SEAS P11RCY/P, suggestions?

[Elbert]

Hi!

Just bought a pair of second hand SEAS P11RCY/P mini-woofers for cheap, thinking they would make for a nice little winter project.

Haven't found much reference to any designs with these babies or any of the other similar SEAS mini-woofers, so if anybody has some ideas on how to get the most out of these, any thoughts or suggestions would be welcome!

[alan-1-b]

There was a small loudspeaker sold with either or all:-
Tandy
Radio Shack
Optimus
Realistic
brand name(s) on it a few years ago.
It had an excellent dipole tweeter and a very mediocre woofer.
I remember thinking then that one of the SEAS P11 series mid-woofers could work well as a substitute woofer in the Radio Shack enclosure.

There is a page on a web-site somewhere, written by some-one who modified his pair of these dipole tweeter equipted loudspeakers for better performance.
Problem is, I cannot now remember where that web-site is, BUT if you do a Search for Radio Shack Dipole Tweeter you could find it.

I think the loudspeaker was named "Linaeum" or similar, and its Model Number was LX5 or LX-5.

There will be a few pairs of the loudspeaker for sale somewhere, and if reasonabale price, then buy a pair and put in your SEAS woofer, and change the crossover in the way the DIY page showed for better performance from the tweeter.

If I remember any more about it I will Post here,
but, is this of any interest to you ?

[Elbert]

Thanks for the reply Alan!

Probably not a route I'll go down as I assume I will bea able to build some enclosures of better than "radio-shack quality", and by the time I get such a pair of boxes to Norway it will probably be a bit costly diue to shipping and everything.

But by all means, if you have something more, it might well be useful in terms of ideas or concepts that can be adapted!

[alan-1-b]

Well, SEAS tweeter HO737-08 19TFF 1 looks a good design,
and is apparently used by a couple of the British manufacturers of LS3/5A type mini-monitors, thus should work well with your P11.

The original specifications for the P11 are on SEAS web-site in their Vintage Drivers section, thus you can calculate cabinet dimensions for it, and see its Sensitivity to compare to the tweeter which will need an L-pad to match it to the woofer.

That woofer will work well to an upper midrange frequency, thus a simple crossover to the tweeter will be possible.
Look at the 30 degrees off-axis plot for the P11 to see a suitable crossover region.

************************************************** ***********

It has come into my mind now that the Radio Shack loudspeaker may have used a 14mm woofer, not 11mm.
I have forgotten exactly what I was thinking of using an 11mm SEAS for, and I didn't follow-up on the Radio Shack project.
I think there was cabinet modifications in the DIY article for it.

Is there no Tandy or Radio Shack stores nor any company licensed to sell those products in Norway ?

[Elbert]

Nope, no such stores in Norway!

Yes, I have the data-sheet off the SEAS web site, and have been playing around with some box simulations.

Obviously, these woofers are intended for vented enclosures, putting them in a sealed box will just not work, except for using them as midranges.

Still, using "conventional" vented alignements like quasi butterworth, super boom-box etc, the enclosures end up very small and the ports ridiculously long.

With -3dB bass shelf alignment, things become a bit more manageable, but this alignment has penalties in terms of a "weird" response shape and much higher group delay..

I actually got a pair of 27TDC/G tweeters in the deal as well (10£ each!) and they should be more than good enough. Having said that, perhaps a pair of small neo-tweeters might be a good idea in terms of allowing closer driver spacing?

[alan-1-b]

27TDC/G ?

On seas.no I see only 27TDC -{H1149-06},
and 27TBC/G -{H1147-06},
and no TDC/G - not even in the Vintage ...
so which is your tweeter ?

