Open baffle Low crossover freq tweeter modification

Hi,

I was trying out this tweeter from Tangband and I quite like the sound.

Tang Band 25-1744S 1" Ceramic Dome Tweeter 264-866

The key is a crossover frequency that is less than 1KHz.

A thought then came to me, what if the back enclosure is removed and I ran it in an open baffle. But alas the, back cover is glued down.

I will like to find out if anybody else has ever tried modifying a 1" tweeter by removing the back cover and using it in a open baffle.

On a different notes, there are a few offerings of which now offers 1" semi-full range that goes down to 200Hz or so. I will probably give that a shot as a widerange tweeter, crossing it at about 500Hz.

Aura NSW1-205-8A 1" Extended Range Speaker Driver 299-014

Has anybody ever tried what I just described, and what is your listening impression.
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
I used to modify dome tweeters this way and the improvements can be worth it to a point. It seems the limitation with dome tweeters is the size of the voice coil, and doing this tends to make them work harder. For such a low crossover point you might have more luck with a compression tweeter.
 
I had a pair of D2904 600000 Scan Speak car tweeters that I took the back off and mounted in Monocor waveguides front and back to achieve a dipole. The 'as shipped' Fs was 750Hz, taking the back off dropped it down to ~450 Hz with lower Cms. Adding the waveguide assisted the level by 4 to 6 dB at low frequency and I ran as low as 1250 Hz crossover. It could manage 600 Hz at low amplitude and as the amplitude went up the X max was easily found by the distortion. I think that taking the back off made it easier to reach the distortion limit though never quantified how much. The sound out the back was very similar to that out the front up to about 8KHz, where the dome excited 1/4 wave resonances caused by the dimensions of the space at the back. Being only at the back they were not able to be solved using a notch filter without the notch also appearing at the front. In my very small tweeters this occured at a frequency that didnt concern me much, though in the Aura these are much lower in the spectrum and the sound at the back is not very good. I find better value elsewhere using standard parts with minimal modification.
 
I noticed that for many tweeters that have a very low Fs (Tangband for example). The power handling is very low for its class, typically less than 10W. I suppose that is because of the high excursion that happens when a frequency this low is used.

Another question that begs to be answered is... how do you take off the back. I know some tweeters have a screwed on back plate, but what about the rest?

Oon
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
Some are glued. It may not be easy to dissolve the glue in place and you may have to break it open. It can be done carefully but there is always a risk.

You might remove the base of the rear cup for starters or you could saw a slot near the rim of the cup so you could slip a screwdriver in behind the pole piece to prise it off. Temperature may make a difference.

You don't want to crack the magnet or allow metal shavings anywhere near this.
 
I am ressurecting this old track. I finally got around to try out the Aura. Unfortunately, the sound is not brilliant. Treble was harsh. So I am kinda back to square one.

I am now thinking of modifying my tangband so that I can have it working as an open baffle. Opening the back would probably lower the Fs by a few hundred Hz. So i would run it crossed at 700Hz or so.

What do you think...

Oon
 
The length of the tweeter structure will probably cause coloration of the sound from the rear and that cant be cleaned up using the signal as the amplitude to the rear is coupled to that at the front. You may give your tang bands an Aura like sound.

If the rear structure of the tang band is very very small then you may get a sound and polar pattern you can live with: until the lesser constrained mobility of the dome sees the coil bottom out in a forgetful moment of high volume and your tweeters will be lost.
You may find it less disheartening to leave the tang band as they are and try the modification ideas on some tweeters you dont care about.
That will keep your tang band available to test better ideas like mounting them back to back with waveguides and independant tuning.
 
Crossover at <1kHz, 1" dome ??? Open back in open baffle, hmmm

Both criteria are not realistic. A 2" cone tweeter or 2-3" fullrance cone driver could do the work.
This from TangBand?? Tang Band W3-926SD 3" Poly Cone Neodymium Full Range Driver
[IMGDEAD]https://www.parts-express.com/data/default/images/catalog/120/264-815_HR_0.jpg[/IMGDEAD]
Even then, don't ask for dipole sound radiation pattern, the baffle makes that impossible at high frequencies. Dipoles and Diffraction
 
Killing the speaker is a risk but they might live through the experience provided you dont bottom out the coil.
I havent done the work of resinstating them to standard, though if I did they certainly won't look like new.
I dont use this single dome dipole tweeter concept today because the volume out the back is coupled to that out the front. I find I prefer the rear volume to be lower than the front.