Plugging Ported Speakers - What does The Amp See?

[<eargiant]

What effect does plugging a ported speaker (designed with that option) have on the amplifier? I'm curious to know if the load on the amp is increased, decreased or does it remain the same?

Thanks in advance.

 

[tyhjaarpa]

It should stay the same as the amp don't know if you have the plugs in or not. If you change this configuration you should run your room correction again as it will change the sound speakers produce.

 

[TLS Guy]

What effect does plugging a ported speaker (designed with that option) have on the amplifier? I'm curious to know if the load on the amp is increased, decreased or does it remain the same?

Thanks in advance.

It will change the impedance in the tuning area. Ported there will be too peaks of impedance either side of the tuning frequency. When you plug the port there will be one peal of impedance.

This is really not such a good idea. The box has to be optimized for the tuned state or it does not work. That leaves an over sized cabinet when the port is plugged.

In addition in the plugged state the enclosure is under damped. A ported enclosure is lightly damped whereas a sealed enclosure should be heavily damped.

This whole concept s just a lousy idea.

 

[tyhjaarpa]

It will change the impedance in the tuning area. Ported there will be too peaks of impedance either side of the tuning frequency. When you plug the port there will be one peal of impedance.

This is really not such a good idea. The box has to be optimized for the tuned state or it does not work. That leaves an over sized cabinet when the port is plugged.

In addition in the plugged state the enclosure is under damped. A ported enclosure is lightly damped whereas a sealed enclosure should be heavily damped.

This whole concept s just a lousy idea.

Some speaker manufacturers provide plugs for ports, like KEF does for the R series. So I would assume some speakers are designed to work like that, but ofc this does not apply to all speakers. I myself haven't bothered to play with the plugs to see what kind of effect it would have.

 

[TLS Guy]

Some speaker manufacturers provide plugs for ports, like KEF does for the R series. So I would assume some speakers are designed to work like that, but ofc this does not apply to all speakers. I myself haven't bothered to play with the plugs to see what kind of effect it would have.

You can't design it like that, Physics is physics. No driver is going to have the optimal box size the same ported or sealed and that is before we get to damping.

This really all comes about because commercial manufacturers play the "my F3 is lower than yours" game. The result is boomy speakers that is avoidable. So then they give you a plug for the port to tame the boom. This results in a much higher F3 although the roll off is now 12 db per octave rather than 24 db per octave. However the boxes are damped for ported and there is not enough fill for the sealed application to damp the box resonance.

If you do prefer the speaker with the port plugged, then you should remove a driver and fill the cabinet completely with Polyfill, but not compress it. You will like it even better then.

 

[<eargiant]

The speakers in question are Bowers & Wilkins 805D2's used solely with a 2 channel amp so no room correction. I have them a bit closer to the front wall than what is optimal as per B&W's recommendations. Plugging the ports (as B&W recommends in a situation like mine) took care of the accentuated bass being created by their proximity to the wall and the fireplace they flank. They now sound as clean as they do away from the wall with no added artificial bass.

Although plugging them reduces bass output I suspected that it would slightly increase their impedance. If I'm understanding this correctly, that is the case.

 

[TLS Guy]

The speakers in question are Bowers & Wilkins 805D2's used solely with a 2 channel amp so no room correction. I have them a bit closer to the front wall than what is optimal as per B&W's recommendations. Plugging the ports (as B&W recommends in a situation like mine) took care of the accentuated bass being created by their proximity to the wall and the fireplace they flank. They now sound as clean as they do away from the wall with no added artificial bass.

Although plugging them reduces bass output I suspected that it would slightly increase their impedance. If I'm understanding this correctly, that is the case.

No it lowers the impedance.

 

[<eargiant]

No it lowers the impedance.

Oops, that's what I meant. I phrased it incorrectly, I meant it increases the load (lower ohm speaker impedance) on the amp.

Thanks for confirming.

 

[TLS Guy]

Those speakers are on the warm side with a slight hump in the 100 to 130 Hz region. Referenced to 500 Hz there is a peak of 5 db at 70 Hz.

This is the measured response of your speakers.

I really hate that type of response. Yes, placing it too close to a boundary will make it much worse.

I rest my case. This is exactly what I'm talking about. The speaker is tuned too low, and you get this peaked response so that you get and F3 in the 40 Hz region from a small speaker. The cost is not acceptable. If the speaker had been tuned as it should have been for a flat minimal ripple response the F3 would be higher but the speaker would sound much better.

So now the manufacturer has the gall to invite you to put lipstick on the proverbial pig, by plugging the port!

Everyday I thank my lucky stars I don't have to go into the market place and purchase speakers.

 

[<eargiant]

Those speakers are on the warm side with a slight hump in the 100 to 130 Hz region. Referenced to 500 Hz there is a peak of 5 db at 70 Hz.

