HH Scott Pro 100 woofers

[Wray & Ting]

Hi All,

I have a pair of (circa 1976) HH Scott Pro 100 speakers that I've had for a few months, and an Optonica SM-3636 amp that I've only had for a few weeks, so I'm not experienced with how these components should sound. Overall I'm impressed by how things sound, having recently upgraded from crummier gear, but I'm fairly confident the speakers are not firing on all cylinders as they are.

I have a nice pair of Sennheiser headphones (HD 598) that sound fantastic to me when listening through the amp with the EQ neutral. However, when listening with these speakers, I find that I need to turn on loudness, as well as give a bump to the bass for the low frequencies to show up to a reasonable level. This is what makes me wonder what's up:

The 15" woofers are replacements, seemingly Realistic 40-1035 (I haven't actually peeked inside the cabinets yet, but the concave dust cap seems to be a dead giveaway). Aside from potentially having quite different sonic character than the originals, and therefore not playing nice with the crossover design, I wonder if the originals may have been a lower impedance, such as 4 ohm (the replacements are 8 ohm). One of the two speakers reads 8.4 ohms, the other 9.3 ohms, and they should be 4 ohm per the specs.

So... does anyone know the impedance of the original woofers? If they were 8 ohm like the replacements, there must be something really out of whack inside the cabinets for the total impedance of both speakers to have doubled (seems unlikely to me). The speakers are quite usable to me in their current state, but the fact I have to juice the EQ on my amp combined with the higher impedance values makes me think their potential sound is much better than what I'm achieving right now. Any help would be much appreciated. This thread has a couple possible schematics, but not driver impedance:

https://audiokarma.org/forums/index.php?threads/hh-scott-pro-100-speaker-specs.598065/

Thanks!

 

[Wray & Ting]

By way of a more general inquiry about speaker design, if a speaker was designed to have a 4 ohm woofer, and it was replaced with an 8 ohm woofer, would the speaker have a poor bass response due to the higher impedance? I guess the crossover network would likely not work as intended either, with a different driver in the system.

 

[RTally]

By way of a more general inquiry about speaker design, if a speaker was designed to have a 4 ohm woofer, and it was replaced with an 8 ohm woofer, would the speaker have a poor bass response due to the higher impedance? I guess the crossover network would likely not work as intended either, with a different driver in the system.

By doubling the driver impedance, the crossover frequency for a first order LP filter is doubled if the inductor is not changed.

Since the other thread identifies the lower crossover as being 700Hz, you could apply test tones to the speaker to see if the woofer rolls off at 700 Hz or at 1400 Hz. I would disconnect the mid when running this test or place the mic directly in front and close to the woofer.

 

[Wray & Ting]

By doubling the driver impedance, the crossover frequency for a first order LP filter is doubled if the inductor is not changed.
Since the other thread identifies the lower crossover as being 700Hz, you could apply test tones to the speaker to see if the woofer rolls off at 700 Hz or at 1400 Hz. I would disconnect the mid when running this test or place the mic directly in front and close to the woofer.

Thanks, it's been nearly 20 years since I've had anything at all to do with RLC circuits. I suspect I would enjoy doing this sort of hands-on testing, but I haven't tried anything like that yet.

Keeping to the theoretical for the moment, would such a high low-pass frequency impair the overall output of low frequencies? At first glance, I would expect the overall mid-range output to suffer in that arrangement, where the mid driver isn't getting the 700-1400 Hz range that it's supposed to, and the woofer (presumably) can't produce sound in that range very well. Just thinking out loud here.

 

[Wray & Ting]

In a related note, I've discovered that my replacement Radio Shack 40-1035 15" woofers have a listed Q_TS value of 0.81, which according to my reading on speaker design makes them (very?) unsuitable for installation in a sealed enclosure. Sounds like a leading candidate for why the bass needs electronic boosting from my amp to sound balanced.