SEAS A26 Speaker Kit

HiFiHarry

Member
2013-02-03 1:50 am
Is there anyone out there who has actually built a pair of cabinets to house the Seas A26 kit sold by Madisond Sound?

There are two drawings on the Madisond web site, and they give different dimensions. I would like to be certain before I cut wood. I know that I shouldn't cut the baffle/motor board before I have the actual drivers in hand, but even so, there should be some consistent plans.

Thanks in advance for your help!
 
This is quite an amazing speaker, IMO. In the tradition of the Wharfedale Melton and the DeVore Oragutan. Easy to listen to in a good room. :cool:

No, I haven't built one, but the design is flexible at 28 litres. You just need to keep the front layout and dimensions similar. Simple strong box required with aperiodic vent on front or back.

[IMGDEAD]http://imageshack.us/a/img706/7533/seasa26.jpg[/IMGDEAD]

The Madisound Speaker Store

A simple 3.3uF and 10 ohm resistor on the tweeter is all that is required. I'd guess the tweeter is offset at 1:1.618 Golden ratio. Valve amps will love it. :)
 
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Hi,
I am also planning to build a pair of speakers based on the Seas A26 kit. It will also be my first DIY project. I was looking at the Zaph SR71 first but I am looking for that vintage sound. I usually like closed enclosures and bass reflex so the Dynaco A25 reissue aperiodic design might be a good compromise.

Though, I find the T35 tweeter that Seas recommends in their factory kit is really expensive.
I was considering switching it for the 27TDFNC (somehow similar to the TDFC). This one has the advantage of being quite linear and much more affordable. Moreover, it has a grid to protect the dome against curious small fingers (as did the original A25 BTW).
The specs say: recommended frequency range 2500-30000Hz, but I wonder if it could match the A26RE4 below 2.5kHz -- while the T35 goes theoretically easily down to 1.5kHz.
I am planning to use the 3.3uF cap in series with an L-pad to adjust the tweeter level.
I have seen A25-replica designs based on the A26RE4 using the Millenium tweeter, the 29TFF/W (2200-25000Hz) or even the TDFC (2500$ the pair for these latter on Annandale!)
My question is then: Does the T35 worth the investment over the more affordable 27TDFNC, considering it is such an old school speaker? And would I need to change the crossover?
Thanks for your replies
 
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I thought Madisound were doing quite a keen price on the drive units bought together! :)

Firstly, this SEAS project is quite an old school idea, but it's not low tech AT ALL. To get big woofers like 8" and 10" working well needs a very special 1.5" tweeter and some tidy natural rolloff in the cone. The problem is the time-alignment distance with the deep bass unit, which drives you to shallow slopes and low crossover for a good result.

They really don't make 'em any more, since the whole two-way market has moved to the easier 6" bass, 1" tweeter idea. Morel make some very good polycones around 6" and less which need no more than a bafflestep coil, but these are best crossed as low as you can.

You always work at crossing over at the mean between the bass cone breakup and the Fs resonance of the tweeter assuming both are reasonably well-behaved. This space gets tight with big cones, but you get the nice bass and solid delivery. It's a pleasant sound and works particularly well with valve amps. :)

What I'm saying, is you are going to struggle with lesser tweeters. A 6"/180mm project like the SEAS Mimir or SEAS Idunn is going to roll in more affordable and better balanced than a modification.
 

prairieboy

Member
Paid Member
2010-11-22 2:31 am
Hi,
I am also planning to build a pair of speakers based on the Seas A26 kit. It will also be my first DIY project. I was looking at the Zaph SR71 first but I am looking for that vintage sound. I usually like closed enclosures and bass reflex so the Dynaco A25 reissue aperiodic design might be a good compromise.

