BTH K-10A: Exciting dual concentric project - larger than big Tannoys!

[Magna Audio]

A while ago Andy aka BTH K-10A approached me about making a pair of cabinets for his large BTH K-10A dual concentric drivers.

These are large format 18" drivers, same baskets as Western Electric 18" but with alinco dual concentric bass unit and horn tweeter units.
Cone area is quite a bit bigger than Tannoy 15" and the horns are two centre mounted rectangular horn units.
BTH = British Thomson Houston, http://en.wikipedia.org/wiki/British_Thomson-Houston

I've not come across these before - they are pretty rare and priced accordingly. Andy assures me they sound great.

Here's how the drivers look:-

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/BTH18basket_side.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/BTH18basket_side.jpg.html)

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/BTH18front.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/BTH18front.jpg.html)

As you can see they are substantial, 20% bigger and and at least 20% heavier than Tannoy 15s.

Talking to Andy about what he wanted from the drivers sound wise and look wise for the cabs, and his having seen my other dual concentric cabinet projects, I did some analysis of the available data (supplied by Andy) and came up with this

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/5bb4001e-c7fb-4b08-ac8b-03e138c0bfcd.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/5bb4001e-c7fb-4b08-ac8b-03e138c0bfcd.jpg.html)

This is based on the GRF-R style look cabinet. I re-modelled the back loaded horn design / internals in Hornresp based on dimensions and Thiele and Small parameters available / those of similar drivers.

This gave me a design I am confident will work well and provide a visual and audible scale that would impress.

The project is now underway with premium quality Scandinavian Birch Ply cut and machined

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_3991-1.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_3991-1.jpg.html)

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_3990-1.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_3990-1.jpg.html)

Weight is estimated to be around 85-90Kg each, 21 and 24mm birch ply being used throughout.

First task with not much to show for the camera: sanding down all the external / visible faces to remove all production cross cuts from the production of the birch plywood.
A word about high quality birch plywood. This is recognized as one of the best materials to build speaker cabinets from.
It has the right damping / resonance qualities and is widely used in quality cabinets for hifi and high-end pro audit, where sound quality is the driving factor. It is also a joy to work with compared to MDF and lesser quality ply.
Scandivian birch is prized for it slow growth and is an excellent hardwood with nice figuring and grain character.

This is done carefully with progression from coarse to medium to fine and then ultra fine 600grit on my Random Orbital Sander.

The first cab construction is now underway I will add photos of the build as it progresses.

I have also been busy getting the necessary components in to complete the build - Acoustic damping felt, Blind nuts, grille fixings, castors etc.
Andy has some nice original BTH badges that would look great on the external crossover boxes that I will build to house the enclosed / substantial crossover units. These will be rigged up most probably with high quality Neutrik speakon connectors - ideal for the 2 way connections needed from the boxes to the cabinets and some nice cabling.

Andy has dropped the drivers and crossovers off - BIG!

Gonna be a great project - I'm excited to hear these babies.

[synsei]

What a fabulous project Steve, looking forward to following your progress. Now these babies are going to do bass at a seismic level, I hope Andy is intending to inform the USGS once they are completed... :D

[walpurgis]

I assume they have their own dedicated crossovers. Are the dual tweeter horn flares aligned vertically or horizontally?

The driver design is very similar to the Altec models, as Andy knows.

These should be pretty impressive when finished.

[Ali Tait]

Wow! and wow again!

Should sound fabulous when done. Love to hear them sometime.

[Magna Audio]

Yes, we are not quite sure about the vertical or horizontal. A case of suck it and see. What works best. That could be room height and width dependent as well as audience dispersal considerations perhaps.
Crossovers are in built like tanks steel boxes, hammerite type paint finished.




I assume they have their own dedicated crossovers. Are the dual tweeter horn flares aligned vertically or horizontally?

The driver design is very similar to the Altec models, as Andy knows.

These should be pretty impressive when finished.

[walpurgis]

Now these babies are going to do bass at a seismic level

Not necessarily Dave, they'll do huge tight bass, but the cut off point for the horn I'd guess is likely to be around maybe 50Hz with a fairly prompt roll-off below that. I'd expect some output down to perhaps 30 or 35 Hz though. Big horns do 'BIG SOUND', but not truly deep bass unless they are gigantic.

[walpurgis]

we are not quite sure about the vertical or horizontal

My guess is that the vertical orientation will work best for imaging.

[Ali Tait]

May be a smaller sweet spot though.

