Peavey SP1 WIth Square magnet HF and LF

[rmlowz]

Hello,

I purchased some SP1s recently and they are not like my other pair I had. These have square magnet woofers and the HF have square magnets also. Are these inferior to the Black widows and 22A HF. Should I buy some black widows and 22As? These are for listening to music in a barn I have. Here are pics if anyone can help. I would greatly appreciate it. I also have a pic of the serial number if anyone knows what year they were made?

Thanks
Rich

[Dookie]

Those are the original Peavey magnets/horn driver/ woofers that came with the first SP1's when they came out. I had a set many years ago. Peavey sourced the woofer from eminence if I remember right. If they sound ok, then use them. You may find it hard to find the right Black Widows 15 spec wise to go into the horn loaded box as the box requires a 4 ohm driver that is designed for the horn loading.
I used mine in my home listen room for some time and thought they sounded fine.

Doug

[Dookie]

There is one thing though. Looks like a different horn "Lens" or someone repaired or replaced the original lenses. That wooden up and down brace and the cut/weld doesn't look right either. Is both the horn "lens" like that? That one is not right, and it may be affecting the sound quality.

Sp-1 horns should look like this.

SP-1 horn.JPG (72.02 KiB) Viewed 2483 times

SP-1 horn2.JPG (80.3 KiB) Viewed 2483 times

[rmlowz]

Thanks for the replies. I appreciate it. They both are like that the HF sections. I have another pair of horns like the ones you pictured. They sound really good. I am going to leave them alone. So, you are saying the square magnet woofers are 8 ohms instead of 4-ohm black widows? You would not happen to know the year of these speakers, would you? I am just curious.

Thanks

Rich

[Dookie]

Thanks for the replies. I appreciate it. They both are like that the HF sections. I have another pair of horns like the ones you pictured. They sound really good. I am going to leave them alone. So, you are saying the square magnet woofers are 8 ohms instead of 4-ohm black widows? You would not happen to know the year of these speakers, would you? I am just curious.

Thanks

Rich

The woofers should be 4 ohms and I'm guessing these are as well. The acoustic loading of the Horn Box makes the amp "see" 8 ohms in the frequency range the horn loads it at. The woofer section is more like a Low/Mid than a subwoofer. It is designed to only go down to 58hz or so. Below 58hz the amp "sees" a 4 ohm load and the horn loading no longer controls the woofer excursion (moving in/out) so it is possible to damage the woofer if it is pushed to reproduce below that 58hz with excessive volume.

I believe those were made around 1986.

Because of the weight of the SP-1 later they made a MFX-1 and FH-1 split. The spec for the woofer section in the FH-1 is the same as the woofer section in the SP-1. https://peavey.com/manuals/80301013.pdf

"WHEN FOUR OHMS IS NOT FOUR OHMS"
There is an enclosure in our product line that we have been making for twenty years called, the FH-1 low frequency enclosure. We use a four ohm loudspeaker in this enclosure; however, as long as the enclosure is operated above its cut-off frequency of 60 Hz, the actual load impedance that the power amplifier sees is nominally eight ohms. Likewise, we use a four ohm loudspeaker in the Mid bass horn of HDH-4 and HDH-1 speaker enclosures. As long as these horns are operated above their cut-off frequency of 300 Hz, the midbass of the enclosure will exhibit an eight ohm load to the amplifier.

The mechanical loading of the loudspeaker by the horn makes an impedance transformation so the amplifier sees a load impedance of 8 ohms within the horns operating bandpass. I mention the horn's operating bandpass because if you operate any horn below its cut-off (-3 dB down point on the low frequency portion of its response curve), the driver reverts back to its original lower impedance. As long as you send horn loaded enclosure frequencies that are above the cut-off, the system will offer a higher load impedance to the power amplifier.

The DC resistance of the loudspeakers discussed above is 3.2 to 3.8 ohms. Mounting the loudspeaker on a horn doesn't change the DC resistance, but a power amplifier driving that horn will see a load impedance that is more than twice that of the nominal four ohm impedance of the individual speaker. Hopefully some of us now understand how a four ohm loudspeaker can become an 8 ohm loudspeaker system when mounted on a properly designed horn.

I had mentioned earlier a situation I discovered in Africa where a technician had a basic understanding of impedance, but he didn't understand how horn loading can change the impedance of a loudspeaker. We used to have a low frequency enclosure called the FH-2. This enclosure had two four ohm loudspeakers wired in parallel within a folded horn. Since each of the loudspeakers was loaded by the horn, the individual loudspeakers were mechanically raised to eight ohms. Therefore, in parallel the two equivalent eight ohm speakers offered a four ohm load to the amplifier when operated in its designated bandpass 60 Hz - 400 Hz.

