Full Range Speaker for SE KT88 build

[breakthastatic]

Hey Guys,

I am in the process of building my first tube amp, a single ended KT88 based on Alex Gendrano's design with some minor changes influenced by porkchop's design. Anyway, I'm going to need some speakers for it. My budget is 1,000 USD for amp and speakers, and I'm blowing 550 on the amp. I emailed Eric over at Tekton speakers, and he recommended his 8.1, built around Fostex's FE207E. At 440 a pair they are at the top end of my price range. My real question is, for around 450 dollars can I build something better for this amp? My woodworking skills aren't nearly as good as my soldering skills, but I know my way around a chopsaw. I'll mostly be listening in the near field, and am mostly interested in a bookcase configuration. Output transformers are Edcor's CXSE25-8-5k. Let me know what you think. Thanks!

- Andrew

[chrisb]

Originally posted by breakthastatic
Hey Guys,

I am in the process of building my first tube amp, a single ended KT88 based on Alex Gendrano's design with some minor changes influenced by porkchop's design. Anyway, I'm going to need some speakers for it. My budget is 1,000 USD for amp and speakers, and I'm blowing 550 on the amp. I emailed Eric over at Tekton speakers, and he recommended his 8.1, built around Fostex's FE207E. At 440 a pair they are at the top end of my price range. My real question is, for around 450 dollars can I build something better for this amp? My woodworking skills aren't nearly as good as my soldering skills, but I know my way around a chopsaw. I'll mostly be listening in the near field, and am mostly interested in a bookcase configuration. Output transformers are Edcor's CXSE25-8-5k. Let me know what you think. Thanks!

- Andrew

Well, yes, with minimal woodworking skills, you certainly get better bang for your buck (i.e. a lot less than $450 driver/material cost) - although "a bookcase configuration" and any enclosure worth its salt for the FE207E could be mutually exclusive.

For near field/small room use, you might well get better synergy with the FE167, or even the FE127/ FX120. There are numerous excellent designs for any of these drivers which handily outperform the standard Fostex recommended enclosures*. While excellent value for a commercial product, IINM, most of the Tekton designs don't break any new ground.

*you could certainly do worse than the library of collected enclosure plans at

http://www.planet10-hifi.com/boxes-fostex.html


full disclosure - see the signature line below

[rjbond3rd]

I have a set of Tekton Design speakers which came with FE126E's, and I swapped them out for FE127eN. They are visually much better than the boxes I make myself. Eric is an excellent guy to deal with, in my experience.

The question is do you want visual appeal in a nice compact enclosure, or are you willing to do what's needed to wring out that last ounce of performance? If you want the second option, you need to big a bigger box than Eric's 8.1 (not sure of the exact volume but it looks around 25 liters to my untrained eye, whereas you can go up to 40-ish liters if you want to tune the bass response).

Regarding the bass response, it's not really how low it goes (though it will go lower in a bigger box). It's the Q of the bass, i.e. whether there's a bump, a flat response and then steep rolloff, or a slow, gradual rolloff that mates well with the tendency of rooms to reinforce the bass (room gain).

It's impossible to say what will work for you, your room and musical tastes, but be aware that a bump in the bass (high Q) can sound incredibly annoying, boomy and "one note" in some circumstances. That applies to any cabinent, not specifically the Tekton but smaller BR's do tend to have a higher Q than larger cabs, sort of by definition. Some cure this by stuffing the port, so maybe that's an option.

Regarding BSC, my Tektons did not come with a circuit, another fellow on AudioCircle did get a BSC in his. I have no complaint of course, just saying you might want to check because (a) if you go with bookshelf placement, presumably you don't want a standard BSC (you probably want none or just barely a touch depending on many factors), and (b) if you end up putting them on stands, pulled into the room a bit, you almost definitely need BSC. A smallish BR with a bump in the response is a way to do BSC without any circuit but that's tricky t o engineer (getting the bump to occur precisely where the baffle width causes the bass response to start dropping, thus achieving a flat response).

If you do get the Tekton, and if it does have BSC, ask Eric to put a bypass cap in the circuit (so the BSC attenuates above a certain low frequency, but the cap ceases the attenuation at a certain high frequency). The FE207E rolls off around 14k so you don't want to lose any of that precious high end (and a cap is cheaper than a supertweeter).

If you do decide to build your own, and you can go to 35 liters, Bob Brines' design is the champ, and you could buy a flat-pack but it would take you just a bit out of your budget so you might scale down to the 6.5" Fostex. http://www.geocities.com/rbrines1/

[serenechaos]

interesting robert,
i forgot bob brines was making bookshelf speakers
http://www.geocities.com/rbrines1/Products.html
but that little FE207 bookshelf jog shows a F3 of 43Hz.
not bad eh!