[Magna Audio]

Seismic bass...

This may be the case. I don't recall the exact Fs (It's on our other main computer), but it is in the low to mid 20's I think. Tannoy Golds 26Hz / HPD are 22Hz.

To quote from Eminence's excellent explanation of T&S / driver properties
http://www.eminence.com/support/understanding-loudspeaker-data/

"As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well."

Cabinet / horn length plays a big part. I get flat (+/- 0dB) 20Hz out of my tapped horns with drivers that have an Fs of 35Hz). However using lab subs with much lower Fs's does not work in a tapped horn (horn length nearly 14').

I am also going to build these with a tear drop in the throat of the horn to barrier HF. I will make these so that they are removable from the driver mounting hole so A/B listening and measuring can be done.


Not necessarily Dave, they'll do huge tight bass, but the cut off point for the horn I'd guess is likely to be around maybe 50Hz with a fairly prompt roll-off below that. I'd expect some output down to perhaps 30 or 35 Hz though. Big horns do 'BIG SOUND', but not truly deep bass unless they are gigantic.

[Reffc]

Great project Steve. Will the crossovers be mounted externally and will the cabs be veneered or left as a self-finish?

[BTH K10A]

I assume they have their own dedicated crossovers. Are the dual tweeter horn flares aligned vertically or horizontally?

The driver design is very similar to the Altec models, as Andy knows.

These should be pretty impressive when finished.

The crossovers as Steve has said, are in steel cases. This is what they lool like inside. Nice air core chokes and good quality caps. Nothing too complex. The one in the pice is from 1958. The X/O frequency is 1700Hz to suit the cut off characteristics of the horn and the polar characteristics of thr bass driver, which is well within is operating range at that point as its good for 5kHz. Versions made by Jensen for a number of US radio manufacturers were even used full range.

http://i46.photobucket.com/albums/f120/emttsd15/IMG_0416-1.jpg

(http://s46.photobucket.com/user/emttsd15/media/IMG_0416-1.jpg.html)http://i46.photobucket.com/albums/f120/emttsd15/IMG_0417-1.jpg (http://s46.photobucket.com/user/emttsd15/media/IMG_0417-1.jpg.html)

These drivers were designed in the mono ere so I assume that an horizontal orientation of the horn would have given the best results. With stereo it may be that a verticle alignment may prove better. My LBL Array 1400's with their verticle horn certainly image more precisely than other JBL studio monitors I've owned but at the expense of a smaller sweet spot.

The design of the K10A is similar to the Altec 604 but has more in common with a mythical dual concentric speaker that Western Electric supposedly built using a 4181a and 555 field coil drivers. The K10A has the same bass driver ( the cone is interchangable with a 4181a ) albeit with an alnico magnet, and a compression driver that uses a pepperpot phase plug in the same vein as Tannoy DC's althoug it has its own alnico magnet to eliminate any intermodulation between drivers.

Steve has come up with a great design and having seen and heard his amazing 5 way horn system he certainly has the skills to get the best out of these drivers. I'm familiar with the bass from a ported cabinet bit it will be interesting to see the difference horn loading makes.

BTH used front and rear horn loaded cabinets for their K18A cinema installations so the cone surround will be ok with the additional stress horn loading imparts.

http://i46.photobucket.com/albums/f120/emttsd15/BTHBassbin.jpg (http://s46.photobucket.com/user/emttsd15/media/BTHBassbin.jpg.html)

[Jonboy]

look very interesting Andy, I'm trying to decide what to do with the university speakers I've got, they need something along the lines you are going cabinet wise

[walpurgis]

Which University speakers do you have Jon? I used to have a pair of the 12" Diffaxials, which sounded pretty spectacular.

[Magna Audio]

The dual range coaxial ones look interesting.

[Magna Audio]

Here is a swatch of various colours that are possible. Obviously more can be done

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4003-1.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4003-1.jpg.html)

Andy requires something dark and rich and has used a deep mahogany and then polished with coloured finishing wax to darken as required. This is the finish that will be applied.
I've learned a few tricks on staining, sanding down then wetting the grain to swell it, then sanding again...
Then the wood is conditioned using a shellac and denatured alcohol preparation. This makes the stain application even and does not result on darkened patches or on the figuring / knots. The wax will be used to tint to match Andy's other furniture.

Onto the build:

Internals are done on both cabs

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4006-1.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4006-1.jpg.html)

As discussed earlier, I have made tear drop baffle inserts that go in the throat of the chambers.
These are recommended by some Tannoy'ists and mentioned on the hilberink site. Covering this in felt probably helps further.

