How to squeeze a new woofer in an old speaker...

First of all, we need to verify if the chosen woofer fits the volume of the speaker.

So, here is the box itself, in a first slobby stage (two way speaker with a 15" woofer and a 1" driver)

From the bottom, this is the volume where the Dayton woofer was mounted in a first stage. As you can see the 1" driver is mounted inside the volume itself:

 (Pict. 1)

This is the same volume, reduced to 85 lt approx:

                                                            (Pict. 2)













And here is the volume closed also from the bottom, for a reduced volume of 55lt:
(Pict. 3)











This is the inner volume with the speaker mounted.

Now, why all these volumes?
When we apply a given woofer to a given volume in a horn speaker like this, the first thing to look at is the impedance match.

Here you can see the graph of the Dayton woofer mounted in the volume, open (in white, look at the Fs in this position and compare to the free air resonance of the woofer.) and with different blocks of polistyrene to empyrically (or should I say slobby) reduce it and see what happens to the impedance  (red and green traces).
The two added volumes of styrene were not very different one from the other, I don't recall now how much, but the general trend was clear to me. In blue it's the impedance of the driver as in Pict.2, with the volume reduced of 30 litres almost.
I built a board to divide the first 30 litres of the volume from the rest, like in Pict.2, and measured the impedance, then I closed another 30 litres from the bottom end of the volume, like in Pict.3:

In red and green are the impedance plots of the left and right speakers, same as blue above, with the Dayton woofer and upper volume sealed (85lt, Pict.2).
In cyan the volume with two thirds closed (55lt).
For my needs, mission accomplished. The two peaks are now similar and for me this is the best I can do.





No, not really. 
I could linearize the impedance considering a possible use of tube amps, for example...
So here is the impedance plot of the woofer with and without RCL equalization for this use:

But what happens to the frequency response?
This is a too early stage for that, but a quick comparison of the green curve and cyan curve gives this:

Response measured in asnearfieldaspossible, mic on the floor, level arbitrary, in red 85lt (Pict.2, green impedance curve) and in white 55lt (Pict.3, cyan impedance curve). We loose something where really there is nothing going on, at 40Hz, but look how much more regular the graph is above 120 Hz and up, where it really counts. Did I mentioned I want to cut at 300 Hz?...

The road map

I decided to go with a cheaper woofer.
This project is an old one, and using an "old school" woofer seems to me more appropriate.
We can find thousands of reasons for the use of a different woofer, but at the end, read the first line...
So, this is it:

• It will be used only up to 300 Hz, where it will blend with a 10" midwoofer, loaded with a conical horn.
•  Then there will be a 1" driver loaded by a Tractrix horn for the frequencies from approx. 1000-1200 Hz up to the top, or at least where it can go!
•  In a second time, if needed, a supertweeter covering from 10-15kHz will be added.
•  At the beginning this system will be driven in single amplification mode, with a passive crossover, that has to be designed in a way that in a second time it will be possible to bi-amp woofer and mid-tw group. 
•  I will then go with multiamping if simple bi-amping will not give the best results.

Enough meat on this barbecue for now.

A new project! The SquawkerOne.

After the Edgar project (sooner or later I will publish it), a three way closed box inspired by the theories of Edgar Villchur and Roy Cizek, after the Barbieri Homage, a project derived from a bass reflex audio kit published by the Italian magazine Suono and designed by the well appreciated Mr. Gian Piero Matarazzo, named Deymos, and finally after the horn design of the LBH, my mind was elucubrating...no no, sorry, slobby mode on: my mind was mumbling around the possibility to build a transmission line.
Then, being still in love with horns and being in possess of two pieces of art from an artist of the past, I decided to face another three way full horn system.
So this time I will not start from a given design and develop it, instead I will start from a given result of a project, but completely forgot somewhere in the past, and try to complete it with a reverse engineering approach.
First, the bass horns.
These were bought by my brother in the '70s, in a shop near my city.
They were part of a design realised by a real master of wood working, the late Mr. Michelangelo dalla Fontana, an ebanist with the passion for hifi. So much passionate, that if you own an old solid wood model of speaker from the well respected Company Chario, you are probably owning a box made by Mr. dalla Fontana's nephew, Vlady.
Now, I really tried to figure out which design was the base for this cornerhorn. The most similar one I found is a project from Germany, the Eckhorn, but it's not exactly the same:

It seems like a Klipschorn with one folding less, the waves go back and forth three times on the same axis, and because of the shorter path I assumed the lower cut-off could have been around 70 Hz or so.
Well, this is not the case. I have measured this bass in my room, using the very same woofer of the LBHs, and I will post the results.
But, to make long things short, it is necessary to find a suitable woofer.
I have studied a lot of possible candidates, at the end I decided to go for an Italian woofer:

Italians do it better, don't they?...
I opted for the Neodimium version of this beast, although the Ferrite version had a higher EBP, but it's a long time I wanted to try a neo woofer, so here we are. I like especially the lack of peacking on the higher frequencies, that could lead on an easier low pass filtering if I will go passive (in audio it's my preferred option...)
Now, a couple of "before" pics of the woofer's horns...

