BFM T48 vs. SP.com 186

[WB]

I stripped a T-Nut when I first installed the woofer, so taking it out was a nightmere

Been there, done that. There's pretty much nothing you can do to remove a spun hidden T-nut without destroying something. That's why I won't use them.

[djtecthreat]

What would I be listening for with a impedance sweep? I can do it later.

Been there, done that. There's pretty much nothing you can do to remove a spun hidden T-nut without destroying something. That's why I won't use them.

What are you using? I wouldn't/can't trust wood screws on a box used for professional work.

[Sydney]

What you see reflected in an impedance sweep is symmetry of the curve and the frequency location of the tuning.
If it is not tuned right the peaks will be at at different frequencies from where they should be and there can be "blips" or irregularities in the otherwise smooth graph.
Ideally you compare against a similar working model.
I compared my impedance sweeps of my T18 and T24 against the published impedance graphs that were available.

[WB]

What are you using?

For my OT12 I used large #14 wood screws. I'm confident they won't break or back out due to vibrations.

I wouldn't/can't trust wood screws on a box used for professional work.

I can understand that. For the DR200 (and T39) I'm going to drill and tap an aluminum backing bar that the driver bolts will thread into. A little extra work because it diy, but worth it imo. I'll take some pictures when I get to that point.

[Tim A]

To address both issues:

Install your T-nuts in the baffle by pulling them in with one of the bolts and a fender washer, do not hammer them in. Use a good strong glue like Gorilla Glue or a polyurethane equivalent from PL or Elmer's to glue it in place. Make sure the glue only gets on the nut flange, not the threads. Once all the T-nuts are installed, test fit the driver to the baffle. These steps do several things. First, by pulling them in instead of driving them you're assured a straight installation. Second, you're assured the threads in the T-nut are good. Do not assume they are, I get a lot of T-nuts that need to have a tap run through them to clean up the threads. Third, the glue will stop it from spinning. Now when installing the driver you know everything lines up and is good.

Testing: Download a test tone and burn it to a CD. I use 31.5Hz, most guys use something lower. If you use a low frequency like 20Hz you won't hear the tone, so be careful. Now, with the driver access cover off, run the CD at low power. This will allow you to test the driver seating and the interior chamber. If there's a leak, you'll hear it. It could sound like anything from a low grade hiss to an air compressor. The pressure in the throat is high enough that it will actually push air back into the chamber. You can repair leaks with PL or use hot glue for instant gratification.

Once you've gotten the driver seat and chamber air tight, install the access cover and run the test again. This will allow you to test the access cover, the exterior joints, and any handles, connectors, etc. The only seams you can't really test are way at the top of the last panel before it gets to the back, but the pressure is low enough in that area that a pinhole leak won't be as critical.

This isn't as technical as an impedance sweep, but it works just fine.

[RubiconProSound]

I wouldn't/can't trust wood screws on a box used for professional work.

I installed car audio for 15 years and used nothing but screws and I never had an issue with a speaker backing out or coming loose. We had a kid get in a car accident and the sub enclosure flew forward and was destroyed; the woofer was still in place...

In my experience If you have enough wood to hold the threads and you use the right screws (Not numer 8...) you won't have a problem. I also don't play soccer with my speaker cabinets or bounce them around so that helps.

[Bill Fitzmaurice]

In my experience If you have enough wood to hold the threads and you use the right screws (Not numer 8...) you won't have a problem. I also don't play soccer with my speaker cabinets or bounce the around so that helps.

+1. I recommend bolts and nuts with drivers that are over ten pounds and/or baffles less than an inch thick. With an inch thick material and a driver of ten pounds or less the 2.5 pound load per screw isn't going to be a problem.

[djtecthreat]

To address both issues:

Install your T-nuts in the baffle by pulling them in with one of the bolts and a fender washer, do not hammer them in. Use a good strong glue like Gorilla Glue or a polyurethane equivalent from PL or Elmer's to glue it in place. Make sure the glue only gets on the nut flange, not the threads. Once all the T-nuts are installed, test fit the driver to the baffle. These steps do several things. First, by pulling them in instead of driving them you're assured a straight installation. Second, you're assured the threads in the T-nut are good. Do not assume they are, I get a lot of T-nuts that need to have a tap run through them to clean up the threads. Third, the glue will stop it from spinning. Now when installing the driver you know everything lines up and is good.

I did all this, as well as dipped the bolts in some lithium grease to prevent any binding. Still managed to strip one.



I will sweep the box later if I can. I still don't think there are any leaks.

[djtecthreat]

I'm not able to do an impedance sweep, but I checked again and again with different tones and I can not detect a leak.

Although the box is performing much better than before, its comparable to an 18" reflex sub I have here (EAW LA118z) in terms of output. It was to my understanding the T48 would stomp all over a reflex sub. Maybe I need to be outside with a stack of 12 to stomp all over reflex boxes?

[Bill Fitzmaurice]

It was to my understanding the T48 would stomp all over a reflex sub. ?

It will. If your's doesn't that indicates that you're only using one, it's not being tested in a proper environment, and the testing isn't being done with the equipment necessary to do so accurately. A seat of the pants 'this one's louder' assessment indoors will only reveal the deficiencies of the room response.

[Dave Non-Zero]

So the t48 sounds louder and deeper than the 186, but the eaw sounds louder than the t48. so the 186 must be pretty bad then! Im glad i found this site before i built any.
I must say i dont believe a single 18 would be louder than a single t48. The 18 may feel more 'pant flapping' if you stand by it, but it WILL NOT fill a club with bass like the t48. The thump you get from direct rad speakers disguises the lack of the fundamentals.
I was standing by a stack of jbl the other night (double 18 sub and double 15 tops) and the thump was pretty good but it just fades away out into the crowd. I know this gets said a lot here, but its true.
I think the reason they thump more than standing near a stack of BFM is because the subs are adding to the midbass that creates the thump, not the bass. so you get 4 speakers attackin you with midbass, unlike the BFM stack that only has the tops to hit you with midbass.

[Bill Fitzmaurice]

I think the reason they thump more than standing near a stack of BFM is because the subs are adding to the midbass that creates the thump, .

Which is covered in the FAQs.
http://billfitzmaurice.net/phpBB3/viewt ... f=10&t=999
Though they would be more appropriately be called MIATFAQ.
Mainly Ignored Answers to Frequently Asked Questions.

[Dave Non-Zero]

I think the reason they thump more than standing near a stack of BFM is because the subs are adding to the midbass that creates the thump, .

Which is covered in the FAQs.
http://billfitzmaurice.net/phpBB3/viewt ... f=10&t=999
Though they would be more appropriately be called MIATFAQ.
Mainly Ignored Answers to Frequently Asked Questions.

Ok, so i shouldnt have said 'think', i should have said 'I KNOW That The Thump Is Caused By Harmonic Distortion Because I Read It In The MIATFAQ And Tell Everyone I Speak To About It At Gigs.'
or as i like to snappily call it IKTTTICBHDBIRIITMIATFAQATEISTAIAG

[Chris_Allen]

IKTTTICBHDBIRIITMIATFAQATEISTAIAG

I'm going to text that to my teenage sister to see how long she will spend trying to figure it out.

[Sydney]

Mainly Ignored Answers to Frequently Asked Questions.

I wondered sometimes if posts to the Educational Links forum were just taking up web site space.
Are those posts helping anyone?