How to add a super tweeter to fullrange driver - newbie question

[musical]

I have just built a pair Fostex FE167E bass reflex speakers recommended by Fostex http://www.fostexinternational.com/docs/speaker_comp/pdf/recom_enclose/167e_enclrev.pdf

I want to add a super tweeter. In the document, Fostex recommends adding a 0.68-0.33uF in series with the Fostex FT96H super tweeter. I am thinking of using a pair of B&C DE35 Neodymium Mylar Bullet Tweeter instead because of price. Product info here B&C SPEAKERS

Has anyone used the DE35 and can recommend it?

How do I come out with a crossover of 5KHz for this? How does Fostex work out the 0.68-0.33uF values? Is the capacitor for setting the crossover frequency only?

My understanding is that assuming the DE35 has nominal resistance of 8ohm and placing it in series with a capacitor will give it a cutover frequency of 5000Hz=1/(2pi*8ohm*C). C is then 25uF. This is way off the 0.68uF for the Fostex tweeter. Could someone help me as I have no experience in this area.

Also, I am thinking of add an LPAD to attenuate the response as the DE35 is more sensitive. How do I do that with the capacitor in this case. Am I doing the right thing or this is total wrong?

 

[Dr_EM]

I believe a popular way (and the way Fostex are implying) to add a supertweeter which is of high sensitivity to a fullrange design is to simply cross it over higher than you would normally, such that at the desired crossover frequency the drivers have the same effective level and the extreme highs are louder by comparison.

Using your selected driver and 5khz point, I might use a 1uF series capacitor. This drops the level of the tweeter at 5khz by 13dB, making the driver output levels at this frequency effectively the same. From 5khz upwards the output will rise.

Personally, I wouldn't cross as low as 5khz with this arrangement. Doing this will make the high treble too prominent. Rather, I'd use about 0.47uF to give a -13dB point around 10.7kHz which should then match quite well with your fullrangers natural response, giving a lift above 10kHz where your hearing tends to be less sensitive anyhow 🙂

I'm not sure that's the best choice for a supertweeter, but I'm not sure what's available where you are so I'll let someone else put forward any alternative suggestions 🙂

 

[chrisb]

I believe a popular way (and the way Fostex are implying) to add a supertweeter which is of high sensitivity to a fullrange design is to simply cross it over higher than you would normally, such that at the desired crossover frequency the drivers have the same effective level and the extreme highs are louder by comparison.

Using your selected driver and 5khz point, I might use a 1uF series capacitor. This drops the level of the tweeter at 5khz by 13dB, making the driver output levels at this frequency effectively the same. From 5khz upwards the output will rise.

Personally, I wouldn't cross as low as 5khz with this arrangement. Doing this will make the high treble too prominent. Rather, I'd use about 0.47uF to give a -13dB point around 10.7kHz which should then match quite well with your fullrangers natural response, giving a lift above 10kHz where your hearing tends to be less sensitive anyhow 🙂

I'm not sure that's the best choice for a supertweeter, but I'm not sure what's available where you are so I'll let someone else put forward any alternative suggestions 🙂

I'd agree with the Doc - if I read the specs correctly, the sensitivity of this particular driver is 14dB higher than the FE167E. If you want to use a horn tweeter, you might want to consider the relatively cheap FT17H.

To my ear, the FE167 sounds fine run full range - I'd be inclined to leave it unfiltered, and dial in the HP to the tweeter by stacking cheap .5mF polyester film caps in parallel until you hear it stepping in, then pull out the last cap. But no matter how you determine the parts value, don't be surprised if "audiophile rated" boutique caps cost more than the tweeter. As I'm well past the age at which I can hear bats echo-location signals,(it'd be buried in the noise floor of my tinitus anyway) I personally avoid the silly priced stuff.

However, I'd probably be remiss if I didn't suggest that even with a well integrated tweeter, this driver is capable of delivering more coherency, depth of image and resolution with the addition of phase plugs and polka dots - those improvements are definitely not hard to perceive.

 

[musical]

Thanks Dr.EM and chrisb for your help and suggestion.

Yes the driver is 14dB higher than FE167E. I though it would be suitable when I found out that the t90A has about the same sensitivity. Maybe this driver is not suitable at all. At the suggested capacitor value of 0.47uF, at 20KHz it is at -7dB point which is about 7dB above the full range driver. I do not know if it is detrimental to my ear even though I cannot hear it, I certainly won't want a baby nearby. I guess I should drop this driver and consider the FT17H instead as it has a more matching sensitivity.

To my ear, the FE167 sounds fine run full range

The reason I want a super tweeter is that I find the high frequency lacking compared to other speakers, so much so that some of the sparkles in recorded music is missing. I am surprised that many people say that it is fine, could it be due to variance in production?

this driver is capable of delivering more coherency, depth of image and resolution with the addition of phase plugs and polka dots - those improvements are definitely not hard to perceive

I know nothing about phase plugs and polka dots. Could you point me to some readings?

 

[kevinkr]

I have a pair of Half Chili Changs that I recently built with FE167. Definitely recommend Planet10's phase plugs, and some damping on the whizzer to control resonances.

The phase plugs help dispersion in the upper octaves significantly, eliminate buzz from the dust cap (which is gone) and look cool.

I damped the whizzers with teased out acousta-stuff wrapped losely around the neck between the whizzer cone and the main cone. There are strong and very audible resonances right from around 190Hz to 600Hz and beyond that I tracked back to the edges of the whizzer cone. Various people have come up with different ways to deal with this issue including the $0.98 tweak, the acousta-stuff tweak is my variant on the idea.

These drivers really need 100hrs or more to properly break in, and that is from wretched personal experience.

And BSC is a good idea with the stock Fostex BR box which IMO is not the greatest.

Take a look at my HCC thread here: http://www.diyaudio.com/forums/full-range/148104-what-build-pair-fostex-fe167.html

You may find it generally useful for tweaking ideas. While not perfect I think the completed and mostly broken in FE167 in HCC boxes sound pretty good actually. Spend some time tweaking and working on listening position and speaker placement and you may find those super tweeters are not really necessary.

 

[chrisb]

Thanks Dr.EM and chrisb for your help and suggestion.

Yes the driver is 14dB higher than FE167E. I though it would be suitable when I found out that the t90A has about the same sensitivity. Maybe this driver is not suitable at all. At the suggested capacitor value of 0.47uF, at 20KHz it is at -7dB point which is about 7dB above the full range driver. I do not know if it is detrimental to my ear even though I cannot hear it, I certainly won't want a baby nearby. I guess I should drop this driver and consider the FT17H instead as it has a more matching sensitivity.


The reason I want a super tweeter is that I find the high frequency lacking compared to other speakers, so much so that some of the sparkles in recorded music is missing. I am surprised that many people say that it is fine, could it be due to variance in production?


I know nothing about phase plugs and polka dots. Could you point me to some readings?

see the commercial site on link in signature line below

(polka dots = EnABL, take a pee-break before sitting down to review the results of a google search) .

 

[musical]

Thank all for your input. I am reading up the Planet10's phase plugs and have questions.

The site says "Finished plugs come with magnetic mounting for snap into place installation with easy adjustment. Blanks can be requested with magnets pre-intsalled but normally ship with none."

What is the difference between a finished plug and a blank with magnets pre-installed? What do I have to do to make a blank into a finished plug?

When I install the phase plug, I have to make sure that it is not touching the whizzer cone? If so, there will be a tiny gap where the dust can enter into the voice coil gap?