Though, I find the T35 tweeter that Seas recommends in their factory kit is really expensive.
I was considering switching it for the 27TDFNC (somehow similar to the TDFC). This one has the advantage of being quite linear and much more affordable. Moreover, it has a grid to protect the dome against curious small fingers (as did the original A25 BTW).
The specs say: recommended frequency range 2500-30000Hz, but I wonder if it could match the A26RE4 below 2.5kHz -- while the T35 goes theoretically easily down to 1.5kHz.
I am planning to use the 3.3uF cap in series with an L-pad to adjust the tweeter level.
I have seen A25-replica designs based on the A26RE4 using the Millenium tweeter, the 29TFF/W (2200-25000Hz) or even the TDFC (2500$ the pair for these latter on Annandale!)
My question is then: Does the T35 worth the investment over the more affordable 27TDFNC, considering it is such an old school speaker? And would I need to change the crossover?
Thanks for your replies

You mention seeing the A25 replica designs, which are probably the ones from World Hi-Fi. Their designs use either the T29CF001 or the 29TFF and seem well thought out and developed. It might be worthwhile to check out their designs as they had two alternate cabinet designs (one a floor stander), and crossovers for both tweeters
 
Well, I am located in France so I cannot benefit of Madisound rebates.
I just ordered two A26re4 and two 27TDFC. These are 300$ less than a pair of T35. I'll give a first try with these tweeters, if they really do not do the job I can still mount two T35 afterwards instead. For the crossover I just ordered the 3.3uF cap, it will be mounted in series, as Seas recommends to filter the T35 tweeter at 2kHz. To me it makes no sense to have a 200$ 94dB/W tweeter like the T35 if it attenuated with a 10Ohm resistor. The sensitivity of the TDFC is still a little bit better than the A26re4, I ordered a few pairs of resistors and give a try using different values. The enclosure will be made out of birch multiply, with lamb wool damping.
 
I thought this was all FEROCIOUSLY difficult, EaZy, but actually, if you understand the basic problem, it is doable. :)

[IMGDEAD]http://imageshack.us/a/img706/7533/seasa26.jpg[/IMGDEAD]

That outside offset to the tweeter is doing a goodish job of time aligning the tweeter. Effectively it sets the tweeter back relative to the woofer. By my estimate, we need a steepish tweeter crossover that has a -9dB point at 3kHz if SEAS's frequency response is to be trusted:
SEAS A26RE4X.

By my estimate you need to set the tweeter back about 3cms. relative to the woofer, and then phase is really rather good. A 3kHz crossover like below really doesn't put too many demands on the tweeter or impedance. You can ignore the woofer filter, that is just my approximation to the frequency curve.

You can do such an offset with a sideways offset approach as in the original kit, or something like this:

[IMGDEAD]http://img9.imageshack.us/img9/3451/michelinokefb200vifaxt1.jpg[/IMGDEAD]

But trust me, time alignment and phase is the issue to getting this combination working well. It may be you do well to attach the front baffle with battens, mount the woofer up top, and have a separate tweeter enclosure on top. :cool:

http://www.diyaudio.com/forums/multi-way/223174-interesting-read-i-found-lossy-cabinet-designs-harbeth.html#post3234256
 

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Madisound confused me as it displays T35C-002 as SEAS Exotic & Excel. Anyway, I believe A26 will be a fantastic project.

For SR71 (half the price and cabinet size):
I have built one last year, all drivers were newly made in 2012. It might be an old project, the design and sound quality is superb!
 
Some of my DIY friends would like also build A26 this year, and your experience will serve as a valuable reference for them.
I have not decided yet. But if I do go for them...I'll go for an open baffle. See picture I got off youtube.

I'll get the "official" tweeter though...since it was built to go as low as 1.8kHz.
 

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DavidLS

Member
2007-03-22 4:17 am
the kit speaker looks like an interesting project to me. Don't think it says but imagine this would be relatively high efficiency for a stand mount with minimal crossover and what seems like efficient drivers - so a good match up for tube amps in a smaller room. Look forward to reading about someone building these...
 
Hi all!

Very interesting speaker. Heaven't build it, unfortunately it's simply too large for my very small listening room. But there is one thing with this speaker that puzzles me...
If you have a look at the attached picture of the crossover and the frequency response for different series resistor values, you'll see that the crossover frequency doesn't change very much with these different series resistor values. Now, from what I've learned, the value of a series capacitor depends on both, the desired crossover point AND the resistance after the cap. In this case the cap is always the same 3,3uF, but the series resistor and the tweeter (6 Ohm nominal) make completely different resistor values, from 12,8 ohm (with the 6,8R) up to 21,0 ohm (with the 15R). So, the 3,3uF cap "sees" resistor values from 12,8 to 21 ohms without any obvious changes in the crossover frequency.
How is that possible?

Thanks a lot!
Martin
 

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