The technician thought he was correct and that perhaps the manufacturer had goofed. So he wired what he thought were two four ohm loudspeakers in series, thinking that he then had an eight ohm load for the power amplifier. However, since these were horn-loaded speakers, he actually changed a four ohm enclosure into a sixteen ohm enclosure. He changed them from two horn-loaded eight ohm speakers that were mixed in parallel to two eight ohm loudspeakers wired in series that now offered a sixteen ohm load for his CS-800 amplifier. So instead of the CS-800 producing 400 watts into 4 ohms (200 to each speaker), it produced only 100 Watts (50 watts to each speaker). Now not only did he have a 6 dB loss in SPL, he totally destroyed the damping or control capability of the power amplifier by reducing his potential damping factor from a rating of 200 to that of 0.5. More on Damping Factor later.

Perhaps now that you have further insight into complex impedance, you may also agree that when misinformed people try to "out think" the manufacturer of a loudspeaker system, they more often than not have their own foot crushed by the wheel that they are trying to reinvent.

I mentioned that loudspeakers should not be wired in series for sound reinforcement applications. And it was all right to wire them in parallel, but that they should each have their own pair of speaker cable leads and be wired in parallel at the output terminals of the power amplifier. This is the professional way of wiring loudspeakers in parallel. All loudspeakers generate a back voltage due to the motion of the voice coil within the magnetic field of the voice coil gap. This is referred to as a Back-EMF or backward-electro-motive-force.

Sir Issac Newton said that for every action there is an equal and opposite reaction. If you would take a fifteen inch Black Widow loudspeaker and hook its terminal up to the input of an oscilloscope and slap the cone abruptly with the palm of your hand, you could cause a voltage to be displayed on the scope greater that 80 volts peak to peak, 40 volts peak, or about 28 volts RMS.

If two loudspeakers are wired in parallel within an enclosure at a distance from the power amplifier, each speaker creates a back-EMF that causes low frequency cancellation as these voltages are out of phase with the incoming signal. When the two loudspeakers are wired in parallel at the output terminals of the power amplifier, the very low internal output impedance (source impedance) of the amplifier (typically 0.02 ohms) acts as a shunt or near short circuit to the back-EMF voltages.

https://peavey.com/c/Impedance-in-Audio-Technology

Doug

[rmlowz]

Thanks, Doug, for the great information. I appreciate it. Do you think I could put my 22A HF driver in with my old horn like the one in your picture. For this enclosure? I want to take the Horn out to paint it. It would be a lot easier to use my other update horns. From what I gather the 22A is titanium and the 22 driver that is in the ones I bought are not give a little more highs? The crossovers in these enclosures are for the 500hz ones.

Rich

[Dookie]

Thanks, Doug, for the great information. I appreciate it. Do you think I could put my 22A HF driver in with my old horn like the one in your picture. For this enclosure? I want to take the Horn out to paint it. It would be a lot easier to use my other update horns. From what I gather the 22A is titanium and the 22 driver that is in the ones I bought are not give a little more highs? The crossovers in these enclosures are for the 500hz ones.

Rich

The Horn Lens are interchangeable if you have 4 SP-1's now. There is just the screws in the front of the box that holds the horns lens in place. This new set you have now someone has done something to the horn Lens then made some kind of adaptor with that piece of wood put in to hold it in place. You will have to take that wood piece out I believe to get the other set of horn lens in. I'm betting what they did to the horn Lens is affecting the sound a thousand times more than the difference between a 22 and 22A.
The difference between the 22 and 22A is very slight. Just a little more power handling (maybe) and the highs may be too close to call. (good marketing or not....) Not sure of your age but most men above the age of 30 or so have little hearing ability above 12,000 to 14,000hz or so. They might say they do but when tested they don't. It is just a fact of life that all men and to a degree all women go through as they get older. When we are in are 40's and 50's we can't hear a lot above 10,000 and 8,000 hz when we are in our 60's. I wouldn't bother changing to the 22A's unless it is easy to switch the horn lens and driver together and you no longer need the 22A/lens combo where they are now.

Doug

[rmlowz]

Thanks Doug,

I will be taking them apart soon to refinish them(restore). I will check it out. Whoever did it had a lot of work to do making welding the metal throat?
I don't get why they did it. is a lot of trouble to fabricate to make everything.

Thanks again,

Rich