DIY. Simple Back Loaded Horn project with vintage BOLTON drivers

Autor

Beitrag

aks07
Stammgast

#1 erstellt: 12. Okt 2008, 06:17

Durga Puja in eastern India is a major affair. We shut down for 4 full days. The entire region is a riot. Roads are choked. Markets are closed. Friends and family roam the town entire nights and sleep the day off. You have two options. Join this riotous melee. Or stay shut at home.

Being a pragmatic guy, I choose to do something fruitful. And what better than a Speaker project ! For a while I had been thinking of a small and simple horn to go with my simple SE tube amp. This amp was just lying idle waiting for right speaker.

I do have a pair of FOSTEX FE206 drivers. After extensively looking around for an enclosure project, I thought the best would be the Sachiko boxes. More details on the frugal horn project website. But this is a huge build. So something smaller and easier was called for. Suddenly I remembered that I had a pair of 4” BOLTON full range bought in 80's and breifly used in a ported box. Since my musical preference was different at that time, the small Bolton was shelved. So here was a speaker that was calling out to be resurrected.

Now which enclosure? I am just building on my hunches and adapted a standard Tetsuo Nagaoka type back loaded horn enclosure. The changes are basically to suit the 12mm thickness marine plywood available in the usual timber shop. Another reason- I can later upgrade the Bolton with something better like a FOSTEX unit.

So off we go. Its still not complete yet, but a work in progress and almost 70% done

Designing/adapting took one day. Procuring the sheet and marking out another day. Cutting the sheet and re-working the goof ups took another couple of day. We now have all the finshed panels ready. Just need to glue them all together.

Pics so far.

THE DRIVER

Bolton 4”. Its rated at a very ambitious 50watts ! But a more conservative figure should be about 12~15watts. Please note that has a that brown cone no longer available. In any case BOLTON quality is down to pits now. Even in 80's (Bolton's peak period) you really needed to sweat to find a matching pair.

DESIGN
Simple and easy to build. Hopefully should perform well

Cutting layout

PLYWOOD

12mm marine ply. 8Ft x 4ft. Cost about Rs, 2,000

All marked up and ready to cut

MISTAKE
A silly marking mistake ensured that one panel was out of size.

Now fixed. Just needs a session with the sander.

All the panels are ready. They were tacked together and polished at the same time. A tolerance of minimum 0.25mm is needed to ensure a completely airtight horn passage inside.

Ply is tricky to work with. Aggressive cutting and planer nibbles away little bits. These will need to be filled in.

Next we shall put together the panels and test the speaker. So please stay tune.

[Beitrag von aks07 am 12. Okt 2008, 06:25 bearbeitet]

aks07
Stammgast

#2 erstellt: 12. Okt 2008, 14:58

I was planning to start the assembly earlier this evening. But to my dismay I found that some panels were slightly twisted. So they get the brute force treatment. Wedged tightly between 2 granites in a Vice and F Clamp they spend the night pondering their fate. Hopefully, they should be straight by morning and we shall be able to glue a few pieces together.

Arj
Inventar

#3 erstellt: 12. Okt 2008, 15:38

cool

this is like a story.. am awaiting the ending and sincerely wishing there is no Twist in the tail ...

sivat
Stammgast

#4 erstellt: 13. Okt 2008, 01:05

AKS,

Sounds very intresting....keep us posted. All the very best.

Do be careful with that hammer...

Regards
Siva.

aks07
Stammgast

#5 erstellt: 13. Okt 2008, 03:44

Thanks Arj-garu and Sivat-garu. Surely will be careful with that hammer.

On a positive note this morning we are able to jury rig the speaker baffle. This was the most critical placement and rest of the horn will be referenced to this peace. Hopefully when i am back from works a few more panels can be glued in. Thanks for your interest and look forward to your comments.

viren
Stammgast

#6 erstellt: 13. Okt 2008, 14:33

Dear aks,

Any horn cabinet is an ambitious build! Very courageous of you to plunge in!

By the way, all Bolton drivers are now vintage. Bolton has shut down. Since the elder Mr. Monga passed away, the progeny had no interest in continuing the business. Another Indian brand fades away!

