Hemp FR8C Enclosure Suggestions

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I recently received a pair of Hemp Acoustic FR8C drivers and am looking for suggestions on a box alignment. I think the final goal is a BIB, but I am looking for a simpler build first to get a feel for the driver and confirm it’s ability before I commit to a BIB. Maybe something with an aperiodic vent (BR for this driver is still quite large) or dipole.

Does anyone have experience with this or the previous version of this driver that is willing to share their design?

Thanks - Chris
 
I would aim for the BIB. I presume you've seen the MLTL's a few threads back. But in the mean time, why not build the little BR that Dan Wiggins designed? The Aperto:

http://www.hempacoustics.com/kits.php

I first used mine in 40L BR's. You can find alignments that work if you tune it low. The group delay will be low too, but the downside is more excursion a ways above tuning. Dan Wiggins knows his stuff. I'm sure there are benefits to the tall baffle, as he says. However, you could also just copy the internal volume and vent in whatever aspect looks good to you. I'd lean towards a wide baffle. You sure won't be disappointed with the BR, and later you'll find the BIB to be a whole different world.

pj
 
PJ,

Thanks for the reply. I saw the 22 liter design on Hemp’s web site, but thought something larger modeled better.

I settled on a BR of about 45 liters or so with a 3” port. I don’t think port noise will be too much of an issue, so I would really like to put the port on the front of the box (box is about 23.5” tall X 14” wide)? I may reuse this box someday for another application which most likely would be wall mounted. Is there any foreseeable issue with a port on the front of the enclosure? What size port did your 40 liter box use? Suggestions on stuffing/enclosure lining would be helpful too.

I am crossing my fingers, as I have a small SE OTL amp that I hope will be able to drive these speakers when finished.
 
As I think about it, it was a 50L enclosure. The port was 2.5" and it didn't chuff (we're only talking 2mm of excursion here!). It was on the back. I was thinking of doing a more permanent BR, and I did plenty of searching for a consensus on port position. If you can do it, rear ported is safer. However, if you put them on a wall, there is no way it will work. The wall should eliminate the need for BSC, so that is a good thing. A front port has some chance of midrange leakage, even if it doesn't chuff. If you are worried about it, you could do side ports I suppose. If you can use MJK's spreadsheets you could model some different port placements. I wouldn't worry about it. Plenty of folks seem to place ports willy nilly without troubles.

I didn't experiment with damping or stuffing as it was a temporary solution. Don't put much of any "stuffing" in there, or you'll mess with the port action. I damped the walls with thick carpet padding (held on with a combination of Super 77 and PL Premium Construction Adhesive). You know the stuff, a bunch of different foam chunks all glued together: cheap and effective. If you want to get fancy, you could use this stuff:

http://www.rawacoustics.com/item__RAW_Ice_Acoustical_1,821.html
or this:
http://www.partsexpress.com/webpage...ID=137&filter=sonic&raid=54&rak=sonic_barrier

This stuff is mainly to damp the cabinet walls, not to tame standing waves. You might start only placing the material on the back, top and one side, as per GM's recommendation. Too much damping can make it sound dead. I put a double layer behind the driver to help damp the backwave. I used more damping than is ideal, as my cabinet was mainly particle board. Build something decent and you can go easy with it.

Tell me about this SE OTL. It sounds like fun. OTL's strongly prefer flat (and high) impedance curves don't they? Instead of the BIB, perhaps something like the Kenobi would be ideal. You could run the toobs on the Hemps and drive the woofer with something else. Then woofer sensitivity wouldn't matter either.

pj
 
Here is the scoop on the SE OTL http://www.transcendentsound.com/single ended.htm . I have had this amp for a few years now. The Transcendent Sound amp is a great “little” amp, but I have yet to find/build a pair of speakers that really works well with this amp. A few years ago I built some 95 db 8 ohm two way line arrays using Tang Band drivers and an AC ribbon, but in the end the speakers still need a little more head room. I guess a horn setup would work nicely, but I have yet to venture down that path.

Anyway, back to the Hemp… did you use any filter with the BR box or BSC? I plan to make the baffle 14” to 15” wide. In the end these speakers will be driven by a different amp and most likely end up in a BIB (these speakers belong to a friend who has solicited me to help him construct the enclosures). Again, a BR is less involved and cost less than constructing a BIB. The BR boxes should hold my friend over until he is able to scrape some additional cash together for the BIB. Besides, I think he is still working on the WAF as the BIBs are quite large.
 
I didn't use any BSC, but it sure wouldn't have hurt. I used 15" wide baffles fairly close to the floor (12", tilted back) and back wall (1-2ft). I initially had them on higher stands (24") without the tilt, but getting them closer to the floor helped the midbass quite a lot. I had them set on cement blocks such that there was a fairly wide surface extending from just behind the baffle to the floor.

pj
 
frugal-phile™
Joined 2001
Paid Member
You can build a smaller box than a BIB but not much simplier...

