Enclosure for a Hemp FR8C

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Scottmoose

Not particularly well. Doesn't have sufficient volume for the driver to get LF gain up to a useful level. Increase the CSA to 198in^2 up from 104.5in^2 & you'll be flat to the high 30Hz zones.

G

Scottmoose said:
Not particularly well. Doesn't have sufficient volume for the driver to get LF gain up to a useful level. Increase the CSA to 198in^2 up from 104.5in^2 & you'll be flat to the high 30Hz zones.

I could do 10" x 20" x42" cabinets. I have the room. What length would you make the port tube off the top of your head?

Scottmoose

4in diameter x 2in long.

G

With the high QT I won't need a BSC circuit I'm assuming.

G

Scottmoose said:
Not particularly well. Doesn't have sufficient volume for the driver to get LF gain up to a useful level. Increase the CSA to 198in^2 up from 104.5in^2 & you'll be flat to the high 30Hz zones.

Have you modeled these dimensions using the TS parameters for a FR8C Scott or is this a best guess? Just curious.

Scottmoose

Not a guess, the dimensions are my own calculation -I quickly checked in MathCAD to confirm.

Baffle-step is unrelated to driver Q. It's to counter the transition from 2pi to 4pi radiation space & the resultant SPL drop-off at the listening position below this point. With as wide a baffle as you can manage, you should be able to push it down a reasonable way, to a point where room-gain will take over, or for positioning near a rear-wall. The FR8C does have a reputation for being a touch bright, so a notch-filter & zobel (similar principle, different reason) might help to tame it. Depends on your taste & the room.

G

Scottmoose said:
Not a guess, the dimensions are my own calculation -I quickly checked in MathCAD to confirm.

Baffle-step is unrelated to driver Q. It's to counter the transition from 2pi to 4pi radiation space & the resultant SPL drop-off at the listening position below this point. With as wide a baffle as you can manage, you should be able to push it down a reasonable way, to a point where room-gain will take over, or for positioning near a rear-wall. The FR8C does have a reputation for being a touch bright, so a notch-filter & zobel (similar principle, different reason) might help to tame it. Depends on your taste & the room.

Thanks for the reply Scott. So just to double check I should use a CSA of 198^2, a height of 42", measured on the inside of the enclosure and just use the normal center for the speaker and port as shown on Martins diagram with a port length of 2" correct?

Nanook

an alternative enclosure...

Check out the Demetri w/ baffle step

easy to build, and works well (I've been listening to them for a month now and really enjoy them).

Scottmoose

Yes. Or, just use Dimitri, as Stew suggests.

G

I would love to build the Dimitri. The problem lies with the dimensions of the enclosure. My space is restricted as far as width goes.

G

Scottmoose said:
Not a guess, the dimensions are my own calculation -I quickly checked in MathCAD to confirm.

Baffle-step is unrelated to driver Q. It's to counter the transition from 2pi to 4pi radiation space & the resultant SPL drop-off at the listening position below this point. With as wide a baffle as you can manage, you should be able to push it down a reasonable way, to a point where room-gain will take over, or for positioning near a rear-wall. The FR8C does have a reputation for being a touch bright, so a notch-filter & zobel (similar principle, different reason) might help to tame it. Depends on your taste & the room.

I will probably modify the existing notch filter (Zobel didn't sound very good with SE amp to my ears) that I am using now to go with the speakers.

Nanook

Bright?

I don't think so. my FR8c are the current type, and if anything some have suggested they are not bright enough (perhaps a super tweeter would be suitable).

My recommendation, RE: too bright. Give the drivers 100 hours or so to break in. if you feel you need top end attenuation, after that, then do it...

planet10

Paid Member
Re: Bright?

Nanook said:
my FR8c are the current type, and if anything some have suggested they are not bright enough (perhaps a super tweeter would be suitable).

The ones with the whizzerectomy?

dave

Nanook

whizzerectomied ones....

even when they had their whizzers I never thought them too bright

stew

pjanda1

It sounds like you've got the Hemps in some enclosures now and you're using a notch filter. Does your current enclosures have BSC? If not, that is why they sound bright. I bet you won't need the notch filter with proper BSC (or enclosures that don't need it, like BIB's). The only Hemp speakers that are bright are those made with shorting rings, like the earliest Hemp Acoustics models. You'll want some sort of shelving circuit with those. Not too many were made, so I doubt that's what you've got. Like most drivers, the Hemps greatly benefit from some break in. It's best accomplished in free air and out of phase, so you get plenty of excursion without damaging your ears or annoying folks. Break in could be an issue to, but only if you've got BSC taken care of.

pj

Nanook

no notch filter...

only BSC. The "not bright enough" comments were prior to the BSC (passive) being implemented. Those that had commented haven't been by the house to do a comparison for themselves.

stew

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