[skite30]

I hooked up the .47 inductor today and early impressions are very favorable. I will listen for awhile before I do anything else but the combo of a couple of weeks extra break in and the inductor has really tamed the harsh vocal transients and upper congestion during complex passages.

[panomaniac]

Good progess, then! Let us know how it shapes up.

In the "Nothing New Under the Sun" dept.:

I was just looking back at an old French magazine article from 1991*.  Using a Siare or Triangle fullrange driver with a Fostex tweet on top the author ends up with 0.33mH on the FR driver.  Surprise, surprise.   

What works, works.

*L'AUDIOPHILE N°17  octobre 1991 (nouvelle series)

[chlorofille]

I have a pair of H.A. FR8Cs in a 190 Litre bass reflex tuned to 30 Hz. Don't need a sub at all !! To tame the high freq response, try adding a baffle step circuit. I've tried the recommended values but it always seemed too harsh, so I finally settled on 6mH inductor and 15Ohm resistor parallel to each other, then wired in series to the speaker. You will most likely get a much more balanced sound.

BEst regards,
-Dee-

[androuski]

Hello,
and happy new year 

I'm looking for FR8C's inductance, this spec. is not available in the manufacturer datasheet ? Anyone to help?
Thanks

[panomaniac]

I measured about 0.38mH on my set.

Thw BSC circuit that Dee mentions above seems like a good idea with any driver like this.

[androuski]

Thanks,
my hemp acoustics FR8C came from an ebay auction, as new part,
I don't know if they are mk1 or 2, I guess they are the latest version available,
do you think inductance could vary from one to another ?

[panomaniac]

Sorry, no.  I don't know....

[markk]

hello

I am new to this AudioCircle so I hope I am posting this note correctly.

I use a pair of Hemptone fr8 speakers in an open baffle with four AE 15 woofers.

Here are a few suggestions that helped calm down the brightness of the Fr8 drivers you are working with.

I have found a tweak on line that you can take a cotton ball and roll and stretch it out and carefully place it behind and all around the wizzer cone (between the wizzer and the main midrange driver).  This seems to calm down some of the brightness in the treble range.
If you do not like the new sound you can always remove the stretched out cotton without any harm.

Also I do not listen to my loudspeakers directly "on axis"  but aimed just a foot or so to the sides of my ears.  You can easily aim and experiment with the amount of toe in by getting a Craftsman laser rangefinder at the hardware store.  I rest the handheld unit just above or below the center of each midrange driver, on the wooden baffle, and get an equal amount of toe in for each speaker.  The closer you toe in  the Fr 8 to your ears the brighter they will sound.  These drivers may sound more time coherent if they are not pointing directly at your ears also.

Also I have found the Fr 8 is very sensitive to the type of loudspeaker cable you use.  I found a very good match by making my own cable using the 6Moons article that uses outdoor extension cord.  You tie both the white and green wires at both ends for the positive terminals and keep the single black wire and attach it to the negative terminals (i think the Omega loudspeakers also use this similar technique but with better quality wire).  Longer wire lengths may also sound better so I have used about 14-15 feet per side.  That is a Mapleshade suggestion and I think it does help.  I also make sure the cables go from the amplifier to the speakers in the same direction by looking at the print on the outside wire cover.

Kimber 8tc also works well with the Fr8 if you would rather get a factory made cable. 8tc did sound better than the 4tc I also tried. The good part about open baffles is that you can easily make very quick cable changes form your amplifier to your speakers.

I think I also read somewhere that a good starting point is to place these drivers 36 inches from the floor to the center of the wizzer.  I did this with some earlier prototypes i made with MDF and that height seemed to work well with these full range drivers.

I hope these suggestions help you out.

Sincerely,

Mark K

[skite30]

Some good suggestions markk. I have placed some wool around the whizzer, that in combination with the .47 inductor have really smoothed things out quite a bit. the .47 may be a bit more than was needed but it sounds much better now. I have them pointed about a foot behind my head which seems to work well. I finally got the alpha 15's broken in and installed. I am really amazed how good these are great tone and I am getting plenty of bass for my room. I am using them fullrange at this point as I haven't decided what low pass filter option to use yet. I am looking at a seperate t-amp line level crossover as one option. I was thinking 150 or 200 on the bass and a corresponding 200-350 high pass on the hemp. Can anyone weigh in on this with experience using line level crossovers? I know Roger at Music Reference stated a thread on this subject and I have read through a lot of the discussion but would appreciate any help with this.
thanks steve

[markk]

Hello Skite30

I recently hooked up my open baffle system with good results as follows-

I run a signal from my preamp to a fixed tube amp to a pair of Hemptone fr8 speakers run fullrange, with no active or passive crossovers at all.

I then run a signal from my preamp to a Behringer Ultragraph Pro FBQ3102 (31 band stereo equalizer) to a DBX 223xl (active stereo 2-way crossover) which connects to an old Krell kav300 integrated amp which is then connected to four AE IB 15 drivers (one pair per side).  The bass drivers are hooked up in parallel so I think the amplifier sees roughly a four ohm load from the two eight ohm drivers per side.  If your spouse ever tries to get you to get rid of your extra amplifiers just say "no".

