Hemp FR8 full range drivers

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Present?

I had sent two out, maybe one for you and one for chris (or one to tweak). The '1001 (the one w/RCA outs on it is the "tweaker's choice", the '5501 is similar except no RCA outs, so the AV cable must be used). The remote works good, the controller will have to be mapped, 'cause I can't remember the controls in relation to the remote. "the Menu" button starts and stops playback.

The '1001s have been favourably compared to $3k-$6k cd players. Not sure if that holds, but certainly can take on most $1k-$1.5k players stock and beat up on them. Hope you enjoy.

As to the stuffing in the Demetris please see the attached picture (link).


interior shot of Demetris

stew
 
I've always been curious about the bracing and damping on the Demetri's baffle. Many folks in the extreme bracing camp still don't brace against the baffle or put damping on it. I'm thinking of folks like the now defunct Northcreek guys, who quite literally, wrote the book on cabinet construction (for conventional BR's and sealed enclosures.) Back in my early days on the Parts Express board, folks would also warn against it. I find it unusual, because we tend to err on the side of much more resonant enclosures than those guys. Thoughts?

pj
 
unbraced panels....

I followed Dave's instrux, and we did use a large brace down the middle of the speaker connected to the back. Not much resonance to speak of, and as soon as moved away from the corner they open up. The "canned" or "cupped" sound I think is due to the increase in mid-bass due to corner loading.

The dampening material is wool felt used for underlay for those that have a sensitivity to off-gassing from synthetic carpet underlay.

Gotta go---ripping apart a turntable tonigt to find out why it sounds so ******* bad.

stew
 
NOT MY TURNTABLE

but a built in China wannabe.

Nothing against the Chinese , but from the parts and pieces that are here, it should sound ok. It doesn't. Further investigation suggests that
  • whoever designed the TT has no clue
  • it is a cosmetic knock-off or designed as "eye candy" only
  • with some thought, and having the errors corrected it could be quite good

Or this particular manufacturer has never done any turntables before.

As it is, all but the granite base and the acrylic platter (and perhaps the motor) may be salvageable. I'm pretty sure the cost to resolve the issues will exceed the cost of starting fresh. New sub-plinth, new bearing, new tone arm...

Perhaps these particular folks should stick with other things.

stew

Oh and thanks to Moray regarding the gifts I got for Christmas from him, some great magazines (some of witch I have never seen), and some hot-rodded output transformers for a PP amp, and complete power supplies for said amp(s)
 
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Variable BSC Circuit Part 1.

There were some questions about the circuit I posted above, so I thought it best to explain what's going on and how to use it and modify it if you want.

The way the PLL (Passive Line Level) filter works is just a voltage divider. Have a look at the basic "Circuit A" in the image below. You'll see a basic voltage divider circuit that attenuates all audio frequencies the same amount. In this case, by about 8.5 dB - a little more than 1/2. A potentiometer works the same way.

In this example we have assumed a low output impedance for the preamp or other source about 50-150 ohms. We assume a reasonable input impedance for the amplifier - here 15K. The voltage is divided between R1 and R2 with Rin. That's why there is a circle around R2 & Rin. Together they = 6K. So the attenuation is more than 1/2 (6dB) in this case about 8.5dB

In Circuit B "BSC" we have put a small cap in series with R2. What does that do? Well... a cap is going to have an AC impedance that changes with frequency. Very handy! Think of the cap as another resistor in series (more resistance) with R2. But it's a "resistor" that changes value with frequency. The lower the frequency, the higher its "resistance" (impedance). This 67nF cap has an impedance of 120K at 20Hz and 1.2K at 2000Hz.

So you can understand how C1 in series with R2 will attenuate the highs more than the lows. More current will flow thru it at higher frequencies, draining them off more than the lows - limited, of course by R2.

You can see the resulting curve charted below. We go from 4.5dB attenuation at 20Hz to 8.5 at 2Khz. A difference of 4dB. Not much, but all we probably need.
 

