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Old 28th March 2004, 08:50 PM   #1
Greggo is offline Greggo  United States
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Default Help me find a woofer that has a natural roll-off and may not need a x-over...

Hello Everyone,

I just ordered a pair of the Fostex FE88ES-R you may have seen my post about earlier, and now I am starting the process of designing a system around it. I have decided that rather than torture the driver into some minimal low end response (it has an Fs of 107 Hz) somewhere near 70-90 Hz, I would look for a woofer driver that could contribute up to any point south of 1 kHz and handle things down low (at least 42 Hz with a good cabinet design). Obviously, given my 40-45 Hz goal I am not a listener that craves any serious bass response, I just want something tight and tunefull to let me know what the bass line is without exciting too many room response issues.

Given my interest in the single driver cult, I was hoping to stay as simple and near cross-over free as possible, maybe even building a small amp to driver the woofer that was designed to be bandwidth limited so as not to interfere with the critical range and imaging of the main driver. Am I dreaming or is this within the realm of the possible???
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Old 28th March 2004, 11:28 PM   #2
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Hey Greggo,

Why nor share your thoughts about size and cabinet design so we have a place to start?

Cal
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Old 28th March 2004, 11:42 PM   #3
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Greggo,

I've been running 2x 8" woofers in sealed boxes with no xover (too lazy to get around to building one - will bi-amp one day...)
for the last 6 months; it sounds fine.

Even more un-kosher - the two drivers aren't the same!!!! couldn't find another of the carbon-fibre cone drivers, so the newest one has a polyprop. cone - that's probably better for just adding lows, the mids are a bit more evident on the carbon fibre cone driver.

I've got to buy some inductors for another project, so I'll try them on this set-up, but I think you're right, if appropriate drivers are used, then no x-over is possible

Pete McK
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Old 29th March 2004, 01:11 AM   #4
Greggo is offline Greggo  United States
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Well, right now I am at the blue sky point, not constrained by any notion of cabinet size and style, and I have a fairly complete shop and good wood working skills so nothing scares for the most part. Since the FE88ES-R is a small driver I did think it would be nice to keep the baffle narrow but this is not really a big deal for me because I think that even a wide baffle can be deisgned along with the rest of the system to image quite nicely.

I have been thinking about a floor stander with a small upper cabinet for the FE88, maybe 7 inches wide by 12 inches tall 14 inches deep. That could be designed as a bass reflex or small transmission line with a goal of helping the FE88 behave well from 90 Hz out to the limit of the driver which is almost 40 kHz. That cabinet could then sit on top of or on stands beside another matching cabinet (in style not necessarily in size) that contained a single or dual woofers, and they could be mounted high. low, on the side, or facing the rear. They could be mounted in a standard fashion or have some kind of physical absorption or tuning device mounted in front of them to help dampen any unwanted peaks or frequency extension. Ideally I suppose I would want the woofer driver to face the rear and have a natural roll off around 900 Hz so as to create a nice bipolar effect in tandem with the FE88 and not be too forcefull in its contribution so as to preserve the point source effect of the FE88 above that range as much as possible. Then its contribution below 90 Hz, though directed toward the rear I would expect that it would still provide a satisfying extension for the listener seated in front of the front firing FE88.

That is a rough starting point, but I have not begun any modeling or serious thought as to the cabinet design because I first want to consider potential woofer drivers and what challenge they would face in attempting to integrate them with the response of the FE88 in as natural a manner as possible, i.e. - no crossover if I can get away with it...

Sorry for the long post, I hope my thinking is clear and I am explaining this correctly....

Thanks,

Greg Jensen
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Old 29th March 2004, 01:38 AM   #5
Greggo is offline Greggo  United States
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Oh yeah, here is another thought I had on this...


Ever notice how with many woofer drivers the on axis response has some peakiness/nastiness but when you look at the 30 degress and then the 60 degree off axis freq response lines things look great and sometimes look like you could just naturally roll in a mid or tweeter to take over from there???

Well I was wondering, what if you mounted such a woofer on a baffle, and then built another cabinet in front of it, an open back cabinet so the woofer could fire straight into it, and that cabinet was stuffed with foam/fiberglass to effectively dampen anything above 8 or 9 hundred Hertz. And then what if you space the gap between the woofer baffle and this open back so that everything coming off the cone at 60 degrees or more was going into free air and everything less was hitting the trap and getting re-directed to the floor through a web of filling that left the sound waves rather lifeless by the time they found their way out.

Any thoughts on this purely physical approach to limiting the woofers response at the listening seat?

Do these break up modes and nasty peaks have a significant effect on the lower range response, meaning am I still compromising the drivers ability to play cleanly from 40-400 Hz as an example by letting my amplifier send it a full bandwidth signal?

Just some more thoughts on this zero crossover quest, which I know is somewhat misguided but I just love the idea of clean and clear wire from an amp to the driver terminals with nothing else in between.

Any Thoughts???

Greg Jensen
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Old 29th March 2004, 04:54 AM   #6
navin is offline navin  India
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how come you chose the Fe88?

i too am looking at a fullrange project.

i am looking at 2 options.

option 1. wall mounted system operating frm 100Hz up.

option 2. small foot print floor stander operating from 45Hz up.

