D8444/D8443 Replacement 5" Speakers: 4 Ohm Issues?

[Jambox_72209]

A couple of things I noticed about the D8443 and an anecdotal report:

1)The pathetic little piezo tweeters are wired to the 8 ohm speakers in parallel. From what I understand, wiring in parallel drops the overall impedance per this formula: multiplication of the two loads divided by the sum of the two loads - i.e. putting two 8 ohm speakers in Parallel results in a 4 ohm load. In this case, those Piezos are likely high impedance but still lower the overall impedance of the total load at least a bit.

2) The amp section has what appears to be a decent sized heat sink, but services two chips and is just a smooth metal bracket with no fins. Is that good enough?

Just last night I put a pair of 5.25" Skar 4 ohm coaxial speakers in my D8443 and scrapped the piezos. So far, these car stereo speakers run like a champ, with a punchier, more modern sound, crisper highs and much improved bass and treble response over the originals ...and somewhat less distortion. In fact the original 8' woofer that remains can't keep up--it distorts at high volume and I am considering putting a switch or pot on it to remove or attenuate it in the mix to clean up the sound.

I can feel a very slight warmth to the rear cover behind the amp, and that is after several hours at moderate volume.
Not too bad so far.

RPX525 | 5.25" 150 Watt Coaxial Car Speakers - Pair | Skar Audio

The Skar Audio RPX525 2-way 150 watt coaxial car speaker set was designed to be price sensitive while also delivering unparalleled sound. These 5.25-inch speakers will make for great factory replacements and are available in a 4-ohm impedance.

www.skaraudio.com

 

[Superduper]

A couple of things I noticed about the D8443 and an anecdotal report:

1)The pathetic little piezo tweeters are wired to the 8 ohm speakers in parallel. From what I understand, wiring in parallel drops the overall impedance per this formula: multiplication of the two loads divided by the sum of the two loads - i.e. putting two 8 ohm speakers in Parallel results in a 4 ohm load. In this case, those Piezos are likely high impedance but still lower the overall impedance of the total load at least a bit.

2) The amp section has what appears to be a decent sized heat sink, but services two chips and is just a smooth metal bracket with no fins. Is that good enough?

(1) The type of piezo tweeters used in these boomboxes have such high impedance (probably 3 digits or more) that they have a virtually unmeasurable affect on the speaker system impedance, even if installed in parallel with the low frequency driver. The very fact that they don’t even need a filter capacitor tells you these aren’t treated like ordinary speaker drivers.

(2) Good enough for factory speaker system. For HD use or lower impedance drivers, there are finned stick on heatsinks available which can be stuck on flat surfaces (or remove the tape and glue on with thermal conductive epoxy). Adding one or more, space permitting will certainly aid thermal cooling of the factory heatsink.

 

[hopey]

I have seen them Called Transducer or Piezo Transducer or Piezo Ceramic Transducer. You can get them in different frequencies and are high impedance low power. Looks like they fit in-between the woofer and tweeter ranges. You can get 3-9k types.



Example: Resonance Frequency 6.3kHz Resonant Frequency Tolerance ±0.6kHz Resonant Impedance (R1) 1000Ω Capacitance 10nF Capacitance Tolerance ±30% Measurement Condition of Capacitance [1kHz] Operating Temperature Range -20℃ to 70℃ Storage Temperature Range -30℃ to 80℃

 

[floyd]

(1) The type of piezo tweeters used in these boomboxes have such high impedance (probably 3 digits or more) that they have a virtually unmeasurable affect on the speaker system impedance, even if installed in parallel with the low frequency driver. The very fact that they don’t even need a filter capacitor tells you these aren’t treated like ordinary speaker drivers.

(2) Good enough for factory speaker system. For HD use or lower impedance drivers, there are finned stick on heatsinks available which can be stuck on flat surfaces (or remove the tape and glue on with thermal conductive epoxy). Adding one or more, space permitting will certainly aid thermal cooling of the factory heatsink.

I agree with Norm 100% because amplifiers that get hot lose efficiency through Heat which means as everyone knows if it gets hot it's not running very efficiently especially with amplifiers they lose some of their power in the form of heat . Extra Cooling is Extra Protection.

 

[floyd]

A couple of things I noticed about the D8443 and an anecdotal report:

1)The pathetic little piezo tweeters are wired to the 8 ohm speakers in parallel. From what I understand, wiring in parallel drops the overall impedance per this formula: multiplication of the two loads divided by the sum of the two loads - i.e. putting two 8 ohm speakers in Parallel results in a 4 ohm load. In this case, those Piezos are likely high impedance but still lower the overall impedance of the total load at least a bit.

2) The amp section has what appears to be a decent sized heat sink, but services two chips and is just a smooth metal bracket with no fins. Is that good enough?

Just last night I put a pair of 5.25" Skar 4 ohm coaxial speakers in my D8443 and scrapped the piezos. So far, these car stereo speakers run like a champ, with a punchier, more modern sound, crisper highs and much improved bass and treble response over the originals ...and somewhat less distortion. In fact the original 8' woofer that remains can't keep up--it distorts at high volume and I am considering putting a switch or pot on it to remove or attenuate it in the mix to clean up the sound.

I can feel a very slight warmth to the rear cover behind the amp, and that is after several hours at moderate volume.
Not too bad so far.

RPX525 | 5.25" 150 Watt Coaxial Car Speakers - Pair | Skar Audio

The Skar Audio RPX525 2-way 150 watt coaxial car speaker set was designed to be price sensitive while also delivering unparalleled sound. These 5.25-inch speakers will make for great factory replacements and are available in a 4-ohm impedance.

www.skaraudio.com

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This answers many questions for us thank you plus that's a pretty nice custom box you got there.

 

[Jambox_72209]

Thanks for the feedback. I am glad I found this forum. The box is a work in progress. It is a recent acquisition from an online estate sale of the same model that I bought at Sam's Club back in the late 80's that I abandoned in 2007. The volume pot works better on this one than my old one. The meter bar is outboard, it is held on by a magnet and I will eventually install some lights from a different module once I find the one I like. The cassette mechanism was absolute trash so I removed the motor, heads, spindles and capstan so I could use that space for 21st century upgrades. The cassette audio chain has noise in the right channel and the Line In is not operating hardly at all. The Line Out and Headphone jacks are fine. Weirdly I am using the mic jacks as an aux-in for an outboard Bluetooth receiver. It sounds OK but I want to wire it to the amp properly. The mic inputs play through in radio mode, mixing with the radio audio, so the only way I can hear the Bluetooth by itself is to place the band selector switch in between band detents to cut off the radio signal, which may be causing damage. Radio works ok but a day or so after the speaker upgrade I noticed crosstalk among stations at the upper end of the FM band--not sure what I did to cause that. I am considering replacing all the electrolytic caps to hopefully improve performance and longevity. I will keep you posted.

This answers many questions for us thank you plus that's a pretty nice custom box you got there.