Moved the trebax l-pad from the crossover to the trebax then installed the capacitor and coil. Played some music and noticed an improvement in the sound quality.
I could hear the dome tweeter a little easier as the trebax is no longer reproducing some of the range the dome is reproducing.
I could hear the dome tweeter a little easier as the trebax is no longer reproducing some of the range the dome is reproducing.
One further question.
For the midax and trebax to have the same output, should they be attenuated by the same amount or does the midax require more attenuation?
With some music the midax sounds balanced with the woofers and with some music the midax sounds a little louder.
I probably could increase the midax attenuation by 1-2dB and both the trebax and tweeter will need to be dropped by the same amount unless the midax should have higher attenuation than the trebax.
Now I see why 15 ohm l-pads would have been a good choice to use as I could have tweaked until I got the sound just right, but then I'd have three knobs to tweak any time I think something doesn't sound right which may not be a good thing.
When I get the tube amp restored that I'm gonna use with this speaker I may use a Schiit 4 band EQ before the amp which will allow me more options to get the sound just right than just a bass and treble control.
For the midax and trebax to have the same output, should they be attenuated by the same amount or does the midax require more attenuation?
With some music the midax sounds balanced with the woofers and with some music the midax sounds a little louder.
I probably could increase the midax attenuation by 1-2dB and both the trebax and tweeter will need to be dropped by the same amount unless the midax should have higher attenuation than the trebax.
Now I see why 15 ohm l-pads would have been a good choice to use as I could have tweaked until I got the sound just right, but then I'd have three knobs to tweak any time I think something doesn't sound right which may not be a good thing.
When I get the tube amp restored that I'm gonna use with this speaker I may use a Schiit 4 band EQ before the amp which will allow me more options to get the sound just right than just a bass and treble control.
Both the Midax and Trebax have very high sensitivities. However no numerical values are stated and we can not assume the sensitivity is the same for each driver.
Goodmans clearly state that, in order to use the horn units in conjunction with direct radiating bass drivers such as yours, variable attenuators are required to provide a flat overall response.
To me, 16 ohm variable L-pad controls were the obvious choice for getting the levels just right in this application.
Goodmans clearly state that, in order to use the horn units in conjunction with direct radiating bass drivers such as yours, variable attenuators are required to provide a flat overall response.
To me, 16 ohm variable L-pad controls were the obvious choice for getting the levels just right in this application.
I may try to attenuate the midax by 1 or 2 dB tomorrow and see how it sounds.
Also given I'm using two woofers, it up close may sound like the midax is louder than it would farther away from the speaker.
If I ever find another pair of the RCA woofers or four identical 8 ohm woofers that will work good in an open back cabinet I'll have two proper cabinets built then I may use something like a mini DSP and four stereo amps which will allow me to time align the drivers and tweak the sound to where they sound their best.
Here's a photo of the box.
Also given I'm using two woofers, it up close may sound like the midax is louder than it would farther away from the speaker.
If I ever find another pair of the RCA woofers or four identical 8 ohm woofers that will work good in an open back cabinet I'll have two proper cabinets built then I may use something like a mini DSP and four stereo amps which will allow me to time align the drivers and tweak the sound to where they sound their best.
Here's a photo of the box.
Ok I'm gonna try to increase the midax attenuation to 10.8 dB which gives me a 10.67 ohm resistor. I'll put two 1 ohm resistors in parallel for .5 ohms and put that in series with the existing 10 ohm resistor. For the 6.07 ohm resistor I'll use a 4.99 ohm resistor in series with a 1 ohm resistor.
If the midax then sounds better matched with the woofers I'll see if the trebax sounds matched to the midax. If so I'm good if not I'll use the same resistors for the trebax.
I'll then verify that the dome is matched to the trebax. If not I'll need an attenuation of 1.5dB which is a series resistor of 2.54 ohms and a parallel resistor of 84.88 ohms.
I can use two one ohm resistors in series and two 1 ohm resistors in parallel to equal 2.5 ohms +/- the resistor tolerance. For the 84.88 ohm resistor I need to see what resistors I have. Perhaps I'll have two 47 ohm resistors for 84 ohms and maybe a 1 ohm resistor if needed.
If the midax then sounds better matched with the woofers I'll see if the trebax sounds matched to the midax. If so I'm good if not I'll use the same resistors for the trebax.
I'll then verify that the dome is matched to the trebax. If not I'll need an attenuation of 1.5dB which is a series resistor of 2.54 ohms and a parallel resistor of 84.88 ohms.