The combination of the Behringer EQ and the DBX active crossover and the integrated amp with volume control gives me lots of flexibility in matching the bass drivers to the full range speakers.

I purchased the EQ and the crossover from my local Guitar Center.  I also had to buy the necessary RCA to XLR to TPS hook up cable and or adapters there since my home audio RCA system now went into this Pro audio type connection but the employees at the store helped me select the cables and adapters I needed.

This seems like a larger up front cost at first but I think I would have spent more in making multiple orders to Parts Express to try and figure out the correct crossover inductor and cap values and crossover points needed to make a good passive crossover.  I also do not have the expertise to make a passive crossover that can take into account for the 6db/octave roll off that starts based on the width of my baffle.  Some members on this site suggested a single large value inductor but I am not sure if that would introduce phase shift issues in relation to my drivers running full range with no crossovers.

I have set the DBX crossover at 250 Hz.  I then set the EQ sliders to start at -6db at 250 HZ, 0db at 125 Hz, +6db at 63 Hz, and then +12 DB at 31 Hz-20hz.  The shape of the slider pots on the front of the Eq looks like a ramp starting at 250 Hz and sloping upwards all the way to 20 Hz.

I think I was able to get away with using the Behringer EQ in part because the Fs of the AE IB 15 drivers is very low possibly even around 16 Hz.  Once you reach the resonant frequency of your bass driver then I think the dipole roll off becomes much greater than 6db/octave.  I think it becomes something like 18Db/octave but the real Dipole experts on this site will know the real roll off amounts.

I was concerned at first that the amp and low frequency drivers would have to work much harder to deal with this 12Db boost at such low frequencies but that is not the case.  The Krell amp is barely warm to the touch and the AE IB 15 drivers do not have to make very large excursions.  I almost have to touch their surrounds to make sure they are moving at times.

I know you said you were happy with your bass drivers hooked up running full range but I do not think you are getting all you could be getting out of these drivers.  I hear a very significant difference when I bypass the Behringer Eq and just let my bass drivers run on their own.  Using the active EQ really helps make a big improvement.

I hope this post helps you out in your Open Baffle Project.

Sincerely,

Mark K

[skite30]

Mark
You have certainly put a lot of work and thought into your system. I am looking to try this project as a passive crossover and possibly bi-amped. I meant to say I really like the sound of the alpha's by themselves but I won't be using them fullrange with the hemp. I am looking at some of the other suggestions made so far along with the speaker level crossover designed by MJK. I am interested in possibly trying a line level crossover and bi-amping the system. I am hoping to get some feedback and guidance on that idea.
thanks steve

[androuski]

Hello,
I'm looking for Hemp acoustics FRD file, may be someone has already got it ?
Thanks

[skite30]

I can't help with the hemp acoustics fr8 I don't have any experience with it.

An update of where this project is at. I have added a 1.2 p-core inductor to the alpha 15a to roll it off starting about 800 hz. I like the sound a lot. Blends very nicely the fr8, the alpha and fr8 are both at about 94 db. at this point. So far so good. I am thinking about adding a tripath or d-class amp to use with the woofer. Think winsome mouse here or something along those lines. I am tinking about adding a line level  low pass crossover at about 150-200 for the alpha and a high pass line level on the fr8 at about 300 hz. I power the fr8 with a music reference em7-5 amp. Any advice or comments? So far having fun with it and not spending too much money.

[Telstar]

I hope this post helps you out in your Open Baffle Project.

Sincerely,

Mark K

Hi Mark,

I've been looking at a good wideband driver for mids to highs and the Hemp seems very nice. Besides padding the whizzer, did you feel the need to do other interventions on it?
You're running it fullrange, without filters, right?

Also, IB15 vs OB15. Using only one woofer per speaker which one would you choose?

[markk]

I hope this post helps you out in your Open Baffle Project.

Sincerely,

Mark K

Hi Mark,

I've been looking at a good wideband driver for mids to highs and the Hemp seems very nice. Besides padding the whizzer, did you feel the need to do other interventions on it?
You're running it fullrange, without filters, right?

Also, IB15 vs OB15. Using only one woofer per speaker which one would you choose?

Hi Telstar

I have been using the Hemptone FR8 for almost a year now and have been very impressed with them considering their price of approx $128.00 each.  I have not had a chance to hear the more expensive lowthers so I guess I do not know what I am missing.

Adding the cotton roll behind the whizzer and using Kimber 8tc cable seemed to be a very good match for this driver in my system.  I do run it fullrange, without filters, using a tube pre and power amp. I have also placed earthquake putty on the inner spokes of the back speaker frame in a rounded manner to try and see if the back wave could exit more smoothly (but I do not know if this did anything or not). I also routed out the back side of my baffles (along the edge of the round speaker holes). The average efficiency of this driver seems to be about 93db and I do notice some tube roar or noise at times compared to my magnepan 1.6 speakers.  I also did lose some range in turning my volume knob compared to the less efficient speakers I was using before. I think this is because my tube amp has a high input sensitivity at around 1volt for full power.  So I have also ordered some Harrison Labs 6db line level attenuators from parts express and will give these a try between the Pre amp and Power amp.  I think this will be able to help with the small tube noise and give my volume knob some more range.

