Jean Hiraga Altec A5 Crossover modification

[tizman]

Hello All.

I recently built this Jean Hiraga crossover for the Altec A5 in order to combine a 511B with a Renkus-Heinz SSD-1800-8 compression driver and a Peavey FH1 with an Eminence Kappa 15C. When I started my build the specs that I looked at for the original LF cabinet that came with the Altec VOTT A5 indicated that it would have a sensitivity close to what the FH-1 with a 15C would have. Apparently, I was mistaken, as the specs for Altecs 828 cabinet show it to be substantially less sensitive than the FH-1 with a 15C. Basically the FH-1 combo is 6-7 DB more sensitive than an 828 cab. I realized almost immediately that there was an issue, as there was obviously too much bass in the output.

I need to attenuate the bass by around 6-7 DB. I added an L-Pad on the output of the Hiraga, as per Pete Riggle's modification of the Hiraga crossover, in order to control the treble, but there is not enough treble even with the L-Pad set to let all the power through to the HF section. Looking at the schematic, there doesn't appear to be any mods that I can make to it that will increase the overall treble level while still maintaining the equalization that the horn/cd combo requires. Am I correct in thinking that my only solution is to add an additional L-Pad to the LF section? Should I move the existing L-Pad to the woofer section, as it is useless on the HF section? Or am I missing something? Any advice would be greatly appreciated.

This is the link for the Hiraga crossover as modified by Pete Riggle....
Altec A7 Voice Of Theatre Speakers - Vertical Tracking Angle on the Fly (VTAF)

 

[ticknpop]

Adding a level control or pad to the woofer circuit will destroy the amplifier damping, retune the bottom end alignment and just about every bad thing you can think of. Either biamp, or get a new woofer. I’m surprised any woofer would be more efficient than a HF horn and compression driver.

You copied the Riggle version Hiagra A - 5 crossover and changed all the drivers ? It isn’t a recipe for a good outcome....... your too far away from the original components to expect this to work well. Having the cabinet and the horn with different drivers Isn’t the same thing.

I copied the JBL 4350 studio monitor crossover, but I had 3 of the 4 original drivers. That worked out give or take some low end response. if your into horns you can hear the 4350 clones at a Toronto diy event (won’t be one until there is a covid vaccine).

 

[Pano]

Unfortunately it looks like you've gone down the wrong path. This published crossover is not at all suited to your speaker. You'll do best to start from scratch. Sorry for the bad news.

Since I was there for the original Hiraga A5 speaker and crossover (I used them for gigs) I know how they can sound. When I built my own A5 and tried to use the published crossover it was not at all satisfactory. I had to start from scratch. The A7-500 crossover was different from that, and the A7-800 a little different still.

 

[AllenB]

As much as loud bass is often seen as an impossible challenge, some like challenges.

Do you have a schematic?

 

[Pano]

About the too much bass, are you really getting 104dB @ 2.83V thru the bandwidth of the FH1? That's a heck of a lot for a woofer. The 511 horn will need attenuation at its bottom end to flatten the response. That's going to eat up a few DB, as you have found.
The best thing to do is measure what have, and start from there.

 

[tizman]

As much as loud bass is often seen as an impossible challenge, some like challenges.

Do you have a schematic?

The schematic can he found in the link in my first post. It is down the page some...

 

[tizman]

About the too much bass, are you really getting 104dB @ 2.83V thru the bandwidth of the FH1? That's a heck of a lot for a woofer. The 511 horn will need attenuation at its bottom end to flatten the response. That's going to eat up a few DB, as you have found.
The best thing to do is measure what have, and start from there.

I just started doing measurements with REW. The preliminary results are that the FH1 with Eminence Kappa 15C is roughly 6-7 DB louder than the 511B with Renkus-Heinz SSD-1800. I’m relatively new at doing measurements but my ears tell me that what I’m seeing in REW is correct. Am I correct in saying that other than the L-Pad on the output, and the shaping LCR, there is nothing else attenuating the HF section in the Hiraga schematic? I’m new to crossovers, so I may be missing something. The published sensitivity of the Altec A5 is 97 DB/W/M for the entire speaker. I couldn’t find the spec for the Altec 828 LF cabinet on its own. The FH-1 with its stock driver has a published spec of 104 DB/W/M. The FH-1 spec is in keeping with the LF portion of the La Scala that it greatly resembles.