 Just arrived...

Here you can see how the throat is made. That wood spacer must be taken into account, as it  probably works as a front loading chamber, considering also the volume of air of a 15" cone...

And here you can see that a woofer was already mounted, with some sort of internal volume chamber that was ripped off, maybe to be able to remove the speakers... 
I like this slobby procedure!
Definitely not from Dalla Fontana's work!

La Musica è finita...gli amici se ne vanno...

E' così.
Li fai nascere, li fai crescere, li sviluppi, soffri e patisci con loro, e gioisci anche...fanno parte di te con i loro pregi e difetti.
Poi, un giorno, prendono il volo e non li vedi più.
Le Little Big Horn sono finite a casa di un giovane 17enne appassionato, che le curerà, amerà e farà cantare meglio che mai, il miglior destino che un autocostruttore possa sperare per le sue creature.
Son cose che fanno sperare per il futuro della nostra passione.
Long Live Rock'n'Roll!
Lascerò questo post a disposizione di Giordano, nel caso volesse condividere con me e quindi con voi alcune foto della nuova sistemazione delle Little Big Horn, nonchè della cura estetica che vorrà dare loro, scostandosi, per fortuna, dalla filosofia cialtronica che anima le mie realizzazioni!


The Little Big Horns have left the house.
In the pure Italian spirit, I would have liked to keep them with me forever, like our mothers do with their childs...
But they are now safe and happy, in the loving hands of a 17 years old Hi Fi passionate: what could possibly be a better ending for a DIY's story?
I will leave this post blank, for new pics that I hope Giordano will share with us about the upgradings he will apply to my babies.

What if.... Let's try the current amplification

I was an happy camper with my horns and whistles.
Then I looked at my amplifier: one Quad 303, perfect for the job, a laid back sound that my 50 years old ears appreciate alot.
But I always felt like I need more "control" and "speed" in the lower end.
Money is an issue, amps are heavy money. I thought about some cheap pro amp, so I hooked up one Carver M1.5t I own from the beginning of this passion, to see if it was possible to drive a 105 dB speaker with one 350 W amp.
In my case, it is not.
The volume control knob is working too close to the beginning, where some non linearity is always possible.
Then, surfing around, I bounced on this Pass and Creazzo  papers about current amplification, and so I decided to try this possibility.
First thing to do, make the impedance response of my speakers flat.



I added to the crossover (red trace) an RCL serie in parallel to the midhigh input, as described in another post. This is already a good result if one plans to use this speaker with a tube amplifier (the blu curve). But it's not flat enough for a current drive, so I added an R in parallel to the woofer input (black curve). This is ok for a current drive, a bit too low for conventional amplification!






So what happens to the frequency response?
In red you see the system's frequency response when conventionally amplified with an equalized Quad 303.
In black you see the very same system, but with a Carver amplifier in current thanks to an added R to the output of the amp of 54 Ohms.So both conditions refer to the red impedance curve.

 1. Red - Quad303, Black - Carver M1.5t + R54Ohms

What surprises, even if expected, is to verify that the spl between 100 and 500 Hz of a 28W RMS amp like the Quad is the same of a 350W RMS when driven in current.

What happen if we add the RCL cell like in the blue trace of the impedance plot?
Here it is:

2. Red - Carver + 33R, Black - Carver + 33R + RCL

After adding the 5Ohms R in parallel to the input, like in the black trace of the impedance plot, the impedance went to a flat 3 Ohms +/- 1 Ohm, linear enough for the current amplification. This allowed to use a 33R instead of 54R, respecting the common sense of a 10 times greater R on the output of the amp respect to the impedance of the speaker.
The result is in the following RTA, where in red we have the conventionally driven Quad303, equalized through the AEQ function of my Behringer DEQ2496 (same as the red trace in graph nr.1), while in black you can see the Carver, similarly equalized and driven in current through the 33 Ohms resistor and the flattened impedance curve. Levels are arbitraries.

