Distortion & 80Hz HPF

[HareBrained]

I'm looking at designing a speaker that will only be used with an active 80Hz 2nd-order high-pass filter. I'm going to be using the Fountek FR88-EX, which is a very low distortion driver (probably qty=1 to keep the cost down). I'm thinking either the DQ25 or the NE19 AL. The woofer is giving me some trouble.

I'd like to use a sub-$50 driver that can play from 80-~350Hz. But I think I want a low distortion as possible. So, I've been looking at a bunch of measurements and I have a question. If I'm using a HPF, do the IB full sweep measurements still accurately reflect the expected performance for that driver? Or at least, will the relative performance for a given set of drivers be the same?

Will the HPF alter the expected performance making what would be considered a "high" distortion driver into something more acceptable? For example, the DA175-8 isn't very clean, but if limited to 80Hz and above, does the distortion improve?

[critofur]

Re: Distortion & 80Hz HPF

Look at Zaph's distortion measurements? It looks pretty clean down to 80 Hz ~ 50 db down.

I built a pair of BAMTMs and my measurements matched his fairly well.

[Pete Schumacher]

Re: Distortion & 80Hz HPF

I'm looking at designing a speaker that will only be used with an active 80Hz 2nd-order high-pass filter. I'm going to be using the Fountek FR88-EX, which is a very low distortion driver (probably qty=1 to keep the cost down). I'm thinking either the DQ25 or the NE19 AL. The woofer is giving me some trouble.

I'd like to use a sub-$50 driver that can play from 80-~350Hz. But I think I want a low distortion as possible. So, I've been looking at a bunch of measurements and I have a question. If I'm using a HPF, do the IB full sweep measurements still accurately reflect the expected performance for that driver? Or at least, will the relative performance for a given set of drivers be the same?

Will the HPF alter the expected performance making what would be considered a "high" distortion driver into something more acceptable? For example, the DA175-8 isn't very clean, but if limited to 80Hz and above, does the distortion improve?

The DA175 is actually quite clean across the spectrum, especially if it is relieved of low bass duties. Its limited Xmax becomes an issue as volume is increased.

I've built a few systems using the DA175, and the thing I noticed with the TM was that when it was used on the HT receiver with HP enabled, midrange performance noticeably improved, allowing it to play to much higher SPL cleanly. And when it's not straining under bass duties, it's a very musical performer.

Distortion levels are way below 1% from 100Hz up at 86dB output, typical listening levels.



A slightly cleaner unit still would be the RS180, but it pushes outside your budget.

[HareBrained]

Re: Distortion & 80Hz HPF

Thanks for the responses. Although my question wasn't about the DA175 directly, I believe I can filter out the answers from the statements.

Essentially, if applying a HPF, only the distortion above that point is of concern and that the sonic performance does improve. But there doesn't appear to be any definitive improved in the distortion performance because of the filter.

I'm actually leaning towards the RS150-4 vented. HD above 80hz is better than -60db and I believe I'll need the extra efficiency of the 4-ohm driver. Or I could use the RS180-4 sealed.

[Pete Schumacher]

Re: Distortion & 80Hz HPF

Thanks for the responses. Although my question wasn't about the DA175 directly, I believe I can filter out the answers from the statements.

Essentially, if applying a HPF, only the distortion above that point is of concern and that the sonic performance does improve. But there doesn't appear to be any definitive improved in the distortion performance because of the filter.

I'm actually leaning towards the RS150-4 vented. HD above 80hz is better than -60db and I believe I'll need the extra efficiency of the 4-ohm driver. Or I could use the RS180-4 sealed.

Go sealed. It better compliments the HP function on most receivers to create a 4th order slope overall. That's the usual target for the sub channel as well.

Distortion in the midrange is not reduced from the levels you see in a distortion sweep by HP filtering. But under actual usage, the removal of the signals that use up the linear excursion will allow the driver to perform to higher SPLs while remaining linear.

[HareBrained]

Re: Distortion & 80Hz HPF

The reasoning for going sealed is a very good one. And after reviewing numerous drivers, it would appear that the RS180-4 is that best compromise of size, dbs, and F3 in a sealed box. The DA175 does look good in price and F3, but is insufficient in SPL. And a pair is more expensive than the RS180. Now I've got to decide on a tweeter. I was thinking something less expensive, but I'm now looking at the Seas 22TAFG.

[Pete Schumacher]

Re: Distortion & 80Hz HPF

The reasoning for going sealed is a very good one. And after reviewing numerous drivers, it would appear that the RS180-4 is that best compromise of size, dbs, and F3 in a sealed box. The DA175 does look good in price and F3, but is insufficient in SPL. And a pair is more expensive than the RS180. Now I've got to decide on a tweeter. I was thinking something less expensive, but I'm now looking at the Seas 22TAFG.

Go with the RS28A or RS28F. Both can cross low to the RS180, and 1500Hz is a good spot. The TAFG is not good below 2500Hz, and you're really pushing the RS180 to go that high. The reason I say "pushing" is that the resonance modes of the RS180 need to be taken care of, and the lower you cross, the more effective the notch will be in keeping sub harmonics of the notch frequencies out of the passband.

If you did go with the pair of DA175, you don't have to worry about a notch filter, and while the pair would cost more, you will get more peak SPL from the DA175 due to the increased overall displacement.

[Deward Hastings]

Re: Distortion & 80Hz HPF

Go with the RS28A or RS28F. Both can cross low to the RS180, and 1500Hz is a good spot.

Pete's exactly right . . . the RS180 is excellent from 80 to 1500 Hz. With proper box size you get a 80 Hz. B2 lf rolloff that works perfectly with a 2nd order highpass at 80 Hz. Add a LR4 (active) lowpass at 1400-1600 Hz. to keep signal off the cone in its "problem" regions and you're golden. It's a perfect match for the RS28 tweeters too . . .

Actually the same applies with the RS150, but in a smaller box with lower overall output . . .

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Re: Distortion & 80Hz HPF

i will agree with pete. i have the da175-8 mtm. crossed at 60 i get distortion. at 80, they really shine................loud.

[HareBrained]

Re: Distortion & 80Hz HPF

BTW, I'm designing an inexpensive 3-way using the Fountek FR88-EX as the mid, as stated in the first post. Much of the concerns stated are not an issue.