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For the P11RCY/P , all ported options are tuned too high in frequency for bass of realistic Hi-Fidelity transient response.
I would use this driver only as a midrange, if I was making a Hi-Fi loudspeaker.
Its 86dB Sensitivity will have between +1dB <--> +2dB added by the resonant passive bandpass filter used for midrange crossover.
I would use a 2nd Order Hi-pass filter somewhere between 450Hz <--> 500Hz to sum with the driver's roll-off in a sealed enclosure to give likely a 4th Order total low frequency roll-off,
and a 2nd order Lo-pass filter at 4.5kHz to sum with the driver's natural roll-off to likely a total of 3rd order treble roll-off.
The parallel connected capacitor in the lo-pass filter could be chosen to resonate with the driver's voice-coil inductance to fill in that small dip at 3.5kHz.
As the driver has 8ohm flat impedance in its low-midrange there is plenty of scope to apply a parallel connected resistor to the driver to assist with impedance matching of the passive crossover.

I would use a 10" SEAS woofer.

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Is there another brand-name drivers' manufacturer in Norway ?

[Elbert]

Bah, my stupid!

The tweeter is of course the 27TBC/G!

Well, as I already have a "full-size" speaker project ongoing, I don't think I'll be using the P11RCY/P as a midrange. SEAS has a midrange version of this driver which would probably have been a better choice anyway in a 3-way..

No, if anything, this is going to be a mini-monitor project.

I realize these drivers will never be able to reproduce any deep bass, but it would be fun to see what a pair of small hi-fi monitors could do!

I found this articel by Troels gravesen rather inspiring: http://www.troelsgravesen.dk/W11XT.htm
Wonder if it would be possible to acheive something similar with the more modest P11RCY/P's?

[alan-1-b]

Hi Elbert,

The tweeter looks to be fine to work with the P11 because it has a roll-off of the final audible octave of treble, thus with the bass roll-off of the P11 considered, you will have similar audio character at both frequency extremes if you reduce the tweeter output with a suitable L-pad.

A 92dB Sensitivity tweeter could be considered a bit wasted with an 86dB bass-mid driver, and if you think so then perhaps use the tweeter with the "full-size" speaker project you have ongoing ... what tweeter is with that currently ?

I read the Troels Gr. article.
If you are going to go to the trouble of making an enclosure with a shelf port in its base -{and that can be got to work well - often better than a cylindrical-port}- then consider making a taller cabinet and making it a quarter-wave tuned pipe, because then you can get a more solid bass performance down to the P11's Fs - around 60Hz - with a bit more true-to-life sound than a ported enclosure can deliver.
Research the "Bailey" enclosure - it is basically a three folds' tapered line of quarter-wave length.
There is a diagram of it in Vance Dickason's "Loudspeaker Design Cookbook" -{at least in the 6th and 7th Editions}.
There are pictures on a few web-sites, but I have forgotten where ...

A similar pipe could be folded instead of the shelf in Troels Gr's enclosure.

What do you prefer to try to achieve ?

[Elbert]

Yes, I do agree that the tweeter is perhaps a bit overkill, it is allso physically large compared to the woofer.

For my "proper" project, I have a pair of those SEAS DXT waveguide tweeters for which i have great expectations.

In stead of using the 27TBC/G's, Im tempted to use a pair of small NEO tweeters in order to move the acoustic axiis of the tweeter and woofer closer for better coherence, a bonus these small woofers shoudl lend themselves well to.

I have a pair of Small VIFA DQ25SC16 tweeters (good review by ZAPH) Which I think could be an interresting match.

A transmission line is very interesting in deed provided it doesn't grow to large.

Since these woofers are small, I'd like to use them for building quite small speakers, otherwise I could just have gone for larger woofers and bigger boxes in the first place!

it strikes me though.. Looking at some of the calculated port lenghts (some of which were long), where would the divide between a 1/4 wave TL and a vented box be??

Mmm

[Elbert]

Seems a transmission line could be a very interresting option in deed..

Just fired up hornresponse and ran some quick and dirty TL sims.. and yup, seems like it is possible to get rather decent response down to 60Hz with a relatively compact line!

I'll post some results once I've done some iterations.