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Variable BSC Circuit Part 2

Now lets look at Circuit C, the variable BSC.
You see that we have added a variable resistor in series with R2 and C1. It’s just a pot or trimmer with the wiper tied back to the input.

Remember in part one how the variable impedance of C1 changed how much the highs are attenuated compared to the lows? Same idea here, except that the resistor is frequency linear. So we are adjusting how much overall attenuation is applied. The higher the resistance of the pot, the less attenuation, right?

This lets us dial in less attenuation, if we want it. Why? To match your room and your ears. Full baffle step attenuation should be 6dB, but in most listening rooms it’s more like 3dB as the room tends to fill in the lows somewhat. As seen in the second chart, the pot allows you to vary how much BSC you get from about 1.5 to 4.5dB. That’s a pretty subtle adjustment, but should be about right for most rooms.

Want more range? Change R2 to about 2~3K. You’ll get more attenuation overall, and more difference, too. The pot value can be changed if you like, but 20K to 50K will work well. Keep R1 and C1 the same.

You can even put a switch across C1 to short it out. The will make the circuit frequency flat again, just like circuit A. By listening to the circuit with out the cap and its “bass boost” you will be able to determine if the circuit is having an effect on your audio. Having a series resistance in line can have the effect of less drive and less bass, so you need to be careful there. How much, if any, will depend on your preamp and amplifier input. But at least you’ll be able to test it.
 
Thank you for very good explanation.

Altough I have used PLL BSC for a long time,the attenuation hasn't been enough with equal size R1 and R2.Thanks to you,now I know to try changing the R2 to a smaller value.

I have found the PLL BSC to have more dynamic and clearer sound than with filters at speaker end.
 
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Omega 2-way Alnico driver in sealed box?

Bill I feel that coating the whizzer made a real difference for the good. I also have open cell foam between the whizzer and cone ( 98 cent tweak) I didn't hesitate to try dammar because the whizzer is paper and not the hemp material that the main cone is. Some people have made negative comments about the whizzer. To my ears it works quite well.

Omega uses a version of the FR8 that is tweaked to their spec's. I don't know how much they differ from the DIY version. I suspect that the difference is significant. Dan has posted his pair for sale after losing a listening room, so apparently despite his enthusiasm they never took over the #1 spot in his home.

Another DIY member, Nodiak, posted about trying to add phase plugs to his pair (the whizzers came off with the dust caps), but hasn't posted on them since.

I have my pair in simple BR cabinets, 82 liters volume, 4" dia x 4" long flared ports, and I sit relatively close to them in a smallish room (11 x 14'). So far, I have found them to sound like the FR graph on Hemps Acoustics' spec sheet - the highs are too hot. This didn't smooth out as much as I had hoped during break in, and toe in is not enough to bring the treble in line. The 'turn-'em-up-and-listen-from-the-next-room' test confirmed that the basic balance is tipped up too much for my taste. I put them into the living room HT system for a while, and while the highs were smoother when listening from a greater distance, the balance was still too tipped up.

To try to tame the highs I'm using a treble shelf network inspired by the Visaton open baffle thread on The Audio Circles board, currently a 0.1 mH coil + 13 Ohm resistor in parallel (no Zobel). A pretty aggressive filter, but 8 Ohms were not enough. There is also a little wool fluff tucked in between the cone and the whizzer, which makes a small but audible difference. I've probably lost too much sparkle at the very top end, but the overall balance is much better, voices are more natural, and I don't miss the extreme highs much.

My mono-buttocked network falls short of full baffle step correction. The midrange balance is best with the boxes against the back wall, but this gives a lumpier bass response in my room. I keep moving them around searching for the best compromise location. I'm sure the FR can be improved with a better network, but I don't have good measurement tools and there's not even a published impedance curve for the FR8 so I'm pretty much flying blind for now.

I'm not done working with them yet. At their best the FR8's do a lot of good things. The bass can be strong and well defined, dynamics are good, there's plenty of detail. If phase plugs can be successfully fitted I think they'd help. I wouldn't be surprised if a little cone or whizzer damping (dammar or Mod Podge) would help too, but again I don't really know enough about what I'm doing to want to make drastic irreversible mods to the drivers.

