Homebrew 4343

[Ian Mackenzie]

Bill,

If what you say in your last post is in fact the case you have (been supplied ) the wrong part. ie If you asked for a pot that is what they would have sent you.

It just won't work properly at all with a 16 ohm pot in there.

Please contact Parts Express or look at their online catalogue.Someone might have the part no, I don't have time to look it up right now The correct L pads are only a few dollars.

As Lord Zilch Von Zilchen-Curvemeister says with shaft facing you connect one probe of the multimeter to the far left tab and measure the Resistance to the centre tab. At full clockwise rotation it should read close to zero ohms. Start turning anti clockwise and it will increase slowly to about 16 ohms. (8 ohms with an 8 ohm L pad)

Now connect the probe to the centre tab and the other probe to the far right tab.

At full clockwise postion it will appear open ciruit (infinite ohms). Turn slowly anticlockwise and it will measure a high resistance (35-60 ohms depending on 8 or 16 ohm L pad) and start to decrease and will be zero ohms at full anitclockwise rotation.

As a further test, connect the probe to the fat left tab and the other probe to the far right tab. At full clockwise rotation it will measure infinite ohms. Then turn slowly anti clockwise and it will measure a high resistance (over 30 ohms) and will decrease slowly to about 16 ohms ( 8 ohms with an 8 ohm L pad).

(The L pad shouuld not be connected to the crossover during the above procedure)


If you are unable to get the above range of measurements then without doubt you have the wrong part.

Ian

[Bill Shenefelt]

[quote=Ian Mackenzie;164488]Bill,

If what you say in your last post is in fact the case you have (been supplied ) the wrong part. ie If you asked for a pot that is what they would have sent you.
I asked for the components used in the crossover for a 4343. The following measurements were made on one of the bigger units used for the 2121 and horn, not the slot radiator which is much smaller in size. It is however connected to give the same type results. The attenuator is not connected to either the speaker or crossover for these measurements. I should note that with the knob full at the ends of travel, it sometimes will give infinite resistance or 0 resistance in the last few degrees of travel. The values I state are thru the full rotatioon but may not include theis "off scale" value at a very end.


Left versus right depend on if the tabs are on the down or up side of the unit. If they are "up" then the speaker is connected across the middle and right (common) tab-the common being the furthest clockwise looking from the stem side. I will continue to use both left and right conotations but will add clockwise or counterclockwise to make it consistant no matter the orientation of tabs.

Center to common measures 0 to 60 ohms as I turn the pot clockwise (this would be in parallel with the speaker -speaker is not connected).


The input from the crossover is on the left tab (furthest counterclockwise, stem up) . I measure about 14 dropping to 0 ohms from the input tab to the speaker center tab as I turn the dial clockwise (this is the resistance that is put in series with the speaker from the crossover. Input to center tab.)

The far right tab is common. From the far left to the far right (input to common) tab I measure from about 14 ohms rising to 60 ohms then infinity just at the very end as I turn the knob clockwise.

Not sure if this matches your description or not due to the tab numbering. Does this sound correct? For these variable units it is the only way they would work to allow proper attenuation of the output. Either they are the correct units or incorrect units wired to give variable output but improper load to the corssover. I did specifically ask JBL for the parts of the 4343 crossover, not specifying pots, caps, inductors or resistors, just all parts except those for the 15 inch 300 cps crossover components as I was going to biamp the 300 cps crossover. They sent me all the inductors, caps, resistors and attenuators but no connections binding posts or wires or terminal strips. I really think I got the correect attenuators.


Yesterday I bit the bullet and enlarged the chambers. They are now 10" wide by 9" high by 11 1/2 inches deep. I almost doubled the depth from before. In the full rear of the chamber I put a piece of 3 inch thick sonex. The chamber toward the front is filled with a loose stuff of some white fiber speaker fiberfill material that seems to have the feel of wool. It is pushed against the upper , lower and side walls but not held tight there. Just forms sort of a basket for the speaker basket.

[Bill Shenefelt]

[quote=Ian Mackenzie;164488]Bill,


As Lord Zilch Von Zilchen-Curvemeister says with shaft facing you connect one probe of the multimeter to the far left tab and measure the Resistance to the centre tab. At full clockwise rotation it should read close to zero ohms. Start turning anti clockwise and it will increase slowly to about 16 ohms. (8 ohms with an 8 ohm L pad) Far right not wleft as it is a rear view though. L pad connections


This is an "inverted view" as it is from the back. I think it matches what you say above.

[Ian Mackenzie]

Bill,

The first graph is a Model using the JBL specified active card (5235) for the 4343. These are spread 12 db butterworth filters. The mid , horn and slot are connected out of phase to the woofer.

The 2nd graph is the LR 24 db slopes are 320hz. All drivers are in phase.

As you can see there is a slight depression centred at 500 hz (91db) and rises to 93 db at 980 herts.

Some notes
In your system you have to appreciate your 2121 may well be peaking out more at 1000 hz as this is a characteristic of the driver and your room acoustic may well be causing a null oin the 300-500 hz region. The dimensions of the baffle will also contribute to ripples in the 2121 passband. Typically mid range and HF driver produce a smoother response with asymetric postioning (off centre) on a baffle.