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4007.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4007.jpg.html)

These are designed to filter out HF from the folded horn - this is no doubt a good thing as the BTH's cross at 1700Hz.

I made yokes for the tear drop baffles to sit in

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4008.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4008.jpg.html)

Padded with foam to prevent any resonance.

Here is the teardrop clamped securely in place

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4010.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4010.jpg.html)

This arrangement means they can be removed through the driver mounting hole. To allow A/B comparison.

Here is what the throat looks like

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4014.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4014.jpg.html)

Then on to mounting the drivers

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4017.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4017.jpg.html)

Blind nuts are used. These are expoxied into to the cabs - not just relying on the spikes (I've once had an genuine Tannoy cab blind nut spin on me and not want to release. Lesson learned)

For this test mount I used a mix of available fasteners - Brass Pan heads, Stainless steel hex cap heads, Black allen headed. Andy can choose;)

With deep mahogany finish the brass pan heads go very nicely - that would be my choice.

The drivers are a bit different to 15" Tannoy Silvers/Golds/HPDs etc, with a basket dimension that required a different cut out in the inner chamber/baffle.

Example of the Black allen head fastener

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4018.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4018.jpg.html)

The brass panhead

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4019.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4019.jpg.html)

The SS allen cap head

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4020-1.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4020-1.jpg.html)

Here's couple of shots with the Top and Base put in temp in place to give an idea

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4022.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4022.jpg.html)

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4025-1.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4025-1.jpg.html)

Speaker connections arrive tomorrow, once fitted I can crack on with the acoustic felt lining inside and then mount the Top and Base permanently, then onto the sloping lower reflector. Plinths, grilles, crossover boxes etc etc.

It will be very interesting to hear these...

If the tear drops work well, it is something I could consider to offer as a retro fit to existing Tannoy GRF-R cabs...

[John]

Looks stunning

[Jonboy]

Which University speakers do you have Jon? I used to have a pair of the 12" Diffaxials, which sounded pretty spectacular.


sorry Geoff only just seen this, they are 15 inch monsters I will dig out a pic

[BTH K10A]

Steve has kindly produced and is posting me a colour sample board to choose the finish for my cabinets. As I live in an old house, light coloured woods just don't work and I've gone for Deep Mahogany stain to match a lot of the origininal fittings.

Below is a pic Steve sent in a link to me. I'ts amazing what a difference the finishing wax makes. In advance of seeing the swatch, I'm pretty sure I know which one I'll go for. ;)


http://i46.photobucket.com/albums/f120/emttsd15/IMG_4026_zps6d951732.jpg (http://s46.photobucket.com/user/emttsd15/media/IMG_4026_zps6d951732.jpg.html)

[Magna Audio]

I think I know too Andy...

Progress.

The first cab is up and about:)

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4029.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4029.jpg.html)

I put an LP in there to give some scale

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4030.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4030.jpg.html)

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4032.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4032.jpg.html)

I think most of you will join me in thinking they are an impressive size and nicely proportioned.

The 2nd cab is close on it heels. Should be conditioned and stained by mid next week. Then focus on grilles and crossover boxes.

[Wakefield Turntables]

stunning! I've got size envy :D

[Macca]

Man, those things look absolutely killer. You could take them out on the road.

[BTH K10A]

Man, those things look absolutely killer. You could take them out on the road.

Yes, I'm very pleased how they're turing out. :)

Getting them up to my house is going to be fun & games :eek:

[Magna Audio]

Cabs finished and dressed with felt. Plinth valances to fit.

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4033.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4033.jpg.html)

Neutrik Speakons fitment to finish and cabling etc. Then on to conditioning and staining in due course.

[Magna Audio]

Plinths are made and fitted.
Everything is now prepped, rubbed down to very fine with the random orbital sander (excellent bit of kit), and readied for the next phase. Conditioning.

Here's another pic of one of the beasties or beauties...

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4061.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4061.jpg.html)

This includes the crossover boxes.

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4059.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4059.jpg.html)

These are banana fitting input and 4 pole Neutrik Speakon out. Further Speakon socket on the rear of the cabs. Good quality OFC copper cable will be used throughout.

Here's a pic with the BTH crossover beside.

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4060.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4060.jpg.html)

The galvanised steel screws are there just for fitting. Will be replaced with solid brass. Andy also has some BTH badges which will be fitted to the X/O boxes...

