How do I get my 6 7" woofers moving?

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P

PENG

Audioholic Slumlord
I think he wants us to tell him more power will make his RTi12 sound better.

Actually I think he should get a hold of a 300W amp (borrow, buy from a place that allows open box return, rent, or whatver), plug a CD player directly into the amp, stay back at least 15 ft, then use the remote to turn on the CD player and hear for himself. He may want to have some ear plugs handy just in case, as there won't be any volume control unless his CD player has the variable output feature. Also, to avoid damaging both speaker, he may want to try just one speaker.
 
dorokusai

dorokusai

Full Audioholic
Dorokusai. I know you are a Polk rep, but here is the info from the Polk website.

Overall Frequency Response 18Hz-27kHz
Lower -3dB Limit 30Hz
Upper -3dB Limit 26kHz
Nominal Impedance 8 ohms
Recommended Amplifier Power 50-500 w/channel
Efficiency 90 dB
Crossover
(mid-high array) 1.8kHz, 12dB/octave low and high pass. 120Hz 12dB/octave high pass
Crossover
(subwoofer) 120Hz, 12dB/octave low pass
Inputs Dual (bi-amp) gold plated 5-way binding posts

So clearly there is a passive crossover at 120 Hz. I'm sorry, but that's a mess. It is too low a frequency to get satisfactory performance from passive components. If you want the crossover at that point, then the three LF units need to be actively powered.
TLS - Roger that. I don't have every spec in the head since its too small, and you are correct. I'm trying to dig up some graphs so I can look at them in regards to G's comments on his findings via software. It all sounds like a case of something we've both read before. I'll bust my head open over a problem but at some point, its time to cut the losses. Not every speaker is going to do what you expect, it's the nature of the beast.

I'd like to get some comments from the engineering department in regards to the 120hz filter. When I get through jousting with them, I'll post the comments verbatim. It isn't going to be a ping pong tournament so what I get, is what I get....you know what I mean?

Mark
Polk Audio CS
 
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G

GeorgeH

Enthusiast
So clearly there is a passive crossover at 120 Hz. I'm sorry, but that's a mess. It is too low a frequency to get satisfactory performance from passive components. If you want the crossover at that point, then the three LF units need to be actively powered.
I'm curious - what would you consider an acceptable lower limit for a LF crossover point in a passive three- or four-way speaker? What goes wrong when you go below this limit?
 
TLS Guy

TLS Guy

Seriously, I have no life.
I'm curious - what would you consider an acceptable lower limit for a LF crossover point in a passive three- or four-way speaker? What goes wrong when you go below this limit?
I will apply at length after I have sent a PM to Dorokusai. But the lowest acceptable frequency for a passive crossover in my view is somewhere between 350 Hz and 400 Hz.

Your question goes to the heart of problems with three ways, unless they are inordinately expensive. I will explain at a later date.
 
G

guitarplyrstevo

Audioholic
Wait TLS guy. I think I'm begging to realize what you guys have been telling me. So the cross over you are taking about is the crossover that is crossing the 2 5.25" speakers to the 3 7" woofers right? I have a sine wave program and I did a sweep of all the frequencies to see where the volume drops and have noticed that at 120hz i get a volume drop in the tower. I am assuming that is were the 5.25" speakers are now off and now the 7" woofers are now on.

So the 3 7" woofers have a significant volume drop because of a passive cross over? I do not understand how a passive crossover is different from an active one.

Also didn't you say something about having an active crossover with a powered amplifier in the tower?
 
TLS Guy

TLS Guy

Seriously, I have no life.
Wait TLS guy. I think I'm begging to realize what you guys have been telling me. So the cross over you are taking about is the crossover that is crossing the 2 5.25" speakers to the 3 7" woofers right? I have a sine wave program and I did a sweep of all the frequencies to see where the volume drops and have noticed that at 120hz i get a volume drop in the tower. I am assuming that is were the 5.25" speakers are now off and now the 7" woofers are now on.

So the 3 7" woofers have a significant volume drop because of a passive cross over? I do not understand how a passive crossover is different from an active one.

Also didn't you say something about having an active crossover with a powered amplifier in the tower?
Hooray! The light bulbs have come on! I have just send a second PM to Dorokusai. I will respond at length on another date about all this. The problem goes to the heart of the matter as to why three way speakers are so problematic. I have another question about all of this in this thread. If you spend 23 K for the B & W 800Ds you will be OK. If you don't you will have serious issues, if you pick a three way with passive crossovers.
 