What you may wish to try is taking the 2121 and measuring the 2121 without any crossover connected (in several different locations) in an attempt to understand its characteristics. Do this for both drivers, then relocate back where you normally have the 2121 on the woofer box with the horn and measure again without the crossover connected to try and determine the effect of the room/ baffle layout on the response.

If you want to to keep the vertical array and the other cards still dont help the falling response you can try and modify the low pass passive filter on the 2121. The problem with actively boosting the low end of the 2121 toio much is it will stress the amps dynamic headroom and the Xmax of the 2121. Just to show you how clever I really am...Muhhahaha the third graph shows the modelled effect of increasing the 1.7 mH inductor in increments of 1.9 mH, 2.15 mH and 2.38 mH. This has the effect of taming the rising response on the 2121 driver. This is simple enough to try by adding a few turns to the inductor (if you have an inductance meter) and doing some measurements with Smart Live to confirm what actually happens. You will of course need to need to modify the gain of the HF amp and adjust the mid, horn and slot levels to shelve the response overall.

The Doctor.

[Bill Shenefelt]

Well here is what I can get with room responce. I canot say the bass traps did anything, at least on the RTA responce. The following RTA plots are with the speakers flat against the wall, about 6 inches off the floor, the 2121 close to the 136A on the baffle, the 2121 enclosure at 1/2 cubic ft now, the 136A slope at 400 cps and the 2121 slope at 300 cps with 5 db boost at about 350cps. I have not received the 12dB/octave cards from Marchand yet so I have not tried Ian's recommended crossover configuration. I ran scans with both pink oise and with a feature called Quick Sweep which gives a fast pink noise sweep.

left channel sweep


Right channel sweep


Both channels driven sweep



Pink noise left


pink noise right


Pink noise both driven



Other than the 60 cps dip which is room for sure, it looks pretty good with about a +- 5dB range. (the scale is marked each 10 dB on the left). I guess that is not bad for room response.

[Bill Shenefelt]

I was trying to measure voltage drive but did not get anywhere with it. I tried conneting my speaker terminal pair instead of the microphone for input to the USB unit. I kept getting the whole drive range from the crossover, not the drive range after the passive crossover. I had the speaker connected and the leads to the + and - terminals on the speaker. I know the speaker is only getting the correct range of frequency but measuring a voltage drive at the terminals shows the full range coming from the active crossover. Not sure if I am doing something wrong trying to measure it this way or not.

[Earl K]

Hi Bill,

Thanks for the update !

FWIW;
- Larger pics would be quite a bit more useful for the rest of us to peruse.
- If TrueRTA doesn't have a "save to jpg" feature then capture a "screen-shot" from the computer ( I don't know the keyboard commands for the PC ) / edit & save the resulting .bmp file ?? as a jpg / & then upload the .jpg into the thread as an attachment .

,,,snip , ,,(the scale is marked each 10 dB on the left).

- The 10 db scale isn't very helpful for determining the "hills & dales" ( it's a bit too flattering ). Try 5 db instead .

[Ian Mackenzie]

Learn how to attach images too.

That way more people will be able to follow and take an interest in what you are up to.

Links are such a temporary thing.....

[Bill Shenefelt]

Learn how to attach images too.

That way more people will be able to follow and take an interest in what you are up to.

Links are such a temporary thing.....

[Bill Shenefelt]

Attachment 24773
I tried saving from paint screenshot and it was terrible so photos will have to do.

[Bill Shenefelt]

This is with the microphone on the floor rug as suggested by Ian.

[Earl K]

I tried saving from paint screenshot and it was terrible so photos will have to do.

- That's unfortunate .

- Here's an FR shot, done by LHF member " dmtp " . This is done with his copy of TrueRTA .



- Ya might want to shoot him a PM and ask for his advice on how to create this sort of uploadable file .

[Bill Shenefelt]

If you select 1/3 octave for a view like in the JBL publication fot the 4343 it looks a lot better. This is quick sweep both channels at listening position. Each vertical step is one dB. I don't expect it to match JBL since I do not have an anocheic chamber so I think it looks decent with no equalization. There is not much I can do with the peak at 40 and the dip at 60 cps without somehow changing the ceiling ht and room dimensions. Looks like other than the 60 and 40 cps realms I am pretty much within +-3dB.

[Robh3606]

Things are getting better. The 2121 level looks a bit up. How do they sound??

Rob

[Bill Shenefelt]

Pretty good I think. I still have to get my turntable set up but with a couple of CDs and tape deck they are nice. I will need to do a little level tweaking amongh the drivers but need to listen to more things to get it right. It is sort of a balancing act since my high frequency hearing is down a good bit above about 7K. To get it good for me and for others is a little tricky. I still am waiting for the 12dB/octave cards to come in to try. Also have my old McIntosh 240 tube amp to get back from repair to see if I want to go 3 way active or maybe use it instead of the Amber amp for the 300+ range. If it works well it may be a better unit on the horns at least. My Apt Holman preamp died so I am using a Nakamichi preamp right now until the Apt and my McIntosh are fixed. Additionally I need to see if a new Grado cartridge is better than my Dynavector diamond(old and may need replaced due to age, not wear though).