How do I know I need a new amp or to bi-amp?

[Sawtaytoes]

I'm wondering what would give me an indication of needing to buy a more powerful amp or if I should bi-amp my speakers (given the option).

My Setups
I have Polk Reserve R700s and they have two 8" woofers. These are subwoofer-sized, and subwoofers typically take a lot of power to sound good. Thing is, I don't know how to tell if I'm stressing my amps too much to driving these speakers.

It seems like all tower speakers are 4ohm, which means you'll actually get significantly more wattage driving them from any given amp than bookshelf speakers in the same line. No clue how that works, but this would make me think I'm probably fine with lower-wattage amps even though subwoofer-sized speakers tend to require significantly more power.

I have these speakers both on my computer and in my home theater:

1. For my computer, I have to turn the current amp way down (50%) to give a reasonable listening threshold at this close distance for 80W/ch @ 4ohm.
2. On my home theater system, both speakers are at -10dB to get 75dBc out of the Monolith X7 amp (300W/ch @ 4ohm).

Is there any indication I can use to verify if getting a more powerful amp or bi-amping would produce a better sound?

 

[TLS Guy]

I'm wondering what would give me an indication of needing to buy a more powerful amp or if I should bi-amp my speakers (given the option).

My Setups
I have Polk Reserve R700s and they have two 8" woofers. These are subwoofer-sized, and subwoofers typically take a lot of power to sound good. Thing is, I don't know how to tell if I'm stressing my amps too much to driving these speakers.

It seems like all tower speakers are 4ohm, which means you'll actually get significantly more wattage driving them from any given amp than bookshelf speakers in the same line. No clue how that works, but this would make me think I'm probably fine with lower-wattage amps even though subwoofer-sized speakers tend to require significantly more power.

I have these speakers both on my computer and in my home theater:

1. For my computer, I have to turn the current amp way down (50%) to give a reasonable listening threshold at this close distance for 80W/ch @ 4ohm.
2. On my home theater system, both speakers are at -10dB to get 75dBc out of the Monolith X7 amp (300W/ch @ 4ohm).

Is there any indication I can use to verify if getting a more powerful amp or bi-amping would produce a better sound?

Bi-amping is a waste of time and money. The Monolith amp provides all the power those speakers can handle. The F3 point of those speakers is 38Hz, so they do not really cover the last octave. Your best option is to invest in a good sub and offload the speakers and amp.

 

[Golfx]

Like TLS guy indicated that amp has ample power (actually more power than needed) for those speakers.

There is an excellent review on this website from 2016 https://www.audioholics.com/amplifier-reviews/monoprice-monolith-7-channel-amplifier-review/3 indicating over 500 watts at 4 ohms.

I’m confused though—you also have another pair of R700s which you are using on your computer?

As he suggested you will not have to worry about needed power—ever—if you get a subwoofer which would transfer low bass notes to the sub thus easing up the demand on both the R700s AND your amp.

 

[Sawtaytoes]

I do have subs on both systems and yes, I have another set of them on my computer.

That amp is an SMSL SA300 which is noted as a class D at 80 watts per channel at 4ohms. I use a Rolls crossover to ensure only stuff above ~50Hz gets passed to the speakers and the rest to the subs.

So having subwoofer-sized drivers isn't an issue so long as I keep the signal over X Hz.

 

[lovinthehd]

I wouldn't call 8 inch drivers sub sized myself. I wouldn't bother with passive bi-amping....

 

[Beave]

It seems like all tower speakers are 4ohm, which means you'll actually get significantly more wattage driving them from any given amp than bookshelf speakers in the same line.

You're looking at that all backwards. The lower impedance, the more power the speaker *demands* from the amp (assuming a given sensitivity). It's not that you *get* more power from the amp so much as that you *need* more power from the amp. It's not a good thing for a speaker to need more power from an amp to play at a given level (though it's not necessarily a problem either).

But as for your speakers, some shady fellow named James measured them on this very site https://www.audioholics.com/tower-speaker-reviews/polk-reserve-r700/conclusion
and he found sensitivity of almost 89dB with a fairly easy impedance load.

So you don't need a ton of power for these to get loud. What you have is plenty.

Also, I agree with the others that passive bi-amping is a waste of effort.