This is the measured response of your speakers.

I really hate that type of response. Yes, placing it too close to a boundary will make it much worse.

I rest my case. This is exactly what I'm talking about. The speaker is tuned too low, and you get this peaked response so that you get and F3 in the 40 Hz region from a small speaker. The cost is not acceptable. If the speaker had been tuned as it should have been for a flat minimal ripple response the F3 would be higher but the speaker would sound much better.

So now the manufacturer has the gall to invite you to put lipstick on the proverbial pig, by plugging the port!

Everyday I thank my lucky stars I don't have to go into the market place and purchase speakers.

They don't sound the way that Graph would lead you to believe. Don't ask me why. They have one of the cleanest, most realistic low-ends out there and they're probably one of the least "warm" speakers I've had here in a while.

I owned the stand-mount speakers that produced the Graph below for almost 2 years.

Side by side (in real life-not on paper) the ones in the graph above have an indisputable "boost" or "hump" in the lower region. The difference was not subtle, the low end of the 805D2's was almost anemic in comparison. With the ones in the graph above, I was able to get away without using a sub because of the accentuated low end they were producing. When I replaced them with the 805D2's (in the same position & unplugged) I decided to purchase a REL S/2 sub to fill in the low end that was now missing. I was OK with that because the 805D2's had exactly what I was looking for, I gained so much even though I lost some of the "perceived" low end (even before plugging). If I had only compared their respective graphs, I wouldn't have expected that to be the case.

IMO when it comes to speakers, sometimes the "Graph" can mislead. A graph cannot tell you how resolving a speaker is or how much air and clarity it has. It cannot tell you when a speaker sounds muffled or thick. Some speakers can create a holographic image with pin-point preciseness that no graph can measure. Had I just been comparing the graphs, I would have thought that the ones depicted above would have been more neutral, flatter and with less of a "peaked response" in the lower region than the 805D2's. They were not.

When it comes to speakers, I've learned to trust my ears and not give so much weight to what the "Graph" looks like (I'm less flexible when it comes to amp measurements). While a speaker graph can be a good guide, it does not tell the whole story and in some cases can be misleading.

 

[Dennis Murphy]

Those speakers are on the warm side with a slight hump in the 100 to 130 Hz region. Referenced to 500 Hz there is a peak of 5 db at 70 Hz.

This is the measured response of your speakers.

.

That's a Stereophile plot. The bass hump is due to the splicing of a nearfield measurement for the woofer to quasi-anechoic 1-meter above 350 Hz. Virtually all of the Stereophile plots look like that unless the speakers is seriously deficient in the bass. Or, to quote John Atkinson, who did the measurement:
"The upper-bass peak in their output will therefore be due to the assumption in the nearfield measurements that the drive-units are operating in a 2pi acoustic environment; ie, mounted in a baffle that extends to infinity in all directions." I'm much more concerned by the treble peaks, and the poor
waterfall plot shown elsewhere in the review. But I do agree that the box volume for a ported alignment for given drivers will not be optimal for a sealed cabinet.

 

[Dennis Murphy]

They don't sound the way that Graph would lead you to believe. Don't ask me why. They have one of the cleanest, most realistic low-ends out there and they're probably one of the least "warm" speakers I've had here in a while.

I owned the stand-mount speakers that produced the Graph below for almost 2 years
.

Good heavens. What speaker is that? I've never seen a Stereophile plot like that. I agree about your comments concerning the limitations of a simple on-axis plot, but if that speaker sounded bloated, it would have measured that way given that a truly flat speaker will always measure with a hump using John Atkinson's protocol. Something isn't right here.

 

[<eargiant]

Good heavens. What speaker is that? I've never seen a Stereophile plot like that. I agree about your comments concerning the limitations of a simple on-axis plot, but if that speaker sounded bloated, it would have measured that way given that a truly flat speaker will always measure with a hump using John Atkinson's protocol. Something isn't right here.

Hi Dennis, honored to see you on this thread. I happen own a set of your original AA Monitors, you really "fixed" those little Pioneers. All those people that were giving the originals rave reviews (I was not a fan) would fall off their chairs if they heard your modified versions. I never got around to setting them up anywhere but I won't sell them because they're excellent budget speakers. I'll find a spot for them sooner or later. I've recommended your new AA's many times when people ask for opinions on a pair of excellent affordable speakers. I would have liked to try your Phil 3's but they weren't going to fit properly in my room layout so I had to pass. The BMR's really interested me also, but again, I thought the location where I have my stand-mounts (added room response) and rear port was going to be an issue especially since they already go so low. If I had had my stand-mounts in an ideal open space, I probably wouldn't have hesitated to order them.