I can use two one ohm resistors in series and two 1 ohm resistors in parallel to equal 2.5 ohms +/- the resistor tolerance. For the 84.88 ohm resistor I need to see what resistors I have. Perhaps I'll have two 47 ohm resistors for 84 ohms and maybe a 1 ohm resistor if needed.
Combining individual resistors to produce a required resistance value is such a basic procedure that I wouldn't bother to spell out in detail.
I'd be more interested in which type of resistors you are combining. Make sure the resulting power rating of the combination is sufficient for the job.
I'd be more interested in which type of resistors you are combining. Make sure the resulting power rating of the combination is sufficient for the job.
Ok while desoldering the existing resistors it appears that I made a mistake.
I needed 10 ohms series and 7.8 ohms parallel.
I got the 7.8 ohm resistor made up right using a 4.99 ohm resistor in series with two 2.7 ohm resistors in parallel, but I for some reason put two 10 ohm resistors in parallel.
I'll remove one 10 ohm resistor and see if the drivers are better matched.
EDIT:
Tried that and the midax is balanced with the woofers and the trebax is balanced with the midax.
Now to see if the dome is balanced. If not I gotta figure what dB the attenuation was and attenuate the dome by that much.
EDIT 2:
The dome seems to be balanced good enough with the trebax.
Speaker sounds much better.
I needed 10 ohms series and 7.8 ohms parallel.
I got the 7.8 ohm resistor made up right using a 4.99 ohm resistor in series with two 2.7 ohm resistors in parallel, but I for some reason put two 10 ohm resistors in parallel.
I'll remove one 10 ohm resistor and see if the drivers are better matched.
EDIT:
Tried that and the midax is balanced with the woofers and the trebax is balanced with the midax.
Now to see if the dome is balanced. If not I gotta figure what dB the attenuation was and attenuate the dome by that much.
EDIT 2:
The dome seems to be balanced good enough with the trebax.
Speaker sounds much better.
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The dome seems slightly too low in output.
With another speaker when the dome seemed slightly too low in output I used a ribbon tweeter I happened to have on hand that is the same ohms as the dome. I have another on hand and may try it tomorrow.
With another speaker when the dome seemed slightly too low in output I used a ribbon tweeter I happened to have on hand that is the same ohms as the dome. I have another on hand and may try it tomorrow.
So still not being satisfied with the sound I did some tweaking. I used a 1.1uF cap (two 2.2uF in series) and a 3.3 ohm resistor in series with the 6 ohm ribbon tweeter that was horn loaded with the small horn having a similar flare to a speaker cone and is square,.
That definitely sounded better when I was close to the speaker, but as I moved farther away the upper treble decreased in output.
So I tried the dome as well and it was worse as it isn't horn loaded.
It then hit me. The midax and Trebax look like they are more of a long throw design and I've been trying to pair them with short throw tweeters.
I have a horn tweeter from a Klipsch KG4 speaker that I may bring to work tomorrow and try.
It is 8 ohms so I'll put a 5 ohm resistor in series with a 3.3 ohm resistor and first try it in place of the trebax with the ribbon disconnected. If it doesn't sound good that way I'll connect the trebax back up and try it in place of the ribbon tweeter.
If nothing works I do have an Altec 811B horn with an Eminence driver on it that I know for sure will be plenty loud enough and have more of a longer throw
That definitely sounded better when I was close to the speaker, but as I moved farther away the upper treble decreased in output.
So I tried the dome as well and it was worse as it isn't horn loaded.
It then hit me. The midax and Trebax look like they are more of a long throw design and I've been trying to pair them with short throw tweeters.
I have a horn tweeter from a Klipsch KG4 speaker that I may bring to work tomorrow and try.
It is 8 ohms so I'll put a 5 ohm resistor in series with a 3.3 ohm resistor and first try it in place of the trebax with the ribbon disconnected. If it doesn't sound good that way I'll connect the trebax back up and try it in place of the ribbon tweeter.
If nothing works I do have an Altec 811B horn with an Eminence driver on it that I know for sure will be plenty loud enough and have more of a longer throw
So I did a thing right after lunch.
Decided to disconnect the trebax and connected the midax to where the trebax normally connects at the crossover as it only required disconnecting one wire and moving another to where the wire was disconnected.
Other than the output dropping to basically zero at 13kHz, I honestly think the midax sounded better than the trebax. Of course it was louder than it should be because I didn't have the l-pad on the midax.
