OK time for some crossover suggestions

[Wardsweb]

In anticipation of the arrival of my new project speakers, I need some crossover help. Given Widgets boxes:

How about Altec 416-8C LF drivers, 511B horns with 802-8G HF drivers and a pair of JBL 077 UHF drivers?

Any pros or cons for going with a JBL 2220 in place of the Altec 416-8C?

Any suggestions on crossover freqs, parts or considerations?

[Earl K]

Hi

Sounds like a fun project !

Any pros or cons for going with a JBL 2220 in place of the Altec 416-8C?

- Personally ( choosing between only those two contenders ) , I'd stick with the 416-8C . Though the cone weights between the two are similar, the Altec has a lower Fs ( higher compliance surround / therefore a lower free-air resonance ) along with a bit more Xmax . The Altec ( I think ) also uses an underhung voicecoil which overall ought to offer a bit better resolution than a 2220 .

- But really my parts recommendation is to add your name onto the wish-list to purchase a pair of JBL 1500Fe woofers ( or even the ME150HS ) . I own ME150H woofs and as a result, my 416-8C(s) are retired . The prices that Harman is asking for these SOTA components represents a great buy to the DIYer . ( While you're at it ), order a pair of the 435AL drivers and then modify those 511b(s) to a 511e(s) . This will give you "THE" JBL system around your parts . IMO: these larger diaphragmed compression drivers are worth the extra cost for the extra resolution they offer. Also consider buying a pair of GPAs' 288-8K clones . I have 288-8K(s) and have yet to hear a better driver ( of that diaphragm size ) .

- Here are some prices, along with a 4338 pic, as well as its' crossover schematic should you descide to buy some of these JBL parts .

[Wardsweb]

The choices of drivers I gave were things I have here and could easily use for this project. So to start I will use the Altec. Do you think the 4338 crossovers will work well enough with these drivers?

LF crossover part # 353151-002
HF/UHF crossover part # 353151-001

Any other suggestions/comments?

[Robh3606]

Hello Wardsweb

I would stick to an Altec crossover to start. I wouldn't drop in one of these JBL ones because at the very least the horns do not load the same. You have a radial horn with the 511B, who knows what exactly the horn in the 4338 is. Those crossovers are designed to work with a specific driver set and driver layout. Take a look at the HF section and you have one of the notch filters there to tailor the response to match the horn and smooth the response. The chances of it working correctly on the 511 are slim at best. Then you have to worry about crossover points, slopes and attenuation. To many things to get wrong right off the bat.

Rob

[Earl K]

Do you think the 4338 crossovers will work well enough with these drivers?

- No, I strongly doubt it. The passives' values are tailored to drivers that have quite different response characteristics compared to the mentioned Altecs . The LCR filter included in the horns' bandpass would be very inappropriate to just arbitrarily place onto Altec gear .

- Off the top of my head, I'd start with Giskards' modified N333 for use as a basic template. He created this quite some time back . His circuit is located here! The bandpass portion ( & maybe the UHF ) will need a bit of reworking to freeup a couple of extra db to better match the efficiency of the Altec 416-8C. The circuit as it stands , is balanced for the lower output of the 2231 woofer . You'll need someone with a SPice network-simulation package to really help you out / & that leaves me out .

- A couple of notes ;
(i) Typically, Altecs' heaviest 1" drivers did not have as much lower midrange strength ( raw output ) as their JBL counter-parts ( ie; the 2420/1/5/6/7 ). IME, these Altecs are closer in sonic performance to the 2410/175 family . This means a bit less lower midrange carving/contouring when designing a passive crossover . This will effect the final values chosen in any JBL crossover adapted for use with Altec components .

(ii) N333 ; Bandpass Changes ( To use the 802-8G or 902-8B with this circuit ) :

- I'd swapout that 16 ohm variable Lpad for an 8 ohm type . I'd also omit the 20 ohm conjugate that is right next to the driver ( since I don't like it's sonic effect on Altec drivers ) . Of course doing this means that all the preceeding values' are now out of whack.
- What do do ? I'd start by reworking the values for the .27mH coil and the 1.5uf cap. These values "see" an approx. 11 ohm load . With that info you can figure out what their Fc points actually are / and then create new ( equivalent values ) for an @ 8 ohm load .
- Next ? Well, further back towards the source ( the amplifier ),the "fixed" Lpad ( comprising the 4 ohm & 20 ohm resistors ) are now able to be reworked to accomplish both ; less bandpass attenuation - as well as maintaining a 12 ohm load for the preceeding passives . ( This "load-maintenance" might equate to simply omitting the 20 ohm parallel resistor or substantially increasing it's value while lowering the value of the 4 ohm ( inline ) to around 3 ohms .

Equation #1; Fc ( for the cap, in Hertz ) = 159155 / ( cap value in uf * AC impedance )
Equation #2; Fc ( for the coil, in Hertz ) = ( 159.155 * AC impedance ) / coil value in mH

Fc for the cap appears to be set at 9650 hz. ( for a 11 ohm speaker load )
Fc for the coil appears to be set at 6500 hz. ( for a 11 ohm speaker load )

- These (2) Fc points might seem like a reasonable starting point for the 511 horn but ( IMO ) they will likely need some tweaking . I assume they are very likely placed a bit close to each other to inititate a little HF boost ( ringing ) for use by the 2308 lense ( the dcr of the coil will control the "Q" of the peak ) . Therefore; a bit of "pole spreading" should be implemented to create more of a standard Butterworth ( or perhaps even Bessel ) transform . A Butterworth transform would equate to a 1 octave spread between the Fc(s) of the coil and the capacitor ( so, a ButterWorth example is; 5500 hz & 11000 hz. These equate to new passive values of .23mH and 1.8uf / respectively ). BTW: these new values would be appropriate if a person is looking for an F3 point around about 8000hz ( assuming the 511/802 combo is ruler flat within that region ) . BTW; The Bessel transform has a pole spread of 1.5 octaves between the reactive elements .

