[scorpion]

With the regard to the success many have had with Eminence Alpha15s as basspeakers in combination with various tops, it would only be fair also to point to another excellent MJK study of H- and U-dipoles of small measures for extremly extended bass respons for little money. The study is here: http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf .

My simulation of two Alphas in a H-dipole with 32" (H) x 16" (W) x 15" (D) excluding 1" thick baffle inner measures shows this picture (LP at 135 Hz L-R 12 dB/oct):



SPL is at 1 m distance 32" high, 1 watt. Could you really do better ? 

/Erling

[Dmason]

"Could you really do better?"

It doesn't get any better..

Kudos... the path is now lit!

[scorpion]

In fact, you can't, as you state Dan ! I ordered 4 Alpha15s !

It is a pity that MJK doesn't contribute here any more. Evidentely he was scared away by aggresive and nasty emails from this circle.
He made some extremly good postings here while contributing.

/Erling

[rajacat]

In fact, you can't, as you state Dan ! I ordered 4 Alpha15s !

It is a pity that MJK doesn't contribute here any more. Evidentely he was scared away by aggresive and nasty emails from this circle.
He made some extremly good postings here while contributing.

/Erling

Erling,

From which distributer did you order your Alpha 15s?

-Roy

[scorpion]

I am in Sweden, Europe.

I got a very decent price from a Swedish distributor: http://www.autemashop.com/category250_1.htm .

/Erling

[rajacat]

Ah....I found a good source. 60 bucks each.
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=290-407

[EProvenzano]

Hi folks!

Pardon my rookie question...
When designing an H baffle do the front extensions need to equal the rear extensions of the H-side frames?
I'm curious because esthetically speaking it would look better if more the the H-frame could hang out the rear...  when does an H-frame start to become a U-baffle? 

I have a B-200 that I want to implement later this summer.  I will surely want to augment the bottom end because I didn't care for the B200 run wide open.

Thanks in advance.

[scorpion]

I got my Alphas. Built quality is very good. Steel frames very solid and probably not prone to resonances.

/Erling

[scorpion]

H-baffle is symmetrical, front and back alike.

EProvenzano, just try. It might be that you have to take down the B200 a bit. If you follow my suggestion with 135 L-R 12 dB/oct low pass you could just fix in B200 at about 260-70 Hz HP.

/Erling

[ttan98]

There is nothing wrong with your simulation, the FR curve looks impressive, what the stimulation does not show is the "speed" of the driver.

I am not sure whether the CSD waterfall  driver testing will give us a better picture.

Anyone here can shed some light in this department.

[Rudolf]

When designing an H baffle do the front extensions need to equal the rear extensions of the H-side frames?
I'm curious because esthetically speaking it would look better if more the the H-frame could hang out the rear...  when does an H-frame start to become a U-baffle?

I believe that there are more than one who don´t realise what happens between a U-frame (driver plane at 0,0 x frame depth) and a H-frame (driver plane at 0,5 x frame depth). It´s not so much about SPL difference - it´s about the polar radiation pattern. Look at this comparison between U-frame, the driver plane one quarter into the frame depth and the H-frame (courtesy of MJK´s H-frame worksheet):







A U-frame (of a given depth) will generally give the highest SPL level, but is a true dipole only at low frequencies.
A H-frame of the same depth does not provide the same SPL level, but is a true dipole across the entire passband.
The quarter depth frame does the complete show: changing from dipole to monopole to cardioid along the frequency range.

So as always: it depends on what you want to achieve and what frequency range you want to talk about.

John K. has explained all the basics here: http://www.musicanddesign.com/u_frame.html

[-Richard-]

Hi Erling/Scorpion ~

I have 3 questions that I would love your feedback on: are you going to incorporate both Alpha S woofers in the same baffle by making an H configuration only where they sit on the baffle... so that the smaller wide range driver does not have "sides" while the 2 woofers below do?

Or are you thinking of separate baffles for them?

OK... one more question... are you planning on hooking them up in parallel... which would drop their impedance to slightly below 4 Ohms and amping them separately from the wide range driver?

1 Alpha sounds quite incredible with the B200's... 2 should flesh out even more lower octave magic!!

Thanks is advance Erling for you help and advice.

Warmest Regards ~ Richard

[scorpion]

Hi Richard,

I'll place the Alphas in a separate H-baffle, two per side, parallel winded. B200s on its own smaller baffle on top. Baffles will be 16" wide.
Graham Maynard evidently used a filler driver with the B200 and that gave me the idea of testing the element from the
'Volks-OB' Monacor SP130X/8 between 200 Hz - 1000-1500 Hz ca to complement and not having to bother about the B200 frequency rise.
But that will just be a test, it may be difficult to integrate the Monacor and the Visaton in a good way even if they tonally are very similar.

This setup will be actively driven and crossed over with separate amps for all elements. I'll come back and report on my doings.

/Erling

[Graham Maynard]

Hi Rudolph,

That's a good set of simulations.