 

[Sawtaytoes]

I appreciate everyone's responses and links to Audioholics review pages.

I bought the Monolith amp and the Polk Reserve speakers only after reading the reviews on Audioholics. I'm already familiar with what's written in those articles, and that's why I asked on this forum.

A few things are bugging me:

1. No one's yet answered my question: how would I know if I need a more powerful amp or if I should bi-amp? What should I look for? Is there something I should be hearing? Can I measure it with an SPL meter, my phone, one of those omni mics I bought for REW (which I still haven't used), or through a receiver's calibration software? Just because the Monolith amp is good, that doesn't tell me if any other amp I buy is also good. Maybe I want to hook these up to a budget receiver in the future. How would I know if this is the right choice?
2. My computer setup isn't on the Monolith amp. This is why I want to know if I need a more powerful amp. I just bought another pair of these reserves for my computer and realized I'm not providing even close to as much power as the Monolith amp. Even though I'm sitting close to them, I still have absolutely no clue if I'm meeting their power requirements. In fact, I have no clue how much power these speakers draw on average at various dB ratings.
3. Every amp I've seen says it produces more power at a lower ohms rating. Does this mean the speaker is able to take more power out of an amp if the ohms rating is lower?
4. Why all the hearsay regarding bi-amping? This is the first time I'd ever heard of passive versus active bi-amping, but after looking it up (https://producerhive.com/ask-the-hive/bi-amping-speakers), I still don't understand why "passive bi-amping is a wasted effort". Sure, you might wind up in a Y-cable situation where you need matching hardware, but it can allow you to have more power if your amps don't provide it. I'd like to see some data rather than "it's bad because I know more than you". Pretty sure you learned this information somewhere. Either way, bi-amping isn't important to me as much as "how do I know if I need to be doing this thing?".
5. In one of the Audioholics YouTube videos from ~6 months ago, they noted the Polk Reserve might be a good case for bi-amping because of the 8" woofers. This is the reason I specifically brought that up.
6. I have a subwoofer with an 8" woofer. To me, anything 8" or over is subwoofer size. Why would that not be the case? As far as I've seen, 8" subs aren't even uncommon, and these woofers are designed to produce low-frequency sounds.

 

[TLS Guy]

I appreciate everyone's responses and links to Audioholics review pages.

I bought the Monolith amp and the Polk Reserve speakers only after reading the reviews on Audioholics. I'm already familiar with what's written in those articles, and that's why I asked on this forum.

A few things are bugging me:

1. No one's yet answered my question: how would I know if I need a more powerful amp or if I should bi-amp? What should I look for? Is there something I should be hearing? Can I measure it with an SPL meter, my phone, one of those omni mics I bought for REW (which I still haven't used), or through a receiver's calibration software? Just because the Monolith amp is good, that doesn't tell me if any other amp I buy is also good. Maybe I want to hook these up to a budget receiver in the future. How would I know if this is the right choice?
2. My computer setup isn't on the Monolith amp. This is why I want to know if I need a more powerful amp. I just bought another pair of these reserves for my computer and realized I'm not providing even close to as much power as the Monolith amp. Even though I'm sitting close to them, I still have absolutely no clue if I'm meeting their power requirements. In fact, I have no clue how much power these speakers draw on average at various dB ratings.
3. Every amp I've seen says it produces more power at a lower ohms rating. Does this mean the speaker is able to take more power out of an amp if the ohms rating is lower?
4. Why all the hearsay regarding bi-amping? This is the first time I'd ever heard of passive versus active bi-amping, but after looking it up (https://producerhive.com/ask-the-hive/bi-amping-speakers), I still don't understand why "passive bi-amping is a wasted effort". Sure, you might wind up in a Y-cable situation where you need matching hardware, but it can allow you to have more power if your amps don't provide it. I'd like to see some data rather than "it's bad because I know more than you". Pretty sure you learned this information somewhere. Either way, bi-amping isn't important to me as much as "how do I know if I need to be doing this thing?".
5. In one of the Audioholics YouTube videos from ~6 months ago, they noted the Polk Reserve might be a good case for bi-amping because of the 8" woofers. This is the reason I specifically brought that up.
6. I have a subwoofer with an 8" woofer. To me, anything 8" or over is subwoofer size. Why would that not be the case? As far as I've seen, 8" subs aren't even uncommon, and these woofers are designed to produce low-frequency sounds.

