HK 525 and LSI 15 question part 2

tnathan

OK so I am thinking about trying to amp my HK to run a set of Lsi15's. Which based on my last post it appears needs to be amped to do it justice.

When looking at the specs the LSI's are asking for an amp that delivers between 20-250 watts. THe specs also say that the Lsi 15 is a 4 ohm speaker.

My question is how do you match the speakers to achieve a good sound stage.

Is it merely an issue of SPL? I was looking at a 6 channel parasound amp which delivers 135 w/c at 8 ohms and 200 w/c at 4 ohms. The rest of my systems speakers are 8 ohm. I assume I will get 135 w/c for my surround speakers and 200 w/c from the lsi15's since they are 4 ohm speakers.

My questions are:
1) Is it wise to power different ohmed speakers from a single amp?

2) Is my math correct. Will I actually get the 200 w/c I need for the lsi15's ? To say it another way, when POLK says they recommend an amp between 20-250 w/c is that being driven into 8 or 4 ohms?

3) If I run this fron a single amp my surrounds will be getting 135 w/c while the fronts are getting 200. Is a 65 watt/channel spread to large to compensate for via dB adjustments on the amp to achieve a good sound stage.

4) are there other factors I need to be taking into account: sensitivity, dB, THD, etc.

Thanks in advance for any thoughts anyone has?

Tim

phuz

1.) Should be fine.

2.) Yes

3.) No, that will be fine.

4.) Not that I can think of. The only thing to keep in mind is that they are different speakers and they will not be a perfect match. Somewhere down the line you might want to think about getting LSi all the way around.

What do you mean by matching spealers to have a good soundstage? The LSi15's are for stereo (2 channel) music right? No need to worry then. The 15's will deliver a nice soundstage. Especially with that Parasound amp. The only matching question should be when listening to multi-channel sources (5.1+, DVD, DVD-A, SACD, etc). Like Mantis said before, the LSi's won't exactly match what you currently have. You may not be able to hear much of a difference, but in the long run if you are anything like me and everyone else here that gets into the LSi line - then you will eventually upgrade to LSi all the way around.

tnathan

Thanks for your reply.

I am new to this but my sound stage issue was wrt 7.1 operation. I was afraid that once I spent the money on this that I would end up with fronts that would be so dominate that you end up hearing only the fronts even in 7.1.

I was just trying to get a feeling for how ballanced the w/c need to be about the system. I have seen other posts where people have put smaller speakers, amps in their surrounds since they tend not to get driven hard. Is there any outer limit? Instead of a parasound amp how about a 2x250 amp and let the surrounds run off of line at 70 w/c. Is that pushing my luck?

I will try to answer my own question based on your last message the goal is similar speakers with similar amps. On the other hand even the full LSi center, back, sides are different speakers with, I assume different w/c requirements.

Thanks again.

Tim

mantis

Just remember this one thing.
You want equal power all the way around and timber matched speakers.

phuz

Originally posted by mantis
Just remember this one thing.
You want equal power all the way around and timber matched speakers.

Like I said I think timbre matching in the long run is important, but I don't think equal power is all that important. You can adjust DB levels on the receiver. Can anyone explain why it's so important to have equal power? And if it's so important why is it that so many people *don't* do it?

HBombToo

Originally posted by phuz

Can anyone explain why it's so important to have equal power? And if it's so important why is it that so many people *don't* do it?

The only thing I can imagine would cause problems would be if the smaller of the 2 amps in power would clip at a given SPL. Outside of that is a stretch for me.

HBomb

tnathan

OK here is the summary of what I learned so far. If someone disagrees let me know. To obtain decent sound quality there are basically two issues sound pressure and timbre.

Sound pressure can be adjusted via the gain control on your amplifier or receiver. However, I saw on parasound that they recommend against gain control as much as possible since it may degrade the signal. So unless your speakers are so missmatched that gain control can't compensate than you should be ok. Moreover, the less you have to adjust. The better. So Mantas's advice seems accurate. The gold standard would be to have perfectly matched speakers with the same efficiency being feed the same signal.

Timbre. As I understand it this is a measure of tonal quality and arises when you have a sound travel from speaker to speaker. For example the sound of an airplane that passes from the front speakers to the rear speakers. If you have some huge speakers in the front with a broad frequency range as your fronts and small speakers with a narrow range as your rears, as the sound of an airplane passes over the sound will change. The goal is to have the sound quality be matched. The posts that describe perfect matching describe the speakers as disappearing and the sound seamlessly passing from speaker to speaker. The gold standard once again would be to have speakers with identical characteristics.

Interestingly, THX says that you should consider a thx certified controller since tonal quality can be effected by speaker location, room design, and even manufacturing variations between the same speakers. I assume that they have some timbre mathcing algorith. However, I am not sure. So according to THX, even using identical speakers from the same manufacturer is still no guarentee of timbre matching. However, logic says it is a great start. I guess as always it will depend on how obsessed you are and how much money you have.

Does anyone have any idea or resources on how to test and or adjust timbre manually. I guess a 7 channel graphic equallizer. But how do you test tone?

mantis

Phuz,

Can anyone explain why it's so important to have equal power? And if it's so important why is it that so many people *don't* do it?

Having equal power is important as HbombToo was on to.It's dynamic range.When things get moving and sound come from around the room,you want everything to be equal.You don't want a dominant channel or channels.
Setting up your speakers with a SPL to the same level won't help balance out the uneven power.
If so many people don't use equal power all the way around,home theater is 2nd on there list of importance.Music I would say is first.
You don't have to use or do anything correctly if you choose not 2.The experience will suffer,but thats your choice.
I tried using unequal power with 2 different power amps and 3 different receivers.It never sounded right to me.The main channels jumped out in your face when things went on.I didn't care for that.For Home Theater,it sounded better when I drove all channels with the given receiver at the time.
Heres what I had setup and to me it failed
Yamaha rxv992
B&K st140
rt1000p's
cs300 center
rt35
I loved the clean power for 2 channel music ,but when I switched to Theater,The mains played louder during dynamic passages.
Pioneer Elite vsx26tx
B&K st140
rt1000p's
cs400i
rt35i's
psw450
Same results.The amp sounded better for 2 channel then theater.
Denon avr3801
B&K st140
Rotel rb960bx
(both amps where tried on main speakers for better hi fi for 2 channel)
rt1000p's
cs400i
fx/500
rt35i's
psw450
Again same results.
You do what you want with your system.I know alot of you mix in power amps and don't do all the channels.Thats your choice.You won't find that in my systems anymore.I tried it and didn't care for it.
Now if you want to add power amps to your theater system, then add them for all channels.Then this way the system will perform the same..........all the way around.
The last mix match thing I tried before I decided to get all of that out was removing the rt1000p's from the system, adding in my Lsi15's,using the Rotel power amp to power the Lsi's, and running the rest of the rt system off the Denon.Man what a mess of a sound that was.I hated it.
I moved the B&K st140 amp to multiroom duty after getting tired of re wiring the system everytime I wanted to do theater or music.Not to mention I went 7.1 back then.I used it to power a pair of rt35's in my masterbedroom.
Does that help any?;)