Fostex w/ Bass Reflex?

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I was trying to find prices for Fostex drivers and I came across the following website: http://www.commonsenseaudio.com/fostextech.html who strongly criticize horn-based enclosure designs. (The site only sells bass reflex designed drivers but their criticisms seemed general.) Since all the other diy sites seem very pro-horn, I was curious: what's up with that? Are they wrong, and if so, why?

Thank you! And I'm sure you'll be seeing more of me in the near future...
 
Well personally, I disagree with them. Not because I'm biased toward horns -most horns aren't very well designed. But IMO, nor are their BR boxes. I remember trying to plug their approximate dimensions into MJK's MathCad sheets and coming away decidedly unimpressed with the response. You can get superior performance out of those units in a smaller MLTL enclosure. See www.quarter-wave.com for more -look in the projects section. Those cabinet designs are free too, and believe me, they work.
 
My opinion of Common Sense Audio is less than favorable. There is no science here and the conclusions simply make no sense.Given that the discussion applies only to full-range Fostex drivers:

1. Properly designed horn cabinets DO work. Most horn cabinets are not well designed, but that is another issue. Horns will play louder than BR's or quarter-wave cabinets (MLTL's) and therefore are more "dynamic". Horns are larger and more intricate than BR's or quarter-wave cabinets for the same driver. Horns tend to be picky about design specs and are not tolerant to construction errors. As with everything else in audio, horns require compromises. One must take the good with the bad.

2. Quarter-wave cabinets are physically smaller than horns and bigger than BR's for the same driver. Well, that's not actually true, since you you really don't want to use the same driver in horns as you do in a quarter-wave cabinet. Use the FExx6 series for horns and the FExx7 series for quarter-wave and and BR's. (You can force an FExx6 into a BR, but IMO, the results are better if you use FExx7's) I have done quarter-wave cabinets for the FE167E and the FE207E with good results. I get bass well below 40 Hz and the great mid's than one expects with single driver speakers. As long as you don't require great SPL, quarter-wave cabinets give a great sound. They are best for small group music, jazz, voice, pre-Wagner classical.

3. BR's give you a mixed bag of compromises. They are the smallest cabinets, the BR's being stand mounted while the quarter-wave cabinets are floor standers. An FE167E BR is not truly full-range, since the F3 of a 24 liter cabinet is around 60 Hz. However, if you use a subwoofer and high pass the FE167E BR at 80-100 Hz, things change dramatically. With the bass load removed from the FE167E, dynamic range is increased dramatially and intermodulation distortion reduced significantly. This is the setup I use for HT -- four FE167E BR's around and a sub. Makes a lot of noise! An FE207E BR of 36 liters IS full-range. F3 is ~43 Hz and F10 ~35, numbers only slightly higher than a quarter-wave cabinet. Modest dynamic range, though. The general conclusion that all BR's have boomy and woolly bass is totally wrong. If the cabinet is designed correctly, a BR can have very listenable bass.

4. NEVER consider using two identical full-range drivers on the front baffle playing the same frequency range. You can use two drivers in a bipole or dipole layout, but never on the same side of the cabinet. The comb filtering between the two drivers will give you fits.

In conclusion, there are no flys on any one of the three cabinets discussed here. It is up to your musical requirements, your construction capabilities, and the size of cabinet you can stand.

Bob
 
if you use a subwoofer and high pass the FE167E BR at 80-100 Hz, things change dramatically. With the bass load removed from the FE167E, dynamic range is increased dramitially and dramatically distortion reduced significantly.

That´s exactly what I´ve observed too.
I run my FE167E´s in 22 L BR cabinets and they sound quite nice on their own, but after some experiments I´ve decided to XO at 80Hz (24dB active) to a pair of Scanspeak 8545 in 30L BR boxes.
I finished the subs yesterday and will probably get time to finish the active crossover tonight.
:D
 
I can just about cope with their semi-omni types with a forward and an upward firing driver. Pass re the cabinet design though -I haven't looked at those. Yet. But personally, I'd avoid their cabinets like the plague and build my own. At least that way I know for certain it's properly designed.