Your Monolith provides all the power your speakers can handle. If you increase the power, then you will blow your speakers. The 80 watt amp is too low a power for high volumes. Remember doubling amp power only gets you 3db more sound pressure. To double the loudness requires an amp 10 times more powerful. That is why I have a bank of amps that is 3,200 watts, which gives me twice the spl. of 320 watts of amp power.

Yes, a lower impedance amp will draw more power from the amp, as long as the amp can provide it. If it can't the amp is inclined to blow up.

The problem with passive bi-amping is that you are still incurring the losses of the passive crossover, and the higher the order of the crossover, the greater the losses. In the case of your Monolith it is fully driving those speakers. If you use two, then you stand a good chance of blowing up your speakers, especially the midrange. If you had a couple of 150 watts amps, you would be back where you started. I believe your speakers in bi-amp mode actually connect to the woofers, and mid tweeter. So if you had a 150 watt amp, and passive bi-amped with another 150 amp, you would gain 3db over using one 150 watt amp, but would be no better off than using one 300 watt amp. In general when passive bi-amping the HF amp just connects to the tweeter via the high pass crossover which only requires a few watts, so you gain nothing. Active bi-amping however allows for design techniques that allow for designing a superior speaker, employing techniques not possible with passive designs.

Your speakers specify an F3 of 38 Hz. So those drivers are not sub drivers. The Thiel/Small parameters of a driver determine whether or not a driver can be employed as a sub driver and NOT the size of the cone. Having said that, very few 8" drivers are actually sub drivers, and even when they are, they tend to be excursion limited. I know there are 8" subs around. However they are fraudulently advertised, and not in fact subs, and do not cover the last octave. In general they are pieces of excrement, designed to have a boomy bass above the last octave.

I hope this helps, but honestly you need extensive education in the science of sound reproduction as you have some serious misconceptions.

 

[ryanosaur]

I appreciate everyone's responses and links to Audioholics review pages.

I bought the Monolith amp and the Polk Reserve speakers only after reading the reviews on Audioholics. I'm already familiar with what's written in those articles, and that's why I asked on this forum.

A few things are bugging me:

1. No one's yet answered my question: how would I know if I need a more powerful amp or if I should bi-amp? What should I look for? Is there something I should be hearing? Can I measure it with an SPL meter, my phone, one of those omni mics I bought for REW (which I still haven't used), or through a receiver's calibration software? Just because the Monolith amp is good, that doesn't tell me if any other amp I buy is also good. Maybe I want to hook these up to a budget receiver in the future. How would I know if this is the right choice?
2. My computer setup isn't on the Monolith amp. This is why I want to know if I need a more powerful amp. I just bought another pair of these reserves for my computer and realized I'm not providing even close to as much power as the Monolith amp. Even though I'm sitting close to them, I still have absolutely no clue if I'm meeting their power requirements. In fact, I have no clue how much power these speakers draw on average at various dB ratings.
3. Every amp I've seen says it produces more power at a lower ohms rating. Does this mean the speaker is able to take more power out of an amp if the ohms rating is lower?
4. Why all the hearsay regarding bi-amping? This is the first time I'd ever heard of passive versus active bi-amping, but after looking it up (https://producerhive.com/ask-the-hive/bi-amping-speakers), I still don't understand why "passive bi-amping is a wasted effort". Sure, you might wind up in a Y-cable situation where you need matching hardware, but it can allow you to have more power if your amps don't provide it. I'd like to see some data rather than "it's bad because I know more than you". Pretty sure you learned this information somewhere. Either way, bi-amping isn't important to me as much as "how do I know if I need to be doing this thing?".
5. In one of the Audioholics YouTube videos from ~6 months ago, they noted the Polk Reserve might be a good case for bi-amping because of the 8" woofers. This is the reason I specifically brought that up.
6. I have a subwoofer with an 8" woofer. To me, anything 8" or over is subwoofer size. Why would that not be the case? As far as I've seen, 8" subs aren't even uncommon, and these woofers are designed to produce low-frequency sounds.

