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Old 17th May 2012, 03:50 PM   #1
soren5 is offline soren5  Denmark
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Lightbulb Full ranger as mid-tweeter | Power handling?

Iíve previously played around with the FAST concept and really liked it. However, I sometimes feel that Iím missing out on mid-bass if I cross at 200-300 Hz. Iíve tested MA Alpair 7.3s and CHR-70.3s supported by TB subwoofers, which sounded best crossed at around 250Hz (LR4 with miniDSP).

My idea is therefore to try woofers that would be able to go higher and then cross at e.g. 600Hz which should be the upper frequency for kick-drums (see attached chart). Currently Iím looking at this 8Ē woofer, which should go reasonably low in a smallish box and also be able to better handle the higher mid-bass kicks.

SEAS H1252-08 L22RNX/P

Crossing at 600Hz leaves me with new possibilities since many FR drivers would be able to deliver a nice response from this frequency and up. I currently have my eyes on the Fostex FF85WK, which some people seem to really like on this forum.

The Fostex FF85WK has a sensitivity of 85.5 dB and a 15W max power handling (xmax is just 0.35mm ). So hereís my question. If I cross this driver at e.g. 600Hz would that mean I could pump more watts into it without going into distortion? The SEAS H1252-08 specs (88dB / 300W) indicates that this woofer could play quite loud, even in larger rooms. Would the FF85WK be able to ďkeep upĒ with the woofer if crossed at 600Hz? Or should I consider the FF105WK or FF125WK, which have higher sensitivity, power handling, and xmax? Iíd like to be able to go ďparty-loudĒ in a 30 sqm room

Any comments or inputs are welcome. Iíd also like to hear if anyone has compared the Alpair 7.3 or CHR-70.3 with the Fostex FF-WK drivers. I really enjoy both of these MA metal drivers, especially for their high frequency capabilities. Do you think the FF-WK drivers would suit my taste?

Thanks!
Attached Images
File Type: jpg Interactive-Frequency-Chart.jpg (163.5 KB, 380 views)

Last edited by soren5; 17th May 2012 at 04:41 PM.
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Old 17th May 2012, 05:33 PM   #2
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Having built a modified version of MJK's small, passive OB using FF85k and Alpha 15a w/ XO effectively at 500 Hz, I would say that 'party loud' is not a good idea with the FF85k. Maybe others hear it differently, but I don't think that driver can go to ear bleed levels and still sound good.

I have no experience with the FF105 or FF125, but I would be inclined to try one of them first.

Cheers, Jim
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Old 17th May 2012, 06:42 PM   #3
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It isn't that you can put more power into the driver, but that if you are feeding the system X watts, then the FR gets only a fraction of that. At 300 Hz the estimate is X/2, for 600 Hz maybe X/4.

The FF85wk is very good, crossing that high will let them play louder (but if loud is a goal, go with a larger mid-tweeter) but it means that you are XOing in the middle of the midrange.

A FAST should always use a woofer that goes a couple octaves past the XO. Fortunatly lots of midbasses that hit 2k + easily. One has to be much carefuller with subwoofers.

Do note that midbass is the range from 40-80 Hz so the FR XOed 250-350 (common for the FF85) will have no impact on that range. More likely a quality of reproduction issue with using a sub where a midbass would be more appropriate

dave
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Old 17th May 2012, 09:59 PM   #4
soren5 is offline soren5  Denmark
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Quote:
Originally Posted by planet10 View Post
A FAST should always use a woofer that goes a couple octaves past the XO. Fortunatly lots of midbasses that hit 2k + easily. One has to be much carefuller with subwoofers.
Wouldn't that depend on the XO order though? A higher 4th or 8th order would somewhat eliminate the need for a woofer with high frequency extension, right?