Regards,
Viren

square_wave
Inventar

#7 erstellt: 20. Okt 2008, 07:26

Dear Aks,
Best wishes on the new project

Would love to see this finished.
Bolton brings back fond memories of my college days when I used to make speakers for my friends to earn pocket money...

Sad to see that brand fading away.

aks07
Stammgast

#8 erstellt: 23. Okt 2008, 01:57

Thanks Viren-ji and square_wave-ji

The progress is very slow as setting up time for each panel is very high. And I am only able to spend about an hour of so in the mornings. But both the boxes are almost ready now. I will start testing soon.

[Beitrag von aks07 am 23. Okt 2008, 02:29 bearbeitet]

square_wave
Inventar

#9 erstellt: 23. Okt 2008, 03:53

Hi aks,
Was chatting with George ollapally yesterday. Looks like he has acquired a new tube amp. Forgot the name...

aks07
Stammgast

#10 erstellt: 23. Okt 2008, 12:26

square_wave schrieb:

Hi aks,
Was chatting with George ollapally yesterday. Looks like he has acquired a new tube amp. Forgot the name... :)

Wait till he sees the new Lyrita SET amp !
George and Susan are scheduled to visit us 2nd week of November. They will be here for 2~3 days. Usual round of Golf and meet ups. I waiting with baited breaths for his comments on this DIY horn .

aks07
Stammgast

#11 erstellt: 09. Nov 2008, 03:37

UPDATE

For past few days I have been listening to the initial impressions. These BOLTON drivers are very transparent. The highs are sufficient for my hearing boundary of 14Khz. The bass is quick and solid. Midrange is quite sharp but a little shouty at times. For trials I was using a Solid State amp. Will re-audition with my reference tube SET. As of now the sound quality is quite well balanced and shows promise.

Pros
-Analytically clean. Fast sound. Transparent midrange. Great presence and soundstanging.

Cons:
-Somewhat lacking in very deep bass. Shouty midrange in some recordings. Finicky with placement and listing position.

The bass is actually pretty impressive considering the limitation of the driver. The horn brings a dramatic increase. I was experimenting by temporarily placing a little Sony shortwave receive on the horn baffle. Suddenly that Sony would sound like it has gained an 8” driver

As of now BOLTON’s are almost there but fail somewhat on the’s so-called X factor. Hoping some burn-in will do them good. But I am certain a better driver like FOSTEX FE103E will bring magic to this cabinet.

We now get down to giving a finishing coat to the cabinet. I was earier thinking of cladding it with Veneer. But my skills with that are not so good. So now I have decided to paint the box.

-2 coats of cement primers have been applied. 12 hours between the coats and polishing with 120 sand paper
-Clay putty will be applied now. 1st layer. Dry. Cutting. 2nd layer. Dry. Cutting
-After a gap of about 60 days and then apply fresh coat of primer and then spray some nice florescent orange colour.

Pics:

Primer stage

This is how we get a tight fit. Putting about 600kgs of welding electrodes after the panels are glued in. 3 days in that condition and the panels are almost fused to each others and begging for mercy. Each electrode box is about 32kgs.

Manek
Inventar

#12 erstellt: 09. Nov 2008, 06:24

Hey nice stuff aks.

I am sure a fostex would do better. The true test would be with your set, do you intend to put in fostex later ?

A while back I did have the chance of hearing a tweeter crossed over with the fostex, first order around 8khz, it was an experiment but the extra high level re-enforcement left us convinced that with a suitable tweeter the combo would shine. Most of the coherence and goodness of the full ranger is preserved with very good highs.

Regards

Manek

aks07
Stammgast

#13 erstellt: 09. Nov 2008, 08:51

Thanks mod sahib

Yes I am thinking of acquiring a pair of FOSTEX 103E. Just waiting for the general economic situation to improve. I already have tons of stuff such as tubes, drivers, transformer and any more loose addition will strain the WAF even further.

My reference 845 SET can not be a full time partner for this Horn. They require slightly bigger speakers to really shine thro. These are good for a smaller amp.

Did you see the cost of Fostex tweeters? I will be never be able to afford them.

Manek
Inventar

#14 erstellt: 10. Nov 2008, 05:05

Aks

Yes I have seen the fostex tweeter price.........very high :-)

Maybe you could use the tannoy supertweeters ? I wonder if they are still in production, the "eye" shaped ones, don't remember the model no. I doubt they are as expensive and if I remember right they would function 15khz and above.
Does one need a horn tweeter from the same manufacturer anyways ?