You've fallen in to the trap many do. I spent a lot of time researching bi-amping. Here's the kicker:
4 out of 5 boutique Speaker Designers said it's pointless. 1 Speaker designer thought it was pointless, but though bi-wiring was effective.

The thing is, you were answered, just not the way you wanted.
Speaker sensitivity will tell you how much power (usually 2.83v) is required to achieve a certain dB level at 1 meter. Shady measured the R700s at 89dB sensitivity and a nominal 6-ohm impedance. The impedance minima doesn't look like it dips below 5ohms in his measurements, and the worst phase angle does not coincide with that impedance minima.
In short, and as Shady reported: these are not a difficult load to drive.
Your Amp, in the Monolith, has more than enough power to handle them. You do not need more power.
But since you insist on asking... your Amp will deliver between 250w and 300w of power (maxed out) to your Speaker and it should produce approximately 113dB of output at 1m.
To be certain: this is an unhealthy SPL level that can produce hearing damage at sustained levels.
Again, you do not need more power.

Now... you make an assumption above that bi-amping will deliver more power to the Speakers.
This is not true.
The amount of power sent to the LF and HF sections of the XO... IS NOT ADDITIVE. The LF and HF sections of the passive XO network built into the Speaker will still see the same amount of power as they would if you just run the wiring conventionally, which is to say a single cable to a single pair of Binding Posts with the Jumper Bars in place.

Bi-amping is not bad. It just does not really do what everybody insists it does. At best, each Amp channel involved will see a different load (so to speak) but this will not result in a difference in SQ.
Perhaps if you had a much more demanding Bass section on your Speakers that required much more current at a severe phase angle, this could result in an audible difference, but you would likely need a more robust amplifier in that specific use case.
That being said, if you really just want to do it, go for it. Just do it properly, and no harm should befall your equipment. However, if you mess something up, you can quite possibly blow your Amp and Speakers both.
This is not meant to be a scare tactic: simply a warning.

Another issue: 8" Woofers? So what.
I have 8" Woofers in my Speakers. They don't require anything special.
My Subs are 13" Woofers. They have their own Amps. I am building 15" Subs. They will require more Power than my other Subs, but learning a little aboiut how these things work isn't difficult.
There are Speakers out there that use 10" and 12" Drivers that are not designed to be used as Subwoofers.
Subwoofers are a specific beast, but the usage is bastardized. I've see 4" Subwoofer Drivers on the market, and they should never be called "Subwoofer Drivers."

There is a lot to learn if you really want to get to know how Speakers and Amps operate. There are a lot of great resources here at AH and in other Forums and Web articles that can help you learn. Likewise, there are a lot of very knowledgeable cats her and at the other Audio Forums who will gladly help you learn more, as well. The caveat there is to not pretend that you know more than you do.

Please rest assured in knowing that your Monolith and R700s are a good match and will serve you well.

Cheers.

 

[ryanosaur]

Oh... and for everybody else... It's a Bi-Amp thread... DRINK!

The Official _/Unofficial/_ AH Drinking Game!

I've been joking about this for far, far too long. It started up as an idea in my head after AH was inundated with people buying lower-tier B&W Speakers and coming on the Forum to find out why they sounded like @$$ once they set them up in their home. :) After that, there were... other topics of...

forums.audioholics.com

 

[PENG]

I appreciate everyone's responses and links to Audioholics review pages.

I bought the Monolith amp and the Polk Reserve speakers only after reading the reviews on Audioholics. I'm already familiar with what's written in those articles, and that's why I asked on this forum.

A few things are bugging me:

1. No one's yet answered my question: how would I know if I need a more powerful amp or if I should bi-amp? What should I look for? Is there something I should be hearing? Can I measure it with an SPL meter, my phone, one of those omni mics I bought for REW (which I still haven't used), or through a receiver's calibration software? Just because the Monolith amp is good, that doesn't tell me if any other amp I buy is also good. Maybe I want to hook these up to a budget receiver in the future. How would I know if this is the right choice?

Unless I missed something, all your questions have been answered by now, but since you highlighted the first questions, I would like to add (or emphasize, if they have been posted already) the following links. Those calculators should help provide you with a clearer answer to your question related to your specific devices and applications.

