hemptone fr8 project questions

markC · « **Reply #20 on:** 16 Dec 2008, 01:47 am »

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=12&pos=2
Just do it. Give in and build a 2-way x-over. Let the full range handle as high as it can and hand off to a tweeter.
It will take some work, but hey, we'll help.

skite30 · « **Reply #21 on:** 16 Dec 2008, 10:28 am »

Any suggestions for a tweeter. Think I will try the inductor that panomanic suggested. That seems to be the easiest way to get started but I am certainly open to any and all suggestions. I have them playing OB now and am really excited by the presentation. I have a couple of small subs but really want to try the alpha's or ae's.

nodiak · « **Reply #22 on:** 17 Dec 2008, 03:02 pm »

It's tough to suggest certain tweeters as it comes down to taste and expense, like having someone order for you at restaurant. Also if there's a difference in efficieny/spl's you need to add resistor, so it isn't always quick and simple. But for those drivers I'd get 92db and up tweeters. There's some ~ inexpensive dome tweeters around, GR-Research for instance.
However, imo, my vote goes for you to start at the other end and work out the bass first. You have 2 subs, each with it's own adjustable plate amp? Set the hemps up, one on each sub, in listening position, and dial up the subs crossover as high as they will go (usually ~ 160 hz). The bass will likely be muddy but still you can adjust things for a decent spl match and have an idea of the full range sound. Then get a pair of Alpha's, and either use the subs plate amps or get another pair of plate amps for the Alpha's.
The point is you can do all that with adjustable plate amps and won't go nuts swapping out passive parts and tweeters. You would also have full range sound. Use the 98 cent tweak on hemps, let them breakin a couple weeks and if treble still needs work try the notch filter mentioned earlier.
That's just one of several possible game plans, but I think a fairly practical one.
Another plan would be to use Martins ob ideas and get 2 Alpha's per side, work out passive crossover to Hemps, and use one amp for this 2 way. I'm not sure how close the 2 Alpha/ one Hemp spl match would be tho.
After you get anything setup figure you'll spend at least 2-4 weeks dialing things in, and longer for your brain to adjust to this stuff.
Don

skite30 · « **Reply #23 on:** 18 Dec 2008, 10:16 am »

Thaks for the info don. I have pretty much done what you suggest with the sub's. I plan on a pair of alpha's after I finish paying for christmas. I will probably use the plate amps from them for now but plan on a rythmik at some point. Hopefully more break in time and the 98 cent tweak will help along with the inductor. Should receive them by christmas.

nodiak · « **Reply #24 on:** 19 Dec 2008, 05:17 am »

Congratulations! You may be one of the first ever to take a frugal and practical step by step approach!

There will be plenty of time to get complicated as the months go by. Will be especially interesting to hear your response when you switch the boxed subs for the Alphas on ob. Good luck and let us know how things are going.
Don

skite30 · « **Reply #25 on:** 20 Dec 2008, 12:21 am »

Well having 4 children will teach you quite a bit about being frugal. While on the subject I ordered a pair of jantzen .47 inductors 15 gauge. I also ordered a pair of alpha 15a's. My next question is if I were to use the hemps fullrange, how would I cut off the apha's passively at about 150 to 200 hz?

Badwater · « **Reply #26 on:** 20 Dec 2008, 12:45 am »

Check out MJKs article on designing a 2 way passive OB for the info you need:

http://www.quarter-wave.com/OBs/OB_Design.pdf

skite30 · « **Reply #27 on:** 20 Dec 2008, 12:55 am »

I read that article awhile ago and it is what originally got me thinking about trying this out. I purchased the dca4's which are basically interchangeable with the fe103e's to that purpose but like the hemp's better. I didn't know if the inductor and cap values would be the samefor the alpha's if I didn't want a crossover to the hemps but just wanted to roll the alpha's off in the 150-200 range.

panomaniac · « **Reply #28 on:** 20 Dec 2008, 07:42 pm »

You'll need a big coil and cap to do it. Get an iron core coil. They aren't cheap, but that's how you have to do it in a passive crossover. Look at around 13mH or more for the coil if you want 150Hz. Otherwise the values that Martin give will be a good starting point (~200Hz)

skite30 · « **Reply #29 on:** 20 Dec 2008, 10:21 pm »

I think Martin's design calls vor a 9mH inductor and a 68uF cap. These would be cofigured the way he describes them in his paper even though they would not be crossed to the Hemp? I would just substitute the 13 for the inductor if I wanted it rolled off lower than 200?