Red - Quad, Black - Carver

I don't want to describe my sensations, I just want to say that in this way the sound is much cleaner, with a prompt and steady bass, refined highs...Ok, just read the curves, they are saying the same! So, I don't really know how much this is an advantage of the current drive respect to the system's modification, but I could reasonably say that I feel free of some muddiness in the lower end, that I would like to associate to the back EMF issue (or its lack) but I am not even sure if this system (which is not, we must remember, a from-birth current drive system) is solving this matter properly... Anyway, when the ears tell you "now it's better than before", we can go to sleep thinking "mission accomplished", and that's what I'm going to do right now.
No, not really, there is one, big, issue in this work: the SPL is much lower than before, too low for a real slobber. I need more juice, because right now the volume knob of the preamp is going to almost the end, and the Carver's LEDs tell that 350W are thrown in the 105 dB speakers, and I need more: the level with the Quad was higher.
So, what to do? Difficult to come back, once tried. A 700 W amp instead of the Carver? It's only a 3 dB difference, should this be enough? Again I'm thinking to bi-amping...let's see what the future will bring.
Suggestions are welcome, as usual!

Aggiornamento

Some little frills, after all it's springtime.
I tried soft sanded glass covers, instead of plan plywood.
Nicer, both on the bottom (first pic) or on the top of the mid horn.
When on top, it allows to place the tweeter on the same line of the mid mouth. 
This affects a lot the phase emission and coherence between mid and tw, considering we have a passive filter not compensating for this. I have tried to listen carefully to the difference between the tweeter on axis from mouth or throat point of view, but with no final results.
Next step will be a 2 way amplification, one for the woofer with adequate delay (anticipation in this case) and one for the mid-high, with the tweeter again in its pristine position, like in the first picture.
Alcune piccole modifiche, sia dal punto di vista estetico che di fine tuning.
Cominciamo con il look:

Ho aggiunto un piano in vetro acidato, "per vedere di nascosto l'effetto che fa". (Grande Jannacci, R.I.P.).

Al solito per mantenere il trend cialtrone la foto è una pessima immagine presa col telefonino.

In un primo momento ho posizionato il vetro inferiormente, come piano d'appoggio per la tromba:

Poi ho provato invece a posizionare il vetro al di sopra, in modo da creare un piano sul quale fosse possibile avanzare il tweeter a filo con il medio, considerando le rispettive bocche:

A me piace di più così.
Certo si crea un problema nient'affatto secondario, ovvero, dato che il sistema è filtrato tutto passivamente, al ritardo di emissione del woofer sul medio-alto si aggiunge anche il ritardo del tw sul medio.
La soluzione che adotterò sarà una biamplificazione tra woofer e medioalto, con regolazione del ritardo e taglio passivo con arretramento del tw in modo che l'emissione alla gola del driver del tweeter e del cono del mid sia sullo stesso piano. Dovrò valutare se e quanto la superfice piana del vetro influisce sull'emissione.
Comunque, nell'attesa di verificare quanto questi sfasamenti di emissione possano nuocere all'ascolto (vi confesso che le prove fatte sulle due posizioni del tw rispetto al medio non ha dato esito) vi pubblico il grafico della risposta attuale con l'aggiunta dei sub woofer (curva verde).
Il basso è prominente, come piace a me, mentre la curva cala secondo Moeller, anche se dal grafico della risposta L+R in mono sembrerebbe molto di più, ma è la rilevazione che è fasulla in alto, basta vedere la risposta del singolo canale (in giallo nel primo grafico) rispetto alla somma dei due più sub (ciano e RTA)
Dovreste vedere le facce di coloro che vengono a sentire il risultato finale...
And here again the actual response of the system, with two subs in mono and equalisation from the DEQ2496 only above 125 Hz, as you can see from red and yellow curves on the first graph. This kind of measure is not trustable above a certain frequency, I would say around 5kHz, because it is made with the two speakers in mono feeded with the same signal. So, the cyan curve as well as the RTA ones are good only to "roughometrically" evaluate the integration between subs and system.

Rosso L no eq, Giallo L eq, Ciano L+R+sub

Rosso - L+R , Verde - L+R+sub

Time for Fine Tuning

Fine, and horns, usually don't play in the same field.
I ended up to the conclusion that this is only a matter of bad designs.
This system however showed immediately its propension to a good sound, not only loud.
But a sort of harshiness was always sneaking out from female vocals, I dominated it with the use of an equalizer, but the request for this system to integrate flawlessly in one home environment, drove me to the conclusion that I had to tune the filter to the speakers in a more professional way than a slob would...
So, here we start:
Fine e trombe, per i detrattori del sistema, non dovrebbero andare d'accordo.
Io sono arrivato alla conclusione che questo succede solo quando le medesime seguono un cattivo progetto.
Ad esempio, mi sembrava di sentire una certa durezza sulle voci femminili, per cui ho deciso di non fare il pigrone e modificare leggermente il filtro per integrare il tweeter, che non è quello di progetto, meglio di quanto fatto.