 

[AllenB]

You could use a 2:1 autotransformer instead of an L-pad on the woofer.

 

[tizman]

Adding a level control or pad to the woofer circuit will destroy the amplifier damping, retune the bottom end alignment and just about every bad thing you can think of. Either biamp, or get a new woofer. I’m surprised any woofer would be more efficient than a HF horn and compression driver.

You copied the Riggle version Hiagra A - 5 crossover and changed all the drivers ? It isn’t a recipe for a good outcome....... your too far away from the original components to expect this to work well. Having the cabinet and the horn with different drivers Isn’t the same thing.

I copied the JBL 4350 studio monitor crossover, but I had 3 of the 4 original drivers. That worked out give or take some low end response. if your into horns you can hear the 4350 clones at a Toronto diy event (won’t be one until there is a covid vaccine).

I had all the parts on hand, and have done some research on the combination. The Renkus-Heinz drivers are the only wild card with respect to my research. There is not a lot of information on them, but Renkus worked on the later Altec drivers before starting his own company, and the specs of the SSD-1800 are similar to the later Altecs. What I could find out implied a similarity with Altec drivers. A 511B with an Altec 8XX or 9XX combined with a La Scala bass bin or a FH-1 has been done by many people. I found a crossover designed by ALK specifically for this combo as well. I didn’t expect there would be any issue with the bass bin being louder than the Horn and CD, and thought that the L-Pad that is at the output of the Riggle version would allow me to bring down the level of the HF if needed. As it is, the opposite is required. Is the LF section of an A5 really that much less sensitive than an FH-1 or La Scala?

 

[tizman]

You could use a 2:1 autotransformer instead of an L-pad on the woofer.

I originally was going to build the ALK crossover for this combo, but didn’t have autotransformers on hand other than the ones in speakers that are currently in use. Buying them from the US with exchange and shipping makes them very expensive. Also, the ALK schematic doesn’t have a shaping section to equalize the HF response. If the LF section was about 6 DB quieter, I’m sure they would sound good. I may pull them out of the speakers they are in if there isn’t an alternate solution. I have an electronic crossover and multiple amps, as building tube amps is my primary hobby, but tried the passive crossover to simplify things for other non-audiophile listeners in the house.

 

[AllenB]

I suppose I'd work up some specs and look for power transformers or similar connected as autotransformers.

Or here's a thought, can you connect the highs to an 8 ohm tap and the woofers to 4 ohms?

 

[ticknpop]

I built LaScalas bottoms with EV woofers in an earlier lifetime with Altec 511 /802s and JBL 2405 tweeters, though the Klipsch mid horn went down to 400 hz. Really didn’t like Klipsh’s use of cheap drivers in general. That was many moons ago.................. now I use electrostatics at home and 1970’s JBL drivers and horns in black plywood 4 ways at work

 

[tizman]

Allen: Two autotransformers delivered were $186. Insanity. Would any power transformer that doubled or halved line voltage work? For example a 120V to 60V or a 120V to 240V? I also have a few pairs of different toroidal transformers that are 120V to 35V. What would using power transformers instead of autotransformers do to the sound quality? I have read about people using toroidal power transformers as output transformers for tube amps but have not tried it myself.

"Or here's a thought, can you connect the highs to an 8 ohm tap and the woofers to 4 ohms?" I do have a couple of amps that have dual secondary output transformers with 4 and 8 Ohm taps, but I did not know that both could be connected to different drivers in a crossover.

Also, if I use a L-Pad that presents the same impedance to the amp of 6 Ohms, of appropriate wattage, to take 6 DB of the LF output, why is that not a good idea?

 

[AllenB]

Would any power transformer that doubled or halved line voltage work?

You could use these, that's a good suggestion. You could also use a split winding as an autotransformer. To that end..

When repurposing a power transformer I prefer not to mix dissimilar windings (thick and thin) in series unless I'm stuck for a value. Standard international split primaries should allow you to pursue 6dB +/- 1dB, or maybe a CT secondary fits the bill. Leave the unused winding open.

This is a lot like speccing an OPT. The self resonance of PTs is often above 1kHz, plenty for sub duty but measure if in doubt.