I don't buy some of their other comments too. Low powered tube amps do not only work well with full-range units. I've got a pair of borrowed Revolver RW45s downstairs which sing with EL84s putting out 3wpc. 10wpc would take your head off. As do the Castle Conway 3s belonging to my parents. And Monitor Audio B4s. And...

Best
Scott
 
My 1st venture into single driver was building the Commonsense MKII enclosures for FE206E`s, and I`m glad I discovered the single driver approach to speaker building. Since I`ve built the Fostex recommended horns for the 206`s and the are IMHO better. I also put Fe207`s in the BR boxes and they worked much better than the FE206`s in a BR. Eventually I`ll sell the Commonsense MKII boxes and build the Fostex double BR boxes for the FE207`s. I have built the double BR boxes for the FE127e`s and was happy with the sound, but if you`re going to take the time, build horns, maybe like the one`s Ron has designed. Everything I`ve heard abut them is positive and I would bet they are better than the Fostex horns, though a little more involved to construct.
 
Bob is being much more polite about "Common Sense" audio than I would be. :D

Incidentally, I use FE207E in bass reflex cabinets. This is a reasonable implementation for apartment life, but certainly not "high fidelity" in terms of being able to produce realistic SPL across the bandwidth.

But the weird idea of slapping a whole range of drivers into bass reflex cabs without severe frequency compensation . . . has no basis in reality.
 
Bob Brines said:

4. NEVER consider using two identical full-range drivers on the front baffle playing the same frequency range. You can use two drivers in a bipole or dipole layout, but never on the same side of the cabinet. The comb filtering between the two drivers will give you fits.

I thought some fullrange driver can be used so such as the Jordan JX6 and earlier the JX53.
 
I built a pair of 4" Fostex F83's into a double base reflex enclosure. Mids and highs are quick and clean and the speakers go surprisingly low for such small drivers.
At louder volumes though, even though the mids improve, the base becomes a little uncontrolled and boomy, flattens out and lacks in depth.
It was a compromise i was willing to make, smaller enclosures (small apartment) less bass but nice clean mids.
 
navin said:


I thought some fullrange driver can be used so such as the Jordan JX6 and earlier the JX53.


ANY two drivers playing the same frequency band and mounted next to each other will begin to form interference patterns as the wave length becomes short with respect to the distance between them. You must low pass the paired drivers before this happens, which totally defeats the purpose of full range singe driver speakers. Using smaller drivers only raises the frequency where the comb filtering begins, but not high enough to be useful for single driver speakers.

I have heard a few people that claim they are not bothered by rapid and dramatic changes in SPL every few inches in the vertical, but I don't think that's the way to go.

Bob
 
Bob Brines said:

ANY two drivers playing the same frequency band and mounted next to each other will begin to form interference patterns as the wave length becomes short with respect to the distance between them. ...

In theory I agree. I have not tried thisin practice. so far I have used either a single driver fullrange or a traditional multiway multi-driver systems. I just was under the impresion that Ted Jordan's JX6 and JX53 were designed specifically to be used in fullrange line arrays.

one option with a driver as small as Jordan's JX6 is to use in a MTM where the center driver is fullrange and the outer 2 drivers are rolled off at say 1K or so. this however will put some odd loads into most amplfiers.
 
navin said:


In theory I agree. I have not tried thisin practice. so far I have used either a single driver fullrange or a traditional multiway multi-driver systems. I just was under the impresion that Ted Jordan's JX6 and JX53 were designed specifically to be used in fullrange line arrays.

one option with a driver as small as Jordan's JX6 is to use in a MTM where the center driver is fullrange and the outer 2 drivers are rolled off at say 1K or so. this however will put some odd loads into most amplfiers.