 In red is the frequency response of the LBH (Little Big Horn) from the listening position, before any cure. In yellow is the response of the room, 366ms after the impulse is generated. With this graph it is possible to "see through" the room's modes and interference: for example, in my case, it is useless trying to equalize the 60Hz and 40 Hz bumps.
The harshiness my golden ears felt could have been generated by that hill around 3 kHz. 
The original mid band-pass filter designed by Mr. Calabrese is very smart: considering the mid horn has to blend with the tweeter at a frequency not lower than 3 kHz, he made the filter resonant, more than a typical Cebishev, so to "pump up" the response up to the 3 kHz required to cross with the tweeter. With the Crites' tweeters this seems to be too much, so I changed the L value on the low pass filter of the midrange, from 0,4 to 0,67mH, the result is seen in green. Much better indeed.
Ho deciso di piallare quella gobba sui 3.000 Hz (in rosso), dovuta ad una mia errata applicazione del filtro progettato sul kit originale da Calabrese, un filtro, mi ripeto, geniale nella sua linearità, (basti pensare che non è presente nemmeno un'attenuazione) e con un accorgimento a livello del Passa - Basso del mid reso risonante per portarne la risposta fino ai 3.000 hz di progetto per l'incrocio col tweeter. Onore a chi sa come si progetta!
Avendo cambiato tweeter, il problema non si pone più. Ma se il T35 Electro Voice si inseriva come un guanto su quel filtro, questo Crites scende di più, perciò la risonanza va ricondotta a più miti consigli. E' bastato sostituire la bobina del filtro originario da 0,4 mH con una da 0,67 per ottenere la risposta in verde.

Now, that awful peak at 500 Hz. I wasn't able to get rid of it. It is present on both speakers, in any position of the mic, but not in the close field. Any clue? Please suggest.
From a listening point of view, much worse seemed that big deep just before the peak, the two together are a mess. So, after trying with notches, phase inversions, etc., I ended up with this: I changed the 3mH inductance in the high-pass of the midrange with an 8mH, that brings together a 1 Ohm Resistance. The result you can see hereunder, red and blue for the two channels:
Ora restava da occuparsi di quella punta a 500 Hz. Essendo presente sia sul sinistro che sul destro, anche a rilevazioni a diverse distanze, ma non in campo vicino, ne ho dedotto che di sicuro non posso pensare di intervenire con l'equalizzazione a posteriori, per cui mi sono concentrato nel cercare di colmare quel gap che si vede tra 250 e 500, cosa che ho fatto cambiando la bobina del Passa - Alto del mid da 3mH con una da 8mH, che porta con sè anche una resistenza di 1 Ohm...
Ecco il risultato, dal punto di ascolto per i due canali:

In the meanwhile, this is the final result on the impedance graphic, much interesting in my opinion, because you can see that now the lowest frequency is no more 2.8 Ohms (because of that resonant filter), but a much more relaxing 3.5 Ohms, and the impedance in the lower portion is around a 10 Ohms, almost resistive...
E qui si vede un effetto secondario molto piacevole delle due modifiche, si può confrontare il modulo d'impedenza con quello nel post nr.2, ossia l'innalzamento del minimo d'impedenza a 3,5 Ohm anzichè 2,8, e il carico che non scende sotto i 10 Ohm praticamente da  70 a 700 Hz, per la gioia del mio Quad 303. Anche la fase è un po' meno reattiva, meglio così.





With an RCL on the input of the filter, we can easily adjust this speaker to be perfect for a tube amp, so here it is:

In red before the cure, in green after. This speaker is calling for a biamp, a good 40 W SS or more on the bass, and a refined tube SE on the midhighs, don't you think?
Nel caso qualcuno volesse rendere il modulo più adatto all'uso con un ampli valvolare "lesso", è possibile applicare una celletta RCL serie in parallelo all'ingresso del filtro, per il risultato qui in verde. non ho finalizzato la cosa perchè non ho un ampli valvolare o a transconduttanza tipo i First Watt, per cui sto bene così, ma se passerò alla biamplificazione riprenderò il discorso.