Appreciate the help

androuski · « **Reply #30 on:** 20 Dec 2008, 10:41 pm »

If you don't want to put anything on your hemp FR8, I'm affraid you have to change the whole crossover design...
Are you sure a single alpha could give a sufficient spl output in low area to match the FR8C sensivity ? These fullrange drivers (I catually own a pair of them, that I appreciate a lot) have a rising spl output from 2000/3000 to 12/13000hz, that may require a notch filter if you want to get a flat output, and this notch filter will also get the sensivity down to 90db...

Supravox has a OB kit design with a 8" going full range and a 12" woofer in the low area, on which they put a single 20mH (6db slope) inductor ; have a look there :

http://www.supravox.fr/kits/panneauplan.pdf

I feel involved in your project

panomaniac · « **Reply #31 on:** 21 Dec 2008, 04:34 am »

It depends on where the hemp rolls off on the bottom end. That's going to be determined by your baffle.
Mine on a ~16" wide baffle started to roll off under about 250Hz. So 200Hz is a good place to meet it with the woofer.
I did not use a hi-pass on the Hemp, just a coil to flatten it.

nodiak · « **Reply #32 on:** 21 Dec 2008, 05:17 am »

What do you guys think about using the 9mH / 68uF on the Alpha, and pano's coil idea on the hemp to flatten it's upper range. Not a guaranteed spl match but a place for skite30 to start (might need resistor). There's also the idea some of us have done with ~ 4.7mH coil on the Alpha and nothing on (ex.) B200's (Richard posted his experience awhile back). I've also used 6.5mH on bass and 40-70uF on fr to get something going.
However if skite30 can use plate amps on the Alphas won't have to worry about a passive.

skite30 · « **Reply #33 on:** 21 Dec 2008, 05:30 am »

I have the subs I can use the plate amps from but will eventually probably get a rythmik to use. For now I would like to try the passive idea. I have ordered a .47 air core inductor for the hemp. If the MJK low pass will reduce the alpha to about 91db and the inductor on the hemp reduces it to about the same. What do you think? I will take a look at the supravox tomorrow. I am not set on anything other than the drivers and am open to all ideas on what everyone thinks will work.

skite30 · « **Reply #34 on:** 21 Dec 2008, 06:24 am »

The baffle will be 20x38. I could go a bit wider or taller but not much.

panomaniac · « **Reply #35 on:** 21 Dec 2008, 06:09 pm »

Martin's project uses a very large baffle, that's why he has the x-over he does.
I never needed the hi-pass filter on the FR8, because on my baffle it rolled off pretty high.

Seems like the 9mH would be a good place to start on your baffle with the Alpha. Then use the cap to pull the curve into 2nd order acoustic @ wherever you need to meet the mid.

I'm using about 11mH on a smaller baffle, 12" driver of ~0.5Qts. I've seen as high as 20mH on big, low Qts drivers.

skite30 · « **Reply #36 on:** 21 Dec 2008, 07:40 pm »

I thought the 20 by 38 baffle is the size Martin uses on the passive design. I will have to look again to make sure. I wasn't planning on using the high pass either just the inductor to smooth the rising response of the hemp. Can't wait to get started. Really appreciate all the help so far.

skite30 · « **Reply #37 on:** 1 Jan 2009, 01:29 am »

I received the alphas and the .47 inductor for the hemp's today. I will hook up the inductor up and listen for awhile and run the alpha's in the living room to loosen them up at the same time. My question is are the inductors directional? Does it matter which way I hook them up?

Graham Maynard · « **Reply #38 on:** 1 Jan 2009, 09:09 am »

No, inductors are not directional, but they can interact and mutually couple.
So keep them their own size distance away from metal objects or each other, and make sure that any closely sited have their axis at right angles to each other.

nodiak · « **Reply #39 on:** 1 Jan 2009, 11:47 pm »

Have pulled out the HA FR8's again and the Scanspeak 9300 in waveguide (if curious google "zaph tmm" for the tw waveguide). I'm in a new room that is brighter and they balance well here (other room pretty damped and tweeter was recessed). Using .5mH on hemps and trying 1-2uF on 9300's. Sound very nice, and sub completes them. So as always the room matters.
In this new place have to set up on a long wall and can't pull speakers out more than 2.5 feet from wall so have gone back to aperiodic cab instead of OB's for now. Will do moderate room treatment.
The waveguide is very helpful for off axis, which is good for havng speakers on long wall and roaming around the room. Before had OB's pulled 5.5 feet out in a narrow but deep room. May try Graham's foam fingers on hemp to help it's dispersion, tho it's not bad as is. Interesting to deal with the set up differences in new place.
Don