Quote:
Originally Posted by planet10 View Post
The FF85wk is very good, crossing that high will let them play louder (but if loud is a goal, go with a larger mid-tweeter) but it means that you are XOing in the middle of the midrange.
Is XO in the lower midrange a bad idea? Why is that? You're the expert here so I'm not doubting your statement, just trying to learn something

My concern is perceived lack of kick drum 'snap'. It's not felt in the same way as the deeper tones, especially when playing electronic music. I thought that since some of the kick drum reach 500 Hz (at least according to the chart I showed before), then perhaps having a woofer crossed higher would help to feel more of these kicks

Jim Shearer states that the FF85WK won't play very loud and sound good, even when crossed at 500 Hz. What's your opinion on this, say in a 30 sqm room? And would cleaner high SPL be achievable by going just one size up to the FF105WK?
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Old 17th May 2012, 10:49 PM   #5
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Quote:
Originally Posted by soren5 View Post
Wouldn't that depend on the XO order though? A higher 4th or 8th order would somewhat eliminate the need for a woofer with high frequency extension, right?
It does, but i'm not a big fan of anything over 3rd order, and given the potential with getting a phase coherent system when the wavelengths are this long when XOing low tend towards 1st order.

Brings up another target goal -- bass drivers cebtres are within a semi-sphere with radius of 1/4 w/l (centre at the centre of the midtweeter)

Quote:
Is XO in the lower midrange a bad idea? Why is that? You're the expert here so I'm not doubting your statement, just trying to learn something
It is exactly in the lower midrange (160-320 Hz) that i am suggesting.

Quote:
My concern is perceived lack of kick drum 'snap'. It's not felt in the same way as the deeper tones, especially when playing electronic music. I thought that since some of the kick drum reach 500 Hz (at least according to the chart I showed before), then perhaps having a woofer crossed higher would help to feel more of these kicks
I'd suggest thst the feel part comes in the mid and upper bass (40-160 Hz)

Quote:
Jim Shearer states that the FF85WK won't play very loud and sound good, even when crossed at 500 Hz. What's your opinion on this, say in a 30 sqm room? And would cleaner high SPL be achievable by going just one size up to the FF105WK?
In an OB with no loading he will be at a disadvantage to the same driver used sealed or in the aperiodic TL i favour.

It is all a matter of trade off between quality & quantity. We have tried FF85, 125, 165 (and 105 are on the break-in bench).... the smaller FF85wk is the most finessed of all we have heard so far. At least until it gets painfully loud.

When Bernie gets the companion WoofTs done for the uFonkenSET we will be playing with XOs up to 500-600 Hz, but the WoofT has 2x4" (subs will be in place for <50-60 Hz)

dave
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Old 17th May 2012, 11:13 PM   #6
soren5 is offline soren5  Denmark
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Quote:
Originally Posted by planet10 View Post
It is exactly in the lower midrange (160-320 Hz) that i am suggesting.
Right, but when I said lower midrange I was referring to my previous suggestion to cross around 600 Hz (that's still lower midrange in my book). I got the impression that you thought this XO point was a bad idea.

Anyway, as you said, this probably comes down to quantity vs. quality, meaning that if I cross higher I can achieve higher SPL but at the cost of loosing some of the sweet mids from the FR driver, correct?

Thanks for the other inputs by the way. Much appreciated
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Old 17th May 2012, 11:35 PM   #7
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Lower midrange is defined as 160-320 hz. Then 2 octaves of midrange (320-640, 640-1250) then upper midrange (1250-2500 Hz)

dave
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Old 18th May 2012, 01:03 AM   #8
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With a minidsp, just try all the cross overs you want. Pay attention to CTC spacing when your xo frequency increases.

There are far greater concerns than power handling when talking about FAST. Consider that when crossing below 300hz it's about the room and sound power. Above 300hz it's about direct response, although power response still plays a major role.

At VI DIY Fest 2011 Dave had a FAST that got really loud. Louder than his Emkens. That had a 1st order filter on a small Fostex. Dave can remind me of the details. The only thing I'd have to say is that I was more focused on the sub-300hz information at the time of listening. The whole (large) room felt like a pressure vessel.
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Old 18th May 2012, 01:12 AM   #9
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FF85Ken + 2 EL166eN, 1st order series somewhere between 300-350 Hz (1 choke + 1 cap (+ bypass cap)). 166s in Scott's tall ML-TL, FF85 in a 10:1 aperiodically damped midTL.

EL166 MTM ML-TL

dave
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Old 18th May 2012, 01:14 AM   #10
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Quote:
Originally Posted by tuxedocivic View Post
The whole (large) room felt like a pressure vessel.
Somewhere on the order of 250m^3

http://www.diyaudio.com/forums/blogs...ing-space.html

dave
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