According to the Hemp Acoustics website, a new version of the FR8 with an improved cone is coming. They say, "In the analyses of our full range FR8DIY the peak exhibited in the midband at around 3-4K was significantly reduced as well the lower treble area around 7-10K is now far more linear, not to mention the high frequencies are more perceivable without being shrill or fatiguing." The graph they show of the difference still shows a significant HF rise, but I'd guess the new version would be worth waiting for.


After removing the whizzers from the Hemp 8's I played them on ob a couple weeks with the Hawthorne Augie for bass, as of course they have basically none on their own (on ob). Very rich full output. Didn't really catch on they lacked highs until compared to FE108ez.

Then rotated CSS125's and FE108ez's each in 10L sealed (cabs were available) to mate with Vifa M22 in 40L vented (ala Dickinson in LCB). The variety has helped me get a better idea what each offers.
Last 2 nights it's Hemp's with M22 bass, they like each other. (GM kindly worked up a mltl for M22, anxious to get that built, should be deeper and a little dryer which sounds good to me).
At this time I don't have a tube amp or even tube pre to go with LM3875 gc integrated, my main amp now. So that isn't fair for the Fostex, barely ok for the Hemp's, but the FR125 seems pretty at home. That's the order I'd put them in for "brightness" and clarity factors vs. "warmth".
But I agree the Hemps have midrange tone and some sweetness. Without the whizzers (I guess?) the highest treble is gone and I've been tempted to go with that and work in a tweeter like the BG Neo 3. But I need to learn what replacing the whizzer would do. Been thinking of Dammaring the whizzer first, think I'll take Jim G's lead and do that. The phase plugs are made for the FE167's and are a bit small. Maybe with pp's and without whiz I'm getting a decent midwoofer. Going to get some Redwood whizzers made by a friend (Dude! Hemp and Redwood, oh yah!) Got some honk, even on ob, but I hear stories of up to 300 hours of break in needed. I'll put them in a 40 L cab (what's immed. available) for awhile to hear their fullrange. Jim G, can you recommend bib cab design? I'm game for that.
The 108's are extraordinarily clear and open and I need to get them in bib or metronone or? to hear some low end from them, to fill things out. And, their designed for tube gear right? I mean they must because with the gc it's too clinical.
FR125's are kinda freaky with so much bass, can't hear the rest as well. Going to xo out the bass and mate with M22 this week so can get a better feel for their mids and highs. At this point they seem the least satisfying -too dark, but I'm sure there's a remedy, open to ideas. The low spl's are a problem for matching to bass drivers. The dipole version must be great tho. BIB's for these huh, have a link?
The new Hemps sound like an improvement, tho these have alot to offer. Just need to try things, bsc sounds like a wise move too. Will try the 98 cent tweak.
BTW, room is ~ 300 ft2, but narrow - 11.5 x 26.5 .
Don


Long before I decided to build and bi-amp a pair of hybrid Sound Lab ESL tweeters/sealed GPA Altec 416-8B midwoofers/Rythmik sealed servo subs, I thought about Louis Chochos’ two-way Alnico drivers. Even now, I am wondering what a pair of these drivers SUPER ALNICO MONITOR would sound like if they were in a sealed box and if my First Watt B4 crossover’s 2 pole Linkwitz-Reilly filter cut their low end off at around 800Hz, to blend with my Altec Alnico 416s. http://www.greatplainsaudio.com/downloads/416-8B Spec Sheet.pdf

Btw, Gary Dahl, who truly realized their virtues when used in a sealed cabinet, and John Sheerin
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-781.html confirmed that the
416s really can do a bit above 1kHz, without becoming directional.

The reviews at 6moons and elsewhere rave about their midrange, but what is the quality of the highs through those
whizzers? How would they compare to, say, the SEAS T35 https://www.madisoundspeakerstore.c...-exotic-t35-x3-06-tweeter-with-alnico-magnet/ ?

OR might there now even be another better performing Alnico MF/HF driver?
 
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