G

guitarplyrstevo

Audioholic
Hooray! The light bulbs have come on! I have just send a second PM to Dorokusai. I will respond at length on another date about all this. The problem goes to the heart of the matter as to why three way speakers are so problematic. I have another question about all of this in this thread. If you spend 23 K for the B & W 800Ds you will be OK. If you don't you will have serious issues, if you pick a three way with passive crossovers.
Ok I understand now. I auditioned some Martin Logan Purity towers which sounded unbelievable. The sound was very flat and deep sounding. I believe he told me that it had a 6 1/2" powered woofer inside. Does that mean that woofer has an active cross over to deliver that deep bass? I swear it sounded like it had an external sub connected to it but it was only the two towers itself. Unbelievable!
 
A

audioholix

Enthusiast
More punch??

Get you self a nice little sub. if you room small, try to get 10in sub boom
 
TLS Guy

TLS Guy

Seriously, I have no life.
Ok I understand now. I auditioned some Martin Logan Purity towers which sounded unbelievable. The sound was very flat and deep sounding. I believe he told me that it had a 6 1/2" powered woofer inside. Does that mean that woofer has an active cross over to deliver that deep bass? I swear it sounded like it had an external sub connected to it but it was only the two towers itself. Unbelievable!
Now you have leaned a valuable lesson and so so has anyone else reading this thread. There is little information below 60 Hz. What is perceived as bass is actually between 60 Hz and 350 Hz or so. So lack of bass in a speaker is much higher than people think. There are a lot of speakers weak in the wind so to speak. Getting a big sub and turning it up does not do the trick, if you are a discriminating listener as you found out.

You took the trouble to audition one of the select few of properly engineered speakers.

Now those speakers produce the bass form two 6.5 inch ported speakers, powered from an internal 200 watt amp. The crossover will be quasi passive/active. The crossover point is 450 Hz.

Now the big point is that the cut off those speakers is 41 Hz, three quarters of an octave above your Polks. Those speakers roll off at 24 db per octave as they are reflex, so they have minimal output where your Polks still have good output.

However since they have good uniform, and well controlled output above 40 Hz, you perceive them as having greater bass output, which they have. The bass is also properly balanced. So you perceived them as realistic and accurate.

You have learned a valuable lesson, please don't forget it!
 
TLS Guy

TLS Guy

Seriously, I have no life.
Get you self a nice little sub. if you room small, try to get 10in sub boom
Just the wrong solution again! Please read this thread and understand it. You only mask a problem that is occurring with the Polks by using a sub and then if the sub is too loud. If you are a discriminating listener you will not be fooled.
 
A

audioholix

Enthusiast
Wanna get loud.

I own a pair of RTi12's and I really want to get the 6 7" woofers moving to get the biggest sound possible. Right now I only have an Onkyo TX-SR574 so its only putting out 80w per channel and it doesn't have any preamp outs. I was thinking about upgrading my receiver in the future and maybe geting a Behringer EP2500 so I can get 300w per side but does that mean that the overall sound will be louder? I don't really need a lot of volume, I really just want to get these speakers moving some air. What are some ways I can achieve this? Or is the only way to crank up the volume really loud?
:) Just finishing my own studio and movie setup in my basement. oh man guess what Denon avr-987 pair of Bose 502
bose vsc10
bose 161 surround,
additional 2nd pair of Bose 502 through Crown 802
pair of Velodyne dls5000r sub 15inches.
Follow with mixer 2024FX Berhinger,
802 BBE.
Look like I don't have to go out to club more ofter now. Let me know what else do need for this? thanks guy
 
TLS Guy

TLS Guy

Seriously, I have no life.
:) Just finishing my own studio and movie setup in my basement. oh man guess what Denon avr-987 pair of Bose 502
bose vsc10
bose 161 surround,
additional 2nd pair of Bose 502 through Crown 802
pair of Velodyne dls5000r sub 15inches.
Follow with mixer 2024FX Berhinger,
802 BBE.
Look like I don't have to go out to club more ofter now. Let me know what else do need for this? thanks guy
SAY NO MORE!!!!!
 
