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Old 22nd January 2013, 05:45 AM   #11
adamt is offline adamt  Australia
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I have the same drivers as you, and built the Nagaoka d-58es horn. Its pretty similar to the standard Fostex, but not strickly for this driver (it was for the 208ss which was a 10kg monster with double magnets) but to me it still sounds pretty good. A couple of points:
1. I have played with all types of damping. My suggestion is sheeps wool in the base of the horn mouth, and a thick piece of underlay on the back wall of the cc. a small amount of wool underneath the driver in the cavity to stop echo. No stuffing in the horn line.
2. I have used bitumen sheets on the back of the driver. Has damped some resonances.
3. I have the T90a with a 0.68uF cap. I have tried second order crossovers, cheap and expensive parts, no tweet etc etc. For me, a cap somewhere between 0.68 and 1.5 first order in phase (positive to positive) works best. Buying a good quality cap is worth it.
4. Plywood is far better than MDF for horns. I have tried both and find MDF sucks the life out of the music.
5. This driver prefers SET amps (low damping factor). I have tried ss amps (strident hf, and no bass), ss class a (liquid, but no bass), PP tubes (dynamic, with good bass but slightly veiled), SET (cohesive if not quite as dynamic as the PP).

Just my opinions which will vary greatly to others!

adam
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Old 22nd January 2013, 06:04 AM   #12
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Quote:
Originally Posted by adejacko View Post
dave,
If you go on the wilmslow site, you'll only see then in MDF, but I emailed and Neil who works there said they'd do them in birch
I knew that and have recommended peopleask before. It is a crime that they would do these horns in MDF.

dave
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Old 22nd January 2013, 02:50 PM   #13
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Adam,
Thanks for the advice. I've had a look a the Nagaoka- 53, seems quite popular. I will try your suggestions for damping. Not sure about the bitumen sheets, are they used as roofing for garages? Might be a bit too much. I would imagine the sheets would be visible too, making the inside look ugly. I don't mind spending a bit of money of good damping. It seems crazy to scrimp on one thing, then spend over 800 on tweeters (will probably go for T900A).

I will definitely buy a good quality capacitor. Will post thread about this and other concerns closer to the end of the build.

As far as amps go, I ordered a SEX amp from Bottlehead. It's been in the UK since 3rd Jan, the customs took 15 days just to look at it, now it's sitting in a depot in Birmingham, and I'm waiting for a letter from Parcelforce (a.k.a. parcelfarce) so I can pay the VAT and other charges (83) before they will deliver it. Ten days to get from the States, 3 weeks in the UK doing nothing. Could have built it by now if they had their act together!
WARNING; if anyone does buy an amp from Bottlehad, email first and ask them to use UPS/fedex etc. it's worth the extra money, unless you have the patience of a saint.
I bought the SEX amp originally for headphones, then decided to build the speakers, that's why I went for the 208's, due to their high SPL. If I could go back in time, I'd get the Stereomour, and Fostex 168 sigmas. I have a smallish listening room, and I think the 208's will be overkill. Then there's the whole extra cost of the tweeter. Nevermind.
I read recently on a thread wrote, 'get the most sensitive speakers possible, then choose your amp'. I've done it back to front. However, I've started looking at other SET amps, to buy or build in the future, so if you have suggestions, I'm all ears. Probably a 2A3 - I've heard the sound is good and the tubes are cheaper than many others.

Hopefully, the SEX amp will arrive in the next couple of days, and I'll have it built before the flat-pack speakers arrive.

dave,
I don't know why Wilmslow don't just offer birch on the site. In all the hifi forums I've seen, birch is recommended. But on a woodworking site, I noticed members suggesting that MDF was better for speakers! Fostex recommended birch, as have most, so that's why I bought it.

If anyone has suggestions for finishing the wood, I would be glad to hear them. Some use oil, varnish, lacquer. I was thinking of a wood stain and varnish. The wax finish is an option, as I won't be letting anyone put their hot coffee cups on the speakers.

Cheers.
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Old 22nd January 2013, 03:13 PM   #14
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MDF is OK for midrange & HF enclosures. Bass enclosures are another matter entirely. You can get good results from it, but it takes some work if you want to avoid large amounts of panel damping, which brings with it its own problems. A quality grade of ply has the advantage of a superior stiffness-to-weight ratio, so it tends to be easier to work with for LF enclosures.
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Old 22nd January 2013, 08:38 PM   #15
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Quote:
Originally Posted by adejacko View Post
...But on a woodworking site, I noticed members suggesting that MDF was better for speakers!
IMHO the whole MDF thing is a myth propagated so well by the marketing departments of speaker companies that even a lot of very good designers believe it. Why? Because it is cheap (with oil going thru the roof, its mass will become more & more a countering measure)

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Old 23rd January 2013, 12:48 AM   #16
adamt is offline adamt  Australia
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I purchase some bitumen self adehesive sheets from a car parts place. Aparently they use them for sound deadening in car panels. I cut it to the size of the magnet and stuck it on there and the frame. It did dampening some ringing, gives you slightly blacker background to the sound, and it is not too expensive (about $30 AUD). How can I tell all this? With sensitive speakers, you seem to be able to hear more detail in the music, so it is defninantly noticeable.

Amp wise, I am using a SET type 45 integrated. It will take 2a3 tubes, but I prefer 45. It has a lovely even tone across the full spectrum and pulls you in to the music. At 1.8watts per side it does not give a lot of drive, and it is just adequate for the 98db speakers. You would not want any lower output. If quiet listening to laid back music is waht you are after, a 2a3 will be fine, and give you occasional bursts of foot tapping happiness. But if you are more into the heavy rock, large scale syphonic works, I would suggest a pp tube amp with a bit more grunt.

