Blocking the ports on the JBL 4645!

[JBL 4645]

Does blocking of one or two of the three ports curse the sub to responded lower in frequency response when tested with an RTA and SPL db?

Will it curse of the sub bass driver to going into excursion via limiting the loudness of the sub bass driver?

Noted the newer JBL 4645B has two ports that extend downwards into the enclosure with 45º bends the frequency response shows a lower response.

JBL 4645C has a single pot slightly winder than the others yet the frequency response shows a lower response.

So will blocking up of one or two of the ports curse risk of damage to the sub bass driver?

[Zilch]

I think I'd leave it alone.

Download WinISD and play with the numbers, perhaps, but that one has been precisely and optimally tuned, I believe....

[JBL 4645]

Zilch

Just the kinder response I was predicting.

Would you believe if I told you someone form the sound & vision site say it will work if I where stuff bathroom towels in the ports! Now that sounds nuts I tried it and noticed the bass response dropping like a stone in water!

[Zilch]

HEY!

That was MY idea!!

[JBL 4645]

Zilch

The use of bathroom towels you’re saying you’re the king of stuffing the ports up with “bathroom towels” is your discovery.

[JBL 4645]

It seems like a good discovery but should be mentioned it could curse the risk of damage to the sub bass driver. I’ve seen it come close doing it this way via blocking off two ports and with a film like Back to the Future where the Delorean approaches the clock tower with a thunder clap low end response that slams very high at 25Hz this would be a few seconds before it hits the lighting conductor. Also at the end of the film where it blasts off, not cool blocking off the ports, it limits the movement of the driver and quite frankly I don’t what to see the sub end up like that LOL, HUGE thing at the beginning of the film.

[sourceoneaudio]

It will reduce bass output -3 db or greater. Ports have two purposes, must be used with a bass reflex driver, and second at the given TFP you get a 3db gain. TFP 's on bigger drivers are usually 30 to 35 hz sometimes lower as long as the driver can handle the excursion factors. Also if you block any of them you will raise the TPF, and bass quality will go south very qwik.

Jeff
J/S-S1A

[sourceoneaudio]

It seems like a good discovery but should be mentioned it could curse the risk of damage to the sub bass driver. I’ve seen it come close doing it this way via blocking off two ports and with a film like Back to the Future where the Delorean approaches the clock tower with a thunder clap low end response that slams very high at 25Hz this would be a few seconds before it hits the lighting conductor. Also at the end of the film where it blasts off, not cool blocking off the ports, it limits the movement of the driver and quite frankly I don’t what to see the sub end up like that LOL, HUGE thing at the beginning of the film.

Those look look like Altec Horns used as exhaust tips?
Never noticed that before.

Jeff
J/S-S1A

[JBL 4645]

sourceoneaudio

Thanks. Well I use the ports as there designed for the sub.

LOL, hmm, they kinder look horns now that you mentioned it