Jims 3 way speaker build

[rpb]

so this is the XO I have in play now. I had another listener come over to hear it and it sounds real nice. I think I need to pause and listen for a bit and pause making changes until I get real familiar with the speakers. Then I can refine further. One note the tweeter polarity should be shown as in phase. For some reason in the SIM the results are better reversed but in reality it is better In Phase

I put your xo in a sim, and it looks very good!

[jimbones]

Ive had some time to just relax and listen. I made a few tweaks but in the end I believe it is the bass that is throwing me off. The bass is very strong at times. This may be due to the fact that it is a fairly efficient driver and gets gain from the floor boundary. Ive played with the mid and tweeter levels to see if they can keep up and I think either the box tuning is off or the woofer is just to loud and not sure how to remedy this.

[rpb]

Ive had some time to just relax and listen. I made a few tweaks but in the end I believe it is the bass that is throwing me off. The bass is very strong at times. This may be due to the fact that it is a fairly efficient driver and gets gain from the floor boundary. Ive played with the mid and tweeter levels to see if they can keep up and I think either the box tuning is off or the woofer is just to loud and not sure how to remedy this.

Try sealing the port. Look at your box sim to see the difference in response. Then see if there is boom, or not.

Rooms alter the bass considerably. You may have a peak at a specific frequency caused by the room. You could measure bass at your seat, and see. Don't expect it to be flat. Just look for standout peaks.

I believe that a high dcr coil could shave a dB or two off the woofer response. Tuning lower could help as well.

[jimbones]

I am really struggling with the bass. It is a quality and quantity issue. There seems to be resonances that are muddying the sound. Its not clear and punchy. At times it seems loud and at others it seems reticent. I was thinking about whether to post here or start a dedicated thread to resolving this.

So far I have played with varying amounts of stuffing inside the cabinet. I also tried plugging the port (very little difference which I am suspicious).
The cabinet itself does not seem to be vibrating excessively. It is braced. I Have the cabinet minimum of 40 inch from side walls and 4 feet from front walls.
I recently lined the port (ala Troels) with carpet padding. (see pic). Seems to quiet some stuff but overall NG.
The things I have yet to do are playing with varying port lengths and diameters. I have read where some people say they had to make the port half the length of what WinISD advises. Sounds like too much….

Questions I have:
Could the cabinet shape be a contributor? Narrower at the rear and wider at the front?
The volume is 65 litres. Or about 2.4 cu ft. and the cabinet is tuned to 33hz That seems correct, no?
Could the port dia be too big? Maybe a 3 inch port?
I have a 6.5 mh coil/110uf cap on the woofer. Not sure a parts change will help. I will listen to the woofer by itself.

In the end I am willing to give up F3 for quality. I have GR Research subs to augment these. I can go to high 30’s or 40hz?





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[johnny5jz]

Is 2.4 cubic feet total enclosure volume not subtracting the port and woofer volume? I don't have my modeling software in front of me, but if 2.4 cubic feet is your total volume, I suspect your enclosure is a bit too small and you are getting a large peak prior to rolloff. You may try lengthening the port and tuning even lower to even out your response. I can try modeling it later and see if my suspicions are correct.

[rpb]

If you didn't already, I'd check to see if the padding resistors on the mid are getting hot, and possibly changing value.

Speaker location can make a big difference. Try 32" from the side walls maybe. Room software may predict the response.

[jimbones]

Interseting. I am using a NAD C272 while I am in this phase of testing the XO. A buddy brought over a Peachtree GaN400 and it improved the overall sound by a mile. The bass improved as well. I need to borrow it again and spend some time with it to see if it was the NAD amp that had crappy bass.

[jimbones]

Found about 3 small air leaks in the rear panel. I used incense stick and played a bass heavy track and watched the smoke curl. I'll fix those but it wasn't much.

[DeZZar]

- recheck the exact NET volume of the cabinet. Subtract braces, midrange isolation box, anything else solid.
- with the leaks plugged up, take a fresh impedance measurement - take fresh woofer nearfield and port nearfield

- do you have detailed drawings of the cabinets you can attach? Something showing all the internal dimensions etc?

[jimbones]

Dezzar, im a bit busy today but I have the info. let me put it together and I will post tomorrow. Thanks for checking in I really appreciate it.

[jimbones]

Dezzar, im a bit busy today but I have the info. let me put it together and I will post tomorrow. Thanks for checking in I really appreciate it.

