Fostex FT17H - hurts my ears - diyAudio
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Old 15th June 2004, 11:54 AM   #1
Anne is offline Anne  Netherlands
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Default Fostex FT17H - hurts my ears

Hi,

I have build some time ago speakers with fostex ft17H tweeters. The tweeters have a 6db filter @ 10khz and have a l-pad wich gives about -2db, to match the other driver wich is 96 - 97 db 1w/1m. With low volume they are ok, But on louder volumes they tend to hurt my ears, especialy if there's is for example a triangle in the music. Very sharp, resonanting sound. It isn't the amplifier or cd player.

Are there people who have the same tweeter and had the same problem? Mabey the 6db cuttof isn't sharp enough and the driver hase brake up problems? First I thought it were my ears, but a friend experienced the same.

any help is appreciated.

Regards,
Anne.
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Old 15th June 2004, 01:30 PM   #2
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I do not know this tweeter but it might be running out of excursion? if it sounds good at low volume then its obviously not a frequency response problem as a break up would still be apparent at low volumes. Try increasing the order of the network and see if that helps.
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Old 15th June 2004, 03:41 PM   #3
Greg B is offline Greg B  United States
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Can you describe your speaker in more detail? What is the other driver?

It sounds to me like the supertweeter is crossed to low. Using a 1.0 or possibly a 1.5uF high pass capacitor is more typical with a driver like the FT17. A crossover at 10kHz will probably require a steeper crossover.

Also, is the other driver *really* 96 db? I suspect that it isn't, especially after the baffle step. Only measurement can tell for sure.

GB
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Old 15th June 2004, 04:37 PM   #4
sreten is offline sreten  United Kingdom
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The FT17H's Fs is apparently 5kHz, if so it wouldn't be the
first tweeter to have problems driven at a reasonable level
at its fundamental frequency.

3rd order slopes are generally recommended for horn tweeters,
this is due to sound engineering principles related to excursion.

sreten.
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Old 15th June 2004, 05:56 PM   #5
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Quote:
Originally posted by Greg B
Can you describe your speaker in more detail? What is the other driver?

It sounds to me like the supertweeter is crossed to low. Using a 1.0 or possibly a 1.5uF high pass capacitor is more typical with a driver like the FT17. A crossover at 10kHz will probably require a steeper crossover.

GB
I'm using a FT17 with a .47uF capacitor to augment the high end with FE167E and am enjoying the combination. No problems such as described by the original post.
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Old 16th June 2004, 12:06 AM   #6
Anne is offline Anne  Netherlands
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Quote:
Can you describe your speaker in more detail? What is the other driver?
Eminence beta 12lt in a 4 cubic feet reflex enclosure. like the afterburner thorsten loesch suggested or poor mans hammer dynamics s12.
Seems the tweeter should sound ok, since several people found it an improvement over the original tweeter used in the hammer dynamics speaker. I've used a zobel on the beta 12lt like the one suggested at the afterburner site.

Mabey I play louder then most people do? I love to hear music once in a while at realistic levels (95-100db peak @ listening spot).

Anne.
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Old 16th June 2004, 12:16 AM   #7
Anne is offline Anne  Netherlands
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Quote:
I'm using a FT17 with a .47uF capacitor to augment the high end with FE167E and am enjoying the combination. No problems such as described by the original post.
Ok, this would indeed mean I cross to low. It isn't possible to increase the crossover frequency since the 12lt get's to 9 - 10Khz.

I will try a second or third order filter, as also suggested in other posts.

Anne.
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Old 16th June 2004, 12:16 PM   #8
Previously: Kuei Yang Wang
 
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Konnichiwa,

Quote:
Originally posted by Anne
Ok, this would indeed mean I cross to low. It isn't possible to increase the crossover frequency since the 12lt get's to 9 - 10Khz.
Actually, the Betal 12 LT has a 4-6db boost in the range between around 1KHz and 5KHz which needs to be equalised, a RLC parallel circuit should be used in series with the Beta 12LT, I'd suggest 8R2, 0.65mH and 8.2uF fir starters. The resultant driver has then around 95db/W/m sensitivity in the midband with a -6db point around 8KHz. I suspect you omited the RLC equaliser and hence the upper midraneg is 6db boosted, which invariably make sthe sound shouty.

You then need to attenuate the FT17H by around 5-6db to match the sensitivity of the Woofer and you need a crossover that is 6db down at 8KHz, which implies a -3db point of 16KHz. So I would recommend a 2R2 Resistor and 1uF Capacitor in series as first cut. This will have the FT17H with around 95db @ 16KHz slowly rising to it's full SPL which in tunr slopes off above 20KHz, so the result should be a more extended response.

The result should be more pleasant.

Sayonara
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Old 16th June 2004, 12:47 PM   #9
Anne is offline Anne  Netherlands
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Quote:
I suspect you omited the RLC equaliser and hence the upper midraneg is 6db boosted, which invariably make sthe sound shouty.
I've used a rcl equaliser, but with slightly different values. I will try you're suggestions and see if this helps.

Thanks,
Anne.
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Old 16th June 2004, 06:05 PM   #10
Greg B is offline Greg B  United States
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OK, first, I'd strongly suggest a coat or two of dammar varnish.

KYW makes a good point in that it is likely that much if not most of the harsh treble is coming from the peaks of the 12LT.

IMO, the supertweeter should be padded down even more, like 10db. Looking at the Beta12LT FR charts, it looks closer to 93db than 97 to me. Besides, if this is out in the room rather than flush against a wall, there will be some additional apparent treble 'gain' from the baffle step.

I finally gave up on my 12LT - or more accurately - tweaked it to death. It finally ended up with no whizzer and a piezo for the highs.

FWIW, I found the beta12LT most pleasant and natural by far in a TQWT. Besides the bass being punchier and more effortless than a bass reflex, the midrange seemed clearer and more natural. Line length was 64" IIRC.

GB
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