The release plans for Demetri (folded ML-Voigt for Hemp FR8/FE207e/FE167e) were just released.

http://planet10-hifi.com/boxes-fostex.html#demetri

demetri3D600.gif


dave
 
Hardman, I reckon you know that your nice "little" OTL should double its output in 15ohm - I guess it will need som impedance smoothing

Yes I am aware of this (amp should be good for about 4 watts at 16 ohm), but have yet to find a speaker project that takes advantage of the wattage gain.

Update – I didn’t ever build the BR boxes for the Hemp driver, but have instead started the BIB. I plan to use a different amp with the BIB too. I hope this thing is worth all the effort... I mean wood. Looks like the Hemp BIB consumes five 4’ X 8’ sheets of wood!
 
frugal-phile™
Joined 2001
Paid Member
seventenths said:
Would the Demetri be suitable for the fe166e ? I'm looking for a less imposing design than the BIB to couple with a small SET.

Scott?

I don't think FE168 would drop into Demetri... but certainly a similar design could be made. Each of these monoliths starts from a cooresponding Metronome, The 168 Metronome is the same height as the 167/207/FR8 but a fair bit smaller in the other dimensions.

It is pretty quick to rough up a 1st draft -- from there closing in on an appropriate width to depth raio requires further iteration.

dave
 
I suspect not to be honest -not without some series resistance anyway as the Q & Vas on the 166 are too low & high respectively for this sort of enclosure to be an ideal match. I'll have a check when I get a spare minute later today though. If you already have the drivers, & want a less imposing design, then either Ron's A166 is the way to go, or if that's too tricky a build, the Factory 168ESigma cabinet should do the job OK with the 166 mounted.
 
hemp aoustics fr8c

I have the current model on open baffle the same size as the old
wharfedale sfb 3. Jaw droping midrange bass deep enough for
me. I have had lowthers alnico, tannoy gold, altec voice of theater
these are a steal and to me a better rounded speaker



best regards
James
 
Jimmy D ...

nice to see someone else try the Hemps on an OB. I did and they are jaw dropping. I encouraged Perry to try a set. He told me that he had tried them (after my experiences were emailed to him) and was floored as well. I truly believe that there is something quite special about the SB3/"JELabs" design

New version FR8C uses a different recipe for the pulp in the cone as far as I know. For the $$ I am not sure it can be beaten (but hey, Dave's 127s are about 1/2 the price and are VERY good). Everyone who has stated that OBs need this or that haven't usually experienced these baffles. With my modifications to the "JELabs" baffles, I feel I have a great "all-rounder". But paint em or stain em first, cause you'll never finish them otherwise.
 
Hello everyone… It’s been a while since I first started this thread so I thought it fitting to report back on our Hemp FR8C experience thus far.

After some thought we (I am building the speaker cabinets for a friend) decided to try the BIB (GM design). This thing is massive and cost a ton to build (three sheets of BB plywood plus one sheet of particle board), but in the end has been somewhat of a disappointment. It is our opinion that bass is lacking even with such a large cabinet (transient response). Therefore we see little reason to devote so much real estate to such a large enclosure.

Stuffing this speaker has proven to be our biggest challenge. I am unable to eliminate the horn colorations (echo effect). I would love to hear from other Hemp BIB builder’s that are satisfied with the design. There is always that possibility that we did something wrong.

Don’t get me wrong, I am not completely giving up on the Hemp FR8C, but finding a suitable enclosure is a must. One thing for sure, the dynamics are amazing and I was really surprised by how little the FR8C beams. I was also surprised by how much I like the upper end of the driver once it had some time to break in.

Nanook’s proposal for a JELabs open baffle is tempting, but my understanding is this design requires specific room placement and I am not sure this will bode well with my friends listen room/family room.

Planet10‘s Demetri is looking more and more like a possibility. What are the benefits of this design vs. an MLTL or BR enclosure?

I am convinced the bass level my friend is looking for is not going to be obtainable with the Hemp driver alone regardless of design, so finding something that will mate well with a subwoofer or large 15” pro driver is a must (we prefer the sub idea over the 15” pro driver approach).

I am tempted to build a simple sealed enclosure and see what type of results we get and then maybe try to incorporate an aperiodic vent. Anyone tried this route?

So what should we try next? I am open to any suggestion, I just want to be sensitive to the fact that my friend has already spent a good amount of money already on wood that hopefully we will be able to salvage somewhat.

On a side note, the BIB/Hemp speaker work with my SE OTL amp (not to ear piercing levels, but doable). In fact, this was really the first time I was able to hear a difference between this amp and my solid state amp. With this speaker the tube amp was by far the better choice. If only those PHY speakers weren’t so expensive (I know others who have my amp that use this driver)…

Thanks – Chris
 
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