be aware that some power amps without warning in reality happens reverse polarity for output verse input.

 

[scottjoplin]

Thank you so much. Very informative. Plenty for me to get my teeth in to.