I have been very happy and impressed with the Acoustic Elegance IB15 drivers.  Recently I found, by experimenting, that if I sent the signal from the pre amp to the dbx crossover and then to the Behringer EQ it seems to produce more bass. This is no problem and I just adjust the volume down a little either on the Dbx or the Behringer voulme controls. 
For me the four IB15's have worked very well and I have crossed them over with the Dbx unit as high as 900hz or so with no apparent problems (but the Dbx does have a steep 4th order slope) so that may have helped the IB15 compared to a 1st or 2nd order crossover slope.  For the most part I cross the IB15's over at about 250Hz or so and just run the Hemptones fullrange with good results.  The build quality of the IB15" is quite impressive for the price.

I do not know much about the OB15. I do not see it listed on the AE website store.

I was also thinking about building a Dipole speaker in the future with only one of the IB15 Drivers per side and trying to make the width of the baffle a bit narrower.

The employees at the Hemptone company also seem to give high marks for their Hemptone FR 5" driver.  They have apparently had very good results putting these in speaker enclosures at two speakers per side one just above the other vertically.  I have wondered if this Hemptone 5" driver would do well in an open baffle.  This smaller 5" version may be a more balanced match for only one Low frequency driver per side.  The only problem with this 5" driver is that it may not have much room behind it to let the back wave escape compared to the front.  The FR8" driver has pretty good spacing between the frame and the magnet assembly.

I think this FR 5" driver is not quite as extended in the uppermost frequencies as the FR 8" driver.

The Hemptone website seems a bit messed up right now and I have not been able to click on the specs of the two drivers like I used to.  I suggest you give them a call and see if they can send the specs of each driver to you.  These specs were also very useful because not only listing the frequency sweep graphs they also provided me with vital cut out information that I needed when I was cutting the holes out of the baffles that would hold the drivers.

I definitely think it would be possible to build a dipole speaker with only one AE IB15 per side.

If you went with only one low frequency driver per side I suggest you read the Enjoy the Music May 2006 article by Dick Olsher. It was a review on the Viastion no box loudspeaker kit.  He gives lots of good technical advise on mounting the bass driver as low as possible to the floor, extending the baffle to the floor with no space, and using wings on both back sides to gain more low frequency driver efficiency.  Even then an adjustable active electronic crossover and a 31 band graphic equalizer would be very helpful in the final dialing in process to match your low frequency and mid-high frequency drivers together.

I hope this reply helps you in your dipole speaker project.

If you could let me know which drivers and how many you decided to go with that would be great.

Sincerely,

Mark K

[Telstar]

Hello Mark,

Thanks for the detailed reply.

I have been using the Hemptone FR8 for almost a year now and have been very impressed with them considering their price of approx $128.00 each.  I have not had a chance to hear the more expensive lowthers so I guess I do not know what I am missing.

(...)

I do not know much about the OB15. I do not see it listed on the AE website store.

I was also thinking about building a Dipole speaker in the future with only one of the IB15 Drivers per side and trying to make the width of the baffle a bit narrower.

The Hemptone website seems a bit messed up right now and I have not been able to click on the specs of the two drivers like I used to.  I suggest you give them a call and see if they can send the specs of each driver to you. 

I'll email them, since overseas calls on a diff timezone are not the simplest things

The hemptone price is great, but I still have to find an european dealer, while I can find the Hemp FR8C (not 100% hemp it seems now) on various places. One alternative would be the Tone Tubby 12" Alnico, but then I would need a tweeter for sure (which adds complexity and cost, not that i dont want to do that).

Having listened to a few OB speakers (but not enough!) I think that larger cones do better for the midrange. 10" would be my minimum size, although there are many excellent 8" fullrangers, such as the the Hemp and Hempcone ones, Audio Nirvana 8" Alnico.
And I also thought to put two 8" per speaker in series, very close and not parallel to each other. This should improve the presence of the midrange and efficiency as well.

I'm shortlisting the drivers, as you may have noticed

For the bass, the choice is much easier. I'll use a U frame and either OB15 or 2x OB12 or Eminence Beta 15.  On this forum Joghn himself advised me to go for the OB15. That'll need eq in my room anyway.
I can post the relevant specs of the AE speakers, because the little gems for OB are not posted on the website, you have to dig into the forums, some are made even by special order.

IB15: Fs=16hz, Qt=0,7, Xmax=18,5mm, power handling=500W, sens.=86dB
OB15: Fs=33,8hz, Qt=0,82, Xmax=18,5mm, power handling=400W, sens.=91dB
OB12: Fs=28hz, Qt=0,47, Xmax=18mm, power handling=(I assume it's 400W too) sens.=89dB

Another interesting and very cheap fullranger is the Beyma 10AG/N, it costs only 50 euros and has got some praise.