The FullRangeDriver forum is still down, but there I posted this comment:-
I would not want any reflections or tuned lengths closer or shorter than the highest frequency at which any driver is required to operate.

I have not liked the dynamic reproduction characteristics from a U-frame compared to a plain dipole, so no matter how compelling the theoretical studies - I am sticking with a plain dipole having no more than physical side supports.

Of course those U-frames can work excellently, but then a very sharp crossover is required in order to ensure that reflections and tuned responses do not interfere within the working passband;  ie. active, which also means a second amplifier.
Then I do not like reproduction where there are additional phase ripples due to high slope crossovers either, so no matter what the theoretical analyses might inform us about the 'flatness' of any frequency response, I personally still prefer more simple implementations.

Hi Ttan,

The test parameters here are not the same as those shown by manufacturers, and few CSDs/waterfalls show detail for low mid reproduction anyway;-
http://www.prodance.cz/
the Alpha-15A;-
http://www.prodance.cz/protokoly/alpha_15a.pdf

That MJK study for the Alpha-15A on a baffle relates to frequency response only.  This driver has quite a high electrical Q which will allow it to develop its own natural tonality, whereas drivers having a lower Q would be much less able to do so.  Its a toss-up between quality and power requirements for the low Q driver.

It might be that Alpha-15As would suit W frame mounting where the Fs could be lowered and the Q naturally damped.  Two in a W housing could physically double the air displacement whilst being no larger than one in a frame;  quality of reproduction ? anyone tried this before ?

Hi Richard.

I tended not to think of an 8>10" driver as infill between bass and mid/hi, but the 8>10" as augmenting the mid/hi, then the 15" augmenting the 8>10" in the low/mid bass only;  and a B200 most certainly does need some mid frequency augmentation if not driven via a passive series network.

Cheers ......... Graham.

[Rudolf]

MJKs excellent study of OB, H- and U-frames let me look into still another aspect that might be overlooked. If we superimpose the three SPL diagrams on page 2 in that study, we get the lower diagram in this drawing:



For just below 40 Hz all three frames have the same nominal efficiency (1W input for all three). MJKs worksheet provide excursion diagrams for his models. I superimposed those too in the upper diagram. If you compare both diagrams, the U- and H-frame achieve the same SPL level with less excursion than the OB.

Looking at about 33 Hz in the upper diagram, the driver does quite the same excursion in all three frames. But the SPL levels for U- and H-frame are bigger than for the OB. So while efficiency for the U- and H-frame might be slightly down, they generally will reach their excursion limits at higher SPL levels than a plain OB.

Rudolf

[scorpion]

It occurred to me that I already had an U-baffle around with two cheap 12" elements with parameters: fs=28, qts=0.62 and Vas= 112 l. I always played it standing which following the results from MJK's models is wrong, it should have been played laying on the long side. This I did, U-baffle dimensions are 60 cm (l) x 30 cm (h) x 26.5 cm (d), and measured the 1 m  response with no filters applied and mic at 15 cm above floor. U-baffle more than 1 m from any wall.



 

/Erling

[Graham Maynard]

Hi Erling,

Those two U-frames on the floor look good.

Any chance of one stacked vertically on top of the other so that we can compare the gain, and differences in the measured level ?

Cheers ....... Graham.

[scorpion]

It is just one U-frame with two speakers inside. If you use MJK's models you will se that raising U-s is not any good. Quite another thing with H-baffles.
However good these cheap elements measure, they are not anywhere near the bassunits of my 'Volks-OB' in performance. They may go lower but sounds doesn't match. But they are a very good example that MJK's simulations work. You still have to use good units to get good results. And for a last point of view, I think U-baffles may sound a bit 'boxy', so I do think they should crossovered low.

/Erling

[scorpion]

Graham,

I put it up on the small side and measured. It is no great difference. I would have expected more. It does sound guite decent up in the frequencies but a bit closed in upwards and boxy. I suppose that my comment of 'boxy' earlier came from this extended response. However with regard to bass presentation they are not in anyway near the performance of the A&D 1524 units of my 'Volks-Ob' regarding speed, distinction and presentation.



But with small means you can do wonders for budget speakers.

/Erling

[Rudolf]

Erling,
the BR 12 are the drivers from the "venetian blinds", right?

If your last measurement is done at the same 1 m distance as the first (and possibly 15 cm above the floor too?), it can´t tell the truth. With such large geometries you have to measure WAY back (listening position?) to detect differencies in the bass performance with some validity. I have seen that with own measurements before.
IMHO the most notable effect of floor mounted drivers is the absence of a delayed floor reflection. Raising the driver 16" will distort the frequency response much more than it will lower the bass level:



The sim is with the original MJK U-frame worksheet data with the Eminence 15A. I only doubled the heigth of the U-frame (red) and moved the driver 16" up from its bottom position (purple).

This seems in line with your measurements where the most noticeable SPL differencies are in the 300-2kHz region and not below 200 Hz.

Rudolf