G

guitarplyrstevo

Audioholic
Now you have leaned a valuable lesson and so so has anyone else reading this thread. There is little information below 60 Hz. What is perceived as bass is actually between 60 Hz and 350 Hz or so. So lack of bass in a speaker is much higher than people think. There are a lot of speakers weak in the wind so to speak. Getting a big sub and turning it up does not do the trick, if you are a discriminating listener as you found out.

You took the trouble to audition one of the select few of properly engineered speakers.

Now those speakers produce the bass form two 6.5 inch ported speakers, powered from an internal 200 watt amp. The crossover will be quasi passive/active. The crossover point is 450 Hz.

Now the big point is that the cut off those speakers is 41 Hz, three quarters of an octave above your Polks. Those speakers roll off at 24 db per octave as they are reflex, so they have minimal output where your Polks still have good output.

However since they have good uniform, and well controlled output above 40 Hz, you perceive them as having greater bass output, which they have. The bass is also properly balanced. So you perceived them as realistic and accurate.

You have learned a valuable lesson, please don't forget it!

So the RTi12's will never give me the sound I want; even if i get an SVS PB13 Ultra because the woofers in the tower are not powered therefore they are not outputting upper bass.

So do you suggest I go with 2-way speakers, since you said 3-way passive speakers are problematic? 2-way with a subwoofer to get the low end where the 2-way cuts off? If so, would the 2-way speakers produce the bass that the RTi12's cannot produce? How?

I found out that the reason why my towers were dropping in volume at 120hz is because the cross over in the receiver was set to 120hz. I then turned off the subwoofer in the configurations within the receiver and set the cross over to 40hz. Now the bass cuts off at around 40hz. It all sounds very even but it still doesnt have that "umph". I guess until i can get a tower that has self powered woofer, I will never get that sound.

One more thing. I have read a lot of reviews on the RTi12's and I have read one review that said bi-amping helps the bass part of the tower. What do you think about this? Wouldn't this be similar to having a powered tower?
 
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TLS Guy

TLS Guy

Seriously, I have no life.
So the RTi12's will never give me the sound I want; even if i get an SVS PB13 Ultra because the woofers in the tower are not powered therefore they are not outputting upper bass.

So do you suggest I go with 2-way speakers, since you said 3-way passive speakers are problematic? 2-way with a subwoofer to get the low end where the 2-way cuts off? If so, would the 2-way speakers produce the bass that the RTi12's cannot produce? How?

I found out that the reason why my towers were dropping in volume at 120hz is because the cross over in the receiver was set to 120hz. I then turned off the subwoofer in the configurations within the receiver and set the cross over to 40hz. Now the bass cuts off at around 40hz. It all sounds very even but it still doesnt have that "umph". I guess until i can get a tower that has self powered woofer, I will never get that sound.

One more thing. I have read a lot of reviews on the RTi12's and I have read one review that said bi-amping helps the bass part of the tower. What do you think about this? Wouldn't this be similar to having a powered tower?
You have the wrong end of the stick again. The problem with your speakers is the passive crossover at 120 Hz. Now if you biamp them you are still going through the same crossover. Now if you were to remove the bass section of the crossover and replace it with an active one, and then power the bass speakers with a separate amp from the electronic crossover, you might get somewhere.

A speaker does not have to be powered to have good bass, it is just that yours would be better off with the elimination of the 120 Hz passive crossover. For speakers with crossovers in that range electronic crossovers are a much better solution.

Now most speakers are two, or two and a half way. This puts the passive crossover between 1.8KHz and 3.5KHz usually. There is a very good reason why these types of speakers are so popular.

I would audition some other speakers, as I don't think you will pull off a mod to your Polks. What speakers are available to audition in your area? For instance what else do they have where you auditioned the Martin Logans?

The specs at Martin Logan where confusing, so I downloaded the manual. They do use an electronic crossover. You can connect Martin Logan Puritys directly to your pre outs. I see the price is about 3.5 K per pair. However you don't have to buy additional amplification, so overall a competitive price. If you really like them, then may be you should consider a purchase.
 
G

guitarplyrstevo

Audioholic
You have the wrong end of the stick again. The problem with your speakers is the passive crossover at 120 Hz. Now if you biamp them you are still going through the same crossover. Now if you were to remove the bass section of the crossover and replace it with an active one, and then power the bass speakers with a separate amp from the electronic crossover, you might get somewhere.

