Frugel-Horn Mk3 Builds & Build Questions

I have planed the oak, cut, assembled and sanded the first of my FHs - the second will be finished similarly this week.
The CHP-70s have been playing 10 hours+ a day for a week in some lashed up BR boxes. I transferred one of the drivers to a folded Tabaq that I finished last month, and, with it playing the left channel, and the FH the right, I had a quiet session while indulging in a bottle of merlot.
The only known construction deficiency in the FH is a lack of felt lining behind the driver.
- do you mean deficient in the design, or your particular build? I'm certain that Dave's full documentation goes into lengthy description and graphics outlining the areas surrounding and "above" the driver in which damping is most critical.

Ah yes, what doesn't go well with a nice merlot - sometimes you're just not in the mood for spirits.

I live very close to the carpet capital of the world, but unable to find felt locally, except under the carpet of my F-150. I used some polyester batting instead, recognizing that it wouldn't perform the required duty, but maybe better than nothing.
A product that I particularly like working with is 1/2" Ultratouch which is composed of felted recycled denim fibres with a bonded fabric backer, but a jute or compressed cotton based upholstery material should work well enough.

My room is such that the left speaker is 3 feet from the side wall, and the right speaker 6 feet from its' side wall. Both baffles are 2 - 3 feet from the front wall.
There seemed to be quite a disparity in the bass performance of the Tabaq(in the corner) to the FH on the right.
So, this morning, I got my Radio Shack SPL meter out and ran through the Stereophile test CD2 warble tones.
Using the C scale, I set my reference level(6ft from the speaker) to 60db at 200Hz(the first tone in the bass seqence) and determined the following:
In the corner(left), the Tabaq sound pressure level was +/- 3db from 200Hz to 40Hz(63db), whereas the FH suffered a bump between 100Hz and 50Hz peaking at 74db(80Hz) dipped to 61db at 50Hz and finished 63db at 40Hz. Nothing audible below 40Hz.
Comparing each speaker in the right channel(non-corner) location, they performed within 2db of each other, albeit, with much reduced low bass output(53db@40Hz).
This is the first horn type enclosure I have built - since both the Tabaq and the FH apparently benefited(?) from room corner loading, is there something peculiar about the FH that would cause the bump in the 50-100Hz octave when in the corner, or possibly lack of felt damping?
What I don't think Scott fully explained in his last post is that the design brief for the FH3 was to include compliance with a range of wide-band drivers in the size class of 3-4". Due to the varied T/S parameters and native FR among them, the degree of internal damping below the driver, as well as dependence on boundary loading will vary.

Completing the warble tone tests, both speakers played within 2db all the way up to 10kHz(limit of my hearing).
Looking forward to completing the other - thanks guys for a beautiful design.
Peter
 
I believe he means that he hasn't been able to find the requisite felt damping yet.

Either way, it's going to need more than that in that channel to attenuate the additional unwanted gain. That's fine, I did design them with more gain than strictly needed with the MA units on the principle that you can always get rid of something you have too much of, whereas it's rather harder to increase what didn't exist in the first place. ;)

Apologies, yes, when designing FH3, the object was for a box that would be tolerant of a wide range of drivers, so requirements for boundary loading as far as LF gain goes varies depending on the unit selected.

I prefer cabernet myself. Or a nice Sicillian syrah. :)
 
I believe he means that he hasn't been able to find the requisite felt damping yet.
I was just concerned that he, or other builders, might have skimmed too quickly through the voluminous FH document, and missed these specific details
I prefer cabernet myself. Or a nice Sicillian syrah. :)
I've yet to find an Argentinian or Chilean red that I didn't like - malbecs, syrahs, cabs and savs - and where we're located, for as little as $10 (Everything Wine - over 3000 brands in stock - eventually we might try them all)
 
Thanks for all the comments.
Scottmoose is correct - deficiency in my build by not having felt damping...yet.
I initially connected the FH with no damping whatsoever below the driver, and there was considerable "plumminess" to the bass, so I added some poly fill and the result was much better. Great sounding speaker - may sell my Apogees!
Peter
 
Finished my FHs a week back so thought I would report on my listening impressions.

I won’t bother with any pics, looks like many other pairs that have been made! Built with 18mm high grade (and expensive) ply, just one slight derivation from plans to accommodate my lack of tools/skills. Straight forward clamp and glue construction.

Managed to find some ½” cotton/wool felt by ripping out some carpet underlay, for other stuffing I used a wool based insulation product I have used in the past on multiple builds including BIBs.

Stating the obvious, my impressions are as much about the driver, Alpair 7, as the FH. Driving with a Tripath TK2050 amp (41hz Amp11 much modified) and Squeezebox Touch (FLAC files) so not top end equipment tho quite capable.

The HF extension and clarity of the drivers is very impressive, the overall sound is clean, dynamic and punchy with great integration of the bass extension. OK, so there is bass missing (as compared to my FE208EZ BIB speakers which is somewhat unfair) but the bass is very clean and has good impact. They are exciting to listen to and exceed what I was expecting from a speaker system at that price. Not sure how loud they will go (scared off a little at seeing a warped Alpair cone in another thread) but listening to a favorite CD yesterday at a level that was very satisfying, full on powerful sound. They look cool too, very happy with the outcome.

