TH-18 Flat to 35hz! (Xoc1's design)

[NEO Dan]

Originally Posted by noSmoking

Hi guys great builds and thank all of you for your info,I connected my sig gen a dynascan 310 to the input of a DEQ2496 to SX3040 to DCX2496 to the 500 watt amp to the sub and turned it on ,was on very low volume [swept from 30hz to 160hz],playing with the knobs,My daughter comes in my garage and says could you turn that down please the dishes and my window in my bedroom is vibrating,
The grill,Idea maybe make some shutters for the opening,the type with wood that slants down,it would keep hands and anything wet out,????
Ns

This is the beauty of programs like REW, in <6 seconds it'll make a couple sweeps and you'll be good to go. If you don't have a super precision multimeter to measure the voltage you can dial it in at 2v instead of 2.83v.


Heck recently I made some REW sweeps while a cop was writing a ticket <10 yards away, though I was a bit nervous on the 15v sweeps .

[noSmoking]

Gosh I'm happy,worked on rewiring the rack ,I needed a volume control on the tweeter amps,that's done so computer to a dac,DEQ2496 to SX3040 To DCX2496 to amps and speakers,got them all dialed in and playing great, I know I will need new set of woofers and not sure about using woffers, mids and tweeters or just a woffer and highend, going to read the thread here on tops for th18 Xoc1's,
Thanks MARTIN for the plans When might those new ones be available?,lol.
I had a dip at 40 and 80 hz so I fixed them and ran without much eq or sonic enhancement,
Stevie Rays low notes came on great I was impressed as usually it sounded distorted when those low notes came out,Still have some work to do But I am happy with this build,
AS I learn ARTA,REW I'll post maybe you guys can give me some suggestion ,
Thanks a lot for all your help and DIYAUDIO for this site!
NS

[NEO Dan]

Be careful with the EQ in the 40-50Hz area this is where the drivers peak excursion occurs.

[noSmoking]

Yes, you are right I heard it flapping a few times there and backed off the juice and it went away,I guess it's time to set up the limiters.I was going to set them for 36hz as that's the lowest it like's before noticeable distorions is heard ,Thanks for the advice!
What tops do you like of what you have tried?
Ns

[NEO Dan]

What's going on at ~36Hz is compression related due to the load on the driver at the box resonance. The driver is susceptible to thermal buildup here because it can't move to cool itself. I would avoid boosting with the EQ anywhere below ~55Hz. If you don't have a boatload of power it should be just fine to HPF between 25-30Hz depending on how hard you run the system. How much power do you have for the subs?

Tops, the short answer... I'd recommend you build some four pi kits with DE250's as the results are better than what you'll get with the active setup IMO. Beyond that I think the JBL 4722HF is a great basis for a high performance 2 way.

[CRESCENDO]

Originally Posted by weltersys

Foam can help eliminate the ringing of metal grills.

I prefer (non-organic) grill cloth, it does not ring, and is easy to clean and does not retain odors.

I was getting ready to buy and install some thin foam tape/weatherstrip (peel back and stick) on the inset wood strips for the grill to rest on to prevent rattling. I think the ringing you're referring to is a bit different. But, now that I'm considering foam/cloth I'm not certain I need that peel & stick foam tape. Guess I could use the foam tape and cut the acoustic foam/cloth to lay on the grill, inside the inset wood strips.

Got a link to that non-organic grill cloth?

[Xoc1]

Originally Posted by Djim

Hi Martin,

I will try to explain. The cone correction makes it function like the sim, which increase the output at the lowest part of the bandpass.

What makes the driver loosing control over the excursion is the 'travelling' of the high pressure zone as result of the excursion (= changing cone volume) in relation to a 'not moving' cab. To keep the control over the excursion, the "Stub" (or "V" in your case) needs to have the highest compression factor, even when the cone moves away from the stub.

Hi Djim
I have repeated the cross sectional area measuring process.
I used the same dimensions as before.
B&C 18SW115 cone mounted on 18mm baffle 53.5cm wide. but added 30mm offset as Xmech.
Areas were measured at 2cm cross section slices - areas added to the spreadsheet and a cone correction curve drawn out to suit the TH18 design.
The result is that when the cone is at 30mm Xmech down, the slope of the cone correction curve is approx 28 degrees.
So I assume that if the slope of the cone correction ramp is bigger than this angle then the high pressure zone will not 'travel' as you described.
Screen grabs of cone model, spreadsheet, and averaged cone correction slope attached.
Regards
Martin (Xoc1)

[weltersys]

Originally Posted by CRESCENDO

Got a link to that non-organic grill cloth?

Acoustone Fabrics for Sound. Improve Quality of Sound When Covering Speakers or Surfaces.

2011 Acoustone
140 - 58th St.
Box: 112, Suite: 9 West
Brooklyn, NY 11220
718-782-5560 / fax 718-782-7367

acoustone@newcastlefabrics.com

Acoustone grille cloth is available in many colors and styles, you will recognize the types used by most amp manufacturers.

I have been using their speaker cloth since the 1970s, and there are plenty of the cabinets still floating around with intact grills. There was a hippy period where I used a dark brown instead of black .

Don't use a 1000 watt par 64 light to look inside the cabinet though, it will melt the cloth in about 5 seconds .

I recently built some outdoor speakers for my deck using a layer on either side of the 3/4" plywood grill frame, the first layer stops most rain unless wind driven, the second layer will stop even wind driven rain or errant drinks.

Art

[Djim]

Hi Martin,

That’s some great modelling again, Martin. I agree with your reasoning about the angle of the cone correction ramp, that it needs to be higher as the 28 degree angle of the cone correction curve. What does surprise me is to see how the centre is expanding in a larger amount compared to the sides. Not sure that is best interpreted into a practical fold, any ideas about that?

[Xoc1]

Originally Posted by Djim

Hi Martin,

That’s some great modelling again, Martin. I agree with your reasoning about the angle of the cone correction ramp, that it needs to be higher as the 28 degree angle of the cone correction curve. What does surprise me is to see how the centre is expanding in a larger amount compared to the sides. Not sure that is best interpreted into a practical fold, any ideas about that?

Hi Djim
I don't see the different shape being a problem.
The difference from the centre to the sides changes as the volume we are accounting for is round and the cone correction is linear. The 3 lines I have simplified it to are just an approximation to enable the opposing shape to be built in timber.
If you look at this screen grab you can see that the lower cone correction line representing xmech having a wider flat face actually still represents a fairly linear path to the opposing timber built cone corrected throat.
An imaginary line drawn thru the imaginary corners seems to line up quite nicely!
Regards
Martin (Xoc1)