A speaker does not have to be powered to have good bass, it is just that yours would be better off with the elimination of the 120 Hz passive crossover. For speakers with crossovers in that range electronic crossovers are a much better solution.

Now most speakers are two, or two and a half way. This puts the passive crossover between 1.8KHz and 3.5KHz usually. There is a very good reason why these types of speakers are so popular.

I would audition some other speakers, as I don't think you will pull off a mod to your Polks. What speakers are available to audition in your area? For instance what else do they have where you auditioned the Martin Logans?

The specs at Martin Logan where confusing, so I downloaded the manual. They do use an electronic crossover. You can connect Martin Logan Puritys directly to your pre outs. I see the price is about 3.5 K per pair. However you don't have to buy additional amplification, so overall a competitive price. If you really like them, then may be you should consider a purchase.
But now can you kind of see why i thought adding more power will give it better sound? Every woofer I saw that was active always had around 300 watts running to the speaker. I just wanted to run that only to the bass secion.The only thing I didn't know about was the passive cross over at 120hz.

But you are right though, last night I removed the strip that connects the binding posts together and only connected the wire to the bottom half; the woofer part of the tower. I cranked up the amp and I was getting the same bass only louder. That cross over is killing me!
 
G

GeorgeH

Enthusiast
Thanks TLS Guy for your repsonse - I look forward to reading your forthcoming post.

On to another question: Is anybody else surprised that room acoustics have not yet been examined as a potential culprit?

I seem to remember reading the room is 9x9. If true, assuming 8' ceilings, you get the first two modes at 62.77 Hz, the third at 70.6 Hz, and the fourth and fifth modes at 125.55 Hz, exactly double the first two modes.

It seems to me that there is huge potential here for some nasty comb filtering (square rooms are well known to have poor acoustical properties). Interestingly, the 4th and 5th modes are very near the suspect 120 Hz frequencey.

To the OP: have you moved your sound meter around the room while the 120 Hz tone is playing? Does it vary significantly as you move it up or down, or front to back, from your normal mesauring position?

Of course, if I misread the room dimensions, well, then, please disregard this post. ;)
 
TLS Guy

TLS Guy

Seriously, I have no life.
I'm curious - what would you consider an acceptable lower limit for a LF crossover point in a passive three- or four-way speaker? What goes wrong when you go below this limit?
I said I would answer you later. So here is my reply. It is of necessity lengthy and somewhat complex To understand this you also have to understand the formidable problem of creating a three way speaker with passive crossovers.

Now the mid driver is also known as the band pass driver. Because passive crossovers have gentle slopes there is a lot of driver overlap. This results in what is called band pass gain. Now this comes about from the addition of the LF, band pass and HF drivers. In order to be able to cope with this in a reasonable way you need to keep the two crossover frequencies about three octaves apart. Now because there is significant out of band response either side of the crossover frequencies the band pass driver has to have a controllable response an octave either side of the crossover frequencies. So the mid, band pass, driver needs to have a response covering five octaves.

Now you know why I'm so interested about full range drivers. More research in this area, is bound to also result in better band pass drivers.

So let us look more closely at the problem confronting the designer of a three way speaker.

First take a look at the problem of constructing a low pass filter in the 120 Hz range.

Now there is a huge problem here. The reason being that the values of the inductor and capacitors involved are huge. Now I leaned years ago not to do this, and I have read many authorities that put the lower acceptable limit for a passive crossover at around 350 Hz at the lowest.

I doodled with an 8 ohm nominal second order three way filters with the low pass to band pass at 125 Hz. This circuit had an inductor of 16 mH and a cap of 103 mfd!

Now those values are huge. That inductor in series with the woofer will have a series resistance of about 1.5 ohms. This will play havoc with the bass tuning. The other solution is to give it an iron core with all the saturation and hysteresis problems that entails. The cap being in the 100 mfd range is going to call for a non polarizing electrolytic type, that are not the best components for a speaker crossover. The other alternative is to parallel expensive polypropylene types.

In addition to that, the crossover is operating close to the impedance peaks of the bass drivers. The interaction of those huge inductors and the speakers within an octave of their double hump impedance peaks from the reflex cabinet tuning, has the potential to create a situation of complex phase angles between voltage and current. This is likely to present a difficult load, and crossovers such as these are well know to actually create amplifier ringing in some amps.