Thanks to the designers for making this project public.
 
Second FH functionally complete and the pair are playing beautiful music. This must be the biggest bargain of my musical life(and that going back to the '60s mono LP days).
The speaker close to the corner of the room still sounds a little "plummy"in the bass. I put about 20g of polyfil behind the baffle of that speaker - maybe a little more is required? Waiting for the felt to arrive - I assume that will not affect the bass region though. I'll do some more testing when fully complete - in the meantime, just enjoying the music.
 
Thanks, guys. I'll double the stuffing in the exit side of the line when I pull the drivers to install felt. The bass bloom seems to be in the 50-100Hz octave. 40hz is +3db. Overall, the bass is not particularly objectionable, though might become tiring over extended listening.
Not boxy sounding at all.
Peter
 
I would like to back to a valve/tube power amplifier for my soon to be built Frugal horns - (either Alpair -7 or EL70's) anyone have any suggestions? I suppose a pre-amp with a low cut-off filter (+/- 20Hz) will be needed to avoid excessive cone displacement?)

Room size = 5m X 6m in an attic so low and sloping ceilings..

All ideas and suggestions very welcome
 
I would like to back to a valve/tube power amplifier for my soon to be built Frugal horns - (either Alpair -7 or EL70's) anyone have any suggestions? I suppose a pre-amp with a low cut-off filter (+/- 20Hz) will be needed to avoid excessive cone displacement?)

Room size = 5m X 6m in an attic so low and sloping ceilings..

All ideas and suggestions very welcome


As alluded to in the other current thread on this subject, if my feet were put to the fire for a recommendation in this application, it'd be for the Alpair7 - your room's not particularly large, and a decent tube amp (even as little as 5-6W of SET) could be very musically detailed combination.

The EL70s could well sound a bit dark in this particular application, and while you've not expressed an interest in the Fostex FE126E, which certainly works well in this box, they could be a bit too aggressively forward in presentation, and even harsh in the upper midrange.
 
Cone displacement at low frequencies shouldn't be an issue. If you're listening to music with high spl, sub 40 Hz content, you've got the wrong speaker and wrong amp (e.g low power tube) for that duty.

As for amp, see if these folks will ship to you: MP-301 MK3 Mini Tube Amplifier with Headphone Output

I have the Mk II version and its a well built, nice sounding integrated amp.

I would like to back to a valve/tube power amplifier for my soon to be built Frugal horns - (either Alpair -7 or EL70's) anyone have any suggestions? I suppose a pre-amp with a low cut-off filter (+/- 20Hz) will be needed to avoid excessive cone displacement?)

Room size = 5m X 6m in an attic so low and sloping ceilings..

All ideas and suggestions very welcome
 
First ever build upcoming - some "pre-advice" please!

I've been wanting to try a speaker build for years, and am finally ready to pull the trigger. I really like the look of the mk3, and the relatively easy build, and from all I've read it should fit my listening styles well (prog rock, prog jazz, jazz, singer/songwriter stuff, acoustic guitar, etc). No head banging to speak of (usually). I'm hoping to get some advice on driver selection before I start. I am in the middle of finishing my dedicated 2-channel listening room, and these will hopefully be the speakers to break in the virgin space. The room is 12' x 17' with 93" ceilings. It will be treated with 4" absorption panels (OC703) on the front wall (behind the speakers), at the first reflection points on the side walls and on the drywall ceiling. Bass traps are in the 2 front wall corners and I am still trying to figure out where to put one or two on the back wall. As this is a dedicated listening room, I'm able to place the speakers where necessary, and have the room to follow the 38% rule, Fibonacci sequence, etc. to locate the speakers and my listening placement relative to them. I can't wait to play around with it! I will be listening almost exclusively to an analog source (vinyl) and my plan is to drive these with a low powered tube amp, which is yet to be purchased. I am not in a position to spend a ton, so I've been looking at something along the lines of a Bottlehead Sex amp, Jolida, etc. So speaker efficiency is a major consideration given the low power.

I'm looking for recommendations on which driver would be a good fit for my space and equipment plan,and whether there's anything else I should know before I dive in. I plan to use 15mm Baltic birch ply, and the cuts will be made by the shop teacher at my wife's high school (she's a teacher) in their woodshop. I will do the assembly and finishing. Again, recommendations are appreciated for this newbie!

Thanks in advance!

Tom
 
Thanks, that is my plan. The floor will be carpeted, but the other surfaces will be reflective. I'll probably need some, but the amount will no doubt depend on the speakers. I expect it to be a process of trial and error since I have no easily accessible way to measure the room otherwise!

Any driver recommendation? I want to order some but am hesitant to just pick one blindly...
 
18mm vs. 3/4" plywood thickness

I've searched around here (Milwaukee area) and none of the specialty wood shops have Baltic birch ply in 15mm or 18mm. I can get 1/2" and 3/4" though. Can I use the 18mm cut sheet with 3/4" (19mm) ply? Any modifications that would be needed?