If you look at the impedance of the FH1 it is around 4 ohms at 20Hz, rising to triple that at 60Hz. You'll want to have higher than 4 ohms of reactance across half, or 16 ohms across the full winding at 20Hz.. or more than 250mH. The primaries on any power transformer smaller than 1kVA should have that at least, try to find one that has a resistance smaller than a few ohms.

What would using power transformers instead of autotransformers do to the sound quality?

You know the answer to this if you have experimented with output transformers. You manage the inductance, the bandwidth, the self resonance. Except that this is for sub duty, I wouldn't worry too much about the finer points of grain oriented steel or winding schemes etc.

I do have a couple of amps that have dual secondary output transformers with 4 and 8 Ohm taps, but I did not know that both could be connected to different drivers in a crossover.

Sure. From the secondary winding, the impedance looking back into the amp is small. In a sense the 4 ohm tap acts like a self contained autotransformer. The only drawback is that this represents -3dB. If you used 4/16 you'd get 6dB.

Also, if I use a L-Pad that presents the same impedance to the amp of 6 Ohms, of appropriate wattage, to take 6 DB of the LF output, why is that not a good idea?

This is the simplest solution. You might need to make minor response adjustments but it will work. Most of us have probably done it.

Some would declare it a waste of power. I notice that the FH1 is 103dB sensitive. What do you use on it, 10W? The L-pad would now use that as well.. less actually as you're aiming to be running the woofer lower than before.

 

[Pano]

97db is about right for the Altec A7/A5. That's the sensitivity of bass section - the horn is attenuated to match. In your unusual case the bass is louder than the horn, so you'll need some creative solutions. You could use two different power amps, of course.

The best is to get some practice with REW. Post you results here and we can look at them. Absolute SPL numbers aren't important at the beginning, just relative responses between bass and horn. It may end up that 104dB is just the peak of the bass and it's response needs to be shaped to a lower level, just like the 511 horn.

Measurements will tell.

 

[freddi]

in piddling with a few Klipsch - style setups, I don't think the FH1 would need attenuation. If the amplifier involved is ~constant voltage, then a transformer could be used on the mid - but still don't think needed.

my little RCA-Fan 8 ohm driver horn measures a bit hot compared to ancient 16 ohm SAHF driver. There should be some bandpass gain too besides what the ear likes.


(fwiw, I have more fun with a Karlson 12 than FH1}

Inroom

Outdoors

 

[tizman]

97db is about right for the Altec A7/A5. That's the sensitivity of bass section - the horn is attenuated to match. In your unusual case the bass is louder than the horn, so you'll need some creative solutions. You could use two different power amps, of course.

The best is to get some practice with REW. Post you results here and we can look at them. Absolute SPL numbers aren't important at the beginning, just relative responses between bass and horn. It may end up that 104dB is just the peak of the bass and it's response needs to be shaped to a lower level, just like the 511 horn.

Measurements will tell.

Pano: I will do some measurements with REW. I am new to REW, having started using it a week or so ago. Should I do a measurement of the entire speaker, or do the drivers separately? Should I move the microphone so it is the same distance from each driver and directly in front of the driver being measured if I do them separately, or keep it in the same position?

 

[tizman]

in piddling with a few Klipsch - style setups, I don't think the FH1 would need attenuation. If the amplifier involved is ~constant voltage, then a transformer could be used on the mid - but still don't think needed.

Freddi: In your graphs, the LF and HF appear to be closer in amplitude than in mine. I will post a whole speaker measurement shortly. The amp I am currently using is a single ended EL84 triode connected amp. I like to keep available wattage on the low side for testing, as I have damaged drivers before by connecting the wrong lead to a more powerful amp.

 

[tizman]

This is the simplest solution. You might need to make minor response adjustments but it will work. Most of us have probably done it.

Some would declare it a waste of power. I notice that the FH1 is 103dB sensitive. What do you use on it, 10W? The L-pad would now use that as well.. less actually as you're aiming to be running the woofer lower than before.

AllenB: Normally I use low wattage SET amps of less than 10 Watts. I will do some measurements and post them with the speaker as is.

 

[tizman]

REW measurements

These are four measurements made with the microphone placed about a meter away from the front of the speakers, and placed slightly above the top of the bass cabinet so that it is pointing at the lower third of the 511B. I have included three images. One is the combination of both speakers (combo), one is for just the HF on, and one is with just the LF on. I also included a measurement of one of my La Scala speakers for reference.