[Magna Audio]

Lots of progress so time for an update...

1st cab brought in and ready for driver loading

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4084.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4084.jpg.html)

Driver cabled - HF and LF

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4085.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4085.jpg.html)

Before connecting up to the BTH drivers I had checked all wiring and buzzed all with my multimeter. Then I tested the X/O's and all my wiring using my Eminence 450w bass drivers.
Essential to make sure LF really is LF and HF really is HF.

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4089.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4089.jpg.html)

All was fine:)

Now testing the BTH driver on X/O

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4090.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4090.jpg.html)

Nice and clear but a bit bass light with no cab.

Driver mounted and under test

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4092.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4092.jpg.html)

This shot gives an impression that they are a bit lighter than in reality. Plus i have not given them final polish so they are a bit waxy / uneven.



Then I spent some time measuring the 1st speaker this morning.

1st one Full sweep 1m on axis

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/BTH18fullsweep1monaxis.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/BTH18fullsweep1monaxis.jpg.html)

Room suck out below 40Hz. 40Hz is giving encouragingly high output, so 4 string bass guitar at 41Hz will be full conveyed...
The HF trail off is probably because the mic is close (1m), it's actually in between the HF horns to an extent.

2nd one Full sweep 1m off axis

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/BTH18Fullsweep1moffaxis-1.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/BTH18Fullsweep1moffaxis-1.jpg.html)

This is same for bass as expected but much better HF response.
+/- 5dB for in room measurements is the goal / best you are going to get, so this is very encouraging 35Hz up.

3rd one is Full sweep with the mic at listening position

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/BTH18Fullsweep35mlisteningpos.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/BTH18Fullsweep35mlisteningpos.jpg.html)

This has enabled the deep bass to level off and is surprisingly flat from 20Hz upwards. This is an amazing plot for bass in room really! Esp as there is no room correction applied at all.
There is a peak where the LF and HF overlap. This might make the sound a bit hard or bright at 1700Hz. Pretty critical freq that.
The lounge the speaker is in is not overly furnished and has 3 large glass panels to the left of the speaker, that might be causing some HF issues in room.
It is an L shaped room.
Also, I will mount the 2nd speaker with the horns vertically and measure to see what that does. Probably not that much as it will fire off the ceiling / floor. But well worth trying.

4th one LF in blue and HF in Red taken in room at listening position.

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/BTH18BlueLFRedHFlisteningpos.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/BTH18BlueLFRedHFlisteningpos.jpg.html)

This shows the X/O point nicely. Adding those two together is not helping that 1700Hz peak seen. Again perhaps the vertical horns might fix this - we'll see.

5th one LF only

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/BTH18LFonlyListeningpos.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/BTH18LFonlyListeningpos.jpg.html)

Plenty of deep bass. All the way to 20Hz! I've only seen that sort of freq with my tapped horns! OK they play flat to 20Hz but these are not far behind!
A real achievement for a 2 way speaker!

Hard to evaluate the sound with just one cab. The HF is very clear, fast and dynamic - so typical of Horn / compression drivers.
Bass is tuneful and detailed with nice subtlety and weight. It will be very interesting to hear what the pair sounds like. Admittedly the room I have these in is not ideal.

[Magna Audio]

Got the 2nd cab in the lounge now. Had a measure and pretty much the same as the other side. Bit more room suck out though on the bass, but as that is room nothing to do about it.
I mounted the HF / drivers vertically on this one. After some L / R comparisons I was convinced that for domestic use the vertical alignment is the way to go.
It's easy to get a much horn HF as you like or just toe them out to have it tuned.
After more listening on various tracks i can say that these are the best Dual concentric speakers I have ever heard.

The HF compression driver unit is clearly superior to Tannoy 15", 12" etc - o contest. One of my reasons for moving away from Tannoy DC's to full scale compression drivers was to get more detail and presence. These BTH certainly have that. Yet they are very sweet. Sax, trumpet, clarinet etc sound great.

I will demo'ing Toccata and Fugue in D minor played by Lionel Rogg as the first track. Scale and push is great. That will get your attention I think Andy!

All this is from one of my little 5W SET amps.
Once warmed up they do sweet, sweet mid and HF. Bass control can be bettered, so if you have a really great amp these will sound even better. Plus my lounge is not the best listening room - so more potential. No way move my 425kg 5 ways out of the music room I'm afraid.

The more I listen the more alluring the sound is...

A couple of pics to follow soon... Just the grilles to complete now.