[rjbond3rd]

Hi Robert, I heard it last year, and it really goes low, low, low. The FE207E is a good, efficient driver. It takes EQ well. I've never heard it with phase plugs but I'd like to.

Robert, what would your recommendation be for breakthastatic's situation (KT88, bookshelves, $450)?

[HareBrained]

You may want to consider the Audio Nirvana line of drivers. I have no direct experience with them, but they appear to have high efficiencies and decent full range output. http://www.commonsenseaudio.com/

You could also go with a set of eNabled drivers from planet10-hifi. They will get the most out of the 2.5W and will be in your price range.

[serenechaos]

Man, I'm not the guy to ask about bookshelves...
I like going the other direction big higher efficiency speakers, low powered amps...

But since you ask; just thinking about what's been mentioned, like you already said, the FE207s just break the budget don't they? ~$195 for drivers + $295 for flat packs from Brines = $490.
Doesn't leave the $26 for the Ed Lafontaine EnABL kit either...

But we don't know what the wood working restrictions are; if flat packs weren't needed this one would still come in under budget. It's a pretty simple "box with holes in it?"
And why the bookshelf restriction--are they going on bookshelves?
or on stands?
Would something w/ the same foot print be acceptable?
I would really prefer the ML TL to the bass reflex, bass not only goes down to F3 = 35, but it's better quality...
And I like horns so much better than TLs I gave a good pair of FE206 TLs away last week...

Back to bookshelves for KT88s--
A pair of FE167 is $170; would come in under budget, even after EnABLing.
MANY possibilities, same as above, or for a little more work, a blh?
Actually, I've got a pair of FE167s stashed I'd like to try in a pair of karlsons.

or--
(as you already know, what I did,) For $200, bought a pair of 108s & a couple sheets of plywood. All simple, straight cuts, built a pair of Nagoka Swans.
Look kinda like very small bookshelf speakers on a stand w/ a box base?
I've never tried anything as powerful as a KT88 amp w/ them though...
and they're less efficient than any of the other options discussed...

Robert, are the Tekton speakers the pair of BRs you brought over w/ one EnaBLEd driver for the comparison?

[rjbond3rd]

Hi Robert, yes those were indeed the Tektons. I agree that an MLTL would sound (a lot) better than a BR. The Swans would sound vastly better and are super low-profile (and moveable).

I guess another crazy, lazy option, if ultra-compactness is required (and box-building is not a forte) would be to just go get some old boxes, find out their volume and stick some fine drivers in there, and use WinISD to calculate a port size. In that case, it might be good to have one of the drivers that are higher excursion. (The Mark Audio CHR-70's are certainly affordable, haven't had the pleasure of hearing them yet and they are of course lower efficiency than the FE207E but in a smaller cab, would perhaps do more bass -- just guessing, haven't heard them or played with them yet).

[serenechaos]

I haven't heard many BRs or Aperiodics that I was impressed with actually. Merlins, can't think of anything else off hand... Kharmas can image really well, but have other problems. & they're both pretty High $.
If I were stuck w/ using a small box for some reason, I'd seriously consider a sealed one.
Easiest, and most compact, if that's a goal.
And can just add subs for bass.

I haven't heard Mark Audio's either, but only read good things about them.
AND,
If he's married to KT88, there's more than enough power for a pair of Jordan 92s. I forgot about those, but very small, and they can sound VERY nice in the right cab.
Heard a pair @ RMAF last year playing vinyl, MONO, through a big homegrown tube amp, was one of the best sounding rooms there I thought. Close to the mega-buck feastrex nessies for a fraction of the $.
Yeah, if I needed something low efficiency, for a higher powered tube amp, THAT'S what I'd build.
(oops, small & thin, but ends up floor standing again...)

[chrisb]

I got my first listen to factory fresh, bone stock Alpair 10's in a pair of 14 liter semi-aperiodic boxes yesterday evening. I'll reserve judgment on the few quibbles I had with their performance compared to a reference standard FE127eN, until after several hundred hours of break-in.

For near field listening with the amount of power you could expect from the KT88's, the Alpairs could be another great candidate.


The CHR70s are a great bargain, but so far I've only heard them in mini monitor sized sealed boxes (circa 4-5 liters - certainly compact enough for bookcase or desk-top). They definitely have some limitations - primarily sensitivity and bass response, and for the experimental types, certainly respond very well to EnABL treatment.

So that's a helluva range from which to choose - 60mm to 200mm, 4~5 liters to 35+

Having said all that, if you're wary of the performance of any of the smaller diameter drivers ( FE103E/FE127/CHR70, etc), I'd look at the FE167 as a great compromise. If you can't avail yourself of a buddy's woodworking skills, Bob could probably do you a flat pack, and if you're truly using them in a bookcase or very near to a rear wall boundary, a BSC is probably not required. With EnABL treatment and phase plugs, these are very special.