Help with 3 way

Howdy everyone. I've recently finished up the construction of a 3 way speaker and have run into some problems. The tweeter and mid sound excellent, but I think I messed up on the woofers cabinet. I think I did the porting, driver placement, and dimensions wrong to where I'm getting some sort of resonances in the ~200hz area and some others as well. I've tried a lot of dampening and plugging the ports but that hasn't helped. It kinda feels like I put a lot of work into these for nothing as this problem totally ruins the speakers. Is there any saving this build?

My drivers are the sd315a, dc130, and d27. internals LxWxH is 28.5x14x13", port is 4"x 10" on the front

I had an impedance sweep posted here but it is not accurate, and too many folks were only looking at the first chart posted and not the rest in the thread and getting data mixed up so I removed it.
 
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Hi, the box is quite big, lots of panel area. If you have tried blocking the port (successfully), sealed any leaks, mid is in its own compartment and isolated the problem is with the bass driver you could: revisit bracing of the box, perhaps add CLD panels inside, make sure the damping material is effective. Measure the system, full polars, and make sure the crossover does what it should. If there is still noise try higher order low pass filter, and so on. What I'm getting at is that I suspect the box is noisy, has output that is not needed or wanted, which pollutes the midrange.

You need to really drill bottom of it, there is likely multiple issues that contribute. Be sure to identify what it is that you hear, catch it with measurements, then try and fix it. If it is unfixable, build another version that fixes the issue(s) without adding more. Also, be sure to find optimal positioning for your system, midrange problems moght be due to reflection of wall behind the speaker.

In general big multiway boxes are tough to build and measure at home. For this reason its simpler to build separate mid/high system and bass system, and end up with a better system.
 
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GM

Member
Joined 2003
My 'kneejerk' response is the ripples at tuning implies the vent is resonating due to eigenmodes 'drumming' it and stuffing it won't do much to quell any reflections back through the driver; if so, ideally need to ridgidly clamp the vent ~2/3 back and damp (mass load) its exterior.
 
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ideally need to ridgidly clamp the vent ~2/3 back and damp (mass load) its exterior.
You can temporarily mass load the exterior of the enclosure also, for the sake of some additional impedance experiments (not sure if that's what you were implying, GM).

Put down a sand bag, lay the long side of the speaker on it, put another sand bag on top, and measure impedance again.

This bag is relatively square/flat to begin with.
https://www.lowes.com/pd/Sakrete-50-lb-Play-Sand-Sand/3055675

And wafflesomd, please clarify (or post measurements if you have them):
The result of the plugged vs. unplugged port.
Whether you're chasing a sound issue or an impedance issue (or both).
If you have measurable problems in frequency response in general. A frequency response measurement at the port opening is worth doing if you haven't.
Do you have in-room response measurements at your listening position? (may address some of tmuikku's positioning points)
 
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I will try mass on the vent.

I'd say this is definitely starting from something audible. I've noticed it's tricky finding the right slope for the woofer, one slope has good lower mids but honky in other areas while one gets rid of the honk but sounds very thin. I'm using eq apo atm and stacking filters, I'd like to get a dsp408 soon.

I notice the port physically vibrates at the troublesome frequencies, will report back on what mass on the port does. it is 4inch pvc countersunk into the baffle, no braces or mounts for it.

I have two brace across the side panels but they do vibrate at the offending freqencies, when listening near the side they almost sound like little radiators, maybe I'm overthrowing that though. it's 3/4" ply. 1.5" baffle and rear panels.

sorry for phone pic but my internet died today from storms. this is mic at port, green is with filter. blue is raw.

20230701_131220.jpg
 
Uh, yes, 4" pvc countersunk in the front panel vibrates. I planned to handle this by gluing the PVC pipe port to a toilet flange. Then gasketing the toilet flange to the front panel, and clamp it down with screws. Toilet flange is in same department as wastewater PVC pipe. Usually it is for 3" PVC pipe.
There are floor flanges for 4" pipe but they are rare and not stocked anywhere locally. A flange with screw holes in it.
 
Is it possible to apply caulking compound at the port/hole interface? Maybe on the inside of the box, so as not to show.
A small amount that will firm up the joint and can still be removed.
Or if the fit is loose enough, maybe some tape on the port to wedge it in place. Again - temporary.
 
Nice cabs!

Is there a midrange compartment? Are the resonance measurements the same with the mid and tweeter disconnected?

At least then you might isolate the issue to the bass driver, braces and port.

Compare to Troels' bracing in the cabinet photos here where the braces reach back to front (cut with big circles) and the port is sectioned off beneath one of such braces

http://www.troelsgravesen.dk/SEAS-3-Way-Classic-mkII.htm
 
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Alrighty, for reference, the snare on this tune here just kinda blows up with what sounds like a resonance.


I am not entirely sure of my filtering on the woofer to mid but it seems to have improved by increasing the slope order and dropping it from 400hz to 300hz. I believe that might be part of my trouble with some of the upper mids below 1k. Hopefully I can get back some data and see how my room is behaving and potentially influencing my issues.
 
Bracing of the box itself doesnt look that bad.

What worries me is front baffle. It has four cutouts closely spaced which reduce its rigidity quite alot. At the same time, according to pictures, its screved on the box only on its edges. That looks like weakest point to me.
The impedance plot shows parasitic resonances around tuning frequency. Thats where alot of air is pumped in and out of the box, creating high acoustic pressure inside. Now the issue may be the port, but I wouldnt be suprised if the front baffle vibrate around tuning frequency like a drum.
Try to add braces between front baffle and the box, so additional support to the baffle is made, especially around the cutouts.

Just my few thoughts.
 
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thanks for the assessment, I'm going to work out a plan for bracing and knock it out this week, i should be able add some to the front as well but there isn't a lot of room between drivers. I honestly find the baffle doesn't have much in the way of vibrations one can feel.

I wish I could find some pictures of what atc 3 ways look like when you take the baffle off to get some ideas.
 
Looks like a nice project, I actually have a wg300 adapter and waveguide that I considered using. Funny it's called an open source project when one of the drivers is available to anyone. I'm a bit worried that even if I get things braced down, the port in the back was probably going to offer better integration.
 
Alrighty, for reference, the snare on this tune here just kinda blows up with what sounds like a resonance.
Talk about 'boom/punch', personally would only use this for how not to mike a bass fiddle, though admittedly a pretty good recording for testing box resonances based on how bad my headphones distorted (y).

Anyway, per this chart it's obvious that the snare's 100-300 Hz fundamentals IS the 'boom/punch' BW means it's got to be spot on along with all the other acoustically powerful instruments in this critical BW and why the pioneer's took great 'pains' to get it right for a recording/playback.

As others have intimated, the goal is to tie all six sides together to keep the box from 'breathing' along with bracing/mass loading the (sub) woofer to this structure (after P10's designs). Also ideally want both vertical & horizontal bracing located at least at an acoustic or 'golden' ratio or at odd panel harmonics, which gives one the most flexibility.