Line arrays and MTM's rolled off at 1K will work, but, again, this defeats the purpose of single-driver full-range speaker. The whole idea of single-driver full-range speakers is to avoid cross overs in the 300-3000 Hz range where the human ear is particularly sensitive to phase changes. If you want to use multiple drivers, you should use a mid-bass that can be crossed above 3K or a mid-tweeter that crosses below 300 Hz. While my efforts are aimed primarily at single driver speakers, I think that my best results have been with 6"-8" BR's crossed near 100 Hz.

Bob
 
Well, I've done another rough check in MathCad using the dims available on the Commonsense site, and adjusting the port for the best response (no idea what they actually are). To be fair, they didn't look too bad, but nothing special. The 2 driver versions looked considerably worse, with peaking at cut-off so I think 'boom' will be the order of the day.

I agree entirely with what Bob said re the arrays. I can't think of one using full-range units that'll work -the driver centres are way too far apart. I'm astonished that there's a short 4 driver one on the Jordan site (and an equivalent for Bandors -surprise, surprise). I don't care how narrow the surrounds are, lobing will be the order of the day there.
 
Scottmoose said:
I don't care how narrow the surrounds are, lobing will be the order of the day there.
But you, like I, haven't heard a Jordan or Bandor 4-array. And the people who have, don't typically describe the sound as "lobey" or "rolled off" or "phasey" or "combed" or whatever adjectives one might think would apply to such a setup. In fact, most people who have heard them use very positive adjectives.

I've posted about this subject more than once, and I've never gotten a satisfactory answer, as to why these Jordan and Bandor arrays "work".

My suspicion is that the short line length (~8") and short CTC distance (~2") creates a situation where the transition from nearfield to farfield array occurs at high enough a frequency (I've done the calcs before based on NFLAWP, but forget exactly) where combing issues aren't disturbing to the listener.

I suspect if you added more drivers (and the Jordan and Bandor drivers are expensive enough that you wouldn't), you'd run into the same problems as the PartsExpress mini-driver array sees, i.e. noticeable drop in high freq response.

Tangband makes a 2"x3" driver, I've been tempted to buy 8 and try a pair of these arrays, just for fun.
 
Bob Brines said:

Line arrays and MTM's rolled off at 1K will work, but, again, this defeats the purpose of single-driver full-range speaker. The whole idea of single-driver full-range speakers is to avoid cross overs in the 300-3000 Hz range where the human ear is particularly sensitive to phase changes. If you want to use multiple drivers, you should use a mid-bass that can be crossed above 3K or a mid-tweeter that crosses below 300 Hz. While my efforts are aimed primarily at single driver speakers, I think that my best results have been with 6"-8" BR's crossed near 100 Hz.
Bob

what if the XO are 1st order. given the wide band capability of drivers like Jordan and Fostex a 6db XO they should be able to be used with a 6db/oct (linear phase) XO.

between using "a mid-bass that can be crossed above 3K or a mid-tweeter that crosses below 300 Hz" I prefer the later. Dont know why.

What is a BR? Bass reflex? are not 6-8" drivers to large and wont they beam above 3K or so.

Scottmoose said:
I'm astonished that there's a short 4 driver one on the Jordan site (and an equivalent for Bandors -surprise, surprise). I don't care how narrow the surrounds are, lobing will be the order of the day there.

I was surprised too. After all Ted Jordan is no slouch. So when he claimed that his drivers are designed to be used in line arrays I assumed he was right. Obviously I figured I did not have the technical background to understand his design(s).
 
tomtt

Horrors! It's even mounted on a curved baffle! Anathema to good sense! At a stroke, remove a primary benefit to having an array in the first place (huge 'sweet area' rather than a 'sweet spot'.). To be fair, it looks nicely built. Just abysmally concieved...

Joe: have a read of this: it's Jim Griffin's white paper on domestic line-array design. This is a real landmark -the last really good one was written back in the 1960s, and dealt more with PA etc applications than hifi useage. Lobing is explained in great detail on pg 11-12 -better than I ever could!http://www.audiodiycentral.com/resource/pdf/nflawp.pdf
 
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