So what I will do is bring in a second midax and the Klipsch horn tweeter tomorrow and do the test with the second midax in place of the trebax and the Klipsch in place of the ribbon tweeter.
I'll then do as I mentioned earlier and try just the Klipsch in place of the trebax and see which combination sounds best.
What's nice is with two midax I won't need to wonder if the attenuation is correct for the midax connected in place of the trebax.
If the second midax and Klipsch sounds better, I'll get a cardboard box large enough to mount both drivers in.
If the Klipsch in place of the trebax sounds best, I'll remove the existing small cardboard box and use some lacing cord to secure it to the box.
EDIT:
I goofed earlier when describing the l-pad.
It should be a 10 ohm resistor connected to the driver + terminal and a 7.8 ohm resistor consisting of a 4.99 ohm resistor and two 4.75 ohm parallel resistors in series for 7.37 ohms which is in parallel with the driver terminals.
Decided to disconnect the trebax and connected the midax to where the trebax normally connects at the crossover as it only required disconnecting one wire and moving another to where the wire was disconnected.
Other than the output dropping to basically zero at 13kHz, I honestly think the midax sounded better than the trebax. Of course it was louder than it should be because I didn't have the l-pad on the midax.
So what I will do is bring in a second midax and the Klipsch horn tweeter tomorrow and do the test with the second midax in place of the trebax and the Klipsch in place of the ribbon tweeter.
I'll then do as I mentioned earlier and try just the Klipsch in place of the trebax and see which combination sounds best.
What's nice is with two midax I won't need to wonder if the attenuation is correct for the midax connected in place of the trebax.
If the second midax and Klipsch sounds better, I'll get a cardboard box large enough to mount both drivers in.
If the Klipsch in place of the trebax sounds best, I'll remove the existing small cardboard box and use some lacing cord to secure it to the box.
EDIT:
I goofed earlier when describing the l-pad.
It should be a 10 ohm resistor connected to the driver + terminal and a 7.8 ohm resistor consisting of a 4.99 ohm resistor and two 4.75 ohm parallel resistors in series for 7.37 ohms which is in parallel with the driver terminals.
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The bass sounds fairly decent. Good enough for the intended purpose.
Probably goes down to about 50Hz and gradually rolls off.
In a proper wood box of the same or larger size, it might go lower, however I do not know the model RCA console these came from so I do not know if the speakers were sealed, ported or open back.
I also did a test connecting the trebax to the high pass crossover for the ribbon and got barely any output even though there was no attenuation so that proves to me the Trebax is indeed inadequate for upper treble reproduction when using any source except an FM tuner.
Now does anyone make an upgraded diaphragm for the Trebax like is sometimes done to some horn tweeters to improve the sound quality?
I am honestly blown away by how the Midax sounds even when used to its upper frequency limit. Easily the smoothest most natural sounding horn I've ever heard. In all honesty I sometimes forget the midrange from 950-5k is coming from a horn if I am not looking directly at the speaker.
That has me puzzled. They could make the Midax so smooth sounding, then we have the Trebax... Not near as smooth sounding, but not harsh sounding either.
Probably goes down to about 50Hz and gradually rolls off.
In a proper wood box of the same or larger size, it might go lower, however I do not know the model RCA console these came from so I do not know if the speakers were sealed, ported or open back.
I also did a test connecting the trebax to the high pass crossover for the ribbon and got barely any output even though there was no attenuation so that proves to me the Trebax is indeed inadequate for upper treble reproduction when using any source except an FM tuner.
Now does anyone make an upgraded diaphragm for the Trebax like is sometimes done to some horn tweeters to improve the sound quality?
I am honestly blown away by how the Midax sounds even when used to its upper frequency limit. Easily the smoothest most natural sounding horn I've ever heard. In all honesty I sometimes forget the midrange from 950-5k is coming from a horn if I am not looking directly at the speaker.
That has me puzzled. They could make the Midax so smooth sounding, then we have the Trebax... Not near as smooth sounding, but not harsh sounding either.
Your 12" RCA drivers are full range (with whizzer cone). Below is what yours may once have looked like:
I'd be interested in seeing them from the magnet assembly side. I presume them to have Alnico magnets.
So I tried the Klipsch in place of the trebax and also the second midax in place of the trebax with the Klipsch in place of the ribbon and the Klipisch in place of the trebax sounded better. I needed to attenuate the driver some so I used the same attenuation as the midax and it got real close but isn't quite loud enough with 9dB attenuation so I'll try 8dB as I can easily do it with a 9 ohm series resistor and a 10 ohm parallel resistor.