The next issue, is that it is virtually impossible to create a passive low pass filter with a slope greater than 12 db per octave in this range. Now the mid driver operating that low will be starting to roll off second order, for a combined electrical and mechanical roll off somewhere between 18 and 24 db per octave. Now it is unlikely the woofer would start to roll off at 120 Hz, so the slopes will not likely sum to a flat frequency response.

The next problem is that 12 db second order filters are inclined to put the drivers 180 degrees out of phase at crossover, therefore creating a deep null at the crossover point. The same would be true between the mid and tweeters with second order filters. The time honored solution is to reverse the phase of the band pass driver. However doing that at 120 Hz, will put a good portion of the bass out of phase with other speakers in the system.

Now with an active electronic crossover and amps to each driver, the interaction of crossover inductors and driver is a non issue. Any order of slope to the desired driver is easily possible. There is no insertion loss from these huge passive components. The insertion loss of a passive crossover at 120 Hz is huge.

So how did this all happen. I think the first answer is marketing. There is a perception that a three way speaker is superior to a two way. I will show you that is not necessarily so.

Let us consider a three way with crossover frequencies at 350 Hz and 4 KHz then the band pass driver needs to have a good response from 200 Hz to 8 KHz.

Now developing a driver to cover that range is a huge R & D undertaking. There is a permanent dearth of good band pass drivers with these characteristics. That is one of the reasons a pair of B & W 200Ds cost $23,000 a pair.

So what if you only have a standard 6.5 inch bass mid driver to press into service as your band pass driver. No way is that going to have a suitable response to 8 KHz. There will be peaks from cone break up long before that. Few would make it to 4KHz.

So crossover points at 120Hz and 1.8 KHz give you your three octave band pass spread, but leave you with a passive crossover in a bad place, unless you design with active filters.

So to summarize this is the dilemma of the three way passive solution.

1). Develop a driver to cover 200 Hz to 8 K Hz like B & W. A formidable undertaking to say the least.

2). Try and smooth the response of the bass mids they selected to well above 4 KHz. That would be a next to impossible assignment.

3). Narrow the band pass range to less than three octaves. That would be a terrible option.

So you can see why two and two and a half way speakers are so popular. With a passive solution it puts the crossover generally in the 1.8 KHz to 3.5KHz range. This is a viable solution. There are now plenty of small bass/mids that can reach below 50 Hz, and some to 30 Hz. This makes for an easy splice to a sub. This explains why the speaker industry is so geared this way.

In order to break the mold and go to extended range integrated systems, we need drivers able to cover much larger frequency ranges and make the powered solution with active crossovers more common.
 
G

guitarplyrstevo

Audioholic
So TLS Guy, how much do you think I can sell my two RTi12's for? It has some scratches along the sides and one on the top. It's the cherry color so it looks real nice.

I've been looking into the Definitive Technology BP7006. What do you think of that tower?
 
mike c

mike c

Audioholic Warlord
please explain to a dumbass ... (me)

so are we saying that the 3 way speaker manufacturers are all dumbasses?
e.g. Polk Audio, Infinity, JBL, etc.?
 
TLS Guy

TLS Guy

Seriously, I have no life.
So TLS Guy, how much do you think I can sell my two RTi12's for? It has some scratches along the sides and one on the top. It's the cherry color so it looks real nice.

I've been looking into the Definitive Technology BP7006. What do you think of that tower?
These are eBay sales in the last week.

http://search-completed.ebay.com/search/search.dll?sofocus=so&sbrftog=1&dfsp=1&catref=C6&from=R40&satitle=Polk+Rti12+speakers&sacat=-1&catref=C6&sargn=-1&saslc=2&sadis=200&fpos=56436&sabfmts=1&saobfmts=insif&fis=2&ft=1&ftrt=1&ftrv=13&saprclo=&saprchi=&fsop=1&fsoo=2

I have never heard Def techs, so I can't comment. Apparently I gather their specs are suspect from some members on these forums. My advice is to make sure you carefully audition your purchase. If you don't like it as much or better than the Martin Logan's you auditioned, then keep saving for the Martin Logan's.

You have now heard something you really like, so you have a point of reference. If you buy something you like less, you will always be irritated by your purchase.
 

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