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terry j 15th September 2007 10:28 AM

desired in room response-what do you go after?
recently we had a thread on 'why flat is inaccurate'. Part of the discussion centred on what is the usual or natural response of most speakers in the average room, and for normal listening it seemed that it is usual and desirable for the high end to roll off, up to ten db I suppose (not that there are any rules here-or are there!).

That is mainly due to beaming in the higher frequencies (?) coupled with the fact that the higher frequencies are also more easily absorbed than the lower.

Now, down the other end it is not unusual to see huge variations in the response, and we all would like to even them out by whatever means available to us, so that ideally all the bass notes are of the same magnitude (and we hope duration).

My question is, at what point does this flat in room response end and the gradual fall of begin?? Does that question make sense??

'Perfectly' flat to 100 hz and then we get what we get?, or do some of you go to two hundred hz if you can, three hundred?

In my case actual room treatment is a little way off yet until I can renovate the room and add bass traps etc, so till then EQ is the only tool I'll be using. Traditionall I don't really go above one hundred hz, but I have no data or information to support that arbitrary point, and so I hope to learn from your collective experiences and knowledge.

richie00boy 15th September 2007 10:35 AM

Have a look into "room gain" for the low end.

AndrewT 15th September 2007 11:12 AM

all my earlier speakers aimed for a 18db/octave Butterworth roll-off in the bass.
I always had a lot of tuning to do to get the bass to sound natural.

Recently I built a sub-bass speaker with a lowpass at 150Hz but was advised to look at a Bessel type roll off.

I ended up with flat to 100Hz then a sloping response falling at approx 3db/octave down to 25Hz and then gradually steepening towards 20Hz.

It did not need any tuning. It goes deep and loud enough and sounds quite natural on deep voice.

I was very surprised at how little signal goes to this speaker even with the low pass set quite high. It measures about half voltage compared to the remainder of the frequency spectrum.

Robh3606 15th September 2007 01:15 PM

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I like some lowend bloom under 50 Hz or so and a can live with gradual roll off above 10K. Through the 100Hz to 10K I like it as flat as I can get it. Here's a 2 meter in room RTA shot of JBL 4344 clones. They are pretty flat on axis and sound very good. They also have reasonably good power response but they really need to to listened to on axis because of vertical beaming of both the midrange horn and ring radiator at the upper end of their respective ranges.

I have another sysyem with a similar resonse curve but rolled off a bit above 10K and it sounds good as well. There is no ring radiator above the compression driver so the system response is limited to the roll off of the compression driver. I think that it really depends on what you like and the drivers and total system balance as to what sounds right and what doesn't. Both systems use compression drivers so you can tailor the response curve with your crossover a bit easier up top to get the desired roll off.

I would do some experimenting to see what sounds the most natural to you and what works best in your room. I don't think there is any one curve that's going to work for everyone. You can argue what's a better curve to the cows come home but in the end it doesn't matter if better curve doesn't sound "right" to you.


RobWells 16th September 2007 09:32 AM

Re: desired in room response-what do you go after?

Originally posted by terry j

My question is, at what point does this flat in room response end and the gradual fall of begin?? Does that question make sense??

'Perfectly' flat to 100 hz and then we get what we get?, or do some of you go to two hundred hz if you can, three hundred?

There is no set point at when the speaker starts to beam. That depends on the power response of the speaker. For example my old scanspeak domes sounded harsh if they were eq'd to measure flat in room, whereas my beyma horns sounded smooth with a similar in room response. (CD horns require some boost at top end)

I've got peq available and only use it for my subs - Then only to cut peaks and give a low end boost, never to 'fill in' dips in response. The problem is that the eq you apply will only be correct for the position you had the mic setup at.

I think you're looking to eq a speaker to give a tilted response ? I think thats a 'cart before the horse' situation. You 'eq' it in the design phase to measure flat outside / anechoic, then it measures tilted in room, each room being different.

If you're looking to setup something like a 3way active in room, I've had best results when concentrating just on the xo points, so that they cross perfectly flat from an octave below to an octave above. The resultant curve is by no means flat, but the sound is pretty smooth and full bodied.

What are you using to measure ? / trying to setup ?


terry j 17th September 2007 07:52 AM

hi all

thanks for responding. Looks like I did not get my question phrased totally correctly, so will try again.

Lets assume we have the 'perfect' pair of speakers, capable of true 20 hz response, or to make it easier a good two way plus sub(s) that will get to 20 hz.

The two way is perfectly flat in the anechoic chamber, and we have suitable room treatments etc so we don't need to fix say above 300 hz.

As usual, the perfect bass response once in the room goes all screwy, with 20 db peaks etc, which we can get rid of by whatever means, traps or eq.

Forget house curves for now, say we want the bass set flat (or we could define flat as following whatever curve we want, without drastic or huge variations in the response). Obviously we want to get rid of the 15 db peak at 40 hz say, and make all the bass equal.

But how high do we (ie you guys) go with making it flat?? Is that more clear??

I have and use the deqx, which makes the speaker flat in it's 'native' response (pseudo anechoic measurements) and then once in the room I can apply room correction to fix the wonky bass response. I do it manually with REW BTW, I find I get better results than the inbuilt automated approach.

In my hypothetical above, we are only using peq to fix the subs as RobWells does. Above what frequency Rob do you no longer apply eq? And what is your reasoning behind it?

It's purely a hypothetical question, trying to get others viewpoints and thinking on the matter. As I say, when correcting the 'subs' I normally don't go above 100 hz, but that is not based on any particular knowledge so am wondering on the theory behind it all.

Thanks for replying guys. Hope I was clearer this time.

Foxx510 17th September 2007 11:50 AM

Don't forget to factor in your own hearing curve, I doubt any two people have the same hearing response. That probably doesn't really relate to your actual question so much, however... To that I would say it depends on the size/shape of the room where the bass will start being affected, and other room elements will affect higher frequencies with reflections/absorption etc. I remember as a live sound engineer having to totally re eq systems in rooms when the punters turned up....

SY 17th September 2007 11:53 AM

In my mind, the Allison dip (a deep interference pattern from the interaction of the woofer with the three nearest boundaries) is the biggest issue for most speakers/most rooms in the midbass. And EQ is not the way to overcome that, it needs to be done by attention to driver positioning.

RobWells 17th September 2007 06:15 PM

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I only use peq on the subs as every time I've applied eq to my mains its not really helped improve subjective sound quality, even though the rta looks better. With the subs it's more to do with response shaping as they need a fair bit of boost in the low end. (cross at 80Hz / 24dB)

I check the subs response at several places across my couch, and try and give each seat a good response. Placement of the couch comes into play here.


Here's my midbass horns measured at seating with no crossovers on them - would you bother to eq them ? I don't. (They are used from 80Hz to 500Hz)

terry j 18th September 2007 03:26 AM

hi robb, are you asking me if I'd eq them?? (i'm honored!!)

You mention no x-over, so that is a natural fall off on the bottom??

Anyway, no from that graph I wouldn't be eq'ing the mains, looks like you could almost call 100 hz the start of where everything rolls off (no the -3 db point but...) and as i've said, traditionally i don't bother too much above that, and from your graph to have an in-room response from 100 up that only varies + - 2.5 db or so is something that ain't broke, so don't fix.

My room DOES have a huge 10 db peak at around 110 hz, so of course I pull that down with eq, you have no such problem.

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