Tweeter questions----open back and low frequency capability

[Ric Schultz]

I have an inexpensive Vifa tweet here and have removed the back of its rear chamber......sounds way better. It has a plastic back on it so was easy to remove. You must leave the felt in place or it whistles down the vented pole piece (2K peak). Can other tweeters have their backs cut off in the same way? How about the Scanspeak, Peeless, Morel, Seas, etc. tweets? Do some have a metal back and can they be removed?

Also, what tweets have the most power handling/maximum xmax to be able to be used very low (1000 hz or lower....cut off at 48db per octave via DSP xover). Using tweet in 12 inch customized waveguide.

Any info would be appreciated. I would hate to have to buy tons of tweets and hack them all apart to find out.

[qwad]

hi, most tweeters have a fixed back, though there are a few chambered ones around; couple that come to mind though not model numbers are from;morel, some dynaudio models also the odd seas aluminium dome tweeters they made [ all the others are soft dome, btw] and an inexpensive one from partsexpress sold by them under the "dayton"brand, and there was a project on their projects page to modify this tweeter to a type of transmission line trying to emulate the unusually loaded tweeter on the bowers and wilkins nautilus speaker. as for the rest you are on your own.
cheers and good luck T.C.

[ScottG]

What you experienced is fairly common in the industry. Note that several of the newer Vifa tweeters are *very* similar to the more expensive Scan Speak tweeters. While there are differences in the motor, they are not substantial differences. The *real* difference then is the nature of the venting and dampening of the driver. Unfortunately without the extra fiber dampening in the rear chamber the linear decay *measures* worse (yet almost always sounds better).

As far as free-air performance is concerned, you will be fairly dramatically increasing excursion (depending on your highpass filter). (..of course if you are using a waveguide then may well be lower excursion levels.) If your "baffle" is large enough you'll also be extending your low freq. extension. However expect that efficiency will drop, particularly within an octave (+) of the driver's lower freq. limit.

Always look to driver sd vs. linear excursion, that should give you a rough primer on drivers that will be more capable of higher spl.s with an "open back". However not all tweeters have a "rear chamber".. so the search can be a bit confusing.

I'm not sure that the Human Loudspeaker tweeter has a rear chamber.. but if it does it would likely be ideal. Decent sd, excellent excursion, and a very odd freq. response that would likely become much more linear if it was made "open back". The other tweeter I can think of is the Fostex FT48D. It also has an elevated response in that 1.5 to 4 kHz region that would likely "drop" if you pop its "back". I'm pretty sure though that excursion is no where near as good as the Human tweeter. Both were designed for 1st order crossover use. (..and I'm not sure if it has a rear chamber either.)

Alternatively you could:

1. Use a driver like the BG Neo series.

2. Use a more "full-range" driver like Aurasound, Bandor, Hi-Vi, and Jordan provide.

or

3. Utilize a carefully designed aperiodic "vent".

Note that sometimes the driver, without the additional rear pressure effecting overall compliance, can become over-damped near fs if it has a particularly stiff suspension. This can lead to less 3-D imaging and more 2-D "cardboard cutout" character.

[gainphile]

http://www.madisound.com/catalog/PDF/NSW2-326-8A.pdf

I use this on my Pluto and it's great.

[Ric Schultz]

Thank you all for your replies. It looks like the Morel tweets might fill the bill. They certainly have a chamber that can have the back cut off. I don't know how an inverted dome would work in a waveguide and the Human tweeter has a high FS. The Aurasound is also inverted and has low sensitivity. I am looking for at least 90db. Probably get a pair of 338s and mod them. Hopefully, for all that money, it will sound noticeably better (Vifa tweet is $27 each).