I respect your abilities so I'll answer your question. The speakers in the graph I posted are the Polk LSiM 703's. I was going to avoid mentioning them because I'm not trying to knock them. They're excellent speakers and I enjoyed them immensely, just different. Regardless of what the graphs would lead one to believe, I felt that even in free space the 703's provided noticeably deeper bass (within their range) than the 805D2's. I used to tell people that the 703's thought they were small floor-standers! I only used their graph to make my point. In the end, the 805D2's provided more of what I was looking for.

Either way, it seems you understand the point I was trying to make (based on experience not knowledge) about graphs.

 

[Dennis Murphy]

Hi Dennis, honored to see you on this thread. I happen own a set of your original AA Monitors, you really "fixed" those little Pioneers. All those people that were giving the originals rave reviews (I was not a fan) would fall off their chairs if they heard your modified versions. I never got around to setting them up anywhere but I won't sell them because they're excellent budget speakers. I'll find a spot for them sooner or later. I've recommended your new AA's many times when people ask for opinions on a pair of excellent affordable speakers. I would have liked to try your Phil 3's but they weren't going to fit properly in my room layout so I had to pass. The BMR's really interested me also, but again, I thought the location where I have my stand-mounts (added room response) was going to be an issue especially since they already go so low. If I had had my stand-mounts in an ideal open space, I probably wouldn't have hesitated to order them.

I respect your abilities so I'll answer your question. The speakers in the graph I posted are the Polk LSiM 703's. I was going to avoid mentioning them because I'm not trying to knock them. They're excellent speakers and I enjoyed them immensely, just different. Regardless of what the graphs would lead one to believe, I felt that even in free space the 703's provided noticeably deeper bass (within their range) than the 805D2's. I used to tell people that the 703's thought they were small floor-standers! I only used their graph to make my point. In the end, the 805D2's provided more of what I was looking for.

Either way, it seems you understand the point I was trying to make (based on experience not knowledge) about graphs.

Thanks for the nice comments--I'm glad you liked the little Pioneers. I'll have to read the review of the Polks and see if I can figure out what's up with that graph.

 

[Beave]

I've always wondered about JA's measurements of the Polk LSiM 703's. I'm not sure he got the bass measured correctly. That plastic piece on the rear port might have messed up his measurements, or he didn't add the port output to the woofer output correctly.

In any case, the speakers were also measured at the NRC, and they show that there is actually a small hump around 100Hz. Otherwise they're fairly flat in the bass, and they're not *way* underdamped like JA's measurements show.

http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=839:nrc-measurements-polk-audio-lsim703-loudspeakers&catid=77:loudspeaker-measurements

 

[Dennis Murphy]

I've always wondered about JA's measurements of the Polk LSiM 703's. I'm not sure he got the bass measured correctly. That plastic piece on the rear port might have messed up his measurements, or he didn't add the port output to the woofer output correctly.

In any case, the speakers were also measured at the NRC, and they show that there is actually a small hump around 100Hz. Otherwise they're fairly flat in the bass, and they're not *way* underdamped like JA's measurements show.

http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=839:nrc-measurements-polk-audio-lsim703-loudspeakers&catid=77:loudspeaker-measurements

I checked out a number of NRC measurements just to make sure that bass hump isn't common--and it isn't--quite the opposite. . So if it measures that way in an anechoic chamber, it would probably sound even worse in a normal room. Your ears are obviously more accurate than John's Stereophile measurement. He must have been up late the night before.

 

[<eargiant]

I checked out a number of NRC measurements just to make sure that bass hump isn't common--and it isn't--quite the opposite. . So if it measures that way in an anechoic chamber, it would probably sound even worse in a normal room. Your ears are obviously more accurate than John's Stereophile measurement. He must have been up late the night before.

Not sure I follow...Did you mean my ear or Beave's?

 

[Beave]

Well, considering my ears have never heard the Polks, I'm hoping/guessing he's referring to your ears!
All I can go by is the measurements I've seen for them.

 

[<eargiant]

Well in that case, I'm flattered to have a comment like that come my way from none other than Dennis Murphy himself. Dennis, thanks for taking the time and confirming what my ears perceived regardless of what the graphs said.

My original load/impedance question was answered. Seems counter intuitive but it's what I was expecting. The amp works harder even though audible bass output is less.

I wanted to make a final point about plugging ports. I really don't see it as a manufacturer "putting lipstick on a pig". The way I see it, in many cases the "hump" does not come with the speakers but is a byproduct of the room and speaker placement. Very few listening rooms/positions are perfect. A difference of a few inches in speaker placement can be dramatic. Sometimes plugging (or partially plugging) the port in certain situations where placement is not optimal (if recommended by the manufacturer) is the lesser of two evils and can yield excellent results.