[walpurgis]

Nice, glad it all worked out well for you. Seems my guess at vertical alignment for the tweeter horn(s) was right. Remarkably good response graphs, I wasn't expecting you to get bass output that low down I must say. I'm sure the mid peak can be sorted without too much bother, maybe a simple notch filter?

[Magna Audio]

Yup, with them horizontal you just can't get away from being on beam. That would be fine in very large room configs, like the Cinemascope installations BTH supplied both projection and sound equipment for. Horizontally they certainly seem to spread the HF out so would be good for a wide sat audience.

Listening to them more they are very effortless and pleasing on the ear. Be very interesting to see what Andy thinks once he has them home and can make more objective listening to what he's heard before.

[Ali Tait]

I'd be interested in a response plot with vertical tweeter Steve. Those drivers measure really well.

[Magna Audio]

Plot of upper part with the horns vertically oriented. Blue line is LF red line is both.

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/d0cb02f4-e7db-45b5-86fe-1b9fe35d111f.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/d0cb02f4-e7db-45b5-86fe-1b9fe35d111f.jpg.html)

This was somewhat off axis. By toeing in / out I could alter the amount of HF energy. This was again at listening position.
Interestingly the bump seems to be all LF, rather than an over active horn. Will have to think about that one. Perhaps it's the room but it was there with the mic at 1m too.

Interestingly the bump 1700 cycles (as the BTH info calls Hz) is not intrusive at all when listening. I tried a wide range of music with lots of energy around that region. There is no notch filter in the X/O. To my mind, passive filters, L-Pads etc are all going to detract from dynamic and freedom of input to the compression driver. Of course if it's too large to live with you have to do something about it. In this case I do not hear that it is a problem.
I should also point out that I don't like DSP correction / filters in compression driver freq range of 330Hz to 15KHz either. Much better to fix by horn, driver and room treatment is possible.

[Ali Tait]

Well they look like they measure better than a lot of wide band drivers, a LOT better than some!

[Magna Audio]

Andy has suggested they may have been designed to run with the HF out of phase with the LF. That might cure the 1700Hz hump. More measuring and I'll report back.

[Marco]

They look absolutely KILLER, Steve - nice work, mate! It'll be interesting to know what Andy thinks, once they've been 'voiced' accurately and he gets them home :)

Marco.

[walpurgis]

Just wondering if the 1.7kHz bump could be a cabinet or horn throat effect that could be damped out. The wavelength of sound if I recall would be around 200mm at 1.7kHz, any opposing cabinet wall faces of that dimension could be the cause. Or could it be a cone reflection/resonance? The radius of the cone would be somewhere near this.

[Magna Audio]

Followed Andy's phasing recommendation and swapped the HF polarity.

The effect is seen below. The blue line is HF phase swapped and red line in phase. 1m off axis.

Blue line is HF swapped. Red line as was.

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/BTH18BlueHFoutofphaseRedinphase1moffaxis.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/BTH18BlueHFoutofphaseRedinphase1moffaxis.jpg.html)

Note that Holmimpulse levels the measurement to the highest point. Still the ~1.6KHz but only by a fraction this time.
This make sense as the crossovers are 2nd order judging by the rolloff and the number of components in them - 2 air cored inductors and 2 caps (2 are paired to get the right capacitance).

I'll swap the other X/O HF over now and have a listen...

There could be some standing waves or other effect there as the region is still up a bit but within +/-5dB.
200mm is pretty small though = nearly 8". The back loaded horn should only see LF so not up around these freqs I would have thought. Its very well damped with felt too and braced so I don't think it is cab resonance, more what was coming off the LF and HF cones.
Who knows though without a lab and lots of time to test.

[walpurgis]

Just a few thoughts crossing my mind looking at these. Is it coincidence that your mid peak (which is now a reduced amplitude bump), is at your crossover point. Looking at your crossover, I'm guessing you have a 12db/oct roll off for the bass and 18db/oct roll in for the HF. Is it possible that the driver outputs overlap enough to cause the bump? Which itself may possibly be near a cone break up peak (it is a big cone).

[Magna Audio]

Here are some more pics

Grilles now fitted

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/IMG_4178.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/IMG_4178.jpg.html)

Crossover boxes with BTH badges that Andy supplied

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/WP_20130918_001.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/WP_20130918_001.jpg.html)

http://i727.photobucket.com/albums/ww272/speedysteve7/hifi/BTH%2018s/WP_20130918_002.jpg (http://s727.photobucket.com/user/speedysteve7/media/hifi/BTH%2018s/WP_20130918_002.jpg.html)

I've listened to them further and like the sound they make.