- As I mentioned, someone with a Spice simulation package can greatly help you out here .

[Wardsweb]

Great info guys - Thanks - I applaud you for your knowlege and willingness to help.

[Earl K]

Wardsweb :

As Robh pointed out ;

- Perhaps its simpler to start with either a N501-8a or N801-8a crossover as a template design .
- I'd try the lower crossover point first .
- The advantage here is that more of the elements are known and applicable to your Altec components
( assuming you can get someone to tell you the LC values for either of these two crossovers ) .
- I'd build from scratch since I don't trust any of the older elements included in these crossovers .

- Then you will need to ;

(A) Add only a JBL UHF circuit ( the UHF in the N333 modified by Giskard is where I would start ).

(B) Turn the horns' "HighPass Circuit" into a "Bandpass Circuit" . Here;

- I'd add a fixed resistive Lpad ( around a 3 db drop ) between the circuits' high pass & low pass elements. The additional series resistance partially breaks up interaction between these two reactive areas. R1 & R2 would be 2.336 ohms & 19.39 ohms with R1 being the series buildout resistor and R2 the parallel resistor. 2.4 & 20 ohm resistors should be just fine as substitute values .

- The added lowpass portion within this newly created bandpass circuit should be modelled along the lines that I've mentioned above . Place the 2 passive elements right after the new fixed Lpad but before the 8 ohm variable Lpad ( assuming it's located in the circuit right before the compression driver ) .

[Wardsweb]

I have these N-801 that are in the A7's now.



and this 3106 I built



So can I just run the output of the 801 HF into the 3106 and use the 3106 for the 802 and 077 ?

[Earl K]

Hi

So can I just run the output of the 801 HF into the 3106 and use the 3106 for the 802 and 077 ?

- You could, though this is more of kludged-togther solution than I'd like to see . ( I'd also like to see a schematic of the Altec network before commenting much more. ) I also wonder about how the 802-8G will respond to the chosen lowpass point of the 3106 . Hopefully you'll measure the final response of this setup .

- Using these two crossovers together means I would bypass ( or maybe reuse & move to the 3106 ) the Variable 8 ohm Lpad found in the N801s' HF output section. I would then (re)install an 8 ohm variable Lpad in the new location I've shown in the graphic .

- That 20 ohm conjugate resistor on the horn section ( in the modified 3106) should be considered optional . The value might need to change ( upwards in my experience with Altec 288-8Ks ). My personal sonic preference is not to have any load resistor in that position when using Altec compression drivers .
OTOH ; I find these resistors quite useful when listening to JBL compression drivers .

- With this setup, you're on your own to find the best individual polarities / to accomplish the best phase transitions for your chosen drivers and network(s) .



regards

[Wardsweb]

Thanks for the schematic. This is the kind of thing I need to see to understand the circuit, what's doing what and where I can change stuff. I think I will start with the stock 801 crossover with the addition of the UHF section of the 3106 on a breadboard, so I can tweak at will. Once it's finalized, I can build a permanent version.

[Earl K]

Thanks for the schematic.

- You're welcome !

- I forgot to mention in the above post ; If the hipass section of the Altec crossover has any padding ( apart from the variable Lpad / even a conjuagte resistor across the line after the LC elements ) then you should remove it .
Or else you'll double-pad the HF signal with the addition of the 3106 .
- This is why you should map out on paper the entire N801 topolgy. Create its' schematic before doing too much more .

[Wardsweb]

Hi

- You could, though this is more of kludged-togther solution than I'd like to see . ( I'd also like to see a schematic of the Altec network before commenting much more. ) I also wonder about how the 802-8G will respond to the chosen lowpass point of the 3106 . Hopefully you'll measure the final response of this setup .

- Using these two crossovers together means I would bypass ( or maybe reuse & move to the 3106 ) the Variable 8 ohm Lpad found in the N801s' HF output section. I would then (re)install an 8 ohm variable Lpad in the new location I've shown in the graphic .

- That 20 ohm conjugate resistor on the horn section ( in the modified 3106) should be considered optional . The value might need to change ( upwards in my experience with Altec 288-8Ks ). My personal sonic preference is not to have any load resistor in that position when using Altec compression drivers .
OTOH ; I find these resistors quite useful when listening to JBL compression drivers .

- With this setup, you're on your own to find the best individual polarities / to accomplish the best phase transitions for your chosen drivers and network(s) .

regards

In this modded 3106 schematic, what is the crossover freq for the 077?

[Earl K]

In this modded 3106 schematic, what is the crossover freq for the 077?

- I'm not positive, but it's high / electrically, it's something like 8500 hz.
- Here are Giskards' voltage drives for both the 3105 and the 3106.
- From those you can see the "electrical crossover points" for F3.
- What you'll get for an acoustical "F3" is undetermined.
- Your application may require tinkering with the values found in the horns lowpass section . ( ie ; if that 802/511 combo refuses to rolloff its HF when you want it to . )
- Here's Todds' "I think we have a keeper" thread .

[Earl K]

up >>>>

[Woofer]

... or maybe you could try bi-amping.
there's some truly marvelous Active X-overs out there these days.
Especially stuff like the DBX DriveRack stuff. eg: http://www.dbxpro.com/ with just about ANY parameter being adjustable.
or alternatively look for something like an old Crown/Amcron VFX-2 with variable x-over points. (wouldn't get rid of mine for anything.....)

Cheers.