Dual driver T18

[Frankenspeakers]

If I may, whats a choke?

Thanks for the review

just 'nother word for inductor or coil

[jbell]

Ok, for all who have been waiting for a chart on my dual T18, here it is.

It is stood on it's side, which I suppose is how someone would use it for a bottom to a 10.5. (except for the extra wrap test)
The extra wrap test didn't work well, cause my unbraced extra wrap was buzzing so bad, that I'm sure it artificially lowered my spl numbers.. so take those with a grain of salt as well.

Check out how flat the response is with the crossover and choke... it's awesome. I stopped measuring at 125hz, but it is worth mentioning that only with the electronic cross and the choke, did response peak in 125hz range, all others continued to climb into midbass range before falling off.

AND just for this test, I made sure I was using about the worst amp possible... so take the 80hz cross with a grain of salt.. what do you expect on a $65 dollar amp? http://www.partsexpress.com/pe/showdetl ... er=300-784

[Mikey]

Very interesting. Although the choke and the 80hz xover do even it out nicely, it's at the expense of 8db. That's a big hit for a little sub, far more than nullifying the added benefit of the second driver.

I'm a bit surprised by the steep fall-off below 50hz. Given the relatively small overall size of the T18, I'd expect a steep fall-off once it reached it's full extension potential, but I thought that would be closer to 41hz. In the old AT plans, Bill said that "The AutoTuba is a variant on the Tuba 18", but I don't recall that Bruce's measurement of the AT had a similar <50hz fall-off (but my memory aint what it used to be LOL). Unfortunately, when my Firefox crashed a few weeks ago, I lost all of my bookmarks, including the link to Bruce's database. If anyone could please supply that link, I'd much appreciate it. In fact, there should be a "sticky" to that link on the forum, IMO.

Thinking out loud ... I wonder if the small mouth of the dual-driver 24"w T18 is the limiting factor regarding extension (?). The mouth of a "stock" T18 is smaller than that of an AT, and the mouth of the 24"w dual-driver is smaller than two "stock" single-driver T18s. In numbers, a "stock" AT's mouth is 182 sq" and a 24"w T18's mouth is 161 sq", so each driver in the dual-driver T18 is seeing less than half the mouth area compared to the same driver in a "stock" AT.

[Bill Fitzmaurice]

I'm a bit surprised by the steep fall-off below 50hz.

I'm not. A cabinet designed to be operated corner loaded indoors shouldn't be anywhere near flat to its fc half-space outdoors.

[Mikey]

I'm a bit surprised by the steep fall-off below 50hz.

I'm not. A cabinet designed to be operated corner loaded indoors shouldn't be anywhere near flat to its fc half-space outdoors.

I wish I had Bruce's AT test results handy ... from memory, I don't think the AT (designed to take advantage of a car's cabin gain) dropped-off as high, tested half-space outdoors. That's why I'm wondering if the much smaller per-driver mouth size of the dual-driver 24"w T18 is the reason for the drop-off at 50hz.

If you took those same two drivers and put them each in a 22"w single driver T18 (~20% over "stock"), would the two combined cabs stay "flat" to a significantly lower frequency? Perhaps to 41hz?

[Sydney]

link to Bruce's database.

Try this encrypted sequence:
www. + bgavinsound. + com + /reference + /Music + /Bill%20Fitzmaurice/
And navigate to the desired subdirectory

* Are the differences due to how they were measured?

BTW Happy belated Bday Mikey
Won't be long till "fiddy"

[AntonZ]

link to Bruce's database.

Try this encrypted sequence:

And for all who read that: please keep it that way, don't post it as a link, neither here nor anywhere else. Bruce deliberately does not post any direct links to his reference archives in order to keep search engines out.

[Mikey]

BTW Happy belated Bday Mikey
Won't be long till "fiddy"

Hehehe thx Sydney ... And thx for the link, too.

Bruce's AT chart from 9/05 shows a pretty similar curve to the T18 chart, but it starts dropping off at about 55hz.

The chart I was remembering was this one:



The AT's response in this chart looks much different than Bruce's AT chart from 9/05, and jbell's T18 chart.

Heck, I dunno.