They are ready for final polish and then Andy can collect or have pro antique furniture movers collect and deliver...

[Magna Audio]

Well Andy arranged a collection / deliver service and Sunday was the day.

The large and heavy cabs were efficiently picked up, wrapped and stowed securely in the van.
Andy has a a steep drive way with a few steps to get them up so strong pro movers was a good call.

I'm sure Andy won't mind if I share his first feedback to me.

"The speakers arrived safely and in the last couple of hours I've played a whole range of music genre's on them. Bass is deep and tuneful with no hint of boom in my room and the soundstage is wide and deep.
I've had to force myself to have a break as they are proving to be quite addictive.
The colour and finish on the cabinets is excellent and matches the room well."

So, that's been a very interesting and satisfying project for me.

[Ali Tait]

Well done Steve, lovely job.

[BTH K10A]

Thought I'd update this thread with a few more pics as I'm still thoroughly enjoying these K10A's. Literally everyone who has heard them comments that they are probably the best speakers they've ever heard. Most of them have led sheltered lives but a few have top quality speakers themselves. I even managed to turn a die hard Quad 57 lover who now begrudgingly admits he prefers them to his Quads:D

These 2 pics are where I lined up all three speaker pairs I currently use for a comparative size shot. Steve's cabinets make the JBL Array 1400's and Westrex 2326A's look tiny, which they certainly are not
http://i46.photobucket.com/albums/f120/emttsd15/IMG_1573_zps539009a1.jpg (http://s46.photobucket.com/user/emttsd15/media/IMG_1573_zps539009a1.jpg.html)
http://i46.photobucket.com/albums/f120/emttsd15/IMG_1577_zps28e5a15a.jpg (http://s46.photobucket.com/user/emttsd15/media/IMG_1577_zps28e5a15a.jpg.html)

This is the Western Electric attempt at a dual concentric driver (very rare) using a 4181a and a 555 (both field coil)
http://i46.photobucket.com/albums/f120/emttsd15/images_zps79013a1e.jpeg (http://s46.photobucket.com/user/emttsd15/media/images_zps79013a1e.jpeg.html)
The K10A for comparison
http://i46.photobucket.com/albums/f120/emttsd15/200906081352474483_zpsb65d8cff.jpg (http://s46.photobucket.com/user/emttsd15/media/200906081352474483_zpsb65d8cff.jpg.html)

Specs on the K10A
http://i46.photobucket.com/albums/f120/emttsd15/bth1_zpsae27024f.jpg (http://s46.photobucket.com/user/emttsd15/media/bth1_zpsae27024f.jpg.html)http://i46.photobucket.com/albums/f120/emttsd15/bth2_zpsb109e998.jpg (http://s46.photobucket.com/user/emttsd15/media/bth2_zpsb109e998.jpg.html)

[walpurgis]

Funny how the chassis/basket looks the same on both the WE and BTH units. OEM?

285,000 Maxwells for the BTH bass side is just greedy! :)

[BTH K10A]

Funny how the chassis/basket looks the same on both the WE and BTH units. OEM?

That's because basically it is, Jensen manufactured 13.5 and 18" bass drivers for a number of other makers in the 1930's such as Capehart, McMurdo, Zenith, E.H. Scott and also provided baskets and cones to Western Electric and IPC who I think made their own field coil units. In Europe BTH manufactured under license from Jensen as did AGA Baltic in Sweden, Goejon in France and Korting (15" version) in Germany.

Accordingly, the BTH and Western Electric cones are interchangeable.

[walpurgis]

Well that explains it (and makes sense). You do know your stuff, you've quoted a few names I don't know and I've been well involved with Hi-Fi since 1970.

[BTH K10A]

285,000 Maxwells for the BTH bass side is just greedy! :)

And supposedly has never been bettered, although I can't vouch for that.

What I can tell you is that you don't want your watch or credit card anywhere near them!

[walpurgis]

And supposedly has never been bettered!

I'm fairly sure some of the Lowther units have been in that territory.

[BTH K10A]

I'm fairly sure some of the Lowther units have been in that territory.

Yes the PM4 probably was

[Barry]

Yes the PM4 probably was

Yes, the magnet of the Lowther PM4 has a total flux density of 385,000 Maxwell. http://theartofsound.net/forum/showthread.php?3829-Manufacturers-Lowther