Thoughts on the Fostex FW305?? [message #46538] |
Tue, 22 March 2005 12:16 ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
one_speed
Messages: 11 Registered: May 2009
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I thought I would try over here and see if anyone was familiar with the Fostex FW305. I'm looking for a LF driver to run up to around 200 hz or so where I'll bring in my Fostex fullranger. I know, a little different than the Pi Speakers, but I know there are a lot of knowledgable folks here that have a lot of experience with the larger efficient woofers. I'll most likely run in a ported configuration. I'd like these to reach down into the low 30's at least. Seems reasonable as the fs is 25 Hz, but perhaps I'm wrong. I'd appreciate any thoughts you'd like to share. Thanks in advance!!
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It is very much like a JBL 2205, 2225 or 2226... [message #46539 is a reply to message #46538] |
Tue, 22 March 2005 17:27 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18758 Registered: January 2001
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Illuminati (33rd Degree) |
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We were just talking about that very thing last Saturday at the Great Plains Audio Club meeting. Seems a natural subwoofer match for Fostex full-rangers to me.The Fostex F200 reminds me of the JBL 2115 and the FW305 reminds me of a 2205, 2225 or 2226. In fact, the cabinet you should use is exactly the same except for the woofer cutout. I haven't used Fostex drivers, but I can tell you that list of JBL's is my all time favorites, so I am pretty optimistic about what the comparible Fostex drivers must sound like. The Fostex FW305 is best used in cabinets from 1.0ft3 to 4.0ft3 tuned to 38Hz. PiAlign suggests 2.25ft3 tuned to 38Hz, exactly like the JBL's. Put it in a Professional Series seven π cabinet and I'll bet it will sound great. If you don't have corners, put it in the Pro four π cabinet instead.
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Thanks!! [message #46540 is a reply to message #46539] |
Wed, 23 March 2005 07:36 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
one_speed
Messages: 11 Registered: May 2009
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Wayne Thank you so much for the info! I tried to download PiAlign, but it looks to be a PC program, and I'm a Mac guy. What I'd like to do, is to model different sized cabs (just curious to see what can be done/not done) and see how the curves look. For instance, if I tuned the box a little lower, (larger box?) how would that effect the curve? If you don't mind, I'd appreciate plans for the Four Pi cab. Also, do you recommend any particular type of crossover? I was thinking a second order, but if a simple first order will work, that would be great. Thanks again for all your help Wayne. Layne
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Re: Thanks!! [message #46541 is a reply to message #46540] |
Wed, 23 March 2005 08:07 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
spkrman57
Messages: 522 Registered: May 2009
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Illuminati (1st Degree) |
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Layne, About time you came over and visited the Pi speaker forum. You will find a lot of useful knowledge here. This is where I started when I found the site during a google for "2205's". Is your fullranger going to have a tweeter section on it??? Wayne can help you out on the crossover section if you give your requirements you need: ie: 12" or 15" bottome end crossover to FR with tweeter covering top end. Something like that with the driver details included helps out a lot. I think the 4 pi-pro cabinets are the ones you are wanting. There are several 4 Pi systems, so it is necessary to select one. For the 2226 or equivalent, the "pro" version 4 pi is what you want. Ron
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Re: Thanks!! [message #46542 is a reply to message #46541] |
Wed, 23 March 2005 10:05 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
one_speed
Messages: 11 Registered: May 2009
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Hey Ron/Wayne I'm not sure I'll use a tweeter, depends on the amps I'll use. I do have a set of the Fostex T90a supertweeters I bought used that I'm sitting one, we'll see if i need them. With the 300Bs, I may need them. But, if I use a digital amp, I may not, as there's so much more top end there. Once I get these built, I want to get your Yamamoto 45 in my system for a listen. As for crossover points, I have been wanting to roll the woofer off at around 200 hz, then bring in the full range. Not quite sure where to have it come in though. Nor am I sure just what kind of crossover to use. I do know I'd like to use just a cap on the fullranger, but could go second order if needed on the woofer. If I do bring in the supertweeter, I would probably just use a small cap and maybe an L-pad. The thought here is to clean up the full ranger. I've read many times where the full ranger will greatly benefit from not producing the lower bass notes. It seems that while back loaded horns and such are still fairly popular with the full range crowd, more a leaning towards rolling off the bottom end in the full ranger and bringing in a big woofer. Thus, you get a cleaner and more defined bottom end as well as mids and high frequencies. As long as you don't cross too high, you shouldn't loose the point source imaging. Thanks again for thoughts and help with this.
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Re: Thanks!! [message #46543 is a reply to message #46540] |
Wed, 23 March 2005 11:01 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18758 Registered: January 2001
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Illuminati (33rd Degree) |
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Cabinets between about 1.5ft3 and 3.0ft3 tuned to 38Hz are B4 alignments, which have flat response curves. Smaller cabinets become increasingly underdamped, but it isn't bad until you are under 1.0ft3. If you make the cabinet larger, up to about 4.0ft3, it becomes increasing more like a C4 alignment. The response curve dips a little in the octave above cutoff and then rises again just above falling rapidly at cutoff. Cabinets larger than 4.0ft3 tuned to 38Hz or above are underdamped, and the peak rapidly becomes very large as the box is made larger. But you can make the cabinet larger and make the Helmholtz frequency lower to create an EBS alignment. This will give extended bass at a reduced level.
As for crossovers, I would use a simple first-order filter at 200Hz. It will work very well in this application because wavelengths of bass frequencies are large, so summing will be good. Basically, as long as the front to back spacing is less than a foot and a half apart, the two sounds sources will combine as one. Just use a 6.0mH coil on the woofer. If you need a passive crossover on the main driver, use a 16 ohm 10 watt non-inductive resistor across the speaker and a 100uF capacitor in series. That large a cap will probably tempt you to run electrolytic, and if so, you might go with a Black Gate N Type. You can also get several smaller values of another capacitor type and connect them in parallel to form 100uF. An example would be to use (5) 20uF polypropylene capacitors.
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Crossover Electronics 101 [message #46544 is a reply to message #46542] |
Wed, 23 March 2005 12:41 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18758 Registered: January 2001
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Illuminati (33rd Degree) |
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For this application, I'd go first-order but always be aware that a speaker's voice coil is an inductor. When you use a series capacitor for a first-order high-pass crossover, that in itself forms a two-pole system. It becomes a resonator. It is damped by the resistance in the system, and sometimes it isn't too bad. But sometimes it is. Add to this the mechanical resonance of the diaphragm and the impedance peaks of a horn, if used, and the single cap crossover merits a closer look.
I almost always prefer to put a resistance in shunt across the driver, usually 2 to 3 times the impedance of the driver, to damp the system and prevent peaking. This isn't usually needed on a low-pass filter, since it is a coil in series with the voice coil. But if you're going to use a capacitor in series with a loudspeaker, it is best to consider the peaking from crossover capacitance, voice coil inductance, horn impedance and mechanical resonance of the diaphragm.
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