Crown Audio - Professional Power Amplifiers
Peak SPL Calculator (hometheaterengineering.com)

Before you use any of those online calculators, be sure to read their instructions first just to make sure you input the correct information.

 

[AcuDefTechGuy]

I have Polk Reserve R700s and they have two 8" woofers. These are subwoofer-sized, and subwoofers typically take a lot of power to sound good. Thing is, I don't know how to tell if I'm stressing my amps too much to driving these speakers.

Dual 8” Woofers is equivalent to a single 12” Woofer in terms of surface area.

I would be comfortable with 100-200W into 8 ohms for single-amp or traditional passive bi-amp.

Now if you are doing “partial active bi-amp” where you remove the speaker jumpers and feed the Woofers with the Subwoofer Outputs from the AVR-to-External-Subwoofer-Amp, that would give you more control over those dual 8” woofers by treating them like separate subwoofers. NHT and RBH are 2 companies who have done this for a very long time on their towers.

Since you are NOT truly disconnecting the internal crossovers of the towers, this is not traditional ACTIVE bi-amp. But in effect, this treats it like active bi-amp. That’s why I call this “partial active bi-amp”.

Feed the AVR’s Sub output to a Subwoofer Amp. Here you are using an ”External XO” from AVR or Sub Amp. Then feed the Sub Amp to the dual Woofers’ speaker post.

But I would start out with the Sub-Amp volume Very Low and increase gradually.

This effectively turns your dual 8” woofers (equivalent to some 12” woofers) into separate subwoofers.

How do you know if your speakers need more power? For most people (I would guess 99% of people ), it’s an educational guess.

Your thinking about subwoofers needing more power is in line with many people. If my speakers had dual 10” (like the Polk L800 towers) or 12” Woofers, I would most definitely use a 200-300W into 8 ohms amp.

Will dual 8” woofers need 200-300W? They might. Or not. Kind of a maybe-maybe not area. It doesn’t hurt to use a 200W amp. But a 100W amp should be fine.

 

[lovinthehd]

Since we're already drinking, here's the Audioholics article on bi-amping / bi-wiring https://www.audioholics.com/frequent-questions/the-difference-between-biamping-vs-biwiring

As to subs, most of us look to response down to 20hz or better to be a true sub, I can't think of any 8" subs that can do that at a reasonable spl or distortion level.

ps For your desktop/nearfield use just how loud are you listening ?

 

[Sawtaytoes]

I think I understand now:

• An 8" woofer isn't really a sub because the response range isn't low enough (now I know ).
• 8" woofers don't require as much power as 10"+ woofers because they don't go low enough to need it.

Home Theater
Monolith amp is super fine for my listening level (under 75dBc according to my SPL meter). I'm only 8-10' away, and I have these both at -10dB on my receiver. Looks like distortion isn't on the table.
To be clear I wasn't asking if I should bi-amp, I was simply asking to know when I need more power and what to listen for. From what it looks like, I play it by ear and guess. There's no real way to know outside of some calculators without the same equipment Audioholics reviewers are using.

Thanks for the calculator links @PENG. These help a lot!

If I'm measuring correctly, my Monolith amp is way overkill. These speakers only use 7dBc at reference level. I could run them on anything it seems unless I'm misunderstanding.

Why wouldn't I just hook them directly up to my receiver? Is it because the Monolith amp has more headroom and a potentially higher quality output?

Computer
I didn't even think to measure how loud I was listening on my PC.

At my computer, I'm 3-5' away from my speakers at any given time. Even 1-2 watts is enough. Wow... Absolutely no need to upgrade my computer's speaker amp unless I want to use something higher quality. But this means distortion shouldn't be an issue on my PC either.

Right now, I have the volume pretty low while the baby's sleeping next to me: 63dBc. At a relatively loud, but still comfortable listening level, it's around 70dBc.

These numbers are correct as long as I'm using my SPL meter correctly and if the pink noise file I downloaded is playing at the correct volume:

• I downloaded Pink Noise from here: https://www.dynaudio.com/support/pink-noise. In the zip, I'm playing the file: 02 Uncorrelated Pink Noise.wav
• I made sure to use the default Windows music player and max out the volume when measuring.