I would like to have the same drivers or similar drivers for both these.

drivers i have considered are the FE103, JX92 maybe with a tweeter on top this would mean only a single cap as a XO.

the other alternate would be to use a smaller fullrange like the JX53 or FE83 XOed to a larger wide range driver like the JX125 or FW108N. this would mean a XOs for the bass and hf units. However if one chooses the drivers propoerly one might be able to manage with a single inductor which has the bass driver in series with it and the hf unit in parallel with it.
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Old 29th March 2004, 04:56 AM   #7
navin is offline navin  India
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where did you find the Fe88?
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Old 29th March 2004, 11:09 AM   #8
Greggo is offline Greggo  United States
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Navin,

I chose the FE88ES-R for a couple of reasons:

1) I am interested in wide range and/or full range drivers, believing that multiple drivers and crossovers make it extremely difficult to get the kind of sound I like most out of stereo system

2) Since most if not all drivers in the above category are challenged at either the lower end and/or higher end of the music frequency spectrum, I thought it best to deal with the lower end challenges for the following reasons:

a) electrical filtering and tone shaping seems to do more damage in the 300 Hz to 6 kHz range than anywhere else.

b) physical seperation of multiple drivers seems to be more challenging in the 900 Hz to 9 kHz range due to lobing, phase, and other issues that affect point source imaging (which is after pitch and timbre is one of my most valued qualities in a system).

c) I don't really care about low bass, and in fact I consider decent bass response below 40 Hz to be more of a liability than an asset due to room problems. I find that solid response into the 50s, with fair response dipping into the 40s, and then just a hint of sound pressure below that point works best for me and the way I like to listen to music and not bother the rest of my family or put up with less deliniated bass lines due to room modes getting excited and causing bloat and overhang of the bass notes

3) The FE88ES-R reminded me of other limited edition drivers from Fostex that have met with great success among audio types that seem to value many of the same things I do in a system. Also, the response curve looked very good to me and the physical design of the driver looked good to me as well. The response looks fantastic from 120 Hz to out past 20 kHz, with a little dip rather than a peak running between 1.4 - 2.8 kHz which I feel will be critical in helping to keep the sound tame rather than shrill as many full range drivers have a rising response in the worst possible place (between 2-5 kHz).

4) Given the fact that lower range sounds are much less directional than higher range sounds, I thought I would have more flexibility in designing a woofer solution to help out below 120Hz than anything else. Looking at potential baffle step issues as well I could mount a woofer above, below, behind, beside, etc... all to varrying degrees depending on how much I wanted the woofer to contribute above 120 Hz knowing that everything below would get to the listening seat regardless of which way the woofer driver was oriented. Also, phase and timing issues, though still important, are much less detrimental in the lower ranges than the mid and upper ranges, so I thought it would be the lesser of all evils.

5) And finally, to answer your second post as well, I like the idea of having something a bit different, somewhat exclusive if you will in so far as these drivers are very difficult to get outside of Japan. If you look at the Single Driver Forum the James Melhuish runs you will find a small group of us that worked on this issue for a while and finally found a solution, here is a cut/paste of the post from a guy namged "Quest" over there:

Hello folks!

Great news! Koji-San from EIFL corp has agreed to take our orders and ship them to us. Here's the detail information:

************************************************** *****************************************


Hi! Quest,

Thank you for your inquiry.

Here is the quote.

FOSTEX FE88ES-R-----------US$ 252/pair +US$ 50 poatage&insurance
=US$ 302/pair

The expected delivery is about 2 weeks after payment.

I accept wire transfer and credit card with 6% card charge.

I look forward to serving you soon.

Regards
*********************************
Koji Wakabayashi
EIFL Co.
1-8 Fujimi 2 Chome Sayama City
Saitama Prf.350-1306 Japan
TEL +81(0)4-2956-1178
FAX +81(0)4-2950-1667
E-mail koji@eifl.co.jp
Website http://www.eifl.co.jp
**********************************
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Old 29th March 2004, 11:14 AM   #9
navin is offline navin  India
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thanks for the reply. how low do you expect the FE88 to go?

I have simialr views as you. bass below 40hz is difficult to tame in a normal living room. esp if the speakers are to be kept near the rear wall (out of the way of kids, pets etc..).
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Old 29th March 2004, 12:41 PM   #10
Greggo is offline Greggo  United States
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Good question... from what I have seen from system graphs of a cabinet recommended by Fostex for this driver and for other similar drivers (similar as far as Q and Free Air Resonance anyways), a hybrid horn (I don't consider most of the Fostex designs to be true horns) can bring things down to the high 70s low 80s before level drops off, and simple bass reflex designs could easily bring things down to 80 or 90 Hz. I will be doing some experimenting to see how the character of the driver changes from open baffle to various sizes of sealed and ported enclosures before I begin to run simulations on box size and port (I don't have any software yet to do that but I intend to get some). I am prepared to keep the FE88 at 120 Hz and above if need be, but I am hoping that I can get great sound all the way down to 90 Hz and then hand off to a woofer from there. I think a cabinet could be designed to bring it down lower, but I am concerned that even at 90 Hz I am asking a lot of the driver and intermodulation distortion will rise tremendously as one journeys from 200 Hz on downward with a single cone driver attempting to cover everything (which is why I may end up just going with 120 Hz as a lower limit design goal). My primary concern will be to design in a manner that best protects the excursion of the FE88 and does not compromise its best musical attributes (assuming it has some because this is a gamble on my part to buy an unproven driver like this one). I am hoping to design a bandwidth limited amp that drives the FE88 and protects it somewhat from information below 90 Hz and then design a bandwidth limited amp that will limit the woofer to some degree above that range. This is all based on the assumption (still much research to do) that I can best manage tonal shaping or frequency limiting at the input to a gain stage and that perhaps with subltle approaches I will have a musical system that produces much less interference to the source signal than a full blown passive crossover would. I am really looking for something like a hybrid between an active crossover and a tube equalizer to go between the pre and power stages, with each gain stage of two amps per channel being directly connected to their intended drivers with nothing else in between, not even binding posts...

Greg Jensen
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