Wonder if standard metal dome would do ? What would be the result if maybe one runs two metal/silk domes a side in series to keep upto the drivers efficiencies ?

What do you reckon would be the sensitivity of the bolton ?

Manek

[Beitrag von Manek am 10. Nov 2008, 17:52 bearbeitet]

viren
Stammgast

#15 erstellt: 11. Nov 2008, 03:41

Hi Manek and aks,

Here's something that's not out of this world!

null]http://www.madisound...ucts_id=286

null

Viren

Manek
Inventar

#16 erstellt: 11. Nov 2008, 04:30

Hmmmm....

37 dollars is really not bad at all.

I remember one which was very expensive........

Manek

aks07
Stammgast

#17 erstellt: 25. Nov 2008, 05:25

I have been using the Horns for last few days. Here is a pic at the penultimate condition. The surface finishing will be done after all the mods are over. Pictured here during the "in-room" trials.

Those vintage BOLTON’s are truly a humbling experience. The genius of Mr. Moga. May he RIP.

I was not expecting the Bolton’s to sound so pleasant. They really seem to have opened up after about 100 hours of burn-in. The harshness is gone; the lows have become more relaxed. But so has the top end as well. It seems to have rolled off a bit. I wonder what would have caused that. At this rate it just might need a super tweeter. At 50 hour mark I had lightly stuffed the horn expansion chamber with some Racron filling. Maybe they are causing it. Any suggestions?

Audition Equipment

- Solid State JLH Class AB clone 30 WPC: Mid pronounced. Not recommended
- Vintage SONODYNE Jetliner amp 15 WPC: Very good matching. A little weak on LO end.
- 845SE 25WPC : Nice low and mid. Very good imaging. But unsuitable as the 845 overpowers the driver and exceed its Xmas.
- EL34 PP 15WPC Triode strapped. No NBF: Same as above but slightly better on HF.
- EL84 10 WPC Push Pull in UL mode. 10dB NFB: Very nice !
- 6550 8 WPC SE: Best overall. Nice blend.
- LM3886 gain clone on 12 volts rails: Same as EL84 PP
- My daughter’s Sony Boombox: Terrible.
- Old HMV gramophone with ECL86 mono amp: Pleasant but the built in elliptical speaker sounded better.
- SONY World band radio: On steroids !

Source:
- Marantz 5001 CDP
- Philips Turntable modified. Tube phonostage
- Technics tape deck
- Line out FM feed from the SONY worldband radio
- Casio model 7000 keyboard to check out specific notes

Interconnects:
- Generic OFC speaker cables
- RF coax IC
- Generic 3 prong IEC power cable

[Beitrag von aks07 am 25. Nov 2008, 06:17 bearbeitet]

Manek
Inventar

#18 erstellt: 25. Nov 2008, 11:08

Maybe when the drivers were raw you were hearing a peak or peaks at certain frequencies above 8-9khz and now they could have evened out a bit after burn in ?

The racron stuffing could have done it as well but that would mean there was a lot of high freq energy coming out of the rear of the driver.the only way to check is to remove the stuffing ?? :-)

Manek

aks07
Stammgast

#19 erstellt: 26. Nov 2008, 09:49

This weekend I will remove the stuffing and report back. But I doubt if the filling is the culprit for frequencies beyond 12khz or so

Howevere, I do feel the racron should have gone in after the drivers had a chance to fully burn in and if there was still harshness.

In any case its not a big loss. The BOLTON is excellent for midrange. I can simply put in FOSTEX FE103 and save the Boltons for a future 3 way project.

aks07
Stammgast

#20 erstellt: 12. Dez 2008, 04:48

I am stopping further work on this project.

The Bolton is a good driver but it cuts out sharply at about 14,000Hz. Its still sounds very pleasant and transparent and good enough for my failing ears, but others report a high freq roll off. Adding a tweeter defeats the original purpose. This Bolton is ideal as midrange driver in 3-way system. In fact I remember SONODYNE in 80’s used this as a midrange.

I am deploying this driver to my Scorpio front speaker. The factory fitted OEM driver is all crap and Bolton will be a good choice.