 

[lovinthehd]

I think I understand now:

• An 8" woofer isn't really a sub because the response range isn't low enough (now I know ).
• 8" woofers don't require as much power as 10"+ woofers because they don't go low enough to need it.

Home Theater
Monolith amp is super fine for my listening level (under 75dBc according to my SPL meter). I'm only 8-10' away, and I have these both at -10dB on my receiver. Looks like distortion isn't on the table.
To be clear I wasn't asking if I should bi-amp, I was simply asking to know when I need more power and what to listen for. From what it looks like, I play it by ear and guess. There's no real way to know outside of some calculators without the same equipment Audioholics reviewers are using.

Thanks for the calculator links @PENG. These help a lot!

If I'm measuring correctly, my Monolith amp is way overkill. These speakers only use 7dBc at reference level. I could run them on anything it seems unless I'm misunderstanding.

Why wouldn't I just hook them directly up to my receiver? Is it because the Monolith amp has more headroom and a potentially higher quality output?

Computer
I didn't even think to measure how loud I was listening on my PC.

At my computer, I'm 3-5' away from my speakers at any given time. Even 1-2 watts is enough. Wow... Absolutely no need to upgrade my computer's speaker amp unless I want to use something higher quality. But this means distortion shouldn't be an issue on my PC either.

Right now, I have the volume pretty low while the baby's sleeping next to me: 63dBc. At a relatively loud, but still comfortable listening level, it's around 70dBc.

These numbers are correct as long as I'm using my SPL meter correctly and if the pink noise file I downloaded is playing at the correct volume:

• I downloaded Pink Noise from here: https://www.dynaudio.com/support/pink-noise. In the zip, I'm playing the file: 02 Uncorrelated Pink Noise.wav
• I made sure to use the default Windows music player and max out the volume when measuring.

Sensitivity can vary with driver size, so not all 10s need more power than 8s. Box size and type plays a role also.

 

[TLS Guy]

Dual 8” Woofers is equivalent to a single 12” Woofer in terms of surface area.

I would be comfortable with 100-200W into 8 ohms for single-amp or traditional passive bi-amp.

Now if you are doing “partial active bi-amp” where you remove the speaker jumpers and feed the Woofers with the Subwoofer Outputs from the AVR-to-External-Subwoofer-Amp, that would give you more control over those dual 8” woofers by treating them like separate subwoofers. NHT and RBH are 2 companies who have done this for a very long time on their towers.

Since you are NOT truly disconnecting the internal crossovers of the towers, this is not traditional ACTIVE bi-amp. But in effect, this treats it like active bi-amp. That’s why I call this “partial active bi-amp”.

Feed the AVR’s Sub output to a Subwoofer Amp. Here you are using an ”External XO” from AVR or Sub Amp. Then feed the Sub Amp to the dual Woofers’ speaker post.

But I would start out with the Sub-Amp volume Very Low and increase gradually.

This effectively turns your dual 8” woofers (equivalent to some 12” woofers) into separate subwoofers.

How do you know if your speakers need more power? For most people (I would guess 99% of people ), it’s an educational guess.

Your thinking about subwoofers needing more power is in line with many people. If my speakers had dual 10” (like the Polk L800 towers) or 12” Woofers, I would most definitely use a 200-300W into 8 ohms amp.

Will dual 8” woofers need 200-300W? They might. Or not. Kind of a maybe-maybe not area. It doesn’t hurt to use a 200W amp. But a 100W amp should be fine.

What you are not correct to say that two 8" speakers are equivalent to a 12" speaker. Two 8" will only double power handling, but will not change F3 or any other parameters. As I pointed out bass extension is governed largely by the Fs of the driver, but also other T/S parameters.

So whether he has 1,2,3 or 4 of those drivers in a vented enclosure, the F3 will still be 38 Hz.

 

[AcuDefTechGuy]

What you are not correct to say that two 8" speakers are equivalent to a 12" speaker. Two 8" will only double power handling, but will not change F3 or any other parameters. As I pointed out bass extension is governed largely by the Fs of the driver, but also other T/S parameters.

So whether he has 1,2,3 or 4 of those drivers in a vented enclosure, the F3 will still be 38 Hz.