[jimbones]

DeZZar really quick and dirty interior volume trapeziod 149.5 sq in x 38 in height is 5681 cu in or 3.3 cu ft.
There is a .2 cu ft enclosure for mid, allow 0.1 for the woofer, 2 braces 3/4 inch thick = .0007 cu ft, the vent = 0.065 cu ft and the tweeter is negligible since it is mounted on a 1 inch thick baffle. Crossovers are external for now. So basically I allowed 0.8 cu ft. Win ISD says 2.5 to 3.0 cu ft. I should have over 2.5cu ft. The only thing is there are volumes of air that maybe acting as resonators since air can flow around certain structures but is limited.

[jimbones]

Doing some more homework I find that I made the mid enclosure on the large side, not so much so but I can make the mid enclosure 2 inches shorter and still have a good Q of 0.75 sealed. I believe the big box is in the way and not sure if it is impeding air flow.I fixed the air leaks on one speaker. I will also reverse the port and put it external to the cabinet and play with tuning.

[rpb]

The Q will not matter much at all. An option to consider, is changing the shape of the mid chamber. ie sloped sides, etc.

[jimbones]

Update: I ran a SIM in a program called SpeakerBuilder Pro 2.0 and it says my Port should be 23.5 inches long!! Thats a bit more than twice what Win ISD specifies. The program says that if I go to a 3 inch port the L is 12 inch.

[johnny5jz]

Your woofer measurement looks like a box that is too small tuned too high. Your box size seems right, but if your tuning is too high, it would look like what you are seeing. Going with a longer port will drop your tuning and should even out the response.

[a4eaudio]

WinISD has always given me impressively accurate results.

[jimbones]

johnny5jz I calculate my net interior volume to be 2.7-2.8 cu ft. I will try the tuning. thanks

[Chris Roemer]

Did you measure the T/S parms of your woofer yourself (or just going by mfr's claims)?
Something seems wonky w/Speakerbuilder 2.0.
A certain (interior) volume box needs a certain length/dia port to be tuned properly (i.e., the driver doesn't alter the box tuning).
A 4"id port tube needs to be about 11" long to tune a 2.75cf box to near 30Hz.
Using SB's specs (Qts=0.28, Fs=22, Vas=7.24cu.ft.), a 30Hz tuning for THAT box looks OK (F3 in the mid 30s). It surely does NOT have a "hump" in it. If anything, it looks a bit "lean".

[jimbones]

Chris it is lean below 50 hz. There seems to be little low bass (30-40hz). I say hump because at 65 hz it gets louder relative to the lower bass region so it sounds a bit boomy. I believe I am close. Some music sounds OK its just not optimal. Any other ideas? Could I be overpowering the room?

[jimbones]

Oh and one thing I forgot, I noticed that there is hardly any air coming out the port (or the velocity is so low) I even put a lit incense stick in front of the port to see what happens to the smoke trail and nada nothing. unaffected. That seems strange

[Chris Roemer]

So, let's say your box's interior woofer volume is 2.75cu.ft.
Exactly what is the current ID and length of your port?
If you can measure impedance (ARTA, or DATS?), you should SEE your tuning freq. (the center of the "valley" between the peaks).

Also, IMO, you have a "low Q" (Qes/Qts) woofer, which are not associated with strong bass.

[DeZZar]

https://techtalk.parts-express.com/forum/tech-talk-forum/1487345-jims-3-way-speaker-build?p=1493007#post1493007

Looked like you were very close to 32hz back here.....but we need to re-baseline with the sealed up leaks etc...

[DeZZar]

The sweet spot for this driver is 32hz tuning in 2.5cu.ft.(70L) for an f3 around 34-35hz.

According to winISD modelling it'll take bags of power in this configuration and should be capable of producing near on 114db prior to baffle step without getting anywhere near its mechanical limit. It'll handle its thermal limit (200W) all way down to 25Hz in this kind of box. At 91db sensitivity to boot I'd say its a pretty good candidate for strong bass performance.

jimbones the last impedance sweep you took showed your tuning was right on 30hz (your system impedance) and another prior to that showed closer to ~32hz. But you've since stated you found leaks - which can play havoc with trying to get tuning right.

Once you have completely sealed up every single leak (including around driver frame and port) can you re-take the impedance sweep (preferably without any crossover parts connected) and re-measure the frequency nearfield for port and woofer and upload (again, without any crossover parts connected). Oh and put all the foam/padding etc you plan on using in place as well.

Even for the nearfield measurements get the speaker away from all boundaries as far as you can and at least up on a chair away from the floor.

[jimbones]

Will do. one question, when you referenced an earlier zma graph, are you saying that was fine and about as good as I could expect. Once I seal up the second cabinet and retake zma and Fr of speaker and port we can see where the new baseline is. Thanks for your help.