I think you will enjoy the SEX.

(I probably could have put that better....)
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Old 23rd January 2013, 02:58 PM   #17
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Adam
Who doesn't enjoy the SEX? I finally got the letter enabling me to pay the VAT charges on my SEX amp. One month to the day since ordering, if it actually does come tomorrow, as promised. I'd like to order a Stereomour or Paramount monoblocks, but I couldn't go through this waiting (and calling, emailing etc to find out where the hell it is) again. So I'm looking for a good 45/2A3 amp kit in the UK, preferably under 800, with about 3 - 5 wpc, that has detailed building instructions.

I noticed the bitumen on one particular DIY audio site (may have been car audio), had never seen it used that way before. I've seen felt used. If the products are cheap, I don't mind testing them out.

I'll probably asking a few questions once I've started building the SEX amp. I've never even used a soldering iron before, so I hope I don't mess it up.
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Old 12th May 2013, 03:59 PM   #18
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The SEX amp was finished a few months ago and the Fostex 208 enclosures are built but need to be varnished. I now know what the Fostex 'shout' is. I've put bitumen and felt in the cc and on the mouth, but high unwanted frequencies are still coming through, so am adding carpet underlay too. The bass is a bit woolly, needs tightening up, and there's that upper-mid peak that ruins the sound. So either phase plugs, which I don't want to use as I don't want to cut the drivers in case I want to sell them in the future, or send them off to a company that alters the cone to improve the response.
Has anyone used a filter to get rid of this peak? Might start a new thread for this, as this one's probably dead.
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Old 13th May 2013, 03:45 AM   #19
adamt is offline adamt  Australia
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Hi adejacko

Now comes the fun bit - the break in period! I found the 208e sigma takes months to fully break in, and in that time you will have some peaks and troughs noticeable in the music. You have two ways of dealing with this...leave it alone, and just soldier through, or tweak like crazy. I think given time, you will undo most of your tweaking when they DO break in. A couple of things you might try...
1. Make sure you are listening off axis. I have them with a slight tilt inward, but not directly pointing at your ears.
2. Try reversing the wires on the T90a (ie connect positive to negative on the amp). This can soften the music and be less direct. For me I dont like it as it becomes more sibilant, but for you it might work.
3. You could put additional stuffing in the chamber, line and even in the base of the horn mouth. This can help damp reflections and give you a more even response. It might suck some of the life out of the music, but will probably make it more listenable short term.
4. Try different capacitors on the T90a. If its too bright, then use a clarity cap (sic) as they seem to rolloff rapidly.
5. Position the speaker away from walls. I found that I have a room peak somewhere around 50hz, but that is room related, not a function of the speaker.
6. You could try a contour filter of 2.2uf + 0.50mh + 8ohm (capacitor, coil, resistor in series wired ACROSS the 208 speaker terminals. This will give you a more even response until it breaks in. Alternatively you could try a swamping resistor of about 47ohms across the speaker terminals. That sometimes works.

As I said, most of these tweaks you will probably eventually remove.

Stick with it as you will be rewarded with a good speaker long term.

have fun! Adam
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Old 14th May 2013, 02:00 PM   #20
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Hi Adam,
Thanks, that very useful stuff. I've already noticed an improvement with the mids over the past few weeks. Also, adding the tweeter helped smooth out the 'shout'. I have both cc's and one speaker's mouth lined with bitumen and felt, the other speaker's mouth is lined with carpet underlay. The former has tighter but weaker bass. I'm thinking of adding some underlay to the cc's (scotmoose suggested lining at least one of the side walls). Also, swapping half the felt and bitumen from one mouth with the underlay from the other. So both speakers' mouths are lined with half bitumen and felt and half underlay. I now understand all the experimenting and tweaking that DIYers have to do.

I have them toed in as you suggested, the sweet spot being about a foot in front of the listening seat. They are too close to the back wall, I can bring them in a bit, but the room is too small to have them in the correct position.

I'm very happy with the tweeters. I'm using the Obligatto caps at 1.5 uF. This gives a Xo of 13800hz, just before the 14 khz roll off. Before I put the T90a on, the mid-range sounded terrible. I know a lot of people use caps at 1uF or less. On the xo calculator I used, a 1uF cap had a XO of near 19800hz, which is just below the 20khz audible range. excuse my naivety, but that just seems a waste of 2 x 180 tweeters.

The main thing I'm bothered with is the bass - there's just not enough of it. I think the SEX amp isn't quite up to it. Also, my source is a Teclast T51 player with dedicated line out. even though it has Wolfson 8740 dac chips, I could do with getting a laptop/notebook and a good quality DAC. This means another 800. And a new amp; a 2A3 or 45 SET amp. I've been looking, and they're not cheap. I might even end up getting a Stereomour from Bottlehead.

One thing I should mention is that my enclosures don't have the double layer of 18mm birch ply on the side walls, only a single. Nor the 3 strips of 18mm on the back. This is how the flatpack came from Wilmslow Audio. To be honest, I'm not too bothered as they are heavy enough as it is. However, this must surely change the dynamics of the enclosures. There's a reason Fostex reinforced the sides, and I don't know how much of a difference it has made. I need to hear a pair of these with the 36mm sides and back, and burnt in drivers etc to know how good they can really sound.
Does anyone ever use equalizers to level the peeks and raise the bass? or is that sacrilege in the SET/horn world? I might try the contour filter you suggested.

Thanks again Adam.
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