You’re saying that a tower with four 8” bass woofers will have an F3 of only 38Hz (bass goes down to 38Hz at -3dB)?

And the Revel Salon2 with three 8” bass woofers will only have an F3 of 38Hz - so the bass goes down to only 38Hz at -3dB?

Revel Ultima Salon2 loudspeaker Measurements

Sidebar 3: Measurements My estimate of the Revel Ultima Salon2's voltage sensitivity was 86dB(B)/2.83V/m. This is slightly lower than the specified 86.4dB but within experimental error of that figure. The speaker's impedance (fig.1) drops to between 3 and 5 ohms between 17Hz and 600Hz, but as...

www.stereophile.com

Isn’t the anechoic F3 about 20Hz in that measurement?

 

[TLS Guy]

You’re saying that a tower with four 8” bass woofers will have an F3 of only 38Hz (bass goes down to 38Hz at -3dB)?

And the Revel Salon2 with three 8” bass woofers will only have an F3 of 38Hz - so the bass goes down to only 38Hz at -3dB?

Revel Ultima Salon2 loudspeaker Measurements

Sidebar 3: Measurements My estimate of the Revel Ultima Salon2's voltage sensitivity was 86dB(B)/2.83V/m. This is slightly lower than the specified 86.4dB but within experimental error of that figure. The speaker's impedance (fig.1) drops to between 3 and 5 ohms between 17Hz and 600Hz, but as...

www.stereophile.com

Isn’t the anechoic F3 about 20Hz in that measurement?

No, you have missed the point. No matter how many drivers of the same drivers used in the Polk speakers you used the lowest F3 point would not change. However, if you used drivers with different T/S parameters then you can get a much lower F3. However as you lower the achievable F3 then the driver will have lower sensitivity and also have excursion limitations. So you end up having to use more of them. So, it is more cost effective to use a bigger driver in the first place. However, if it is not a sub, then you are committed to a speaker with a wide front panel and diffraction issues. That is why I designed my cabinets the way I did, to solve that problem.

This goes back to the issue of why pro subs have a significantly higher F3 than domestic ones. The reason is that the pro drivers have much higher flux density in the magnets, and have much higher sensitivity, to achieve adequate spl. in large spaces.

The take home is that there is an inverse ratio between sensitivity/efficiency and spl.

 

[AcuDefTechGuy]

No matter how many drivers of the same drivers used in the Polk speakers you used the lowest F3 point would not change. However, if you used drivers with different T/S parameters then you can get a much lower F3.

If someone were to ADD two more 8" woofers to the Polk R700 to make it FOUR 8" Woofers, they would have to use a much BIGGER Cabinet with different parameters/design. They are not going to put 4 x 8" bass woofers into the same size cabinet and parameter as the Polk R700.

The point is that MATHEMATICALLY two 8" woofers have about the same SURFACE AREA as a single 12" woofer. And given certain speaker designs/parameters, the dual 8" woofers could have SIMILAR F3 as a single 12" woofer.

We are not saying that all dual 8" woofers will have the same F3 as all single 12" woofers.

 

[TLS Guy]

If someone were to ADD two more 8" woofers to the Polk R700 to make it FOUR 8" Woofers, they would have to use a much BIGGER Cabinet with different parameters/design. They are not going to put 4 x 8" bass woofers into the same size cabinet and parameter as the Polk R700.

The point is that MATHEMATICALLY two 8" woofers have about the same SURFACE AREA as a single 12" woofer. And given certain speaker designs/parameters, the dual 8" woofers could have SIMILAR F3 as a single 12" woofer.

We are not saying that all dual 8" woofers will have the same F3 as all single 12" woofers.

Well of course you have to increase cabinet size as you add drivers. If you have two drivers, then that doubles the VAS, and that means you have to double the cabinet size, if you add four then you have to quadruple it. The point is that although the cabinet size will increase, the F3 won't using the same drivers. However sensitivity will increase which is the major gain. This occurs not only because of the addition, but also the impedance drop.
So two 8 ohm drivers in parallel will give you 6db more sensitivity over one. That is 3db for halving the impedance and 3db from the proximity driver coupling. That is just another illustration of Hoffman's iron man's law.