When finance permit I will buy a pair of Fostex 103 to use the enclosure. I have spent lot of resources and hard work to abandon the horn enclosure.

Manek
Inventar

#21 erstellt: 12. Dez 2008, 05:18

why don't you put the driver in the scorpio after you find a fostex pair ? As long as it sounds good to you who cares about what others think ?

Manek

Manek

Arj
Inventar

#22 erstellt: 13. Dez 2008, 04:24

aks07 schrieb:

. The factory fitted OEM driver is all crap and Bolton will be a good choice.

Even the Head Unit is a POS

. i went in for an aftermarket set myself. if you can put an amp it adds wonders to the midbass/bass as well.

aks07
Stammgast

#23 erstellt: 13. Dez 2008, 17:36

The original drivers are intolerable now. They crack, distort, modulate and what not. They need to go ASAP. I think till the time I am able to buy better drivers, Bolton should be fine.

I changed the head unit within one hour of taking delivery of the vehicle. From the dealer drive first to auto accessory shop. The OEM Kenwood unit fetched Rs 5K and a SONY unit was installed for a balance payment of Rs . 3,000.

quadtech
Ist häufiger hier

#24 erstellt: 22. Dez 2008, 13:29

I have a pair of FE206Es too, waiting for
a cabinet. I considered the Sachikos, but
rejected them for the same reason - WAF.
Now, planning to put them in the Fostex recommended
cabinet for the FE208 Sigma. Apparently, this
design is a good fit for the Fe206Es. Hopefully
should start on it next month.

BTW, what software did you use to create the
cutting plan? The one I played with prints out
a big bold "DEMO only" across the printed cutting plan.

aks07
Stammgast

#25 erstellt: 23. Dez 2008, 12:33

Welcome to the forum and thanks for your comments. Will look forward to your build report

WAF permitting a Sochiko type double horn cabinet is the way to go for the FE206. This is per all reports.

I too have been waiting for favourable conditions before pushing the WAF envelop at our household. Thanks to the ongoing 845SE project its already critical. No sane woman wants exposed wires carrying 1,200 volts DC in her living room.

I use an open source programme called Inkspace for the layouts. Its free, easy and serves the purpose. A couple of years ago I went “legit” and deleted all those wonderful but pirated AutoCAD etc from my machine. Now running Ubantu and only open source stuff.

A cutting plan of sort is absolutely necessity even if you are employing a carpenter. And do measure 5 times, and cut only once !

quadtech
Ist häufiger hier

#26 erstellt: 24. Dez 2008, 08:54

aks07 schrieb:

Welcome to the forum and thanks for your comments. Will look forward to your build report

Thanks! I am Prasad from Hyderabad, getting back
to DIY after nearly two decades.
I completed my KT-77 PP amp recently. Pics here -

http://picasaweb.google.com/prasadb/TubeAmp#

aks07 schrieb:

WAF permitting a Sochiko type double horn cabinet is the way to go for the FE206. This is per all reports.

Sure, but there are good reports (from Scott Moose himself too) on the FE206E in a factory 208 Sigma enclosure.
Anyways, the decision is still open till I start cutting
the ply!

aks07 schrieb:

I use an open source programme called Inkspace for the layouts. Its free, easy and serves the purpose.

I went pure open src since 1996 or so. Now on OpenSuse and I have inkscape for a few things. But there is nothing like optimik on linux for cutting plans.

aks07 schrieb:

A cutting plan of sort is absolutely necessity even if you are employing a carpenter. And do measure 5 times, and cut only once !

Planning to do everything myself. But that means buying too many tools. I plan to outsource the cutting and do the rest myself.

- Prasad

aks07
Stammgast

#27 erstellt: 24. Dez 2008, 16:39

I think that’s a better approach if you are not going to many projects. Secondly, you can not trust the carpenter to really spend time to ensure absolutely airtight horn. You need to do that yourself over a longer period of time. Realistically give 1 month for each box. You will glue one panel, wait for a couple of days, then proceed to other panel. That takes time and a carpenter will just try to nail the panel. You can’t be at his back 24 hrs.

Your KT77 build looks very nice. You have pretty nice components and the chassis is absolutely great. Please accept my complement. Can you post the detains in a new thread?